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

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

2 Outline OPERA experiment Event location procedure n t candidate Background estimation Conclusion 2

OPERA: Oscillation Project with Emulsion

appearance of n t in a pure n m beam Search

3 OPERA: Oscillation Project with Emulsion tracking Apparatus CERN 732km LNGS High-energy long baseline n m beam OPERA Direct search for n m n t oscillations by looking at the appearance of n t in a pure n m beam Search for the sub-dominant n m n e oscillations for 13 measurement 3

4 CNGS neutrino beam n m < E > 17 GeV L 730 km ( n e + n e ) / n m 0.87 % * n m / n m 2.1 % * n t prompt Negligible * * Interaction rate at LNGS Expected interactions for 22.5 x p.o.t. (nominal pot in 5 years): ~ n m CC + NC ~ 160 n e +n e CC ~ 114 n t CC ( m 2 = 2.5 x 10-3 ev 2 ) ~ 8 t decays are expected to be observed (BG<1) 4

5 The OPERA Collaboration 160 physicists, 30 institutions, 11 countries Belgium ULB Brussels Croatia IRB Zagreb France LAPP Annecy IPNL Lyon IPHC Strasbourg Germany Hamburg Israel Technion Haifa Italy Bari Bologna LNF Frascati L Aquila, LNGS Naples Padova Rome Salerno Japan Aichi Toho Kobe Nagoya Utsunomiya Korea Jinju Russia INR RAS Moscow LPI RAS Moscow ITEP Moscow SINP MSU Moscow JINR Dubna Switzerland Bern ETH Zurich Turkey METU Ankara 5

6 Direct observation of t decay topologies in nt cc events Decay kink n t t Requires high resolution detector (δx~1 μm, δθ~1 mrad) µ Needs large target mass n µ 6

7 Direct observation of t decay topologies in nt cc events Decay kink ECC brick n t 1 mm t Pb emulsion layers Requires high resolution detector (δx~1 μm, δθ~1 mrad) Needs large target mass - use nuclear emulsions - alternate emulsion films with lead layer 7

8 Direct observation of t decay topologies in nt cc events Decay kink n t 1 mm t ECC brick electronic trackers Pb emulsion layers Requires high resolution detector (δx~1 μm, δθ~1 mrad) Needs large target mass Prediction the region of the target where each event occurred Interface films (CS) - use nuclear emulsions - alternate emulsion films with lead layer - Electronic trackers 8

Emulsion Cloud Chamber (ECC) brick sandwich of 56 lead plates 1 mm + 57 emulsion films

3 Changeable Sheets (CS): tightly packed removable doublets of emulsion films glued to

5cm ECC = stand-alone detector: momentum measurements for hadrons (multiple Coulomb (

9 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 ( kg (weight 8.3 Changeable Sheets (CS): tightly packed removable doublets of emulsion films glued to the downstream face of each brick 75.4 mm 125mm 8.3kg 10X 0 n beam 102mm 10.2cm 12.5cm ECC = stand-alone detector: momentum measurements for hadrons (multiple Coulomb ( scattering ( de/dx ) Pion/Muon separation at low energy electron identification and energy measurements for e,γ 9

The Detector Veto plane: RPC Total mass of the target: 1250 tons Electronics B O R E X I N O nm m-veto Muon Spectrometer Target Target BMS Muon Spectrometer Target and Target Tracker (6.

10 The Detector Veto plane: RPC Total mass of the target: 1250 tons Electronics B O R E X I N O nm m-veto Muon Spectrometer Target Target BMS Muon Spectrometer Target and Target Tracker (6.7m) 2 Target : bricks, 28 walls High precision tracker Instrumented dipole magnet Target tracker : 31 XY doublets of 256 scintillator strips for Brick selection Muon tracks reconstruction 6 4-fold layers of 1.53 T drift tubes 22 XY planes of RPC in both arms Muon spectrometer (8 10 m 2 ) 10

11 OPERA Detector 11

12 Brick finding task Event trigger and reconstruction Brick identification Selection of a brick most probably containing the neutrino interaction Reduce scanning load Minimize the target mass loss 12

13 CS - Interface emulsion films: high signal/noise ratio for event selection and scanning time reduction Scin. strips s ~ 7 mm n beam ECC 2.6cm Changeable Sheet (CS) s ~ 20 mrad 13

Brick scanning - Automatic scanning stations ~ 25

commercial optics and mechanics Scanning speed:

14 Brick scanning - Automatic scanning stations ~ 25 bricks are daily extracted from target and analyzed using high-speed automatic systems European Scanning System S-UTS (Japan) Customized commercial optics and mechanics Scanning speed: 20 cm 2 /h Hard-coded algorithms Scanning speed: 75 cm 2 /h 14

15 Vertex location and event analysis in ECC CS tracks 5 mm Emulsion gives 3D vector data, with a few microns precision of the vertex accuracy. 15

16 Vertex location and event analysis in ECC Scanback CS tracks 5 mm Emulsion gives 3D vector data, with a few microns precision of the vertex accuracy. 16

17 Vertex location and event analysis in ECC Volume scan Scanback CS tracks 5 mm Emulsion gives 3D vector data, with a few microns precision of the vertex accuracy. 17

18 Vertex location and event analysis in ECC Volume scan Event reconstruction Scanback CS tracks 5 mm Emulsion gives 3D vector data, with a few microns precision of the vertex accuracy. 18

19 n t СС candidate top view side view n kink point 3 g1 g2 primary vertex 2 8 (daughter) 6 4 (t cand) 1 radiation length interaction length The viewer of scintillation Target Tracker n beam Event ECC pink color 19

20 Kinematical analysis VARIABLE AVERAGE Selection criteria kink (mrad) 41 ± 2 >20 decay length (mm) P daughter (GeV/c) 1335 ± 35 Pt (MeV/c) within 2 lead plates >2 >300 (g attached) g attachment to the vertices Prob. of attach. to 1ry vtx* Prob. of attach. to 2ry vtx* 1 st g < nd g *probability to find an IP larger than the observed one missing Pt (MeV/c) <1000 g2 (1.2 ± 0.4 ± 0.4) GeV (deg) 173 ± 2 >90 The uncertainty on Pt due to the alternative g2 attachment is < 50 MeV. 1ry vertex 2ry vertex g1 (5.6 ± 1.0 ± 1.7)GeV 20 20

21 cut Features of the decay topology and kinematical cuts red bands: values for the interesting event with uncertainties Reject hadron interactions with small P t at secondary vertex cut cut Reject NC events with larger missing P t at primary vertex cut 21

22 Azimuthal angle between the resulting hadron momentum direction and the parent track direction Signal : f =180 o t-decay X (hadron shower) t - f n t p - BG: small f kink x n m f p - p - n t N t - X n m N n m p - X Blue: MC - NC Black: MC - t cut 22 rad 22

23 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 - Invariantmassofthetwoγ-rays: 120 ± 20 (stat.) ± 35(syst.) MeV/c2 (consistent with the p0 mass) - Together with the secondary hadron assumed to be a p they have an invariant mass of 640 MeV/c2 - The decay mode is compatible with:, nt( 770 ) ρ t the branching ratio of which is ~ 25% 23 23

24 Background sources Prompt n t ~ 10-7 /CC Decay of charmed particles produced in n e interactions ~ 10-6 /CC Double charm production ~ 10-6 /CC Decay of charmed particles produced in n m interactions ~ 10-5 /CC Hadronic reinteractions ~ 10-5 /CC 24 24

25 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) 25 25

26 Charm background Charmed particles have similar decay topologies to the t n m,e m,e - m + D + e + h + primary lepton misidentified 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. 26

Simulation of the reinteraction BG Background evaluation by using state-of-the-art FLUKA code, upgrade of the Proposal simulations 160 million events (0.

27 Simulation of the reinteraction BG Background evaluation by using state-of-the-art FLUKA code, upgrade of the Proposal simulations 160 million events ( GeV/c) of p +,p -,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 p + Pion angular deflection Pt of secondary pion 20 mrad 300 MeV/c mrad GeV/c

Hadronic reinteractions Hadronic tracks in neutrino interactions with kink topology far from the primary Hadronic interactions in test beam brick search for decay-like interactions track far away

28 Hadronic reinteractions Hadronic tracks in neutrino interactions with kink topology far from the primary Hadronic interactions in test beam brick 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 pt larger than 200 MeV/c, while 10.8 are expected from simulations. 28

29 Background estimation and expected event numbers Decay channel Analysed sample 22.5x10¹⁹ p.o.t. Loc. Eff. Exp. Num. BG Exp. Num. BG t m ± ± t e ± ± t h ± ± t 3h ± ± Total ± ±

30 n e СС candidate 14 n e candidate events have been observed. 30

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 t 1-prong hadron decay topology has been

31 Summary The Collaboration has completed the study of 92% of the neutrino data taken in the CNGS beam in the runs One muonless event showing a t 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 n t candidate event is compatible with the expectation of 1.65 signal events. The significance of the observation of one decay in the t h channel is 95% This result is an important step towards the first detection of neutrino oscillations in direct appearance mode in the n m n t channel, the n t signature being the identification of the t -lepton created in its charged current interaction

The OPERA Experiment

The OPERA Experiment Observation of a First ν τ Candidate Event in ν µ ν τ Appearance Search Group Report Annika Hollnagel University of Hamburg Institute for Experimental Physics DPG Frühjahrstagung 2011,