1. 2008 European School of High-Energy Physics - Trest, Czech Republic - 19 August - 1st September Target Tracker Data Analysis In OPERA Experiment S. Dmitrievsky, S. Zemskova - JINR OPERA Experiment The OPERA experiment is designed for direct observation of appearance in the CNGS long baseline beam (from CERN to Gran Sasso Laboratory) as a result of oscillation. OPERA exploits nuclear emulsions as very high resolution tracking devices for the direct detection of tau leptons produced in the charge current (CC) interaction of the with matter of the detector. OPERA ECC Brick Lead plate(1mm) / Emulsion Film (OPERA film) Sandwich 125mm 100mm Lead Plate Emuslion Film (OPERA Film) 125mm 100m m Pb Emulsion layers  1 mm CNGS Beam Beam optimized to have the maximal number of Charged Current interactions (given the baseline L=730 km)  production threshold 3.9%  /  negligible  prompt 17 GeV 0.73% ( e + e )/  L/E ~ 43 km/GeV, not optimal for P osc Beam energy and contamination Signal and background events n m -n t oscillation channel 0.174.22.9 -  µ- -  µ- 0.175.03.5 -  e- -  e- 0.244.43.1 -  h- -  h- 0.171.30.9  -  3h Background: Charm Hadron interaction Muon scattering  m 2 = 3.0 x 10 -3 eV 2  m 2 = 2.5 x 10 -3 eV 2  - decay channels 15.00.76 ALL Signal ÷ (  m 2 ) 2 – Full mixing 10.4 Preliminary OPERA subsidiary physics programme includes measurement of upper limit of at level The first CNGS neutrino test run took place in August 2006.. Alignment of TT with the help of muon tracks Alignment of the TT is essential for track reconstruction and the brick finding. Making use of straight cosmic muon tracks we clarify a geometrical position of the TT modules (the angles of rotation around of coordinate axes and displacement along the axes). We need to set local coordinate systems of modules to general system of coordinates of the experiment. We can see summary difference between experimental points and calculated tracks before alignment and after 3 iteration on these pictures. Target Tracker 7 m 6.9m 1.7m Plastic scintillator strips (AMCRYS-H, 6.7m x 2.6cm x 1cm) readout by Kuraray WLS fibres + Hamamatsu PMT’s (64 channels) Target Tracker tasks: Target Tracker tasks: ● Trigger:  > 99% ● Brick finding :   70  80% ● Initiate muon tagging 31 walls Detection of the  appearance signal Two conflicting requirements:  Large mass  low Xsection  High granularity  signal selection  background rejection Target:1800 tons, 5 years running 30 000 neutrino interactions ~150  interactions ~15  identified < 1 event of background Toplogy selection:  Kink signature The challenge is to identify  interactions from  interactions   -- Decay “kink”  -- ~1 mm  oscillation -- Autumn 2007 CNGS Commissioning and Physics RUN If intensity as in August 2006 : 1.7 10 13 pot/extraction (70% nominal) If extraction scheme as in November 2006: 3 double fast extraction per 36 s SPS cycle If typical 70 % efficiency of the machines complex If target filling programme as scheduled Target mass505(37%) → 615(46%) tons Beam intensity 0.43  10 19 pot ≈ 10% nominal year ≈ 10 × flux in 2006 Events in bricks180 Charm events10 3 weeks of CNGS commissioning run + 3 weeks of physics run following June CERN SPSC recommendation OPERA detector : 2 identical super-modules (target, TT, Spectrometer) + veto system Target and Target Tracker (6.7m) 2 ● Target : 77500 bricks, 29 walls ● Target tracker : 31 XY doublets of 256 scintillator strips + WLS fibres + multi- anodes PMT for Brick selection Calorimetry 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 SM2  ID, charge, p  p/p < 25% Wrong charge < 0.3%  ID, charge, p 0.68 kton Brick Finding An essential issue in OPERA is finding of a target brick where the neutrino interaction took place. For this purpose the OpBrickFinder program was developed that performs the vertex brick identification using the information from the target tracker and spectrometer. Our brick finding (BF) strategy includes the following steps: - event cleaning; - muon track identificatin and reconstruction; - hadron shower axis reconstruction; - the most probable vertex wall determination: For a vertex wall determination we use a multilayer perceptron (MLP) with standard back propagation training algorithm. Expected BF Efficiency: 1 brick extraction:~70% 2 bricks extraction:~85% 3 bricks extraction: ~90% Output variables of the neural network are probabilities of each wall to be a vertex wall. The wall finding efficiency achieved so far is ~85% for events - localization of the most probobal vertex bricks: After the vertex wall is selected by the NN, we use its position, a muon track, and/or a shower axis parameters to determine x-y coordinates of the vertex brick in the wall. 5 years of data taking Nominal beam intensity 4.5*10^19 p.o.t./year 1.35 kton target mass (25% reduction w.r.t. proposal) Neutrino int. in TT