Backward Angle Omega Meson Electroproduction (The Final Analysis Presentation)

Transcription

1 Backward Angle Omega Meson Electroproduction (The Final Analysis Presentation) Wenliang (Bill) Li UofR Ph.D Student (this work) WM Post-doc Ph. D supervisor: Garth Huber 1

2 Outline Introduction to the data (history) Theory Experiment and technique Results and Outlook 2

3 Introduction: Data Come from 6 GeV Era (Fpi-2 experiment) Fpi-2 (E01-004) 2003 Spokesperson: Garth Huber, Henk Blok Standard HMS and SOS (e) configuration Electric form factor of charged π through exclusive π production Q2=2.45 GeV2 Low ϵ π Low ϵ ω p Primary reaction for Fpi-2 p(e, e π+)n Coincidence time In addition, we have for free p(e,e p)ω High ϵ Kinematics coverage W= 2.21 GeV, Q2=1.6 and 2.45 GeV2 Two ϵ settings for each Q2 π+ ω High ϵ p Coincidence time epx missing mass epx missing mass LT Separation! 3

4 Mandelstam variables (s,t,u-channels) Projectile Before Target Before t: Four-momentum-transfer squared between target before and after interaction. u: Four-momentum-transfer squared between virtual photon before interaction and target after interaction t-channel: -t ~ 0, after interaction Target: stationary, Meson: forward Measure of how forward could the meson go. u-channel: -u~0, after interaction Target: forward Meson: stationary Measure of how backward could the meson go Target After 4

5 t-channel π vs u-channel ω0 Production Mark Strikman: A proton being knocked out of a proton process e n e π+ p(e, e π+) n HMS along the q-vector (pγ*) pπ+ is parallel to pγ* (Forward) pω is anti-parallel to pγ*(backward) Exclusive channel! p(e,e p)ω We donot detect any part of decayed ω Contain physics background Full L/T separation on this u-channel process One of the last Hall C 6 GeV analysis1 e ω e p p(e, e p)ω 5

6 Exclusive ω Electro-Production Data S 6 V e G A CL ta a D Closest data set to ours is the Hall B Morand data Fpi-2 Hall C 2004 Q2 GeV2 W GeV x -t GeV2 > < < 0.5 Zeus (Breitweg et al., 2000) ~0.01 < 0.6 Cornell (Cassel et al., 1981) <1 JLab Hall C (Ambrozewicz et al., 2004) ~0.5 ~ < , , , 4.74 HERMES (Airapetian et al., 2014) DESY (Joos et al., 1977) JLab Hall B (Morand et al., 2005) JLab Fpi-2 (2017) 6

7 Regge Trajectory Model by JM Laget Hall B Fpi-2 W (GeV) x Q2 (GeV2) -t (GeV2 ) -u (GeV2) < 2.7 > Real γ Virtual γ Fpi2 kinematics Physics observables parameterized In t, W (s), Q2, x x and W are fixed Q2 Evolution Wavelength of the probe t Evolution Impact parameter What about u? J. M. Laget, Phys. Rev. D 70,

8 t-channel Forward Real γ Virtual γ J. M. Laget, Phys. Rev. D 70, 2004 M. Guidal, J.-M. Laget, and M. Vanderhaeghen. Physics Letters B400(1):6 11, Regge Trajectory: Real photon vs virtual photon u-channel Backward Soft structure -> Hard -> Soft transition! Fpi2 kinematics 8

9 Parton Based Model: TDA Factorization? Nucleon to Meson Transition Distribution Amplitude (TDA) Backward angle analog of GPD. Translate from -t space to -u. Translate V DA to N DA No consensus on the TDA factorization regime If t is impact parameter, physical meaning of u is unclear. Interaction of Interest: u-channel pseudocalar meson and vector meson productions Two Predictions of TDA: (B. Pire, K. Semenov, L. Szymanowski, Phys. Rev. D, 91, (2015)) The dominance of the transverse polarization of the virtual photon resulting in the suppression of the longitudinal cross section by at least 1/Q2: σt > σl. The Characteristic 1/Q8-scaling behaviour of the σt for a fixed Bjorken x. 9

10 Experimental Setup Beam HMS HMS (QQQD) SOS SOS (QDDbar) High Momentum Spectrometer (SOS) Angle Acceptance: 6msr Momentum: GeV/c Momentum Acceptance: +-9% Angular, Position Resolution: 1mr and 1mm Angle Acceptance: 9msr Momentum: GeV/c Momentum Acceptance: +-20% High Momentum Spectrometer (HMS) 10

11 Experimental Setup and Acceptance Charged Particle HMS detector ( focal plane) layout, SOS is very similar Trigger: 3/4 planes of Hodoscopes Q2 =2.45 hsyptar Low ε High ε Data-simulation comparison for acceptance parameter Q2 =

12 hsbeta (velocity ratio) PID Cuts SOS Calorimeter e p RF beam burst Detail on the next page SOS Cherenkov (npe) SOS: select electron SOS-HMS Coincidence time Calorimeter cut Cherenkov cut 99% efficiency HMS: select proton Coincidence timing cut Hebeta (particle velocity) Aerogel Cut Cherenkov Cut: veto e+ HMS Aerogel (npe) 12

13 Coincidence Subtraction Blob events: good events Tail event: losing momentum due to multiple scattering Zero event: hsbeta=0! Cause: Missed the fiducial cut during the reconstruction Late Random Real Early Random Multiple scattering: dipole exit window to the last layer of hodoscope Time flow 13

14 HMS Dummy Subtraction HMS hsytar SO S Cryotarget Beam Dummy Target (Cell Wall contribution) Cryotarget SOS ssytar Tuna can shaped With thin Al cell wall Dummy Target 4cm apart Al sheets Dummy target distribution is corrected for the real/dummy target thickness difference before subtracted from the real proton events 14

15 Analysis: e+h Elastic Cross-Section Coincidence e+h elastic Cut Elastic Sim Elastic Data Dummy Data Fitted Result: ± Blue line: fitted average Pink Shade: fitted error band Dotted Line: point-to-point error band Extracted cross section is consistent with Bosted, AMT (Arrington, Melnitchouk, Tjon Phys. Rev. C 76, (2007)) and Brash empirical e-p elastic cross section parameters. ±2.0% (point to point) error from Heep will be included to the final Omega analysis systematics 15

16 Rosenbluth Separation Rosenbluth Separation requires Separate measurements at different ε (virtual photon polarization) 2 All Lorentz invariant physics quantities: Q, W, t, u, remain constant Beam energy, scattered e angle and virtual photon angle will change as the result, thus event rates are dramatically different 16

17 Physics Background Subtraction ω (782 MeV) η (547) ρ (770) 2π HERMES Empirical parameterization with Soding factor η (947) 17

18 Iterative Procedure (Recipe) to A Full LT Separation Improve φ coverage by taking data at multiple HMS angles, -3o<θpq <+3o. θpq=0 -u=0.0 θpq=-3 θpq=+3 Background Subtraction -u=0.3 -u=0.5 3 u bins 8 phi bins Unseparated X-section Combine ratios for settings together, propagating errors accordingly. Separated X-section Extract T, L, LT, TT via simultaneous fit Empirical Model 18

19 Fitting step (Background Subtraction) Integration Range Fitting Range Fitting data within the with four simulations Fitting Subtracting background distributions Obtain omega experimental yield: Each simulation distribution has scale factor Data (blue point) Xspace Sim (green) ρ Sim (light blue) ω Sim (red) η or η (black) Simulation Sum (pink) 19

20 Fitting Quanlity Control Fitting Quality Control Omega Comparison Background Comparison Zero Comparison 20

21 Integration step Integration Limit Intergrating within the integration limit Obtain Omega simulation yield: Reconstructed Kinematics and Optical Parameters 21

22 Yield Ratio and Simulated Cross-Section Model Cross Section 0<u<0.10 (t~4.1) 0.10<u<0.17 (t~4) 0.17<u<0.32 (t~3.8) R=1 Exp/Sim Yield Ratio Q2=1.6, Low ε=

23 Unseparated Cross Section (Money Plot) 0<u<0.10 (t~4.1) 0.10<u<0.17 (t~4) 0.17<u<0.32 (t~3.8) High ε=0.59 Low ε=0.33 Q2 =1.60 Anti-parallel Kinetics u-bin 0<u<0.19 (t~4.9) 0.19<u<0.30 (t~4.7) High ε=0.55 Anti-parallel Kinetics u-bin 0.30<u<0.50 (t~4.5) Q2 =2.45 Low ε=

24 Separated Cross Section Sig Q2 =1.60 Sig Q2 =1.60 vs -u Sig Q2 =2.45 Q2 =1.60 Sig Q2 =1.60 Sig Q2 =1.60 Sig Q2 =2.45 Q2 =2.45 Sig Q2 =2.45 Sig Q2 =2.45 Observations: SigT fall slow, SigL fall faster SigLT is small, Sig TT has sign flip for different Q2 values 24

25 Uncertainties budget 25

26 σu vs -u CLAS 6 data Large Angle Emission Forward Angle Physics (low -t) Backward Angle Physics (low -u) Minimum Interaction Radius Point-like structure? Soft structure -> Hard -> Soft transition! First time in electroproduction Soft structure -> Hard -> Soft transition! In photoproduction First observation for the backward ω electroproduction peak! Calls for the resurrection of the backward angle study through Regge based model (JML, etc.) M. Guidal, J.-M. Laget, and M. Vanderhaeghen. Physics Letters B400(1):6 11, Backward Angle Omega Electroproduction Peak! 26

27 Backward Angle Omega Electroproduction Peak! σu vs -u CLAS 6 data Backward Angle Physics (low -u) Forward Angle Physics (low -t) 27

28 28

29 Partonic Model: TDA Prediction (Private Communication) W=2.21 GeV, Q2 =1.6 GeV W=2.21 GeV, Q2 =2.45 GeV σt vs -u σt vs -u Over predicted by a factor of 7! Almost bang-on! TDA Calculation by B. Pire, K. Semenov, L. Szymanowski, Private Communication. (2015) Optimal Q2 range for TDA: >10 GeV2 TDA prediction has impressive agreement with data at Q2 =2.45 GeV2 Studying the effectiveness of JML model and TDA model is equivalent to studying the evolution of the proton structure 29

30 Analysis Status and what have we learned Analysis Status: Final round of uncertainty review is under way Expected publication data: summer 2018 Contacted theory group Achieved Objectives Studying the model effectiveness in both Regge Based Model and TDA is the studying the QCD transition Established a new experimental access to the previously accessible kinematics Abstracted the theory framework that can be used to study the previously ignored backward angle process Final release of the result calls for more studies on backward angle physics, particularly among the junior physicist. Software avaliable: 30

31 Backward Angle Physics Stratagy We are ready for the -u channel physics studies. Variary of existing and proposed backward angle physics, i.e recent CLAS paper by K. Park What can we learn? Regge Model GPD/TDA factorization High -t High -u Gap?! Stratagy moving forward with backward physics Large angle region (large -t and -u) scan by CLAS L/T separation near the meson (-t) and baryon (-u) Hall A and C Q2 evolution for L/T cross section Real photon data from GlueX Low -t Low -u CLAS 12 LOI: Backward DVCS and DVMP Previous studies done by Charles, Carlos in Hall A 2 HRS capable of resolving DVCS peak, with limited kinematics Hall C Possible L/T separation with full kinematics! HMS + SHMS may not have enough resolution HMS + SHMS + NPS? (Currently under study) Hall A/C LT separation near meson and baryon pole (extreme forward/backward angle) Q2=1 GeV, W=1.5 GeV Hall A VCS, G. Laveissière, et. al, phys.rev.c79:015201,

32 Thank you e p p(e, e p)x e NPS 32

33 Future Backward Meson Production Opportunities e p p(e, e p)x e X Hall C pi0 production HMS and SHMS Coincidence Mode Simulation by Garth Huber 33

34 Background Extraction and Check Worse example Missmass edge example Sum of the data from each bin sum of the Omega sim from each bin Reconstructed Missing Energy For the worse example 34

35 hsbeta (velocity ratio) PID Cuts SOS Calorimeter e p RF beam burst Detail on the next page SOS Cherenkov (npe) SOS: select electron SOS-HMS Coincidence time Calorimeter cut Cherenkov cut 99% efficiency HMS: select proton Coincidence timing cut Hebeta (particle velocity) Aerogel Cut Cherenkov Cut: veto e+ HMS Aerogel (npe) 35

36 Missing Mass Distribution Background Extraction Integration limits and fitting limits Exclusion criteria Exclude the radiative only omega bins Exclude the low statistics bins 36

37 Bin Exclusion criteria Low Statistics Radiative Tail 37

38 Background Extraction and Check Worse example Missmass edge example Sum of the data from each bin sum of the Omega sim from each bin Reconstructed Missing Energy For the worse example 38

39 Standard Physics at Hall C (Jefferson Lab) s-channel Physics t-channel Physics Detector Detector GlueX J/psi photoproduction What about u? Should we include u? 39

40 High t Data from CLAS Hall B (2005) Morand et al., Eur. Phys. J. A 24, 445 (2005). e Beam Hall B Experiment e1-6 Oct 2001 Jan 2002 Beam energy: GeV Kinematic coverage: W : GeV Q2: GeV2 -t : < 2.7 GeV2 x: Event selection: Reconstructed e-px missing mass consistent with the ω mass Data published in 2005: Morand et al., Eur. Phys. J. A 24, 445 (2005). Missing mass reconstruction e-px 40

41 Regge Trajectory Model by JM Laget Hall B W (GeV) Fpi2 x Q2 -t 2 (GeV ) (GeV2) Hall B Fpi-2 -u (GeV2) < 2.7 > Real γ Virtual γ Hard Scattering Mechanism schematics t-channel Forward u-channel Backward Fpi2 kinematics J. M. Laget, Phys. Rev. D 70,

42 Nucleon Fragmentation Process After interaction n (938 MeV) Before interaction e + H t-channel SOS Remains at target position H(e, e π+)n Standard nucleon Fragmentation gives a weird picture ω (770 MeV) HMS u-channel SOS Remains at target position Allows for kinematic settings which was previously not available H(e,e p)ω HMS Exclusive Chanel: ω is not tagged Allows for kinematic settings which was previously not available 42

43 Omega Data Analysis Fpi-2 (E01-004) 2003 Spokesperson: Garth Huber, Henk Blok Standard HMS and SOS (e) configuration Electric form factor of charged π through exclusive π production Q2=2.45 GeV2 Low ϵ π Low ϵ ω p Primary reaction for Fpi-2 Coincidence time In addition, we have for free p(e, e π+)n p(e,e p)ω High ϵ epx missing mass π+ ω High ϵ Kinematics coverage W= 2.21 GeV, Q2=1.6 and 2.45 GeV2 Two ϵ settings for each Q2 p Coincidence time epx missing mass 43

44 44

45 Q2 =1.60 GeV2 B. Pire, K. Semenov, L. Szymanowski, Private Communication. (2017) 45

46 Nucleon DA Model 46

47 Missing Mass Distribution Background Extraction Data (blue point) Xspace Sim (green) ρ Sim (light blue) ω Sim (red) η or η (black) Simulation Sum (pink) Background Sum Omega Fitting Limits (red dashed line): Not fixed, fit 95% data distribution Integration Limits (blue dashed line): Zero= Data Omega- Bg Fixed for all u-phi bins! Bin Exclusion criteria: Radiative tail exceeds 50% total ω sim Less that 100 raw counts 47

48 Yield Ratio and Simulated Cross-Section Model Cross Section 0<u<0.10 (t~4.1) 0.10<u<0.17 (t~4) 0.17<u<0.32 (t~3.8) R=1 Exp/Sim Yield Ratio Q2=1.6, Low ε=

49 Proton Structure: Known and Unknown Proton Dynamic Structure Static proton structural map is known Unknown Parton Distribution Interaction Transition (evolution) of the proton structure General description of the proton structure Goal: Study the transition of the proton structure 49

50 Modulus Check for SigLT and SigTT 50

51 Proton Structure Description Hadronic Model Partonic Model 51

52 52

53 Trajectory 53

54 Proof: These are not Elastic Events! Normalized Yield (1mC Beam charge) ω (782 MeV) Polynomial + ω Simulation η (947) η (547) ρ (770) + 2π Missmass of p(e,e p)x Good News! We see other Scalar and Vector Mesons: ρ, η, η, two-π phasespace Bad News! Channel is not clean! Worse News! We can t use Polynomial fit!! 54

55 Missing Mass Distribution Left Center Most Challenging Issue: Background Subtraction! Omega is not always in the center Four sets of Monte-Carlo is used fit the data Right ω + ρ + Phase-space + η or η 55

56 Mandelstam variables (s,t,u-channels) 56

57 Exclusive ω Electro-Production Data a JL b ll B a H Closest data set to ours is the Hall B Morand data Fpi-2 Hall C 2004 Q2 GeV2 W GeV x -t GeV2 > < < 0.5 Zeus (Breitweg et al., 2000) ~0.01 < 0.6 Cornell (Cassel et al., 1981) <1 JLab Hall C (Ambrozewicz et al., 2004) ~0.5 ~ < , , , 4.74 HERMES (Airapetian et al., 2014) DESY (Joos et al., 1977) JLab Hall B (Morand et al., 2005) JLab Fpi-2 (2017) 57

58 58

59 Rutherford Experiment Atomic Structure Rutherford Experiment: What about nucleons? Need both forward and backward scattered alpha particles to yield complete atomic structure! Does t-channel physics contain all the nucleon structure information? u-channel physics contain unique information whose meaning is unclear (B. Pire et. al) How do we access u-channel physics? 59

60 Separation Method Q2 =1.60 High ε=0.59 0<u<0.10 (t~4.1) Low ε=

61 Motivation Motivation Probing dynamic property of the proton structure Objective Establishing a new approach Dependent on the properties of the probe Backward-angle (u-channel) observables LT separation Studying the transition of QCD Proton Partonic Model Hadronic Model n Transition? 61

62 Jefferson Lab Hall C Main Structure Hall C Two Super-Conducting Linear Accelerators Experimental Hall: A,B, C, D High precision high beam current LT separation April 2017: 12 GeV upgrade completed New spectrometer is on line 62

63 Message to the world and thank you Studying the model effectiveness in both Regge Based Model and TDA is the studying the QCD transition Established a new experimental access to the previously accessible kinematics Abstracted the theory framework that can be used to study the previously ignored backward angle process Final release of the result calls for more studies on backward angle physics, particularly among the junior physicist. 63

64 Updated Uncertainties since the Thesis Defense version Updated version Sig Q2 =2.45 Sig Q2 =2.45 Fitting Error is now used as the Statistical Error New method used for computation the scale error Sig_LT and Sig_TT now have scale error band 64

65 Theory Motivation: Regge Trajectory Model by JM Laget Hall B Fpi2 W (GeV) x Q2 -t 2 (GeV ) (GeV2) Hall B Fpi-2 -u (GeV2) < 2.7 > Real γ Virtual γ Hard Scattering Mechanism schematics t-channel Forward u-channel Backward Fpi2 kinematics J. M. Laget, Phys. Rev. D 70,

66 Missing Mass Distribution Background Extraction Data (blue point) Xspace Sim (green) ρ Sim (light blue) ω Sim (red) η or η (black) Simulation Sum (pink) Background Sum Omega Fitting Limits (red dashed line): Not fixed, fit 95% data distribution Integration Limits (blue dashed line): Zero= Data Omega- Bg Fixed for all u-phi bins! Bin Exclusion criteria: Radiative tail exceeds 50% total ω sim Less that 100 raw counts 66

67 Conclusion 67