Doctoral Thesis ETH No. 16984 Study of Atmospheric Neutrino Detection in Liquid Argon Time Projection Chamber A dissertation submitted to the Swiss Federal Institute of Technology Zurich for the degree of Doctor of Sciences presented by Yuanyuan GE R. Sc, University of Science and Technology of China born on August 24th 1980 citizen of P. R. China accepted on the recommendation of Prof. Dr. Andre Rubbia, examiner and Prof. Dr. Félicitas Pauss, co examiner December 2006
1 Abstract This dissertation presents a study of atmospheric neutrino detection in the liquid Argon lime projection chamber. The LAr TPC technique has been demonstrated by the ICARUS R&D prolamine. It possesses good particle identihcation capabilities based on the excellent caloiimetrie measurement and precise 31) image reconstruction. A R&D program investigates possible extrapolation to a 100 klon LAr TPC The kinematic reconstruction of quasi elastic scattering events of at mospheric ufl is canied out in this giant TPC Due to the nuclear effects, the reconstruction resolutions aie better foi higher energy events. For Ev < 0.5 GeV and Ev > 0.5 GeV events, the resolutions of the reconsliucted vu energy aie 12.8% and 0.1% and the reconstructed angle1 resolutions aie 201 and 11\ A 25% resolution of the reconstructed L/E is achieved foi nonhoiizontal u,, with Ev > 0.5 GeV. By selecting the events with precisely reconstructed L/E, the first oscillation maximum can be clearly resolved after two years data collecting. The Earth inattei effects will enhance1 the oscillation e>f ;/;, J^ir, > v, and v, <> e'spex'ially when the1 neutrinos pass through the1 Earth's ewe1, a constructive interference1 betwern the1 MikheyevSmimovWolfens! ein (MSW) resonances in the1 mantle and in the ('e)ie1 will induce a socalled parametric resem.mce, wliich enhance1 the1 oscillation furthet. The1 matter effects em the1 a!mospheric neutrinos are expected to be1 e)bseirveel in the1 giant LAr TPC at 3<r significance level for about 4 yeais running, provided the following oscillation parametets: (Amj3) sm2ö23, sin22(9n) (3.5 x 10"3 ev2, 0.5, 0.01).
11 Zusammenfassung Die\se Dissertation präsentiert eine Stuelie1 über den Nachweis vem atmosphärisehen Neutrinos in eùner FlüssigargemDriflkammer. Die Anwenelbarkeit der ElüssigargemDriftkarnmerTechnik wurele1 ve)in ICARUS R&L) Programm deme)iistrieirt. Sie1 verfügt über e'ine1 gute1 Teilehenielentifikation basierenel auf eler ausgezeichnete1!! kalorischen Messung und der präzisen 3DReikonstruktie)ii. Ein R&iD Programm untersucht o\no mögliche Vergrösserung der FlüssigargonDriflkanrmer a,uf 100 Kilotorrrrerr. Die kirremal ische Rekonstruktion (juasie^astischer Wechsel wirkungen von atrrrosplrarisclrerr uß wird in dieser Riesendiiftkammer stattfinden. nuklearer Effekte ist Infolge1 die RekonstruktiemsAunosuug besser für Ereignisse mit luaioi Errcrgie. Für Ereignisse mit Eu < 0.5 GeV und Ev > 0.5 Ge'V ist elie Auflösung elet v,, Energie 12.8%. bzw. 0.1%, und elie rekonstruierte1 Winkelauflösung ist 20". bzw. IT'. Eine relative1 Auflösung von 25%) der rekonstruierte'ri Werte für L/E wird erreicht fur nichthorizontale un mit E > 0.5 GeV. Durch Selektierurrg der Ereignisse mit präzis rekonstruierten Wer ten für L/E kann elas erste Maximum der Oszillation nach zwei Jahren Datenmahme klar aufgelöst werelen. Die1 Effekte verursacht durch elie Materie der Erde verstärken elie vt,» v, und v, > ulht Oszillationen. Besonders in dem Fall, in welchem elie Neutrinos den Erdkern durchemereu, iireluziert eine konslruktive Interferenz zwischen eleu MikheyevSmimovWolfenstein (MSW) Resonanzen) im Mauten und im Kern eine1 sejgenannte parametrise'he Resenianz. welche elie Oszillation weiter verstärkt. Man erwartet, elie Einflüsse der Materie auf die atme)sphärischeii Nenitrmos in der RiesendriftkammeT nach ungefähr vier Jahren Mcsszeit mit enner Signifikanz von 3er zu beobachten, unter Annahme der fblgenieleni Oszillatienisparameter: (An?2,, sin2 Ö23, sin22ö13) (3.5 X 10"3 cv2, 0.5, 0.04).
Acknowledgements I am grateful for the help and suppent e)f many people. First and forennost, I wemld like to thank my super visor, Prof. A. Rubbia. Yemr profbunel scientific knowleelge1 anel exceptional advice have been of great help anel inspiratiem thremghout my PhD. I have1 been fortimate to have the opportunity e>f working with sueh a ge>e>d physicist. Man\ thanks ibi srrppe)rtmg anel helping me out during the "dark time1" when my application to ETH was in question. I also want to thank Prof. Wilfreel F. van Gunsteren for' offening me the1 great help on mv applic.rtion. I wish te> thank Prof. Félicitas Pauss for your willingness to act as ce) exaininen and your critical readmg of this thesis. Additional thanks fen yemr kind helps earlier on my entrance1 e'xams. I feel very obhgated te> Dr. Andreas Badcrtscher for patiently i)ioofreading the1 manuscripl. 1 am especially lhankful to ftetsa for taking care of all the adrnmrstrative affairs and her generous aids in marrv e>ther occasions thremgh all these years. There are several others who have made important eoutributiems to the1 work presemteel in this thesis. Dr. Paola Sala has helped to prepare the T000 Monte) Carle) hies anel the1 analysis cekies. Anselme) anel Diege) Garcia Gamez have prepared the GEANT 1 e,e)eleis. I appreciate their work very much. Many thanks te) Dr. Javier Rice) and Pmf. A. Buene) for useful discussions. I would like1 to thank all the former anel current eolleagues: Anselme), Curst av. Ines, Leo, Lilian, Marcelle), Marco, Markus, Marta, Paolo, Polina, Rice), Tlneriv, Uhsse anel Zuxiang. Especially, I thank Pe>lirra for many mteresting conversations anel e)ffeiing the lift te) the eanteem almost ewer y elay. T thank Liliarr for helping in translating frenn other languages to English anel Iranslaling the abstract to the Zusammenfassung e>f tins thesis. Thank von be)!h fen elieening me1 up when I was upset anel for many times of kinel invitatienis te) interesting activities All of you have' made my PhD a great experience. I would like te> take this opportunitv te) thank all the1 friends I have1 met in Zurieh anel in Gerreva for having n ge>e)d time together. Special thanks te) Yaquau, Jiang Yi, Jiawei, Zhou Yue anel many e>then Chinese1 friends. Yem have made my life in Switzerland a wonderful memory. 1 am proud of having yemr friendships. Last but rre>l least, 1 am indebted te) my parents and my sister for all their suppent anel errcemiagememt. I wish te> thank my husbanel, Haibe>, for everything. m
IV ACKNO WL EDGFAŒNTS Seite Leer / Blank leaf
Contents Abstract/Zusammeiifassung i Acknowledgements iii List of figures x List of tables xi 1 Introduction 1 1.1 History of the1 Neutrino 1 1.2 Neutrino Oscillation 2 1.2.1 Neutrino Oscillation in Vacuum 2 1.2.2 Atine)spheric Neutrino Experiments 4 2 Prediction of Atmospheric Neutrino Event Rates 9 2.1 Ature)spheric Neutrino Flux 9 2.2 Neutrino Event Rate's 13 3 Liquid Argon Time Projection Chamber 21 3.1 Detector Principle1 21 3.2 The ICARUS T000 Detector 22 3.2.1 Innen* Detee'ten 23 3.2.2 Celling System 2(i 3.2.3 Purification System 28 3.2.4 Monitoring System 30 3.3 A Conceptual Design of 100 kton LAr TPC 34
vi CONTENTS 4 Detector Performance 37 4.1 Event Reconstruction 37 4.1.1 Hit Reconstruction 37 4.1.2 Cluster Reconstructiem 38 4.1.3 Thre\"dimensional Rjeconstiuctiem 41 4.1.4 Finding Straight Segments 41 4.2 Correctron of Electron Ilecejuibinatienr Effect 47 4.3 Particle1 Identification 48 4.3.1 /j/tt/k/p Se1 parat ron 18 4.3.2 e/vr0 Se'paratienr 51 AA v QF Event Sol<xtion 60 5 Study of Atmospheric u,, Quasi Elastic Events 67 5.1 5.2 v QE Events irr the T600 Module 68 v QE Event in the 100 ktorr TPC 70 5.2.1 Overvrew 70 5.2.2 Reconstructiem e>f Muem and Proton Momenta 72 5.2.3 Recemstruetrem e>f the i/fl Kinematics 70 5.3 L/E Distribution of Atmosphenic vt, QE Events S3 6 Matter Effects of the Earth 87 0.1 Neutrino Flavor Oscillation in Matten 87 0.1.1 Twofamily mixing 87 6.1.2 Threefamily mixing 88 6.2 Oscillât ieni of Atmospheric Neutrinos in the1 Earth 00 0.3 Impact e)f Matten Effects em Observatiems 93 Conclusions 101 Bibliography 103 Curriculum Vitae 107
e>f List of Figures 1.1 A diagram of an atmospheric neutrino experiment 5 1.2 SuperKamiokande L/E analysis 7 1.3 The alle)wed oscillation parameter regions at SuperKamrokande 7 2.1 Comparison of energy dependence of atmospheric v(. vt, v^ and un pre1 dictexl by the FLUKA and the HKKM models 12 2.2 Comparison of zenith angle1 dependence of atme>spheric u,. uf, vtl anel vjt prcflicted by the1 FLUKA anel the1 HKKM models 12 2.3 Flux ratio of zr as a funetiem e>f energv 13 2.4 Normalized ene)ssseie>tie)ii a (JE and DIS interactions fen ;/f, vfl anel vt calculated with the NUX program 14 2.5 Energv distribution of v(, vl% vil anel vß CO events with FLUKA flux ine>del. 18 2.6 Zenit h angle distribution of u(, v(, vfl, vfl, vt anel vt CC events 18 2.7 Energy distribution of ut and vt CC events for hve1 different Am2 values with FLUKA flux model 10 3.1 The1 drawing shows the LAr TPC detection principles 22 3.2 Schematic view of the ICARUS TG00 cryostat 23 3.3 Transvensal view of the ICARUS T600 dete'ctor 24 3.1 Picture of the inner ektevten layout inside one TPC 24 3.5 Picture1 of the1 tlnee wire planes. of a TPC installed in the1 TOO!) dete'ctor. 25 3.6 The signal shape from the minimum ionizing particle em the single wire... 27 3.7 PMT mounting m the hist halfmodule structure 28 3.8 Scheme en T300 puriiicatie>n system 29 3.0 Schematic view e)f the' cryostat seen frenn the" top io 3.10 Drawing e)f the1 purity memitor and readout scheme 31 vii
viii LIST OF FIGURES 3.11 Pietuie erf a mounted puritv memiten1 in the Faraday cage 31 3.12 Picture of the mounted level meters at the back left side1 32 3.13 Pictures e)f the wall petition meter <i',i 3.14 Picture of themounted wall peisitiem ureter to the wire chamber frame... 33 3.15 Pk'tuie erf a elecennpe)seel wire position meter 33 3.16 Sehematic layout erf a 100 kton liquid Argon deteete>r 30 1.1 Parameters charaeterizirrg a hit prexluced by a mtp track on a Cenlevtiem wire 38 4.2 Twe) hits in Cerflen'tiem plane are well htte'd with the function of Eej. 1.1... 39 4.3 Cluster ircemstrue'tiem for an lex'tron sheiwer event anel a muem decay event. 40 4.4 2D projections erf a k)w multiplicity hadronic interactienr 42 4.5 3D ree'enrstrue'tiem erf a k)w multiplicity hadrennv interact rem 43 4.6 Two built segments of a simulated nmon nup track 15 4.7 The straight segments finehng algenithni reserves the uß QE track into muon and prerfem segments 46 1.8 Distribution of the distance between the1 true' vfl QE verte'x anel the closest rec'oristriicted geometrical intersee'tie)n 47 4.9 The distributiems erf the re'cemstruete'el energy befe>re anel aft en elevtron recombinal ion correction 49 4.10 Scatter plot erf the < de/dv > versus kinetic energy for fully simulated muons, kaons and protons 50 4.11 The image's erf a simulateel elect rem and neutral pieni in the Collection plane1. 51 4.12 Distributiems erf the de/dx of olootrons anel piems on different wire's at the1 beginning of the event 52 4.13 The c~ anel 7rn can be separated with 90% c~ identification erficiemey anel 3.7% erf 7T contamirratiorr by a < de/dx > cut at 2.21 MeV/cm 54 4.11 The 7r contamination (black squares) fer an ew'tiem ielentification efficiency erf 90% as a fniictioir erf the particle' eniengy 5(i 4.15 The elistiibrrtrems erf the likeliliootl ratio fen the' same e anel 7rn events ana lyzed by the < de/dx > cut method unelen the1 ele'ctre)ii hyperfhesis 58 4.16 rfwo dimensiemal plot she)wmg the centelatiem between the < de/dx > anel L, 59 4.17 Projectcd images erf two v,, QE MC events in the Trrelue'tiem anel Collection views 61
1, l, ~ Z(v, 1 LIST OF FIGURES ix 4.18 The 2D projection erf a v^ re'semant interaction in the Irreluction anel Col lection vievvs 62 4.19 The 2D projection erf a vt CC MC event in the lnductiem anel Collection views 62 4.20 Preijected images erf two v^ NC MC events in the1 Induction and Collectieni views 63 4.21 Seatter {rferf erf' the1 total number erf 2D tracks vs. the1 longest length erf' the 2D track piojectiem 64 4.22 Selevtion erfficieney erf i/fl QE events as a function erf the rreutrino enengy.. 65 5.1 The energy distribution of the generated atmospheric v,, eharged enrrent events 68 5.2 Relative en or distributiems erf the rcconsti ucteel irmorr enengy anel v,, en ergy, for ut, QE events simulateel in T600 69 5.3 Rerfative1 errer distribution erf the1 calculates! E[/c according te) Equatiem 5.1. 70 5.4 Distributern erf the1 visible energy nornrali/eel to the1 trrre neutrino energy. 71 5.5 Relative enren distribution erf E' " ü7ti,/0.855.. The resolut ion is 13.8%. 71 5.0 The image erf a i/ QE event with a shent pierfem track, where the1 true?/,, vertex is e)verk)oked by the straight segmenit hireling algerithm 73 5.7 A v{l QE evemt with a bifurcation track in the drifting elirevüeni 75 5.8 Distributiems erf the relative errer of the recemstrueneel pre)! em momentum, p'"/p'"" 1 78 5.9 Distributiems of the le'lative1 error erf the recemstructcd muem mennenitum, pui/p"<" 1 79 5.10 Distributiems erf the relative1 errer of the reicemstrue'tejel vp momentum, p"</p<"" when Ev <_ 0.5 GeV 79 5.11 Distributiems erf the relative enrer erf" the reconstruct<3d v^ mennenitum, p>"/p"i" when Ev > 0.5 ficv 80 5.12 Distributrorrs erf the difference between the le'construeted and the' real valueof the1 incoming neutrino zenith angle1, O'J' ()[/"' 81 5.13 Distiibutienrs erf the difference between the' reconstructed! and the real value1 erf' the1 scattering angle1 between nemtrhre) anel mireni. Z(vtp.)'" p)h"'''. 81 5.14 Distributiems erf the1 renative1 enren erf the j//( energy reconstruct eel aceeneling te) the kinematic relatiem, E'k't'JE1^/ 1 82 5.15 Distnbutiems erf the relative errer erf the vn energy icconstrue'teel frenn the' visibleenergy and according te> the energy cemservation, E',',l/E',,',"' 82 5.16 Scatter plot of L'"/L1"" versus eosine zenith angle' ce)sot, of vfl QE events. 84
26m X LIST OF FIGURES 5.17 Distribution of relative errer of recemstrucled (L/E) for vp QE events with \cos&\ > 0.4 85 5.18 Distributern erf relative error erf reconstructed (L/E) for vlt QE events with \eos<c)\ > 0.4 anel E > 0.5 CeV 85 5.19 The distributions of the reconstructed L/E of the1 survived vtl and the real L/E erf the uu without oscillation 86 5.20 The1 ratio of the oscillation distributiem to the nonoscillatieni distribution as a functiem erf L/E 86 6.1 Dependence of P(vc > u,,^) on the neutrino energy, according to Equa tion (6.22) for different zenith angles 0 with cos (),, berfweeii 1 and 0.84. 95 6.1 Dependence of P(vt. > vlht) e>n the neutrino cnergy, according te> Equatieni (6.22) for different zenith arrgles () with cos By between 0.82 anel 0.66 90 0.2 The phases <f>tlt anel <pr as a function of the neutrino energy for' different zenith angles 97 6.3 The correlation between the energy and the zenith angle for (j)m of the neutrinos TT anel <j>r ir respectively 98 6.4 The mixing angles 6(, 9,u anel 0C as a function of the neutrino energy. 98 6.5 Color contour plot of the oscillation probability P(ve erf A7ii22:i/2E sin22(913 vs. > viht) as a function ' 99 6.6 The eleipenelence on cosf)(/ of the ratios of the1 upward genng //like and «= like nnrlticev events 100
' List of Tables 2.1 QE and DIS event rales anel average1 energie's of u, and vt for FLUKA and HKKM flux models 16 2.2 QE anel DIS ewenf rate's anel average' emengies erf ;//t and ufl for FLUKA and HKKM flux models 10 2.3 NC event rate^ anel average energies of v and v for FLUKA anel HKKM flux models 16 2.4 Chaige current event rates (Evts/kt/year) erf vt and vt 17 1.1 Free parameters use^l in finding a change1 erf segment directions 45 4.2 Piorr contamination and < de/dx > cut values with a fixeel 90% elec tron elficiency when different number erf' wires are1 combiner! te) calculate < de/dx >. 53 4.3 Pion contamination with 90%, electron efficiency anel < de/dx > cut values at eliffereiit hidden! particle energies 55 5.1 Containment erf atniexsphenic vu QE and uonqe events in T600 08 5.2 The1 remaining ufl (JE events after the momentum reconstrue!km 70 5.3 Resolution erf reconstructed v^ kinematic quantities for two energy ranges. 78 XI
Chapter 1 Introduction 1.1 History of the Neutrino The neutrino was first postulated in 1930 by Wolfgang Pauli m order to rescue1 the laws of enengy and angular moment nur conserva tiem in the betadecay process erf atomic nuclen [1]. Theoietically, it has te) be electrically neutral and very light aire! have spin 1/2. hi 1934, Enrice) Fermi formulated a theery describing the nuclear beta decay [2]. Fermi theory provided strong evidence foi the1 existence1 of the nemtiine>, but it was not until 1950 that the neutrinos emit (eel by nuclear reactors were directly observed by Fred Reines anel Clyde Cowan via the1 inverse beta decay, v, +p > n 4 e ' [3,1]. The1 In 1902, Lcelerman. Schwartz, anel Stcinbcrgcr performed the first accelerate» uemtiine) experiment at the Brookhnvcn Labenateny using a high energy v,, beain [5J. This exper iment proveel that the neutrino emitted in beta deeay (ut) is different from the ncntrme) emittecl in pion decay (vt,) [(>]. Thus, it was suggested that to each charged leptem a corresponding uemtiine) flavor is associated. The third genenation of leptorrs, r, was discovered in (+e~ annihilât ion in 1975 [7]. bi 1990, the1 LEP experiment at CERN showed that then1 are1 ne) more than three lypcs of light neutrinos by precisely measuring the Z decay width [8]. However only recently, the tan neutrine) (i/r) was observe1*! by the1 DONUT experiment [9], The1 parity conservation in weak interaction was questioned by Lee and Yang in 1956 [10. anel in 1957, CS. Wu performed the classical experiment erf measuring the angular distributiems of electrons from the beta decay erf polarized b0co atoms and elennonstrateel that the1 parity is maximally violate*! in weak interactions [11]. The' helicily ol neutrinos was directly measured to be 1 by Golelhaber [12] in 1958. The kinennatical analysis erf berfa decavs have1 se) far only provided experimental upper benmcls for (he rest masses of the electron nemtrino and thus direct measurements do nerf e>xelue!e rrrassless nentrirreis. The1 best direct measurements of the electrem neu!lino mass give an upper bound erf 2 e'v/c2 [13]. 1
1,2,3) CHAPTER 1. INTRODUCTION 1.2 Neutrino Oscillation The enrrent understaneling of neutrinos and their intenactions is covered in the Standaiel Model erf electroweak interactions. There1 exist three1 generations of leptons, the electrem, muon anel tan and thcnr associate*! neutrinos. The1 neutrino is only lerftharrde*! and exactly massless. The leptems can only interact within the asseiciated double!, so that the leptem flavor number is conserved. Neutrinos only interact weaklv. through the charge*! cnirenl (CC) channel meeliated by the W boson or the neutral current (NC) charme1! by the Zü boson. mediated If neutrinos really have vanishing mass, then the mass eigenstates \v\), \vi) <md \v^) could be elcfined via \vt anel iv and no flavor oscillations should then be erfbscrved. But if nentlinos do have masses, flavor oscillations can take place. Neutr ino oscillatiems were first hypothesize*! by Bnrrro Pe)ntecorvo in 1957 [14,15], and independently bv Z. Maki, M. Nakagawa and S. Sakata in 1962 [10]. In 1964. a deficit of ueutrine>s hour lire sun was hist observed by Ray Davis with the Homestake' experiment [17,18], where only about half the amount of solar neutrinos pieeücted bv solar modeis were measuied. The nerrtrine) anomaly has also been e)bserved m other neutrino sources ewer the1 years, and all indicate that neutrinos oscillate1. 1.2.1 Neutrino Oscillation in Vacuum Tf nemtrinos have1 mass, the flavor basis \va) (a e, rx, r) which diageniahzes the electroweak mleraenion llamiltonian will in general be1 a superposition erf the mass eigen states I/;,) (/ which diagonalize the free Hamiltonian. They are related thremgh a nemeliagonal unitary trarrsformation: (\»A v. u \»2) (i.r \Wr)J and the unitary mixing matrix U can be1 factorizeel in terms erf three mixing angle 6\2, 0\\ anel t923, that characterizes mixing between the two states, airel a single phase1 <5n which breaks chargeparity (CP) conservation: A o o\ ( '" 0 sue!d"\ ( CL2 Sl2 0\ U 0 C'2'A 'S2,S 0 1 0 6'12 Cl2 0 1 "523 C23/ \sl3e'd]t 0 en ) ^ 0 0 \j (1.2) where su siu0t;, c, ros 6, In other words, particles interact as flavor eigemstates but propagate as mass eigen states. The time evolution eciuatioir for the flavor eigenstates with momentum p is given by i%vh^ü (1.3) dt
m2 sm2 i/p2 sin2, 1.2. NEUTRINO OSCILLATION 3 where IIq = dtag{ei, E2, E^} is the fiee Hamiltonian in the mass ergenstates basis. Assuming that the mass states are produced with a common energy E, in the1 îelativistic limit E, 9 0 I rrif ~P + ^~p + 1j± (1.4) the common phase iritre>duced by /; and m2 can be suppresseel anel Equation approximate*! by dv 1 U dt 2E i A> 0 0 \ 0 Amj, 0 \0 0 Am, y 1.3 can be Uxv (1.5) where Am2 zez m2 eigenstates. is the difference1 erf' the1 sejuareel masses erf the two related mass Tf we assume1 that tlie mixing matrix U is real, and in the one mass scale approximation I hat \Am22l\ < \Amfn\ ^ Ar»^ = \Am2\, (1.6) the oscillation probabilities can be written in the1 following form: P[y,»«/,) = 1 (20u) sm2 (~~) (17) P (ut ^) P(^ + vr) = sin2 (20!,) sin2 (M sin2 (^f\ 0 «) i>0>, vt) = sin2 (201d)cos2 (023) sm2 (~~~) (19) P (// > «/, ) / Am2 if \ (20,,) cos4 (0ld) sin2 f7^ ) (110) whenx L is the neutrine) path length anel E is the neutrino energy. In practice1, the current empirical evidemce srrggests that the1 two mixing angle's 0\2 and 023 fire large and 013 is small. In this regime1, the1 threeflavor oscillation effectively decouples to (lie following sets of twoflavor oscillations: Long Range Oscillations: This mode1 is associated with measurements of v, disappearance in serfar neutrinos anel kmg baseline reactor experiments. The1 oscillaiiem proba!)ility is given by: P(u( * ullyt),, /l.27a?/72;(ev2)l(km)\ ~sin22012sin2 ^ ^ijl^ j (1.11) Short Range Oscrllatious: This mode is assexiated with measurements erf uß disappearance in atmospheric neutrinos and long baseline vt, beam experiments. The oscilla!ion probability is given by:.,fu27am2,(cv2)l(km),2oû P(v ut) ~ ~ sin^ 2023 sir^ ( {G^ ] (1.12)
_ \N(ylt ' 4 CHAPTER 1. INTRODUCTION SubDominant Short Range Oscillatiems: This meide is associate*! with searches for ue disappearance in short baseline1 reactor neutrino experiments. The oscillation probability is given by: P (u, ~ :W) ~ 2 sin2 20L3 sin2 (^ ^py ] 2 fl.27amucv2)l(km)\ (113) The1 factor 1.27 = 103/(4/ic) units. lesulls from the conversion from natural units te) laboratory 1.2.2 Atmospheric Neutrino Experiments The primary cosmic rays hitting the atmosphere1 consist of about 98% hachons and 2% elee'trons. The hadremic compenient is denninated by protems («a 87%) particles (œ 11%) and luavier nuclei («2%). The high energy cosmic rays interact with nuclei in Earth's atmospheie mixed with n le) create particle showers. In these cascades, pions and kaons are1 produced, which will decay to a muon and a muon neutrino. Tlie1 muons will in (urn decay into an elect rem and two neutrirre)s. These processes can be summarized as follows: p, lle+n >X + 7r1/A'+ n /KL ^ ^ + uß(ült) //± f± > + vt(v,) I V,,(&,,) The fluxes erf atmospheric neutrinos provide an excellent source for neutrino oscillalion studies. The characteristic signature of neutrino oscillations is a deviation from the expected flux L/E as varies. As shown in Figure 1.1, a detector locate*! near the surface of Hie Earth sees neutrinos that travel only ~10 km coming from the top, while ueutrinejs that arrive1 from below the detector travel more than 12'000 km. This broad range of baselines couple*! witli the atmospheric neutrino energy spectrum, which extends up to 100 GeV (falling like E 27), make observations erf'atmospheric neutrinos sensitivity to An?2 down to KT5 ev2. The îatio erf the number of u,, to the number erf vt is approximately 2. While the absolute1 atmospheric neutrino flux is known to 20%, tlie flavoi ratio of muon and elcctrou neutrinos is known to within 5%). The1 historically important oscillation is tire doubleratio desired as measurement lor the neutrino I ^)/N(ut+v()l^ntil \N(v I ^)/N(v,+ut)\lllltcltll K Arrv deviation of R fioin 1 is a hint for possible oscillatiem, even if it cannot be derfenmined whether muon ueutrinos or electron neutiinos are responsible. Most experiments prefei a i?valuc around O.G. Another evidence for neutrino oscillations is the significant updown asymmetry erf high enengy vfl. Since the cosmic rays arrive at the earth almost isotiopicallv arrd tire
1.2. NEUTRINO OSCILLATION cosmic ra/ neutrino Figure 1.1: A diagram of an atmospheric neutrino experiment. Earth has a spherical form, we can exped the1 flux of atmospheric ueutimos to be updown symmelric. While the measure*! doubleratio erf the upward going anel downward was less than 1. This going Up even!s defined as (up/ down) ta>sl t lvd/ (up/down) ( )tctlll implies that the upwaid going vß disappear during the long journey thiough tlie Earth, which agrees with the oscillation hypothesis. In addition, the zenith angle distributions for v, and vß events suggcst that the deficit is only found in upwaid going ut,, while the uc samples follow the expected distribution. Several experiments have undertaken measurements of the flavor content erf spheric nentrino fluxe's. the atmo The1 in s I measurements of the atmospheric v( and vß flux weie performed in the1 1980s bv the 1MB 19 and Kamiokande [20] experiments using watei Ceicirkov detectors. Atmospheric nentiinos were detect eel leptons emitted in chaiged curierrt neutrino interactions. by the flavor erf tlie emitted leptem. topology erf!he Cerenkov rings. by observing Cerenkov rings jnoduced by charged The neutrino flavor was tagged Electrons and muons were separated by analyzing the Since electrons are less massive than muons, they undergo mole multiple1 scattering and therefore produce1 fuzzier Cerenkov rings. Both 1MB and Kamrokarrde calculated the double ratio R (Equation 1.11). Botli expeniments observed a deficit in the vjt flux relative to the expectation, measuring ratios erf R 0.54^^;; pu fo 070 05 and R 0.00 0 06 i 0 05 221, respeclively. The atmosphenic v, and ;//; flux was also measured using iron caloriincter detectors, e early experiments, NUSEX [23] and Ftejus [24], observed no evidence1 lor a deficit in
2.4 ] 0 CHAPTER 1. INTRODUCTION the vß flux. A more precise measurement was performe*! by the Soudan 2 experiment [25]. Soudan 2 used a 1 kton calorimeter detector compose*! erf active1 drift tube's within a passive steel structure to sample the1 particle tracks and showers produced by neutrino interactions. The1 signature1 of an atmospheric neutrino interaction was an event with a contained interaction vertex. Soudan 2 observed a deficit in the vß flux relative1 to the1 expoctation, measuring a ratio R 0.72_!_q iy 0 07 P^b SuperKamiokande1 is a water Cerenkov detector containing 50 kt of ultrapure water in a eylindrical stairrless steel tank [27[. For tlie1 analysis an innen1 fiducial volume of 22.5 kt is usee!. SuperKamiokande has performed precise measuremerits of the atmospheric ;/, and vfl flux. The huge fiducial volume of the' SuperKamiokande1 deneetor enables a latge sample erf niultigev charged current neutrino interactions to be aecnured. Tlie latest oscillation results wete reported in [28]. They performed a twoflavor ut, * vr oscillation analysis using the atmospheric nemtrinos data acquired between April 1990 and November 2001, e oiiesponding to a 92 ktonxyear exposure. Figure 1.2 shows the1 plot of the ratio of the1 data over nonoscillated MC events as a function of L/E. A dip is observed around L/E =500 km/cev which sliould correspond to the first oscillation maximum. From the L/E analysis, tlie obtained 90% C.L. allowed parameter region was 1.9 x 10'1 ev2 < Am2 < 3.0 X 10 d cv2 and sin2 20 > 0.90 and the bestfit point is at sin2 20 Am2 x 10~3 ev2. An improved analysis teehnicjue, which incorporates the best features erf the L/E analysis and the zenith angle1 distribution, gives a better 90% C.L. allowed region of 2.0 x 10 3 ev2 < Am2 < 3.0 x 10 A ev2 and sin2 20 > 0.93. This is shown in Figure 1.3..0,
99% 1.2. NEUTRINO OSCILLATION I I f I Mill Twjr *i mnrmr r i i i mi 1 3 10 10" 10 L/E (km/gev) Figure 1.2: SuperKamiokande L/E analysis. The1 ratios of the dala to tlie1 MC events without neutrino oscillation (pomls) arc plot I eel as a function of the recoils! rue! cd L/E, together with the besttit expectation for twoflavor vn 4 vt oscillations (solid line). The error bars are statistical only. Also shown are the bestfit expectation for neutrino decay (dashed line) and neutrino decoherence (dotted hue) [28]. 2 10 T, "> 1 T T... 'i 1 > tu E < i C.L \ i 90% C.L. v 68% C.L. 10 i.i.i '.1.1. 0.7 0.75 0 8 0.85 0.9 0.95 sin220 Figure 1.3: The 08, 90 and 99%) C.L. allow**! oscillation parameter tegions given by a new highresolution! woflavor» us, ut oscillation analysis at SupenKamiokaiidc.
8 CHAPTER 1. INTRODUCTION Seite Leer / Blank leaf
Chapter 2 Prediction of Atmospheric Neutrino Event Rates 2.1 Atmospheric Neutrino Flux As we1 have1 seen, the study of atmospheric neutrino oscillation is carried out by the comparison of the calculated and measured neutrino fluxes Reliable calculations erf the atmosphenic neutrino flux are essential for the1 cenreet interpretation of the measured data and the detenruination of the1 oscillation parameters. To predict the neutrino flux produced by the intenaetions of primary cosmic rays, one ireeds to know the primary cosmic ray flux, the atmosphere's profile, and to simulate the chain intenactions of tlie cosmic ray particles with tlie atmosphere components and the transport of charged particles in the geomagnetic tieid. There was aoncdimcmsional flux calculation, developed in which the secondary mesons and thenr decay products are assumed lo be in tlie same diieetion as their patent particle, therefore neglecting the transverse1 momentum of the1 secondaries arrd the bending of charged secondaries in the1 geomagnetic tieid. The onedimensional calculation was widely used in tlie past when the computer powei was limited and it is a very practical approximation at high energy, since1 only a small fraction erf the cosmic rays whose1 trajectoiy will hit the detector are needed to be urreler the consideration. But the effect of t rails verse momentum is most import ant at low enengy. Many groups have1 updated the onedimensional flux calculation to three dimensions by including the angular distribution of the produce*! neutrino [29 33]. We compared (he calculated fluxes of two most popular models m this section. One is called HKKM model, devclopcel by Honda et al. [31,34] primarily for the need of the1 SuperKannokande experiment. Another is called FLUKA model [33,35]. The fluxes arecalculated for the site of Gran Sasso and at the solar minimum. The two models use tlie1 same primai y cosmic ray flux mode1! base*! on the1 Bari erf spec trum [30] but with different fitting parameters. They both adopt the realistic geomagnetic field model IG1YF [37] to calculate the rigidity (total momentum divided bv total enatge) 9
10 CHAPTER 2. PREDICTION OF ATMOSPHERIC NEUTRINO EVENT RATES cutoff at certain locations for certain directions, in order to determine whet hen a primary trajectory is allowed or forbidden to icach the» atmosphere. The FLUKA mode1 has no1 yet simulated the bending erf the charged secondaries in the geomagnetic field inside the atmosphere, which mostly cause an EastWest asymmetry [38] in the azimut hal angle1 distribution. The1 mam difference between the two models is the different hachonic interaction mod els that they adopted. The1 HKKM model chose tlie1 DMP.TET111 [39, 10] model, which gives the best agreement in measuiing the secondary cosmic ray muons and gammarays, while the FLUKA mock1! uscs the FLUKA package [41], which is good of hachonic interactions and is verified by accelerator data. at the1 simulation Figure 2.1 shows the fluxes of atmospheric vt, v,, u,, and z/f, as a function of the neutrino energy. aftei The plotted values are inlegrated over the zenith and a/imuth angles, multiplying E2r> and applying au adjustment factor, as noted in the figure1 for betten illustration. The f)uxes decrease as the1 energy increases when E > 1 GeV, because1 then the muons have less chance te) decay before they arrive to the ground and produce1 neutrinos This is more manifest for electron neutrinos, since muon decay is the main source1 erf production erf electron neml linos. From tlie1 plot of the1 ratio of the FLUKA model ewer HKKM mock1!, it is cle'ai that there are nicne neutrinos predicted by the FLUKA model than by the HKKM model in the subgcv range1, and the1 opposite in the1 multigev range, especially at very high energy. The difference between the models is within 20%,. Figure 2 2 shows the zenith angle distributions, wheie the fluxes are integrated over theenergy and averaged over all azimuthal angles. We find that the zenith angle dependences of different calculations are very similar, except near tlie vertical direction and neat the horizon. Figure 2.3 shows the flux ratio of v{l + ufl to vt + i?t as a function of neutrino energy. The flux ratio is expeeled to be 2 at low energy; for high energy above a few GeV, I heratio is greater than 2 liecause the high energy muons reach the ground without decays and as a result, the number of ut, decreases. In the zenith angle distribution, there is a prominent bump emerging around tlie horizon, which is a characteristic feature of tlie1 3D calculation at low énergie1«horizontal directions. foi near The thiee1 effects which determine the zenith angle follows [42]: distribution are summarized as Geomagnetic Field The rigidity cutoff due to the geomagnetic field is the highest in the1 equatorial region and the lowest in tlie polar legion and is different at diffcient locations for different directions. Tims, the primary cosmic ray fluxes are1 not isotroprc anymore after the bending in the1 geomagnetic field, ft causes the1 updown asymmetry for low enengy neutrinos. The geomagnetic effects vanish for high enengy particle's above (he rigidity cutoff. Neutrino Yields
2.1. ATMOSPHERIC NEUTRINO FLUX 11 The ncmtiino yieid rs (he average1 number of the1 neutrinos produced bv a primary cosmic ray particle, ft is straightforward that a more horizontal shower means a longer path allowing lire muons to decay and to generate neutrinos. On the other hand, tlie air density decreases along the horizontal direction, which has the effects that the charged pious or kaons have higher possibility to decay rather than interact. Thus, the neutrino yield is higher at horizontal direction. But this enhancement is only manifested at high energy. Because1 for low energy neu trinos, the decay length is short and the decay probability is 100% m all directions. This effect is also present in the1 onedimensional calculation. Spherical Geometry of Neutrino Source If we assume that the1 atmospheric neutrinos are generated tlie atmosphere1 and the primary cosmic ray flux is isotropic, in a spherical shell erf the situation could be understood by considering two extreme cases. When the neutrinos are at extremely low energy, they are emitted emasi isotropically by the cosmic ray particles, i.e., isotropieallv emitted from an element of tlie atmosphere. For an observer inside1 tlie1 shell, the flux per unit solid angle measured by the1 obsenven decreases monolonically witli cos2 (),,. Thus, the observed neutrino flux is enhanced stiongly around horizontal direction. When the uenlrino has sueh a high energy that it is almost col linen î with the primary particle, the observer inside the shell measures an isotropic flux îegardlcss of his position. The realistic situation would be an intermediate case1 between flic1 two extremes. Thus, it is the geometric effect that causes the1 horizontal enhancement at low energy. This cflec! can only be shown by the threedimensional calculation. We can seje that the1 two atmospheric neutrino flux models give1 consistent results. dominant souice erf discrepancies is bclicvcd to be the hadronic interaction model. The The FLUKA model is estimated to have a 7%) uncertainty for the1 primary spectrum, 15% foi tlie1 interaction model, 1% for the1 atmosphcic profile1, 2% for the geomagnetic field and a total 17%) uncentainty. The HKKM model has about 10% lmcentaintv when tlie neutrino energy is befovv 10 GeV, but the1 uncertainties arc1 still large when the neutrino energy is above 10 GeV, due to the uncertainties of the primat y cosmic ray flux and the inteiaction mode1 above 100 GeV. In any case, the flavor ratio is always much less dependent on the hachonic model and an uncertainty erf ±2 5%) is expected. ~
> FLJKA 9 iou HKKM \Jx15 ">. 5 10' i,x3 10' 10 E (GeV) * 1 8 1 S ~ 1 4 r ve 1 a 1 08 06 0.4 0.2 r..i 1 E.iGeV) Figure 2.1: Atmospheric neutrino fluxes multiplied h\ E2vh. calculated with the FLLTKA and HKKM models (top) and their ratios (bottom) The fluxes are calculated for the Gran Sasso site and at the solar minimum. f04r JC Z "E0.35 ~ FLUKA HKKM 0 25 j^ 02 Ï" 015 ' l<\) 0.1 ' y 0 05 ' cos(zemth angle! 5 * < *16 r ^ 14 1 2 \. ~~ 08 i_ 0.6 0.4 02 i,, I. cos(zem!h angle) Figure 2.2: Zenith angle dependence (top) of atmospheric neutrinos, integrated over the energj and averaged o\er all azimuth angles, for the FLUKA and the HKKM models and the ratio of the FLUKA flux over the HKKM flux (bottom). The V/j and v _ ha\e similar flux. The fluxes are calculated for the Gran Sasso site and at the solar minimum. LO \ A O c c CO ~0 * H I PS tq Pz O So Co :
^ 2.2. NEUTRINO EVENT RATES 13 Ç 10 > FLUKA + ZI. > Honda 101 _i i i i i 10 Ev(GeV) Figure 2.3: Flux ratio of models. as a function of energy, for tlie FLUKA and (he HKKM vt + vt 2.2 Neutrino Event Rates The atmospheric neutinios interact with the Argon atoms in the LAr TPC (see1 Chapter 3). The nemtrino interactions are calculated with tlie1 NUX program [43]. NUX was developed to fulfill the needs of low energy neutrino expeniments and it can trea! (he incotning neutrino energies from 10 MeV to 10 TeV. NUX can generate neutral current (NC) and charged current (CC) processes. The CC evemts are drvided into the three main categories: 1. cjuasi elastic scattering (QE) 2. deep inelastic scattering (DIS) 3. chaini production H lakes into account the nuclear effects: tlie Fermi motion, Pauli blocking and reinter action of the produced hadrons. NUX has been successfully crosschecked with NOMAD data. Figure 2 4 shows the calculated crosssections for charged cut reut irrten actions of three flavors of neutrinos and antineutrinos. The QE and DfS event rates (for one ktonxyear exposure) and average energies for v, and z/f, vfl and vj{ are listed in Tallies 2.1 and 2.2. Similarh, the NC e^enit iatejs are
of " l_.11 14 CHAPTER 2. PREDICTION OF ATMOSPHERIC NEUTRINO EVENT RATES ^* > a* O 1.2 ve QE+DIS b V n QE 0.8 0.6 04 0.2 / / 1. / 1 ^"v*x*%^ r.,, Mil.V'r.. V Iff1 1 10 10J 10* 10* DIS Ev(GeV) *r* > a> 0.4 <5 v u 0.35 / 0.3 LU 0.25 0.2 0.15 0.1 0,05 / i I \ 0 r l.li,.l p 1 1_ 1 l" f i11 :t ^ ^r.. J...ljjuL^^j.^l.jj i n\ _ LUI Ev(GeV) Figure 2.4: Normalized crosssection calculated with the NUX program. Ev QE and DIS interactions for //,,, v,, and vt
tt/4. 2.2. NEUTRINO EVENT RATES 15 listed in Table 2.3. Since the neutrino flavor can no! be identified with a NC interaction in the detector, the total number of vt and vlt NC events are listen!. Considering the twoflavor oscillation v^ > vt, the i/t flux can be1 calculated according to Equation 1.L2. The number of vt and vt CC event rates for five different Am2 values, assuming Q2i arc listed in Table 2.4. For each type1 of interaction, the event rates from tlie FLUKA and the HKKM flux models arc compaied. It can be seen that the1 FLUKA model has a largee absolute normalization than the HKKM model arid the difference between the two models is within 10%. Figure1 2.5 shows the energy distributions erf the vc(v,) and v^v^) CC evcnls in loga rithmic scales. Tlie energy distributions of vt(vt) CC events for five different Am2 values are shown in Figure1 2.7. All of the drawn even! rates aie calculated according to the1 FLUKA flux mode1!. Figme 2.6 shows the zenith angle dependence of all the ncmtrino flavors for both flux models. vt only appears from the1 upward going direction, since only (hen the1 v)t has enough probability to oscillate1 into i/t.
I (> CHAPTER 2. PREDICTION OF ATMOSPHERIC NEUTRINO EVENT RATES At mospheric v( CC (Evts/kt/ year) v, CC Evts/kt/year) Flux Model DIS QE Tot DIS QE Tot FLUKA 2002 22.9 49.0 71.9 7.2 8.4 15.0 (Ê(GvV)) (2.83) (0.02) (3.12) (0.79) HKKM 2001 22.7 45.G Ü8.3 7.2 7.8 15.0 (Ë(GeV)) (3.01) (0.64) (3.42) (0.85) Table1 2.1: QE and DTS event rates and average1 eneigies of //,, and v,, for 0.1 GeV< Ev <100 GeV. for FLUKA and HKKM flux mochs. Atmosphenic i/ CC (Evts/kt/war) u,t CC, (Evts/kt/yeat) Flux Model DIS QE Tot DIS QE Tot FLUKA 2002 42.0 80.1 122.1 15.3 18.5 33.8 (Ë(GcV)) (4.53) (0.72) (4.89) (0.90) HKKM 2004 43.3 74.0 117.3 15.8 17.4 33.2 (É(GcV)) (4.78) (0.77) (5.19) (0.98) Table 2.2: QE and DIS event rate's and average energies of vfl and ;//t, for 0.1 GeV^ E <100 GeV, for FLUKA and HKKM flux models. Atmospheric v, \ v NC v, +i/ NC Flrrx Model (Evts/kt/year) (Evts/kt/year) FLUKA 2002 23.2 9.0 ( (GeV)) (3.73) (4 08) HKKM 2004 23.4 9.1 (Ë(GeV)) (3.97) (4.40) Table 2.3: NC event rates aud average eneigies erf v and v, for 0.1 GeV< Ev <100 GeV, foi FLUKA and HKKM flux models.
0.01c 2.2. NEUTRINO EVENT RATES 17 Atmosphenic Arn2 0.0005eU2 Am2 0.001 ev'2 Flux Model(//r) FLUKA 2002 (Ä(GoV)) Ï1KKM 2004 (E(GeV)) DIS QE Tot 0.08 0.08 0.16 (11.62) (6.11) 0.09 0.09 0.18 (11.52) (6.09) DIS QE Tot 0.21 0.12 0.33 ( 13.64 ) (7.39) 0.23 0.13 0.36 (13.52) (7.35) Am2 rr 0.0035c V2 Am2 0.005CV2 Am2 0.01c V2 DIS QE Tot DIS QE Tot DIS QE Tot 0.42 0.14 0.56 (22.06) (8.86) 0.46 0.15 0.61 (22.01) (8.78) 0.46 0.15 0.61 (24.36) (8.89) 0.50 0.17 0.07 (24.36) (8.82) 0.50 0.13 0.63 (26.40) (10.10) 0.54 0.14 0.68 (26.49) (10.03) Atmospheric Am2 = 0.0005eU2 Arn2 ~ O.OOleU2 Flux Modeil(z/r) FLUKA 2002 ( (GoV)) HKKM 2004 (Ë(GeV)) DIS QE Tot 0.03 0.03 0.06 (11.63) (6.78) 0.03 0.04 0.07 (11.71) (6.80) DIS QE Tot 0.07 0.05 0.12 (13.55) (8.06) 0.08 0.06 0.14 (13.68) (8.08) Am2 0.0035e\/2 Am2 0.005cU2 Am2 V2 DIS QE Tot DIS QE Tot DIS QE Tot 0.15 0.07 0.22 (21.68) ( 9.95) 0.17 0.07 0.24 (22.04) (10.01) 0.17 0.07 0.24 (23.86) (9.91) 0.18 0.08 0.26 (24.39) (9.99) 0.18 0.07 0.25 (25.84) (ff.14) 0.20 0.07 0.27 (26.54) (11.21) Table 2.4: Charge current event rates (Evts/kt/year) of ut and vr, for 0.1 GeV< Ev <100 GeV, for FLUKA and HKKM flux models. Tlie vt is oscillated from vtl and the1 flux is calculateel according to Equation 1.12. Five different Arn2 values are taken and maximal mixing is assumed: 02i tt/4.
'. 18 CHAPTER 2. PREDICTION OF ATMOSPHERIC NEUTRINO EVENT RATES c> o 'Ä T3 CM co +_, ci cu rri 1> fee cd TD o w cc :T TD *=5 + T V..S T. 9^ ia Un :? K o Q <l) rfl o TD 11 i i I 11 ' 11 11 I 11 i I i 11 I 1111 4 <M i (D <i> fl CM (jbaa/pt/svvg) osoap/np p cd fc S O ^ tri TD 0/ O tf ^ ^ hj q; ^ " 3 tut) S 03 CO 13.t H rfl ^."S ri _; Ci r! 3 4) ft sj INI o +j ~i. H ' «J.1 o C" ii CM CC 0),n CO 3 td of) (1/ CC h cd cc CC 0 Is o CC TD «S Cu 33 CO +J 1^ a +J O _ 3 i> ij o Cv CT "Ö _, CD dy H "*< rfl ^ CC. 0) p w O >3J cd CD cc Ö "3 K^v CD o z X Ö 4J O r[ 11 o CD tu  c td aj s b CD G O O CD s 3 In I 'I i li I Ii ' I A80/JB3Ä/P1/BJA3 k" ^ii'iii i I I» Im I *. O T «Aa3/jesfyp /s)a3 w, CO r* «CD cx L^ o :n ji CN I' CD o CD. CD O 3, rjd cc ^1. cri <D tu ÏÏ i^ Ö s
2.2. NEUTRINO EVENT RATES 19 Evt Rates (FLUKA) I Evt Rates (FLUKA) >oos.0.05 ; Am2=5x1CTe\r Am2=1x10 ev «: À % l 0 04 0 03 0.02 QE DIS QK DIS Tot Tor 10 *?0 30 40 50 60 70 80 90 Ev(GeV)... i. ii^. '. ' i. T) 10 20 30 40 50 60 70 80 90 E,(GeV) Evt Rates (FLUKA) I Evt Rales (FLUKA) l >0 06 r % Am2=3.5x10"3eV2 Am2=5x10~3 ev2 DIS DIS fut Tot L"i w.'. ' ".1... IU 10 20 30 40 50 60 70 80) 90 Ev(GeV) ''!'''»' li'jj^'jk'j.i. 10 20 30 40 50 70 80 90 E,(GeV) Evt Rates (FLUKA) Am2=1x10~2eV2 0.03 0 02 QE DIS 0 01 Tot.'.".Jj ) 90 E.(GsV) Figure 2.7: Energy distribution of vt and vt CC events of five oscillation scenarios with FLUKA flux model foi an exposure1 of one ktonxvear. The QF events (dashed line), DIS events (pointed line) and the1 sum of them (solid line) are shown.
20 CHAPTER 2. PREDICTION OF ATMOSPHERIC NEUTRINO EVENT RATES
Chapter 3 Liquid Argon Time Projection Chamber 3.1 Detector Principle The technology of the Liciuid Argon Time1 Projection Chambe4r (LAi TPC) was first proposed by C. Rubbia in 1977 [Tlj and was developed and demonstrated le) wotk for latge1 masse1«by the1 extensive R&D program for the ICARUS (Imaging Cosmic and Raie Underground Signals) project. The choice of Argon as the liquid medium is justified by the fact that it must be a noble4 gas in order to permit long electron drifts. Out of tlie stable five noble1 gases in nature (He, Ne1, At, Kr and Xe1) the his! two cannot be used in Ihe liciuid form, since1 a microbubble forms around tlie electron, slowing down the dtift piocess. Of the two remaining liquids, em!> Argon has reached the industrial exploitation which is commensurate to our task. Argon is a byproduct of the1 liciuefaction of air and consequent production of hemic! Nitrogen and Oxygen. Argon is relatively abundant since it makes about 0.0% of air. The cos! in the1 liciuid form is relatively modest, f«0.5 Euro/kg, corresponding to 0.5 MEuro (0.8 MSF) for 1 kiloton. The1 detector is essentially a large cryogenics coûtai nor filled with liejuid Argon seiving as both the neutiino target îeadout system which measures the4 ionization and the detecting medium, and equipped with an electronic signal induced by the charged particles. A uniform electric field is applied inside1 the volume1 of liquid Argon and an array of sensing wire planes are placeel at one end of the drift field. The wiies in a plane are p. n ai lei to each other and the orientation of wnes are different be'twenn planes. When the charged paitieies traverse the LAr TPC, they ioiiizc\s the1 argon atoms and produce ionelectron pairs. Ions and eieetrons arc4 forced to move toward the electrodes with opposite penalities uncle1! tlie1 applied electric field. Since tlie1 ions are heavier and drift much slower than the électrons, onlv the electron signals are used. Due1 to tlie e4le4ctiostatie shielding of the adjacent grids, only on the first plane the1 signal starts as soon as tlie1 ionizing particle1 crosses the1 chamber and can be use4d to de4termine the lefeience lime for the electron drift (/0) arid to trigger the DAQ system. 21
22 CHAPTER 3. LIQUID ARGON TIME PROJECTION CHAMBER The time1 t0 can also be cktcrmincd by the coincident defection of the scintillation light emitted from the ionization. Thus, each wire in tlie re4ad a wire plane, a twodimensional projection out plane records a part of the ionization track and from of the ionization event can be reconstructed! when1 one1 coordinate is given by tlie wile position anel the olher by tlie drift distance, which corresponds to the diift time multiplied by the electron drift velocity. Tlie1 drift time4 is common for diiferent projections after correcting the gap distance between read out planes. Thus, with at least two wite planes, of the event topology is possible. See Figure 3.1 for illustration. a full thre4edunensiona] reconstrue!ion The1 electrostatic shielding between sensing wires ensures that the signals are only induced on the wire's nearby and hence4 allows a good localization in space. The spatial resolution depends on the wire pitch. The ioni/ed electrons arc collecter! on the1 last readout plane. The detector is operated in non amplification tlie ejections are proportional to the depositee! energy, possesses excellent calorirnetiic capability. mode and the1 number of which ensures that the LAr TPC A lot of experience has been gathered during (he ten years of studies with differcnt si/e4s of prototypes [45 49) in ICARUS, and finally a GOO tons TPC (TÜÜ0) has been constructed and te4sted successfully at the surface1 with cosmic rays [50]. Moie technical derails about the TG00 detector will be given in tlie4 next section. wire (plane i) Wire planes Scintillation Figure 3.1: The drawing shows the LAr TPC defection principles. 3.2 The ICARUS T600 Detector The ICARUS T000 del eel or has been fully assemblcd and transported to the INFN Cran Sasso Laboratorv (LNGS) in December 2003. The main cryogenic centaine1! of tlie1 T000 detector houses two identical and independent parallelepipeds filled with liciuid Argon and with external dimensions of 4.2 x 3.9 x 19.9 m3 e4aeii. The walls of each halfirrodulc (T300) are4 made of aluminum honeycomb panels. The1 whole volume is surrounded by a
ij lllh ICARUS lhoo Dh IPC I OR (hernial insulation Lree s and an <\tenia 1 slue kling la\ei against ueilitems (h iguies 3 2 anel Sirjn il i><\lihroiicjhs Ll\k e oolirui ( ire uit HV fccdthrouejhs 'V ^ yy<j,y~,x>> j ' ni >, Aluminum i onlaiik r Cx.t"rn il themial instil ition ^yci iguie \1 Se hemat le view of Hie4 ICARUS FOOO e nostat 3.2.1 Inner Detector Time4 Projection Chambers I he4 miiei detee toi of e ae li I Î00 consists ol two 'IPCs with tlie dimensions o( AU m wide A 0 m high and 19 ( in long I lie two I PC s Ciefeiied to as left and light ehambeis) shale a e ommon cathoek at the ecntet m t he longit udmal diiee lion anel have thieewiie planes at both sides 1 his sets a dnft length ot 1 5 m (ot both ehambeis I he top side ol the (ivostat hosts the exit flanges eqmpped with e isogenic teedllnoughs for the1 eleetneal e ounce 1 ion ol the wites with the leadout eleetlomes anel lot all the mteinal insti umenlation (I'M Is LAr putitv uionitois. le\e 1 and te mpetaluie piobcs etc ) i he lhie4e wite plain s an i mm a]ait fioin each olhei \\ ne dnee fions m the f hieeplanes aie1 one nie d at 0 and 1 (>0 with tes[)e1< I to the lion/ontal du cet ion i he (list plane (0 ) and thesecond plain ( I 00 ) fae mg thednft \ojume woi k m indue (ion mode ane! are called Induct ion I plane and Induction II plane 1 he thud plane1 ( 00 ) woiks m c h ugec oil«e t ion mode a\k\ is e ailed ( ollee tion plane I he wues.ue1 made of stainless stee1 with a diainetei o[ 150//m I heptte h betwe e n adjae e nt wires is,5 mm Thus theie ate 2112 v\ nes m Indue tion 1 plane and 5000 wite s m Indue turn II and ( ollee lion plane A pie tuie ol the i lnee wire plane's is shown m FlgUM 3 5