Electromagnetic shower reconstruction with emulsion films in the OPERA experiment F. Juget IPH Université de Neuchâtel On behalf of the OPERA collaboration CALOR 08 – Pavia – May 28th 2008

Physics motivation Appareance search of    oscillations in the parameter region indicated by S-K for the atmospheric neutrino deficit.  Search for  appearance in the CNGS  beam  Search for   e : put new constraints on    Actual result: (CHOOZ): sin 2 2  13 < 0.1 Recent results (SK,MINOS): best fit:  m 2 = eV 2 and sin 2 2  23 = 1.00

The Cern Neutrino to Gran Sasso (CNGS) program 730 km CERN  beam optimized to study the  appearance by  detection in the parameters region:  m 2  2.4  eV 2 and sin 2 2   1.0 Beam mean features: L=730 km ; =17 GeV ( e + e )/  =0.87% ;  prompt negligible _ In shared mode  4.5x10 19 pot/year  2900  CC/kton/year  13  CC/kton/year expected at Gran Sasso

Principle: direct observation of  decay topologies in  cc events bricks → target mass: 1.35 ktons Requires high resolution detector (δx~1 μm, δθ~1 mrad ) : use photographic emulsions Needs large target mass: alternate emulsion films with lead layer 10.3 cm 12.8 cm 7.5 cm =10 X 0 The basic unit: The BRICK sandwich of 56 Pb sheets 1mm + 57 emulsion layers (weight 8.3kg)

Veto plane (RPC) High precision tracker Instrumented dipole magnet ● 6 4-fold layers of ● 1.53 T drift tubes ● 22 XY planes of RPC in both arms Muon spectrometer (8×10 m 2 ) SM1 SM kton Target and Target Tracker (6.7m) 2 ● Target : bricks, 29 walls ● Target tracker : 31 XY doublets of 256 scintillator strips + WLS fibres + multi- anodes PMT for Brick selection Muon tracks reconstruction The OPERA detector

Bern emulsion scanning lab. Emulsion scanning is performed in a fully automatic way. About 40 microscopes are operational in the various OPERA scanning laboratories. 2 mm Automated emulsion analysis 2 emulsion layers 50  m plastic base 200  m

Off-line emulsions scanning 3D Microtracks reconstruction Microtracks alignment via the plastic base BASETRACK Reconstruction Vertex/Decay Basetracks alignment of several emulsions TRACK Vertex reconstruction - Momentum measurement by Multiple Scattering - Electron identification and energy measurement - dE/dx for  /µ separation at low energy  CC interaction

ν μ CC interaction Only “straight” tracks (hadrons) are reconstructed and attached to the vertex  Need dedicated algorithm for EM shower reconstruction

Electron reconstruction and identification Reconstruction principle: Starting from a given basetrack a “backpropagation” method collect basetracks in a cone using connection criteria (slopes and positions) e/  separation: Method use a neural network based on the reconstructed shower longitudinal profile and the number of collected basetracks 6 GeV electron (real data) in 20 emulsions ~3.3 X 0

Efficiency: 90% for E > 2 GeV with  contamination <1% (at 1 GeV the contamination is ~ 5 %) 80% efficiency is obtained at 1 GeV with 1%  cont. Small dependence on sheet number (published in JINST 2 P02001 february 2007) Electron reconstruction and identification Electron efficiency Pion contamination

Electromagnetic shower energy measurement Method: use also a neural network based on the reconstructed shower profile and the number of collected basetracks which are both very energy dependant Resolution for 41 plates: (25% at 5 GeV- 35% at 2 GeV) Longitudinal profile Energy resolution

 ij  meas  2 meas = * X X0*p2X0*p2 +  2 RMS  ij Resolution on Basetracks Pb jj ii  ij Basetracks of one reconstructed track Principle : to use the angular differences  ij of particle tracks mesured in emulsions, due to multiple coulomb scattering in lead. This has to be well known or measured For a given track, the rms of the slope diff.  ij is linked to the particle momentum Em Momentum measurement for charged hadron

-Very good linearity between reconstructed momentum and pion momentum - Obtained momentum resolution is ~ 20%-30% at 2 GeV Momentum resolution for charged hadron (ncell = Number of crossed emulsions) Test-beam at CERN ( ) : OPERA brick exposed to pions at different energies MC pions made with OPERA simulation software

4 tracks associated to the vertex with = 9  m EM shower -  conversion from  0 - well attached to the vertex IP = 29  m Gamma energy: 7.7 GeV 43 mm 17 mm ν μ CC interaction in OPERA (data from october 2007 run) muon

CONCLUSION In addition of its very good tracking information capability, the OPERA brick can be used as a fine sampling EM calorimeter. –Good electron identification and energy measurement at high energy For E>2GeV, 90% efficiency with low hadron contamination (<1%) Energy resolution is ~20-40% for E > 2 GeV Momentum measurement of charged hadrons using Multiple Scattering –Momentum resolution ~ 20-30% for P up to 6 GeV These results fulfill the requirements for the kinematical analysis needed for the OPERA goals The OPERA detector will be completed in June 2008 in time with the beam –May 16th bricks were already inside the detector (86.5%) –~130 beam days foreseen in 2008 –Expected ~ events with 1  event! OPERA is running and is confident to fulfill its goal: First evidence for direct apparition in neutrino oscillation

BACKUP

 Find the right brick to extract x y Plastic scintillator + wave length shifting fiber + 64 channel multi-anode Hamamatsu PM ~ 99% detection efficiency  trigger - brick finding: ε brick ~ 80% - initiate muon tagging WLS fiber photon particle 2.63 cm 6.86 m The OPERA Target Tracker

Dipole magnet + RPC (inner tracker) Drift tubes (precision tracker) - ε miss charge ~ ( )% - Δp/p < 20% for p < 50 GeV -  id > 95% (with target tracker)  h   ,e +,h D +, D + scsc  Inner tracker (RPC in magnet) and precision tracker (drift tube, 8 m length) The OPERA Muon Spectrometer  Performant  tagging (improvement of  efficiency and tag of  CC events)   charge measurement to reduce background induced by charm decay:

Bricks filling with the BMS

   oscillation sensitivity  decay channels  (%) BR(%) Signal Background  m 2 =2.5x10 -3 eV 2  m 2 =3.0x10 -3 eV 2   µ   µ   e   e   h   h   3h ALL  BR=10.6% full mixing, 5 years 4.5x10 19 pot / year Main background sources: - charm production and decays - hadron re-interactions in lead - large-angle muon scattering in lead

SK 90% CL (L/E analysis) Discovery probability % Last MINOS measurement 3 σ sensitivity 4 σ sensitivity OPERA ν τ observation probability

1 st CNGS run: August 2006  No brick in the detector  Used for electronic detectors, DAQ, GPS commissioning and tests of CNGS-OPERA information exchange  121 hours of real beam operation ( 70% of nominal intensity  1.7  pot/extraction)  Integrated intensity: 7.6  pot Time selection of beam events: T OPERA - (T CERN +T flight ) <  T gate T flight = 2.44 ms GPS Time Stamp resolution ~ 100 ns  T gate ~ 10.5  s  The events time distribution is peaked around the 2 extractions peak times within negligible cosmic-ray background Cosmic ray events

OPERA beam events  319 beam events collected:  3/4 external events (interaction in the rock)  1/4 internal events (interaction in the detector)  CC in rock (rock muons)  CC in the magnet

Events direction Zenith angle of muon track: z θy >0 θy <0 θyθy θyθy Cosmic ray MC simulation from MACRO parametrization Beam events: = 3.4  0.3° (as expected) More details in R. Acquafredda et al., New J. Phys.8 (2006) 303

Target Tracker + Brick Walls Spectrometer  What the brick cannot do:  trigger for a neutrino interaction  muon identification and momentum/charge measurement  need a hybrid detector On-line analysis of electronic data Brick finding algorithm Selected brick is removed from the target and exposed to cosmic rays (alignment). Emulsions are developed and sent to scanning stations / labs OPERA: an hybrid detector

Events detection sequence 1- Brick tagging by Target Tracker: 2- Brick removed with the BMS (Brick Manipulating System) Automatic emulsions scanning:  ~30 bricks will be daily extracted from the target  Distributed to several labs in Europe and Japan  2 high-speed automatic scanning systems:  The European Scanning System (commercial products, software algorithms)  The S-UTS (Japan) (Dedicated hardware, hard coded algorithms) 3- Brick exposed to cosmic rays for sheets alignment 4- Brick disassembled and emulsions developed  - Neutrino interaction trigger - Brick localization (brick finding)

An emulsion doublet “Changeable Sheets” (CS) is attached at the downstream face of each brick: - Packed in light-tight envelope - Can be remove without opening the brick  used to tag tracks predicted from TT reconstruction  found tracks in CS are predicted in the most downstream films of the bricck  Brick Changeable sheets Target Tracker Target Tracker to Brick connection: changeable sheets This procedure was successfully tested with cosmic muons in spring 2007 with the first inserted bricks

Predictions from electronic detectors are followed back inside the brick sheet to sheet in one microscope view (~300x300 microns) up to its stopping point All found stopping points are considered as possible vertex point and a large area around is scanned (5x5 mm 2 5 sheets before and 5 after)  confirm and reconstruct the vertex “Scanback” strategy Large scan around a stopping point Vertex confirmed with 2 tracks in addition of the “scanback” track

A track is the result of the connection of two microtracks on opposite sides of a plate The European Scanning System Performances of the European Scanning System  Scanning speed: 20 cm 2 /h/side (40 GB/day/microscope of raw data)  Purity: 10 fake tracks / cm 2 (slope < 0.5)  Efficiency: up to 95% using tracks, ~100% using microtracks (however, background is larger with microtracks)  0.3÷0.7μm precision for reconstructed tracks

130 days for the CNGS 2.4*10 19 p.o.t Start: June End : Nov. 10 th Total number of interactions 2780  CC events 2090  NC events 620 e  e events 20 Charm decay90 Tau candidate eV 2 ) 1.0 Rencontres de Moriond EW 2008 C.Pistillo - Bern Univ. 16 The 2008 OPERA run