Indication of ν µ ν e appearance in the T2K EXPERIMENT

Transcription

1 Indication of ν µ ν e appearance in the T2K EXPERIMENT θ 13 Alain Blondel University of Geneva On behalf of the T2K collaboration Alain Blondel UNIGE seminar -- The T2K experiment theta_13 1

2 There are today THREE compelling and firmly established observational facts that the Standard Model fails to account for: -- neutrino masses -- the existence of dark matter -- the baryon asymmetry of the universe The fact that neutrino have masses and mix is established by neutrino oscillations The neutrino masses offer a chance to explain the baryon asymmetry in the most natural way via *** LEPTOGENESIS *** by a combination of -- fermion number violation (authorized by neutrino masses and GUT) -- three families of neutrinos ==> leptonic CP violation (authorized by the mixing of three families with large mixing angles) Alain Blondel UNIGE seminar -- The T2K experiment theta_13 2

3 The neutrino mixing matrix: 3 angles and a phase δ ν 3 m 2 23 = ev 2 ν 2 1 m 2 12 = ev 2 OR? ν 2 1 ν 3 m 2 12 = ev 2 m 2 23 = ev 2 θ 23 (atmospheric) = 45 0, θ 12 (solar) = 32 0, θ 13 (Chooz) < 13 0 Unknown or poorly known θ 13, phase δ, sign of m 13 2 Alain Blondel UNIGE seminar -- The T2K experiment theta_13 3

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5 Oscillation maximum 1.27 m 2 L / E =π/2 Atmospheric m 2 = ev 2 L = GeV Solar m 2 = ev 2 L = 1 GeV Consequences of 3-family oscillations: I There will be ν µ ν e and ν τ ν e oscillation at L atm Oscillations of 250 MeV neutrinos; P (ν µ ν e ) (acc) P (ν µ ν e ) max =~ ½ sin 2 2 θ 13 (reactor) P (ν e ν e ) max =~ 1 - sin 2 2 θ 13 + (small) + (small) II There will be CP or T violation CP: P (ν µ ν e ) P (ν µ ν e ) T : P (ν µ ν e ) P (ν e ν µ ) 1 st maximum second maximum III. we do not know if the neutrino ν 1 (which contains more ν e) is the lightest one (natural?) or not. Alain Blondel UNIGE seminar -- The T2K experiment theta_13 5

6 P(ν e ν µ ) = A 2 + S A S sin δ P(ν e ν µ ) = A 2 + S 2-2 A S sin δ P(ν e ν µ ) - P(ν e ν µ ) P(ν e ν µ ) + P(ν e ν µ ) sinδ sin ( m 2 12 L/4E) sin θ 12 = A CP α sin2 2θ solar term sinθ need large values of sin θ 12, m 2 12 (LMA-- we have it!) but *not* large sin2 θ 13 need APPEARANCE P(ν e ν e ) is time reversal symmetric (reactors or sun are out) can be large (100%) for suppressed channel (one small angle vs two large) at wavelength at which solar = atmospheric and for ν e ν µ, ν τ asymmetry is opposite for ν e ν µ and ν e ν τ Alain Blondel UNIGE seminar -- The T2K experiment theta_13 6

7 Three family oscillations and ν µ ν e oscillation Mezzetto L= π/2.54 E/δm 2 l = π/2.54 E/ m 2 Alain Blondel UNIGE seminar -- The T2K experiment theta_13 7

8 P(ν e ν µ ) = A 2 + S A S sin δ P(ν e ν µ ) = A 2 + S 2-2 A S sin δ P(ν e ν µ ) - P(ν e ν µ ) P(ν e ν µ ) + P(ν e ν µ ) sinδ sin ( m 2 12 L/4E) sin θ 12 = A CP α sin2 2θ solar term sinθ need large values of sin θ 12, m 2 12 (LMA-- we have it!) but *not* large sin2 θ 13 need APPEARANCE P(ν e ν e ) is time reversal symmetric (reactors or sun are out) can be large (100%) for suppressed channel (one small angle vs two large) at wavelength at which solar = atmospheric and for ν e ν µ, ν τ asymmetry is opposite for ν e ν µ and ν e ν τ Alain Blondel UNIGE seminar -- The T2K experiment theta_13 8

9 NOTES: Asymmetry can be very large. Stat. sensitivity in absence of bkg is ~independent of θ 13 down to max. asym. point Asymmetry changes sign from one max. to the next. Sensitivity at low values of θ 13 is better for short baselines, sensitivity at large values of θ 13 is better for longer baselines (2d max or 3d max.) sign of asymmetry changes with max. number. 100% T asymmetry for sin δ = 1 error Max. Asymmetry Stat. error with no background Alain Blondel UNIGE seminar -- The T2K experiment theta_13 9

10 Idea of T2K was born hep-ex/ combining: -- existing SuperKamiokande detector (50kton W.Č., 22.5 kton fiducial) -- JAERI-KEK Japanese Proton Accelerator Research Complex (JPARC) at TOKAI including a high power, 0.75MW/50GeV Proton Synchrotron -- baseline 295 km neutrino energy for first maximum is ~600 MeV achievable by pion-decay beam at 2.5 degrees off-axis Alain Blondel UNIGE seminar -- The T2K experiment theta_13 10

11 神岡 Kami oka 東海 Tō kai 11

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13 University of Geneva: N. Abgrall, J. Argyriades, A. Blondel, A. Bravar, F. Dufour, A. Ferrero, A. Haesler, A. Korzenev, S. Murphy, M. Ravonel, G. Wikström Alain Blondel UNIGE seminar -- The T2K experiment theta_13 13

14 OVERVIEW p π µ-mon ν 30 GeV off-axis on-axis 2.5 o 0m 120m 280m 2.5 degrees off-axis beam - Low energy, narrow band beam tuned at osc. max. - Neutrino peak ~600 MeV/c Near 280 m from target extrapolate ν energy spectrum and flux to SK - INGRID: on axis to monitor beam direction - ND280: off axis to measure ν µ and ν e interaction rates and backgrounds NA61 at CERN hadro-production measurement 295 km Far detector 295 km - Very large water Cerenkov detector - Very good µ/e separation capability for sub-gev neutrinos Alain Blondel UNIGE seminar -- The T2K experiment theta_

15 T2K physics goals Experiment is optimized for the search of ν ν µ e oscillation θ 13 P(ν µ ν e ) sin 2 2θ 13 sin 2 θ 23 sin(1.27 m 2 23 L/E ν ) -- is also able of precision measurement of ν ν µ ν µ oscillation θ 23, m 2 23 P(ν µ ν µ ) 1-sin 2 2θ 23 sin (1.27 m 2 23 L/E ν ) -- and measurements of cross-sections around 600 MeV in the near detector Alain Blondel UNIGE seminar -- The T2K experiment theta_13 15

16 θ 13 sin 2 θ 12 = sin 2 θ 23 = 1.0 m 2 12 = ev 2, m 2 23 = ev 2 sin 2 θ 12 = sin 2 θ 23 = 1.0 m 2 12 = ev 2, m 2 23 = ev 2 90% C.L. 750kW X 5 years X 22.5 kton fid. short baseline little sensitivity to matter effects, but sensitive to δ CP Alain Blondel UNIGE seminar -- The T2K experiment theta_13 16

17 Appearance: Dis-appearance MINOS & Super-K Nu 10 T2K nominal: 3.75MW 10 7 s sin 2 2θ 13 < (90% C.L.) for 5 years@750kw = p.o.t@30 GeV Alain Blondel UNIGE seminar -- The T2K experiment theta_13 spectrum centered on oscillation maximum very rapidly sensitive to Atm. Params. sin 2 2θ m 2 23 <1x10-4 ev 2 17

18 Beam Line Alain Blondel UNIGE seminar -- The T2K experiment theta_13 18

19 T2K 1 st ν event in Super-K 19 06:00 JST, Feb. 24, rd ring 1 st ring 2 nd ring [ 1 st ring + 2 nd ring ] Invariant mass: MeV/c 2 (close to π 0 mass) Momentum: MeV/c Alain Blondel UNIGE seminar -- The T2K experiment theta_

20 Beam Monitors Alain Blondel UNIGE seminar -- The T2K experiment theta_13 20

21 Near Detector Complex ND280 Off-Axis suite of fine grain detectors/tracker inside a 0.2 T magnetic field (UA1/NOMAD magnet) ND280: measurements of -- CCν µ events (normalization, disappearance) -- CCν e events -- π 0 events Backgrounds to ν µ ν e search On-axis INGRID scintillator-iron detectors measurement of beam angular profile Alain Blondel UNIGE seminar -- The T2K experiment theta_13 incoming neutrino beam 21

22 IN GRID Alain Blondel UNIGE seminar -- The T2K experiment theta_13 22

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24 Search for ν ν µ e appearance 1. Event selection at SK 2. Prediction of number of expected events (oscillation/no oscillation) 3. Systematic errors 4. Open the last three cuts 5. Inspect what you see 6. results most slides that follow from T2K seminar at KEK, K. Sakashita (KEK) Alain Blondel UNIGE seminar -- The T2K experiment theta_13 24

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26 Unbiased event selection SK event selection was fixed before run. Possible because SK is a mature & well understood detector. For ν µ disappearance analysis For Timing coincident w/ beam time (+TOF) Fully contained (No OD activity) ν e appearance search Vertex in fiducial volume (Vertex >2m from wall) E vis > 30MeV µ-like ring n o of rings =1 E vis > 100MeV e-like ring No decay electron Inv. mass w/ forced-found 2 nd ring < 105MeV E ν rec < 1250MeV NB: slide shown at NUFACT10 October 2010 Alain Blondel UNIGE seminar -- The T2K experiment theta_13 26

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32 ν e ν µ ν τ Alain Blondel UNIGE seminar -- The T2K experiment theta_13 32

33 UNIGE: Bravar, Abgrall, Murphy, Ravonel, Argyriades, Korzenev, Haesler Alain Blondel UNIGE seminar -- The T2K experiment theta_13 33

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35 End of exposure was -- dramatically decided by external event TOKAI TOKYO Alain Blondel UNIGE seminar -- The T2K experiment theta_13 35

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38 The Off-Axis Near Detector Cannot be Water Cherenkov: -- pile-up -- (worse) granularity of small vs large detector UA1/NOMAD magnet donated by CERN fine grain detector of light material (even water!) -- Scitillators with MPPC readout ( channels!) -- TPC tracker Alain Blondel UNIGE seminar -- The T2K experiment theta_13 38

39 (MPPC) Alain Blondel UNIGE seminar -- The T2K experiment theta_13 39

40 TPC s 3 TPC s, 1.8 x 2 x 0.70 m 3 sensitive area World s Largest TPC with micro-pattern read out (MicroMeGas) TPC modules built at CERN/UNIGE Alain Blondel UNIGE seminar -- The T2K experiment theta_13 40

41 A few ND280 neutrino interaction candidates ν µ quasi-elastic candidate single pion candidate DIS candidate Alain Blondel UNIGE seminar -- The T2K experiment theta_13 41

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46 (factor 2) Alain Blondel UNIGE seminar -- The T2K experiment theta_13 46

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58 6 candidates after all cuts! N exp =1.5±0.3 for sin 2 2θ 13 =0 Alain Blondel UNIGE seminar -- The T2K experiment theta_13 58

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60 Look at the events properties Alain Blondel UNIGE seminar -- The T2K experiment theta_13 60

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62 hmmmmm.? Alain Blondel UNIGE seminar -- The T2K experiment theta_13 62

63 Result of the ν e appearance search with 1.43 x p.o.t. The observed number of events is 6 The expected number of events is 1.5 ± 0.3 if θ 13 =0 the probability to observe six or more candidate events is (equivalent to 2.5σ significance) We will be eagerly waiting for more data to obtain a larger significance! Alain Blondel UNIGE seminar -- The T2K experiment theta_13 63

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66 90% C.L sin 2 2θ 13 Alain Blondel UNIGE seminar -- The T2K experiment theta_13 66

67 Final remarks 1. the T2K experiment is working very well! 2. Although the significance is only 2.5 sigma the analysis procedure is such (cuts fixed in advance, sample defined by external events) that a statistical fabrication can be completely excluded. 3. T2K is now under reconstruction: beam expected to resume (if no bad surprise) in November if it is confirmed that θ 13 is large this will have consequences on the design of the next generation of experiments (good for NOvA in first instance) 5. this summer will be very exciting on the neutrino front: new results from (at least) MINOS, OPERA, DCHOOZ are expected COME TO NUFACT11 at CERN/GENEVA 1-6 August 2011! Alain Blondel UNIGE seminar -- The T2K experiment theta_13 67

68 A few reserve slides Alain Blondel UNIGE seminar -- The T2K experiment theta_13 68

69 Event display single-ring µ-like events Pµ= 1061 MeV/c 1 decay-e Pµ= 1025 MeV/c 1 decay-e Alain Blondel UNIGE seminar -- The T2K experiment theta_13 69

70 Event display multi-ring µ-like event Pµ= 1438 MeV/c 2 decay-es Alain Blondel UNIGE seminar -- The T2K experiment theta_13 70

71 Vertex and direction (FC, Evis>30MeV) Points : Reconstructed event vertex Arrow : 1st-ring direction Beam direction Vertex X vsy Vertex R vsz FV ID wall FV ID wall Alain Blondel UNIGE seminar -- The T2K experiment theta_13 71

72 Super KamiokaNDE Energy scale stability Stopping µ(momentum/range) RMS/MEAN T2K period : 0.31% (SK-IV all : 0.39%) Decay-e (momentum) RMS/MEAN T2K period : 0.28% (SK-IV all : 0.45%) Energy scale has been quite stable. Alain Blondel UNIGE seminar -- The T2K experiment theta_13 72

73 750kW in 2014 Alain Blondel UNIGE seminar -- The T2K experiment theta_13 73