dark matter searches at baksan underground scintillator...

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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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


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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)


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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


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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


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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


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


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


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 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 τ+τ-

IceCube 2013, hard

IceCube 2013, b b

Baksan 1978-2009, W+W

-

Baksan 1978-2009, b b

Baksan 1978-2009, τ+τ-

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