Dark Matter Detectionwith Liquid Xenon

Masahiro Morii

Harvard UniversityLaboratory for Particle Physics and Cosmology

21 August 2009 1

Dark MatterExistence of Dark Matter is well establishedfrom its gravitational effects Coma cluster [Zwicky], Galaxy rotation curve [Rubin] Weak gravitational lensing, Bullet cluster

Amount of Dark Matter is inferred from cosmological data ~22% of the energy of the Universe Local density 0.3 GeV/cm3

Identity of Dark Matter is unknown Majority must be cold and non-baryonic i.e. made of particles that are not a part of the SM

Dark Matter is a particle physics problemas much as a cosmology problem

21 August 2009 Dark Matter 2

WIMP Dark MatterNo shortage of candidates, but…WIMPs are the front runners ~100 GeV new particles with weak

(and gravitational) interactions Such a particle would naturally have

the right thermal relic density Predicted in many BSM theories

(e.g. the LSP)

Since the annihilation cross section is constrained by therelic density, we can predict:

21 August 2009 Dark Matter 3

s(cc Æ ff )

s(cf Æ cf )

s(ff Æ cc )

Direct detection

Production at colliders

Direct WIMP Detection

Best limits on the WIMP-nucleoncross section are ~5x10-44 cm2

CDMS : Ge and Si crystals at 10 mK, 121 kg-day exposure

XENON10 : liquid Xe, 136 kg-day

For LSPs, the interesting region is around 10-44 cm2

Smaller cross sections possible, but increasingly difficult to reconcile with the flavor problem

Next generation of experiments aim for <10-45 cm2

21 August 2009 Dark Matter 4

Liquid XenonWIMP-nucleus cross section ∝ A2

Xe (A = 131.3) gives high signal rate

100 kg-year exposure can probeσ(WIMP-p) < 10-45 cm2

Key liquid Xe properties High density: 3 g/cm3

High boiling point: 165K Good scintillator: 42 photons/keV

λ = 175 nm easy to detect with PMTs High ionization yield: W = 15.6 eV

High electron mobility, low diffusion No long-lived radioactive isotopes besides double-beta decays

85Kr must be removed by charcoal chromatography

21 August 2009 Dark Matter 5

Two-Phase Xe Detector

PMTs collect prompt (S1) and proportional (S2) light signals S1-S2 delay Drift length S2 light pattern Horizontal

location

S2/S1 ratio differs markedly between electron and nuclear recoil >98.5% rejection of EM backgrounds

Good scaling to larger masses 1 m3 holds 3 tonnes Instrumentation ∝ (mass)2/3

Backgrounds improve with size due to self shielding

21 August 2009 Dark Matter 6

LUX ExperimentLUX is a 350 kg (100 kg fiducial) liquid Xe experiment Located in the Davis cavern, Sanford

Underground Lab in Homestake, SD

XENON10 technology has beenimproved to achieve <1 bkgd. in100 kg-year Xe purification system has 300 kg/day

throughput using a heat exchanger Ultra-low activity Ti vacuum vessel replaces SS + Cu PMTs have low activity (9/3 mBq of U/Th per tube) and high QE (27%) 183 m3 purified water tank shields the detector from neutrons

Recoil energy threshold <5 keV σ(WIMP-p) = 5x10-46 cm2

21 August 2009 Dark Matter 7

LUX Collaboration

Brown, Case Western, LBNL, Harvard, LLNL, Maryland, Texas A&M, Rochester, South Dakota, YaleFunded by DOE & NSF

21 August 2009 Dark Matter 8

Harvard GroupHarvard joined LUX in June 2009 Morii (50%) is the PI

Took up a critical-path item: post-amplifier 120 channels of receiver-amplifier-shaper for the PMT signals Full system is needed in November

Harvard took over production from UC Davis Oliver and Morii improved the LLNL design New LPPC engineer, Meghna Kundoor, working on testing Components in hand. PC boards in fabrication On track for November delivery

Recruiting a postdoc and 1–2 graduate students Will take part in detector integration, commissioning Develop analysis software framework

21 August 2009 Dark Matter 9

preamp

postamp

FAD

C

Dig

ital T

rigg

er

An

alo

g T

rigg

er

LUX Status and SchedulePrototype LUX0.1 is operating at Case 1 liter of liquid Xe viewed by 4 PMTs Test cryogenics and Xe purification

system >1 m electron drift achieved in 3

days

Assembly of LUX in Sanford surfacebuilding will start in November All major components are in hand Building is being fitted out Fully-assembled LUX lowered

to Davis cavern (4,850 ft) in Spring 2010 Dark Matter search will start!

21 August 2009 Dark Matter 10

LZ ProposalLZ = LUX scaled up to 1500 kg (1200 kg fiducial) Joint collaboration of LUX and ZEPLIN-III LUX infrastructure designed to accommodate LZ

σ(WIMP-p) = 2x10-47 cm2 in 2 years 2000-fold improvement over current limits

Cost of liquid Xe ~$1000/kg Maximize the fiducial/total mass ratio by rejecting

single-scatter γ-ray background with liquid scintillator

Harvard will assume larger responsibilities Development of low radioactivity, high-QE PMT Complete analog electronics chain (pre + postamp)

MRI-R2 proposal submitted this month 3-year construction Data taking in 2013

21 August 2009 Dark Matter 11

Summary and Prospect

Exciting time for Dark Matter detection Cosmology points us to compelling particle physics Liquid Xe technology has the potential for first observation

Harvard is entering DM hunting with strong commitment Producing critical component for the LUX experiment PMTs and analog electronics for the proposed LZ experiment

Discovery potential of LUX is excellent σ(WIMP-p) = 5x10-46 cm2 covers the SUSY-favored region Dark Matter search run will start in 2010

LZ will push the sensitivity to 2x10-47 cm2 by 2015

21 August 2009 Dark Matter 12