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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
I DM particles scatter o� nuclei in the Sun
I DM can become gravitationally trapped
I Accumulation and annihilation of DM in the center of theSun
I Neutrino �ux from the direction towards the Sun
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Baksan Neutrino Observatory
Baksan Underground Scintillator Telescope
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Baksan Underground Scintillator Telescope
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Baksan Underground Scintillator Telescope
I depth: 850 hg/cm2
I size: 17 m × 17 m × 11 m
I 3150 tanks of size70 cm × 70 cm × 30 cm
I angular resolution: about 1.5◦
I time resolution: 5 ns
I general trigger rate: 17 Hz
I muon �uxes upward/downwardratio: ∼ 10−7
General view
In operation since 18 December 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
I time resolution is about 5 ns (Yu. Andreyev et al., 1979,
S.P.Mikheev, 1984)
I probability of imitation of �wrong� direction is considerablydiminished if more then two planes involved
I two special triggers for upward muons: T1 - for zenith anglerange 95◦÷180◦, T2 - for almost horizontal events: 80◦÷100◦
Trigger T1
I ≥ 3 scintillator planes
I ≥ 2 negative ∆t
I ≤ 3 external scintillator planes
Trigger T2
I = 2 vertical scintillator planes
I = 0 horizontal scintillator planes
I ∆t ≥ 30 ns (pathlength ≥ 10 m)
trigger rate 0.02 Hz (1800 events per day)
Baksan Underground Scintillator Telescope
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Event selection: additional cuts
Cuts Level 1
I Only one reconstructed track with β < 0
I Enter point should be below exit point
I For T2: exclude events with 0 < φ < 180 with respect to leastshallow depth
Cuts Level 2
I Only through going tracks (no stopping muons or neutrinointeractions inside)
I Muon range inside detector > 500 g/cm2 (excluded muonswith Eµ < 1 GeV)
I Geometrical cuts to exclude events close to plane edge (1.5 m)
I −1.3 < 1/β < −0.7 (from MC: 95% of upward-going events)
December 1978 � November 2009; livetime 24.12 yrs;1700 muons after Cuts Level 1; 1255 muons after Cuts Level 2
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 Eµ > 1 GeV
E�ciency of registration upward-going muon with E > Eth is about 0.3
Baksan Underground Scintillator Telescope
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Signal simulation
I DM particles can become gravitationally trapped in the Sun
I (Anti)Neutrinos are produced in the result of DM annihilationsproduced in the center of the Sun
I Propagation of neutrinos in the Sun and Earth
I Expected muon �ux from dark matter annihilation in the Sun
Φµ =ΓA
4πR2×
∑νj ,ν̄j
∫ mDM
Eth
dEνjP(Eνj ,Eth)dNνj
dEνj
P(Eνj ,Eth) - probability of neutrino-muon conversion,
IdNνj
dEνj- spectra of neutrino at production point - depend on
annihilation channel: χχ̄→ ...
I Benchmark channels: bb̄ (soft spectrum), W+W− and τ+τ−
(hard spectrum)
Signal simulation
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Signal simulation: overview and parameters
I We use our C program; compare results with WIMPsim(M.Blennow, J.Edsjo, T.Ohlsson, 2008)
I Initial neutrino spectra at the center of the Sun (M.Cirelli,N.Fornengo et al., Nucl.Phys. B727 (2005) 99)
I Annihilation point near the center of the Sun
I Neutrino oscillations, 3× 3 scheme (∆m21 = 7.63 · 10−5 eV2,
|∆m31| = 2.55 · 10−3 eV2, δCP = 0, sin2 θ12 = 0.32, sin2 θ23 = 0.49,
sin2 θ13 = 0.026, D.V. Forero, M. Tortola, J.W.F. Valle, arXiv:1205.4018 )
I Matter e�ects: solar model, J.N.Bahcall, A.M.Serenelli½ S.Basu(2005)
I NC and CC interactions (including τ -mass e�ects) in the Sun andthe Earth: change in neutrino �uxes and spectra
I ντ regeneration: ντ → τ− + ..., τ− → ντ , ν̄e , ν̄µ + ... - secondaryneutrinos
Signal simulation
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Comparison with WIMPsim: νµ spectra at 1 a.u.
For the same initial neutrino spectra
0.001
0.01
0.1
1
10
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
dNν/
dz (
ann-1
)
z=Eν/mDM
b b, mDM = 100 GeV
WimpSim, νµ at 1 a.u.our calculations, νµ at 1 a.u.
0.001
0.01
0.1
1
10
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
dNν/
dz (
ann-1
)
z=Eν/mDM
W+W-, mDM = 100 GeV
WimpSim, νµ at 1 a.u.our calculations, νµ at 1 a.u.
0.001
0.01
0.1
1
10
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
dNν/
dz (
ann-1
)
z=Eν/mDM
τ+τ-, mDM = 100 GeV
WimpSim, νµ at 1 a.u.our calculations, νµ at 1 a.u.
0.001
0.01
0.1
1
10
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
dNν/
dz (
ann-1
)
z=Eν/mDM
W+W-, mDM = 1000 GeV
WimpSim, νµ at 1 a.u.our calculations, νµ at 1 a.u.
Signal simulation
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Muon �ux calculation
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0 5 10 15 20 25 30
dNµ/
dγ (
1/N
µ)
γ (deg)
τ+
τ-, mDM = 90 GeV
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0 5 10 15 20 25 30
dNµ/
dγ (
1/N
µ)
γ (deg)
b b, mDM = 90 GeV
I Muons are produced in neutrino CC interactions
I Mean muon energy losses in rock (D.E.Groom, N.V.Mokhov,S.I.Striganov, 2001)
〈 dEdx 〉 = −(α(E ) + β(E )E )ρ
I Multiple Coulomb scattering
Signal simulation
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Upward going muons:
December 1978 - November 2009; livetime 24.12 yrs, 1255 events
Years1980 1985 1990 1995 2000 2005 2010
)*10
00-1
Rat
e (h
our
0
2
4
6
8
10
12
14
)-SunµΨCos(-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
)-S
unµ
ΨdN
/dC
os(
0
20
40
60
80
100
120
1978-2009
Event rateMuon distribution with respectto position of the Sun
About 50 events per year Direction to the Suncorresponds to cos Ψµ−Sun = 1
Data
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Data and expected background
December 1978 - November 2009; livetime 24.12 yrs
)-SunµΨCos(-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
)-S
unµ
ΨdN
/dC
os(
0
10
20
30
40
50
60
70
80
90
100
Data 1978-2009 years with true Sun below Hbackground
0
10
20
30
40
50
60
0 5 10 15 20 25
Nev
ents
Ψµ-Sun(°)
Data 1978-2009Background
Sun below horizon
Number of signal andbackground events insidecone half-angle γ
Background � from data with shifted position of the Sun
Data
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Optimization of analysis
In previous analysis we used cone half-angle γ which contains 90%of signal events
Optimization (Hill, Rawlins, 2003);expected limit on muon �ux:
sensitivity =N̄90(γ)
x(γ)× Seff (x)× T,
where x(γ) is a fraction of eventinside cone half-angle γ, N̄90 - meanexpected upper limit
2
4
6
8
10
12
14
16
10 100 1000
γ, d
eg.
mDM, GeV
W+W
-
b bτ+τ-
The e�ective area: Seff (Eth) =∫
dEdθ S(E ,θ)×ε(Eth,E ,θ)×Φµ(E ,θ)∫dEdθ Φ(E ,θ)
Data
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Upper limits on muon �uxes from DM annihilations
1e-16
1e-15
1e-14
1e-13
1e-12
1e-11
1e-10
10 100 1000
Φµ,
cm
-2 s
-1
mDM, GeV
Super-K 2011, W+W
-
Super-K 2011, b b
IceCube 2012, hard
IceCube 2012, b b
ANTARES 2007-2008, W+W
-
ANTARES 2007-2008, b b
ANTARES 2007-2008, τ+τ-
Baikal 1998-2002, W+W
-
Baikal 1998-2002, b b
Baikal 1998-2002, τ+τ-
Baksan 1978-2009, W+W
-
Baksan 1978-2009, b b
Baksan 1978-2009, τ+τ-
Φlimµ = N90(γ)
x(γ)×Seff×T, Eµ > 1 GeV;
Results
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Recalculation to upper limits on SD
G. Wikstrom, J. Edsjo, 2009
I Firstly, we recalculate Φµ → ΓA
I In equilibrium between capture and annihilation processes:ΓA = CDM/2
I Capture rate is determined by the SI and SD elastic crosssection of DM particles on nucleons (Gould, 1987)
I Recalculation ΓA → σSDp , σSI
p (Olga Suvorova, S.D., 2010)
ΓA = ΓSDA + ΓSI
A ,
σSDp
ΓSDA
· ΓUpp.Lim.A = σSD,Upp.Lim.
p ,σSI
p
ΓSIA
· ΓUpp.Lim.A = σSI ,Upp.Lim.
p
I Upper limits on SD cross sections are strong - a lot ofhydrogen in the Sun
Results
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Upper limits on SD elastic cross section
1e-40
1e-39
1e-38
1e-37
1e-36
1e-35
10 100 1000
σ χp
SD
, cm
2
mDM, GeV
DAMA no channeling 2008
PICASSO 2012
KIMS 2011
SIMPLE 2011
D8: CMS q q→j (χχ )
D8: ATLAS q q→j (χχ )
ANTARES 2007-2008, W+W
-
ANTARES 2007-2008, b b
ANTARES 2007-2008 τ+τ-
Super-K 2011, W+W
-
Super-K 2011, b b
IceCube 2012, hard
IceCube 2012, b b
Baikal 1998-2002, W+W
-
Baikal 1998-2002, b b
Baikal 1998-2002, τ+τ-
Baksan 1978-2009, W+W
-
Baksan 1978-2009, b b
Baksan 1978-2009, τ+τ-
Results
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Summary
I Analysis of upward-going muon data collected for 24.11 yearsof livetime by neutrino experiment at Baksan UndergroundScintillator Telescope has been performed
I No signi�cant excess was found in search for muon signal fromdark matter annihilations in the Sun
I New limits on muon �ux, annihilation rate, elastic crosssections
Conclusions
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Thank you!
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Backup slides
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Systematic uncertainties
I Experimental uncertainties: ≈ 8% (instability of work ofphotomultipliers, season variations, dead tanks, ...).
I Neutrino oscillation parameters: ≈ 5% for W+W− and bb̄,≈ 8% for τ+τ−
I Neutrino nucleon cross section - up to 10% (even higher forEν < 10 GeV)
I For limits on SD and SI cross sections: astrophysicaluncertainties (chemical composition of the Sun, local darkmatter density ρχ, DM velocity distribution, ...)
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Comparison of upper limits for W+W− and τ+τ− channels
I Comparable limits on muon �uxesI Number of neutrinos (and antineutrinos) per annihilation:≈ 1.0 for W+W− and ≈ 2.6 for τ+τ−
I E�ect of oscillations
0
1
2
3
4
5
10 100 1000
Φµ,
osc
/Φµ,
no
osc
mDM, GeV
b b
W+W
-
τ+τ-
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Upper limits on SI elastic cross section
1e-45
1e-44
1e-43
1e-42
1e-41
1e-40
1e-39
1e-38
10 100 1000
σ χpS
I , cm
2
mDM, GeV
DAMA no channeling 2008
CoGeNT 2010
XENON100 2012
CDMS 2010
ANTARES 2007-2008, W+W
-
ANTARES 2007-2008, b b
ANTARES 2007-2008 τ+τ-
IceCube 2013, hard
IceCube 2013, b b
Baksan 1978-2009, W+W
-
Baksan 1978-2009, b b
Baksan 1978-2009, τ+τ-