Satoru Yamada for the Super-Kamiokande collaborationInstitute of cosmic ray research, University of Tokyo

Search for WIMP annihilation in the Sun with Super-Kamiokande

Spin Independent (SI) Spin Independent (SI) scattering and scattering and Spin Dependent (SD)Spin Dependent (SD) scatteringscattering

Spin Independent Spin Dependent

Not depends on spin of target nuclei but target mass number.Cross section A∝ 2

Depends on spin of target.Coupling mainly uncoupled nucleon-> Have advantage for proton target

For the indirect searchFrom the earth(SI) 104-106 m2 ν 　 detector -> event rate @1kg Ge detectorFrom the Sun(SD) 10-500m2 ν 　 detector -> event rate @50g H detector

1, Indirect WIMP search for the Sun

M.Kamionkowski et.al. Phys.Rev.Lett.74:5174-5177,1995.

Possible　anihilation　channels:χχ →　bb-　(Soft　channel)　　　　　　　→ 　W ＋ W －　 (Hard　channel)　　　　　　→ 　 ZZ　,　HH　　etc..

Indirect WIMP search for the Sun

Sun

WIMPWIMP

①scattering

Earth

ＳＫ

②annihilation

ν

μ

①scattering

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.

Upmu for the WIMP searchUpmu for the WIMP searchThe energy of WIMP induced neutrino is estimated GeV- a few TeV region. -> upmu is the good category to search this

Effective area S=1200m2

Contained σ 　∝　 Eν 　　 V=const. NSK ∝ Eν

Upgoing μ σ 　∝　 Eν 　　 V∝ Eν 　 　　　　　 NSK ∝ Eν

2

Muon pass in the rock ~ 1km (1TeV muon)

2,Solar WIMP annihilation search in SK

upward going muon(upmu)→ used for WIMP search

Categories of high energy neutrino (atmospheric neutrino) events in SK

Fully Contained (FC) (E ~1GeV)

Event categories

Stopping (E~10GeV)

Through-going (E~100GeV)

Eν （ GeV ）

Partially Contained(PC)(Eν~a few GeV)

Upward going muon (upmu) event in SK

Event categories

Stopping (E~10GeV)

Through-going

•Non-showering (E ~100GeV)

•Showering (E >1000GeV)

Upward going muon event was used for WIMP analysis. There are 3 categories of upmu event in SK.(Effective area ~ 1200 m2)

9/18

Neutrino energy spectrumfor upmu events

Neutrino energy (GeV)1e51 100

Example of upward thru-going muon events

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 ν MC 　 (with oscillation)sin22θ=1, Δm2=2.5×10-3

　 eVCross: data

Sun SunSun

Data and MC are consistent.

3, Upmu data in SK I/II/III phases

Distributions of θsun

0 degree = direction of the Sun

Red: 　 Atmospheric ν MC(with 　 oscillation)Cross: data

0-5 0-10 0-15 0-20 0-25 0-30 θSun(degree)

Stopping

0-5 0-10 0-15 0-20 0-25 0-30

Non showering

No significant excess was observed here.

0-5 0-10 0-15 0-20 0-25 0-30

Showering

θSun(Degree)θSun(Degree)

4, Upmu flux limitRelationship between acceptance-cone and WIMP mass

•　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

SUN

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- )

Estimate cone-angle (soft channel)• 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)

bb (soft channel)

WIMP mass(GeV)

Co

ne

hal

f an

gle

(d

eg.) νe (total)

νμ(total) ντ （ total ）

WIMP induced Neutrino flux @ Earth 100 GeV WIMP

Energy　spectrum　of　WIMP　induced　nu

• 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)

Co

ne

hal

f an

gle

(deg

.)

WW(hard channel)

WIMP mass(GeV)

WIMP induced Neutrino flux @ Earth 100 GeV WIMP

Estimate cone-angle (hard channel)

　　　　　　 νe(total)　　　　　　　 νμ(total)　　　　　　　ντ （ total ）

Energy　spectrum　of　WIMP　induced　nu

Table for new cone angle for soft channel (SKI,II,III:3109.6 days)

A:Stopping upmu ,B: non-showering upmu C: showering upmu

ΧΧ 　 　 massmass(GeV)　(GeV)　

ConeCone(deg.(deg.))

A:datA:dataa

A:MCA:MC B:datB:dataa

B:MCB:MC C:datC:dataa

C:MCC:MC Expected　Expected　compositiocomposition　of　WIMP　n　of　WIMP　induced　induced　signalsignal(A:B:C)(A:B:C)

1010 3030 6363 62.562.5 184184 200.3200.3 3939 33.733.7 98:2:098:2:0

100100 1010 1010 6.76.7 1919 22.522.5 55 3.83.8 78:16:678:16:6

10001000 66 33 2.72.7 88 7.27.2 11 1.41.4 59:29:1259:29:12

1000010000 55 11 1.91.9 77 4.64.6 11 0.90.9 28:52:2028:52:20

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.

A:Stopping upmu ,B: non-showering upmu C: showering upmu

Table for new cone angle for hard channel (SKI,II,III: 3109.6 days)

ΧΧ 　 　 massmass(GeV)(GeV)　　

ConeCone(deg.)(deg.)

A:A:datadata

A:A:MCMC

B:B:datadata

B:B:MCMC

C:C:datadata

C:C:MCMC

Expected　Expected　composition　composition　of　WIMP　of　WIMP　induced　induced　signalsignal(A:B:C)(A:B:C)

80.380.3 88 44 4.24.2 1414 13.413.4 33 2.52.5 44:40:1644:40:16

100100 77 33 3.33.3 1010 9.99.9 22 2.22.2 42:41:1742:41:17

10001000 33 00 0.50.5 22 2.12.1 11 0.30.3 40:41:1940:41:19

1000010000 33 00 0.50.5 22 2.12.1 11 0.30.3 24:54:2224:54:22

90% upmu flux limit from the Sun90% upmu flux limit from the Sun （（ Soft channelSoft 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.

Best limit was obtained below ~103 GeV WIMP

WIMPWIMP massmass(GeV) (GeV)

θθSunSun

(deg.)(deg.)Flux Flux limit limit ×10×10-15-15

(cm(cm--

22secsec-1-1) )

1010 3030 8.98.9

100100 1010 6.56.5

10001000 66 3.83.8

1000010000 55 4.24.2

Note:SK2004-> soft dominant (bb 80%)Others-> soft channel(bb 100%)

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.

Best limit was obtained below ~200 GeV WIMP

WIMPWIMP massmass(GeV) (GeV)

θθSunSun

(deg.(deg.))

Flux Flux limit limit ×10×10-15-15

(cm(cm--

22secsec-1-1) )

80.380.3 88 5.05.0

100100 77 4.14.1

10001000 33 2.52.5

1000010000 33 2.72.7

SK2004 -> soft dominant chOther -> 100% W+W-

Translate into limit of WIMP SD cross sectionRecently, 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.

Cross　section/muon　flux　(cm

2km

2y)

bbt t

τ+τ-

W+W-

10-38

10-39

10-40

10-41

10-42

10-43

10-44

5, Limit of WIMP SD cross section

Limit of spin-dependent(SD) cross section

Direct detection

ν telescopesThis work

11/18

WIMP WIMP mass(GeV)mass(GeV)

SD cross SD cross section(Soft)section(Soft)

SD cross SD cross section(Hard)section(Hard)

1010 1.51×101.51×10-38-38

101022 4.53×104.53×10-39-39 2.74×102.74×10-40-40

101033 2.30×102.30×10-38-38 1.91×101.91×10-39-39

101044 6.88×106.88×10-36-36 3.41×103.41×10-36-36

For the low mass WIMP, we got the good limit

Considering to exploresub-10GeV region

Simulation code is currently not available yet.

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.

WIMP annihilation in Earth

WIMP accumulation rate

C0 : 5.7e15/s (sun)ρDM = 0.3GeV/ccvDM = 230km/s

C: accumulation rate

∝ A2

coupling mainly to an un-paired nucleon:

Neutrinos From GC