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
Spin Independent
Spin Dependent
Not depends on spin of target
nuclei but target mass number.
Cross section ∝ A2
Depends on spin of target.
Coupling mainly uncoupled
nucleon
-> Have advantage for proton
target
For the indirect search
From the earth(SI) 104-106 m2 ν detector -> event rate @1kg Ge detector
From the Sun(SD) 10-500m2 ν detector
-> event rate @50g H detector
M.Kamionkowski et.al. Phys.Rev.Lett.74:5174-5177,1995.
Indirect WIMP search for the Sun
WIMP
WIMP
①scattering
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.
②annihilation
3, Neutrinos interact inside the earth,
Sun
and produced muons can be detected
in SK.
ν
μ
Earth
ＳＫ
Possible anihilation
channels:
χχ → bb- (Soft channel)
→ W＋W－ (Hard channel)
→ ZZ , HH etc..
2,Solar WIMP annihilation search in SK
Upmu for the WIMP search
The energy of WIMP induced neutrino is estimated GeV- a
few TeV region. -> upmu is the good category to search this
Contained
σ ∝ Eν
V=const.
Upgoing μ
σ ∝ Eν
V∝Eν
NSK ∝Eν
NSK ∝Eν2
Effective area S=1200m2
Muon pass in the rock ~ 1km (1TeV
muon)
m
n
Categories of high energy neutrino (atmospheric
neutrino) events in SK
Event categories
Fully
Contained (FC)
(En ~1GeV)
Partially
Contained(PC)
(Eν~a few GeV)
Stopping m (En ~10GeV)
Through-going m (En ~100GeV)
upward going muon(upmu)
→ used for WIMP search
Eν（GeV）
Upward going muon (upmu) event in SK
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
Stopping m (En ~10GeV)
Through-going m
•Non-showering (En ~100GeV)
•Showering (En >1000GeV)
1
100
1e5
Neutrino energy (GeV)
9/18
Example of upward thru-going muon events
3, Upmu data in SK I/II/III phases
cosθSun distributions for up-mu events
•SKI~III upmu samples
Red:Atmospheric ν MC
(with oscillation)
sin22θ=1,
Δm2=2.5×10-3 eV
Cross: data
(3109.6 days <- 1679.6days@2004 SK result)
•Cos θSun = 1 means the direction of
the Sun
Data and MC are consistent.
Sun
Sun
Sun
Distributions of θsun
Stopping
0 degree = direction of the Sun
Red: Atmospheric ν MC
(with oscillation)
Cross: data
No significant excess was
observed here.
0-5
Non showering
0-5
0-10
0-15
0-20
0-10
0-15
0-20
0-25
0-30
0-20
0-25
0-30
θSun(degree)
Showering
0-25
θSun(Degree)
0-30
0-5
0-10
0-15
θSun(Degree)
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
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)
νe (total)
νμ(total)
ντ（total）
WIMP induced Neutrino flux
@ Earth 100 GeV WIMP
Cone half angle (deg.)
Energy spectrum of WIMP induced nu
bb (soft channel)
WIMP mass(GeV)
Estimate cone-angle (hard channel)
• 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)
νe(total)
νμ(total)
ντ（total）
WIMP induced Neutrino flux
@ Earth 100 GeV WIMP
Cone half angle(deg.)
Energy spectrum of WIMP induced nu
WW(hard channel)
WIMP mass(GeV)
Table for new cone angle for soft channel (SKI,II,III:3109.6 days)
A:Stopping upmu ,B: non-showering upmu C: showering upmu
C:MC
Expected
compositio
n of WIMP
induced
signal
(A:B:C)
200.3 39
33.7
98:2:0
19
22.5
5
3.8
78:16:6
2.7
8
7.2
1
1.4
59:29:12
1.9
7
4.6
1
0.9
28:52:20
Χ
mass
(GeV)
Cone A:dat
(deg a
.)
A:MC
B:dat
a
B:MC
10
30
63
62.5
184
100
10
10
6.7
1000
6
3
10000 5
1
C:dat
a
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.
Table for new cone angle for hard channel (SKI,II,III: 3109.6 days)
A:Stopping upmu ,B: non-showering upmu C: showering upmu
Cone
(deg.)
A:
data
A:
MC
B:
data
B:
MC
C:
data
C:
MC
Expected
composition
of WIMP
induced
signal
(A:B:C)
80.3
8
4
4.2
14
13.4
3
2.5
44:40:16
100
7
3
3.3
10
9.9
2
2.2
42:41:17
1000
3
0
0.5
2
2.1
1
0.3
40:41:19
10000
3
0
0.5
2
2.1
1
0.3
24:54:22
Χ
mass
(GeV)
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
WIMP
mass
(GeV)
θSun
Flux
(deg.) limit
×10-15
(cm2sec-1)
10
30
8.9
100
10
6.5
1000
6
3.8
10000
5
4.2
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+WWIMP
mass
(GeV)
θSun
Flux
(deg. limit
)
×1015
(cm2sec1)
Best limit was obtained below ~200 GeV WIMP
80.3
8
5.0
100
7
4.1
1000
3
2.5
10000
3
2.7
5, Limit of WIMP SD cross section
Translate into limit of WIMP SD cross section
Cross section/muon flux (cm2km2y)
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
10-38
limit from up-mu
flux limit.
10-39
bb
10-40
10-41
tt
W+W-
10-42
10-43
10-44
τ+τ-
Limit of spin-dependent(SD) cross section
WIMP
mass(GeV)
SD cross
section(Soft)
SD cross
section(Hard)
10
1.51×10-38
102
4.53×10-39
2.74×10-40
103
2.30×10-38
1.91×10-39
104
6.88×10-36
3.41×10-36
Considering to
explore
sub-10GeV region
Simulation code is
currently not
available yet.
Direct detection
This work
ν telescopes
For the low mass WIMP,
we got the good limit
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
∝ A2
coupling mainly to an un-paired nucleon:
C: accumulation rate
C0 : 5.7e15/s (sun)
ρDM = 0.3GeV/cc
vDM = 230km/s
Neutrinos From GC