Stefano Scopel

Stefano Scopel

Daejeon, 24-26 september 2009

Review of dark matter searches and comments on CMO DM

search

International Workshop on Double Beta Decay Search, SNU, Seoul, October 15-17 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 CaMoO4 coul be used to search for WIMPS

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

*

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

Ωdark matter~ 0.22

The concordance model

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”)

The properties of a good Dark Matter candidate:

subdominant candidates – variety is common in Nature →may be easier to detect

*

(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:

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

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

*

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

•susy

conserved symmetry

DM candidate

R-parity

K-parity

T-parity

χ (neutralino)

•extra dimensions

•little Higgs

B(1)(KK photon)

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

<σannv>int=∫<σannv>dxxf

x0

xf=M/Tf

x0=M/T0

Tf=freeze-out temperature

T0=present (CMB) temperature

Xf>>1, X non relativistic at decoupling, low temp expansion for <σannv>:

<σannv>~a+b/xif σann ~0.1 pbarn (weak-type interactions) → ΩX~0.1-1

…+ cohannihilations with other particle(s) close in mass + resonant annihilations

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

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

Searches for relic WIMPs

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

χ + N χ + N • Indirect searches. Signals due to χ - χ

annihilations

χ + χ n, n, g, p, e+, d -- -

g gf f

W+W-

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

W+H-, W-H+ Zh, ZH, ZA

-

Annihilations taking place in celestial bodies where χ’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 Galactic center, clumpiness

g gf f

W+W-

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

W+H-, W-H+ Zh, ZH, ZA

-

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 neutralinoThe neutralino is defined as the lowest-

mass linear superposition of bino B, wino W(3) and the two higgsino states H1

0, H20 :

021

011

)3(21

~~~~ HaHaWaBa

neutral, colourless, only weak-type interactions

stable if R-parity is conserved, thermal relicnon relativistic at decoupling Cold Dark

Matter (required by CMB data + structure formation models)

relic density can be compatible with cosmological observations: 0.095 ≤ Ωχh2 ≤ 0.131

IDEAL CANDIDATE FOR COLD DARK MATTER

~ ~~ ~

3 4

SUGRA(a.k.a. CMSSM)

focus point

[Feng, Machev, Moroi, Wilczek]

stau coannihilation Higgs funnel

[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)

solves the μ problem, i.e. why μ~MEW

superpotential:

Higgs soft terms in the NMSSM:

NMSSM particle content: MSSM+ 2 Higgs (CP-even, CP-odd)1 neutralino dof

The lightest neutralino:

CP-even Higgs:

Relic density and direct detection rate in NMSSM[Cerdeño, Hugonie, López-Fogliani, Muñoz, Teixeira]

relic abundance direct detection

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)

tachyons

Landau pole

unphysical minima

W

H1

H2/2

χ,H lighter

χ singlino

Z

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

• μ Higgs mixing mass parameter

• tan β ratio 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±)

• mq soft mass common to all squarks

• ml soft mass common to all sleptons

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

• R ≡ M1/M2

~

~

~

~

~

~

~

SUGRAR=0.5

Can the neutralino be ?

Cosmological lower bound on mχ

upper bound on ΩCDMh2

scatter plot: full calculation

curve: analytical approximation forminimal ΩCDMh2

[Bottino, Fornengo, Scopel, PRD68,043506]

M1<<M2,μ

(à la Lee-Weinberg)

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, astro-ph/0307403

Neutralino – nucleon cross section Color code:● Ωχh2 < 0.095 Ωχh2 > 0.095

The elastic cross section is bounded from below

“funnel” at low mass

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

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)n

is conserved → LKP (Lightest KK particle) is stable•1-loop corrections (Cheng &al, 2002): LKP=1st

excitation of weak hypercharge boson B(1)

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:

if cohannihilating particle annihilates than LKP→ relic abundance

fasterslower

smaller

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

KK leptons

Δ≡fractional mass splitting

ΩB (1)h2=0.1

•low direct detection signals:

Δ≡(mq1-mB1)/mB1

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)

x

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

counter-rotation

solid: CDMS, vesc=650 km/sec

dots: ZEPLIN vesc=650 km/sec

long dashes: CDMS, vesc=450 km/sec

PRD71,043516,2005

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 eventsN~ (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)]

ω=2π/T0

DAMA disfavoured by other direct searches

From Savage et al., arXiv:0901.2713

small viable window with MWIMP 10≲

KIMS spin independent limits (CsI)

Nuclear recoil of 127Iof DAMA signal regionruled out

ρD=0.3 GeV/c2/cm3

v0=220km/svesc=650km/s

PRL 99, 091301 (2007)

Systematic uncertaintyFitting, Quenching factorenergy resolution...combined in quadrature~ 15% higher than w/o syst.

no light target in CsI → in principle Na in DAMA more sensitive for 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

Quenching• 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)

•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

C2~3, d=interatomic spacing

a0=0.529 Å (Bohr radius)

critical angle:

• 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

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

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

no channeling

channeling

•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

Channeling effect in crystals

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•EDELWEISS II•XENON10n (n=1,2,3,….)•ZEPLIN II•WARP•CUORE•COUPP •PICASSO•ANAIS•모루 ? 모모 ? 이’ s… •…

scintillators

Ionization+heat (cryogenic)

dual-phase TPC

Heat experiment (CUORICINO)

metastable bubbles

scintillator

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:

CDMS 2008

100 kg year1 keV threshold

B=0

B=0.1

B=1

B=10

B=1e-4

B=1e-3

B=1e-2

Some simple estimations:

100 kg year10 keV threshold

CDMS 2008

B=0

B=0.1

B=1B=10

B=1e-4

B=1e-3

B=1e-2

Some simple estimations:

5 kg year1 keV threshold

CDMS 2008

B=0

B=0.1B=1

B=10

B=1e-4B=1e-3

B=1e-2

Some simple estimations:

5 kg year10 keV threshold

CDMS 2008

B=0

B=0.1

B=1B=10

B=1e-4

B=1e-3B=1e-2

Other projected sensitivities and some theoretical predictions

Bottino et al

Trotta et al

Ellis et al

CaMoO4

CDMS 2008 SuperCDMS 25kg

XENON10 2007

XENON100 6000 kgd

CMSSM, Ellis et al

CMSSM, Markov chain Trotta et al

Effective MSSM, Bottino et al

Eth=10 keV(5 and 100 kg year)

Eth=1 keV(5 and 100 kg year)

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

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)

Historical remark

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

2 3 45

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