The Quest for Dark Matter with the XENON Experiment

Blank

Elena Aprile Columbia University

Milos Conference, May 22, 2008 What is the Universe made of?

>95 % UNKNOWN Dark Energy

Dark Matter in Galaxy Clusters

Gravity of the stars not enough to hold clusters together. Clusters must be held together by gravity of unseen DM Dark Matter in Galaxy Clusters

Quasar Galaxy Cluster => All cluster mass measurements Dark give Ωm > 0.15, so majority of mass Matter must be some new non-baryonic form (remembering Ωb ~ 0.05)

Earth

HST Image (1994) (Dark Matter) M-Reconstruction Dark Matter in Galaxies

Inferred from Flat Rotation Curves

First Measurement: Vera Rubin . !BB %INE VON DER 3EITE wEDGE ONi BETRACHTETE 'ALA XIEMIT7ARP"ILD2"OTTEMA

0 !BB3CHEIBENGALAXIENLASSEN SICH MITTELS EINES 4ILTED 2ING -ODELLSDARSTELLEN"ILD92E VAZ 'ENF

0 !BB$IE&ORMEINES7ARPSËH fhe]hWcc[di_dZm_hWX[hc_jjb[hm[_b[ Z[h Wajk[bb[d Lehij[bbkd] m_hZ `[Z[ =W# NELTAUFDENERSTEN"LICKEINEM _d Z[h BW][" Z_[i[ 7dWboi[d c_j Z[h [h# bWn_[led[_d[ch_[i_][d>Wbe"[_d[hMeb# )NTEGRALZEICHEN LINKS 3CHAUT \ehZ[hb_Y^[d :[fhe`[aj_ed X[h Z_[ ][# a[Wki`[d[dec_di[d:kdab[#CWj[h_[# MANSICH'ALAXIENJEDOCHGENAU iWcj[ 7kiZ[^dkd] Z[h =WbWn_[ ZkhY^# J[_bY^[d" [_d][^bbj$ M[dd cWd [_d[d ER AN DANN BESITZEN DIE 7ARPS pk\^h[d$ :_[i ][iY^_[^j c_jj[bi [_d[h iebY^[d >Wbe d_Y^j Wbi ak][b\hc_] Wd# DER 'ASSCHEIBEN DIE &ORM EI CeZ[bbh[Y^dkd]" m[bY^[ Z_[ =WbWn_[ _d d_ccj" iedZ[hd c_j pm[_ eZ[h ]Wh Zh[_ NES)NTEGRALZEICHENSMIT3ERIFEN [_d[ ]he[ PW^b ][][d[_dWdZ[h ][d[_]# kdj[hiY^_[Zb_Y^bWd][d7Yî[dWkiijWjj[j RECHTS j[h H_d][ Wk\j[_bj ½J_bj[Z#H_d]#CeZ[bb¼" ZW^[hZ[hDWc[½jh_Wn_Wb¼ "ieZWii[hWX# 7XX$ - $ =b[_Y^p[_j_] [hc]b_Y^j Z_[i ][ÔWY^jkdZkdj[hKcijdZ[d][][dZ_[ [_d[ [_d][^[dZ[ Kdj[hikY^kd] Z[h ;_# ij[bbWh[IY^[_X[][d[_]j_ij"m_hZZWi=Wi ][diY^W\j[dledMWhfi$ _c?dd[dX[h[_Y^Z[h=WbWn_[Z[cIY^m[# :_[ WbeiZ_[A_d[cWj_akdZL[hj[_bkd]Z[i mkhZ[cWd;dZ[Z[h\d\p_][h@W^h[Wk\ =Wi[ikdj[hAedjhebb[^Wj7XX$/ $:_[i[i ObservationsL[hX_[ of]k d]interstellar[d]WbWaj_iY ^gas[hI Y(21^[_X cm[dW kHI-Emission\# 8_bZ m_h ZLine)ZkhY ât8 large[eXWY^j radiikd][ d kd j [ h # c[haiWc"kdZpmWh_dkdi[h[c[_][d[d ijjpj0:_[MWhfii[jp[ddcb_Y^_cc[h => the rotationC_bYîjhW curves[dioij[c $areM[i [constantdjb_Y^ X[ii [ash far][dW kasZ eonehjWd "canmeZ _measure![ij[bbWh[dI Y ^ [ _X[ d 0 !BB $IE INNERE =>STELLAR ∼ 10E x[h a[moreddjc Matter,WdZWiF âsd eonec[d "canm[d ddirectlycWd [ dseeZ[d $=> 3CHEIBE IST GEGEN DEN TRIAXIA led Wk[d Wk\ =WbWn_[d iY^Wkj$ ;i mW# LEN (ALO GEKIPPT )M !UENBE h[die][dWddj[;Z][#Ed#=WbWn_[dieb# REICHDER'ALAXIEISTDIE3CHEIBE Y^[" Z_[ cWd h[Y^j ][dWk led Z[h I[_j[ NGC5204 WENIGER DICHT UND MASSEËRMv(r) ER i_[^j " _d Z[h[d 7k[dX[h[_Y^[d H[dpe SIEGEHORCHTDAHERDEM'RAVITA IWdY_i_'/-,iebY^[MWhfi[haWddj["kdZ TIONSPOTENTIAL DES $UNKLEN (A pmW bulge,h_dl disk_[h &l ehalod\d\kdj[hikY^j[d<b# HI-component LOS b[d${X[hZ_[KhiWY^[vZ _~[ iconst[iF^dec[di ^WX[di_Y^Z_[7ijhedec[di[_j^[hl_[b[ =[ZWda[d][cWY^j"[_d[[_d haloZ[kj_][B# ikd]Z[iFheXb[ci_ijWX[hdeY^d_Y^j_d I_Y^j$;_d[C]b_Yâ[_j_ijZ_[Z[h=[p[_# –1/2 j[dm_hak d]bulgele &d diskX[dWYv^ X~W hrj[d =WbWn_[d$ @[ZeY^ÓdZ[jcWdWkY^_d_ieb_[hj[d=W# bWn_[daNotbWhW kai ]good[X_bZ [fit!j[Mr Whfi$ ;_d[ WdZ[h[ c]b_Y^[ ;habhkd] \h Z_[i[iF^dec[db_[\[hdie][dWddj[jh_# A B C D U. Klein et al., SuW Sept. 2005 Wn_Wb[ >Wbei :kdab[h CWj[h_[$ =[c

34%2.%5.$7%,42!5- 3EPTEMBER Large Scale Structure

Measurement: 2dF Survey Simulation:http://krone.physik.unizh.ch/~moore/

Dark matter dominates & provides first structures in the Universe

Simulation results depend primarily on whether the dark matter is hot (relativistic) or cold (non- relativistic) when structures were formed Most of the Universe’s matter must be Cold Dark Matter Dark Matter & Particle Physics ✦Dark matter as WIMPs (Weakly Interacting Massive Particles) ➡ stable (formed in the big bang, freeze-out)

➡ neutral (no EM interaction, only gravitational effects observed) ➡ heavy (mass ~ 100 GeV to 1 TeV)

8 Weakly Interacting Massive Particles

!""#$%!""#$%&'()#%&'()#%*%*%+,-#$%+,-#$%&'()#&'()# WIMPs:

106 per second through your thumb without being noticed!

1015 through a human body each day: only < 10 will interact

If their interaction is so weak, how can we detect them? WIMPs Production by Accelerators

χ q q χ

χ - q q- χ

CERN LHC

Geant4., ﬁg. from H. Baer WIMPs Indirect Detection

χ q χ q

χ q- χ q- WIMPs Direct Detection

χ q χ χ

χ q- q q

scattering off nuclei in terrestrial detectors..deep underground.. to shield them from cosmic radiation WIMPs Direct Detection

WIMP χ0 10-100 WIMPs/liter, v ≈ 10-3c

WIMPs scatter elastically with nuclei: ER

Rate ∼ N ρχ/mχ <σχ-N>

N = Number of target nuclei in detector WIMP ρχ = Local WIMP Density

<σχ-N> = Scattering Cross Section 0 Rate << 1 Event/kg/Day χ

WIMP WIMPs Density in our Galaxy

Measured Rotation Curve of the Milky Way: ﬂat up to ≈ 50 kpc

12 Mvirial = 1-2×10 Msun

θ Halo R Disk

Bulge

Acceptable range: 3 ρ0 = 0.3 - 0.6 GeV/cm (Klypin, Zhao & Somerville 2002) 5 ~ 10 larger than in the universe at large WIMP-Nucleon Cross Section Nucleon

Nature 448, July 19, 2007

95% 68% 1 event/kg/yr XENON100

10 events/ton/yr XENON1T CMSSM (Roszkowski, Ruiz, Trotta) Experimental Challenges

Ultra Low Background (< 10-4 evts/ WIMP Scattering kg/keV/day) 18 evts/100-kg/year

(Eth=5 keVr) deep underground labs 8 evts/100-kg/year

(Eth=15 keVr) low radioactivity materials

active/passive shielding

Very large target mass (1000 kg)

Very low energy threshold (KeV)

Excellent long-term stability dR σ ρ  Qm  = 0 0 exp − N F2 (Q) Event-Discrimination (WIMPs=NR, 2  2 2  dQ πv0mχ µ  2µ v0  Background=ER) World Wide WIMP Searches

Boulby SNOLAB ZEPLIN DEAP/CLEAN DRIFT PICASSO Yangyang Homestake KIMS DUSEL-ISE

Frejus/ Modane Kamioka Soudan EDELWEISS XMASS CDMS Gran Sasso CRESST DAMA/LIBRA WARP XENON

17 Why (Liquid) Noble Gases for DM Searches ? Cryogenic Noble Liquids: Basic properties

• Suitable materials for detection of ionizing tracks:  Dense, homogeneous, target and also detector  Do not attach electrons  High electron mobility (except neon in some conditions)  Commercially easy to obtain and to purify  Inert, not flammable, very good dielectrics

Liquid Radiation Collision Electron Energy loss Boiling point Density length length mobility Cost Element @ 1 bar (K) ( /cm3) dE/dx (MeV/cm) (cm2/Vs) ρ X0 (cm) λ (cm)

Neon 1.2 1.4 24 80 27.1 high&low $

Argon 1.4 2.1 14 80 87.3 500 $$

Krypton 2.4 3.0 4.9 29 120 1200 Xenon 3.0 3.8 2.8 34 165 2200 $$$ The Merits of LXe for Dark Matter

Recombination depends on type of recoils (stronger for nuclear recoils) Xe+ Ionisation ✦Large nucleus (A~131) : good for SI +Xe plus SD sensitivity (~50% odd isotopes) Electron/nuclear recoil Xe + ✦scalability : relatively cheap ($1500/kg) and 2 “easy” cryogenics at 160 K Excitation +e- background reduction: via self-shielding (recombination) ✦ wavelength (Z=54, ρ=3 g/cc) depends on gas Xe* Xe** + Xe e.g. Xe 175nm Ar 128nm ✦intrinsically background free: Kr in Xe can +Xe be puriﬁed to ppt level Xe * ✦low threshold : high scintillation yield (~80% 175nm 2 175nm of NaI but much faster) Triplet Singlet 27ns 3ns

✦gamma rejection: electron and nuclear time constants recoil discrimination 2Xe 2Xe depend on gas e.g. Xe 3/27ns Ar 10/1500ns XENON: Two Phase Time Projection Chamber Based on the extraction of the quasifree electrons from liquid into vapor phase (B.A. Dolgoshein et al., Sov. J. Part. Nucl. 4 (1973) 70. ) The XENON10 TPC

✦ Pulse Tube refrigerator: stable operation at 170 K ✦ TPC active volume: 20 cm (Φ) x 15 cm (H) - 15 kg Pulse tube ✦ PTFE Teﬂon: ~95% UV reﬂectivity at 175 nm refrigerator ✦ 89 PMTs (R8520): 20% QE, low radioactivity

89 PMTs PTFE 15 kg LXe XENON10 Gamma/Neutron calibration

~ 99.5 % gamma events are rejected below the nuclear recoil mean Self-Shielding in XENON10 TPC near top PMTs near bottom PMTs

Z (15 cm total)

15 < drift time < 65 μs, r < 80 mm (5.4 kg ﬁducial mass) Overall Background in Fiducial Volume ~0.6 event/(kg day keVee) XENON10 at the Gran Sasso Underground laboratory XENON10 Pb/Poly Shield Detector

3100 mwe ﬂat overburden (surface muon ﬂux reduced by 106)

24 XENON10 SI WIMP-Nucleon Cross Section Upper Limits

Phys. Rev. Lett. 100, 021303 (2008) (90 % CL)

CDMS II 8.8 x 10-44 cm2 at 100 GeV 4.5 x 10-44 cm2 at 30 GeV XENON10

supersymmetry models

25 XENON10 SD WIMP-Nucleon Cross Section Upper Limits (90 % CL)

Natural Xe has non-zero nuclear spin isotopes: 129Xe (spin-1/2) @ 26.4% and 131Xe (spin-3/2)@ 21.2%. Both contain unpaired neutron thus XENON10 is mostly sensitive to WIMP-neutron spin-dependent couplings, yielding the best sensitivity to-date.

pure neutron couplings pure proton couplings

ZEPLIN-II KIMS: CsI CDMS-II 73Ge XENON10 ZEPLIN-II NAIAD CDMS-II 73Ge KIMS: CsI XENON10 PICASSO

CMSSM

SuperK

CMSSM

26 XENON10 Heavy Majorana NeutrinoUpper Limits (90 % CL)

27 Feb 08: CDMS Reports a new WIMP-Nucleon Cross Section Limit

28 XENON100 : the current step in the XENON program (2007-09)

A new and improved TPC design guided by the XENON10 experience and for the same underground location and passive shielding

Bell • 170 kg LXe (vs. 20 kg in XE10); 50 kg ﬁducial mass (vs. 5 kg in XE10). Grids x10 ﬁducial mass Structure Top PMTs • 242 R8520 PMTs with lower Teflon background and higher QE (vs. 89 in Panels with Active LXe Target HV XE10) Racetracks • lower background stainless steel Active LXe Shield cryostat and inner chamber Bottom PMTs • a factor of 100 lower background Shield PMTs Cathode Mesh

Vacuum Cryostat

29 XENON100 Sensitivity Reach by 2008

CDMS II

XENON10

XENON100

30 +UCLA recently joined (now ~30) 31 XENON100 Detector Assembly 4

Welding the top cover

Guillaume Plante - XENON - April 16, 2008

32 The XENON100 TPC Assembly: the

170 kg LXe (70 kg target)

33 The XENON100 Photomultipliers

• 1 “ square metal channel Hamamatsu R8520-06-Al • Low radioactivity (<1 mBq U/Th per PMT) • 98 on top - 80 on bottom - 64 in active LXe shield • QE~23% for top array; QE~33% for bottom array

34 Status of XENON100: Installed Underground at LNGS

• Shield modiﬁcation/improvement:Jan 08 • Detector underground: Feb 08 • Xe Puriﬁcation/ Kr-distillation: May-June 08 • Gamma/Neutron Calibration: May-July 08 • 1st DM Search: Aug-Sep 08 XENON100 (Feb.2008) XENON10 (2006-2007)

3543

XENON100: Expected gamma background rate

0.01 evt/kg/keVee/day (10 mdru) in 50-kg ﬁducial mass

Operating the detector for two months (~3000 kg-d exposure) will give: <1 background event (with 99.5% ER rejection, within 10 keVee window) 37 XENON100: Expected neutron background rate

Neutron rates in XENON100 in the energy region of 4.5 – 26.9 keV

Material Neutron rate [mdru] Stainless steel 2.93e-4 simulated neutron background PMTs 3.18e-4 Teflon 16.26e-4

Copper 0.11e-4 Poly 4.87e-4

Total 2.74e-3

The total neutron bg from detector materials and shielding in XENON100 is 0.9 single neutron recoils/year

38 XENON1T : the next step in the XENON program (2009-12)

• Studies of a TPC design with full coverage of a new ultra low radioactivity 3 “ photodetector (QUPID) started • Ultra low energy threshold and long-term stability • Experiment proposal being prepared for Fall 08 for construction start in 2009 • Modest construction cost: ~$20M shared by NSF + DOE + Foreign • Within 2012 XENON1T will explore the full region in CMSSM space (or accumulate WIMP statistics for DM physics)

39 The XENON Phased Program (2006-2012) and Beyond

XENON10 XENON100 XENON1T Detectors (2006-2007) (2007-2009) (2009-2012)

Fiducial Mass (kg) 5 50 1000

Gamma background -2 -4 (dru: events/kg/keV/day) 1 10 goal: <10

Neutron background < 1 per year < 1 per year goal: < 1/two years

Exposure 2 months 2 months 2 year

lower bkg, higher QE Photodetectors R8520 R8520 QUPID (or + R8520)

-45 2 -47 2 WIMP Sensitivity -43 2 2 x 10 cm 3 x 10 cm at 100 GeV 0.9 x 10 cm (projected) (projected) SuperXENON : the next step is a 20 T Experiment for DUSEL

40 If DM is due to new physics at the 100 GeV scale it is likely that two- phase Xe detectors will lead the race to ﬁnd it. Direct searches essential to complement LHC and Indirect searches

XENON10 (2007) XENON100 Projected (2009) CDMS (2008) SuperCDMS 25kg Projected (2012) LUX 300kg Projected (2010)

XENON1T Projected (2012)