First results on appearance mode neutrino oscillations from OPERA

1. Belgium IIHE-ULB Brussels Russia INR RAS Moscow LPI RAS Moscow ITEP Moscow SINP MSU Moscow JINR Dubna Italy Bari Bologna LNF Frascati L’Aquila, LNGS Naples Padova Rome Salerno Croatia IRB Zagreb Switzerland Bern ETH Zurich France LAPP Annecy IPHC Strasbourg IPNL Lyon Tunisia CNSTN Tunis Japan Aichi Toho Kobe Nagoya Utsunomiya Turkey METU Ankara Germany Hamburg Münster Israel Technion Haifa Korea Jinju Lake Louise Winter Institute 2011 20-26 February 2011 – Lake Louise First results on appearance mode neutrino oscillations from OPERA A. Pastore Bari University and INFN, Italy on behalf of the OPERA Collaboration 180 physicists, 32 institutions in 12 countries

2. Outline • OPERA physics motivation • The CERN Neutrinos to Gran Sasso project • nt hunting • OPERA at work • Conclusions and outlook A. Pastore, LLWI 2011

3. Neutrino oscillations: fundamental achievement (I) 3 eigenstates of mass, flavor: Unitary matrix UPMNS: 3 Euler rotation angles + 1 CP phase Measured by solar n experiments & by KamLAND Measured by atmospheric and accelerator n experiments Mainly constrained by reactor experiments (CHOOZ, PaloVerde) A. Pastore, LLWI 2011

4. Neutrino oscillations: fundamental achievement (II) CERN OPERA  appearance in a beam 730 km 730 km LNGS • Super-K (1998): atmospheric neutrino • anomaly interpretable in terms of • oscillations • CHOOZ:   e oscillation excluded as • dominant process responsible for • atmospheric neutrino disappearance • Super-K signal confirmed by K2K and • MINOS (   oscillation) Direct observation of nappearance from n oscillation at atmospheric scale still missing A. Pastore, LLWI 2011

5. P+C  (interactions)  p+, K+ (decay in flight)  m+ + nm ~ 1 km, 2.5 m vacuum K+, π+ 20–50 GeV 400 GeV/c diameter: 80cm & 115 cm current: 150kA & 180 kA The CERN Neutrinos to Gran Sasso beam conventional neutrino beam with a high intensity and high energy proton beam, intense short beam pulses and small beam spots (< 1 mm) • - 400 GeV/cprotons from the CERN SPS on a graphite target • 6 s cycle length, 2 extr. every 50 ms, 10.5 ms pulse length • beam intensity2.4 1013 pot/extr • average power at the target 510 kW • - neutrinos from pions and kaons decaying in flight A. Pastore, LLWI 2011

6. The CERN Neutrinos to Gran Sasso beam LNGS CERN L = 732 km Pr( ) & CC(E) convolution maximized  high E beam (“appearance”- optimized) CC CC Shared SPS operation, 200 days/year

7. nm  ntt -+ X t m- nt nm(17 %) h- ntn(po)(50 %) e- nt ne(18 %) p+ p-p- ntn(p0)(14 %) “kink” topologies nt ~ 0.6 mm @ 4.5·1019 p.o.t./year, 200 days/yearfor OPERA (~1.25 Kton) detector: ~ 4700 CC+NC / year ~ 30 e + eCC / year ~ 25 tCC / year (m2 = 2.5 x 10-3 eV2) expected neutrino interactions _ The Oscillation Project with Emulsion tRacking Apparatus experimental signature detector requirements: large mass, high resolution (for signal selection and background rejection) @22.5 1019 pot

8. 8.3 Kg (10.2*12.5)cm2 t n 1 mm Pb Emulsion layers OPERA: the hybrid solution OPERA: nuclear emulsions + electronic detectors ECC brick:57 emulsion films sandwiched between 1mm Pb plates 1 emulsion film: 2 emulsion layers (44m thick) poured on a 200 m plastic base CS 1 Changeable Sheet doublet (CS)/brick: two refreshed emulsion films,vacuum packed and glued onto the downstream brick face ~ 150000bricks in the OPERA target (~ 1.25 kton) physics in an ECC brick: • ninteractions and decay topology reconstruction • measurement momenta by MCS • e/p separation • electromagnetic calorimetry • when electronic detectors enter the game: • trigger for a neutrino interaction • muon identification and momentum/charge measurement A. Pastore, LLWI 2011

9. The OPERA detector@LNGS OPERA low radioactivity rock Laboratori Nazionali del Gran Sasso (Italy) • 1400 m rock overburden • cosmic µ reduction ~ 106 (1 /m2/h) Surface INFN laboratory 980 m the underground lab is at about the same altitude

10. The OPERA detector@LNGS SM1 SM2 Veto(RPC) Target + Target Tracker (6.7m)2 ● target/SM: ~75000 bricks (Pb – nuclearemulsions) Mass/SM 0.625 kt ● Target tracker : 31 doublets XY (256 plastic scintillator strip + WLS fibres+ multi-anodes PMT) for trigger, brick selection and calorimetry High precision trackerDipole magnet ● 6 4-fold layers of ● 1.53 T drift tubes ● 22 XY planes of RPC muon spectrometer (8×10 m2) [~3100 m.w.e. overburden, ~1 cosmic μ / m2 x hour] [Ref. JINST 4 (2009) P04018]

11. Event analysis in OPERA • on-line analysis of electronic data • brick finding algorithm for events ‘on time’ • with the beam • remove brick and scan CS: the interface • between brick and TT (spos≈ 10 mm, sq ≈ 20 mrad) • confirmation of the extracted brick • development of the brick to be sent in a • scanning Lab for ‘CS to brick connection’ • (spos ≈ 70 mm, sq ≈ 8 mrad), event location, • decay search studies, etc .. [2009 JINST 4 P04018]

12. Piezo-controlled objective lens High speed CCD Camera (3 kHz)‏ • Synchronization of objective lens and (constant speed) stage • Hard-coded algorithms, custom electronics • Customized commercial optics and mechanics • asynchronous DAQ software modular, de- centralized, approach OPERA films data taking: automatic microscopes ~ 20 bricks daily extracted from the target analyzed using high-speed automated systems (≥ 20 cm2/h) European Scanning System S-UTS (Japan) Common Data Base for data sharing/publication A. Pastore, LLWI 2011 ~90% tracking efficiency spatial resolution < 1 m and angular resolution < 2 mrad

13. Electronic detectors performances density x length of the muon track Hadronic energy deposited in TT Momentum X charge for muons Total reconstructed energy in events with at least one identified muon Tranverse profile of hadronic showers Energy resolution A. Pastore, LLWI 2011

14. 9 8 7 6 5 4 3 2 1 mm IP distribution for: ntevents (MC) NC+CC nm events (MC), NC+CC nm events (Data) Prec (GeV) IP distribution for nt events (MC) 1 2 3 4 5 6 7 8 Pbeam (GeV) expanded scale s = (22±4)% p test beam Measurements performed on several selected OPERA soft muon events ECC analysis performances (I) Ip measurement: particles momenta measurements by MCS

15. detection and p0 mass reconstruction ECC analysis performances (II) 2 em showers give a reconstructed mass 160±30 MeV/c2 e+ e-  e-pair  EM shower energy measured by shower shape analysis and Multiple Coulomb Scattering method 70% of 1-prong hadronicdecays include one or more0 importance of gamma detection Gamma detection: how to… detection of shower detection e-pair at start point E = 8.1 GeV 1 s mass resolution: ~ 45% E = 0.5 GeV A. Pastore, LLWI 2011

16. CNGS physics runs pot 2010 * nominal value: 4.5 1019 pot In total 9639 events collected (within 1sw.r.t. expectation from pot)  2.1 nominal years in 3 years 2009 2008 A. Pastore, LLWI 2011 days

17. OPERA data analysis status 2889 neutrino interactions located, 95% of the 2008-09 expected yield. Number of events for which the analysis is released: 1088 (187 NC) (1.85 × 1019 pot corresponding to 20% of the total statistics) With the above statistics, and for Dm223 = 2.5 x10-3 eV2 and full mixing, OPERA expects: ~ 0.5ntevents A. Pastore, LLWI 2011

18. 4 mm charm decays inside the OPERA target x-view 1ry m Decay search procedure defined (ip evaluation, small angle kink search, extra-tracks search) Decay Search extensively applied to located interactions data sample 1ry vertex kink Charm topology analogous to  : reference sample for the decay finding efficiency D0 hypothesis: F.L.: 313.1 mm, f: 173.20, invariant mass: 1.7 GeV daughterm 1.3 mm D0 hypothesis charm candidate (dimuon) 20 charm candidate 3 of them with 1-prong kink topology. Expected: 16.0 ± 2.9 out of which 0.80 ± 0.22 with kink topology Expected BG: ~ 2 events (loose cuts: work in progress to reduce BG) flight length: 1330 microns kink angle: 209 mrad IP of daughter: 262 microns daughter muon: 2.2 GeV/c decay Pt: 0.46 GeV/c A. Pastore, LLWI 2011

19. the first nt candidate event (I) • The primary neutrino interaction consists of 7 tracks of which one exhibits a visible kink • Two electromagnetic showers caused by g-rays, associated with the event, have been located (total radiation length downstream the vertices: 6.5 X0) • none of the tracks is compatible with being an electron track • for tracks 1, 5 and 6 P(m) < 10-3 (p-range consistency check) • remaining tracks are hadrons (interaction seen) • residual probability of nmCC event (possibly undetected large angle • muon) is ≈ 1%. “Nominal” value of 5% assumed A. Pastore, LLWI 2011 * probability to find an IP larger than the observed one

20. With the available statistics** (Dm232 = 2.5 x10-3 eV2 , full mixing) OPERA expected ~ 0.5 nt events ** at the time of observation the first nt candidate event (II) • Kinematical variables are satisfying all • selection criteria for hadronic kink  first ntcandidate ! • defined in the proposal • candidate to the t 1-prong hadron decay mode • invariant mass of g-rays 1 and 2: • 120 ± 20 (stat)± 35(syst) MeV/c2 • supporting the hypothesis p0 g g • assuming the charged decay product as p-, the invariant • mass of p- and 2 gammas: • 640+125-80 +100-90MeV/c2 • compatible with the r(770) mass *assuming both g1 and g2 attached to 2ry vertex (uncertainty on Pt due to the alternative g2 attachment is < 50 MeV/c ) 2ry vtx compatible with: t h (np0) nt A. Pastore, LLWI 2011

21. for the 1-prong hadronic channel 0.007±0.004 (syst) background events are expected for the analyzed statistics • - Background evaluation by using state-of-the-art FLUKA code (upgrade wrt Proposal) • Kink probabilities integrated over the nμ NC hadronic spectrum yield (same cuts as for • the tau analysis) a BG probability of (3.8 ± 0.2) x 10-5kinks/NC (2 mm Pb, cuts • on event global kinematics applied) • - First cross-checks of the simulation were performed on a scan-forth tracks sample and on dedicated test-beam data, showing a good agreement with the simulation, although still statistically limited the first nt candidate event (III) Evaluation of background sources: • promptnt ~ 10-7/CC • decay of charmed particles produced inneinteractions ~ 10-6/CC • double charm production~ 10-6/CC • decay of charmed particles produced innminteractions ~ 10-5/CC • hadronic reinteractions (UPDATE wrt Proposal) ~ 10-5/CC A. Pastore, LLWI 2011

22. the first nt candidate event (IV) Background expectations 1-prong hadron t decay channel: (~ 50% syst. error for each component) 0.011 events (reinteractions) 0.007 events (charm, assuming standard mu ID) --------------------------------- 0.018 ± 0.007 (syst.) events 1-prong hadron BCK for all decay modes: 1-prong hadron, 3-prongs + 1-prong μ + 1-prong e : 0.045 ± 0.020 (syst.) events total BG Background fluctuation probabilities to 1 event: 1-prong hadron channel only: P=1.8%  2.36ssignificance All tau decay modes included in search: P=4.5%  2.01ssignificance A. Pastore, LLWI 2011

23. neCC interactions 10 electron neutrino interactions have been reconstructed in the OPERA target A. Pastore, LLWI 2011

24. Conclusions and outlook • -The OPERA experiment is approaching its fourth physics run. • the analysis of a sub-sample of the neutrino data taken in the CERN CNGS • beam in the 2008-2009 runs lead to the reconstruction of a number of • interesting topologies such as charm decays candidates and neCC • interactions in agreement with the expectations. • - one muonless event showing a t 1-prong hadron decay topology has been • detected and studied in detail. It passes all kinematical cuts required to • reduce the physics background. • It is the first ntcandidate event in OPERA, with statistical significance of • 2.36 s (1prong hadronic decay mode) and 2.01 s (all decay modes). • analysis on 2008+2009 full sample data will be finished in less than two • months, according with the present scanning speed. • - analysis of 2010 events is being performed in parallel. • thank you for your attention! A. Pastore, LLWI 2011

25. backup A. Pastore, LLWI 2011

26. Expected neutrino flux @ LNGS CC event rate@ 4.5 1019pot 600  CC/kt/ 1019pot 5.5 e CC/kt/ 1019pot A. Pastore, LLWI 2011

27. 4- evidence 3- evidence OPERA Discovery probability (%)‏ m2 (eV2)‏ OPERA sensitivity MINOS 2008 5 years, nominal 4.5 1019 pot A. Pastore, LLWI 2011

28. Event tracks’ features A. Pastore, LLWI 2011 muonless event (favored hypothesis)

29. OPERA Kinematical analysis OPERA nominal analysis flow applied to the hadronic kink candidates: (more refined selection criteria being developed were not considered here to not bias our analysis) 10 years old criteria (@Proposal)  Blind analysis • kink occurring within 2 lead plates downstream of the primary vertex • kink angle larger than 20 mrad • daughter momentum higher than 2 GeV/c • decay Pt higher than 600 MeV/c, 300 MeV/c if ≥ 1 gamma pointing to the decay vertex • missing Pt at primary vertex lower than 1 GeV/c • azimuthal angle between the resulting hadron momentum direction and the parent track direction larger than π/2 rad A. Pastore, LLWI 2011

30. Features of the decay topology… 41 ± 2 mrad Kink angle Accepted kinks > 20 mrad Blue: MC NC Black: MC - t 1335 ± 35 mm red bands: values for the “interesting” event with uncertainties Decay length Missing Pt at primary vertex Missing Pt at primary vertex ..and kinematical cuts to be passed cut cut 570 +320-170MeV GeV/c 12 +6-3 GeV Reject NC events with larger missing Pt (neutrino) Pt at decay vertex Daughter momentum Reject hadron interactions 470 +230-120MeV cut cut A. Pastore, LLWI 2011 rad GeV/c mm GeV/c 32

31. OPERA: charm background primary lepton not identified ,e- ,e + e+ h+ D+ Charmed particles have decay topologies similar to the  ones • charm production in CC events represents a background source to alltdecay channels • this background can be suppressed by identifying the primary lepton  ~ 95% muon ID • for the 1-prong hadronic channel 0.007±0.004 (syst) background events are expected for the analyzed statistics • further charm BG reduction is under evaluation by implementing the systematic follow-down of low energy tracks in the bricks and the inspection of their end-range, as done for the “interesting” event. For the latter we have 98-99% muon ID efficiency. A. Pastore, LLWI 2011

32. Simulation of the reinteraction BG with FLUKA… multi-prong 1-prong …cross check I (scan-forth data) …cross check II (4GeVp test-beam data) signal region 8 times track length of tau search • no events in the signal region • 90% CL upper limit of 1.54 x 10-3 kinks/NC event • nr of events outside the signal region confirmed by MC (within the ~30% statistical accuracy of the measurement) A. Pastore, LLWI 2011 18 times track length of tau search