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Dark Matter Searches at Baksan Underground Scintillator Telescope
M.M.Boliev, S.V.Demidov, O.V.Suvorova, S.P.Mikheev, INR RAS

16th Lomonosov Conference on Elementary Particle Physics 24 August 2013


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Outline

I Baksan Underground Scintillator Telescope (BUST) II Event selection III Signal simulation IV Sun survey by BUST V Results VI Conclusions


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Signal from DM annihilations in the Sun

DM particles scatter o nuclei in the Sun DM can become gravitationally trapped Accumulation and annihilation of DM in the center of the Sun Neutrino ux from the direction towards the Sun


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Baksan Neutrino Observatory

Baksan Underground Scintillator Telescope


Baksan Underground Scintillator Telescope


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Baksan Underground Scintillator Telescope
General view depth: 850 hg/cm size: 17 m

2

3150 tanks of size 70 cm

ç

17 m

ç

11 m

angular resolution: ab out 1.5 time resolution: 5 ns general trigger rate: 17 Hz

ç

70 cm

ç

30 cm



muon uxes upward/downward ratio:

10-

7

In op eration since 18 Decemb er 1978

Baksan Underground Scintillator Telescope


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Baksan Underground Scintillator Telescope

Baksan Underground Scintillator Telescope


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Time-of-ight method and event selection
time resolution is ab out 5 ns

S.P.Mikheev, 1984)

(Yu. Andreyev et al., 1979,

probability of imitation of wrong direction is considerably diminished if more then two planes involved two sp ecial triggers for upward muons: T1 - for zenith angle range

95 ? 180

, T2 - for almost horizontal events:

80 ? 100



Trigger T1

Trigger T2

3

2

3

scintillator planes negative

=2 =0

vertical scintillator planes horizontal scintillator planes ns (pathlength

t

external scintillator planes

t 30

10

m)

trigger rate 0.02 Hz (1800 events p er day)

Baksan Underground Scintillator Telescope


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Event selection: additional cuts
Cuts Level 1 Only one reconstructed track with

<0
with resp ect to least

Enter p oint should b e b elow exit p oint For T2: exclude events with shallow depth Cuts Level 2 Only through going tracks (no stopping muons or neutrino interactions inside) Muon range inside detector with

0 < < 180

>

500 g/cm

2 (excluded muons

EÅ < 1

GeV)

Geometrical cuts to exclude events close to plane edge (1.5 m)

Decemb er 1978 Novemb er 2009; livetime 24.12 yrs; 1700 muons after Cuts Level 1; 1255 muons after Cuts Level 2

-1.3 < 1/ < -0.7

(from MC: 95% of upward-going events)

Baksan Underground Scintillator Telescope


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MC simulation and reconstruction
O.Suvorova, M.Boliev, S.Mikheev et al., 1996

Neutrino

Muon

Muon energy threshold

EÅ > 1

GeV

Eciency of registration upward-going muon with

E >E

th is ab out

0.3

Baksan Underground Scintillator Telescope


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Signal simulation
DM particles can b ecome gravitationally trapp ed in the Sun (Anti)Neutrinos are pro duced in the result of DM annihilations pro duced in the center of the Sun Propagation of neutrinos in the Sun and Earth Exp ected muon ux from dark matter annihilation in the Sun

Å =

A ç 4 R 2

mDM

dEj P (Ej , Eth )
j , j ? Eth

dNj dEj

P (Ej , Eth ) - probability of neutrino-muon conversion, dNj dEj - sp ectra of neutrino at pro duction p oint - dep end on
annihilation channel: Benchmark channels: (hard sp ectrum)

... ? ? b b (soft

sp ectrum),

W +W

- and

+

-

Signal simulation


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Signal simulation: overview and parameters
We use our C program; compare results with WIMPsim (M.Blennow, J.Edsjo, T.Ohlsson, 2008) Initial neutrino spectra at the center of the Sun (M.Cirelli, N.Fornengo et al., Nucl.Phys. B727 (2005) 99) Annihilation point near the center of the Sun Neutrino oscillations, 3 ç 3 scheme (m21 = 7.63 Ç 10-5 eV2 , |m31 | = 2.55 Ç 10-3 eV2 , CP = 0, sin2 12 = 0.32, sin2 23 = 0.49, sin2 13 = 0.026, D.V. Forero, M. Tortola, J.W.F. Valle, arXiv:1205.4018 ) Matter eects: solar model, J.N.Bahcall, A.M.SerenelliÍ S.Basu (2005) NC and CC interactions (including -mass eects) in the Sun and the Earth: change in neutrino uxes and spectra neutrinos
regeneration:
-

+ ...,

-

, e , Å + ... - secondary ??

Signal simulation


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Comparison with WIMPsim: Å spectra at 1 a.u.
For the same initial neutrino sp ectra
10 WimpSim, Å at 1 a.u. our calculations, Å at 1 a.u.
+W W , mDM = 1000 GeV

10

WimpSim, Å at 1 a.u. our calculations, Å at 1 a.u.
+W W , mDM = 100 GeV

1 dN/dz (ann-1)

1 dN/dz (ann-1)

0.1

0.1

0.01

0.01

0.001 0.1 0.2 0.3 0.4 0.5 0.6 z=E/mDM 0.7 0.8 0.9 1

0.001 0.1 0.2 0.3 0.4 0.5 0.6 z=E/mDM 0.7 0.8 0.9 1

10

WimpSim, Å at 1 a.u. our calculations, Å at 1 a.u. +-, mDM = 100 GeV

10

WimpSim, Å at 1 a.u. our calculations, Å at 1 a.u. bb, mDM = 100 GeV

1 dN/dz (ann-1)

1 dN/dz (ann-1)

0.1

0.1

0.01

0.01

0.001 0.1 0.2 0.3 0.4 0.5 0.6 z=E/mDM 0.7 0.8 0.9 1

0.001 0.1 0.2 0.3 0.4 0.5 0.6 z=E/mDM 0.7 0.8 0.9 1

Signal simulation


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Muon ux calculation
Muons are produced in neutrino CC interactions Mean muon energy losses in rock (D.E.Groom, N.V.Mokhov, S.I.Striganov, 2001)
dE dx

Multiple Coulomb scattering
dNÅ/d (1/NÅ) dNÅ/d (1/NÅ) , mDM = 90 GeV
+-

= -((E ) + (E )E )

0.1 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02

0.07 0.06 0.05 0.04 0.03 0.02 0.01 bb, mDM = 90 GeV

0.01 0 0 5 10 15 20 25 30 (deg) 0 0 5 10 15 20 25 30 (deg)

Signal simulation


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Upward going muons:
Decemb er 1978 - Novemb er 2009; livetime 24.12 yrs, 1255 events Muon distribution with resp ect Event rate to p osition of the Sun
Å-Sun)

Rate (hour -1)*1000

14

120 1978-2009 100

12

10

dN/dCos(

80

8 60 6 40 4

2

20

0

1980

1985

1990

1995

2000

2005

2010

0 -1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

Years

Cos(

0.8

1
Å-Sun)

Ab out 50 events p er year

Direction

to

the

Sun

corresp onds to

cos Å-

Sun

=1

Data


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Data and expected background
Decemb er 1978 - Novemb er 2009; livetime 24.12 yrs Numb er Sun b elow horizon
100 90 80 70 60 50 40 Data 1978-2009 years with true Sun below H background

of

signal events

and inside

background cone half-angle


Data 1978-2009 Background

Å-Sun)

dN/dCos(

Nevents
1

60 50 40 30 20

30 20 10 0 -1

10 0 0 5 10 15 20

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

Cos(

0.8

Å-Sun)

Å

-Sun(

25 À)

Background from data with shifted p osition of the Sun

Data


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Optimization of analysis
In previous analysis we used cone half-angle of signal events



which contains 90%

Optimization

(Hill,

Rawlins,

2003);
16 14 12 , deg. 10 8 6 W+Wbb +-

exp ected limit on muon ux:

sensitivity =
where

? N 90 ( ) , x ( ) ç Seff (x ) ç T
is a fraction of event

x ( )

inside cone half-angle exp ected upp er limit

? , N

90 - mean

4 2 10 100 mDM, GeV 1000

The eective area:

Seff (Eth ) =

dEd S (E ,)ç (Eth ,E ,)çÅ (E ,) dEd (E ,)

Data


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Upper limits on muon uxes from DM annihilations
lim = Å
1e-10 1e-11 1e-12 1e-13 1e-14 1e-15 1e-16 10 100 mDM, GeV 1000

N 90 ( ) x ( )çSeff çT

, EÅ > 1 GeV;
Super-K 2011, W W Super-K 2011, bb IceCube 2012, hard IceCube 2012, bb ANTARES 2007-2008, W+WANTARES 2007-2008, bb ANTARES 2007-2008, ++Baikal 1998-2002, W W Baikal 1998-2002, bb Baikal 1998-2002, +Baksan 1978-2009, W+WBaksan 1978-2009, bb Baksan 1978-2009, ++ -

Results

Å, cm-2 s-1


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Recalculation to upper limits on SD
G. Wikstrom, J. Edsjo, 2009
Firstly, we recalculate In equilibrium b etween capture and annihilation pro cesses:

Å A

A = C

DM

/2

Capture rate is determined by the SI and SD elastic cross section of DM particles on nucleons (Gould, 1987) Recalculation

A

SD p

SI , p (Olga Suvorova, S.D., 2010)

A = SD + SI , A A
SD p

SD A

Ç Upp A

.Lim.

=

SD ,Upp .Lim. p

,

SI p

SI A

Ç Upp A

.Lim.

=

SI ,Upp .Lim. p

Upp er limits on SD cross sections are strong - a lot of hydrogen in the Sun

Results


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Upper limits on SD elastic cross section
1e-35 DAMA no channeling 2008 PICASSO 2012 KIMS 2011 SIMPLE 2011 D8: CMS qqj () D8: ATLAS qqj () ANTARES 2007-2008, W+W ANTARES 2007-2008, bb ANTARES 2007-2008 +Super-K 2011, W+WSuper-K 2011, bb IceCube 2012, hard IceCube 2012, bb Baikal 1998-2002, W+WBaikal 1998-2002, bb Baikal 1998-2002, +Baksan 1978-2009, W+WBaksan 1978-2009, bb +Baksan 1978-2009, 10 m 100 , GeV 1000

1e-36

-

1e-37
SD



p

, cm 1e-38 1e-39 1e-40

2

DM

Results


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Summary

Analysis of upward-going muon data collected for 24.11 years of livetime by neutrino exp eriment at Baksan Underground Scintillator Telescop e has b een p erformed No signicant excess was found in search for muon signal from dark matter annihilations in the Sun New limits on muon ux, annihilation rate, elastic cross sections

Conclusions


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Thank you!


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Backup slides


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Systematic uncertainties

Exp erimental uncertainties:

photomultipliers, season variations, dead tanks, ...). Neutrino oscillation parameters:

8

% (instability of work of

Neutrino nucleon cross section - up to 10% (even higher for

8%

for



+ -

5%

for

W +W

- and

? bb

,

E < 10

GeV)

For limits on SD and SI cross sections: astrophysical uncertainties (chemical comp osition of the Sun, lo cal dark matter density



, DM velo city distribution, ...)


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Comparison of upper limits for W + W
Comparable limits on muon uxes

-

and + - channels

Numb er of neutrinos (and antineutrinos) p er annihilation:

1.0

for

W +W

- and

Eect of oscillations

2.6

for

+

-

5 bb W+W+-

4
noosc osc

3

/Å, Å, 2 1 0 10 m
DM,

100 GeV

1000


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Upper limits on SI elastic cross section
1e-38

1e-39 DAMA no channeling 2008 CoGeNT 2010 XENON100 2012 CDMS 2010 ANTARES 2007-2008, W+WANTARES 2007-2008, bb ANTARES 2007-2008 +IceCube 2013, hard IceCube 2013, bb Baksan 1978-2009, W+WBaksan 1978-2009, bb Baksan 1978-2009, +-

1e-40



p

SI

, cm2

1e-41

1e-42

1e-43

1e-44

1e-45 10 m
DM

100 , GeV

1000