The Electronic Detectors of the hybrid OPERA Neutrino Experiment

1. The Electronic Detectors of the hybrid OPERA Neutrino Experiment Regina Rescigno (University of Salerno) for the OPERA Collaboration 15th Lomonosov Conference on Elementary Particle Physics

2. Belgium ULB Brussels Italy Bari Bologna LNF Frascati L’Aquila, LNGS Naples Padova Rome Salerno Russia INR RAS Moscow LPI RAS Moscow ITEP Moscow SINP MSU Moscow JINR Dubna Croatia IRB Zagreb France LAPP Annecy IPNL Lyon IPHC Strasbourg Switzerland Bern ETH Zurich Japan Aichi Toho Kobe Nagoya Utsunomiya Germany Hamburg Turkey METU Ankara Israel Technion Haifa The OPERA Collaboration 160 physicists, 30 institutions, 11 countries Korea Jinju 2

3. Introduction • The OPERA detector is designed to search for nt appearance in a nm beam • Detector installed underground in the Gran Sasso Laboratory, 730 km away from CERN, where the CNGS (CERN neutrino beam to Gran Sasso) nm beam is produced Expected neutrino interactions for 22.5 ×1019 p.o.t: (*) Interaction rate 3

4. Mechanical structure Changeable Sheet Doublet(CS) in separate envelope Brick: 57 nuclear emulsion films interleaved with 56 lead plates (1mm thick) Muon spectrometer: Target area: ~150,000 bricks (total target mass ~ 1.25 kt) arranged in 54 walls Walls of ECC brick interleaved plastic scintillator tracker walls Instrumented dipolar magnet for muon spectrometry 10.2cm 12.5cm The OPERA detector SM1 SM2 nm Veto 4

5. ECC brick 1 mm electronictrackers   Pb emulsion layers interface films (CS) Principle of the experiment • Hybrid technology: Electronic detector and nuclear emulsion • ELECTRONIC DETECTOR • triggers the acquisition for neutrino events • predicts the region of the target where each event occurred • Helps particle identification • provides measurements of the relevant kinematical quantities for each event 5

6. The Veto System • The veto tags the interactions occuring in the material and in the rock upstream of the target • Two layers of glass Resistive Plate Chambers (GRPC) • Global sensitive area ~ 200 m2 • 97% efficiency in streamer mode 6

7. The Target Tracker • Main tasks: • Trigger on neutrino events • Location of the interaction inside the target • Provide calorimetric information on the event • TT wall: two planes of 256 strips (horizontal and vertical): 256 × 256 cells • TT walls and brick walls are interleaved • Strips signal transported at both ends by WLS fibres read by 64-channel PMTS • 0.8 cm resolution, 99% efficiency 7

8. The Target Tracker • Event data extracted every 50 ms. • Trigger: at least 2 XY coincidences in the TT (threshold 1 p.e.) on time with the CNGS clock. • A set of algorithms (Neural Network, Kalman filter) is used to identify the brick where the interaction occurs, providing a probability map. • The brick finding efficiency is about 60% when the brick with the highest probability to contain the event is analysed and it reaches 80% when the second most probable brick is extracted Event time difference w.r.t. the closest extraction Time distribution of events in the neutrino run 8

9. TT 2.6cm ECC Brick 10cm 12.5cm The Target Tracker Position accuracy of the predictions of the ED (muons) Angular accuracy of the predictions of ED (muons) 9

10. The Muon Spectrometer • Goals of the spectrometer: • Muon identification • Momentum measurement • Charge discrimination • 1.52 T magnetic field bending particles in the horizontal plane • 24 slabs of magnetized iron interleaved with 22 RPC planes • 6 station of 4 planes of staggered vertical drift tube per SuperModule: • 2 station in front of the magnet • 2 between both arms • 2 behind 10

11. High Precision Tracker (HPT) • Muon momentum extracted from two independent deflections of the particle in the magnetic field • Spatial single-tube resolution ~ 250 mm 11

12. RPC’s • 3500 m2 Bakelite RPC’s operated in streamer mode • Tracking of the muon particle • Range measurement of the stopping particles • Hadronic energy reconstruction in the spectrometer • Coarse tracking of showers RPC efficiency 12

13. Brick Manipulator System • Used to insert all bricks • Used to extract the candidate bricks (with a vehicle going inside the trays and bringing back the bricks) • Extraction in parallel with CNGS data taking 13

14. 20 m Neutrino interactions in the ED How neutrino interaction events look like in the OPERA electronic detectors 1m: event with a m in the final state 0m: event without a m in the final state 14

15. Monte Carlo (MC) simulations • The know differential neutrino cross sections for the CC-DIS, CC-QE, CC-RES and NC-DIS processes on an isoscalar target are convoluted with the CNGS neutrino flux • The expected number of interactions is computed together with the relative fraction of each process (the target mass and the number of p.o.t. are taken into account) • The fractions of each process are corrected for the non-isoscalarity of the target in the OPERA detector • The final states of the events are generated using the NEG MC program developed in the framework of the NOMAD experiment • The event developement in the detector is simulated using GEANT3 Virtual MC simulation package, version 1.10. 15

16. DATA (dot) MC (lines) Studies of quantities measured in the ED • Momentum resolution < 20 % (p< 50 GeV) • Charge misidentification: 1.2% (2.5 GeV < p < 45 GeV) Muon momentum reconstruction Momentum × charge 16

17. Studies of quantities measured in the ED Muon identification criterion Track length × density (range for muon identification) DATA (dot) MC (lines) Muon identification efficiency ~ 95% (length × density > 660 g cm-2) Muon reconstruction and identification are in good agreement between Data and MC 17

18. Studies of quantities measured in the ED • Deposited energy computed by using the TT subdetector • 5 p.e. for mip (2.15 MeV) Energy reconstrucion Empty dots: MC Full dots: DATA p.e. for a m.i.p. track as a function of the distance from each end DATA (dot) MC (lines) DATA (dot) MC (lines) Energy deposited in the TT for 1m event Energy deposited in the TT for 0m event 18

19. Studies of quantities measured in the ED • TT hit position weighted by the number of collected p.e. • The muon track has been removed for the longitudinal profile. Hadronic shower profile DATA (dot) MC (lines) DATA (dot) MC (lines) 19

20. NC/CC ratio estimation using the ED The visible NC/CC ratio takes into account • NC/CC true ratio (0.3) RNC/CC • Fiducial volume selection efficiency • Muon Identification efficiency • Events migration due to misidentification CCNC The 2008 and 2009 event position: Green: MC – interactions inside OPERA target Purple:MC – interactions outside OPERA target, mainly surronding rock NC/CC ratio measurement after removal of external bkgnd accumulationat target borders: Data 2008: NC/CC= 0.230 ± 0.014 (stat.) Data 2009: NC/CC= 0.230 ± 0.009 (stat.) MC: NC/CC= 0.236 ± 0.005 (stat.) 20

21. Conclusions • The OPERA electronic detectors have been working since 2006 • In the two first physics running years -2008 and 2009- the electronic detectors were fully operational for more than 98% of the active beam time • Neutrino interactions are identified and reconstructed using the measurement of in the electronic detectors • Studies on the comparison between data and Monte Carlo have been performed both on muons and on hadronic showers • The performances of the electronic detectors are reliable and understood 21

22. Spares 22

23. NC/CC ratio estimation using the ED 23