Status of a search for neutrinos from diffuse dark matter annihilation

neutrino.fuw.edu.pl

Status of a search for neutrinos from diffuse dark matter annihilation

Status of a search for neutrinos

from diffuse dark matter annihilation

2009/11/14

Piotr Mijakowski (Warsaw)

Super-Kamiokande Collaboration Meeting


Diffuse search idea

» Investigation is limited to „most optimistic” but

model independent WIMP annihilation channel

χ + χ → ν + ν

» Relevant for DM decay modes, DM diffuse

annihilation

Illustration of 100 GeV

DM annihilation signal

Tail due to redshift

smearing

» Due to distinctive energy spectra of

WIMP-induced neutrinos coming from

that „golden channel” it is possible to

test data against characteristic

distortions in energy and cos spectra

» Use method of min χ 2 to find best

allowed WIMP contribution

• upper 90% CL limit on WIMPinduced

neutrinos

» Derive conservative upper limit on

WIMP total self-annihilation cross

section

neutrino energy

(*) J.F.Beacom et al., Phys. Rev. D76, 123506 (2007)


» My strategy so far... „bottom->up” approach

• start with fit on single distributions

• add new samples, check, perform combined fit

• address systematics later

... long way

» New strategy -> global FIT using Roger’s Osc3++/

• „top->down” approach

• fit on all samples together - PC, FC µ-like, FC e-like,

UPMU (cosθ, E)

• systematics and relations between samples adressed

properly by oscilation fit package

3


1. „Bottom-up” strategy

4


Search for WIMP diffuse signal in UPMU sample

» In HE region (>~30 GeV) it is possible to

use only UPMU sample and FIT could be

only based on cosθ distrubutions

» In UPMU data we don’t have information on

true neutrino energy

» proportions of events among different

subsamples (like in STOP & THRU) are

changing with energy ... that is additional

bound for FIT

STOP

SK1

500yrs MC

(apr08)

THRU

WIMP signal input for UPMU fit

» WIMP induced-ν’s are mimic by atm MC

muons with ‘isotropic weights’ (WIMP

induced neutrinos are isotropic)

» ‘isotropic weights’ are changing with

energy -> need to use the correct one

for the considered WIMP energy

Arbitrary normalization

distributions

normalized to

same integral

5


UPMU FIT example (STOP+THRU)

MC: normalized by livetime

SK1 90

M WIMP = 90 GeV

signal: MC with true Eν = 88-92GeV

GeV

FIT result

WIMP signal before FIT

α – atm MC normalization parameter

β – WIMP signal normalization parameter

β can be interperted as % of total

MC(STOP+THRU) that can be added as DM signal)

6


UPMU FIT example (STOP+THRU)

SK1

MC: normalized by livetime

M WIMP = 90 GeV

signal: MC with true Eν = 88-92GeV

90

GeV

FIT result

alpha 1.06+-0.06

beta 0.06+-0.05

chi2 (chi2/DOF) 17.65 (0.98)

#WIMPs 124+-100

90% CL 258.7

7


UPMU fit summary (‘old approach’)

Fitted no of WIMPS / SK1 UPMU THRU+STOP


#WIMPS

Significance of fitted WIMP signal


[σ]

STOP+THRU

β=0 30 GeV 56 GeV 90 GeV 200 GeV 400 GeV 600 GeV 1 TeV

α

1.12

+-0.02

1.15

+-0.06

1.065

+-0.065

1.058

+-0.055

1.046

+-0.048

1.041

+-0.047

1.046

+-0.045

1.054

+-0.042

β -

-0.03

+-0.05

0.054

+-0.061

0.061

+-0.050

0.071

+-0.042

0.079

+-0.042

0.074

+-0.039

0.067

+-0.035

χ 2

(χ 2 /dof)

19.18 (1.01)

18.74

(1.04)

18.40

(1.02)

17.65 (0.98)

16.38

(0.91)

15.57

(0.87)

15.62

(0.87)

15.66

(0.87)

#WIMPs

(fitted)

-

-71.6

+-108.0

108.7

+-122.9

123.9

+-100.1

142.9

+-85.4

159.7

+-84.0

149.7

+-79.4

134.5

+-71.7

90% CL -

139.5

(6.11%)

280.5

(12.3%)

258.7

(11.3%)

254.7

(11.2%)

268.8

(11.8%)

252.8

(11.1%)

227.7

(10%)


SK1 FC

FC+PC fit example

M WIMP = 5.5 GeV

signal: MC with true Eν = 5.4-5.6GeV

SK1 FC

90% CL

(α=1.1,β = -0.025)

99% CL

FIT result

alpha = 1.1+-0.012

beta = -0.025+-0.004

Evis [GeV]

SK1 PC

SK1 PC

Cosθ

chi2 = 85.35

chi2/DOF = 1.61

#WIMPs = -241.5+-41.7

90% CL = 15.2

(0.3% of all FC+PC DATA)

Evis [GeV]

Cosθ

What was the upper limit

before with separated fit

PC (cos+E): 54 evts

FC (cos+E): 3.2 evts

90%

CL

9


PC+FC fit summary

FC(cos)+FC(E)+PC(cos)+PC(E) (µ-like only)

β=0 2 GeV 4 GeV 5.5 GeV 10 GeV 15 GeV 20 GeV

α

1.071

+- 0.011

1.076

+-0.013

1.096

+-0.012

1.1

+-0.012

1.103

+-0.012

1.098

+-0.012

1.093

+-0.012

β -

-0.006

+-0.008

-0.023

+-0.005

-0.025

+-0.004

-0.028

+-0.004

-0.024

+-0.004

-0.019

+-0.003

χ 2

(χ 2 /dof)

118.94

(2.244)

118.4

(2.23)

98.33

(1.86)

85.35

(1.61)

80.77

(1.52)

86.48

(1.63)

93.37

(1.76)

#WIMPs

(fitted)

-

-52.5

+-72.8

-216.3

+-47.6

-241.5

+-41.7

-265.3

+-43.0

-223.3

+-39.2

-186.0

+-36.8

90% CL -

92.0

(1.8%)

22.1

(0.4%)

15.6

(0.3%)

15.2

(0.3%)

14.9

(0.3%)

15.6

(0.3%)

» No WIMP contribution allowed

over the entire energy range

(FC, PC Energy distrubutions used

in FIT give strong bound)

Upper

Limit

» Stable fit results >~5 GeV

10


2. „Top-down” strategy (Osc3++)

11


WIMP signal

illustration

(SK1,SK2,SK3)

5.6 GeV,

β = 10

WIMP event = event taken

from atm. MC (5.4-5.8 GeV)

x isotropic weight x β

(normalization weight)

assuming flux ν e =ν µ (=ν τ ) for WIMP signal 12


WIMP signal

illustration

(SK1,SK2,SK3)

5.6 GeV,

β = 10

WIMP event = event taken

from atm. MC (5.4-5.8 GeV)

x isotropic weight x β

(fitted normalization weight)

assuming flux ratio of ν µ /ν e same as atm. ν’s 13


WIMP signal

illustration

(SK1,SK2,SK3)

5.6 GeV,

β = 10

WIMP event = event taken from

atm. MC (5.4-5.8 GeV) x

isotropic weight x flux weight

x β (fitted normalization weight)

assuming flux ν e =ν µ (=ν τ ) for WIMP signal 14


WIMP signal

illustration

(SK1,SK2,SK3)

30 GeV,

β = 50

WIMP event = event taken from

atm. MC (5.4-5.8 GeV) x

isotropic weight x flux weight

x β (fitted normalization weight)

assuming flux ν e =ν µ (=ν τ ) for WIMP signal 15


WIMP signal

illustration

(SK1,SK2,SK3)

30 GeV,

β = 50

WIMP event = event taken from

atm. MC (5.4-5.8 GeV) x

isotropic weight x flux weight

x β (fitted normalization weight)

assuming flux ratio of ν µ /ν e same as atm. ν’s

16


WIMP signal

illustration

(SK1,SK2,SK3)

90 GeV,

β = 50

WIMP event = event taken from

atm. MC (5.4-5.8 GeV) x

isotropic weight x flux weight

x β (fitted normalization weight)

assuming flux ν e =ν µ (=ν τ ) for WIMP signal 17


Summary

» current apporoach: WIMP induced-ν’s hyphothesis checked over the

wide energy range by a sampling WIMP energies

• LE range: using µ-like FC (E,cosθ) + PC(E,cosθ)

• WIMP contribution strongly unfavored w/o systematics

• HE range: THRU+STOP samples

• Stable limit >50 GeV: ~11% of DATA could be fitted by WIMP signal

at 90% CL (upper limit)

» new approach: started to use Roger’s Osc3++/ package

• allows global fit using all existing SK1-SK3 samples, including

knowledge on systematic uncertainties

• compare with current approach results which should give a good

guideline

» plan

• conclude the fit over the all energy range using a ‘new approach’

• calculate the limit on total self-annihilation cross section

18

More magazines by this user
Similar magazines