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Satoru Yamada for the Super-Kamiokande collaboration

Search for WIMP annihilation in the Sun with Super-Kamiokande. Satoru Yamada for the Super-Kamiokande collaboration Institute of cosmic ray research, University of Tokyo. 1, Indirect WIMP search for the Sun. Spin Independent (SI) scattering and Spin Dependent (SD) scattering.

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Satoru Yamada for the Super-Kamiokande collaboration

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  1. Search for WIMP annihilation in the Sun with Super-Kamiokande Satoru Yamada for the Super-Kamiokande collaboration Institute of cosmic ray research, University of Tokyo

  2. 1, Indirect WIMP search for the Sun Spin Independent (SI) scattering and Spin Dependent (SD)scattering Spin Independent Spin Dependent Depends on spin of target. Coupling mainly uncoupled nucleon -> Have advantage for proton target Not depends on spin of target nuclei but target mass number. Cross section ∝ A2 For the indirect search From the earth(SI) 104-106 m2 νdetector -> event rate @1kg Ge detector From the Sun(SD) 10-500m2 νdetector -> event rate @50g H detector M.Kamionkowski et.al. Phys.Rev.Lett.74:5174-5177,1995.

  3. Indirect WIMP search for the Sun 1, In the sun, spin dependent interaction of WIMPs with nuclei occur. When wimp velocity becomes smaller than escape velocity, they are accumulated into the center. 2, 2 WIMPs near the center annihilate. As the final state of the annihilation, neutrinos are generated. 3, Neutrinos interact inside the earth, and produced muons can be detected in SK. WIMP WIMP ①scattering ①scattering ②annihilation Sun ν Possible anihilation channels: χχ → bb- (Soft channel) →W＋W－ (Hard channel) →　ZZ , HH etc.. μ Earth ＳＫ

  4. Upmu for the WIMP search 2,Solar WIMP annihilation search in SK The energy of WIMP induced neutrino is estimated GeV- a few TeV region. -> upmu is the good category to search this Contained σ　∝　EνV=const. NSK∝Eν Upgoing μ σ　∝　EνV∝Eν NSK∝Eν2 Effective area S=1200m2 Muon pass in the rock ~ 1km (1TeV muon) m n

  5. Categories of high energy neutrino (atmospheric neutrino) events in SK Stopping m (En ~10GeV) Through-going m(En ~100GeV) Eν（GeV） Event categories Fully Contained (FC)(En ~1GeV) Partially Contained(PC) (Eν~a few GeV) upward going muon(upmu) → used for WIMP search

  6. Upward going muon (upmu) event in SK Stopping m (En ~10GeV) • Through-going m • Non-showering (En ~100GeV) • Showering (En >1000GeV) Upward going muon event was used for WIMP analysis. There are 3 categories of upmu event in SK.(Effective area ~ 1200 m2) Event categories Neutrino energy spectrum for upmu events 1 100 1e5 Neutrino energy (GeV) 9/18

  7. Example of upward thru-going muon events

  8. 3, Upmu data in SK I/II/III phases cosθSun distributions for up-mu events • SKI~III upmu samples • (3109.6 days <- 1679.6days@2004 SK result) • Cos θSun = 1 means the direction of • the Sun Red:Atmospheric νMC(with oscillation) sin22θ=1, Δm2=2.5×10-3eV Cross: data Data and MC are consistent. Sun Sun Sun

  9. Distributions of θsun Stopping Red:Atmospheric ν MC (withoscillation) Cross: data 0-5 0-10 0-15 0-20 0-25 0-30 θSun(degree) Showering Non showering 0-5 0-10 0-15 0-20 0-25 0-30 θSun(Degree) 0-5 0-10 0-15 0-20 0-25 0-30 0 degree = direction of the Sun No significant excess was observed here. θSun(Degree)

  10. 4, Upmu flux limit Relationship between acceptance-cone and WIMP mass SUN • The direction of scattered muon after ν–nucleon scattering spreads wider when energy of parent νis low. • •Neutrino energy spectrum is uniquely determined when WIMP mass and certain annihilation mode are assumed • →The cone including more than 90％WIMP induced up-mu • can be defined for several WIMP masses

  11. Annihilation channel • Among possible decay channels, these two channels are considered to calculate flux limit. • Soft annihilation channel (χχ→bb) • - Hard annihilation channel (χχ→W+W-)

  12. Estimate cone-angle (soft channel) νe (total) νμ(total) ντ（total） bb (soft channel) Cone half angle (deg.) WIMP mass(GeV) • Estimated the cone half angle(90% of signals included) when certain channel is dominant(Here, soft channel). • If the annihilation mode: χχ　→　bb is dominant(branching ratio for bb ~1), WIMP induced neutrino flux become softest among the all channel.(soft channel) Energy spectrum of WIMP induced nu WIMP induced Neutrino flux @ Earth 100 GeV WIMP

  13. Estimate cone-angle (hard channel) νe(total) νμ(total) ντ（total） WW(hard channel) Cone half angle(deg.) WIMP mass(GeV) • Estimated the cone half angle(90% of signals included) when certain channel is dominant (Here, hard channel). • If the annihilation mode: χχ　→　WW is dominant (branching ratio for WW ~1), WIMP induced neutrino flux become hardest among the all channel. (hard channel) Energy spectrum of WIMP induced nu WIMP induced Neutrino flux @ Earth 100 GeV WIMP

  14. Table for new cone angle for soft channel (SKI,II,III:3109.6 days) A:Stopping upmu ,B: non-showering upmu C: showering upmu WIMP annihilation channel -> neutrino energy spectrum -> obtain composition of event categories @ SK e.g. For lower energy region, we can almost ignore the thru-mu category, which has large atm-nu b.g.

  15. Table for new cone angle for hard channel (SKI,II,III: 3109.6 days) A:Stopping upmu ,B: non-showering upmu C: showering upmu

  16. 90% upmu flux limit from the Sun（Soft channel） The relationship between WIMP mass and θSun which 90% of WIMP induced upmu contains are simulated assuming soft annihilation channel is dominant. Using this relationship, 90% upmu flux limit from the Sun as a WIMP mass is obtained. Note: SK2004 -> soft dominant (bb 80%) Others -> soft channel(bb 100%) Best limit was obtained below ~103 GeV WIMP

  17. 90% upmu flux limit from the Sun(Hard channel) As same as the soft channel, the 90% upper upmu flux limit from the Sun as a WIMP mass for the hard channel is obtained. SK2004 -> soft dominant ch Other -> 100% W+W- Best limit was obtained below ~200 GeV WIMP

  18. Translate into limit of WIMP SD cross section 10-38 10-39 10-40 10-41 10-42 10-43 10-44 bb t t W+W- Cross section/muon flux (cm2km2y) τ+τ- 5, Limit of WIMP SD cross section Recently, new relationship between σSD and flux limit is presented by G. Wikström, J. Edsjö (arXiv:0903.2986v2.). We used this conversion factor to obtain SD cross section limit from up-mu flux limit.

  19. Limit of spin-dependent(SD) cross section Considering to explore sub-10GeV region Simulation code is currently not available yet. Direct detection νtelescopes This work For the low mass WIMP, we got the good limit 11/18

  20. 6, Summary • - Upward-going muon can be used to measure high energy (>~10GeV) neutrino flux at SK detector • SKI/II/III upmu data were analyzed for searching neutrinos from WIMP annihilation in the Sun. • - increased statistics : 3109.6days • - 3 up-mu categories(stopping, non-showering thru-mu, showering thru-mu) are used • No significant difference between data and atmospheric MC. • - The limit was set for up-mu flux from the Sun and spin dependent cross section of WIMPs. • SK has better sensitivity in the low WIMP mass region(<102~103GeV) compared with other experiments.

  21. WIMP annihilation in Earth

  22. WIMP accumulation rate ∝ A2 coupling mainly to an un-paired nucleon: C: accumulation rate C0 : 5.7e15/s (sun) ρDM = 0.3GeV/cc vDM = 230km/s

  23. Neutrinos From GC

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