N - Warszawska Grupa Neutrinowa

neutrino.fuw.edu.pl

N - Warszawska Grupa Neutrinowa

Ogólnopolskie Zebranie Neutrinowe, 8.II.2010, Katowice

”Search for neutrinos from diffuse

Dark Matter annihilation

in Super-Kamiokande"

Piotr Mijakowski

Instytut Problemów Jądrowych, Warszawska Grupa Neutrinowa


OUTLINE

» Super-Kamiokande:

data samples

» Search for WIMPs with

Super-Kamiokande

P.Mijakowski 8.II.2010, Katowice

2


Super-Kamiokande

Water Cerenkov detector in Kamioka, Japan

• in operation since 1996

• 50kton water, 22.5kton

fiducial volume

• 12k inner PMTs /2k

outer PMTs

detect light; possible

reconstruction of energy

and direction of

neutrinos

40m

• SK investigates

atmopsheric/cosmic,

solar & accelerator ν

40m

• detect SN1987 ν’s

• neutrino oscilation

discovery (1998)

3


How neutrinos interact?

Charged Current

Neutral Current

Elastic Scattering

ν + N->µ/τ/e+p+…

ν + N->ν+n+…

ν + e - ->ν+e - 4

ν


Fully contained

Super-K data sample

(event classification)

Upward-going muons

Partially contained

UPMU

» total ν energy » only partial energy

information

deposited

» E>30MeV » E vis > 300MeV

» not good ν direction

reconstr. (for low energy)

» e/µ identification

» downward going

muons are neglected

(mainly BKG atm µ)

» no ν energy information

» good ν direction info

5


Super-K data sample

expected number of atm. ν events in

each event category as a function of ν energy

Depending on true neutrino energy

different event categories

(samples) are populated

Atmospheric neutrinos interaction rate:

FC = ~8.3 events/day

30MeV – ~20GeV

PC = ~0.7 events/day

300MeV – ~100GeV

UPMU = 1.5 events/day

from ~2GeV –

Monte Carlo for atmospheric ν’s

6


WIMP annihilation to neutrinos

qq ( cc ,bb,tt,...)

χχ → ll → .....→ ν ,γ,e, p ,H 2

,

W ± ,Z,H


Search for neutrinos

from DM annihilation (approaches)

Directional flux

related to regions of increased DM

density:

• core of Sun, Earth, Galaxy

Center

• constrain SD/SI σ χn

Diffuse flux:

• flux averaged over large cosmic

volumes (many galactic halos) or

over Milky Way

• constrain DM self-annihilation cross

section

(*) S.Desai et al., Phys.Rev. D70 (2004) 083523

7


DM self-annihilation cross section

- cross section averaged over the relative velocity distribution

„freeze out” of the relic particle

» Sets the obs. DM mass density

Ω Μ = 0.27 ± 0.02 WMAP (2006 r.)

-> in thermal relic scenarios:

~ 3 x 10 -26 cm 3 /s

» Sets the annihilation rate in DM halos

2

- DM number density

P.Mijakowski 8.II.2010, Katowice

8


Diffuse search idea

» Investigation is limited to „most optimistic” but

model independent WIMP annihilation channel

χ + χ → ν + ν

neutrino energy = WIMP mass

signal is isotropic

Illustration of 100 GeV DM

annihilation signal

Tail due to redshift

smearing

» Relevant for DM diffuse annihilation

and also for DM decay modes

» Due to distinctive energy spectra of WIMPinduced

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

» Derive conservative upper limit on WIMP

total self-annihilation cross section ,

lifetime τ DM

neutrino energy

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

9


Upper bound on DM total annihilation cross section

MOTIVATION

» If one combine neutrino based limit with

null results from other searches for DM

annihilation products -> provide

conservative upper limit on total

» Existing limit based only on data available for general

public (made by J.F Beacom et all.)

» No dedicated anylysis from experiments

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

Assumption: BR = 100% for

Consequence:

General upper limit on the total DM self annihilation cross section. Why?

Least detectable particles bounds total cross section most conservatively -> all other limits

(derived from other ann. products, like γ’s) would be more stringent than that; limit on cross

section derived that way cannot be overreached (with only SM final states)

10


PROCEDURE OUTLINE:

Anylysis idea

» Use (ν e , ν e ), (ν µ, ν µ )

» Investigate energy (FC, PC) & cosθ (UPMU, FC, PC)

distributions

» Simulate DM annihilation diffuse signal

» Test the DM annihilation singal hypothesis in atmospheric

neutrino data by minimazing χ 2 distributions:

depends on ν

oscillation parameters

FC: fully contained

PC: partially contained

UPMU: upward going muons

χ 2 =

nbins


i=1

( N obs i

− ( α ⋅ N atmν WIMP

i

+ β ⋅ N )) 2

i

σ i

2

α – atm MC normalization parameter

β – WIMP signal normalization parameter

for every WIMP mass

α,β fitted

11


How to simulate WIMP signal?

» WIMPs of a certain energy can be mimic by atmospheric

MC ν’s with true energy around that specific energy

WIMP-induced neutrinos

are isotropic! … need to

reweight MC to mimic

them properly ‘isotropic

weights’

w/o oscillations

WIMPS

True neutrino zenith angle BEFORE

interaction and detector sim

P.Mijakowski 8.II.2010, Katowice

12


UPMU FIT example (STOP+THRU)

SK1 DATA 1489.2 days

(years 1996-2001)

MC 500yrs livetime

M WIMP = 90 GeV

signal: MC with true Eν = 88-92GeV (weighted)

90

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


SK1 DATA 1489.2 days

(years 1996-2001)

MC 500yrs livetime

UPMU FIT example (STOP+THRU)

M WIMP = 90 GeV

90

signal: MC with true Eν = 88-92GeV (weighted)

GeV

FIT result

alpha 1.06+-0.06

beta 0.06+-0.05

χ2 (χ2/DOF) 17.65 (0.98)

#WIMPs 124+-100

90% CL 258.7


P.Mijakowski 8.II.2010, Katowice

15


FC+PC fit example

M WIMP = 5.5 GeV

signal: MC with true Eν = 5.4-5.6GeV (weighted)

SK1 FC

SK1 FC

SK1 DATA 1489.2 days ( years 1996-2001)

MC 500yrs livetime

90% CL

99% CL

(α=1.1,β = -0.025)

SK1 PC

Evis [GeV]

SK1 PC

Cosθ

FIT result

alpha = 1.1+-0.012

beta = -0.025+-0.004

χ2 = 85.35

χ2/DOF = 1.61

#WIMPs = -241.5+-41.7

Evis [GeV]

Cosθ

90% CL = 15.2 evts

(0.3% of all FC+PC DATA)

16


global FIT

» 12 sampling energies in range

4 GeV – 1 TeV

• 20GeV UPMU (cosθ only)

FC,PC

UPMU

---- 1σ band

» No WIMP contribution allowed

over the entire energy range

• FC, PC Energy distrubutions

used in FIT give strong bound

FC,PC

UPMU

» 90% CL upper limit on allowed

number of WIMP induced-n’s

17


„full approach” fit

» Presented strategy...

• fit based only on FC µ-like+PC or UPMU (STOP+THRU) samples

• systematic uncertainties not included

» „full approach” fit:

• on all available samples together – PC + FC µ-like + FC e-like +

UPMU (cosθ + E)

• FC can be divided even into many more subsamples which are

being used in SK neutrino oscillation analyses

• ... using all available knowledge about relations/proportions between

these samples

• instead of fitting ATM MC normalization parameter α it would be better

to fit oscillation parameters (Δm 23 , θ 23 ... etc.) which actually stand

behindoscillated ATM MC

• there are 122 systematic terms in SK – in final approach their

influence need to be included as well

P.Mijakowski

8.II.2010, Katowice

18


„full approach” fit

» Let’s fit:

β - WIMP signal normalization parameter

Δm 23 , θ 23 + 122 ε i (systematic terms)

125 parameters to fit in

~600 x 3 = 1800 bins

Like...

- flux normalization

- energy calibration

- ring separation

- FC, PC, UPMU reduction

P.Mijakowski

Number of bins of

cosθ & energy

distributions of all

available samples

- FC/PC separation

- upward stopping/through-going µ separation

- particle identification

- DIS, π production, meson production, nuclear effects…

- Solar activity

8.II.2010, Katowice

SK1, SK2, SK3 data

SK1: 1996-2001

SK2: 2002-2005

SK3: 2006-2008

19


„full approach” fit

» How to include systematic uncertainties in χ 2 calculation ? Add „pull

terms”...

χ 2 =

2


⎛ Nsyserr ⎞ ⎞

N obs i

− ( N atmν WIMP

i

+ β ⋅ N ) i

⋅ ⎜ 1+ ∑ f i j

⋅ε j

nbins⎜

⎟ ⎟


⎝ j=1 ⎠ ⎠

∑ +

i=1

depends on ν

oscillation parameters

» In case of „poissonian” χ 2 :

(better to use when bins may ocassionally contain small # events)

σ i

2

secret knowledge

Nsyserr


j=1




ε j

σ j

fitted




2

sys. error





nbins

⎛ Nsyserr ⎞

obs


χ 2 = 2 N atmν WIMP

( i

+ β ⋅ N i ) ⋅ ⎜ 1+ ∑ f i j

⋅ ε j

⎟ − N N obs

i

+ N obs i

ln

i


∑ ⎜

⎝ j=1 ⎠

⎛ Nsyserr ⎞ ⎟ +

i=1 ⎜

N atmν WIMP


( i

+ β ⋅ N i ) ⋅ ⎜ 1+ ∑ f i j

⋅ε j


⎟ ⎟


⎝ j=1 ⎠ ⎠


Nsyserr


j=1




ε j

σ j




2

P.Mijakowski 8.II.2010, Katowice

20


FC

5.6 GeV

WIMP signal

illustration

DATA (SK1,SK2,SK3)

ATM neutrino MC

(with oscillations)

5.6 GeV DM signal

(simulation)

PC

DATA

SK1: 1489.2 days

SK2: 798.6 days

SK3: 518.1 days

ATM MC (SK1+2+3)

1500 yrs livetime

UPMU

cosθ

assuming flux ν e =ν µ =ν τ

for WIMP signal


FC

30 GeV

WIMP signal

illustration

DATA (SK1,SK2,SK3)

ATM neutrino MC

(with oscillations)

30 GeV DM signal

(simulation)

PC

DATA

SK1: 1489.2 days

SK2: 798.6 days

SK3: 518.1 days

ATM MC (SK1+2+3)

1500 yrs livetime

UPMU

cosθ

assuming flux ν e =ν µ =ν τ

for WIMP signal

22


FC

90 GeV

WIMP signal

illustration

DATA (SK1,SK2,SK3)

ATM neutrino MC

(with oscillations)

90 GeV DM signal

(simulation)

PC

DATA

SK1: 1489.2 days

SK2: 798.6 days

SK3: 518.1 days

ATM MC (SK1+2+3)

1500 yrs livetime

UPMU

cosθ

assuming flux ν e =ν µ =ν τ

for WIMP signal

23


FC

90 GeV

WIMP signal

illustration

DATA (SK1,SK2,SK3)

ATM neutrino MC

(with oscillations)

90 GeV DM signal

(simulation)

PC

ONLY ν µ

NO ν e

UPMU

cosθ

assuming flux ν e =ν µ =ν τ

for WIMP signal

24


90 GeV

β min = 0.00208

β

could be interpreted

as fraction of total

ATM MC that can be

replaced with WIMPs

---- 99% CL

---- 90% CL

---- 1σ

Δm 2 23

sin 2 2θ 23

» #WIMPs and 90% CL numbers relevant for

SK1 (for comparison with prev. approach)

» new fit:

• Δm 2 23 also fitted (in range 0.0019-0.0023)

Δm 2 23 = 0.00208 was picked up as best

fitted paramater;

• sin 2 2θ 23 (0.98->1.0); sin 2 2θ 23 = 1.0

90 GeV

old approach

STOP+THRU

only

new w/o

electron ν

signal

χ 2 /dof 0.98 1.118

#WIMPs

(fitted)

124±100 60

90% CL 259 166

P.Mijakowski

SK best 2 flavor oscilation fit χ 2 /dof = 1.121

8.II.2010, Katowice

25


global FIT

‘full approach’

» ‘full approach’ incorporates all

SuperK knowledge over entire

data energy range: systematic

uncertainties, relations between

samples, proper treat of

oscilltions etc.

-> powerful tool

» No WIMP contribution allowed

over the entire energy range:

derived 90% CL upper limit

» There are some features to

understand in new fit results

• prev. fit results can be used for

a crosscheck

prev. fit

new fit

prev. fit

new fit

---- 1σ band

---- 1σ band

26


Next step

» Derive limit on DM-induced neutrino diffuse flux and total self-annihilation

cross section (and DM decay lifetime) under a few DM galactic halo

distribution models

» Limit on DM-induced neutrino

diffuse flux and DM annihilation

cross section constrains on

DM evolution models in early

universe and resulting DM

distribution ( is expected to be

at ~10 -26 cm 3 /s for standard

thermal relic scenarios)

» Preliminary calculations show that

this analysis can improve the

existng world limit by 1-2 orders of

magnitude

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

P.Mijakowski

8.II.2010, Katowice

27


SUMMARY

Search for neutrinos from diffuse DM annihilation

• Preliminary checked over wide energy range that no statistically significant

DM annihilation signal can be accomodated by SK data

• ... thus we can derive conservative limit on DM self-annihilation cross

section (and DM lifetime τ DM ); We can place limit on total even

though we consider only one specific annihilation channel (our approach is

model independent)

• In this dedicated analysis we expect to improve the existing world neutrino

limit on by 1-2 orders of magnitude (especially in low energy)

P.Mijakowski 8.II.2010, Katowice

28


Dziękuję za uwagę


BACKUP


5.6 GeV

Δm 2 23

β min = -0.00326

90% CL(PDG adjusted)

β

could be interpreted

as fraction of total

ATM MC that can be

replaced with WIMPs

sin 2 2θ 23

» #WIMPs and 90% CL numbers relevant for

SK1 (comparison with prev. approach)

» fit:

• Δm 2 23 also fitted (in range 0.0019-0.0023)

Δm 2 23 = 0.00210099 was picked up as

best fitted paramater;

• sin 2 2θ 23 (0.98->1.0); sin 2 2θ 23 = 1.0

P.Mijakowski

5.6 GeV

old approach

PC+FC (E

+cosθ) w/o

electrons

new with

electron

signal

χ 2 /dof 1.61 1.116

#WIMPs

(fitted)

-241±42 -48

90% CL 15.6 36

SK best 2 flavor oscilation fit χ 2 /dof = 1.1206

31


Limit on DM self-annihilation cross section

» Let’a assume only annihilations in Halo:

RHS:

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

Average intensity of DM annihilation products from the field of view can be

cast as:

LHS: my upper

limit from fit

spectrum of annihilation products

1/2 accounts for DM being its own antiparticle

1/4π is for isotropic emission

= 8.5 kpc - the line of sight integration of the DM

density

- depend on cone-half angle


5.6 GeV

flux normalization

anti-nu_mu / nu_mu ratio

( e_nu < 10gev )

33


30 GeV

nu_mu / nu_e ratio

( e_nu < 5gev )

anti-nu_mu / nu_mu ratio

( e_nu < 10gev )

34


Super-K phases

SK-I

runs 1996-2001

accident in 2001

SK-II

runs 2002-2005

~50% PMTs

SK-III

runs Sep/2006-sep/2008

fully reconstructed

added acrylic shells for PMTs

SK-IV from 6/Sep 2008

• new electronics/DAQ/online software

• ready for T2K beam


Cerenkov ring categories

How can we distinguish interacting neutrino flavor?

» e-like » µ-like

fuzzy rings (due to E-M showers)

solid rings


WIMP capture and annihilation

ρ χ

χ

SUN

Earth

σ scatt

ν µ

ν int.

µ int.

Γ capture

Γ annihilation

χ scattering in the Sun

detector

χ

µ

χ annihilation

Z

ν

P.Mijakowski 21.04.2009, Warszawa 37

χ

ν


Search for WIMPs in SuperK (directional flux)

EARTH

SUN

GC

(*) S.Desai et al., Phys.Rev. D70 (2004) 083523

» Search for excess of neutrinos in SK1 data (1679.6 live days)

» WIMP mass range 18GeV-10TeV -> neutrino energy: ~5 GeV – 5 TeV

» Data sample: upward through-going muons

» Currently new analysis: more data, lower energy neutrinos also included (T.Tanaka)

P.Mijakowski

8.II.2010, Katowice

38


SuperK – WIMP-induced neutrino flux

limit from Sun

Limit: WIMP-induced upward muons (SUN)

simulation

Cone which contains 90% of neutrino

flux form WIMP annihilation in Sun

(*) S.Desai et al., Phys.Rev. D70 (2004) 083523

P.Mijakowski

8.II.2010, Katowice

39


SuperK – WIMP-induced neutrino flux

limit from Galactic Center

Limit: WIMP-induced upward muons (GC)

simulation

Cone which contains 90% of neutrino

flux form WIMP annihilation in GC

(*) S.Desai et al., Phys.Rev. D70 (2004) 083523

P.Mijakowski

8.II.2010, Katowice

40


SuperK limit for neutralino elastic cross

section (spin independent)

» Comparison with direct

detection: assuming only

spin-independent interactions

in Earth/Sun & equilibrium

between annihilation and

capture rate

comparison with direct detection

» Currently: lowest limit in direct

detection -> CDMS II:

3.8 . 10 -44 cm 2 for 70 GeV WIMP

(*) S.Desai et al., Phys.Rev. D70 (2004) 083523

P.Mijakowski

8.II.2010, Katowice

41


SuperK limit for neutrialino elastic cross

section (spin dependent)

» Limit 100 times lower

than from direct search

experiments

» DAMA annual

modulation due to axial

vector couplings ruled

out by this SK result

P.Mijakowski

11.I.2010, Wrocław

42


Upper bound on DM total annihilation cross section

J.F. Beacom approach:

» No upward fluctuations in available data

» Limit on DM-induced neutrino diffuse flux

and DM annihilation cross section

(constrains on DM evolution and

distribution)

» combining with γ searches -> provide

conservative upper limit on total

» Existing limit based only on data available for general

public (made by J.F Beacom)

» No dedicated anylysis from experiments

Assumption: BR = 100% for

Consequence:

General upper limit on the total DM self annihilation cross section. Why?

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

Least detectable particles bounds total cross section most conservatively -> all other limits

(derived from other ann. products, like γ’s) would be more stringent than that; limit on cross

section derived that way cannot be overreached (with only SM final states)


Atmospheric neurinos in SK

Atm. ν µ (MC)

expected number of neutrino events in

each event category as a function of neutrino energy

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