STRANGE PARTICLE PRODUCTION IN HIGH-ENERGY ELECTRON PROTON COLLISION

Transcription

1 SRANGE PARICLE PRODUCION IN HIGH-ENERGY ELECRON PROON COLLISION ZUKHAIMIRA BINI ZOLKAPLI FACULY OF SCIENCE UNIVERSIY OF MALAYA KUALA LUMPUR 13

2 SRANGE PARICLE PRODUCION IN HIGH-ENERGY ELECRON PROON COLLISION ZUKHAIMIRA BINI ZOLKAPLI DISSERAION SUBMIED IN FULFILMEN OF HE REQUIREMENS FOR HE DEGREE OF MASER OF SCIENCE DEPARMEN OF PHYSICS FACULY OF SCIENCE UNIVERSIY OF MALAYA KUALA LUMPUR 13

3 UNIVERSII MALAYA ORIGINAL LIERARY WORK DECLARAION Name of Candidate: ZUKHAIMIRA BINI ZOLKAPLI (I.C/Paport No: ) Regitration/Matric No: SGR9118 Name of Degree: MASER OF SCIENCE (EXCEP MAHEMAICS AND SCIENCE PHYLOSOPHY) itle of Project Paper/Reearch Report/Diertation/hei: SRANGE PARICLE PRODUCION IN HIGH-ENERGY ELECRON PROON COLLISION Field of Study: PARICLE PHYSICS I do olemnly and incerely declare that: (1) I am the ole author/writer of thi Work; () hi Work i original; (3) Any ue of any work in which copyright exit wa done by way of fair dealing and for permitted purpoe and any excerpt of extract from, or reference to or reproduction of any copyright work ha been dicloed exprely and ufficiently and the title of the Work and it authorhip have been acknowledged in thi Work; (4) I do not have any actual knowledge nor do I ought reaonably to know that the making of thi Work contitute an infringement of any copyright work; (5) I hereby aign all and every right in the copyright to thi Work to the Univerity of Malaya ( UM ), who henceforth hall be owner of the copyright in thi Work and that any reproduction or ue in any form or by any mean whatoever i prohibited without the written conent of UM having been firt had and obtained; (6) I am fully aware that if in the coure of making thi Work I have infringed any copyright whether intentionally or otherwie, I may be ubject to legal action or any other action a may be determined by UM. Candidate Signature Date Subcribed and olemnly declared before, Witne Signature Name: Deignation: Date ii

4 ABSRAC he trangene total cro ection for ep neutral current deep inelatic cattering (DIS) have been meaured uing HERA-II data at a center-of-ma energy of 318 GeV with the ZEUS detector at HERA. he 3 & 7 running period data were ued with an integrated luminoity of 4. 6 pb -1 and compared with ARIADNE Monte Carlo (MC) prediction. he differential production cro-ection of,, K were meaured in two different kinematic region, Q DA 5 GeV for high and Q DIS ample and 5 Q DA 5 GeV for low Q DIS ample. he differential cro ection were meaured a function of (,, ), p (,, ) he baryon-antibaryon production aymmetry, defined a and Q in the DIS ample. ( ), and the baryon- ( ) ( ) meon ratio were tudied and the reult were compared with ARIADNE MC prediction. he baryon production proce i not well undertood yet and therefore it relie much on phenomenological model like the Cluter and String Model. he tudy on baryon antibaryon rapidity correlation in ep colliion can anwer thee problem. he tracking information from the Micro Vertex Detector (MVD) wa ued to oberve the effect on the trange particle production when uing thi extra tracking information during the obervation of baryon and in addition to the Central racking Detector. K meon production at the ZEUS detector, iii

5 ABSRAK Jumlah keratan renta kuark ganjil untuk perlanggaran tak kenyal tanpa ca antara e dan p telah diukur menggunakan data HERA-II pada tenaga puat 318 GeV di mein pengean zarah ZEUS di dalam meen pemecut zarah HERA. Data tahun 3 & 7 dengan nilai kilauan berepadu 4. 6 pb -1 telah digunakan dan keputuan akhir dibandingkan dengan imulai Monte Carlo. Pengkamiran penghailan keratan renta,, dan K telah diukur dalam dua rantau yang berbeza kinematik di mana QDA 5 GeV untuk ampel perlanggaran tak kenyal dengan nilai Q tinggi dan 5 Q DA 5 GeV untuk ampel perlanggaran tak kenyal dengan nilai Q rendah. Dalam ampel perlanggaran tak kenyal, pengkamiran penghailan keratan renta ini telah diukur ebagai fungi p (,., ), (,, ) dan Q. Penghailan aimetri baryonantibaryon yang dedifinaikan ebagai ( ), dan nibah penghailan baryon kepada ( ) ( ) meon dikaji, dan kemudian keputuan kajian dibandingkan dengan imulai Monte Carlo ARIADNE. Proe penghailan baryon maih tidak difahami dan hanya bergantung kepada model fenomenologi eperti Cluter Model dan String Model. Kajian terhadap korelai kepeatan baryon terhadap antibaryon dalam perlanggaran ep boleh menjawab peroalan terebut. Maklumat penjejakan dari Pengean Mikro Vertex (MVD) telah digunakan untuk melihat kean ke ata pengeluaran zarah pelik apabila menggunakan maklumat penjejak tambahan emaa pemerhatian baryon dan pengeluaran meon pada pengean ZEUS, di amping Pengean Penjejak engah (CD). iv

6 ACKNOWLEDGEMEN Bimillahirrahmanirrahim, Alhamdulillah. Firt and foremot, thank to Allah SW, who with Hi willing giving me the opportunity to complete thi Mater diertation. hi diertation wa prepared for the Department of Phyic, Faculty of Science, Univerity of Malaya, Kuala Lumpur, Malayia. I dedicate thi diertation to my father, En. Zolkapli Bin Shafie and to my mother, Puan Rohena Binti Laji, for their motivation, love and patience. I am deeply indebted to my upervior Prof. Dr. Wan Ahmad ajuddin Bin Wan Abdullah whoe help, guide, alway be patience, timulating uggetion and encouragement helped me in all the time of reearch for and writing of thi thei. Next, thank you o much to ZEUSMal colleague, Dr. Faridah Mohd Idri, Prof. Dr. Zainol Abidin Ibrahim, to all my family member, ZEUS Collaboration member, UM Phyic Department, and other for their corporation, encouragement, contructive uggetion and full of upport for the diertation completion, from the beginning till the end. hank you to Univerity of Malaya for upporting my financial problem by giving me a fellowhip during thi period of tudie. Alo thank to all my friend and everyone, that ha been contributed by upporting my work and help me during thi diertation progre till it i fully completed. Lat but not leat, my deepet thank and appreciation to the pecial mate of mine, Muhammad Azri Bin Zahari. hank you all. v

7 ABLE OF CONENS Original Literary Work Declaration... Abtract.. Abtrak... Acknowledgement. able of Content... Lit of Figure. ii iii iv v vi x Lit of able. xvii Lit of Symbol and Abbreviation. xxi Chapter 1: Introduction 1.1 hei outline 4 Chapter : Phyic Overview.1 he Standard Model Quark.. 8. Quark Parton Model. 1.3 Quantum Chromodynamic (QCD) Deep Inelatic Scattering (DIS) Electron-Proton Scattering HERA Kinematic 15.6 Baryon Production Strange Quark Production....7 Phyic Motivation of the hei... 3 vi

8 Chapter 3: Experimental Set-up 3.1 he HERA ep Collider he ZEUS Detector he Central racking detector (CD) HERA-II Micro Vertex Detector (MVD) ZEUS Analyi and Computing Model Data Proceing: the ZEUS Recontruction Factory ZEUS Analyi Facility (ZARAH) ZEUS Analyi ORANGE Monte Carlo and Event Simulation he Lund String Fragmentation Model in JESE Event Generator ARIADNE/DJANGOH Event Recontruction & Selection Event Recontruction Deep Inelatic Scattering (DIS) Event Recontruction Event Selection Online Event Selection Offline Event Selection High Low Q DIS.. 48 Q DIS... 5 vii

9 Chapter 4: racking Enhancement with the Micro Vertex Detector (MVD) 4.1 Introduction Vlite Recontruction racking Signal to Background Ratio Dicuion and Concluion Chapter 5: and K Selection 5.1 Strange Particle Recontruction rack Recontruction Identification of p ( p ) candidate Identification of K candidate Efficiency, Purity and Acceptance 66 Chapter 6: Reult and Dicuion 6.1 otal Cro-Section Differential Cro-Section Q 5 GeV 71 DA Incluive baryon cro-ection in bin of Q, () p and () Incluive baryon cro-ection in bin ofq, p () and () Incluive baryon cro-ection in bin of Q, p ( ) and ( ) Incluive K meon cro-ection in bin of Q, ( K ) p and ( ) Q 5 GeV DA viii

10 6...1 Incluive baryon cro-ection in bin of Q, p () and () Incluive baryon cro-ection in bin of Q, p () and () Incluive baryon cro-ection in bin of Q, p ( ) and ( ) Incluive K meon cro-ection in bin ofq, p ( ) and ( ) Baryon-to-Antibaryon Production Aymmetry Low Q DIS Event (5 Q 5 GeV ).. 99 DA 6.3. High Q DIS Event ( Q 5 GeV ). 11 DA 6.4 Baryon-to-Meon Ratio Low 6.4. High Q DIS Event (5 Q DIS Event ( Q 5 GeV ). 16 DA Q 5 GeV ). 17 DA 6.5 Baryon Antibaryon Rapidity Correlation Rapidity Correlation Event Selection and Strangene Production Reult and Dicuion Concluion 115 Chapter 7: Concluion. 116 Bibliography. 1 ix

11 LIS OF FIGURES Figure 1: Flow chart of the elementary particle tudie. Figure.1: he fundamental particle of the Standard Model. Figure.: Hierarchy of the quark. Figure.3: Quantum Chromodynamic proce. Figure.4: Lowet order Feynman diagram for Charged Current and Neutral Current Deep Inelatic Scattering (DIS) Figure.5: Feynman diagram for a Neutral Current DIS colliion. a) he 4-vector of incoming and outgoing particle. b) he Lorentz invariant calar defining the event. Figure.6: he imulated picture of Neutral Current and Charge Current proce in Deep Inelatic electron-proton cattering in HERA. Figure.7: String fragmentation in x t pace. Figure.8: If a vertex pair q q i produced inide a colour fluctuation region panned by q q 1 1, an effective diquark-antidiquark pair ha popped out in a tepwie manner. he model allow for everal breakup in the colour fluctuation region, creating one or ome meon among the antibaryon and baryon, a hown to the left. Figure.9: A popcorn example with two curtain quark pair. Figure.1: Poible mechanim of the trange quark production. Figure 3.1: Flow in the data proceing proce in High Energy Phyic Experiment. x

12 Figure 3.: he data from HERA wa tored here. Figure 3.3: he HERA and PERA accelerator aerial view at the DESY campu in Hamburg, Germany. HERA wa at 15-3 m underground with circumference 6.3 km. Figure 3.4: he HERA collider with the four experiment H1, ZEUS, HERMES and HERA-B. Figure 3.5: A mall egment of the HERA tunnel. he proton beam i travelling in the large vacuum tube in the middle to the right while the electron beam tube i below that. Figure 3.6: Cutaway of the ZEUS detector Figure 3.7: Cro ection of the ZEUS detector in the vertical plane, ide view. Figure 3.8: Cro ection of the ZEUS detector in the vertical plane, top view. Figure 3.9: Cro ection in tranvere plane containing the nominal interaction point. Figure 3.1: he ZEUS coordinate ytem. Figure 3.11: Integrated luminoity collected by ZEUS for the and - 7 period, hown eparately for each year. he plot are taken from [57] Figure 3.1: he ZEUS Micro Vertex Detector (MVD) Figure 3.13: a) A ection through the barrel MVD, howing the arrangement around the beam-pipe of each the MVD ladder. b) A photograph of one half of the MVD, howing the barrel ladder, one half of each of the forward wheel and the cable and ervice [1]. Figure 3.14: Flow diagram of event analyi in the ZEUS detector. Simulated and actual event were run concurrent and compared to extract correction factor from pqcd calculation. xi

13 Figure 3.15: he ZEUS analyi environment Figure 4.1: Hadronic decay mode of Figure 5.1: he, and invariant ma ditribution for the high Q DIS event. Hitogram on the left ide repreent the invariant ma plot for ZEUS data where the olid curve repreent the fit of a Gauian for the ignal combined to a econd order polynomial function for the background. he MC i normalized to the data and repreent by the red line while the pule repreent the ZEUS data, i how by the hitogram on the right ide. Figure 5.: he, and invariant ma ditribution for the low Q DIS event. Hitogram on the left ide repreent the invariant ma plot for ZEUS data where the olid curve repreent the fit of a Gauian for the ignal combined to a econd order polynomial function for the background. he MC i normalized to the data and repreent by the red line while the pule repreent the ZEUS data, i how by the hitogram on the right ide. Figure 5.3: he K ma ditribution for the high Q DIS event. he hitogram on the left ide repreent the invariant ma plot for ZEUS data where the olid curve repreent the fit of a Gauian for the ignal combined with a econd order polynomial function for the background. he MC i normalized to the data and repreent by the red line while the pule repreent the ZEUS data, i how by the hitogram on the right ide. Figure 5.4: he K ma ditribution for the low Q DIS event. he hitogram on the left ide repreent the invariant ma plot for ZEUS data where the olid curve repreent the fit of a Gauian for the ignal combined with a econd order polynomial function for the background. he MC i normalized to the data and repreent by the red xii

14 line while the pule repreent the ZEUS data, i how by the hitogram on the right ide. Figure 6.1: Differential cro-ection for production in low Q DIS event with 5 Q DA 5 GeV a a function of Q, () p and (). 3 & 7 HERA-II data and ARIADNE MC are hown. Figure 6.: Differential cro-ection for production in low Q DIS event with 5 Q DA 5 GeV a a function ofq, p () and (). 3 & 7 HERA-II data and ARIADNE MC are hown. Figure 6.3: Differential cro-ection for 5 Q 5 GeV a a function of II data and ARIADNE MC are hown. production in low Q, ( ) Q DIS event with p and ( ). 3 & 7 HERA- Figure 6.4: Differential cro-ection for K production in low Q DIS event with 5 Q DA 5 GeV a a function of Q, ( K ) p and ( ). 3 & 7 HERA-II data and ARIADNE MC are hown. Figure 6.5: Differential cro-ection for production in high- Q DIS event with A QDA 5 GeV a a function of Q, () p and (). 3 & 7 HERA-II data and ARIADNE MC are hown. Figure 6.6: Differential cro-ection for production in high QDA Q DIS event with 5 GeV a a function ofq, p () and (). 3 & 7 HERA-II data and ARIADNE MC are hown. xiii

15 Figure 6.7: Differential cro-ection for production in high Q DIS event with QDA 5 GeV a a function of p and ( ). 3 & 7 Q, ( ) HERA-II data and ARIADNE MC are hown. Figure 6.8: Differential cro-ection for K production in high Q DIS event with QDA 5 GeV a a function of Q, ( K ) p and ( ). 3 & 7 HERA-II data and ARIADNE MC are hown. Figure 6.9: he aymmetry for ZEUS 3 & 7 data and ARIADNE Monte Carlo ample a a function of, Q and P in the laboratory frame for Low Q DIS event with 5 Q 5 GeV. he N (), N () i the number of and baryon, DA repectively. he error bar repreent the tatitical error for the meaurement. Figure 6.1: he aymmetry for ZEUS 3 & 7 data and ARIADNE Monte Carlo ample a a function of, Q and P in the laboratory frame for Low Q DIS event with 5 Q 5 GeV. he (), () i the differential cro DA ection of and baryon, repectively.he error bar repreent the tatitical error for the meaurement. Figure 6.11: he aymmetry for ZEUS 3 & 7 data and ARIADNE Monte Carlo ample a a function of, Q and P in the laboratory frame for High Q DIS event with Q 5 GeV. he N (), N () i the number of and DA baryon, repectively. he error bar repreent the tatitical error for the meaurement. Figure 6.1: he aymmetry for ZEUS 3 & 7 data and ARIADNE Monte Carlo ample a a function of, Q and P in the laboratory frame for High xiv

16 Q DIS event with Q 5 GeV. he (), () i the differential cro ection DA of and baryon, repectively. he error bar repreent the tatitical error for the meaurement. Figure 6.13: he ( ) / K ratio for ZEUS 3 & 7 data and ARIADNE Monte Carlo ample a a function of, Q and P in the laboratory frame for Low Q DIS event with 5 Q 5 GeV. he (), () and ( ) i the differential cro DA ection of and baryon, and tatitical error for the meaurement. K meon repectively. he error bar repreent the Figure 6.14: he ( ) / K ratio for ZEUS 3 & 7 data and ARIADNE Monte Carlo ample a a function of, Q and P in the laboratory frame for High Q DIS event with Q 5 GeV. he (), () and ( ) i the differential cro DA ection of and baryon, and tatitical error for the meaurement. K meon repectively. he error bar repreent the Figure 6.15: An illutration of the particle pair correlation propoed in the tring model due to haring of a common tring break-up. he dotted line repreent a tring and the olid curve decribe the development of a q q or D D pair created at ome break-up point in a tring. Here q, q, D, D, B, B and M denote a quark, antiquark, diquark, antidiquark, baryon, antibaryon and meon, repectively. Figure (a) how the correlation between a baryon-antibaryon pair. he figure (b) and (c) how uch correlation for baryon-meon and meon-meon pair, repectively [4]. Figure 6.16: he correlation for ZEUS 3 & 7 data compared to the ARIADNE data. he black triangle repreent the data while the red circle for the MC. he figure clearly how correlation between baryon and it antiparticle, antibaryon. xv

17 Figure 6.17: he rapidity ditribution for the Deep Inelatic Scattering event. he MC i normalized to the data and repreent by the line while the pule repreent the ZEUS data. clearly correlated at low rapidity difference. Figure 6.18: Rapidity ditribution for lambda v antilambda. he upper figure repreent the ditribution for ZEUS 3 & 7 data ample while the below figure for ARIADNE MC data ample. xvi

18 LIS OF ABLES able 1: Claification of the elementary particle. he fermion contitute matter. he boon are the force carrier. able.1: he Fundamental Force in Nature. able 4.1: he ignal to background ratio for the MVD+CD compared to the CD. he performance of the MVD+CD detector i better than the CD only detector. able 5.1: Propertie of the trange particle. able 5.: he number of recontructed trange particle at the detector level in HERA- II. able 5.3: he,, and K recontruction acceptance for high Q DIS and low Q DIS event. able 6.1: Differential baryon cro-ection, d, meaured a a function of Q, p () and () in data. he number of baryon, N and the differential cro ection d are lited for each range of Q, () p and (). able 6.: Differential baryon cro-ection, d, meaured a a function of Q, p () and () in MC. he number of baryon, N and the differential cro ection d are lited for each range of Q, () p and (). xvii

19 able 6.3: Differential baryon cro-ection, d, meaured a a function of Q, p () and () in data. he number of baryon, N and the differential cro ection d are lited for each range of Q, () p and (). able 6.4: Differential baryon cro-ection, d, meaured a a function of Q, p () and () in MC. he number of baryon, N and the differential cro ection d are lited for each range of Q, () p and (). able 6.5: Differential baryon cro-ection, d, meaured a a function of Q, p ( ) and ( ) in data. he number of baryon, N and the differential cro ection ( ). d are lited for each range of Q, ( ) p and able 6.6: Differential baryon cro-ection, d, meaured a a function of Q, p ( ) and ( ) in MC. he number of baryon, N and the differential cro ection ( ). d are lited for each range of Q, ( ) p and able 6.7: Differential K meon cro-ection, d, meaured a a function of Q, p ( ) and ( ) in data. he number of K meon, N and the differential cro ection d are lited for each range of Q, ( K ) p and ( ). able 6.8: Differential K meon cro-ection, d, meaured a a function of Q, p ( ) and ( ) in MC. he number of K meon, N and the differential cro ection d are lited for each range of Q, ( K ) p and ( ). xviii

20 able 6.9: Differential baryon cro ection, d, meaured a a function of Q, p () and () in data. he number of baryon, N and the differential cro ection d are lited for each range of Q, () p and (). able 6.1: Differential baryon cro ection, d, meaured a a function of Q, p () and () in MC. he number of baryon, N and the differential cro ection d are lited for each range of Q, () p and (). able 6.11: Differential baryon cro ection, d, meaured a a function of Q, p () and () in data. he number of baryon, N and the differential cro ection d are lited for each range of Q, () p and (). able 6.1: Differential baryon cro ection, d, meaured a a function of Q, p () and () in MC. he number of baryon, N and the differential cro ection d are lited for each range of Q, () p and (). able 6.13: Differential baryon cro ection, d, meaured a a function of p and ( ) in data. he number of baryon, N and the Q, ( ) differential cro ection ( ). d are lited for each range of Q, ( ) p and able 6.14: Differential baryon cro ection, d, meaured a a function of p and ( ) Q, ( ) in MC. he number of baryon, N and the differential cro ection ( ). d are lited for each range of Q, ( ) p and xix

21 able 6.15: Differential K meon cro ection, d, meaured a a function of Q, p ( ) and ( ) in data. he number of K meon, N and the differential cro ection d are lited for each range of Q, ( K ) p and ( ). able 6.16: Differential K meon cro ection, d, meaured a a function of Q, p ( ) and ( ) in MC. he number of K meon, N and the differential cro ection d are lited for each range of Q, ( K ) p and ( ). able 6.17: he average to K production ratio for HERA-II data compared to the previou HERA-I data. he tatitical uncertaintie are hown for the data. able 6.18: he number of and for ZEUS 3 & 7 data. able 6.19: he number of and for ARIADNE. xx

22 LIS OF SYMBOLS AND ABBREVIAIONS HERA Hadron Electron Ring Accelerator DESY Deutche Elektronen Synchrotron H1 H1 Detector ZEUS ZEUS Detector HERMES HERMES Detector HERA-B HERA-B Detector HERA-II Hadron Electron Ring Accelerator-II PERA Poitron-Electron andem Ring Accelerator SM Standard Model DIS Deep Inelatic Scattering MVD Micro Vertex Detector QFD Quantum Flavor Dynamic QCD Quantum Chromodynamic QED Quantum Electrodynamic SLAC Stanford Linear Accelerator Center PDF Parton Ditribution Function xxi

23 PDF Parton Denity Function CC Charged Current NC Neutral Current Lambda Baryon Anti-Lambda Baryon K Kaon-Short p Proton Pion Plu Pion Minu Z Z Gauge Boon W W Gauge Boon e Electron e Poitron Photon B B Meon B Anti-B Meon q Quark q Anti-Quark xxii

24 Q he quare of the four-momentum tranfer q between the incoming electron and the cattered electron. CP Charge Parity CAL Uranium Scintillator Calorimeter UCAL Uranium-Scintillator Calorimeter FCAL Forward Uranium Scintillator Calorimeter BCAL Barrel Uranium Scintillator Calorimeter RCAL Rear Uranium Scintillator Calorimeter VXD Vertex Detector CD Central racking Detector FD Forward racking Detector RD Rear racking Detector SRD Small-angle Rear racking Detector RD ranition Radiation Detector MVD Silicon Micro Vertex Detector FMVD Forward Micro Vertex Detector BMVD Barrel Micro Vertex Detectror FMUI Forward Muon Detector (located inide) BMUI Barrel Muon Detector (located inide) RMUI Rear Muon Detector (located inide) xxiii

25 FMUO Forward Muon Detector (located outide) BMUO Barrel Muon Detector (located outide) RMUO Rear Muon Detector (located outide) S Straw ube racker DCA Ditance to the Cloet Approached JB Jacquet-Blondel DA Double Angle MC Monte Carlo GEAN GEometry ANd racking VCRAK V(XD)C(D)RA(C)K FORRAN FORmula RANlation BN Baryon Number CP Charge Parity HERACLES NC and CC ep interaction (uing parameterization of tructure function or parton denitie) with radiative correction: ingle photon emiion from the lepton line, elf-energy correction and the complete et of one-loop weak correction can be included [5]. DJANGO Interface between HERACLES (QED correction to order QED ) and LEPO/ARIADNE (QCD matrix element and parton hower/colour dipole radiation) to give complete ep event [5]. xxiv

26 ARIADNE A program for imulation of QCD cacade implementing the color dipole model [5]. LEPO Deep inelatic lepton-nucleon cattering baed on LO electroweak cro ection (incl. lepton polarization), firt order QCD matrix element, parton hower and Lund hadronization giving complete event. Soft colour interaction model give rapidity gap event [5]. JESE he Lund tring model for hadronization of parton ytem [5]. LO Lowet Order Z ZEUS oftware track finding package xxv

27 CHAPER 1 Introduction In recent year phyicit have uncovered a lot of information about the Univere that urround u. hi earch ha revealed that, beyond the evidence of our eye, there i a eething world of tiny particle and meenger that pa between them, endlely changing in energy, in pace, and in time. A large new idea on the matter tructure undertanding wa made by phyicit when it wa later found out that the atom wa made up of of electron, proton and neutron. Figure 1: Flow chart of the elementary particle tudie. Particle are alo the ubject of earching for elementary particle. Particle are made up of quark and lepton and were explored uing particle accelerator and detected by particle detector. Quark held together by gluon and come in 6 flavor 1

28 including up, down, charm, trange, top and bottom and 3 colour and interact by the colour force which i the origin of the trong interaction. Quark in pair make up meon and in three make up baryon, which both are included in hadron a particle and interact by the trong interaction. Lepton including electron, electron neutrino, muon, muon neutrino, tau and tau neutrino, interact via photon in electromagnetic force and intermediate vector boon in weak force, which are crucial to electroweak unification. he Standard Model i the mot advanced quantum theory known yet which decribe how elementary particle interact. he Standard Model heory (SM) of particle phyic provide a framework for explaining chemitry and nuclear phyic (low energy proce). It additionally provide an explanation for ub-nuclear phyic and ome apect of comology in the earliet moment of the univere (high energy proce). It i a imple and comprehenive theory that explain all the hundred of particle and complex interaction with only 6 quark (up, down, trange, charmed, top and bottom), 6 lepton (electron, muon, tau, electron neutrino, muon neutrino and tau neutrino) and 4 gauge boon that act a the force carrier particle (photon, gluon, Z and W ± ). he Standard Model alo decribe the trong, weak and electromagnetic fundamental interaction, uing mediating gauge boon. All the known matter particle are compoite of quark and lepton, and they interact by exchanging force carrier particle. he Standard Model ha been confirmed experimentally to the great accuracie. But it doe not explain everything. For example, gravity i not included in the Standard Model. A claification of elementary particle i given in able 1.

29 able 1: Claification of the elementary particle. he fermion contitute matter. he boon are the force carrier. Electromagnetic force i the force between ma with electromagnetic charge, which attract and/or repel each other. he trong force i the force that bind or more proton againt electric repulion and form a nucleu. he weak force i the force that caue the nuclear fiion. Gravity i the force between matter with ma, which attract each other. he firt experiment which have been made in unravelling the tructure of matter during the lat century wa the -particle cattering experiment on a metal foil, carried out by Ernet Rutherford in hi experiment relie on the very baic concept that the angular and energy ditribution of the cattered point-like tet particle are related to and can reflect the inner tructure of the target. he ignificance of thi experiment i that it clearly howed that the atom ha a hard compact component, the atomic nucleu. Many year later, nuclei were found to be compoed of proton and neutron. hi bring our knowledge of the elementary block of matter from atom to proton and neutron. o look inide the atomic nucleu require pecial type of microcope known a particle detector. he Heienberg uncertainty relationhip tell u that higher energy i required in order to probe maller ize of matter. By the ue of electric field, 3

30 electrically charged particle uch a electron or proton were accelerated to within the fraction of the peed of light and then mahed into target of matter or head on into one another. he reult of uch colliion can reveal the deep tructure of matter. hey how not only the quark that eed the atomic nucleu, but have alo revealed exotic form of matter with weird name - trange, charm, bottom, and top and heavier form of the electron, known a muon and tau. he Hadron Electron Ring Accelerator, HERA wa the firt and o far the only electron-proton collider in the world ituated at DESY in Hamburg, Germany. he HERA project ha been in operation ince 199 with two general purpoe detector, H1 and ZEUS, and two dedicated purpoe detector, HERMES and HERA-B. he latter two experiment are the fixed target experiment that were tarted in1995 and. During it operation, the HERA collider produced two type of data, HERA-I and HERA-II that runned in different period. he HERA-I data were collected during the running period from 199 to while the HERA-II data were collected during the running period from 3 to 7. hi thei i baed on the HERA-II data, elected by the ZEUS detector at HERA collider with a total integrated luminoity of 4.6pb -1, during the running period between 3 & 7. he objective of thi thei are (i) to tudy the correlation on baryon-antibaryon production in ep colliion baed on the LUND tring model and (ii) to tudy the effect of uing Micro Vertex Detector (MVD) tracking information to find track in addition to the Central racking Detector (CD) for the earche of trange particle, and K. 4

31 1.1 HESIS OULINE he thei wa arranged a follow. An introduction i given in thi chapter. he econd chapter give an overview of the phyic concept which decribe all the procee that happened during the particle colliion. he HERA phyic, trangene phyic, particle correlation phyic and the motivation of the thei are preented in thi chapter, a well a decribing the quark parton model and model to imulate trange quark production in DIS and photoproduction event. Chapter 3 goe on with the explanation about the experimental et-up, the decription of the HERA collider, the ZEUS detector and it component that are relevant to the analyi, the Micro Vertex detector (MVD) component, offline election of event, decribing the trigger and cut ued in the particle recontruction, a well a a brief decription of the Monte Carlo data et ued to compared the different et of reult. he fourth chapter review the uage and the effect of the Micro Vertex Detector in the production of trange particle, and K. he trange particle recontruction, baryon characteritic and identification of p, p and K _ candidate were dicued in Chapter 5. Chapter 6 dicue on the total cro-ection, differential cro-ection, baryon-toantibaryon production aymmetry, baryon-to-meon ratio and the baryon antibaryon rapidity correlation in ep colliion reult of the meaurement and the correponding dicuion and Chapter 7 conclude the thei. 5

32 CHAPER Phyic Overview.1 he Standard Model he Standard Model of particle phyic i a very ucceful theory to decribe the fundamental contituent of matter and the interaction between them. A of right now, we know of 1 fundamental particle: ix quark and ix lepton a hown in the Figure.1 below. here are currently hundred of identified particle made from combination of thee twelve fundamental particle and cientit are till finding more. Figure.1: he fundamental particle of the Standard Model 6

33 able.1: he Fundamental Force in Nature According to the Standard Model, particle and force are both manifetation of the underlying quantum field. Since thee field can be een a particle, we can ay that all matter and force are made of a few kind of particle. he Standard Model predict that there are three baic force, and two familie of matter. he force include the electromagnetic force and the weak force (which can be een a a unified electroweak force) and the trong force. hey work over different range and have different trength. Gravity i the weaket but it ha an infinite range. he electromagnetic force alo ha infinite range but it i many time tronger than gravity. he weak and trong force are effective only over a hort range and dominate only at the level of ubatomic particle. he weak force i much tronger than gravity but it i indeed the weaket of the other three. he trong force i the tronget force among all the four fundamental interaction. Each of thee force i carried by particle, a hown in able.1. Of thee particle, only the graviton have not yet been found, although mot phyicit are fairly confident that they will be. 7

34 he gravitational force, mediated by graviton i the force of attraction between all mae in the univere, epecially the attraction of the earth ma for bodie near it urface. he electromagnetic interaction decribe the quark-lepton interaction, and it i mediated by photon. he electromagnetic force and the weak force are unified into the electroweak force, decribed by the Quantum Flavor Dynamic (QFD). he weak interaction decribe tranition between quark or lepton generation, and it i mediated by vector boon, W ± when the interaction involve a charge tranfer, and Z when it i a neutral tranfer. he Strong interaction are mediated by gluon and i reponible for the binding of quark into hadron and it i decribed by Quantum Chromodynamic (QCD) [18]. he Standard Model provide a quantum field theory of the firt three force, taking pecial relativity into account. Gravity i the odd force out, becaue there i no verified quantum theory of gravity. he quantum theory ued to decribe the micro world, and the general theory of relativity ued to decribe the macro world. No one ha managed to make the two mathematically compatible in the context of the Standard Model..1.1 Quark In the mid-196, Gell-Mann introduced the concept that point-like particle ( quark ) exited inide the proton [13]. hi idea wa mainly baed on the effort to decribe the rich pectrum of meon and hadron reonance that were dicovered during the 195, which wa interpreted a excited bound tate of thee point-like contituent. Later, in 1968, new data from SLAC electron cattering experiment hinted that the proton wa in fact built up out of point-like particle which phyicit at that time called parton. he experiment proved that high-energy electron have a large 8

35 probability of cattering with large energy tranfer and into large angle. he exitence and propertie of quark were firt inferred from hadron pectrocopy by Gell-Mann and independently by Zweig in 1964 and the cloe correpondence between the experimentally oberved hadron and thoe predicted by the quark model remain one of the tronget reaon for the belief in the exitence of quark. Quark and antiquark are the particle which carry electric charge. Since pion were firt produced in the laboratory in the early 195, everal hadron then have been oberved and all have zero or integer electric charge:, ±1 or ± in unit of e, where e i the fundamental unit of electrical charge. hey are all bound tate of the fundamental pin ½ quark, whoe electric charge are either + ⅔ or -⅓, and/or antiquark, with charge -⅔ or +⅓. he quark themelve have never been directly oberved a ingle, free particle and thi fact initially make it difficult for quark to be accepted a anything other than convenient mathematical quantitie for performing calculation. In order to tudy the quark, we need to tudy the hadron firt. Hadron are important becaue free quark are unobervable in nature and o to deduce their propertie, we are forced to tudy hadron [13]. Figure.: Hierarchy of the quark 9

36 . Quark Parton Model Even though the quark model wa ucceful in decribing the variety of baryon, there wa a period of time when phyicit debated whether thee quark were really phyical entitie and not jut non-phyical artifact required by calculation. During thi period, Feynman introduced the o-called Parton Model [35] which gave the bet decription of what the experiment really revealed. In thi Parton Model, the caling behavior of the tructure function were quickly undertood a cattering on charged point-like particle in the proton. he eential idea i that the photon i interacting with free charged pointlike particle inide the proton which i called parton. In the Parton Model, we accept that the quark are the building block of hadron and play a direct role in the hort ditance dynamic. he knowledge about the tructure of hadron i decribed from the Parton Ditribution Function (PDF) and the parton fragmentation function. he baic idea of the Parton Model i that at high energy-momentum tranfer Q, an electron catter from an effectively free quark or antiquark and the cattering proce i completed before the recoiling quark or antiquark ha time to interact with it environment of quark, antiquark and gluon. Proton conit of 3 parton, identified with the QCD quark. During the interaction, the proton i frozen. Electron proton cattering i the um of incoherent electron quark cattering. he PDF can explain the proton tructure and i defined a the probability denity for finding a particle with a certain longitudinal momentum fraction x at momentum tranfer Q. hi PDF decribe the ditribution of hort ditance parton within hadron, while the parton fragmentation function wa decribing the ditribution of long ditance hadron within the fragmentation debri of an eentially iolated parton. 1

37 he experiment at Stanford confirmed the anticipated [19] phenomenon called cale invariance (Bjorken caling) which proved that the cattering of high-energy electron on the proton wa independent of Q. he fact that the tructure function at very high energie become le dependent on Q and only dependent on the ingle variable wa predicted by Bjorken in the late 6. Bjorken aid that if large Q (high-energy) photon reolved point-like contituent in proton, the tructure function would become MW v, Q ) F ( ), (.1) 1( 1 vw v, Q ) F ( ), (.) ( where q. p / Q Mv / Q i the dimenionle variable. he tructure function F 1, are independent of Q for fixed value of. hi i the analogue to the in 4 ( / ) behavior of the momentum tranfer in the famou Rutherford experiment, which led to the identification of the atomic nuclei and wa the main argument that the photon i interacting with point-like particle, parton, ince many phyicit at that time did not believe that quark were real phyical object. he coming year after the Stanford experiment, many experimental reult indicated that thee parton had quantum number from the quark model and a for today it ha become clear that the parton in Feynman parton model can be identified a quark. 11

38 .3 Quantum Chromodynamic (QCD) Figure.3: Quantum Chromodynamic proce Quantum chromodynamic, familiarly called QCD, i the modern theory of the trong interaction. Nowaday QCD i ued to decribe mot of what goe on at high energy accelerator, trying to undertanding what proton and neutron are and how they interact. Quantum chromodynamic appear a an expanded verion of Quantum electrodynamic (QED) wherea in QED there i jut one kind of charge, while QCD ha three kind of charge, labeled by color. QED i the theory of light interacting with charged matter, where photon repond to the preence or motion of electric charge [18]. QCD tate that quark are confining, where gluon and quark cannot exit a iolated particle. A baryon cannot be fragmented into it contituent, the quark even if the tronget force are applied. Intead of breaking into part, the baryon create one or everal additional particle via the elf-interacting and quantum-mechanical dynamic of the gluon field that connect the quark within the baryon [47]. he color charge of QCD, red, green and blue have propertie analogou to the electric charge. In particular, the color charge are conerved in all phyical proce and there are photon-like male particle called gluon, which repond in appropriate 1

39 way to the preence or motion of color charge, very imilar to the way photon repond to an electric charge. For all their imilaritie, there are everal difference between QED and QCD. Firt of all, the repone of gluon to color charge, a meaured by the QCD coupling contant, i much more energetic than the repone of photon to electric charge. he econd one i that gluon can alo change one color charge into another, in addition to jut reponding to the color charge and yet the color charge i conerved [18]. he third difference between QCD and QED i that gluon repond directly to one another, quite unlike photon. hi i becaue gluon repond to the preence and motion of color charge and they carry unbalanced color charge while photon are electrically neutral. Colored particle are alway produced with their correponding anti-colored particle, by ymmetry. If thee particle move away from each other it become energetically favorable to produce new quark-antiquark pair which then combine to form the colorle obervable known a hadron..4 Deep Inelatic Scattering (DIS) When a high-energy electron (or poitron) collide with a proton, a in HERA collider, the implet nuclear reaction that can occur i that a quark i ejected to give a highenergy jet of particle. hi i Deep Inelatic Scattering (DIS) and i mediated by the exchange, between the electron and the quark, of a virtual photon;, W or Z [53]. In thi proce, we call it deep becaue the photon penetrate the proton deeply and inelatic becaue the proton break up. he cattering proce not only involve valence quark, but can alo occur by mean of virtual quark-antiquark pair that appear temporarily within the proton. 13

40 Indeed, the proton may be conidered a coniting of a continuum of different combination of parton, that i to ay (anti)quark and gluon, and depending on how violently it i truck by the exchanged boon [18]. hu the PDF of the proton are function both of the fraction x of the proton taken by a given parton and of the virtuality Q of the exchanged boon [53]. he DIS experiment paved the way for undertanding the tructure of the proton and neutron which wa interpreted in the parton model..4.1 Electron-Proton Scattering In electron proton colliion, electron wa ued a a probe of the proton tructure. At HERA collider, the phyic wa preliminary focued on teting our comprehenion of the trong force, providing u information of the multihadron production; help u to identify eparate hadron and reonance. he electron-proton interaction continue via the exchange of a virtual vector boon, either a γ or a.4. During thi proce, when the energy tranfer Z or a W a hown in Figure Q become larger, the proton break up, firt into reonant baryon tate and later (higher Q ) to complicated multi-particle tate a i illutrated in Figure.4. Figure.4: Lowet order Feynman diagram for Charged Current and Neutral Current Deep Inelatic Scattering (DIS) 14

41 here are two type of interaction during the Deep Inelatic Scattering (DIS) proce. he firt one i the Charged Current (CC) proce. hi proce occur when the exchanged boon emit from the electron i a charged W particle, which collide with the proton, conequently leaving a neutrino in the final tate. he econd interaction i the Neutral Current (NC) proce. During thi proce, the electron will emit an electrically neutral exchange-boon, uch a γ or Z particle, to collide with a quark (or gluon) within the proton. he interaction are generally of the form hown in Eqn..3. Here, X i generally a high multiplicity hadronic ytem. ' e P e X (NC); e ( e ) P ( ) X (CC) (.3).5 HERA Kinematic Figure.5: Feynman diagram for a Neutral Current DIS colliion. a) he 4-vector of incoming and outgoing particle. b) he Lorentz invariant calar defining the event. 15

42 Figure.5 how an electron proton cattering interaction chematically in HERA. During the head-on electron and proton colliion at high energy, the electron will emit a gauge boon (neutral boon, photon or Z for the Neutral Current DIS interaction, and charge boon, W ± for the Charge Current interaction). hi gauge boon will interact with the parton inide the proton tructure, and then produce new hadron. hi proce i called Deep Inelatic Scattering proce. Figure.6: he imulated picture of Neutral Current and Charge Current proce in Deep Inelatic electron-proton cattering in HERA. From the Figure.6 above, we can ee that the Neutral Current interaction will produce electron and hadron in the final tate, while the Charge Current interaction will produce neutrino and hadron in the end of the proce. For thi thei, we will tudy the NC DIS interaction. In the Figure.5(a), the 4-vector k and k decribe the incoming and outgoing electron, P decribe the proton and q i for the exchange boon. he NC DIS interaction can be written a: e( k) p( P) e'( k') X( P') (.4) Auming that k, ' k, P and ' P are the four vector of the initial and final electron of the incoming proton and of the outgoing hadronic ytem, the uual variable decribing the propertie of electron-proton cattering [16] are 16

43 Q ' q ( k k ), (.5) ( k P), (.6) W ( q P) p, (.7) Q x, (.8) P. q q. P y, (.9) k. P q. P v, (.1) m N where ' q k k define the 4-momentum tranfer from the lepton to the proton from which follow that P ' P q, P decribe the proton and q i for the exchanged photon. Q i the quare of the four-momentum tranfer q between the incoming electron and the cattered electron. x i the fraction of the longitudinal momentum of the truck quark in the proton, if it i aumed that the parton tranvere momenta inide the proton and the parton mae can be neglected compared to Q. y i the relative energy tranfer of the electron to the proton, with repect to the proton ret frame. he dimenionle variable x and y will be ueful in characterizing the high energy limit and correpond to the fraction of the incident energie carried by the interacting particle. he centre-of-ma energy quared of the proton ytem i: Q ( k P) k. P (.11) xy 17

44 where the approximation i that the particle mae are mall compared to the centre-ofma energy and thi approximation i very good for the HERA machine. Hence, for a given centre-of-ma energy, any two of x, y and kinematic. Q fully defined the ep cattering he centre-of-ma energy, W, of the hadronic ytem i: W ( q P) P. q q (.1) he incluive differential cro ection, integrated over all poible hadronic final tate, i a function of two variable which uniquely determine the kinematic of the event. hee variable are mot eaily recognizable a the energy and the production angle of the cattered lepton. However, the differential cro ection i uually expreed in term of two variable, x and Q, defined in Eq. (.6) and Eq. (.9) [16], d dxdq y y A xf1 ( x, Q ) (1 y) F ( x, Q ) ( y ) xf3 ( x, Q ) (.13) where, for Q M W, Z (the ma quared of the intermediate vector boon), A GF / x for neutrino and anti-neutrino with G F the Fermi contant, and A 4 4 / xq for charged lepton with the electromagnetic coupling contant. he tructure function, F i, may depend on the kinematic of the cattering and the choen variable are x and Q [16]. 18

45 .6 Baryon Production he tring fragmentation model [6] i able to give generally very good decription of the ditribution of hadron in quark and gluon jet [1]. In the Lund String Hadronization model, the confining field i expected to behave a a relativitic tring, i.e. like a vortex line in a uperconductor. he model contain firt a decription of the decay of a traight tring, and econdly the aumption that gluon behave a tranvere excitation or kink on the tring. he gluon kink have no inherent influence on particle compoition. he tring can break by the production of q q pair, which are pulled apart by the tring tenion. A the q and q move apart, the potential energy tored in the tring increae, and the tring may break by the production of new ' ' q q pair, o that the ytem plit into two color-inglet ytem ' q q and q ' q. If the invariant ma of either of thee tring piece i large enough, further break may occur. In the Lund tring model, the tring break-up proce i aumed to proceed until only on-ma-hell hadron remain, each hadron correponding to a mall piece of tring with a quark in one end and an antiquark in the other [5]. When a quark meet an antiquark from a neighboring pair, they can form a final tate meon, a hown in Figure.7 [31]. Figure.7: String fragmentation in pace. 19

46 Baryon production i a more complex proce than the production of meon. B B correlation in rapidity are in agreement with the aumption that the B and the B are produced a neighbour or next to neighbour in a tring break-up. he ditribution in the angle between the baryon and the thrut axi (i.e. the general tring direction) in the B B i not pherically ymmetric [4, ]. Recent data from polarized e e annihilation how that baryon are more frequent in quark jet than in antiquark jet [37]. hu baryon-antibaryon pair do not originate from iotropically decaying cluter. Intead the ditribution can be undertood if the B and B are pulled in oppoite direction at the tring break-up. he tring break by the production of a diquark-antidiquark pair in a 3 3 color tate, which become contituent in the baryon and the antibaryon [7]. o improve agreement with experiment, a more general framework for baryon production wa preented in the popcorn model [8], in which diquark a uch are never produced, but rather baryon appear from the ucceive production of everal q q pair [5]. Aume that a color field i tretched between e.g. a red quark, r and an antired antiquark, r. he tring can break if a rr q q pair i produced and pulled apart by the tring tenion. We can alo imagine that a b b pair i produced a a virtual fluctuation. If the rb ( r b ) i in a color antitriplet g (triplet g ) tate, the color field between the produced quark and antiquark will correpond to a triplet color field with the ame trength a the original field. hu equal force in oppoite direction act on the new quark and the new antiquark. In accordance with the uncertainty principle, they can move around freely for a time inverely proportional to their energy. hee quark are called curtain quark, from the picture of ring on a curtain-rod, liding back and forth with no frictional

47 loe and without changing the propertie of the rod. In ditinction to curtain quark, the quark that caue the tring to break are called vertex quark. If the tring break within the color fluctuation region, an effective diquark-antidiquark pair i produced, ee Figure.8 and Figure.9 [31]. Figure.8: If a vertex pair i produced inide a color fluctuation region panned by, an effective diquark-antidiquark pair ha popped out in a tepwie manner. he model allow for everal breakup in the color fluctuation region, creating one or ome meon among the antibaryon and baryon, a hown to the left. Figure.9: A popcorn example with two curtain quark pair. 1

48 .6.1 Strange Quark Production he production of the trange quark can be either from the hard interaction or from pure fragmentation proce. he fragmentation proce become important for trangene production at HERA. Production of the trange quark during the electron proton colliion at HERA can be explained by variou mechanim. he firt mechanim i Boon-Gluon fuion proce, a hown in Figure.1(i). During thi proce, the () quark are produced when the exchange boon couple with a gluon from the proton. hi i the major channel to produce trange quark. he econd trange quark production mechanim i given in Figure.1(ii), decribing the gluon-plitting proce. In thi proce, photon interact with parton from proton, produced gluon, and gluon plit into () quark. he third mechanim i hard cattering of ea quark, a hown in Figure.1(iii). In thi proce, there i no valence quark among proton contituent. But a the Q increae, the () quark can be reolved by the virtual photon and can be knocked out to form a final trange hadron. he fourth trangene production channel i the heavy flavor decay. In thi proce, trange quark were produced from the decay of heavy quark uch a charm or beauty quark. However, the trange production from thi mechanim i contrained by the low rate of the heavy flavor production. Strange quark could alo originate from fragmentation proce, where the trange quark emerge from gluon fluctuation in the parton hower intead of being directly involved in the hard cattering proce.

49 Figure.1: Poible mechanim of the trange quark production 3

50 .7 Phyic Motivation of the hei Particle phyic i the tudy of the baic element of matter and the force acting among them. It aim to determine the fundamental law that control the character of matter and the phyical univere. Strange hadron production in particularly baryon are not well undertood but thee trange particle are intereting becaue of their behaviour uch a low ma, high tatitic and clean ignal. Due to the conervation of trangene, lightweight particle do not decay a quickly if they exhibit trangene. he particle lifetime will be longer when the number of trangene i high. he meaurement of the trange hadron can anwer everal phyic problem and can how that trange quark are like other quark, behave a point-like particle. he obviou way to determine if the proton i built up out of point-like particle i to compare the way the cro-ection behave, ince it depend heavily on the proton tructure function. By meauring the total cro-ection, we can know the probability of interaction between mall particle. he baryon-antibaryon production aymmetry could give a hint on how the preence of the initial proton affect the production in the final tate. While tudy on baryon to meon ratio can anwer the quetion on how do baryon and meon formed and the quetion on how doe quark become hadron can be anwered by tudying the rapidity particle correlation between baryon and antibaryon. 4

51 CHAPER 3 Experimental Set-up In order to explore the tructure of hadron in particle phyic, it require projectile whoe wavelength are at leat a mall a the effective radii of the nuclei or hadron. hi determine the minimum value of the momentum p = h/ λ and hence the energy required. In particle phyic experiment, particle accelerator were ued to collide two particle at high energy and at peed near to the peed of light.high energy wa required in order to produce new and untable particle. hi reveal a diadvantage of fixed-target experiment when large centre-ofma energie are required. he centre-of-ma energy i important becaue it i a meaure of the energy available to create new particle. In the laboratory frame, at leat ome of the final tate particle mut be in motion to conerve momentum. Particle phyic experiment are a modern verion of Rutherford table-top experiment, on cattering of alpha particle with thin metal foil. Figure 3.1: Flow in the data proceing proce in High Energy Phyic Experiment. 5

52 Figure 3.: he data from HERA wa tored here. 3.1 he HERA ep Collider he Hadron Electron Ring Accelerator, HERA wa the firt and o far the only electronproton collider in the world ituated at DESY in Hamburg, Germany. he DESY (Deutche Elektronen Synchrotron, German Electron Synchrotron ) i the bigget reearch center for particle phyic, with ite in Hamburg and Zeuthen [16]. he main purpoe of DESY are fundamental reearch in particle phyic and reearch with ynchrotron radiation. HERA i located under the DESY ite nearby Volkpark around 15 to 3 m underground and ha a circumference of 6.3 km and conit of two eparate accelerator, HERA and PERA. he contruction of thee two-ring accelerator took from May 1984 until November 199. he beam were egmented into 18 colliding bunche each, providing a bunch croing rate of 1 MHz. here are four experiment ituated at HERA. he two collider experiment H1 and ZEUS were the main general multi-purpoe detector in HERA and have been in operation ince 199. In 1995 the HERMES experiment tarted the data taking uing the polarized electron beam on a 6

53 fixed polarized ga target. hi detector wa deigned for invetigating the pin ditribution of the quark in proton and neutron. he HERA-B i a proton-proton fixed target experiment, operated between and wa contructed in order to meaure the Charge Parity violation in B-meon ytem. HERA conit of two torage ring mounted on top of one another, except at the interaction point inide the detector ZEUS and H1. One ring i for electron/poitron, operate at room temperature with normal conductor, while the other one i proton torage ring, and required uperconducting magnet operating at a temperature of 4.4 K. hoe temperature were required to produce magnetic field of 4.65 which wa neceary to bend the high momentum proton in the arc of the ring. hi magnetic field limited the proton energy to 9 GeV. he proton and electron/poitron beam in the torage ring were not continuou, but rather grouped into bunche which collide every 96 n, thereby etting the maximum rate of colliion. At very high energie with colliion of electron/poitron at energy of 7.5 GeV with proton at 9 GeV, HERA offered phyicit to tudy the unique poibility of phyic topic. he tructure of the proton contituent (quark and gluon), a well a other intereting phyic topic uch a photon tructure, pertubative Quantum Chromodynamic (jet and heavy quark), neutral, charged current and electroweak proce wa tudied in HERA. 7

54 Figure 3.3: he HERA and PERA accelerator aerial view at the DESY campu in Hamburg, Germany. HERA wa at 15-3 m underground with circumference 6.3 km. Figure 3.4: he HERA collider with the four experiment H1, ZEUS, HERMES and HERA-B. Figure 3.5: A mall egment of the HERA tunnel. he proton beam i travelling in the large vacuum tube in the middle to the right while the electron beam tube i below that. 8

55 3. he ZEUS Detector Figure 3.6: Cutaway of the ZEUS detector he ZEUS experiment wa one of two general purpoe e - p colliding beam experiment at the Hadron Electron Ring Accelerator (HERA) at Deutche Elektronen Synchrotron (DESY) in Hamburg, Germany. he goal of the ZEUS detector wa to determine with high preciion the energie, direction and nature of ingle particle and particle jet created in the interaction. he ZEUS detector wa located in the South Hall of HERA with dimenion 1 m 1 m 19 m and it total weight wa 36 ton. below. he overview of the ZEUS detector in variou cro ection cut can be found 9

56 Figure 3.7: Cro ection of the ZEUS detector in the vertical plane, ide view. Figure 3.8: Cro ection of the ZEUS detector in the vertical plane, top view. 3

57 Figure 3.9: Cro ection in tranvere plane containing the nominal interaction point. he heart of the ZEUS detector wa the uranium cintillator calorimeter (CAL) which meaured energie and direction of particle and particle jet with high preciion. hi hermetically encloed the tracking detector which meaured the track of charged particle uing wire chamber and which conited of: a vertex detector (VXD), the central tracking detector (CD), forward (FD) and backward (RD) drift chamber and in the forward direction a tranition radiation detector (RD) to identify high energy electron/poitron. hee chamber were urrounded by a thin uperconducting olenoid coil producing an axial magnetic field of 1.43 ela for determining the momentum of charged particle from back curvature [16]. he ZEUS detector main part a hown in Figure 3.6, Figure 3.7 and Figure 3.8 are a follow; he high-reolution Uranium-Scintillator Calorimeter (UCAL) [34]: wa ued to meaure energie and direction of particle and jet with high preciion. CAL conited of three part: the forward (FCAL), the barrel (BCAL) and the rear 31

58 (RCAL) calorimeter. Each part i ubdivided into tower and each tower i longitudinally egmented into one electromagnetic ection and either one (in RCAL) or two (in BCAL and FCAL) hadronic ection. he mallet ubdiviion of the calorimeter i called a cell. he CAL energy reolution, meaured under tet-beam condition, are ( E ) / E.18 / E for poitron and ( E ) / E.35 / E for hadron, with E in GeV. he timing reolution of the CAL i ~1 n for energy depoit greater than 45 GeV; Central racking Detector (CD) [6], aided by an axial magnetic field of 1.43 ; Micro Vertex Detector (MVD) [4], intalled in after the recontruction. MVD i deigned for more precie meaurement of the track recontruction and track momentum value; 3-component (forward, barrel and rear) ytem of muon chamber; 3 inner chamber (FMUI, BMUI, RMUI) and 3 outer (FMUO, BMUO, RMUO); Small-angle Rear racking Detector (SRD) which improve the angular reolution on the cattered electron in the rear direction. Figure 3.1: he ZEUS coordinate ytem. he ZEUS coordinate ytem i a right-handed Carteian ytem, with the z axi pointing in the proton beam direction, referred to a the forward direction, and the x 3

59 axi pointing toward the center of HERA. he coordinate origin i at the nominal interaction point. he polar angle,, i meaured with repect to the proton beam direction. he azimuthal angle in the x-y plane i called. A full decription of the ZEUS detector i given in [45]. A brief decription of the component that are mot relevant for thi analyi i given below. he main component of the ZEUS detector that are ued in thi analyi are the tracking detector, epecially the central tracking detector (CD) [6] and the microvertex detector (MVD) [4]. Figure 3.11: Integrated luminoity collected by ZEUS for the and -7 period, hown eparately for each year he Central racking Detector (CD) he Central racking Detector provide the meaurement of particle momentum, vertexing, particle id via energy lo and alo participate in the trigger at all level. Energy lo happened when charge track were croing ome material, it will loe ome energy per unit length. he ZEUS CD wa conceived to detect and identify the charged particle with high preciion over a wide range of Q. 33

60 he CD operated in a magnetic field of 1.43 provided by a thin uperconducting olenoid and CD conited of 7 cylindrical drift-chamber layer, organized in nine uperlayer covering the polar angle region he CD wa filled with a ga mixture of 8% Argon (Ar), 13% Carbondioxide (CO ) and 5% Ethane (C H 6 ). When charged particle pa through the ga, the ga will ionized into negatively charged electron and poitively charged ion. he electron moved to the poitively charged ene wire and the ion drift toward the negatively charged ene wire becaue of the preence of electromagnetic field in the detector. he ubequent collection and amplification of the ignal pule create a detectable ignal (indicating the paing of the charged particle). he electronic read out collected thee ignal. he pule meaured with the ene wire wa proportional to the energy lo of particle paing through the CD. Particle identification wa poible uing meaurement of the mean energy lo, de / dx, of charged particle in the ga of the active volume. he odd numbered (axial) uperlayer contain drift wire that run parallel to the z-axi. he even numbered (tereo) uperlayer are oriented at a mall angle with repect to the z-axi (pleae refer Figure 3.9). hi allow both r and z coordinate to be meaured. he hit in CD were combined to recontruct particle trajectorie. he tranvere momentum reolution for full-length CD track wa ( p )/ p.58p.65.14/ p, with p in GeV. he average reolution that ha paed through all uper layer in r plane in CD wa ( ) (18m)/63. cm. While the average reolution that had paed through all uperlayer in z-direction in CD i ( ) ( mm)/63. cm [6]. 34

61 3.3 HERA-II he ZEUS detector wa upgraded at that time in a number of area to prepare for the phyic opportunitie of HERA-II. he HERA upgrade produced about a factor of five in improvement in luminoity delivered to the experiment and aimed to accumulate 1 fb -1 of data in the HERA-II program. In order to take advantage of thi, the ZEUS detector wa upgraded in everal area: the ilicon microvertex detector (MVD); the traw-tube tracker (S); and the luminoity monitor [1]. HERA-I produced deep inight into QCD and laid the foundation for the tudy of the pace-like electroweak interaction at high Q. HERA-II promied to build on thoe foundation to open new field of preciion electroweak tudy and earche for the phyic beyond the Standard Model [1] he Micro Vertex Detector (MVD) he Micro Vertex Detector wa intalled in /1 for HERA-II data in order to be ueful for tagging heavy flavor meon. hi detector provided the capability to recontruct econdary vertice diplaced from the primary by ditance of the order 1 m. It central barrel conited of 3 ladder, each of which contain five module of four ingle-ided ilicon microtrip detector arranged in pair with orthogonal trip direction. he elliptical hape of the beam pipe i neceary to avoid the intene ynchrotron radiation generated by the new uperconducting quadrupole. hi hape implied a complex geometry in which ladder were placed uch that mot emerging charged particle interected the three detector layer. 35

62 Figure 3.1: he ZEUS Micro Vertex Detector (MVD) he MVD ilicon tracker conited of a barrel (BMVD) and a forward (FMVD) ection [4]. he BMVD contained three layer and provided polar-angle coverage track from 3 to 15. he four-layer FMVD extended the polar-angle coverage in the forward region to 7. After alignment, the ingle-hit reolution of the MVD wa 4 μm. he tranvere ditance of cloet approach (DCA) to the nominal vertex in XY wa meaured to have a reolution, averaged over the azimuthal angle of (46 1/ p ) μm, with p in GeV. he Micro Vertex Detector wa aligned with a combination of track from comic event and ep event in the HERA collider. MVD could only detect the charge particle. A charged particle paing through the ilicon trip, they caue mall ionization current which can be detected and meaured. In thi analyi, and K 36

63 are neutral, o we cannot oberved them directly by the CD and the MVD. However we can oberve them through their decay product. Figure 3.13: a) A ection through the barrel MVD, howing the arrangement around the beam-pipe of each the MVD ladder. b) A photograph of one half of the MVD, howing the barrel ladder, one half of each of the forward wheel and the cable and ervice [1]. 37

64 3.4 ZEUS Analyi and Computing Model Figure 3.14: Flow diagram of event analyi in the ZEUS detector. Simulated and actual event were run concurrent and compared to extract correction factor from pqcd calculation. 38

65 3.4.1 Data proceing: the ZEUS Recontruction Factory he data taken by the ZEUS experiment are proceed on a PC farm running Linux a operating ytem. Recontruction i performed in a emi-automated way under the ZEUS Recontruction Factory (ZRF), a framework baed on MySQL, PHP4 and Apache with LSF a the underlying batch ytem. he production ytem ha the flexibility to ue alo reource of the ZEUS analyi facility (ZARAH) when they are free. After the end of ZEUS data taking period all dataet have been recontructed and then re-proceed with improved calibration contant and recontruction oftware [57] ZEUS Analyi Facility (ZARAH) ZARAH i the central ZEUS data analyi facility. It provide the computing infratructure & upport for batch data analyi ("data mining") and the event data torage facilitie of the experiment. he core of the ZARAH facility i a computation cluter which conit of the PC baed batch farm and the torage facilitie of the experiment. he acce to the ZEUS event repoitory i highly optimized through the implementation and uage of the pecial ervice like zelite tag databae for an efficient event election and a dik cache ytem for the data torage and tranfer between the tape repoitory and the farm node. he preent ZARAH PC farm conit of 6 dual-proceor node, where node have.6 GHz Opteron CPU on a yan motherboard, are baed on Intel Xeon 3.6 GHz and node have Xeon. GHz,. he LSF batch ytem integrate thi 39

66 facility with the recontruction farm. I/O from & to ma torage relie heavily on the dcache ytem [57] ZEUS Analyi Figure 3.15: he ZEUS Analyi Environment 4