search for dark matter with xenon - xenon group at mainz

Dark Matter Direct Detection of WIMPs

Search for Dark Matterwith XENON

Christopher Geis & Pierre SissolInstitute of Physics

Experimental Particle and Astroparticle Physics (ETAP)Johannes-Gutenberg Universitat Mainz

Pizza seminar6 December 2013

Pizza seminar, 6 December 2013 Ch. Geis & P. Sissol 1 / 46


Outline

Dark Matter

Direct Detection of WIMP Dark Matter with XENON

Summary



Outline

Dark Matter


Summary



Evidences for Dark Matter

What is the universe made of?


Springel et. al. (2008) arXiv 0809.0898



Galaxy Scale - Rotation Curves

Rotation velocity of spiral galaxies:

v(r) =

√G ·M(r)

r

Expected: → v ∝ 1√r

But observed:

v = const⇒M(r) ∝ r

⇒ ρ(r) ∝ r−2

⇒ Big mass has to be present in the Galaxybesides the visible mass!

→ Halo of invisible matter causes constant velocity: Dark Matter




Cluster Scale - Velocity Dispersion

“Falls sich dies bewahrheiten sollte,wurde sich also das uberraschendeResultat ergeben, dass dunkle Ma-terie in sehr viel grosserer Dichtevorhanden ist als leuchtende Ma-terie”Zwicky, F. Helv.Phys.Acta 6 (1933) 110-127

Fritz Zwicky (1933) measured the velocitydispersion in the Coma cluster much higher thanexpected.

Virial Theorem:

〈V 〉+ 2〈K〉 = 0

V = −N2

2G〈m2〉〈r〉 , K = N

〈mv2〉2

M = N〈m〉 ∝ 2〈r〉〈v2〉G

∑

mGalaxies




Cosmic Scale - Cosmic Microwave Background

Before decoupling of the Baryon-Photon plasma, primordial fluctuations can justexcite sound waves in the plasma, but can start already growing in thecollisionless Dark Matter

Courtesy: David Spergel

These sound waves leave an imprint on the last scat-tering surface of the CMB as the universe turns trans-parent




Cosmic Scale - Cosmic Microwave Background

Planck Collaboration (2013) arXiv 1303.5075

For a statistically isotropic gaus-sian random field, the angular powerspectrum can be constructed by de-composing in spherical harmonics:

∆T (n) =∑

am` Ym` (n)

D` =1

2`+ 1

∑|am` |2

→ Anisotropies are sensitive to the Baryon/CDM densities

ΛCDM model affirmed:

ΩΛ = 0.6825 Ωch2 = 0.1203 Ωbh

2 = 0.022




Energy Density Content of the Universe

There is a huge amount of Dark Matterin the universe and even more of DarkEnergy.Actually the “usual“ baryonic matteris the exotic one in the universe!

Cosmic sum rule:

ΩΛ + Ωc + Ωb = 1




ΛCDM Model

Does correctly predict the following observations:

Existence and structure of the CMB

The large-scale structure of the universe:→ ”bottom-up scenario” → CDM

The abundance of hydrogen, deuterium andhelium:Big Bang Nucleosynthesis

Accelerated expansion of the universe:→ “Cosmological constant”Λ

Springel+ (2005)

→ Standard model of cosmology!



Models without Dark Matter

Is it possible that DM is illusionary?

MOND (Modified Newtonian Dynamics) assumes that Newton’s law is notexactly true for a 1

Modification of Newton’s law to F = ma · µ(a/a0), with µ(x) = 11+x

NGC 2903

Sanders & McGaugh, ARAA40:093923,2002

Excellent fits to galactic rotation curveswith

a0 = 1.8 · 10−8 cm/s2



Models without Dark Matter

MOND vs. Dark Matter

MOND fails on the scale of clusters of galaxies where it cannot explain extramass in cores of big galaxy clusters! Dark Matter is required

→ TeVeS might solve this, due to different laws of deflection of light!

But: MOND & TeVeS have not yet provided a satisfactory understandingof the CMB unisotropies and structure formation while the ΛCDM-Modelhas!



Dark Matter Candidates

What is Dark Matter?

”If it’s not DARK, it doesn’t MATTER“

http://www.particlezoo.net




Baryonic Dark Matter

Ωb > Ωlum

⇒ Dark Matter could consist of MACHOs (Massive Astrophysical Compact HaloObjects)

Detection possible via gravitational microlensing when the MACHO transits anobject behind

Hubble shot: LRG 3-757

Projection of few discovered MACHOsfor the whole Halo is not large enoughto explain large invisible mass.

→ MACHOs just sum up to . 8 %of the Dark Matter Halo!L. Wyrzykowski et al., EROS-2 Collaboration (2010)




Dark Matter in the Standard Model

Dark Matter can just interact weakly and/or gravitationally!




Neutrinos as Dark Matter

Cosmological point of view:

Neutrino cosmic mass fraction: Ωνh2 =

∑mνi

93.4 eV

To account for all the dark matter: Ωch2 = 0.12→ mν ≈ 10 eV

But: Actual experimental upper limit mν < 2.2 eV (Mainz/Troitsk)

CMB anisotropies lead to Ωνh2 < 0.0067→ mν < 0.2 eV

Neutrino mass not enough to account for all the ”missing mass” in theuniverse.

They are so called “Hot Dark Matter“ and just a small contribution toDark Matter, since the universe structure formation affirms cold darkmatter!




Dark Matter in the Standard Model

→ Standard Model doesn’t provide a candidate for Cold Dark Matter




Sterile Neutrinos

Small extension of the SM by adding right-handed neutrinos which are justunderlying the gravitational force.

- Not necessarily 3 generations

- Mass could be in the keV - Regime

- Sterile Neutrinos may mix withordinary Neutrinos and couldparticipate in weak interactiondecays

The decay νS → ν + γ produces a sharpX-ray line which should be visible in X-rayspectra of galaxy clustersSearch for those lines ruled out largebut not all parts of the models param-eter space!

Courtesy of: A. Boyarsky, D. Iakubovskyi, O. Ruchayskiy

νS

θα

ℓ±α

W±

γ

να




Axions and ALPs

Arise in the Peccei-Quinn solution of the strong CP-Problem in QCD

- Introduction of a U(1) symmetry compensates the violating term

- Spontaneous breaking of that symmetry implies a new particle, the Axion

- Introduction of more than one U(1) symmetries lead analogously to ALPs(Axion Like Particles)

Axion mass is ma ≈ eV(107 GeV/fa

), coupling to ordinary matter is ∝ f−1

a

Assuming Ωχh2 ≈ 0.13→ Axions with 10µeV masses can account for all Dark

Matter.

→ Axions and ALPs not yet detected but and exclusion limits are set, butare still possible candidate for Dark Matter




WIMPs

WIMPs (Weakly Interacting Massive Particles) are hypothetical particles to solvethe Dark Matter Problem.

By definition they are characterized as follows:

- Just interacting weakly and gravitationally

- Not interacting via electromagnetic and strong force

- Large mass compared to the standard particles

- Possible scatter cross-section off nuclei

- Possible annihilation cross-section to standard particles




WIMP Freezeout in the early Universe

At early times in the universe (T Mχ) WIMPswere in thermal equilibrium with SM particles

χ+ χ←→ qq, `¯, . . .

At the time T < Mχ annihilation becomesBoltzmann supressed

WIMPs cannot annihilate any longer →Constitution of primordial relic population thatstill exists today ”freeze out”

Ωχh2 ≈ 0.12→ 〈σAv〉 ≈ 2.5 · 10−26 cm3/s

→ “WIMP miracle“

G. Jungman, M. Kamionkowski and K. Griest,Phys. Rept. 267, 195 (1996)

〈σAv〉 = thermally averaged annihilationcross-section of χχ into lighter particles.

Ωχh2 ≈

3 · 10−27 cm3/s

〈σAv〉



Supersymmetric Models

Supersymmetric Particles

A supersymmetric transformation Q turns a bosonic state into a fermionic stateand vice versa

Q |Boson〉 = |Fermion〉

Q |Fermion〉 = |Boson〉




So many SSMs...




Minimal Supersymmetric Standard Model

- Realization of R-Parity: R = (−1)3(B−L)+2S

R = 1 for SM particles, R = −1 for superpartners

- Large number of parameters

- Reduction of parameters → CMSSM

- Assuming R-Parity is conserved → Lightest Supersymmetric Particle (LSP)must be stable!

→ LSPs are the most favoured candidate for WIMPs




Supersymmetric Dark Matter

Candidates for the LSP as Dark Matter particles are:

- Sneutrino ν: Superpartner of ν. Experimentally ruled out, but sterileSneutrinos are still discussed

- Gravitino G: Superpartner of the not yet discovered Graviton G. Relicabundance and decay of other non stable SSM particles could sum up to theexpected value of ΩCDMh

2 ≈ 0.13

- Axino a: Superpartner of the Axion a.

- lightest Neutralino χ0: Linear combination of γ, Z0, H0a and H0

b

Most fashionable/studied WIMP candidate.Relic abundance of Ωχ0 ≈ 0.1 −→ Neutralino mass mχ ≈ 100 GeV

Experiments put great effort to discover a LSP → Pierre’s Talk



Outline

Dark Matter


Summary



Dark Matter detection

Three ways to detect Dark Matter

HE particle colliders(LHC, ...)

Figure: CERN

SM

χ

SM

χ

Pro

du

ctio

nIn

direct

Detection

Direct Detection

Satellites, telescopes(PAMELA, FGST,IceCube, ...)

Figures: PAMELA, IceCube



Dark Matter detection

Direct Detection modes

Interaction

Phonons

Charge Scintillation

EDELWEISS

CDMS / SuperCDMS

PICASSO

SIMPLE

COUPP

CRESST

ROSEBUD

DAMA

KIMS

DEAP-3600

CoGeNT

XENON, LUX / LZ, DarkSide



Non-xenon technologies

Is there a signal?

DAMA/LIBRA: DM signal as annual modulation (8.9 σ C.L.)

Experiments which claim to have detected a signal

DAMA/LIBRA

CoGeNT

CRESST-II and CRESST-Si

CDMS

2012 J. Phys.: Conf. Ser. 375 012002PRL 106, 131301 (2011)2012 J. Phys.: Conf. Ser. 384 012013arXiv: 1304.4279v3



Non-xenon technologies

Possible WIMP regions?

] 2WIMP Mass [GeV/c3 4 5 6 7 8 9 10 20 30 40 50 60 70 100

]2

WIM

P-N

ucle

on C

ross

Sec

tion

(SI)

[cm

-4210

-4110

-4010

-3910

COUPP (2012)

EDELWEISS (2010/2011)

CRESST-II (2012)

DAMA (Savage, 2009)

CoGeNT (2012)

ZEPLIN-III (2011)

XENON10 (2011)

SIMPLE (2012)

CDMS (2010/2011)

CDMS-Si (2013)

XENON100 (2012)

XENON1T (2017)

LUX (2013)

Buchmueller (2011)

Roszkowski (2013)

EURECA

Edelweiss 3

SCDMS at SNOLAB

Neutrino background

CRESST-II (running)

COUPP (2012)COUPP (2012)

Data: dmtools.brown.edu



XENON

The XENON100 Experiment

Laboratori Nazionali del Gran Sasso(LNGS)

XENON100

Figure: LNGS

below 3600 m water equivalent

161 kg of xenon

62 kg detection volume99 kg active veto

Astropart.Phys. 21 (2004) 523-533



XENON

Veto and Shielding

Veto PMTs viewing active vetovolume around detection volume

Figures: XENON100 Collaboration

Different shielding layers around detectorcopper

polyethylene

lead

water



XENON

Why use xenon?

provides largest expected event rate forlow-mass WIMPs

dR

dEr=

ρ0

mNmχ

∫ ∞vmin

vf(v)dσWN

dER(v,ER)dv

mχ = 100 GeV/c2, σ = 10−43 cm2

Figure: 2007 J. Phys.: Conf. Ser. 60 58almost equal fraction of even and oddmass number isotopes→ investigate spin-independent ANDspin-dependent WIMP-nucleoninteractions

self-shielding properties

high density(liquid at boiling point: 3.057 g

cm3 )

transparent for its own scintillation light

no long-lived radioactive isotopes (goodpurification possibility)

relatively easy handling / cooling (178 K)and easy scalable



XENON

The Time Projection Chamber (TPC)




XENON

Fiducialization

coordinate:x-y

S2-signal

Detection of S2 signal pattern → x-y position

Electron drift time |t(S2) - t(S1)| → z position

Definition of fiducial volume (here: 34 kg) toexclude near-edge events

coordinate:z




XENON

Background discrimination Figures: XENON100 Collaboration

ratio S2S1 gives information about interaction

Distinction of electronic and nuclear recoils as discrimination method

Ongoing research in low-energy region



XENON

Xe response of low-energy nuclear recoils

Relative scintillation efficiency Leff: S1Leff−→ recoil energy

Charge yield QY : S2QY−→ recoil energy

Future studies in Mainz: precision measurements of Leff and QY with the MainzTPC

Figures: Physcial Review D 88, 012006 (2013)



XENON

XENON100 Results

224.6 live days with 161 kg xenon

upper limit for WIMP cross-section:2.0 · 10−45 cm2 (mχ = 55GeV/c2) at90 % C.L.

two events in ROI

“no excess due to a dark matter signal“(26.4 % prob. for two events inbenchmark region)

PRL 109, 181301 (2012)



XENON

XENON100 Results

spin-independent

PRL 109, 181301 (2012)

spin-dependent

PRL 111, 021301 (2013)



XENON

LUX

85.3 live days with 370 kg xenon

upper limit for WIMP cross-section:7.6 · 10−46 cm2 (mχ = 33GeV/c2) at90 % C.L.

160 events in ROI

“all observed events being consistent withthe predicted background of electronrecoils.“(p-value of 0.35 for background-onlyhypothesis)

arXiv:1310.8214

PMTs with higher QE than XENON100

better light yield due to electric grids with higher transparency

new calibration method using tritiated methane (Emax = 18 keV) → ER band anddetection efficiency calibrations with unprecedented accuracy

(arXiv:1310.8214)



XENON

WIMP exclusion

] 2WIMP Mass [GeV/c3 4 5 6 7 10 20 30 40 100 200 1000 2000 10000

]2

WIM

P-N

ucle

on C

ross

Sec

tion

(SI)

[cm

-4710

-4610

-4510

-4410

-4310

-4210

-4110

-4010

-3910

COUPP (2012)

EDELWEISS (2010/2011)

CRESST-II (2012)

DAMA (Savage, 2009)

CoGeNT (2012)

ZEPLIN-III (2011)

XENON10 (2011)

SIMPLE (2012)

CDMS (2010/2011)CDMS-Si (2013)

XENON100 (2012)

XENON1T (2017)

LUX (2013)

Buchmueller (2011)

Roszkowski (2013)

EURECA

Edelweiss 3SCDMS at Soudan

SCDMS at SNOLAB

Neutrino background

Data: dmtools.brown.edu



XENON1T

The XENON1T Experiment

Laboratori Nazionali del Gran Sasso(LNGS)

XENON1T

Figure: LNGS

Figure: XENON Collaboration



XENON1T

XENON1T - properties

arXiv:1206.6288 [astro-ph]

Cryostat:

1 m diameter, 1 m height of active volume

≈ 2.2 t of xenon

∼ 1.1 t active volume∼ 1.1 t active veto

≈ 250 PMTs

essentially scaling up XENON100 by about a factor of 10

⇒ background reduction by a factor of 100

Estimated sensitivity:

10−47 cm2

for spin-independent search



XENON1T

The Muon Veto for XENON1T

Figure: XENON Collaboration

9.6 m diameter x 10.5 m height

ultra-clean water, continuouspurification

84 PMTs to measure Cerenkovradiation

reflective foil on tank walls androof (also wavelength-shifting)

reduction of expectedmuon-induced neutron backgroundsignal

construction started in September (roof cladding), wall cladding andmounting of PMTs in spring



Summary

The existence of Dark Matter is based on a variety of evidencesfrom astronomy, astrophysics and cosmology

The WIMP is one of the most promising candidates for Dark Matter

Many different models provide intuitively particles with WIMP properties

Various experiments are searching for Dark Matter particles using diverse methods

Currently detectors employing xenon set the most stringent limitson WIMP mass and cross-section

Future experiments are under construction and aim to even better sensitivities



Any questions?

Thanks to the Mainz XENON Group.


search for dark matter with xenon - xenon group at mainz

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