Indirect Detection of WIMPs Joakim Edsj Stockholm University - - PowerPoint PPT Presentation

Indirect Detection of WIMPs

Joakim Edsjö

Stockholm University Sweden edsjo@physto.se

ν 2004

Paris, June 19, 2004

Outline

• WIMP candidates

– will focus on the neutralino in the MSSM

• Ways to search indirectly for WIMPs
• Direct detection versus neutrino telescopes
• Recent developments in Earth rates

(gravitational diffusion revisited)

• Comparison of future searches

Many groups work on this, e.g.

• Ellis, Falk, Olive, Santoso, Spanos et al.
• Bottino, Donato, Fornengo, Scopel et al.
• Baer, Belyaev, Krupovnickas, O’Farrill, Tata et al.
• Silk, Bertone, Hooper, et al.
• Nezri, Orloff, et al.
• Roszkowski, Nihei, Ruiz de Austri, et al.
• Bergström, Baltz, Edsjö, Gondolo, Ullio, Schelke et

al.

• …

The neutralino as a WIMP

The neutralino: The neutralino can be the lightest supersymmetric particle (LSP). If R-partity is conserved, it is stable. The gaugino fraction

˜ χ0

1 = N11 ˜

B + N12 ˜ W 3 + N13 ˜ H0

1 + N14 ˜

H0

2

Zg = |N11|2 + |N12|2

Will focus on the neutralino in the MSSM as a dark matter WIMP candidate.

Calculational flowchart

• 1. Select model parameters
• 2. Calculate masses etc
• 3. Check accelerator constraints
• 4. Calculate the relic density
• 5. Check if the relic density is cosmologically OK
• 6. Calculate fluxes, rates, etc

Calculation done with Ωχh2 The relic density Ωχh2 = 0.103+0.020

−0.022

from WMAP+SDSS M.Tegmark et al., astro-ph/0310723

DarkSUSY 4.1 available on www.physto.se/~edsjo/darksusy astro-ph/0406204

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0.05 ! !h2 ! 0.08 0.08 ! !h2 ! 0.12 0.12 ! !h2 ! 0.2

• J. Edsjö, 2004

Neutralino Mass (GeV) Zg / (1-Zg)

The parameter space mχ − Zg

LEP

Low sampling

Ωχh2 < 0.05 Ωχh2 > 0.2

In this and the coming plots, sfermion coannihilations are not included in the relic density calculation (yet). Higgsino Mixed Gaugino

WIMP search strategies

• Direct detection
• Indirect detection:

– neutrinos from the Earth/Sun – antiprotons from the galactic halo – antideuterons from the galactic halo – positrons from the galactic halo – gamma rays from the galactic halo – gamma rays from external galaxies/halos – synchrotron radiation from the galactic center / galaxy clusters – ... Use CDMS @ Soudan to constrain our models Focus on these Use these to constrain

• ur

models (future)

Annihilation in the halo

Neutral annihilation products

• Gamma rays can be searched for with Air

Cherenkov Telescopes (ACTs) or GLAST.

• Signal depends strongly on the halo profile,

χχ → γγ, Zγ, ν χχ → γ, ν Φ ∝

• line of sight

ρ2dl

• Diffusion of charged particles. Diffusion model with

parameters fixed from studies of conventional cosmic rays (especially unstable isotopes).

• Current detectors are e.g. HEAT, Caprice and BESS.

Future detectors are e.g. AMS, Pamela and GAPS.

Annihilation in the halo

Charged annihilation products Diffusion zone χχ → ¯ p, ¯ D, e+

Direct detection

current limits

• CDMS @ Soudan,

astro-ph/0405033

• Direct detection

experiments have really started to explore the MSSM parameter space!

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4 Gaugino-like Mixed Higgsino-like Excluded, CDMS Soudan, May 2004

Neutralino Mass (GeV) Cross section, !SI (pb)

• J. Edsjö, 2004

Neutralino Capture

χ Sun µ

Detector

Earth νµ

Silk, Olive and Srednicki ‘85 Gaisser, Steigman & Tilav ‘86 Freese ‘86 Krauss, Srednicki & Wilczek ‘86 Gaisser, Steigman & Tilav ‘86

ρχ σscatt Γann Γcapture ν interactions velocity distribution σann

Neutrino Telescopes

Capture Capture in Sun

• Mostly on Hydrogen
• Both spin-independent and

spin-dependent scattering

Capture in Earth

• Mostly on Iron
• Essentially only spin-

independent scattering

• Resonant scattering when

mass matches element in Earth

• Capture from WIMPs bound

in the solar system

Figure from Jungman, Kamionkowski and Griest

Review of capture rate calculations

• 1985: Press & Spergel, ApJ 296 (1985) 679:

Capture in the Sun

• 1987: Gould, ApJ 321 (1987) 571:

Refined Press & Spergel’ s calculation for the Earth.

• 1988: Gould, ApJ 328 (1988) 919:

Pointed out that the Earth cannot capture efficiently from the halo since the Earth is deep within the potential well of the Sun (vesc≈42 km/s)

• 1991: Gould, ApJ 368 (1991) 610:

WIMPs will diffuse around in the solar system due to gravitational scattering off the planets. Net result is that the velocity distribution at Earth is approximately as if the Earth was in free space, i.e. the 1987 expressions are still valid.

Earth Capture

Why are low velocities needed?

• Capture can only occur when a WIMP scatters off a nucleus

to a velocity less than the escape velocity

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Cutoff velocity ucut (km/s) Wimp mass (GeV )

allowed forbidden

Capture on Fe most important. For a given lowest velocity of the velocity distribution, we can

• nly capture WIMPs

up to a maximal mass.

Diffusion effects of the planets

• Gravitational scattering off one planet causes diffusion along

spheres of constant velocity with respect to that planet.

• When seen from another planet’

s frame, the velocity can have changed.

25 20 15 10 5 5 10 15 20 5 10 15 20 25

Speed at the Earth (km/s) Speed at the Earth (km/s)

u♀ = 3 u♀ = 4 u♀ = 5 u♀ = 6 u♀ = 7 u♀ = 8 u♀ = 9 u♀ = 10 u♀ = 12 u♀ = 14 u♀ = 16

The net effect is that Venus and Jupiter diffuse to velocities down to 2.5 km/s The velocity distribution at Earth is ‘as in free space’

• A. Gould, ApJ 368 (1991) 610, J. Lundberg & J. Edsjö, PRD69 (2004) 123505.

Possible problems: solar capture

• 1994: Farinella et al, Nature 371 (1994) 314:

Simulations of asteroids thrown out of the asteroid belt showed that they were typically forced into the Sun in less than 2·106 years.

• 2001: Gould and Alam, ApJ 549 (2001) 72:

If Farinella’ s results hold for general WIMP orbits, the bound WIMPs in the solar system could be depleted.

• 2004: J. Lundberg and J. Edsjö, PRD69

(2004) 123505:

Numerical simulation of WIMP orbits to find out if this is the case.

Velocity distribution at Earth

! " #! #" $! $" %! %" &! &" "! "" '! '" (! #!

!#$

#!

!##

#!

!#!

#!

!)

#!

!*

#!

!(

#!

!'

P hase space densit y: FMx /ρx [sm− 1] W I M P velocit y u at t he E art h (km / s) W it hout solar depl. B est est im at e R aw num erical C onservat ive U lt ra conservat ive G aussian

• Without solar

capture, Gould’ s results

• f ‘capture as

in free space’ are confirmed.

• Including solar

capture, we get a significant suppression at low velocities, not as bad as initially thought, but still significant

Earth capture rates

!" !"" #"" $"" %"" !""" %""" !"

&

!"

'

!"

!"

!"

!#

!"

!(

!"

!&

!"

!'

Capture rate [s− 1] WIMP mass (GeV) Best estimate Conservative Ultra conservative Gaussian

Up to almost an order of magnitude suppression at higher masses!

σscatt = 10−42 cm2

Earth annihilation rates

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• J. Lundberg and J. Edsjö, 2003

0.05 # "h2 # 0.2

Neutralino Mass (GeV) Suppression of annihilation rate

#

sup max

#

sup min

Annihilation and capture is not in equilibrium in the Earth

⇩

The annihilation rates are suppressed by up to almost two

• rders of

magnitude!

ΓA = 1 2C tanh2 t τ

Neutrino-induced muon fluxes from the Earth

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lim

!SI

lim

! !SI ! 0.1!SI

lim

0.1!SI

lim

! !SI

• J. Lundberg and J. Edsjö, 2004

Eth

" = 1 GeV

!SI

lim

= CDMS 2004 0.05 # "#h2 # 0.2

Neutralino Mass (GeV) Muon flux from the Earth (km-2 yr-1)

BAKSAN 1997 MACRO 2002 AMANDA 2004 SUPER-K 2004 IceCube Best-Case

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lim

!SI

lim

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lim

0.1!SI

lim

! !SI

• J. Lundberg and J. Edsjö, 2004

Eth

" = 1 GeV

New solar system diffusion !SI

lim

= CDMS 2004 0.05 # "#h2 # 0.2

Neutralino Mass (GeV) Muon flux from the Earth (km-2 yr-1)

BAKSAN 1997 MACRO 2002 AMANDA 2004 SUPER-K 2004 IceCube Best-Case

Usual Gaussian approximation New estimate including solar capture

Maxwell-Boltzmann velocity distribution assumed.

Neutrino-induced muon fluxes from the Sun

• Compared to

the Earth, much better complementarity due to spin- dependent capture in the Sun.

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!SI

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• J. Edsjö, 2004

Eth

" = 1 GeV

!SI

lim

= CDMS 2004 0.05 # "#h2 # 0.2

Neutralino Mass (GeV) Muon flux from the Sun (km-2 yr-1)

BAKSAN 1997 MACRO 2002 SUPER-K 2004 IceCube Best-Case Antares, 3 yrs AMANDA-II, 2001

A note about velocity distributions

f(v) v

Capture sensitive to the low-velocity region Direct detection sensitive to the high-velocity region

Remember the different velocity dependencies!

Neutrino-induced fluxes and future direct detection limits

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• J. Edsjö, 2004

Eth

! = 1 GeV

0.05 " "h2 " 0.2

Neutralino Mass (GeV) Muon flux from the Sun (km-2 yr-1)

BAKSAN 1997 MACRO 2002 SUPER-K 2004 IceCube Best-Case Antares, 3 yrs Sun bkg !SI

lim

= 10-9 pb at best

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• J. Lundberg and J. Edsjö, 2004

Eth

! = 1 GeV

0.05 " "#h2 " 0.2 !SI

lim

= 10-9 pb at best New solar system diffusion

Neutralino Mass (GeV) Muon flux from the Earth (km-2 yr-1)

AMANDA 2004 BAKSAN 1997 MACRO 2002 SUPER-K 2004 IceCube Best-Case

Sun Earth

Future direct detection limit is assumed to be GENIUS/CRESST- like with a sensitivity down to 10-9 pb.

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0.05 ! !h2 ! 0.08 0.08 ! !h2 ! 0.12 0.12 ! !h2 ! 0.2

• J. Edsjö, 2004

Neutralino Mass (GeV) Zg / (1-Zg)

Comparing future searches in the parameter space

mχ − Zg

LEP

Low sampling

Ωχh2 < 0.05 Ωχh2 > 0.2

Comparison of future searches I

Direct detection, SI Future limit is assumed to be GENIUS/CRESST-like with a sensitivity down to 10-9 pb.

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Neutralino Mass (GeV) Zg / (1-Zg)

Comparison of future searches II

Earth Sun IceCube-like, 1 km3 running for 10 years (10 years live time) IceCube-like, 1 km3 running for 10 years (5 years live time)

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Neutralino Mass (GeV) Zg / (1-Zg) 10

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Neutralino Mass (GeV) Zg / (1-Zg)

• Compare with future

suggested mission GAPS (Gaseous AntiParticle Spectrometer, K. Mori et al, ApJ 566 (2002) 604)

• Require at least one

event (background ≈ 0) at low energies with e.g. GAPS

• Antideuteron production

yields from F . Donato, N. Fornengo and P. Salati,

• Phys. Rev. D62

(2000) 043003.

Comparison of future searches III

Antideuterons

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Neutralino Mass (GeV) Zg / (1-Zg)

Comparison of future searches IV

γ γ Z γ Significant signal in ACTs or GLAST towards the galactic center with a NFW profile.

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Neutralino Mass (GeV) Zg / (1-Zg)

• Large parts of

the MSSM parameter space can be probed by future experiments

• The halo model is

assumed to be an optimistic NFW profile.

• LHC e.g., will cut

into this plane mainly from the left and top.

Comparison of future searches V

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Neutralino Mass (GeV) Zg / (1-Zg)

Conclusions

• Detection prospects of neutralinos are

reasonably good.

• For ‘standard’ halo models, direct detection

seems more promising than the neutrino-flux from the Earth, especially after including the depletion of WIMPs due to solar capture

• The neutrino-flux from the Sun is

complementary to direct detection due to spin-dependent capture in the Sun

• Searching for antideuterons also seems

promising.