elena aprile columbia university for the xenon...

DMSAG - 29 June, 2006 Elena Aprile, Columbia University

The XENON Dark Matter Experiment

Elena AprileColumbia University

for the XENON Collaborationhttp://www.astro.columbia.edu/~lxe/XENON/


XENON: a brief history

• Sep 2001: XENON concept proposed to NSF• Sep 2002: NSF award to CU (with subcontracts to Brown/Princeton/Rice) for 2-year R&D phase• Sep 2003: Proposal to NSF to start design and construction of the 1st TPC module, XENON100.

Proposal favorably reviewed but collaboration (Yale + Florida added) correctly asked to complete first R&D phase with a prototype at the 10 kg scale (XENON10).

• Oct 2004: NSF award to CU (with subcontracts to Case/Yale/Rice/Florida) for 3-year. Brown & LLNL submit proposals to DOE for XENON10 subsystems (DAQ/Shield/HV). Visit several underground laboratories. Choice b/w Soudan & LNGS. Depth favors LNGS. XENON10/100 reviewed and accepted by LNGS Scientific Committee and Director.

• March 2005: Meeting at DOE (Aprile/Gaitskell/Bernstein) to present XENON10 case. Support follows with award to Brown and LLNL. In 2005 collaboration focused on testing a variety of prototypes with mass up to several kg. Two important measurements made and a full 3D imaging Xe dual phase (XENON3) is built and tested. Modifications of XENON3 lead to XENON10 (15 kg). Commissioning detector at Nevis Lab completed in Feb 2006.

• March 2006: Move XENON10 equipment to LNGS on March 2. Start underground installation on March 7. XENON10 is filled on March 18. Note: spokesperson is 100 % on project (on leave from teaching in Fall 05 (double teach in Fall 06) and on sabbatical in Spring 06).


XENON Concept: Overview

• Modular design: 1 ton LXe (XENON1T) in ten modules (XENON100). Module is a 3D position sensitive dual-phase (liquid/gas) XeTPC with 100kg active Xe target

• Background Discrimination based on:

1. simultaneous detection of scintillation (S1) and ionization (via proportional scintillation S2)

2. Event localization in 3D, from drift time (σZ) and upper PMTs hit pattern (σX,Y)

• XENON10 prototype at LNGS to validate performance:

• Light Detection ≈ 2 pe / keV @ 1kV/cm• WIMP Analysis threshold ≈ 20 keV• Background Rejection >99% • 3D Position Resolution:σZ ~0.3 mm; σX,Y ~10 mm• Current phase funded by NSF and DOE


Motivation for Liquid Xenon as Dark Matter Target

! Large A (~ 131) good for SI σ~ A2 but need low threshold ! 129Xe (26.4%) and 131Xe (21.2.4%) good for SD σ! No radioactive isotopes - Kr85 contamination can be at

ppt as demonstrated by XMASS – no U/Th

! Target and detector in one homogeneous, self-triggering, self shielding and compact volume (X0 = 2.8 cm)

! Excellent charge and light yields (Wp =22.4 eV; We=15.6eV for mip; For NR, QF ~0.2)

! Background Discrimination Methods: Simultaneous Charge and Light detection plus 3D event localization

! Commercially easy to obtain and to purify – reasonable cost for tonne scale detectors. ‘Easy’ cryogenics at ~165K

! Inert, not flammable, very good dielectric

Integrated Rates Above Threshold

Differential Rates


XENON Dark Matter Goals

• 2006-2007

•2008-2009

•>2010


The XENON10 CollaborationColumbia University

Elena Aprile (PI), Karl-Ludwig Giboni, Maria Elena Monzani, , Guillaume Plante*, and Masaki Yamashita

Brown University Richard Gaitskell, Simon Fiorucci, Peter Sorensen*, Luiz DeViveiros*

Case Western Reserve University Tom Shutt, Eric Dahl*, John Kwong* and Alexander Bolozdynya

Lawrence Livermore National Laboratory Adam Bernstein, Norm Madden and Celeste Winant

Rice University Uwe Oberlack , Roman Gomez* and Peter Shagin

Yale University Daniel McKinsey, Richard Hasty, Angel Manzur*, Kaixuan Ni

RWTH Aachen University, GermanyLaura Baudis, Jesse Angle*, Joerg Orboeck, Aaron Manalaysay*

Laboratori Nazionali del Gran Sasso, ItalyFrancesco Arneodo, Alfredo Ferella*University of Coimbra, Portugal

Jose Matias Lopes, Luis Coelho*, Luis Fernandes, Joaquim Santos


9 young PostDoc scientists- 11 graduate studentsMany of them at LNGS


Undergraduate Students at LNGSAlison Andrews (Colgate Univ) and Hannah Yevick (UPenn):Nevis REU StudeRuth Toner (Yale Univ)


What do you know presently about the detailed performance of your technology?

LXe Scintillation Efficiency for Nuclear Recoils! The most important parameter for DM search - measured in Fall 03-Spring 04! No prior measurement at low energies

Aprile at al., Phys. Rev. D 72 (2005) 072006

LXe Ionization Efficiency for Nuclear Recoils! XENON concept based on simultaneous detection of recoil ionization and scintillation! No prior information on the ionization yield as a function of energy and applied E-field

Aprile et al., PRL (2006), astro-ph/0601552

Development of XENON3 & 10 Dual Phase 3D sensitive TPC prototypes! Validated Cryogenics, HV, DAQ systems with 6kg prototype (XENON3) – Aug- Nov 2005! Demonstrated low energy threshold and 3D position reconstruction! Installed/tested larger (15 kg) detector in same cryostat (Dec 05- Feb06)! XENON10 operational underground (no shield) since March 18, 2006! Optimization of detector response to ongoing at a very aggressive pace! Shield construction almost completed - Start XENON10 DM run by end July 2006


Scintillation Efficiency of Nuclear Recoils Columbia and Yale Columbia RARAF

2.4 MeV neutrons

Borated Polyethylene

Lead

L ~ 20 cm

θ

BC501AUse pulse shape discrimination and ToFto identify n-recoils

p(t,3He)n

LXe

Aprile et al., Phys. Rev. D 72 (2005) 072006


Number of Electrons from Nuclear Recoil Events

Two independent expts at Columbia and Case with small (~100 g Xe ) dual phase detectors

AmBe - 107 neutron/sec

PbXe

57Co and 137Cs

Hamamatsu R9288 2” PMTs , same as used in detector for QF measurement


Xe-Recoils Ionization Yield and Field Dependence

Energy threshold: 10 keVr

Columbia +Brown and Case

Aprile et al., astro-ph/0601552,submitted to PRL


Stopping Power and Ionization Yield in LXe higher stopping power -> higher ionizing density ->more recombination -> less ionization yield


Gamma Background DiscriminationELASTIC Neutron Recoils

INELASTIC 129Xe40 keV γ + NR

INELASTIC 131Xe80 keV γ + NR

137Cs γ source

Upper edge -saturation in S2

AmBe n-sourceNeutron

ELASTIC Recoil

improvement expected with 3D imaging detector

5 keVee energy threshold = 10 keV nuclear recoil

γ leakage mainly from edge events

80% NR acceptance [-1.65σ, 1 σ]

Gaussian fit

80% NR acceptance

Performance of the small test detector

Expected improvement with a 3D sensitive detector

Threshold 5keVee (10 keVr)

Case Detector


Field Non-uniformity and Edge Events

Neutron Inelastic 19F110 keV γ40 keV

Liquid Xenon

γ

Gas Xenon

Teflon (PTFE)

ELASTIC Nuclear Recoil


XENON3: A Dual phase TPC with multi PMTs

" 21 (GXe) + 14 (LXe) Hamamatsu R8520-06-Al

" 5 cm drift gap; 10 cm diameter electrodes

"Metal Channel, compact ((2.5 cm)2x3.5cm))

" Square anode (good fill factor : 66.2%).

" Expected Back: 238U / 232Th = 15 / 3 mBq

" Quantum Efficiency : >20 % @178nm


XENON3 Data: Edge events can be well identified

Neutron Elastic Recoil

40 keV Inelastic (129Xe)+ NR

80 keV Inelastic (131Xe)

110 keV inelastic (19F)+ NR

Neutron Elastic Recoil



5 mm radial cut clearly reduces gamma events leaking into the nuclear recoils region (DD- 2.5 MeV neutrons irradiation) Co-57

(Pos I)

XY position reconstruction of 122 keV Co-57 gammas from side


XENON10

Pulse tube cryocooler

15 kg LXe

Vacuum Cryostat

Re-condenser

# Prototype of the XENON100 module, to test all major technologies and feasibility issues. Active shield around target replaced by a single active volume to be cut with 3D event localization.

#TPC active area ~ 20 cm diameter; LXe drift gap= 15 cm $22 kg (15 kg active) Xe mass

#Custom designed HV feedthrough, constructed as a shielded PTFE cable .

#TPC electrodes and PMTs contained in UHV SS vessel enclosed by vacuum cryostat.

#89 Hamamatsu 1” square PMTs (R8520-06-AL) operated at – 95C: 48 in GXe and 41 in LXe

# Pulse Tube Refrigerator coupled via cold finger to Xevolume. LN2 cooling for safety.

# Liquid level defined by a “diving” bell and adjusted by gas bypass. Positive pressure required (recirculation)

#Limited selection of detector materials for this 1st

implementation of the concept.


Columbia Nevis Lab: Feb 2006


XENON10: TPC Details

Bottom PMT Array, PTFE VesselTop PMT Array

PMT Base (LLNL)

LN Cooling Loop

Level Meters (Yale)

Grids , Tilmeters (Case)

HV- FT


XENON10: Underground at LNGS• LUNA1 Box is assigned to XENON10. Feb 06: modifications to space and electrical systems start. • March 2006: XENON10 is shipped from Nevis Labs to LNGS and commissioning starts underground. Set up experiment in nearby new Box made available for operations w/o shield. • LNGS Engineering and Machine shop support made available to XENON10 for shield castle design and construction. Executive drawings given to local contractor for shield commissioning.

Occupancy

Borexino

OPERA

HALL CHALL B

HALL A

LVD

CRESST2

CUORE

CUORICINO

LUNA2

DAMA

HDMSGENIUS-TF

MI R&DXENON

COBRA

ICARUS

GERDAWARP


XENON Box: March 7 2006XENON Box: March 10, 2006


XENON Box: March 12, 2006

Yamashita, ColumbiaGiboni, Columbia

Gomez, Rice


XENON10: XENON10: PMTsPMTs Calibration (1) Calibration (1) The gain of each PMT in XENON 10 is measured by means of an LED system: one LED

is installed close to the top PMTs array to illuminate bottom PMTs; the other LED is installed close to the bottom array and illuminates the top PMTs

both LEDs are equipped with a

PTFE light diffuser, to ensure uniform light distribution to all the PMTs in the

array

toptop PMTsPMTs arrayarrayLED for bottomLED for bottomPMTsPMTs calibrationcalibration


XENON10:XENON10: PMTsPMTs Calibration (2)Calibration (2)

The LEDs are driven by a pulser (oscillating at a fixed frequence); a copy of the pulseroutput triggers the DAQ

detected light pulsedetected light pulse

time of the LED pulsetime of the LED pulse

start of DAQ windowstart of DAQ window

1 1 µµss

500 ns500 nscharge charge

integration integration windowwindow

300 ns300 ns


XENON10:XENON10: PMTsPMTs Calibration (3)Calibration (3)We acquire LED data in single photoelectron condition; charge spectra are fitted with a single gaussian (or with a more complex function, to take into account the noise peak

and the multi-p.e. contribution)

Typical PMT spectrum in Typical PMT spectrum in single p.e. condition:single p.e. condition:

Gain: 2.20 x 10Gain: 2.20 x 1066

Sigma: 1.13 x 10Sigma: 1.13 x 1066

single p.e. responsesingle p.e. response

noise peaknoise peak


XENON10:XENON10: PMTsPMTs Gain Stability Gain Stability LED calibrations are performed at least every two days, to monitor PMTs Gain stability

�� we observe gain fluctuations up to 10%we observe gain fluctuations up to 10%•• this is consistent with the systematic error of the measurementthis is consistent with the systematic error of the measurement•• fluctuations are not correlated with temperature, pressure, etcfluctuations are not correlated with temperature, pressure, etc..•• no trend is observed (no degradation of the PMT response)no trend is observed (no degradation of the PMT response)

gain history for 3 samplegain history for 3 sample PMTsPMTs


XENON10: : 3D Event LocalizationEvents are localized in X,Y,Z:1) Z position determined by drift time,

time b/w S1 and S22) X&Y positions reconstructed from

S2 detected by top 48 PMTs (in gas), based on a simulated map.

S2S1

3D event localization is in good agreement with MC (data from a Cs-137 calibration run).

Min-Chisq position reconstruction for an edge event.


XENON10: Energy Calibration (Light and Charge)

662 keV γ

662 keV γ

S1 and S2 are both position dependent. 3D localization is thus important to provide precise detector’s response.

S1 and S2 are both position dependent. 3D localization is thus important to provide precise detector’s response.

For 662 keV γ at 40<R<60 mm and 0<Z<50 mm :S1: 2.0 pe/keV σ/E: (9.7 ± 0.7)%

Various factors (e.g. variation in light collection, electric field uniformity and strength, liquid xenon purity) need optimization to reach the best resolution.

Various factors (e.g. variation in light collection, electric field uniformity and strength, liquid xenon purity) need optimization to reach the best resolution.

For 662 keV γ at 80<R<90 mm and 100<Z<150 mm :S2: 375 pe/keV (~8 pe/e-)σ/E: (8.0 ± 0.8)%


XENON10: Alpha Recoils

S1S2

Event from Alpha

•Alpha events come from the following sources:

-Radioactivity on detector’s surface-i.e. Implanted Po events from Rn-222 decay chain-3D TPC :Easy to avoid by powerful position reconstruction

-Radioactivity in LXe itself--depends on the type of Purifier (i.e. Oxisorb known to be a problem)-- XMASS: U/Th (33±7)x10-14/<23x10-14 g/g @Cryodet2006--Not observed yet in XENON10 (< about 10 min live time)-- Both experiments use SAES getters as purifiers


XENON10: Alpha Events Identification by PSD and S2/S1Ta

il/To

tal

Fast decay

S1S2 S2•S1

Gamma Alpha

Small S2/S1

2 events in 10 min from detector surfaceNo events from LXe itself, yet

S1 S1

S2


XENON10: Gas Purification Systemoxygen equivalent impurities in LXe kept to <<1ppb by continuous gas recirculation through high temperature getter. Continuous and reliable operation of all system components over severalmonths of operation at Nevis Lab and now for two months at LNGS. Electron lifetime, monitored with charge (S2) vs drift time, corresponds to attenuation length >> 1 meter.

LNGS system built at Coimbra


“Built-in”cryocooler“Built-in”cryocooler

XENON10: Cryogenics System

Pulse Tube Cryocooler:Advantages: Just switch on! -Precise temperature and pressure control-LN2-Free operation-Quiet, maintenance free for long time operation-XENON10 machine in use since 2003. >6000 hr of operation- Stability within +/-0.025 K

Can afford:-up to ~200W @165-170K


XENON10: Cryogenics Operation Stability


XENON10: Slow Control System (Yale)

Xe PressureXe Pressure

High Voltages High Voltages & Currents& Currents

Level MetersLevel MetersCryogenic Cryogenic TemperaturesTemperatures

Room Room TemperaturesTemperatures

Flow MeterFlow Meter

InclinometerInclinometer Cryostat Cryostat VacuumVacuum

XeSCS XeSCS computercomputer

XeSCS XeSCS serverserver

Alarm computer Alarm computer @ Yale@ Yale

Status & Status & alarm ealarm e--mailsmails

Mobile phone Mobile phone messagesmessages

Webpage Webpage (monitor only)(monitor only)

XeSCS clients XeSCS clients (monitor & control)(monitor & control)

Underground LNGSUnderground LNGS

Above ground Above ground LNGSLNGS

Outside Outside WorldWorld

• Developed in Java using Java RMI for remote interface.

• Platform Independent.• Monitors ~330 channels.• Remote high voltage control.• Scalable to more instruments or

computers.


XENON10: Liquid Purity Monitor (LNGS)

% A “small” Purity Monitor, to be placed on the bottom of the XENON10 detector, inside the same cryostat and on the same circulation line in order to get a fast and reliable response of the lifetime as the chamber.

% Both set-ups were designed and built by the Gran Sasso collaborators

Particular of theCsI photo-cathode made at Nevis


XENON10: Material Screening (RWTH-Aachen)

• Dedicated LBF at Soudan: SOLO (operated by Brown and RWTH-Aachen)

• 2HPGe detectors: Gator (RWTH-Aachen) 2kg, DiodeM (Brown) 0.5kg

• Typical background: ~ 60 counts/h (40-2700 keV) • Screened materials up to date:

- SS (inner vessel)- Hamamatsu PMTs (R9288 and R8520)- PMT bases and their resistors, capacitors - poly shield- Ceramaseal and Kyocera feedthroughs- Teflon (inner detector)

• Next steps:- Larger effort to qualify all XENON materials/shields - improve sensitivity by reducing Gator/DiodeM backgrounds (inner OFHC Cu lining to suppress 210Pb bremss.)

- screen individual R8520 PMT components, work together withHamamatsu to achieve similar or lower radioactivity/area as for R8778-MOD PMTs of XMASS - start screening XENON100 materials.

Move GATOR to LNGS


XENON10: PMTs Screening (RWTH-Aachen)

Pb X-rays

54Mn841 keV

65Zn1125 keV

40K1460 keV

208Tl2615 keV

214Bi609 keV

214Pb352 keV

Gator PMT and backgroundspectra: ≈ 44 kg days

•Hamamatsu R8520-06-AL PMTs; detection of 238U chain and 40K, upper limits on 232Th chain and 60Co

(54Mn and 65Zn = cosmogenics, T1/2≈300d)

•Results not consistent: Four PMTs : 17.2/<3.5/12.7/<3.9;Two PMTs: <18/<6/<5/<11/<6/36/- mBq/PMT

•Will count more PMTs next month


XENON10: Screening and Geant4 MonteCarlo) (RWTH-Aachen• Large (2kg) HPGe (GATOR) at Soudan, as part of the SOLO facility (operated

by Brown and RWTH-Aachen)• To have LBF dedicated to XENON100 materials screening, GATOR will be

moved to LNGS

• The background model is based on Geant4 Monte Carlo simulations (RWTH-Aachen, Brown, Columbia)

• Detailed XENON-10 geometry implemented (J. Orboeck/RWTH-Aachen)


XENON10: BG Simulations (RWTH-Aachen)

• The background is dominated by the R8520-AL PMT contribution (17.2/<3.5/12.7/<3.9 mBq/PMT for U/Th/K/Co),followed by the SS of the inner and outer vessels (21/61/12/101 mBq/kg for U/Th/K/Co)

• => ~ 400 mdru after afiducial volume cut (FVC): 1.2cm top, 1cm bottomand 2cm in radius (8.9 kg LiXe fiducial mass)(details in talk by R. Gaitskell)

No cuts: 15 kg LiXe FV cut: 8.9 kg LiXe

L. DeViveiros/BrownJ. Orboeck/RWTH-Aachen

Energy range: 4-20 keVee


XENON-10 BG Simulations

• Relative contributions to the gamma background (shown are single-hits in the fiducial volume of 8.9 kg LiXe):

R8520-PMTsOuter SS canInner SS can

Overall MC spectrum Low-energy regionJ. Orboeck/RWTH-Aachen


What do you still need to know to extend the reach of the technology?

1) Operate XENON10 in its shield to determine the true background rate, identify its sources anddemonstrate rejection power of S2/S1 and 3D event localization.

2) Pursue more aggressive program of materials screening and selection to get to the low background goal which will enable the sensitivity reach allowed by mass and discrimination

3) Invest in a collaboration with Hamamatsu to lower activity of PMTs for LXe. The XMASS PMTs(R8778) have lower U/Th level than the XENON PMTs and their goal is 1/10 below current.

4) Continue MC studies and analysis development to optimize sensitivity reach of XENON10. At the same time invest in simulation and design studies for XENON100, capitalizing on technologies already proven by collaboration. The potential of large mass and more favorable background level with increased ratio of effective/total volume should be exploited for an experiment in 2008 at σ~10 -45

5) Realizing XENON100 experiment at LNGS allows us to make the most of the investment in shield, infrastructure and know-how already in place.Depth of LNGS is not a limiting factor (need more Poly and an active muon shield)


Do you have a base design for the technology application to dark matter and

how far can it take you?

XENON1

～20cm

～60cm R&D: 2002-5 DM search:2006-7

～10cm

XENON10

XENON3

XENON Scale-Up 2005-9

XENON100

DM Search:2008-9


Strategy for XENON Scale-Up

Fastest path to an experiment with sensitivity reach of a few 10-45 by 2008 :

(1) Use technologies and methods established to-date(2) Scale-up mass to maximum allowed by available shield(3) Keep all LXe active and use 3D position to cut volume(3) LNGS depth not a limitation for physics reach(4) Non-negligible asset to have space at LNGS before a DUSEL

Requiirements:(1) Establish on a firm basis current PMTs activity and reliable methods to

reduce it, in cooperation with Hamamatsu (use 3rd year NSF funds)(2) Study with MC the optimum geometry for the maximum reach, using the

feedback from XENON10 on discrimination & threshold(3) Effort on materials screening and selection ongoing(4) Detailed Engineering by end ‘06. Construction completed by Summer ’07(5) Full commissioning depends on funding for PMTs and Electronics(6) Estimated 2 M$ construction cost ( US ) + 0.5M$ Foreign)

XENON10 in its shield


XENON100: Preliminary Design

Columbia/RWTH-Aachen

900 mm

1050

mm

XENON100 in same shield


XENON100: A Preliminary Design

Columbia/RWTH-Aachen

364 PMTs

400 PMTs

PTR

field shapingrings

300 kg LXe


XENON100: Thermal DesignB. Roidl/RWTH-Aachen

• Contributions from:! cylindrical shape (thermal conduction + convection): ≈ 20 W! lid and bottom of detector (thermal conduction + convection) ≈ 15 W! connection to the inner vessel and PMTs (thermal conduction): ≈ 20 W + 5 W! overall thermal radiation ≈ 20 W

λPTFE=0.7W/(mK)

λCu=380W/(mK)

λpolyurethane=0.022W/(mK)

Ti=165KTo=285K

h=50

cm

650mm ø695mm ø710mm ø850mm ø

⇒Overall heat load ≈ 80 W+ 40W used for Xe-recirculation

⇒Total heat load ≈ 120 W

⇒With 180 W cooling power of PTRthe surplus will be ~ 60W

=> cooling down of surrounding structures=> lower thermal loads for the detector itself

Pol

yure

than

e

Cop

per

PTF

E


XENON100: BG and Projected Sensitivity Reach

• The background will be dominated by the PMT arrays (400 top, 364 bottom)Fiducial Volume:radial cut = 5 cm; depth cut =6 cm top & 6 cm bottom

$ (~123 kg LXe) $ Call it XENON100!

• Assumption: R8520-06-AL (current PMTs) at 17.2/<3.5/12.7/<3.9 mBq/PMT (U/Th/K/Co)⇒ BG in fiducial region = 31 mdru

• Assumption: R8778-MOD, 6.2/2.3/46.7/3.9 mBq/PMT/1’’ (U/Th/K/Co)⇒ BG in fiducial region = 17 mdru

• Assumption: if overall PMT radioactivity x 15 lower than R8520-06-AL⇒ BG in fiducial region ≈ 2 mdru

⇒ With 99.5% discrimination the reach of XENON100 is ≈ 2 x 10-45 cm2 for WIMP-nucleon cross sections (as in original XENON100 proposal and LNGS LoI)


European funding sources for XENON100

• Aachen (with Bonn): proposal for a Cluster of Excellence “Crossing the energy frontier: physics at the Terascale”; 12 PIs, 6.5 M €/year for 5 years. Funds mostly into postdoctoral and PhD fellowships and junior research groups (but also for development of new (astro)particle physics instrumentation)

• Aachen-Coimbra-LNGS: proposal to the Research Framework Program (FP7) of the European Union (2007-2013, approved total budget 53 billion €, 15% on ‘frontier research’, first call for proposals in early 2007)

• Internal funds at Coimbra• Interest of a group from University of Barcelona, Spain

• INFN funds for XENON100 at LNGS

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