1. 1 Accelerator Neutrino Oscillations Results and Prospects Koichiro Nishikawa Institute for Particle and Nuclear Studies KEK III International Pontecorvo Neutrino Physics School 16-26 September, 2006

2. 2 The present observations are good at discovering a surprise (if it is a large effect) for which small scale (controlled) experiments do not have enough sensitivity. –Long baseline (100 – 10 8 km) size of earth, Sun size by luck They are however not good at measuring underlying parameters very precisely. Inherent uncertainties exist in calculation of various observables: –Fluxes of solar neutrinos on Earth Nuclear reaction cross sections, chemical compositions, opacity, etc. –Fluxes of atmospheric neutrinos Primary cosmic ray flux, nuclear interactions, etc. Find model-independent observables –Solar neutrinos: Comparison of NC and CC interactions Spectral shape, day/night effect, etc –Atmospheric neutrinos  /e ratio Zenith angle distribution

3. 3 Accelerator experiment Neutrinos can be measured more than once –Relative change of spectrum Effect of oscillation depend only on neutrino energy (fixed distance) Beam energy can be chosen –Type of detector –Neutrino energy determination method can be chosen

4. 4 Critical issues Only the product F(E i ) x  (E i ) are measurable –Flux times cross section as a function of E The P(  →   must be determined by minimizing the followings –  (E) poorly known at low-medium energy Two measurements at different distances can reduce the the effect of ambiguities of cross sections –F near (E ), F far (E  different from 1/r 2 unless decay at rest Different spectrum due to finite decay length and acceptance at two distances – decay volume and distance –PID and E  determination of observed events background processes (eps. NC, etc.) different in near, far

5. 5 Neutrino beams from accelerator with existing technologies Produce mesons by strong int. and let them decay in weak int. 1. Neutrinos from stopping  ’s and  ’s (LSND KARMEN) unique spectrum of  e no problem of Far/Near, cross section, energy determination 2. Neutrinos from in-flight decays Wide Band Beam - sign selected by horn system but wide  p band accepted, the highest intensity of   CHORUS, NOMAD,K2K, MiniBooNE, MINOS, CGSN…..) –Off-axis beam Dichromatic beam-momentum selected by B and Q mangets –clean but the acceptance beam line limits intensity

6. 6 Decay at Rest (DAR) Small intrinsic e contamination few x 10 -4  decay in flight contamination ?  Inverse beta decay well known 

7. 7 LSND/KARMEN Experiments 800MeV LINAC – 1mA –600  sec width –10msec rep. Mineral oil (Cherenkov pattern) prompt e and  (2.2 MeV) p(n,  )d 800MeV Rapid cycling syn –200  A –200 nsec width –20msec rep. Gd loaded scintillator prompt e and  7.8MeV) Gd(n,  single measurement at one position E  e + from anti- e + p→e + +n unique spectrum for anti-  e

8. 8 Signal and Background

9. 9 Gamma Ray Distribution

10. 10 LSND Final Results

11. 11 KARMEN Distributions

12. 12 With NOMAD and reactor experiments

13. 13 sin 2 2   m 2 (eV 2 ) It is impossible to have only 3 neutrinos involved if all of the effects are the result of neutrino oscillations. Either some of the data are not due to oscillations, or there must be at least one undiscovered “sterile” neutrino or there must be CPT violation in the neutrino sector. or exotic processes ‘Evidence’ of oscillations   e e       

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16. 16 Experimental issue ‘MiniBooNE’ single detector – compare the results with MC only signal = no muon, shower like events, not  Backgrounds = NC  production, e in the beam PID e,  Hadron production knowledge –    production by 8 GeV proton →normalization and HE components to interact with NC  –K to give K e3 decay (K→  e+ e)

17. 17 A neutrino interaction model  /E (10 -38 cm 2 /GeV) E (GeV)

18. 18 Intrinsic ν e (from K&μ decay) : 236 events Other  ν μ mis-ID: 140 events π 0 mis-ID: 294 events (Neutral Current Interaction) LSND-like   e signal: 300 events Approximate number of events and Background expected in MiniBooNE   Charged Current, Quasi-elastic   Charged Current, Quasi-elastic 500,000 events 500,000 events Background Signal ~10 -3 of total neutrino events

19. 19 Signal Mis-ID Intrinsic ν e Δm 2 = 1 ev 2 Δm 2 = 0.4 ev 2 Sensitivity to a Signal

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21. 21 PID e  seperation e-  seperation NUANCE adjustment photon propagation in oil simulation HARP data on  K

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28. 28 Checking the reproducibility of  ’s, detector sim.

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30. 30 ~10 -3 of total neutrino events

31. 31

32. 32 Accelerator-based Long Baseline Neutrino Oscillation Experiments Long = distance>>decay region

33. 33 Wide Band Beam Maximum available neutrino intensity Protons hit target Pions  produced at wide range of angles Magnetic horn to focus  Rock shield range out   beam travels through earth to the experiment  decay /  decay ~10 -2,, Ke3→~1% e contamination

34. 34 Horn in K2K 200m p+Al   +   + +  HE LE Need measurements of high energy (muon monitor) and low energy (neutrino events at near detector) secondary particle direction

35. 35 Neutrino Beam p t ~35MeV/c  Typical characteristics  e  decay vol.) lifetime of  ~ 0.01 production cross sectionof K/  ~ 0.1 and K e3 ~0.01  divergence ~ 10mrad/E(GeV) Horn focuses to about a few mrad Far/near is not scale as 1/r 2

36. 36 Neutrino event vertex distribution at 300m from target Width HE-LE LE 0.5<E   GeVHE 1<E   GeV cm FWHM 4m/300m~ 10 mrad FWHM 2m/300m~ 6 mrad divergence is dominated by decay angle at these energies

37. 37 Critical issues (reminder) Only the product F(E i ) x  (E i ) are measurable –Flux times cross section as a function of E The P(  →   must be determined by minimizing the followings –  (E) poorly known at low-medium energy Two measurements at different distances can reduce the the effect of ambiguities of cross sections –F near (E ), F far (E  different from 1/r 2 unless decay at rest Different spectrum due to finite decay length and acceptance at two distances – decay volume and distance –PID and E  determination of observed events background processes (eps. NC, etc.) different in near,far

38. 38 Critical issues-1  (E) poorly known at low-medium energy –Nuclear physics at GeV region –Pauli blocking –Nucleon Form factor –Final state interaction inside nucleus For several 100~1000km baseline SciBooNE Minerva

39. 39 Quasi-elastic scattering cross-sections Two form factors M V fixed by e.m. (CVC) Axial V form factor  /E   cm 2 /GeV) 1 10 100 GeV n   p W

40. 40 Data on charged current processes Not well known Especially 2~3 GeV →SciBooNE →Minerva

41. 41 Neutrino spectrum and the far/near ratio (in K2K) beam 10 -6 1.0 2.0 Far/Near Ratio E  (GeV) beam MC w/ PION Monitor Angular acceptance (well collimated for HE) Finite decay volume length (shorter for HE, Near better accep. for MH ) 300m 250km

42. 42 Accelerator Neutrinos Present Status K2K (1999-2005 Completed) MINOS (2005-) OPERA (2006-)

43. 43 1995 – Proposed to study neutrino oscillation for atmospheric neutrinos anomaly. 1999 –Started taking data. 2000 –Detected the less number of neutrinos than the expectation at a distance of 250 km. Disfavored null oscillation at the 2  level. 2002 –Observed indications of neutrino oscillation. The probability of null oscillation is less than 1%. 2004 –Confirm neutrino oscillation at the  level with both a deficit of  and the distortion of the E spectrum. 2004 Nov.6 –Terminated K2K due to horn trouble and high residual radiation level Brief history of K2K

44. 44 K2K experiment  monitor  monitor Near detectors (ND) ++  Target+Horn 200m decay pipe SK 100m ~250km  12GeV protons ~10 11   /2.2sec (/10m  10m) ~10 6   /2.2sec (/40m  40m) ~1 event/2 days  Signal of oscillation at K2K Reduction of  events Distortion of  energy spectrum (monitor the beam center) E ~10 5 /2 days

45. 45 Particle detection at 250km away (BG: 1.6 events within  500  s 2.4×10 -3 events in 1.5  s) T SK T spill GPS SK TOF=0.83msec 112 events Decay electron cut.  20MeV Deposited Energy No Activity in Outer Detector Event Vertex in Fiducial Volume More than 30MeV Deposited Energy Analysis Time Window  500  sec  5  sec T DIFF. (s) - 0.2  T SK - T spill - TOF  1.3  sec

46. 46 Analysis Overview Observation #, p  and   interaction MC Measurement  (E ), int. KEK Far/Near Ratio (beam MC with  mon.+ HARP ) Observation # and E  rec. Expectation # and E  rec. (sin 2 2 ,  m 2 ) SK

47. 47 Overall normalization error on Nsk for Nov99~ (Event) Stat0.280.37% KT3.324.37% SK2.283.00% Flux+2.81 -2.59 F/N+4.26 -5.55 NC/CC+0.15 -0.23 nQE/QE+0.38 -0.61 CT0.460.60% Total+6.53 -7.37 5.34% KT: dominated by FV error SK: also. Errors HARP~1 %

48. 48 Pion Monitor: pion distribution after horn Measure Momentum / Angle Dist. of π’s Just after Horn/Target +Well known π Decay Kinematics +Well Defined Decay Volume Geometry ⇒ Predict ν μ Energy Spectrum at Near Site Far Site Ring Image Gas Cherenkov Detector (Index of Refraction is Changeable) To Avoid Severe Proton Beam Background, ν μ Energy Information above 1GeV is Available (β of 12GeV Proton ~ β of 2GeV π)

49. 49 Good agreement with old data. (Cho et.al.) Beam MC based on Cho et al. Error assignment based on this measurements pp  w1w1 w2w2 w3w3 w4w4 ….. : : : : p ,   gives two C-light peaks fit with  wi C-light) index of refraction : p  threshold position of ring :  

50. 50 Thin target data need assumption of secondary interaction in target Total cross section of p-Al Horn magnetic field ambiguity Proton beam profile

51. 51  spectrum shape HARP, Pion monitor and MC comparison Far/Near ratio vs E

52. 52 NEUT: K2K Neutrino interaction MC CC quasi elastic (CCQE) –Smith and Moniz with M A =1.1GeV CC (resonance) single  (CC-1  ) –Rein and Sehgal’s with M A =1.1GeV DIS –GRV94 + JETSET with Bodek and Yang correction. CC coherent  –Rein&Sehgal with the cross section rescale by J. Marteau NC + Nuclear Effects  /E (10 -38 cm 2 /GeV) E (GeV)

53. 53 Near detector measurements 1KT Water Cherenkov Detector (1KT) Scintillating-fiber/Water sandwich Detector (SciFi) Lead Glass calorimeter (LG) before 2002 Scintillator Bar Detector (SciBar) after 2003 Muon Range Detector (MRD) Muon range detector

54. 54 1KT Flux measurement The same detector technology as Super-K. –Sensitive to low energy neutrinos. –Sensitive for NC Far/Near Ratio (by MC)~1×10 -6 M: Fiducial mass M SK =22,500ton, M KT =25ton : efficiency  SK-I(II) =77.0(78.2)%,  KT =74.5% N SK exp =158.4 N SK obs =112 +11.6 -10.0

55. 55 Near Detector Spectrum Measurements 1KT –Fully Contained 1 ring  (FC1R  ) sample. SciBar 2 track nQE (  p >25  ) –1 track, 2 track QE (  p ≤25  ), 2 track nQE (  p >25  ) where one track is  SciFi –1 track, 2 track QE (  p ≤25  ), 2 track nQE (  p >30  ) where one track is  (p    ) for 1track, 2trackQE and 2track nQE samples   (E ), nQE/QE

56. 56 0-0.5 GeV 0.5-0.75GeV 0.75-1.0GeV 1.0-1.5GeV E QE (MC) nQE(MC) MC templates KT data P  (MeV/c)  (MeV/c) flux  KEK (E ) (8 bins) interaction (nQE/QE)

57. 57 Flux measurements  2 =638.1 for 609 d.o.f –  ( E  < 500) = 0.78  0.36 –  ( 500  E < 750) = 1.01  0.09 –  ( 750  E <1000) = 1.12  0.07 –  (1000  E <1500) = 1.00 –  (1500  E <2000) = 0.90  0.04 –  (2000  E <2500) = 1.07  0.06 –  (2500  E <3000) = 1.33  0.17 –  (3000  E ) = 1.04  0.18 – nQE/QE = 1.02  0.10 The nQE/QE error of 10% is assigned based on the sensitivity of the fitted nonQE/QE value by varying the fit criteria.  >10  (20  ) cut: nQE/QE=0.95  0.04 standard(CC-1  low q 2 corr.): nQE/QE=1.02  0.03 No coherent:  =nQE/QE=1.06  0.03 (E ) at KEK E

58. 58 Super-K oscillation analysis Total Number of events E rec spectrum shape of FC-1ring-  events Systematic error term f x : Systematic error parameters Normalization, Flux, and nQE/QE ratio are in f x Near Detector measurements, Beam constraint, beam MC estimation, and Super-K systematic uncertainties.

59. 59 Log Likelihood difference from the minimum. sin 2 2 m 2 [eV 2 ] lnL - 68% - 90% - 99% - 68% - 90% - 99%

60. 60  disappearance versus E shape distortion sin 2 2 m 2 [eV 2 ] N SK (#  ) E shape Both disappearance of  and the distortion of E spectrum have the consistent result.

61. 61 sin 2 2 0.002 0.004 0.006 0.0 0.2 0.4 0.6 0.8 1.0 Normalized by area N obs =112 N exp =158.4 +9.4 -8.7 Distortion of the neutrino spectrum Rate Best fit sin 2 2  =1  m 2 =2.77 x 10 -3 Allowed region Null oscillation hypothesis excluded at 4.4 

62. 62 K2K upper bounds on  → elimit sensitivity K2K-I+II (#obs.=1, #B.G.=1.70) upper limit (90% CL) sin 2 2   e =0.13 @2.8e-3 eV 2 sin 2 2   e =0.13 @2.8e-3 eV 2

63. 63 Conclusion K2K Oscillation analysis on June99 ~November 6, 05 full data 1.Long Baseline experiment can be done! 2.Both SK rate reduction and E rec shape distortion has been observed 3.Null oscillation hypothesis has been excluded by 4.41   m 2 =1.88~3.48x10 -3 eV 2 for sin 2 2  =1 @ 90%CL 5.sin 2 2 ,  m 2 are consistent with atmospheric neutrino results upper limit (90% CL) sin 2 2   e =0.13 @2.8 ｘ 10 -3 eV 2 6.e-appearance search is limited by statistics, upper limit (90% CL) sin 2 2   e =0.13 @2.8 ｘ 10 -3 eV 2 7.Many studies on low energy neutrino interaction continue

64. 64 MINOS experiment Two neutrino detectors Long baseline neutrino oscillation experiment Fermilab’s NuMI beamline 735 km

65. 65 Neutrino beamline 120 GeV protons hit graphite target Two magnetic horns focus positive pions and kaons Mesons decay in flight in evacuated decay pipe giving rise to almost pure υ μ beam Adjustable neutrino beam energy νμνμ Target Horns Decay Pipe Absorber Hadron Monitor Muon Monitors Rock μ+μ+ π+π+ 10 m 30 m 675 m 5 m 12 m 18 m Z. Pavlovic

66. 66 Adjustable beam energy Changing target position changes neutrino beam energy 10 cm most favorable for oscillation analysis Data in other configurations used for systematic studies LE event composition: –92.9% υ μ –5.8% υ μ –1.3% υ e / υ e After target replacement run at 9cm - 10 cm - 100 cm - 250 cm Target position:

67. 67 MINOS Detectors Functionally identical –2.54cm thick steel planes –4.1×1cm scintillator strips –Multianode PMT readout –Magnetized B~1.3T Coil Near Detector Far Detector Near Detector: –1 km from target –1 kton –282 steel and 153 scintillator planes Far Detector: –735 km from target –5.4 kton –484 steel/scinitllator planes

68. 68 Neutrino interactions  CC Event NC Event long  track + hadronic activity at vertex short event, often diffuse 3.5m 1.8m Monte Carlo υμυμ μ XX υ υ Likelihood procedure used to differentiate between NC and CC events NC contaminations in lowest energy bins E υ = E shower +P μ

69. 69 Event classification Good agreement between data and MC for input variables y=E shw /E υ

70. 70 Event Classification Event Classification Parameter rejected as NC like

71. 71 Tuning hadron production MC for ND data Fit ND data from all beam configurations : various Target-horn configuration Simultaneously fit ν μ and ν μ spectra (Use MIPP data in future) υ μ LE010/185kA LE010/185kA LE100/200kA LE250/200kA

72. 72 Beam matrix method Construct beam matrix using MC Use Near Detector data to predict the “unoscillated” spectrum at the Far detector Spectrum known at 2-4% level X =

73. 73 Observed FD events Energy dependant deficit Data Sample FD Data Expected (MC) Data/Prediction (Matrix Method)  All 563738±30 0.76 (4.4  )  (<10 GeV) 310496±20 0.62 (6.2  )  (<5 GeV) 198350±14 0.57 (6.5 

74. 74 Far Detector Data timing to spill time Time stamping of the neutrino events is provided by two GPS units Timing of neutrino candidates consistent with spill signal Easy to separate cosmic muons (0.5Hz) Time distribution is as expected NuMI only mode

75. 75 Systematic errors Systematic shifts in the fitted parameters are computed using MC “data samples” (at best fit point) Uncertainty Shift in Δm 2 (10 -3 eV 2 ) Shift in sin 2 (2θ) Near/Far normalization  4% 0.065<0.005 Absolute hadronic energy scale  10% 0.075<0.005 NC contamination  50% 0.0100.008 All other systematic uncertainties0.041<0.005 Total systematic (summed in quadrature)0.110.008 Statistical error (data)0.170.080

76. 76 Far spectrum Best fit for 2.5x10 20 POT  2 /n.d.f = 41.2/34 = 1.2

77. 77 Allowed region Fit is constrained to physical region: sin 2 (2  23 )≤1  2 /n.d.f = 41.2/34 = 1.2

78. 78 Unconstrained fit  2 /n.d.f = 40.9/34 = 1.2

79. 79 Summary Analyzed data using 2.5×10 20 POT Systematic errors well under control MINOS disfavors no disappearance hypothesis by 6.2σ (<10GeV) Best fit to oscillation hypothesis yields: Forthcoming results: –υ μ → υ e search –υ μ → υ s search

80. 80 Forthcoming improvements Use antineutrinos + neutrinos Expanded FD fiducial volume Improved event reconstruction + selection 3.5×10 20 POT through 8/07 Next year significant proton accelerator improvements –4.6×10 20 ppp (demonstrated in MI)

81. 81 K2K and MINOS have established neutrino oscillation in muon-neutrino disappearance as observed in atmospheric neutrino observation in Super-Kamiokande

82. 82 Collaboration : 13countries 37 Institutes An Emulsion-Counter Hybrid experiment for Tau neutrino Appearance Detection. OPERA OPERA Detector CNGS Beam 730km CNGS First Neutrino to Gran Sasso at 2006 August Current phase: Installation of Emulsion target (ECC Bricks)

83. 83

84. 84

85. 85 Expected signal and background in OPERA in 5 years  mrad I.P.=5-20  m

86. 86 Beam events: ~horizontal tracks Beam angle: 3.35° from below Cosmic rays muons Tracks zenith angle (no beam timing requirement) 319 on-spill events are observed ¾ muons coming from the rock ¼ neutrino interactions in the detector (CC+NC) The observed numbers are consistent with the expectation Detector live-time ~95% First neutrino : Muons from Neutrino Interactions 2006 August Recorded "Rock Muon" event CERN

87. 87 Summary First CNGS Neutino in 2006: total 8.2x10 17 pot –Electric detector's performance was confirmed. –Succeeded to connect tagged muons from the Electric detector to the Emulsion target (CS and ECC). Current status in Gran Sasso: ECC brick production and installation is going on. –Current production and insertion Speed ~300ECC/day about 1/3 of planned. Need speed up  700ECC/day. –until the end of April 2007 CNGS 2007 run is planned in this Autumn. –OPERA will start the Physics RUN with 60,000ECC bricks. –~300 neutrino interaction  ~10 charm events for decay detection and analysis. And <1 Tau neutrino event.

88. 88 Three generation neutrinos

89. 89 Current status of neutrino mass and mixings Anything new? Solar + KamLAND  12,  m 12 2  23,  m 32 2  13,  m 31 2 Only upper limit on  13 No info. on  Atmospheric MINOS 、 K2K

90. 90 Three Flavor Mixing in Lepton Sector e   Weak eigenstates m1m1 m2m2 m3m3 mass eigenstates  12,  23,  13 +  (+2 Majorana phase)  m 12 2,  m 23 2,  m 13 2 c ij = cos  ij, s ij =sin  ij

91. 91 Present Knowledge solar neutrino (SK,SNO), reactor (KamLAND) Matter effect fix the sign of m 2 12 atm. neutrino (SK), long-baseline (K2K,MINOS) Oscillation probability sqaured is measured reactor neutrino exp.(CHOOZ), K2K, MINOS   to be the larger component in e      to be the larger component in e   

92. 92 Three ambiguities  23 （ octant ） and  2 fold ambiguity for    undetermined sign of  m 2 1 ３ 2 fold ambiguity for mass “best fit”  23 =45 : no octant ambiguity 1 2 3

93. 93 Regardless of ‘ambiguities, only the measurements of  can open the next phases of progress