2. A. Chukanov On behalf of OPERA collaboration JINR, Dubna TAUP 2011, Munich, 5-9 september, 2011

3. Outline OPERAexperiment OPERA experiment Event location procedure Event location procedure candidate  candidate Background estimation Background estimation Conclusion Conclusion OPERA experiment, A. Chukanov7 september 20112

4. OPERA experiment, A. Chukanov OPERA: Oscillation Project with Emulsion tRacking Apparatus CERN LNGS 732km High-energy long baseline  beam Direct search for    oscillations by looking at the appearance of  in a pure  beam Search for the sub-dominant   e oscillations for  13 measurement 7 september 20113 OPERA CNGS

5. OPERA experiment, A. Chukanov CNGS neutrino beam 7 september 20114 17 GeV L730 km ( e + e ) /  0.87 % *  /  2.1 % *  prompt Negligible * * Interaction rate at LNGS  Expected interactions for 22.5 x 10 19 p.o.t. (nominal pot in 5 years): ~ 24300  CC + NC ~ 160 e + e CC ~ 114  CC (  m 2 = 2.5 x 10 -3 eV 2 ) ~ 8  decays are expected to be observed (BG<1)

6. Belgium ULB Brussels Croatia IRB Zagreb France LAPP Annecy IPNL Lyon IPHC Strasbourg Germany Hamburg Italy Bari Bologna LNF Frascati L’Aquila, LNGS Naples Padova Rome Salerno Japan Aichi Toho Kobe Nagoya Utsunomiya Israel Technion Haifa Korea Jinju Russia INR RAS Moscow LPI RAS Moscow ITEP Moscow SINP MSU Moscow JINR Dubna Switzerland Bern ETH Zurich Turkey METU Ankara http://operaweb.lngs.infn.it/scientists/?lang=en The OPERA Collaboration 160 physicists, 30 institutions, 11 countries 7 september 20115OPERA experiment, A. Chukanov

7. Pb emulsion layers 1 mm ECC brick Interface films (CS) electronic trackers Direct observation of  decay topologies in  cc events OPERA experiment, A. Chukanov Requires high resolution detector (δx~1 μm, δθ~1 mrad) Needs large target mass Decay “kink”   µ µ - use nuclear emulsions - alternate emulsion films with lead layer 7 september 20116 Prediction the region of the target where each event occurred - Electronic trackers

8. Emulsion Cloud Chamber (ECC) brick sandwich of 56 lead plates 1 mm + 57 emulsion films consisting of two emulsion layers on each side of a plastic base (weight 8.3 kg)‏ Changeable Sheets (CS): tightly packed removable doublets of emulsion films glued to the downstream face of each brick OPERA experiment, A. Chukanov ECC = stand-alone detector: momentum measurements for hadrons (multiple Coulomb scattering)‏ Pion/Muon separation at low energy (dE/dx)‏ electron identification and energy measurements for e,γ 12.5cm 10.2cm 125mm 102mm 75.4 mm 8.3kg 10X 0 beam 7 september 20117

9. The Detector OPERA experiment, A. Chukanov Electronics Muon Spectrometer Target BOREXINOBOREXINO   -Veto Target Muon Spectrometer BMS Target and Target Tracker (6.7m) 2 Target : 77500 bricks, 28 walls Target tracker : 31 XY doublets of 256 scintillator strips for Brick selection Muon tracks reconstruction 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 ) Veto plane: RPC 7 september 20118 Total mass of the target: 1250 tons

10. OPERA Detector OPERA experiment, A. Chukanov7 september 20119

11. Event trigger and reconstructionBrick identification Selection of a brick most probably containing the neutrino interaction Reduce scanning load Minimize the target mass loss OPERA experiment, A. Chukanov Brick finding task 7 september 201110

12. CS - Interface emulsion films: high signal/noise ratio for event selection and scanning time reduction ECC 2.6cm beam Changeable Sheet (CS) Scin. strips OPERA experiment, A. Chukanov  ~ 7 mm  ~ 20 mrad 7 september 201111

13. OPERA experiment, A. Chukanov Brick scanning - Automatic scanning stations ~ 25 bricks are daily extracted from target and analyzed using high-speed automatic systems S-UTS (Japan) Customized commercial optics and mechanics Scanning speed: 20 cm 2 /h Hard-coded algorithms Scanning speed: 75 cm 2 /h European Scanning System 7 september 201112

14. Vertex location and event analysis in ECC CS tracks Scan- back Volume scan Event reconstruction 5 mm OPERA experiment, A. Chukanov Emulsion gives 3D vector data, with a few microns precision of the vertex accuracy. 7 september 201113

15. 2 11 3 22 7 5 1 6 8 (daughter) 4 (  cand) 1 radiation length 0.033 interaction length primary vertex kink point beam top view side view Event ECC  pink color The viewer of scintillation Target Tracker OPERA experiment, A. Chukanov   СС candidate   СС candidate 7 september 201114

16. OPERA experiment, A. Chukanov 15 Kinematical analysis VARIABLEAVERAGE Selection criteria kink (mrad)41 ± 2>20 decay length (  m) 1335 ± 35 within 2 lead plates P daughter (GeV/c) 12 +6 -3 >2 Pt (MeV/c)470 +230 -120 >300 (  attached) missing Pt (MeV/c) 570 +320 -170 <1000  (deg) 173 ± 2>90 7 september 201115 Prob. of attach. to 1ry vtx* Prob. of attach. to 2ry vtx* 1 st  <10 -3 0.32 2 nd  0.100.82 *probability to find an IP larger than the observed one 1ry vertex 2ry vertex  5.6 ± 1.0 ± 1.7  GeV  1.2 ± 0.4 ± 0.4) GeV  attachment to the vertices The uncertainty on Pt due to the alternative  attachment is < 50 MeV.

17. Features of the decay topology and k inematical cuts red bands: values for the “interesting” event with uncertainties cut OPERA experiment, A. Chukanov7 september 201116 cut Reject NC events with larger missing P t at primary vertex Reject hadron interactions with small P t at secondary vertex

18. OPERA experiment, A. Chukanov Azimuthal angle between the resulting hadron momentum direction and the parent track direction Signal :  =180 o  -decay X (hadron shower) --   kink  N   - X --  x BG: small  --   -  N  - X  17 Blue: MC - NC Black: MC -  rad cut 7 september 201117

19. OPERA experiment, A. Chukanov 18 Event nature and invariant mass reconstruction - 7 prongs at the primary vertex: 4 identified hadrons and 3 with a probability < 0.1% of being a muon - The parent track exhibits a kink topology and the daughter is identified as a hadron through its interaction. Its impact parameter w.r.t. the primary vertex is (55 ± 4) μm where it is smaller than 7 μm for the other tracks -Two γ-rays point to the secondary vertex. The event passes all the selection cuts defined in the experiment proposal - Invariant mass of the two γ-rays: 120 ± 20 (stat.) ± 35(syst.) MeV/c2 (consistent with the  0 mass) - Together with the secondary hadron assumed to be a  − they have an invariant mass of 640 MeV/c2 - The decay mode is compatible with:  → ρ− (770) , the branching ratio of which is ~ 25% 7 september 201118

20. OPERA experiment, A. Chukanov 19 Background sources Prompt  ~ 10 -7 /CC Decay of charmed particles produced in e interactions ~ 10 -6 /CC Double charm production ~ 10 -6 /CC Decay of charmed particles produced in  interactions ~ 10 -5 /CC Hadronic reinteractions  ~ 10 -5 /CC 7 september 201119

21. OPERA experiment, A. Chukanov 20 Background estimation Estimation obtained from MC simulation (brick finding, scanning CS films, track connection from CS to brick, track following, vertex reconstruction) MC was validated with the help of: - OPERA data - pion test beam (interactions of primary hadrons) - CHORUS measurements (charmed meson production) 7 september 201120

22. OPERA experiment, A. Chukanov Charmed particles have similar decay topologies to the  Charm production in CC events represents a background source to all tau decay channels -- ~ 95% of this background can be suppressed by identifying the primary lepton by electronic detector -- ~ 1.5% of this background can be suppressed from track follow-down: - topology of their endpoint; - range-momentum correlation; - energy loss measurement in the last fraction of their range. ,e ,e - +e+h++e+h+ D+D+ primary lepton misidentified Charm background 7 september 201121

23. OPERA experiment, A. Chukanov 22 Simulation of the reinteraction BG Background evaluation by using state-of-the-art FLUKA code, upgrade of the Proposal simulations 160 million events (0.5-15 GeV/c) of  +,  ,K +,K -,p impinging 1 mm of lead, equivalent to 160 km of hadronic track length Kink probabilities evaluated by applying the same cuts as for the tau analysis Typical scattering distributions for : 5 GeV  + 20 mrad 300 MeV/c Pion angular deflection Pt of secondary pion mradGeV/c 22 7 september 201122

24. search for “decay-like” interactions track far away from the primary vertex no background-like interaction has been found in the signal region 10 single-prong interactions have been observed with a p T larger than 200 MeV/c, while 10.8 are expected from simulations. OPERA experiment, A. Chukanov Hadronic reinteractions 7 september 201123 Hadronic tracks in neutrino interactions with kink topology far from the primary Hadronic interactions in test beam brick

25. OPERA experiment, A. Chukanov 24 Decay channel Analysed sample22.5x10¹⁹ p.o.t.Loc. Eff. Exp. Num.BGExp. Num.BG →→ 0.390.02±0.011.790.09±0.040.54 →e→e 0.630.05±0.012.890.22±0.050.59 →h→h 0.490.05±0.012.250.24±0.060.59  → 3h 0.150.04±0.010.710.18±0.040.64 Total1.650.16±0.037.630.73±0.15 Background estimation and expected event numbers 7 september 201124

26. OPERA experiment, A. Chukanov e  СС candidate e  СС candidate 14 e candidate events have been observed. 7 september 201125

27. 26 Summary The Collaboration has completed the study of 92% of the neutrino data taken in the CNGS beam in the 2008-2009 runs One muonless event showing a  → 1 -prong hadron decay topology has been detected and studied in details. It passes all kinematical cuts required to reduce the physics background   The observation so far of a single   candidate event is compatible with the expectation of 1.65 signal events. The significance of the observation of one decay in the  → h channel is 95% This result is an important step towards the first detection of neutrino oscillations in direct appearance mode in the    channel, the  signature being the identification of the  -lepton created in its charged current interaction. OPERA experiment, A. Chukanov7 september 201126