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OPERA and its Tau Neutrino Candidate

OPERA and its Tau Neutrino Candidate. Caren Hagner, Universität Hamburg. Neutrino mass, mixing and neutrino oscillations OPERA experiment Detector performance Special events: charm, v e v T candidate Outlook. Neutrino Mass and Mixing. θ sol. θ 13 , δ. θ atm. θ 23 ≈ 45 o.

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OPERA and its Tau Neutrino Candidate

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  1. OPERA and its Tau Neutrino Candidate Caren Hagner, Universität Hamburg • Neutrino mass, mixing and neutrino oscillations • OPERA experiment • Detector performance • Special events: charm, ve • vT candidate • Outlook

  2. Neutrino Mass and Mixing θsol θ13, δ θatm θ23 ≈ 45o θ13<13o, δ ? θ12 ≈ 33o Δm2solar = m22 - m12 ≈ 8·10-5eV2, |Δm2atm | = |m32 - m22| ≈ 2·10-3eV2

  3. Neutrino Oscillations (simplified) with θ23 ≈ 45o propagation determined bymass-eigenstates source createsflavor-eigenstates detector seesflavor-eigenstates v2 τ vτ v3 vμ W W μ p,n hadrons slightly different frequencies→ phase difference changes Flavor eigenstates vμ, vτ Mass eigenstates v2,v3

  4. MINOS Results: Fit to Oscillation Hypothesis (best fit) (for 7.2·1020pot)

  5. OPERA:Oscillation Project with Emulsion tRacking Apparatus Neutrino beam (vμ) from CERN to Gran Sasso Underground Lab (Italy) Goal: Observation of vτ Appearance LNGS 732 km Physics runs: 2008 and 2009 completed, 2010 ongoing

  6. CNGS beam (“pure” vμ) comparison of CC-event rates: Prompt vτ negligible ( ≈ 10-7) 400GeV p on graphite target Total exposure expected: 22.5·1019 pot 4.5·1019pot/year

  7. Profile of neutrino beam @ LNGS CNGS beam at 732km(FLUKA 2005)

  8. OPERA: vτ detection τ- vτ W kink p,n hadrons 1 mm t- μ- nτ Hadrons Lead Emulsions τ-decay: trident Typical topology of τ-decay:“Kink” within 1mm from vertex

  9. Background Processes Background nmCC + charm prod. charm muon misidentified m Most important background processes: • Charm production and decay • Hadron re-interactions in lead • Large angle myon scattering in lead Signal m, e, hadron ntCC t

  10. Expected Signal Assume: Maximal mixing, 22.5x1019pot (=5years @ 4.5x1019pot/year) Expected events: ~ 23600 vμ CC+NC interactions ~ 160 ve interactions~ 115 vτ CC interactions~ 10 identified vτ< 1 background

  11. OPERA target: lead-emulsion-bricks 57 emulsion / 56 lead 10X0 100mm 8kg lead-emulsion-brick (total ≈ 150.000) target mass:≈ 1,35 kton 105000 m2 of lead surface111000 m2 of film surface(9 million films) „Emulsion Cloud Chamber“ (ECC)

  12. Hybrid Target Structure CS doublet alignment by Compton electrons: 2.5 microns

  13. OPERA - Detector Supermodule 1 Supermodule 2

  14. OPERA - Detector TargetSM1 Target SM2 Target Region:- Target Tracker (Scintillator) - Lead/Emulsion Bricks (75.000 per Supermodule)

  15. OPERA - Detector Target μ v X B B Magnetic Spectrometer: Magnet-Region:Iron & RPCs Precision Tracker:6 Planes of Drifttubes

  16. The Electronic Detectors Target Trackers(Plastic Scintillator) 1.52 T

  17. Magnetic Spectrometer muon momentum Data (black hist.) vs MC 10000 drift tubes (length 8m) – built at DESY spatial resolution ≈ 250 mm RPCs cm 17

  18. Reconstruction (I): Magnetic Spectrometer

  19. Rekonstruktion (II): Brick Finding

  20. Brick Validation with Changeable Sheet Develop this brick Scanning effort/event: CHORUS 1x1 mm2 DONUT   5x5 mm2 OPERA 100x100 mm2 So far, 640.000 cm2 of CS surface have been scanned in OPERA

  21. Handling the ECC bricks • Inserting and extracting the bricks by Brick Manipulation System (BMS) • Aligning the films (X-ray and cosmics) • Developing the films • Scanning

  22. OPERA – Brick Manipulation System • automatic extraction of 25 bricks / 8 hour shift • ~90’000 bricks handled until 2009 for the extraction of ~7000 event bricks

  23. Brick Analysis To Dubna Bern Padova Bologna To Japan LNGS Roma To Ankara LNF Bari Napoli Salerno The selected bricks are sent to scanning labs(at present 12)

  24. Performance of Emulsion Film Detector sensitivity15 grains/44 microns mip electron ～100 keV 20 μm Emulsion Layer (44 microns) basic detector: AgBr crystal, size = 0.2 micron detection eff.= 0.16/crystal 1013“detectors” per film Plastic Base (205 microns) Emulsion Layer intrinsic resolution: 50 nm deviation from linear-fit line. (2D) 24 A. Ereditato - CERN - 4 June 2010

  25. Scanning of Emulsions European Scanning System (ESS) Japanese Scanning System (S-UTS) 4 systems + sub systems 33 systems in Europe Total scanning power : 325 cm2/h Total scanning power : 660 cm2/h

  26. Scanning 2d image: 16 tomographic images Field of view: 44 mm emulsion sheet 300mm Vertex reconstruction & kinematical analysis

  27. CNGS beam performance & statistics pot 8·1019 2010 8558 evts (scan input) collected until 20/9/2010 2009 2008 Days 27

  28. Example of a CC event: ‚kink‘-topology

  29. Example of a NC event: ‚kink‘-topology The measured ratio NC/CC is ≈20%, as expected from simulations

  30. Event statistics (June 2010) This analysis corresponds to ~35% of the 2008-2009 run statistics, = 1.89 x 1019 pot 1813 events found in the target (scan input) Events with neutrino vertices located by scanning: 1617 (Brick tagging efficiency) x (vertex location efficiency) ≈ 60% Events for which “decay search” was completed: 1088 (187NC, 901CC) With the above statistics, and for Dm223 = 2.5 x10-3 eV2 and full mixing, OPERA expects: ~ 0.5 vt events 30 A. Ereditato - CERN - 4 June 2010

  31. Impact Parameter Measurement IP distribution for: ntevents (MC) NC+CC nm events (MC), NC+CC nm events (Data) IP distribution for ntevents (MC) expanded scale Mean IP = 104.3 µm Impact Parameter (µm) Impact Parameter (µm)

  32. Momentum Measurementwith ECC and Electronic Detector Momentum measured in ECC (by multiple Coulomb scattering) Prec (GeV) ECC p test beam error bar: 68% CL Pbeam(GeV) Dp/p s = (22±4)% Electronic Detector

  33. γ – Detection and Reconstruction of π0 mass EM shower energy measured by shower shape analysis and Multiple Scattering method E = 8.1 GeV E = 0.5 GeV 2 EM showers give a reconstructed mass ~ 160 MeV reconstructed mass from 2 EM showers ~ 160 MeV

  34. p0 mass resolution (real data) 35 gamma pairs 1 s mass resolution: ~ 66 MeV

  35. -  + e+ h+ D+ Charm candidate event (dimuon) x-view 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 1ry muon 1ry vertex kink daughter muon Background, if primary muonnot identified

  36. Charm candidate event (4-prong) D0 hypothesis: F.L.= 313.1μm, φ = 173.20, invariant mass = 1.7 GeV 36 A. Ereditato - CERN - 4 June 2010

  37. Main Kinematic Cuts for Charm Events • P(daughter) >2.5 GeV/c, Pt(kink) > 0.5 GeV/c (for kink events) • looser cuts for multi-prong events. • 20 charm candidate events selected by the kinematic cuts, • 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 Examples of distributions: 37 A. Ereditato - CERN - 4 June 2010

  38. ne candidate event From a subsample of ~ 800 located events we detected 6 necandidates Additional physics subject: study nm-ne oscillations

  39. The vT candidate event Muonless event 9234119599, taken on 22 August 2009, 19:27 (UTC) (as seen by the electronic detectors) 39 A. Ereditato - CERN - 4 June 2010

  40. vT candidate: from CS to vertex location a kink is detected Large area scanning Full reconstruction of vertices and gammas Scan-back in ECC CS predictions CS predictions µm

  41. reconstructed vT candidate event

  42. PL17 PL18 PL19 PL20 PL21 5 7 1 3 2 (further out) 1 Primary vertex kink point (secondary vertex) Tau (4) Daughter (8) Proton (2) 6 1mm lead

  43. Decay length Red regions:measured values for vT candidate red bands: values for the “interesting” event with uncertainties Daughter momentum Kink angle reject < 20 mrad cut rad GeV/c mm A. Ereditato - LNGS - 31 May 2010

  44. Interpretation of the event • Invariant mass of g gsystemcompatible with p0mass value. • Invariant mass of the p g gsystem compatible with r (770) • r appears in about 25% of the t decays: • t → r (p p0) nt OPERA collaboration:„Observation of a first ντ candidate event in the OPERA experiment…”,Phys. Lett. B 691 (2010) 138.

  45. Significance of vT Observation • We observe 1 event in the 1-prong hadron t decay channel • background expectation for 1 prong hadron decay : 0.011 events (reinteractions) • + 0.007 events (charm) • = 0.018 ± 0.007 (syst) events 1-prong hadron • probability that the observed event is due to background: 1.8 % • significance of vT observation in OPERA: 2.36 σ • background from all decay modes: • 0.045 ± 0.020 (syst) events total BG • probability that the observed event is due to background: 4.5 % • significance of vT observation in OPERA: 2.01 σ

  46. Oscillation Analysis for Dm223 = 2.5 x 10-3 eV2 and full mixing, we expect: 0.54 ± 0.13 (syst) nt CC events in all t decay channels and 0.16 ± 0.04 (syst) nt CC events in the 1-prong hadron t decay channel and we have observed 1 event. We can exclude at 90% CL, that |Dm223 | > 7.5 x 10-3 eV2 (for full mixing)

  47. Outlook • 2010: Getting close to nominal 4.5x1019pot • 2011: Negotiations with Cern ongoing, aim at partial compensation for 2012 break • 2012 (?): LHC stop → no SPS, no pots • We need enough pots (22.5x1019) to obtain a significant (4σ) result with high probability • All events of 2008 and 2009 scanned by end 2010. • Waiting for more vT candidates…

  48. OPERA Collaboration 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 IPNL Lyon IPHC Strasbourg Tunisia CNSTN Tunis Japan Aichi Toho Kobe Nagoya Utsunomiya Turkey METU Ankara Germany Hamburg Münster Rostock Israel Technion Haifa Korea Jinju

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