PRL 114, 141301 (2015)

PHYSICAL REVIEW LETTERS

week ending
10 APRIL 2015

Search for Neutrinos from Annihilation of Captured Low-Mass Dark Matter Particles
in the Sun by Super-Kamiokande
K. Choi,19,* K. Abe,1,30 Y. Haga,1 Y. Hayato,1,30 K. Iyogi,1 J. Kameda,1,30 Y. Kishimoto,1,30 M. Miura,1,30 S. Moriyama,1,30
M. Nakahata,1,30 Y. Nakano,1 S. Nakayama,1,30 H. Sekiya,1,30 M. Shiozawa,1,30 Y. Suzuki,1,30 A. Takeda,1,30 T. Tomura,1,30
R. A. Wendell,1,30 T. Irvine,2 T. Kajita,2,30 I. Kametani,2 K. Kaneyuki,2,30 K. P. Lee,2 Y. Nishimura,2 K. Okumura,2,30
T. McLachlan,2 L. Labarga,3 E. Kearns,4,30 J. L. Raaf,4 J. L. Stone,4,30 L. R. Sulak,4 S. Berkman,5 H. A. Tanaka,5
S. Tobayama,5 M. Goldhaber,6 G. Carminati,7 W. R. Kropp,7 S. Mine,7 A. Renshaw,7 M. B. Smy,7,30 H. W. Sobel,7,30
K. S. Ganezer,8 J. Hill,8 N. Hong,9 J. Y. Kim,9 I. T. Lim,9 T. Akiri,10 A. Himmel,10 K. Scholberg,10,30 C. W. Walter,10,30
T. Wongjirad,10 T. Ishizuka,11 S. Tasaka,12 J. S. Jang,13 J. G. Learned,14 S. Matsuno,14 S. N. Smith,14 T. Hasegawa,15
T. Ishida,15 T. Ishii,15 T. Kobayashi,15 T. Nakadaira,15 K. Nakamura,15,30 Y. Oyama,15 K. Sakashita,15 T. Sekiguchi,15
T. Tsukamoto,15 A. T. Suzuki,16 Y. Takeuchi,16 C. Bronner,17 S. Hirota,17 K. Huang,17 K. Ieki,17 M. Ikeda,17 T. Kikawa,17
A. Minamino,17 T. Nakaya,17,30 K. Suzuki,17 S. Takahashi,17 Y. Fukuda,18 Y. Itow,19 G. Mitsuka,19 P. Mijakowski,20
J. Hignight,21 J. Imber,21 C. K. Jung,21 C. Yanagisawa,21 H. Ishino,22 A. Kibayashi,22 Y. Koshio,22 T. Mori,22 M. Sakuda,22
T. Yano,22 Y. Kuno,23 R. Tacik,24,32 S. B. Kim,25 H. Okazawa,26 Y. Choi,27 K. Nishijima,28 M. Koshiba,29 Y. Totsuka,29
M. Yokoyama,29,30 K. Martens,30 Ll. Marti,30 M. R. Vagins,30,7 J. F. Martin,31 P. de Perio,31 A. Konaka,32 M. J. Wilking,32
S. Chen,33 Y. Zhang,33 and R. J. Wilkes34(Super-Kamiokande Collaboration)
1

Kamioka Observatory, Institute for Cosmic Ray Research, University of Tokyo, Kamioka, Gifu 506-1205, Japan
Research Center for Cosmic Neutrinos, Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan3
Department of Theoretical Physics, University Autonoma Madrid, 28049 Madrid, Spain
4
Department of Physics, Boston University, Boston, Massachusetts 02215, USA
5
Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T1Z4, Canada
6
Physics Department, Brookhaven National Laboratory, Upton, New York 11973, USA
7
Department of Physics and Astronomy, University of California, Irvine, Irvine, California 92697-4575, USA
8
Department of Physics, California State University, Dominguez Hills, Carson, California 90747, USA
9
Department of Physics, Chonnam National University, Kwangju 500-757, Korea
10
Department of Physics, Duke University, Durham North Carolina 27708, USA
11
Junior College, Fukuoka Institute of Technology, Fukuoka, Fukuoka 811-0295, Japan
12
Department of Physics, Gifu University, Gifu, Gifu 501-1193, Japan
13
GIST College, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea
14
Department of Physics and Astronomy, University of Hawaii, Honolulu, Hawaii 96822, USA
15High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
16
Department of Physics, Kobe University, Kobe, Hyogo 657-8501, Japan17
Department of Physics, Kyoto University, Kyoto, Kyoto 606-8502, Japan18
Department of Physics, Miyagi University of Education, Sendai, Miyagi 980-0845, Japan
19
Solar Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi 464-8602, Japan
20
National Centre For Nuclear Research, 00-681 Warsaw, Poland
21
Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794-3800, USA
22
Department of Physics, Okayama University, Okayama, Okayama 700-8530, Japan
23
Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
24
Department of Physics, University of Regina, 3737 Wascana Parkway, Regina, Saskatchewan S4SOA2, Canada
25
Department of Physics, Seoul National University, Seoul 151-742, Korea
26
Department of Informatics in Social Welfare, Shizuoka University of Welfare, Yaizu, Shizuoka 425-8611, Japan
27
Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea
28
Department of Physics, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan
29
The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan
30
Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, University of Tokyo,
Kashiwa, Chiba 277-8582, Japan
31
Department of Physics, University of Toronto, 60 Street, Toronto, Ontario M5S1A7, Canada
32
TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T2A3, Canada
33
Department of Engineering Physics, Tsinghua University, Beijing 100084, China
34
Department of Physics, University of Washington, Seattle, Washington 98195-1560, USA(Received 8 January 2015; published 6 April 2015)
20031-9007=15=114(14)=141301(6)141301-1© 2015 American Physical Society

PRL 114, 141301 (2015)

PHYSICAL REVIEW LETTERS

week ending
10 APRIL 2015

Super-Kamiokande (SK) can search for weakly interacting massive particles (WIMPs) by detecting
neutrinos produced from WIMP annihilations occurring inside the Sun. In this analysis, we include
neutrino events with interaction vertices in the detector in addition to upward-going muons produced in thesurrounding rock. Compared to the previous result, which used the upward-going muons only, the signal
acceptances for light (few-GeV=c2 -200-GeV=c2 ) WIMPs are significantly increased. We fit 3903 days of
SK data to search for the contribution of neutrinos from WIMP annihilation in the Sun. We found no
significant excess over expected atmospheric-neutrino background and the result is interpreted in terms ofupper limits on WIMP-nucleon elastic scattering cross sections under different assumptions about theannihilation channel. We set the current best limits on the spin-dependent WIMP-proton cross section for
WIMP masses below 200 GeV=c2 (at 10 GeV=c2 , 1.49 × 10−39 cm2 for χχ → bb̄ and 1.31 × 10−40 cm2for χχ → τþ τ− annihilation channels), also ruling out some fraction of WIMP candidates with spinindependent coupling in the few-GeV=c2 mass range.
DOI: 10.1103/PhysRevLett.114.141301

PACS numbers: 95.35.+d, 14.80.Nb, 96.50.S-, 98.70.Sa

Weakly interacting massive particles (WIMPs) arefavored as particle candidates for nonbaryonic cold dark
matter (DM), as their interaction strength can explain thethermal relic abundance of DM [1–3]. A promising way toidentify a WIMP DM particle is to search for excess
neutrino flux generated by WIMP self-annihilations inside
the Sun [4–7] (WIMP neutrinos). As the Sun travels on the
Milky Way arm, WIMPs in the DM halo could occasionallybecome gravitationally bound after losing energy byscattering off nuclei in the Sun. The WIMPs then pairannihilate in the deep solar core, producing neutrinos fromdecays of the annihilation products which propagate outward through the Sun and may be detected in terrestrial
neutrino detectors. An excess of a high-energy neutrinos
from the Sun, with energies much greater than the ∼O(10 MeV) solar-fusion neutrinos, observed in neutrino
detectors can be interpreted in terms of WIMP annihilation
rate. We assume that WIMPs annihilate via a single channel
to a pair of fermions or bosons. Also, we assume that the
WIMP capture and annihilation rates are in equilibrium,
which enables us to remove the WIMP-annihilation crosssection dependence and allows comparison to direct detection results on WIMP-nucleon elastic scattering crosssection.
Thanks to the hydrogen-rich composition and large
gravity of the Sun, tight limits on the spin-dependent(SD) scattering cross section of WIMPs on protons havebeen placed by neutrino telescopes such as SuperKamiokande (SK) [8], IceCube [9], Baksan [10], and
ANTARES [11]. Recent event excesses or annual modulation signals reported by direct detection experiments suchas DAMA/LIBRA [12], CoGeNT [13], CRESST [14],CDMS II Si [15] and conflicting null results from otherdirect- and indirect-detection experiments motivate a careful search for light WIMPs below 30 GeV=c2. As typicalresulting neutrino energies are roughly one-third to onehalf of the WIMP mass [2] or lower, the SK detector’ssensitivity to few-GeV neutrinos makes it suitable for thissearch [16–19].

Super-Kamiokande is a cylindrical water Cherenkov
detector located in the Kamioka mine in Japan. The innerdetector (ID) of 22.5 kton fiducial volume is instrumented
with 11 129 20-in. Hamamatsu photomultiplier tubes(PMTs) and the outer detector (OD) is instrumented with
1885 8-in. PMTs for use as a veto. Information about theexperimental setup of the detector and its calibration, data
reduction, and event reconstruction can be found elsewhere[20–22].
The SK high-energy neutrino data include neutrino
events with visible energy > 30 MeV and are divided into
three categories: among contained events in which theneutrino interacts inside the ID, fully contained (FC) events
have observed Cherenkov light entirely contained in the ID,
partially contained (PC) events additionally have an exiting
particle that deposits energy in the OD. Upward-going
muons (up-μ) are produced by neutrino interactions in therocks and water surrounding the detector. FC events are
distributed in seven sub-GeV (visible energy < 1.33 GeV)and six multi-GeV (visible energy > 1.33 GeV) subcategories, and then further divided based on particle identification (e-like or μ-like), number of reconstructed
Cherenkov rings, number of decay electrons, and so on.
PC events are classified as “OD stopping” or “OD throughgoing” based on their energy deposition in the OD. Up μ’s
either stop in the detector (stopping) or pass through thedetector (through-going). Through-going up-μ events arefurther divided into “showering” and “nonshowering”
categories [23].
A signal from a 10-GeV=c2 WIMP will mostly fall in the
FC sub-GeV and multi-GeV samples, and heavier WIMP
signals will be mainly distributed in the PC and up-μ
categories. To increase signal acceptance for light WIMPs,FC and PC events are included in the WIMP search sample.
We take into account all neutrino flavors (νμ , ν̄μ , νe , ν̄e , ντ ,and ν̄τ ). Compared to the previous analysis [8], which used
up-μ events only, the signal acceptance has increased 47
times for the 10-GeV=c2 bb̄ channel.
The analysis in this Letter uses data accumulated during
the SK I–IV run periods. The SK-I (1996–2001), SK-II

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(2002–2005, with half PMT coverage), and SK-III (2006–2008) periods correspond to 1489, 799, and 518 days oflive time for the FC and PC samples, and 1646, 828, and636 days of live time for the up-μ sample, respectively. The
SK-IV period started in 2008; this analysis uses 1096.7 live
days of FC, PC, and up-μ data collected until March 2012.
The Monte Carlo simulation [21,24] originally generated
for the primary atmospheric neutrino flux [25] is divided
into two independent samples and is used for two purposes:
first, to predict atmospheric-neutrino background, andsecond, to produce the WIMP neutrino signal by reweighting to match the signal flux and spectrum. To predict theatmospheric-neutrino background, a 250-year MC sample
per SK run period is normalized to the live time of each SK
run period and oscillated with parameters sin2 θ13 ¼ 0.025,
sin2 θ12 ¼ 0.304, sin2 θ23 ¼ 0.425, Δm221 ¼ 7.66 × 10−5 eV2 ,and Δm232 ¼ 2.66 × 10−3 eV2 . In the other 250 years of
MC sample per run period, events coming approximatelyfrom the solar direction are selected and then weighted by
the ratio of WIMP neutrino flux to original atmosphericneutrino flux. To simulate the neutrino flux from WIMP
annihilation in the Sun at SK, we used the WIMP MC
simulator WIMPSIM 3.01 [26]. Focusing on the light
WIMP search, we considered WIMP masses from 4 to
200 GeV=c2 for χχ → τþ τ− =bb̄=W þ W − channels. The
spectrum of the bb̄ channel is “softest” and the τþ τ−
channel produces a “harder” spectrum.
In order to discriminate the large background of atmospheric neutrinos at low energies, which have an ∝ E−2.7
power-law spectrum, and to take into account the energydependent angular correlation for low-energy events, we
perform a least-squares fit which makes full use of the800

Sub-GeV angle

energy, angle, and flavor information. Under the hypothesisthat the collected SK data consist of both atmospheric
neutrinos and WIMP neutrinos, we compare data to MC
calculations. The data and MC calculations in the 18
subcategories are distributed into 480 bins based onreconstructed momentum and cos θsun , where θsun is theangle between the Sun and the reconstructed event direction. Figure 1 shows an example of data distributions
compared to the expected WIMP-induced signal. We fit thedata using the least-squares technique based on Poisson
statistics to find the amount of signal contribution added tobackground that best matches the data. For each mass andannihilation channel, the energy spectrum and flavor
composition of signal neutrino flux are fixed and theglobal normalization of the signal flux is allowed to vary
freely. The “pull” approach allows us to incorporate
systematic uncertainties [27] in the fitting as
 X
N
exp
data
χ ¼ min 2
fN expþ N datalnðN dataii =N i Þg
i − Ni
2

fϵj g

i¼1

J  2 
X
ϵj
þ
;
σj
j¼1

where




J
J
X
X
χ
BG
i
i
1
þ
þ
βN
1
þ
¼
N
f
ϵ
g
ϵ
N exp
i
j j
j j ;
i
i
j¼1

400

PC + stopping muon angle

Multi-GeV angle

0

400

0.5

0
-1

1

Cosθsun

Sub-GeV energy

4000

4000

2000

0
10-1

1

momentum [GeV/c]

-0.5

0

0.5

0
-1

1

-0.5

CosθsunEventsEvents

6000

200
100

200

600

Multi-GeV energy
Events

-0.5

300

600

EventsEventsEvents0-1

SK I-IV data
Background MC
Signal MC(6 GeV/c2 bb )Signal MC(200 GeV/c2 τ+τ-)j¼1

is the number of eventsand i is the index of the bins, N datai
observed in each bin, N BG
isthebackgroundexpectation in
i

2000

1000

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PHYSICAL REVIEW LETTERS

PRL 114, 141301 (2015)

2000

0
1

10

momentum [GeV/c]1020Cosθsun0.5

1

Through-going muon angle

400
200
0
-1

-0.5

0

0.5

1

CosθsunFIG. 1 (color online). Angular and reconstructed momentum [GeV=c] distributions of SK I–IV data (black crosses), atmosphericneutrino background MC events (normalized to data live time, blue solid line), WIMP neutrino signal MC events for the 6-GeV=c2 bb̄
channel (magenta dotted line) and the 200-GeV=c2 τþ τ− channel (cyan dashed line) at 90% upper limit, magnified 30 times forvisibility. Among seven sub-GeV samples, the single-ring e-like 0-decay-electron and μ-like 0,1-decay-electron samples are combined
and shown in the left-hand column. In the middle column, six multi-GeV samples are combined and shown. PC and up-μ samples areshown in the right-hand column.

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PRL 114, 141301 (2015)

TABLE I. χ 2min , Δχ 2 at β ¼ 0, Δχ 290 (Δχ 2 for 90% Bayesian upper limit), 90% upper limit on the muon-neutrino flux from WIMP
annihilations in the Sun at SK and SD, SI, and IVDM scattering cross section limits for each WIMP mass and annihilation channel.
mχ(GeV=c2 )
4
6
10
20
50
80.3
100

200

Annihilation
channelχ 2minΔχ 2 at
β¼0

τþ τ−
bb̄
τþ τ−
bb̄
τþ τ−
bb̄
τþ τ−
bb̄
τþ τ−
WþW−
bb̄
WþW−
τþ τ−
bb̄
WþW−
τþ τ−

508.1
507.8
507.8
507.4
507.6
507.4
509.0
509.0
508.9
508.8
509.0
508.9
508.9
508.9
508.9
508.9

0.87
1.24
1.25
1.65
1.40
1.65
0.06
0.04
0.14
0.17
0.06
0.14
0.16
0.12
0.07
0.08

Δχ 290νμσ SD;p(Bayesian) (×1012 km−2 y−1 ) (×10−40 cm2 )
4.4
4.9
4.9
5.4
5.1
5.4
2.4
3.0
2.3
2.3
2.4
2.3
2.3
2.3
2.4
2.4

150
294
70.8
140
31.0
53.1
13.2
19.8
2.67
1.09
7.54
0.63
0.70
2.81
0.17
0.19

the bin, N χi is the number of events of signal MC in the bin,where β, the global normalization parameter for signal,
stands for the allowed fraction of signal, σ j is the 1σ valueof the jth systematic uncertainty, ϵj is its pull, and f ij =σ j(gij =σ j ) is the predicted fractional change of the number ofbackground (signal) events in the ith bin due to a 1σ changeof the jth systematic uncertainty. In the pull approach, χ 2 isestimated by solving δχ 2 =δϵj ¼ 0 for all ϵj ’s [27].
For background (signal), 66 (48) sources of systematic
uncertainties are considered. A total of 16 systematic
uncertainties related to neutrino interaction in SK areconsidered in common for both background and signal.
Another 14 uncertainty sources related to event reduction
and 11 sources related to event reconstruction and selection
are calculated for SK I, II, III, and IV independently andconsidered for both signal and background. For background MC events, a total of 25 uncertainties related tothe prediction of atmospheric-neutrino flux, including 1σ
uncertainties on oscillation parameters, are considered. All
the uncertainties in neutrino interaction, event reduction,
reconstruction, selection, and background atmosphericneutrino flux are similar to those described in Ref. [28]except the ones related to zenith angle distributions. These
uncertainties are listed elsewhere (for example, Tables VI,
VII, and VIII in Ref. [28]). For signal MC events, seven
uncertainties related to the oscillation of WIMP neutrinos
during propagation through the Sun, vacuum, and Earth areconsidered. The full systematic uncertainty has up to a 10%
effect on the WIMP sensitivity, where the largest contributions come from neutrino interaction and atmosphericneutrino flux uncertainties.
The best-fit value of β, βmin is defined as the value atwhich χ 2 is minimized with respect to β. For all tested
WIMP hypotheses, we found the resulting βmin values are

2.22
17.2
1.63
14.9
1.31
14.3
1.42
23.4
1.28
3.13
31.9
2.80
1.24
44.9
3.00
1.33

σ SI;p (fn =f p ¼ 1) (fn =f p ¼ −0.7)(×10−43 cm2 )(×10−41 cm2 )
87.3
456
44.5
240
21.2
120
11.9
89.9
4.92
8.26
71.3
6.26
2.76
63.4
4.23
1.88

24.5
128
12.2
67.5
5.95
44.8
4.47
39.0
2.14
3.73
32.7
2.87
1.26
30.4
2.03
0.90

all consistent with the hypothesis of no WIMP neutrino
contribution, and we set 90% upper limits assuming that theobtained χ 2 values approximately follow a normal distribution. To set a physically meaningful confidence limit, wefollow a Bayesian approach [29] and renormalize the βdistribution in the physically allowed region (β > 0). The
fitted χ 2 values at minimum (χ 2min ; DOF is 479), the Δχ 2
value at β ¼ 0 from the minimum, and the Δχ 2 values for
90% upper limit (Δχ 290 ) calculated with the Bayesian
approach are shown in Table I for the tested WIMP mass
and annihilation channels.
Figure 2 shows the derived 90% upper limit on the
muon-neutrino flux from WIMP annihilations in the Sun at
SK. The limit shown here for νμ is an example; limits onother flavors or antineutrinos are determined by appropriate
flavor scaling for the given WIMP annihilation channel
assumption. The sensitivity study was done by substituting
SK data with 500 sets of toy MC data generated for the
hypothesis of no WIMP-annihilation contribution and theresult is shown together in Fig. 2 as a band representing a
1σ range of results.
Using DARKSUSY 5.0.6 [30], we convert the upper limiton the neutrino flux to upper limits on WIMP-nucleon crosssections. We assume that WIMPs have only a single type ofinteraction with a nucleus, either an axial vector interactionin which WIMPs couple to the nuclear spin (SD) or a scalarinteraction in which WIMPs couple to the nucleus mass
[spin independent (SI)]. The SI coupling can have different
couplings to neutrons (f n ) and protons (f p ). We consider
two representative examples: the commonly assumed
isospin-invariant case (f n =fp ¼ 1) and the case of isospin-violating dark matter (IVDM) [31] with destructive
interference f n =f p ¼ −0.7 [32–35]. The latter is calculated
based on Ref. [36]. Also assumed are a standard DM halo

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muon neutrino flux[/km2/y]

1015

1014

1013

1012

τ+τ10

W+ W

bb

-

102

WIMP mass [GeV/c2]

FIG. 2 (color online). The 90% upper limit on total integrated
muon-neutrino flux from WIMP annihilations in the Sun at SK
for the τþ τ− channel in red solid line, bb̄ in green dashed line,
W þ W − in blue dot-dashed line. The shadowed regions show 1σbands of the sensitivity study results (color scheme is the same asfor data).

There are several sources of uncertainties related to the
WIMP capture process. Uncertainty in the composition of
the Sun is considered by comparing the DARKSUSY
default choice BS2005-OP model with the BS2005AGS,OP model [47] with lower heavy element abundances.
For the uncertainty in the nuclear form factor, we comparedthe Helm-Gould form factor [7] used in DARKSUSY to the
choices in Refs. [48,49]. These effects are predicted to besmall in the SD-coupling case and up to 25%, 45%
respectively in the SI-coupling case where heavier elements
than hydrogen contribute to the capture. The effect of
uncertainties in the velocity distribution of WIMPs isdetermined in Ref. [50] to be up to 40% (25)% for SD(SI) couplings. The effects of the planets on the capture rateis determined to be negligible [51,52]. Solar evaporation is
expected to have no impact above a WIMP mass of
4 GeV=c2 [16,53–55]. These uncertainties are added inquadrature and indicated by the shadowed regions in
Figs. 3 and Fig. 4. Uncertainty in the local WIMP density
will make a similar vertical shift of the limits for all direct
and indirect detection experiments, and so is not indicated.
In conclusion, the result of the first WIMP search using
contained events in SK is presented. No significant signal
excess was found for 4–200 GeV=c2 WIMP hypotheses.
The derived upper limit on the SD WIMP-proton crosssection places the most stringent constraint to date for
WIMP masses below 200 GeV=c2 even for the softest (bb̄)
channel, assuming the equilibrium condition between
WIMP-nucleon SI Cross section [cm -2 ]WIMP-proton SD Cross section [cm-2]

with local density 0.3 GeV=cm3 [37,38], a Maxwellian
velocity distribution with a rms velocity of 270 km=s, and asolar rotation speed of 220 km=s. The results are listed inTable I. They are also plotted together with other experimental results in Fig. 3 for SD coupling and Fig. 4 for SI
coupling for the isospin-invariant case. For IVDM, we notethat for the result given in the Table I, the entire CDMS II Si[15] 90% C.L. signal region will be in tension with ourτþ τ− channel result.

10-35
DAMA/LIBRA

10-36
-37

10

SIMPLE

IceCube (bb)

PICASSOBAKSAN (bb)

-38

10

+

-

IceCube (τ +τ -/W W )-39

10

SK (bb)++ -BAKSAN (τ τ )SK (τ+τ- )+-BAKSAN (W W )-SK (W W )

-40

10

10-41

10

-39

10

XENON10 S2-only

WIMP mass [GeV/c 2]

102

FIG. 3 (color online). 90% C.L. upper limits on SD WIMPproton cross section calculated at DARKSUSY [30] default are
shown in red solid line with uncertainty bands to take account of
uncertainties in the capture rate for the bb̄, W þ W − , and τþ τ−
channels from top to the bottom. Also shown are limits from otherexperiments. IceCube [9] in brown dashed line: bb̄ (top) / W þ W −or τþ τ− (bottom); BAKSAN [10] in pink dot-dashed line: bb̄(top), W þ W − (middle), τþ τ− (bottom); PICASSO [39] (bluelong-dashed line); SIMPLE [40] (green long dot-dashed line).
The black shaded region is the 3σ C.L. signal claimed by DAMA/LIBRA [12,41].

IceCube (b b )-40

DAMA/LIBRA
CoGeNTCDMSlite

SK (bb)10-41

SK (τ+τ- )10

10

IceCube (τ + τ - /W + W - )+-SK (W W )-42

CDMS II Si-43

XENON100
LUX

10

10

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SuperCDMSCRESSTIIWIMP mass [GeV/c 2]

102

FIG. 4 (color online). 90% C. L. upper limits on the SI WIMPnucleon cross section (plotting scheme is the same as Fig. 3).
Also shown are event excesses or annual modulation signals
reported by other experiments: DAMA/LIBRA (black shaded
regions, 3σ C.L.); CoGeNT [13] (magenta diagonally crosshatched region, 90% C.L.); CRESSTII [14] (violet horizontallyshaded regions, 2σ C.L.); CDMS II Si [15] (blue vertically shaded
region, 90% C.L.); and limits: IceCube [9] in brown dashed line:bb̄ (top), W þ W − or τþ τ− (bottom); SuperCDMS [42] (cyandotted line); CDMSlite [43] (blue long dot-dashed line);
XENON10 S2-only [44] (dark green dash triple dotted line);
XENON100 [45] (green dash double dotted line); LUX [46](orange long-dashed line).

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PHYSICAL REVIEW LETTERS

capture and annihilation rates. For the SI-coupling casewith 100% annihilation to τþ τ− , we exclude new regions
for WIMP masses below 6 GeV=c2.
We gratefully acknowledge cooperation of the Kamioka
Mining and Smelting Company. The Super-Kamiokande
experiment was built and has been operated with funding
from the Japanese Ministry of Education, Culture, Sports,
Science and Technology, the U.S. Department of Energy,
and the U.S. National Science Foundation.

*

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