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Yu . G . Kudenko Institute for Nuclear Research, Moscow

Neutrino oscillation results from the T2K experiment. Yu . G . Kudenko Institute for Nuclear Research, Moscow. PNPI , Gatchina, 25 May 2012. OVERVIEW. Neutrino oscillations T2K features - Off-axis neutrino beam - Near and Far neutrino detectors

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Yu . G . Kudenko Institute for Nuclear Research, Moscow

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  1. Neutrino oscillation results from the T2K experiment Yu. G. Kudenko Institute for Nuclear Research, Moscow PNPI, Gatchina,25May 2012

  2. OVERVIEW • Neutrino oscillations • T2K features • - Off-axis neutrino beam • - Near and Far neutrino detectors • - Analysis principles • Experimental data • Oscillation results • - Disappearance • - e Appearance • Future prospects

  3. Стандартная Модель Три типа (аромата) нейтрино:e Нейтрино – партнеры заряженного лептона W eeWW  Нейтрино - безмассовые частицы Сохраняются лептонные числа LeLL Невозможны переходы (осцилляции) одного типа нейтрино в другой CP в лептонном секторе сохраняется Эксперименты на LEP (ЦЕРН): из ширины распада Z бозона следует, что существуют только три типа легких активных нейтрино N = 2.984 ± 0.008

  4. Гипотеза нейтринных осцилляций Б.М. Понтекорво: идея массивных нейтрино и осцилляций – 1957 г. • один тип нейтрино переходит в другой • необходима ненулевая масса исмешивание • вероятность осцилляции зависит от массы нейтрино, • энергии нейтрино E и расстояния L  e  L источник детектор Собственные состояния слабого взаимодействия массовые состояния Собственные (активные) состояния не совпадают с массовыми состояниями

  5. Oscillation industry Homestake, USA Sage, Russia Borexino, Italy Gallex SNO SK Solar ’s 1970  …. MACRO, Italy Soudan2, USA Atmospheric ’s SK, Japan KamLand, Japan CHOOZ, France Reactor ’s K2К,Japan Minos, USA OPERA, Italy LSND, MiniBooNe, США Accelerator ’s ….  2011

  6.  oscillations and mixing Standard Model: neutrinos are masslessparticles 3 families solar atmospheric link between atmospheric and solar U parameterization: three mixing angles12 2313 CP violating phase 12~340 23~450 two independent m2 sin2213 <150 at 90% CL ?? 13 , mass hierarchy ,  ??

  7. Issues in neutrino physics (by Summer 2011) • Absolute mass scale • Neutrino mixing 13 • Mass hierarchy m223 > 0 or m223 < 0 • CP violation CP • Dirac or Majorana • Sterile neutrinos T2K

  8. Oscillation experiments: Appearance and Disappearance L – distance from  source to detector E – neutrino energy T2K measures both: - Appearance (e) - Disappearance ()

  9. Long-Baseline Neutrino Oscillation Experiment SuperK         Tokai Токио JAPAN

  10. Т2К milestones Proposal approval2003 Construction2004-2009 Start data taking2010 Earthquake 11 March 2011 First physics result June 2011 JPARC recovery December 2011 Restart data taking January 2012 Physics Run March 2012 – June 2012

  11. Principles of measurement • Intensive neutrino source • Near detector  measurement of unoscillated neutrino spectrum • Far Detector  measurement of oscillated neutrino spectrum • Extrapolate flux from Near Detector to Far Detector (Far/Near ratio) • Estimate νμ rate (without oscillation) at Far Detector • Compare to measured νe (νμ) rate (spectrum) to observe • oscillation and extract oscillation parameters • Reduction systematic errors using data from K2K, NA61, SciBooNe, MiniBooNe Disappearance Appearance P(νμ→νμ) ≈ 1−sin22θ23sin2(Δm223L/4Eν) P(νμ→νe) ≈ sin22θ13sin2θ23 sin2(Δm213L/4Eν)

  12. Experiment T2K

  13. JPARC JPARC: Ер = 30 GeV Power = 750 kW

  14. SuperK q Decay Pipe Target Horns T2K off-axis beam → 0 deg - 30 GeV proton beam at JPARC - Quasi-monochromatic  (95%) beam - Peak energy ~700 MeV tuned to oscillation maximum - ~0.4% e at peak energy - Reduced high energy tail  reduces background

  15. ND280 off-axis detector UA1/NOMAD CERN magnet operated at 0.2 T magnetic field Fine Grained Detector (FGD) measure beam flux, E spectrum, flavor composition through CC -interactions, backgrounds CC-1 water and scintillator target Time Projection Chamber (TPC) measure charged particle momenta, particle ID via dE/dx measure backgrounds/pion cross section Pi-Zero Detector (P0D) optimized for NC 0measurement measure e contamination Electromagnetic Calorimeter (ECAL) measure e contamination photon detection (from 0) in P0D and tracker charge particle ID and reconstruction Side Muon Range Detector (SMRD) measure momentum for lateral muons cosmic rays trigger background suppression SMRD 280m downstream from pion production target

  16. ND280 off-axis  beam

  17. Super-Kamiokande IV Inner detector 1114620” PMTs 41.4m Outer detector 18858” PMTs 39m Far detector ~11000 PMTs with FRP+Acrylic cover 40% photo-coverage Total weight 50 kt Fiducial 22.5 kt -, e-, e+ Cherenkov cone Main backgrounds in appearance measurements: 0 from neutral currents – suppression factor ~100 e contamination in  beam - ~0.4% at peak energy

  18. /eevents in T2K Signals and Backgrounds BKG SIGNALS electrons Beam intrinsic e (<1%)  wider energy distrib.  e CCQE CCQE ’s p p nm n nm ne g p0 nx electrons EM shower Multiple Scattering  Ring has “fuzzy” edge electron is relativistic  Opening angle is maximal muons Low Scattering  Ring has sharp edge g NC nx EM showers of ’s from  can fake an electron

  19. T2K Timing L = 295 км TOF = 985 s GPS stability 50 ns Each spill has 8(6) microbunches 56 ns width 580 ns separation ~2.5 sec

  20. Beam data x 1018 x 1012 Run 1 (2010 Jan - 2010 Jun) 50kW stable operation Run 2 (2010 Nov - 2011 Mar) reached 145kW Total p.o.t. : 1.43 x 1020 ~2% of T2K final goal Run 1 protons per pulse accumulated p.o.t. Run 2 Run 1 Run 2 Run 1 Run 2 ~1.5events /1014 p.o.t. ±1mrad INGRID interaction rate stable for Run 1 & 2 nbeam center measured by INGRID well within ±1mrad (dE<<2%@SK) (Beam direction & intensity also monitored by Muon Monitor spill-by-spill)

  21.  events in ND280 FGD, Run 1, 6 microbunches INGRID, Run2, 8 microbunches Clear timing structure of neutrino events in ND280 corresponds to the JPARC beam structure

  22. Analysis principles • Flux prediction: • proton beam measurements • hadron production data • (NA61 CERN) • Super-K measurements: • select CCQE nmand ne • candidates • compute NSKMC w/o oscillations • normalize NSKMC using ND280 • measurements  • NSKexp=(RmND,Data/RmND,MC)x NSKMC • evaluate oscillations • parameters by comparing • with NSKobs • ne: number of events • nm: number of events and • E spectra shape combined • ND280 measurements: • inclusive CC nm • RmND,Data/RmND,MC • nerate measurement as • a cross-check • Neutrino interactions: • n interactions models • external cross-section data

  23. Neutrino flux prediction nm flux at SK T2K beam simulation based onhadron production measurements • NA61/SHINE (CERN) measured hadron production in (p, q) using 30GeV protons and graphite target • p outside NA61 acceptance and K production modeled with FLUKA ne flux at SK Total number:  in ND e in SK (ne analysis) • m decay is dominated at low En • can accurately be predictedby NA61 p measurement Partial error cancellation after ND correction

  24. ND280 measurements Using Run 1 data (2.9 x 1019 p.o.t.) Inclusive nmCC measurements Tracks starting in FGD and identified as m by TPC dE/dx and curvature Intrinsic beam ne measurement TPC dE/dx to select electron tracks R(ne/nm) = 1.0 ± 0.7(stat.) ± 0.3(sys.) % Data consistent with MC based on NA61 data and n interaction simulations

  25. Event selection in SK (I) Event selection for both μ and e: - SK synchronized to beam timing using GPS - Fully contained (FC) events in the Inner Detector, minimal activity in the Outer Detector - Vertex in Fiducial Volume (FCFV) - Number of rings = 1 - PID algorithm to distinguish e-like and μ-like events 121 FC events  = 27 ns

  26. T2K Far Detector Selection Event selection in SK (II) Fiducial Volume Full Contained events (FCFV) PID: e-like and μ-like events Number of rings = 1 88 FCFV events 41 single ring events 8 e-like events, 33 -like events -like e-like 8 e-like events and 33 -like events

  27.  disappearance 4 июля 2011 А.О. Измайлов ИЯИ РАН

  28. events 1 2 3 Vertex distribution in SK 1 T2K beam 2 3 103.6 events in case of no oscillation

  29. disappearance Reconstructed E ratio: data/ MC (w/o oscillation) Reconstructed E No oscillation hypothesis excluded at 4.5σ

  30. Systematic uncertainties Systematics on SK expected events

  31. Oscillation result Two independent oscillation fits Both use Feldman-Cousins unified method Maximum likelihood (method A) and likelihood ratio (Method B) Method A: Best fit: sin2(2θ23)=0.99, |Δm223|=2.6x10-3 eV2 sin2(2θ23)>0.85 2.1x10-3<|Δm223|(eV2)<3.1x10-3 Very good consistency between the two fits Method A Method B Method B: Best fit: sin2(2θ23)=0.98, |Δm223|=2.6x10-3 eV2 sin2(2θ23)>0.84 2.1x10-3<|Δm223|(eV2)<3.1x10-3 Preliminary

  32. T2K, SK and MINOS T2K result is in a good agreement with SK and MINOS

  33. e appearance 4 июля 2011 А.О. Измайлов ИЯИ РАН

  34. e Signal & Background at SK e- Oscillation Signal νμ → νe n p (undetected) e- Beam eBackground νe If one photon missed n p (undetected) γ  NC Background  π0 γ n N + others (undetected)

  35. e events (1) Energy deposited in ID >100 MeV 7 events 8 e-like single-ring FCFV events after “basic” selection criteria T2K neselection cuts in SK optimized for intrinsic beam neand NCpo background minimization After all cuts: - signal efficiency 66% - intrinsic ne rejection 77% - NC background rejection 99% (3) (2) (4) Force reconstruction to fit two e-like rings assumption, require Minv<105 MeV  6 events No Michel electrons  6 events Reconstructed neutrino energy <1250 MeV  6 events 4 июля 2011 А.О. Измайлов ИЯИ РАН

  36. e vertex distributions After all cuts 6 final candidate events remained!

  37. e events OD distributuions OD event distributions show no indication of contribution from outside ID

  38. Expected background 1.5 ne candidates expected with zero q13 hypothesis Systematic uncertainties Smaller cross-section and SK uncertainties for signal events 4 июля 2011 А.О. Измайлов ИЯИ РАН

  39. Significance - Clear signal of e appearance - Indication of large 13

  40. e and 13 accelerator experiment   e 13 CP-even CP-odd Solar Matter

  41. 13 Feldman-Cousins method to produce confidence intervals for sin22q23=1.0and Dm223=2.4x10-3 eV2 Normal mass hierarchy Inverted mass hierarchy • Normal mass hierarchy and dCP=0: • best fit: sin22q23=0.11 • 0.03<sin22q23<0.28 at 90% C.L. • Inverted mass hierarchy and dCP=0: • best fit: sin22q23=0.14 • 0.04<sin22q23<0.34 at 90% C.L.

  42. 6 e events Expected BG 1.5±0.3evts About a year ago, T2K published FIRST clear indication of electron neutrino appearance (13 ≠ 0)

  43. 13 : one year story from an upper limit to precise measurement ! • θ13 has been well measured by different experiments • Interest now focused to the Mass Hierarchy determination & measurement of the CP phase Normal Hierachy MINOS Inverted Hierachy T2K June 15, 2011 T2K first indicationofθ13 ≠ 0 with 2.5 σsignificance MINOS June 24, 2011 MINOS θ13 =0 disfavored @1.7 σ Nov, 2011 Double Chooz Double Chooz θ13 ≠ 0 @3σ combined with T2K and MINOS Daya Bay March, 2012 Daya Bay Sin²2θ13 = 0.092 ± 0.016(stat) ± 0.005(syst) 5.2σ significance RENO April, 2012 RENO Sin²2θ13 = 0.113 ± 0.013(stat) ± 0.019(syst) 4.9σ significance

  44. 13 landscape (May 2012) 5 experiments published 13 results since June 2011 13 9  1 deg

  45. Earthquake 11 March 2011 • Землетрясение магнитудой 9.011 марта 2011 • около 24000 погибших и • пропавших без вести из-за цунами и землетрясения Tsunami Seismic center Fukushima nuclear power stations Tokai Kamioka Tokyo 100km ●

  46. Recovering from Earthquake First  event at SK - JPARC resumed operation in December 2011 - Neutrino beam is back in December 2011 - T2K short test run in January 2012 - Data taking since March 2012 First FC  event at SK First  event in ND280

  47. T2K status 25 April 2012  events at SuperKamiomande SK running efficiency > 99% 2012 (run3) 48evts/5.9e19pot (2010-2012) 169 evts@ 2.0e20pot • Taking high quality data very efficiently • - Double statistics by June 2012

  48. 13 is large  next step?

  49. Search for CP violation

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