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Takaaki Kajita (ICRR, U.of Tokyo)

III International Pontecorvo Neutrino Physics School Alushta, Ukraine, Sep. 2007. Atmospheric neutrinos -status and prospect-. Production of atmospheric neutrinos Some early history (Discovery of atmospheric neutrinos, Atmospheric neutrino anomaly) Discovery of neutrino oscillations

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Takaaki Kajita (ICRR, U.of Tokyo)

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  1. III International Pontecorvo Neutrino Physics School Alushta, Ukraine, Sep. 2007 Atmospheric neutrinos -status and prospect- • Production of atmospheric neutrinos • Some early history (Discovery of atmospheric neutrinos, Atmospheric neutrino anomaly) • Discovery of neutrino oscillations • Studies of atmospheric neutrino oscillations • Sub-dominant oscillations –present and future- Takaaki Kajita (ICRR, U.of Tokyo)

  2. Studies of atmospheric neutrino oscillations

  3. Introduction We know that neutrinos have mass: Future experiments nenm nt q23=45±8 q13 < 11 q12=34±3 nenm nt n3 n3 Atmospheric LBL n2 Solar KamLAND n2 n1 n1 Small q13 and Dm122 << Dm232 OK to interpret the present data with 2 flavor oscillation framework: P(na nb)=1-sin22qij・sin2(1.27Dmij2・L/E)

  4. Event statistics in atmospheric neutrino experiments More than 20,000 now. TK and Y.Totsuka, RMP73, 85 (2001) Sorry: MINOS not included yet.

  5. today Super-Kamiokande: history and plan SK-I SK-II SK-III accident SK full reconstruction The following discussion: based on the SK-I+II (or SK-I) data

  6. (Dm2, sin22q)

  7. SK-I: 92 kton・yr SK-II: 49 kton・yr Total: 141 kton・yr SK-I+II atmospheric neutrino data CC ne SK-I: hep-ex/0501064 + SK-II 800 days CC nm No osc. Osc.

  8. Down-going Up-going Estimating the oscillation parameters Transition point (as a function of energy)  Dm2 Accurate measurement possible due to small syst. in up/down (2% or less) Confirmation of non-oscillated flux

  9. nmnt2-flavor oscillation analysis (SK-I + SK-II combined analysis) CC ne CC nm Plep UP through showering FC 1ring e-like FC multi-r e-like FC 1ring m-like FC multi-r m-like PC stop PC thru UP through non-showering Multi-GeV UP stop 38 event type and momentum bins x 10 zenith bins  380 bins Sub-GeV Each box has 10 zenith-angle bins Various detector related systematic errors are different between SK-I and SK-II. SK-I and SK-II data bins are not combined. 380 bins for SK-I + 380 bins for SK-II  760bins in total

  10. Definition of c2 Number of data bins Number of syst error terms Poisson with systematic errors Nobs : observed number of events Nexp : expectation from MC ei : systematic error term si: sigma of systematic error c2 minimization at each parameter point (Dm2, sin22q, …). Method (c2 version): G.L.Fogli et al., PRD 66, 053010 (2002).

  11. 70 systematic error terms ● (Free parameter) fluxabsolute normalization ● Flux; (nu_mu + anti-nu_mu) / (nu_e + anti-nu_e) ratio ( E_nu < 5GeV ) ● Flux; (nu_mu + anti-nu_mu) / (nu_e + anti-nu_e) ratio ( E_nu > 5GeV ) ● Flux; anti-nu_e / nu_e ratio ( E_nu < 10GeV ) ● Flux; anti-nu_e / nu_e ratio ( E_nu > 10GeV ) ● Flux; anti-nu_mu / nu_mu ratio ( E_nu < 10GeV ) ● Flux; anti-nu_mu / nu_mu ratio ( E_nu > 10GeV ) ● Flux; up/down ratio ● Flux; horizontal/vertical ratio ● Flux; K/pi ratio ● Flux; flight length of neutrinos ● Flux; spectral index of primary cosmic ray above 100GeV ● Flux; sample-by-sample relative normalization ( FC Multi-GeV ) ● Flux; sample-by-sample relative normalization ( PC + Up-stop mu ) ● Solar activity during SK1 ● Solar activity during SK-II ● MA in QE and single-p ● QE models (Fermi-gas vs. Oset's) ● QE cross-section ● Single-meson cross-section ● DIS models (GRV vs. Bodek's model) ● DIS cross-section ● Coherent-p cross-section ● NC/CC ratio ● nuclear effect in 16O ● pion spectrum ● CC ntcross-section Detector, reduction and reconstruction (21×2) (SK-I+SK-II, independent) Flux (16) ●Reduction for FC ●Reduction for PC ● Reduction for upward-going muon ● FC/PC separation ● Hadron simulation (contamination of NC in 1-ring m-like) ● Non-n BG ( flasher for e-like ) ● Non-n BG ( cosmic ray muon for mu-like ) ● Upward stopping/through-going mu separation ● Ring separation ● Particle identification for 1-ring samples ● Particle identification for multi-ring samples ● Energy calibration ● Energy cut for upward stopping muon ● Up/down symmetry of energy calibration ● BG subtraction of up through m ● BG subtraction of up stop m ● Non-necontaminationformulti-GeV 1-ringelectron ●Non-necontaminationformulti-GeV multi-ringelectron ● Normalizationofmulti-GeV multi-ringelectron ● PC stop/through separation ninteraction (12)

  12. nm nt2 flavor analysis 1489 days (SK-1)+ 800 days (SK-II) Dc2 distributions Best Fit: Dm2 = 2.5 x 10-3 eV2 sin2 2q = 1.00 c2 = 839.7 / 755 dof (18%) Preliminary 1.9 x 10-3 eV2 < Dm2 < 3.1 x 10-3 eV2 sin2 2q > 0.93 at 90% CL

  13. Allowed Parameter Space from atmospheric and Accelerator Long Baseline experiments Accuracy: Dm2: Atm LBL, sin22q: still atm.

  14. L/E analysis

  15. m-like multi-GeV + PC Motivation: Really oscillation ? Before 2004, what we knew was that neutrinos change flavor if they propagate long enough distances. Other mechanisms were proposed to change the neutrino flavor. For example, they were neutrino decay or neutrino decoherence models. oscillation decay decoherence These models explained the atmospheric neutrino data well.

  16. L m Pmm = (cos2q + sin2q ・ exp(– ))2 2t E L 1 Pmm = 1 – sin22q・ (1 – exp(–g0 )) 2 E L/E analysis SK collab. hep-ex/0404034 oscillation decoherence decay Should observe this dip! • Further evidence for oscillations • Strong constraint on oscillation parameters, especially Dm2

  17. L/E plot in 1998 SK evidence paper… Due to the bad L/E resolution events, the dip was completely washed out. (Or neutrinos decay….) Something must be improved….

  18. FC single-ring m-like Full oscillation 1/2 oscillation D(L/E)=70% Selection criteria Select events with high L/E resolution (D(L/E) < 70%) Events are not used, if: ★horizontally going events ★low energy events Similar cut for: FC multi-ring m-like, OD stopping PC, and OD through-going PC

  19. L/E distribution SK-I+II, FC+PC, prelim. (Preliminary) MC (no osc.) MC (osc.) Mostly down-going Mostly up-going Osc. • The oscillation dip is observed.

  20. Allowed oscillation parameters from the SK-I+II L/E analysis SK-I+II (preliminary) Slightly unphysical region (Dc2=0.5) 2.0 x 10-3 eV2 < Dm2 < 2.8 x 10-3 eV2 sin2 2q > 0.93 at 90% CL Consistent with the zenith-angle analysis

  21. decoherence decay SK-I+II (preliminary) Decoh. Decay Osc. SK-I+II L/E analysis and non-oscillation models c2(osc)=83.9/83dof c2(decay)=107.1/83dof c2(decoherence)=112.5/83dof Oscillation gives the best fit to the data. Decay and decoherence models were disfavored by 4.8 and 5.3 s, resp.

  22. Seach for CC nt events

  23. Search for CC nt events (SK-I) CC ntMC CC nt events nt hadrons t nt hadrons ● Many hadrons ．．．． (But no big difference with other (NC) events．) BADt- likelihood analysis ● Upward going only GOOD Zenith angle Only ～ 1.0 CC ntFC events/kton・yr (BG (other n events) ～ 130 ev./kton・yr)

  24. Selection of nt events Pre-cuts: E(visible) >1,33GeV, most-energetic ring = e-like Max. distance between primary vertex and the decay-electron vertex E(visible) Number of ring candidates Sphericity in the lab frame nt MC Atm.n MC data Sphericity in the CM frame

  25. Up-going Zenith-angle Likelihood / neural-net distributions Down-going (no nt) Likelihood Neural-net

  26. Zenith angle dist. and fit results Hep-ex/0607059 Likelihood analysis NN analysis Data scaled t-MC Number of events nm, ne, & NC background cosqzenith cosqzenith Fitted # of t events Expected # of t events Zero tau neutrino interaction is disfavored at2.4s.

  27. Constraints on non-standard oscillations

  28. nx nsterile nx nsterile Oscillation to nt or nsterile ? m-like data show zenith-angle and energy dependent deficit of events, while e-like data show no such effect. nmnt or nmnsterile Difference in P(nmnt) and P(nmnsterile) due to matter effect Propagation Z Neutral current interaction Interaction

  29. Testing nmnt vs. nmnsterile Neutral current Matter effect High E PC events (Evis>5GeV) Multi-ring e-like, with Evis >400MeV Up through muons nt nmnsterile nsterile nmnsterile nmnt nmnt (PRL85,3999 (2000)) Pure nmnsterile excluded

  30. Limit on oscillations to nsterile nm(sinx・nsterile+cosx・nt) If pure nmnt, sin2x=0 If pure nmnsterile, sin2x=1 SK-1 data Consistent with pure nmnt SK collab. draft in preparation

  31. Mass Varying Neutrinos (MaVaN)? Neutrino dark energy scenario • Relic neutrinos with their masses varied by ambient neutrino density (A.Nelson et al. 2004) • Possibly their masses also varied by matter density or electron density beyond the MSW effect Check the MaVaN model in atmospheric data • Dm2→Dm2×(re/r0)n (r0=1.0mol/cm3) • mass varying with electron density • 2 flavor Zenith angle analysis (assuming sin22q=1.0) • SK-I dataset

  32. Neutrino flight length Super-K detector: 1000m underground below the top of Mt. Ikenoyama About 350m above see level Down-going neutrinos fly in the air except for the last 1 to (a few) km.

  33. Excluding a pure MaVaN scenario n vs Dm2 for MaVaN model c2-c2min (@Dm2=1.95x10-3) Dm2 c2-c2min Standard oscillation n n Best fit : Dm2=1.95×10-3eV2 n=-0.03 c2=172.2/178 dof Dm2→Dm2×(re/r0)n Tested MaVaN scenario is strongly disfavored

  34. Constraining decoherence parameter Pure decoherence is excluded at about 5s. It might be possible that oscillation and decoherence co-exists. nm survival probability for oscillation + decoherence Constraining the decoherence parameter with SK L/E analysis

  35. New constraint on decoherence parameter SK collab. Draft in preparation SK-I+II c2min = 83.8/81 d.o.f (g0,Dm2,sin22q)= (0 GeV,2.4x10-3eV2,1.0) g0 <1.4x10-22GeV (90%C.L.) More than factor 10 improvement over the previous upper limit (2×10-21GeV) (Lisi et al, PRL 85, 1166 (2000) g0(×10-21GeV)

  36. Sub-dominant oscillations - present and future - Super-K INO MEMPHYS Hyper-K UNO

  37. Present and future osc. experiments Present: Study of dominant oscillation channels Future: Study of sub-dominant oscillations Known: Unknown: q12, Dm122 q23, |Dm232| q13 Sign of Dm232 nenmnt n3 or n2 n1 If q23 ≠p/4, is it >p/4 or <p/4 ? (CP) Solar, KamLAND Atmospheric Long baseline  Future atmospheric exp’s

  38. q13

  39. Earth model Simulation Core Mantle Search for non-zero q13 in atmospheric neutrino experiments (Dm122=0 and vacuum oscillation assumed) Since ne is involved, the matter effect must be taken into account.

  40. Matter effect cosQ En(GeV) Search for non-zero q13 in atmospheric neutrino experiments (Dm122=0 and vacuum oscillation assumed) Monte Carlo, SK 20yrs 1+multi-ring, e-like, 2.5 - 5 GeV Assuming n3 is the heaviest: Electron appearance s213=0.05 s213=0.00 null oscillation cosQ Electron appearance in the multi-GeV upward going events.

  41. SK-I multi-GeV e-like data Multi-GeV, single-ring e-like Multi-GeV, multi-ring e-like (special) No evidence for excess of upward-going e-like events  No evidence for non-zero q13

  42. n2 n3 n1 n2 n3 n1 q13 analysis from Super-K-I Hep-ex/0604011 Normal Inverted

  43. c2 distributions SK-1 CHOOZ limit If the shape of c2 continues to be like this, (factor ～2) more data might constrain the interesting q13 region at 90%CL.

  44. Future sensitivity to non-zero q13 s22q12=0.825 s2q23=0.40 ~ 0.60 s2q13=0.00~0.04 dcp=45o Dm212=8.3e-5 Dm223=+2.5e-3 20yrs SK (450kton・yr) Approximate CHOOZ limit sin2q23=0.60 0.55 0.50 3s 0.45 0.40 3s for 80yrs SK ~4yrs HK (1.8Mton・yr) But probably after T2K/Nova… Positive signal for nonzero q13 can be seen if q13 is near the CHOOZ limit and sin2q23 > 0.5

  45. Search for non-zero q13 with nm disappearance in atmospheric n exp. INO/2006/01 Project report But I was unable to fine the sensitivity plots for magnetized iron detectors. Sorry…

  46. Sign of Dm2

  47. Sign of Dm2 Very important to measure the charge of leptons  Magnetized detector • If Dm232 is positive, resonance for n •  If Dm232 is negative, resonance for anti-n q13 (With resolution) INO/2006/01 Project report Blue = normal Red = inverted

  48. CC ne CC ne 1-ring e-like Multi-ring e-like Others Others Fraction CC ne CC ne Can we discriminate positive and negative Dm2 in water Ch.? s(total) and ds/dy are different between nandanti-n. If Dm232 is positive, resonance for n  If Dm232 is negative, resonance for anti-n n + ds/dy n y=(En-Em)/En SK atm. n MC En(GeV)

  49. Electron appearance for positive and negative Dm2 Single-ring e-like Multi-ring e-like Relatively high anti-ne fraction Lower anti-ne fraction. Positive Dm2 Negative Dm2 null oscillation cosQ cosQ Small (Large) effect for Dm2 <0 (>0).

  50. n2 n3 n1 n2 n3 n1 3s 3s c2 difference (true – wrong hierarchy) Dm2: fixed, q23: free, q13: free Exposure: 1.8Mtonyr = 80yr SK = 3.3yr HK True= True=  Water Ch. and magnetized muon detectors have similar sensitivity

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