Review of dark matter searches and comments on CMO DM search
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Review of dark matter searches and comments on CMO DM search. Stefano Scopel. International Workshop on Double Beta Decay Search, SNU, Seoul, October 15-17 2009. Daejeon, 24-26 september 2009.

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Review of dark matter searches and comments on CMO DM search

Stefano Scopel

International Workshop on Double Beta Decay Search, SNU, Seoul, October 15-17 2009

Daejeon, 24-26 september 2009

  • historically direct underground DM searches started as a by-product of neutrinoless double-beta decay experiments

  • not a review on experiment – I will discuss the motivation for DM searches and why CaMoO4coul be used to search for WIMPS


* For a review on cryogenic DM searches see tomorrow’s talk by Y.H. Kim

Ωdark matter~ 0.22

Evidence for Dark Matter

  • Spiral galaxies

    • rotation curves

  • Clusters & Superclusters

    • Weak gravitational lensing

    • Strong gravitational lensing

    • Galaxy velocities

    • X rays

  • Large scale structure

    • Structure formation

  • CMB anisotropy: WMAP

    • Ωtot=1

    • Ωdark energy~0.7

    • Ωmatter~ 0.27

    • Ωbaryons~0.05

    • Ωvisible~0.005

The concordance model


subdominant candidates – variety is common in Nature

→may be easier to detect

The properties of a good Dark Matter candidate:

  • stable (protected by a conserved quantum number)

  • no charge, no colour (weakly interacting)

  • cold, non dissipative

  • relic abundance compatible to observation

  • motivated by theory (vs. “ad hoc”)

(Incomplete)List of DM candidates

  • Neutrinos

  • Axions

  • Lightest Supersymmetric particle (LSP) – neutralino, sneutrino, axino

  • Lighest Kaluza-Klein Particle (LKP)

  • Heavy photon in Little Higgs Models

  • Solitons (Q-balls, B-balls)

  • Black Hole remnants

  • Hidden-sector tecnipions

Weakly Interacting Massive Particles (WIMPs)

Particles with mass between a few GeV and a few TeV with cross sections of aproximately weak strength

The idea was introduced 35 years ago for massive neutrinos.Now neutrinos are ruled out, but there is no shortage of alternative WIMPs!

acronym “WIMP” eventually coined in mid ‘80

WIMP=Weakly Interacting Massive Particle

Kolb, Turner, The Early Universe

page 310

Pioneering work on direct DM searches @ Homestake mine in late ’80s:

however, today the sneutrino is not completely dead (rescaling due to relic density not applied to the signal at the time, see later)

few GeV<M<few TeV excluded both for neutrinos ad sneutrinos


most popular thermal WIMP candidates from particle physics (solve hierarchy problem: MW/MPl~ 10-16)

DM candidate

conserved symmetry

  • susy


χ (neutralino)

  • extra dimensions


B(1)(KK photon)

  • little Higgs


BH (heavy photon)

all thermal candidates, massive, with weak-type interactions (WIMPs)




The thermal cosmological density of a WIMP X is given by

ΩXh2 ~ 1/<σannv>int


T0=present (CMB) temperature


Tf=freeze-out temperature

Xf>>1, X non relativistic at decoupling, low temp expansion for <σannv>: <σannv>~a+b/x

if σann~0.1 pbarn (weak-type interactions) → ΩX~0.1-1

New physics at the TeV scale (“WIMP Miracle”)

…+ cohannihilations with other particle(s)

close in mass + resonant annihilations

Weakly Interacting Massive Particles can be detected!

The same class of interactions that keeped WIMPS in thermal equilibrium in the early Universe could allow their detection today




g g

f f



HH, hh, AA, hH, hA, HA, H+H-

W+H-, W-H+

Zh, ZH, ZA

g g

f f



HH, hh, AA, hH, hA, HA, H+H-

W+H-, W-H+

Zh, ZH, ZA

 n, n, g, p, e+, d



Searches for relic WIMPs

  • Direct searches. Elastic scattering of χ off nuclei(µ WIMP local density)

    χ + Nχ + N

  • Indirect searches. Signals due toχ -χannihilations

χ + χ

  • Annihilations taking place in celestial bodies whereχ’s have been accumulated:n’s up-going m’s from Earth and Sun

  • Annihilations taking place in the Halo of the Milky Way or that of external galaxies:enhanced in high density regions(µ (WIMP density)2)Þ Galacticcenter, clumpiness

WIMP direct detection

  • Elastic recoil of non relativistic halo WIMPs off the nuclei of an underground detector

  • Recoil energy of the nucleus in the keV range

  • Yearly modulation effect due to the rotation of the Earth around the Sun (the relative velocity between the halo, usually assumed at rest in the Galactic system, and the detector changes during the year)

A couple of examples:

the neutralino and the KK photon

GUT unification of gauge couplings

The neutralino





  • The neutralino is defined as the lowest-mass linear superposition of bino B, wino W(3)and the two higgsino states H10, H20 :



  • neutral, colourless, only weak-type interactions

  • stable if R-parity is conserved, thermal relic

  • non relativistic at decoupling  Cold Dark Matter (required by CMB data + structure formation models)

  • relic density can be compatible with cosmologicalobservations:0.095 ≤Ωχh2 ≤ 0.131


stau coannihilation

Higgs funnel

focus point

[Feng, Machev, Moroi, Wilczek]


(a.k.a. CMSSM)

[Ellis, Olive, Santoso, Spanos]

  • only few regions cosmologically allowed

  • variants (e.g. non-universality of soft masses at the GUT scale or lower unification scale) that increase Higgsino content of the neutralino→ lower relic abundance and higher signals

neutralino density tends to be too large

Direct detection in SUGRA

[Ellis, Olive, Santoso, Spanos]

The Next-to-Minimal MSSM (NMSSM)

2 Higgs (CP-even, CP-odd)


1 neutralino dof

solves the μproblem, i.e. why μ~MEW


Higgs soft terms in the NMSSM:

NMSSM particle content:

The lightest neutralino:

CP-even Higgs:

Relic density and direct detection rate in NMSSM

[Cerdeño, Hugonie, López-Fogliani, Muñoz, Teixeira]

relic abundance

direct detection

Landau pole


χ,H lighter χ singlino





unphysical minima

M1=160 GeV, M2=320, Aλ=400 GeV, Ak=-200 GeV, μ=130 GeV, tan β=5

(sizeable direct detection)

  • very light neutral Higgs (mainly singlet)

  • light scalars imply more decay channels and resonant decays

  • neutralino relatively light (< decay thresholds) and mostly singlino

  • high direct detection cross sections (even better for lower M1)

Effective MSSM: effective model at the EW scale with a few MSSM parameters which set the most relevant scales


  • M1 U(1)gaugino soft breaking term

  • M2 SU(2) gaugino soft breaking term

  • μHiggs mixing mass parameter

  • tan βratio of two Higgs v.e.v.’s

  • mA mass of CP odd neutral Higgs boson (the extended Higgs sector of MSSM includes also the neutral scalars h, H, and the charged scalars H±)

  • mqsoft mass common to all squarks

  • mlsoft mass common to all sleptons

  • A common dimensionless trilinear parameter for the third family (Ab = At ≡ Amq; Aτ≡ Aml)

  • R ≡M1/M2








Can the neutralino be ?

Cosmological lower bound on mχ


[Bottino, Fornengo, Scopel, PRD68,043506]

scatter plot:

full calculation

upper bound on ΩCDMh2

curve: analytical

approximation for

minimal ΩCDMh2

(à la Lee-Weinberg)

 “funnel” at low mass

DAMA/NaI modulation region, likelyhood function values distant more than 4 σ from the null result (absence on modulation) hypothesis, Riv. N. Cim. 26 n. 1 (2003) 1-73,


Color code:

● Ωχh2 < 0.095

Ωχh2 > 0.095

Neutralino – nucleon cross section

tight correlation between relic abundance and χ-nucleon cross section:

The elastic cross section is bounded from below

The KK photon in Universal Extra Dimensions (UED)

[Appelquist, Cheng, Dobrescu, PRD67 (2000) 035002]

  • all SM fields propagate in the 5th dimension

  • dispersion relation in 5 dim:

  • implies an infinite tower of KK massive states

  • in the effective 4-dim theory, since p5=n/R

  • (R-1>300 GeV from EW tests, n=0,1,2,3…)

  • compactification on S1/Z2:

  • allows to get rid of unwanted dof at zero level→translational invariance broken in 5th dim

  • residual invariance under discrete πR translations

  • →KK parity (-1)nis conserved → LKP (Lightest KK particle) is stable

  • 1-loop corrections (Cheng &al, 2002):

  • LKP=1stexcitation of weak hypercharge boson B(1)



if cohannihilating particle annihilates than LKP→ relic abundance



B(1)relic abundance

[Servant,Tait, NPB650,391;New J. Phys. 4,99; Kakizai & al., PRD71,123522; Kong, Matchev, JHEP0601,038]

  • coannihilations (many modes with similar masses)

  • resonances (MNLKP ~ 2 x MLKP)

  • general rule of coannihilation:

both cases are possible : KK quarks and gluons vs. KK leptons

ΩB (1)h2=0.1

KK leptons

Δ≡fractional mass splitting

  • low direct detection signals:


Typically, WIMP-nucleon cross section for KK-photons is smaller than for a neutralino. For instance (Servant, Tait,NJP4(2002)99):

(assuming Higgs-exchange dominance)


Belli, Cerulli, Fornengo, Scopel, PRD66,043503 (2002)

Upper limit on σscalar(nucleon) from CDMS and ZEPLIN: a scan of different models

A. Bottino, F. Donato, N. Fornengo and S. Scopel, PRD72 (2005) 083521


solid: CDMS, vesc=650 km/sec

long dashes: CDMS, vesc=450 km/sec

dots: ZEPLIN vesc=650 km/sec


Annual modulation of WIMP direct detection in a nutshell

Expected rate: R=R0+Rm cos[ω(t-t0)]

ω=2π/(1 year)

t0=2 june

Rm/R0~5÷10 % (few percent effect)

If N=# of events, assuming a 5% effect a 5 σ discovery requires:

5/100 X N > 5 X N½

modulation amplitude

poissonian fluctuation

⇒N > 10.000 events

N~ (incoming flux) x Ntargets x (cross section) x (exposition time)

expected rates: 0.1 events/kg/day

⇒a few x 100 kg x day required

hard to do: need large masses, low backgrounds, operational stability over long times…

The DAMA/Libra result (Bernabei et al., arXiv:0804.2741)

0.53 ton x year (0.82 ton x year combining previous data)

8.2 σ C.L. effect

A cos[ω (t-t0)]


DAMA disfavoured by other direct searches

small viable window with MWIMP≲ 10

From Savage et al., arXiv:0901.2713

KIMS spin independent limits (CsI)

ρD=0.3 GeV/c2/cm3



Systematic uncertainty

Fitting, Quenching factor

energy resolution...

combined in quadrature

~ 15% higher than w/o syst.

Nuclear recoil of 127I

of DAMA signal region

ruled out

PRL 99, 091301 (2007)

no light target in CsI → in principle Na in DAMAmore sensitivefor mwimp≲ 20 GeV (but maybe not if channeling is important)

for mwimpo≳ 20 GeV KIMS limit does not depend on scaling law for cross sections


  • in ionizators or scintillators the energy of a recoiling nucleus is partially transferred to electrons which carry the signal

  • q = quenching factor = fraction of nuclear recoil energy converting to ionization or scintillation (q=1 for γ’s from calibration)

  • simplistic view: recoiling nucleus experiences low stopping power of surrounding electronic cloud for kinematical reasons (mass mismatch between nucleus and single electrons)

  • most of the energy is converted to lattice vibrations (heat)

  • q~0.09 for I, q~0.23 for Na, q~0.3 for Ge. Measured with monoenergetic neutron beam

  • standard theory: Lindhard et al., Mat. Fys. Medd. K. Dan. Vidensk. Selsk. 33 (1963) 1; SRIM code

  • a useful application:dual read-out (bolometer + ionizator, bolometer + scintillator) allows discrimination between nuclear recoils (signal) and background (γ’s and β’s) (CDMS, Edelweiss)

Channeling effect in crystals

(Dobryshevsky, arXiv:0706.3095, Bernabei et al., arxiv:07100288)

critical angle:

C2~3, d=interatomic spacing

a0=0.529 Å (Bohr radius)

  • anomalous deep penetration of ions into crystalline targets discovered a long time ago (1957, 4 keV 134CS+ observed to penetrate λ~ 1000 Å in Ge, according to Lindhard theory λ~ 44 Å)

  • when the ion recoils along one crystallographic axis it only encounters electrons → long penetration depth and q~1

Channeling effect in crystals

(Dobryshevsky, arXiv:0706.3095, Bernabei et al., arxiv:07100288)

  • the channeling effect is only relevant at low recoil energies (<150 keV)

  • detector response enhanced → smaller WIMP cross sections needed to produce the same effect → smaller threshold on recoil energy and sensitivity to lighter masses


  • this effect was neglected so far in the analysis of WIMP searches. It is expected in crystal scintillators and ionizators (Ge, NaI)

  • no enhancement in liquid noble gas experiments (XENON10, ZEPLIN)

  • channeled events are lost using PSD in scintillators

  • channeled events are lost using double read-out discrimination (CDMS, Edelweiss)

  • quenching measurements are not sensitive enough to see channeled events (q=1 peak broadened by energy resolution)

Channeling effect in crystals

A Bottino, F. Donato, N. Fornengo and S. Scopel, arXiv:0710.0553

  • including channeling the DAMA region moves to lighter WIMP masses and lower cross sections

  • maximazed effect, i.e. q=1 whenever ψ<ψc

  • if q<1 the region could lie in between

no channeling


KIMS and annual modulation

[S.K.Kim talk, KIAS extended workshop 2009]

Many Dark matter searches on Earth:

DM searches in the world (running or projected)

  • DAMA

  • KIMS

  • CDMS


  • XENON10n (n=1,2,3,….)


  • WARP





  • 모루? 모모? 이’s…


Ionization+heat (cryogenic)

dual-phase TPC

Heat experiment (CUORICINO)

metastable bubbles


Background wall reached (shielding is a background source itself): discriminating techniques needed

Exclusion plots on coherent WIMP-nucleon cross section

Comment on CaMoO4 and Dark Matter direct detection

  • neutrinoless double-beta search (Q=3034 keV) high threshold

  • Second cryogenic phase might eventually reach low threshold (<10 keV) and good resolution for DM searches

  • Low background needed (<<0.1 counts/kg/day/keV @low energy) → discriminating technique using phonons and scintillation at the same time

  • Molibdenium enriched in 100Mo, no isotopes with spin → only sensitive to coherent interaction

  • Oxygen sensitive to low WIMP mass, Mo to high WIMP mass

By-product of ν-less ββ search!

Some simple estimations:


100 kg year

1 keV threshold




CDMS 2008




Some simple estimations:



100 kg year

10 keV threshold




CDMS 2008



Some simple estimations:


5 kg year

1 keV threshold




CDMS 2008




Some simple estimations:



5 kg year

10 keV threshold




CDMS 2008



Other projected sensitivities and some theoretical predictions

Eth=10 keV

(5 and 100 kg year)


CDMS 2008

SuperCDMS 25kg

XENON10 2007

Bottino et al

XENON100 6000 kgd

Eth=1 keV

(5 and 100 kg year)

Trotta et al

CMSSM, Ellis et al

Ellis et al

CMSSM, Markov chain Trotta et al

Effective MSSM, Bottino et al

Historical remark

Name “neutrino” proposedby Enrico Fermi in the international congress organized in Rome from 11 to 17october 1931

-ino=suffix in italian for small (ex: neutrino=small neutron, cuoricino=small cuore)











Besides E. Fermi(1) in this picture: R. Millikan(2), M. Curie(3), G. Marconi(4), N. Bohr(5), A. Sommerfeld(6), A. H. Compton(7), P. Ehrenfest(8), W. Heisenberg(9), E. Majorana(10)

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