Indirect detection of Dark Matter …. from an experimental point of view ….

Indirect detection of Dark Matter …. from an experimental point of view ….

Jan Conrad

conrad.at.fysik.su.se

A Decade of New Experiments XXXVII SLAC Summer Institute,August 3-14, 2009.

09-02-02 /

Me

The reason why I am not at SLAC

Ellen, 14 month

Thanks for suggesting this solution to Greg Madejski and JoAnne Hewett (we’ll see if it works).

09-08-07 Jan Conrad, Stockholm Universitet

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• Questions can be adressed to me by mail: [email protected] (there are no stupid questions!)

• During lectures I usually try to read the audience, which will not be possible positive and negative feedback would be very useful (via mail).


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Goal for the lectures.

• You should understand the experimental approaches to indirect detection of dark matter and what we can expect in the next decade.

• You should understand that DM indirect detection is challenging and what the challenges are

• I hope I can give you some additional insight in what to make of the presented results.

• I hope I will be able to convey the message that revolutions are on the horizon.


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Contents and non-contents

• Not in this lecture(s):– Why DM ? Tegmark,Weiner– DM candidates Weiner– Results will be presented mainly if they illustrate a special point for newest results: see talks by Moskalenko, Pearce, Burnett, Egberts

• Lecture I– Preliminaries (minimal theoretical background)– The set up– Charged cosmic rays,

• Signatures• Astrophysics and backgrounds

– A detour cosmic ray diffusion in the Galaxy– Instrumental background

• Experimental approaches• PAMELA, ATIC, FERMI results on charged cosmic rays. • GAPS

Also important for gamma-rays --- lecture II


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• Lecture II– Gamma-rays

• Signatures• Astrophysics and backgrounds• Experimental approach and experiments• Source confusion• Selected Results

– Neutrinos• Signature• backgrounds• Experimental approach and experiments• Selected results• Impact of Astrophysics

– Interplay between different indirect experiments– Indirect indirect detection (multi-wavelength)

Some additional slides contain more detailed information …


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The set-up

• Prime DM candidate: Weakly Interacting Massive Particle (WIMP), denoted by

• Mass: ~ 10 GeV - ~ 10 TeV

• ”Weakly” interacting

• Experimental signatures (roughly) applicable to a variety of candidates:– Supersymmetric neutralino– Kaluza Klein– Axino, Gravitino, SuperWIMPs– ….etc. etc.

• Other CDM candidates: – axions ( discussed if time)

For motivation and theory: see Neil Weiners talk


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The set-up: WIMP annihilation or decay

W-/Z/q

W+/Z /q

0

e

e±

Indirect detection rate = (particle physics part) × (astrophysical part)

PPP APP

Anti-p, anti-d


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Signal: general considerations

• Particle physics part– DM particle’s spin mass, annihilation cross section, branching fraction

into final states and yield for a given final state (given by underlying theory (KK,MSSM, IDM etc).

For experimentalist: Analysis optimized for given signature

• Astrophysical part – (Density of DM particles)2, diffusion, absorption (where applicable)

For experimentalists: Where to look for the signal?

orders of magnitude parameter space (x-sections)

> Order of magnitude uncertainties

More details in respective section. Note there is virtually no experiment dedicated solely (or even mainly) to IDMD !!! (one exception: GAPS …. will be discussed.)

)(EYvPPP 1326103: scmvbenchmark


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Cosmic rays

W+/Z /q_

W-/Z/q

e±

Anti-p, anti- d

e+

e-

Dark Matter on Galactic scalesDark Matter on Galactic scales


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Cosmic rays: signatures

Positron fraction and spectrum

Antiproton fraction and spectrum Anti-deuteron

spectrum


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APP: cosmic ray propagation in the Galaxy: why we need to talk about it:

• Cosmic rays produced in secondary processes provide a formidable background to DM searches with anti-particles.

• Photon-production by Galactic cosmic rays provide a formidable background to DM searches with gamma-rays

• Any potential signal in CR will need to be interpreted with effects of the propagation in mind

Strong et al, ApJ 537, 736, 2000 Strong et al, ApJ 613, 962, 2004

Diffuse gamma-ray prediction 1 Diffuse gamma-ray

prediction 2


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B-field

APP: cosmic ray propagatioin in the galaxy

Radiation field

Gas

e

p

Gas

π0 γγ π± e±

B-field

p-bar,

brem

s

π± e±

sync

h IC

Li, B

Diffusion

reacceleration

convection

energy loss

spallation

decay

CNO

π0 γγDM

To some: To us:


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Many other experiments will be important for indirect detection:

• By standard, quantitatively described by diffusion equation (see additional slides) with a number of assumptions (e.g. GALPROP code)

• Constrained through CR and gamma-ray observations

• Diffusion coefficient Primary/secondary nuclei ratio (HEAO-3, ACE,PAMELA,CREAM,TRACER)

• Interstellar radiation field: optical,FIR,CMB (DIRBE, FIRAS)

• Interstellar gas (H1,HII) 21cm, CO surveys (Bonn,Parkes)

• B-field radio surveys (Jodrell Bank, Parkes ,WMAP, Planck)

• Spallation, pion production cross-sections accelerators

For a more detailed account: Moskalenko, SSI 2008


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Cosmic ray anti-matter: detection principle

Calorimeter

Scintillator (TOF)

Scintillator (TOF)

PID (TRD,Cherenkov)

PID (TRD,Cherenkov)

magnet

Anti-coincidence (scintillator)


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Examples: PAMELA and AMS-02, spectrometer

1.2

m,

450

kg

1.5

m,

~60

00

kg


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Examples for ”calorimeters”: ATIC/FERMI/HESS

1500 kg, h=1.2m

e+

e–


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Example: PAMELA and ATIC

• Launched: June 15, 2006 from Baikonur,

• Quasi-polar orbit

• Expected livetime: > 3 years

• Three flights (2001,2003 and 2008)

• Total livetime: 50 days


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Instrumental backgrounds for e+,e-,γ

Hadronic background is dominant.

Fermi γ ~ 105-6

PAMELA, AMS ~ 104-5

ATIC, Fermi electrons ~ 103-4

Necessary rejection factors:


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Hadron/electron discrimination

• Main idea:– Veto detectors (Anti-

coincidence)

– difference in shower shape for em/hadronic showers in calorimeter

– Background rejection gets harder with rising energy

– Full analyses apply combined information of several detectors in multivariate classification (Neural networks …)


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Example: Fermi electron analysis.


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Anti-proton/proton ratio

500 days of data, 109 triggers, ca. 1000 anti-protons, ca. 107 protons, background < 3 %

Compatible with secondary production

O. Adriani et al. Phys.Rev. Lett. 102:051101,2009

6 anti-protons

ca 600 > 5 GeV


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Positron fraction: the PAMELA anomaly

Conventional production: GALPROP

Strong & Moskalenko Astrophys.J.509:212-228,1998

Conventional production:

Delahaye et. al

arXiv:0809.5268

500 days of data, 150 k electrons, 10k positrons

Very soft electron spectrum (index: -3.54) at odds with

Fermi (see later)

Errors include background removal uncertainty

O. Adriani et al. Nature 458:607-609,2009


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Possible sources

• No extra source:– Experimental– Non standard diffusion

• Extra source– Dark matter – Conventional sources

• Pulsars

• Supernovae

P. Biermann et al., arXiv:0903.4048 D. Malyshev et al. 0903.1310

L. Bergström et al., Phys.Rev.D78:103520,2008

B. Katz et al., arXiv:0907.1686

M. Schubnell, arXiv:0905.044


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Pulsars invoked already 20 years ago ….


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e++e- spectrum: the ATIC anomaly

Statistical errors only, background subtracted

HEAT

BETS

PPB-BETS

xEmulsion chambers

background GALPROP

Sol. Mod.

ATIC collab. Nature 456, 362-365(2008)Based on ATIC 1 + ATIC2


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Fermi-LAT as an electron detector

Fermi-LAT effective

geometric Factor

Residual hadron contamination

< 20 %

Cf: ATIC effective geometric factor

(less for PAMELA)

Energy resolution: ~ 20 %@ 1 TeV

(cf. ATIC ~ 2 % @ 150 GeV

cf. PAMELA ~ 6 % @ 200 GeV )

ATIC background


28reject KK model that fits ATIC at 99% (including E resolution).

e++e- spectrum

6 month of data

• ATIC is gone??

• Data is compatible with power-law (- 3.04).

• Is there a deviation from power-law?

± 15 %

ATIC:

1724 events > 100 GeV

Fermi:

171431 events> 100 GeV

3.8 σ 5.1 σ , Isbert (ATIC, TANGO in Paris 2009)

One slide on possible explanations in appendix

Also see Eun-Suk Seo’s topical talk

A. Abdo (Fermi-LAT) Phys.Rev.Lett.102:181101,2009

F. Aharonian (HESS), arXiv:0905.0105


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…and explanations ….

D. Grasso et al., arXiv:0907.0373

Bergström et al. 0905.0333

P. Biermann et al., arXiv:0903.4048

• No extra source:– Experimental (for ATIC)

– Non standard diffusion

• Extra source– Dark matter

– Conventional sources• Pulsars

• Supernovae


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A remark on boost-factors

• The annihilation cross-section is set by DM abundance in Big bang freeze out not sufficient to explain observed alleged signal.

• ”Boost” of rate has been invoked:

L. Bergström, arXiv 0903.4849

e.g. Sommerfeld factor

~ 0-1000? (requires modifications to model)

DM substructure

~ 10??


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If it is DM, what would it mean?

• Data prefers models with mostly leptonic annihilation channels (in fact, muons)

• Most models predict rather large masses (> 1 TeV).

• This is hard to accomodate within MSSM considering the anti-proton (gamma) constraint.

• Most models need an additional enhancement of annihilation cross-section (”boost”).

• Most models make predictions which are testable with soon existing data (gamma-rays).

One can ask how much sense it makes to do this considerations at this point of time ….. some groups even publish theoretical analysis on preliminary data …. which I think is not very useful (unless you go with

Carlo Rubbia (alleged): ”Better wrong than late” )


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AMS

PAMELA

Fermi

ATIC

HESSspectrometers

”calorimeters”

PEBS

GAPSPPB-Bets CALET

future exp.

Cosmic ray detectors of relevance to DM

BESS-polar CREAM

TRACER

auxiliary

VERITAS


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Cosmic ray experiments: comparison


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GAPS detection principle_D

LadderDeexcitationsn=1, l=1

NuclearAnnihilation

n=1

n=2

n=3

n=4

n=5

n=6

n=nK~15

no,lo

Atomic Transitions

*

*

*

Auger e-

Refilling e-

The antiparticle slows down & stops in a target material, forming an excited

exotic atom with near unity probability

A time of flight (TOF) system tags candidate events and records velocity

Deexcitation X-rays provide signature Pions from annihilation provide added background suppression

*

Plastic Scintillator TOFSi(Li) Target/Detector

44 keV

30 keV

Slide stolen from Jason Koglin,Columbia U.


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GAPS sensitivity

GAPS white paper

2011 prototype

2014 flight


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Summary (cosmic rays):

• General:– CR probe DM on Galactic scales– Cosmic ray propagation in the Galaxy is important for gamma-rays

and cosmic rays needs imput from a variety of experiments.– Instrumental and astrophysical backgrounds are challenging.– Anti-deuterons provide a potential smoking gun signal

• Status:– PAMELA let the genie out of the bottle– Signatures detected which could be the first sign of DM.– The experimental situation is confusing with different (apparently) not

consistent results (ATIC vs. Fermi !, PAMELA vs. Fermi ?).

• Outlook:– Future experiments (AMS-02,PEBS) and additional data will be

crucial: • For constraining backgrounds for e.g. gamma-rays and cosmic

rays.• For distinguishing signal hypothesis.

Indirect detection of Dark Matter …. from an experimental point of view ….

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