Docstoc

Atmospheric neutrino results from Super-Kamiokande

Document Sample
Atmospheric neutrino results from Super-Kamiokande Powered By Docstoc
					Y.Itow, Atmospheric neutrino results from Super-Kamiokande   TAUP07 13/09/2007




          Atmospheric neutrino results
             from Super-Kamiokande



                                          Yoshitaka Itow
               Solar-Terrestrial Environment Laboratory,
                                       Nagoya University
                    for Super-Kamiokande Collaboration
Y.Itow, Atmospheric neutrino results from Super-Kamiokande   TAUP07 13/09/2007

  Menu

   Introduction
   Standard neutrino oscillation analysis
        2 flavor oscillation results in zenith angle
         nt appearance results
         Subdominant oscillation driven by solar terms
   Exploring exotic mode
        MaVaN (Mass Varying Neutrino) scenario
        Neutrino decay / decoherence in L/E
        Sterile neutrino admixture
   Status of SK-Ⅲ and future
Y.Itow, Atmospheric neutrino results from Super-Kamiokande              TAUP07 13/09/2007


  Super-Kamiokande detector

                                                              50kt water Cherenkov
                                                              1000m underground
                                                              ID viewd by 11176 PMT
                                                              2m thick OD for veto
                                                              Fiducial mass 22.5kt


                                                   42 m
                                                               Operation since Apr 1996




                        39.3 m
  Y.Itow, Atmospheric neutrino results from Super-Kamiokande    TAUP07 13/09/2007
   10 years of Super-Kamiokande
            1996.4 Start data taking

            1998 Evidence of atmospheric n oscillation (SK)

SK-I        1999.6 K2K started

            2001 Evidence of solar n oscillation (SNO+SK)

            2001.7 data taking was stopped
                    for detector upgrade
            2001.11 Accident
                partial reconstruction
            2002.10 data taking was resumed

SK-II       2005 Confirm n oscillation by accelerator n (K2K)
            2005.10 data taking was stopped for
                   full reconstruction

            2006.7 data taking was resumed
SK-III
Y.Itow, Atmospheric neutrino results from Super-Kamiokande   TAUP07 13/09/2007




    nm-nt oscillation results
         Atmospheric n categories at SK
Y.Itow, Atmospheric neutrino results from Super-Kamiokande                TAUP07 13/09/2007



n         FC            n           PC                       Stopping m     Through going m



                                                                   m               m
                                                  m



                                                                  n          n
                   Energy spectrum of n for each event category




                                                             up-stop m
                                                             up-thru m
Y.Itow, Atmospheric neutrino results from Super-Kamiokande             TAUP07 13/09/2007

    Up-showering m
      Upgoing through muon sample is
            separated into “showering” or “non-showering”

                                                             68% n to thru-m res.
                                                             •1.25o (showering, this fig)
                                                             •1.0o (non-showering)
Y.Itow, Atmospheric neutrino results from Super-Kamiokande                    TAUP07 13/09/2007
Zenith Angle Distributions (SK-I + SK-II)
                                               nm–nt oscillation (best fit)       Livetime
                                               null oscillation                   •SK-I
                                                                                   1489d (FCPC)
    P<400MeV/c             P<400MeV/c
                                                                                   1646d (Upmu)
                                                                                  •SK-II
                                                                                     804d (FCPC)
                                                                                     828d(Upmu)

    P>400MeV/c             P>400MeV/c

                                                                                    m-like
                                                                                    e-like




            All distributions agree with oscillated expectations
 Y.Itow, Atmospheric neutrino results from Super-Kamiokande       TAUP07 13/09/2007
2 flavor oscillation analysis
                                                               sin22q=1.0

               Best Fit: Dm2 = 2.5 x 10-3 eV2
                          sin2 2q = 1.00
               c2 = 839.7 / 755 dof (18%)
   Dm2 (eV2)




               Dm2 =(1.9~3.1) x 10-3 eV2
               sin2 2q > 0.93 @ 90% CL

                                                                   Dm2
                                                              Dm2=2.5x10-3eV2




                                sin22q




                                                                   sin22q
Y.Itow, Atmospheric neutrino results from Super-Kamiokande           TAUP07 13/09/2007

  nt appearance search                              in cc t-enhanced sample



    t-like selection;
      efft=43%,
      S/N=5%

                           multi ring


          t

     nt                decay-e
 Y.Itow, Atmospheric neutrino results from Super-Kamiokande                   TAUP07 13/09/2007
nt appearance search
zenith angle distribution of t enrich sample
                                                               Ntotal(cosq)=aNtau+bNBKG

                                                              • a (tau normalization) = 1.76
       Tau excess                                             • b (BKG normalization) = 0.9
                                                              • c2/dof=7.6/8
                                                                        =16.3/9 assuming no tau
                                                               result:
                                                               • fitted t excess 59.6 ±20.7
                                                                                            14.8
                                                               • total t excess 138 ± 48 ± 31.6
                                                                   (signal eff. = 43.1%)
                                                               • expected 78.4 ± 26 (syst.)

                                                              NN result
                                                              • fitted t excess 52.3 ±18.7
                                                              • total t excess 134 ± 48 ± 16
                                                                                           27.2
  t enrich sample is consistent with                              (signal eff.=39.0%)
  nm-nt oscillation                                           • expected 78.4 ± 27 (syst.)
Y.Itow, Atmospheric neutrino results from Super-Kamiokande   TAUP07 13/09/2007




   Oscillation with solar term and
   determination of octant of q23
 Y.Itow, Atmospheric neutrino results from Super-Kamiokande                         TAUP07 13/09/2007

Subdominant oscillation w/ solar term in e-like events
                                                                   O. L. G. Peres and A. Yu. Smirnov,
                                                                              hep-ph/0309312
  Since simple two flavor oscillations depend on
    sin22q23. octant of q23 ( q23 < 45o or > 45o )                                     c223 : s223
    degenerates.
                                                   n2
  LMA parameters , i.e.,
                                                                                s212 :      c212       Dm212
  (Dm212 =(7.4~9.2)×10 -5 , tan2q12 =0.28-0.58)
                                                   n
   can contribute to low energy atmospheric ne in 1                                  ne        nm nt
    subdominant oscillations

P(ne      ne)                     = 1 – P2
P(ne      nm) = P(nm         ne) = cos2 q23 P2              P2 : 2n transition prob. ne  nm , t
                                                                  in matter   driven by Dm212
P(ne      nt) = P(nt         ne) =   sin2   q23 P2

  ne decrease rate by ne oscillation : 1 – P(ne  ne) = P2
  ne increase rate by nm oscillation : r P(nm                         n e)     = r cos2 q23 P2

            cos2 q23 = 0.5 @ q23=45o , r = F0(nm) / F0(ne) ~ 2 (for low energy n)
Y.Itow, Atmospheric neutrino results from Super-Kamiokande               TAUP07 13/09/2007


  Sub-GeV e-like zenith angle
                    X : zenith angle
                    Y : N_e (3 flavor) / N_e (2 flavor full-mixing)

   Sub-GeV e-like                        Pe : 100~400 MeV/c           Pe : 400~1330 MeV/c




               cos q                                 cos q                    cos q

                       sin2 q23 = 0.4                        Dm212 = 8.3 x 10-5 eV2
                       sin2 q23 = 0.5                        Dm223 = 2.5 x 10-3 eV2
                       sin2 q23 = 0.6                        sin2 2q12 = 0.83
Y.Itow, Atmospheric neutrino results from Super-Kamiokande                    TAUP07 13/09/2007

    Result of sin2 q23 determination (SK-I + SK-II)
                                                             Assuming sin2 q13 = 0
 c2 – c2min distribution as a function
 of sin2 q23 where the other oscillation                           Solar terms off :
 parameters are chosen to minimize c2                              The 1-2 parameters
                                                                   (Dm212 , sin2 q12)
                                                                   are fixed at zero.
                                                                    best-fit : sin2 q23 = 0.50

                                                                   Solar terms on :
                                                                   The 1-2 parameters
                                                                   are scanned.
                                                                    best-fit : sin2 q23 = 0.52
                                                                           (sin2 2q23 = 0.9984)



              w/o 1-2 parameters                             No evidence for the deviation
              w 1-2 parameters                               of sin2 q23 from 0.5.
Y.Itow, Atmospheric neutrino results from Super-Kamiokande   TAUP07 13/09/2007




   Constraint for exotic scenarios
 Y.Itow, Atmospheric neutrino results from Super-Kamiokande          TAUP07 13/09/2007

MaVaN (Mass Varying Neutrino) model

    Neutrino dark energy scenario
     Relic neutrinos of which 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 additional matter effect in atmospheric data

        • Dm2→Dm2×(re/r0)n                               (r0=1.0mol/cm3)
                                        mass varying with electron denstiy
        • 2 flavor Zenith angle analysis
        • assuming sin22q=1.0
        • SK-I dataset
Y.Itow, Atmospheric neutrino results from Super-Kamiokande                        TAUP07 13/09/2007
   Result for MaVaN-type matter effect
      n vs Dm2 for MaVaN model                                           c2-c2min (Dm2=1.95x10-3)




                                                              c2-c2min
Dm2




                                                                                    n
                                                                            c2-c2min (n=-0.03)



                            n


                                                             c2-c2min
      Best fit : Dm2=1.95×10-3eV2
                 n=-0.03
                 c2=172.2/178 dof

MaVaN type models tested are disfavored                                           Dm2
 Y.Itow, Atmospheric neutrino results from Super-Kamiokande                         TAUP07 13/09/2007
L/E oscillation analysis
                                           c2osc == 1 – sin22qsin2(Dm L )
                                                                                2
  Neutrino oscillation :                      Pmm 83.9/82 d.o.f
                                                                    E
  Neutrino decay :                         c dcy ==107.1/82sin2q x exp(– m (4.8σ)
                                            2
                                              Pmm (cos2q + d.o.f, Dc = 23.2 L ))2
                                                                      2

                                                                                   2t E
  Neutrino decoherence :                   c2decmm= = 1 – 1 sind.o.f,
                                              P     112.5/82 22q x         Dc2  exp(–g0 L ))
                                                                           (1 – = 27.6 (5.3σ)
                                                              2                          E
               survival probability                                                        SK-I+II


                                                                    data



                                                                                      decoherence
                                                                                         decay


                                                                  oscillation
Y.Itow, Atmospheric neutrino results from Super-Kamiokande                           TAUP07 13/09/2007
  oscillation+decoherence                                        oscillation+decay
                                                                                          m L
Pmm = 1 –
                  1
                     sin22q x (1 – exp(–g0 L )           Pmm = sin4q + cos4q x exp(–           )
                  2                        E                                              t E
                    Dm2L                                          +2sin2q cos2q x exp(–   mL)
              ×cos(       ))
                      2E                                                 Dm2L             2t E
                                                                  ×cos(     )
                                                                           2E




                                                     Dm2 (eV2)
  Dm2 (eV2)




                   g0 (×10-21GeV)                                        m/t (GeV/km)
c2min = 83.8/81 d.o.f                                  c2min = 83.8/81 d.o.f
(g0,Dm2,sin22q)= (0 GeV,2.4x10-3eV2,1.0)               (m/t,Dm2,cos2q) = (0 GeV/km,2.4x10-3eV2,0.5)
g0 <1.4x10-22GeV (90%C.L.)                             m/t <3.2x10-5GeV/km (90%C.L.)
Y.Itow, Atmospheric neutrino results from Super-Kamiokande                  TAUP07 13/09/2007


  Sterile neutrino admixture
                                                                Based on Fogli et al
                                                                PRD 63 (2001) 053008
    n 1   cos                 sin  n t                  for 2+2 mass hierarchy, 4-
     
    n   - sin                        
                                  cos n s 
                                                                flavor mixing can be
     2                                                    converted into two 2-flavor
                                                                mixings


             sin2 vs Dm2



                                                             24.5% of sterile neutrino
                                                             admixture is allowed at
                                                             90% C.L.
Y.Itow, Atmospheric neutrino results from Super-Kamiokande   TAUP07 13/09/2007




  SK-Ⅲ status and future
Y.Itow, Atmospheric neutrino results from Super-Kamiokande   TAUP07 13/09/2007

  SuperKamiokande-III




  •Full 20”PMT with acrylic cover
   and FRP case
  •Top and bottom outer detector
   (OD) is optically separated from
   barrel OD
  •Calibration system and sources
   are improved.
Y.Itow, Atmospheric neutrino results from Super-Kamiokande                   TAUP07 13/09/2007
   Zenith angle distribution @ SK-III
         Sub-GeV e-like               Sub-GeV m-like
                                                             data : Aug/2006-Mar/2007
         p<400MeV/c                   p<400MeV/c                   166days
                                                              MC w/o oscillation
                                                              SK-III data

        Sub-GeV e-like                Sub-GeV m-like
                                                             events/day
        p>400MeV/c                    p>400MeV/c                   SK-III             SK-II
                                                             FC 8.31±0.22          8.22±0.10
                                                             PC 0.57±0.06          0.54±0.03

        Multi-GeV e-like           Multi-GeV m-like +PC




    SK-III start the data taking and analysis.
    zenith angle dependence is also observed in SK-III
Y.Itow, Atmospheric neutrino results from Super-Kamiokande                  TAUP07 13/09/2007
New feature of SK-III : Outer Detector (OD) segmentation
  Wall and endcaps of OD are                                 less light creeps around the
  optically separated.                                       detector corner




            Easy reduction of “Conner Clipper muons ”
                           Benefit for PC and upgoing muon analyses
Y.Itow, Atmospheric neutrino results from Super-Kamiokande   TAUP07 13/09/2007


 Toward SK-Ⅳ New electronics development
 Will be installed in 2008 (before                            Ethernet
  T2K)                                                         daughter board
   Based on QTC + TDC chip
   “Record all hits” policy
   Wide dynamic range (<1000p.e.)
   Via fast Ethernet readout
   Possible complicated and
    intelligent trigger
 Impact for atm n physics
   increased m-e decay tagging
    efficiency
   challenge for neutron tagging
    (2.2MeV g)                       QTC                         TDC
Y.Itow, Atmospheric neutrino results from Super-Kamiokande   TAUP07 13/09/2007
  Summary
     2 flavor zenith angle analysis
       Best fit: (Dm2, sin22q)=(2.5x10-3eV2, 1.00)
      1.9x10-3<Dm2<3.1x10-3eV2, sin22q>0.93 at 90%C.L.
     t appearance
    t enriched sample is consistent with nm-nt oscillation
                               14.8
        excess    138±48± 31.6
       expected 78.4±26 (syst.)
     Subdominant oscillation w/ solar term
      So far no measurable deviation of sin2q23 from 0.5
     Survey of exotic modes
     No MaVaNs, n decay, decoherence or sterile scenarios
     SK-III status and future
     Analysis started well.
     New electronics coming next year before T2K !

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:0
posted:8/17/2012
language:
pages:27