XENON Dark Matter Experiment (NSF/DOE)

XENON Dark Matter Experiment (NSF/DOE) Rick Gaitskell Particle Astrophysics Group, Brown University, Department of Physics (Supported by US DOE HEP) see XENON information at http://www.astro.columbia.edu/~lxe/xenon/ http://xenon.brown.edu/ Gaitskell v10 1

The XENON Collaboration Columbia University Elena Aprile (Spokesperson), Karl-Ludwig Giboni, Sharmila Kamat, Kaixuan Ni, Masaki Yamashita, Marie-Elena Brown University Richard Gaitskell, Simon Fiorucci, Peter Sorensen, Luiz DeViveiros University of Florida Laura Baudis, Jesse Angle, David Day, Joerg Orboeck, Aaron Manalaysay Lawrence Livermore National Laboratory Adam Bernstein, Chris Hagmann Celeste Winant Case Western Reserve University Tom Shutt, John Kwong, Alexander Bolozdynya, Eric Dahl Paul Brusov Rice University Uwe Oberlack, Peter Shagin, Roman Gomez Yale University Daniel McKinsey, Richard Hasty, Angel Manzur Gran Sasso National Laboratory, Italy Francesco Arneodo and Alfredo Ferella University of Coimbra, Portugal Jose A.M. Lopes and Joaquim Santos 2

Dark Matter Goals XENON10 - Sensitivity curve corresponds to ~2 dm evts/10 kg/month Equivalent CDMSII Goal for mass >100 GeV (Latest 2005 CDMSII result is x10 above this level) With only 30 live-days x 10 kg fiducial - Zero events - would reach XENON10 sensitivity goal (90% CL), but we would like to do physics! Important goal of XENON10 prototype underground is to establish clear performance of systems XENON100 - Sensitivity curve corresponds to ~2 dm evts/100 kg/month Background Simulations for XENON10 indicate it could reach b/g suppression necessary to reach this sensitivity limit, but with 10 kg target would only give ~2 dm evts/10kg/year - no physics. XENON1T 10-46 cm 2 ~1 dm evts/1 tonne/month SUSY Theory Models DAMA Dark Matter Data Plotter http://dmtools.brown.edu EDELWEISS ZEPLIN I CDMS II XENON - 10 kg XENON - 100 kg XENON - 1T CDMS II goal NOTE THAT GOAL IS TO DO PHYSICS ON WIMP (rates/month), NOT SIMPLY SET A DETECTION LIMIT 3

DM Direct Search Progress Over Time (2006) ~1 event kg -1 day -1 ~1 event 100 kg -1 yr -1 Based on Review Article: Gaitskell, Ann. Rev. Nucl. and Part. Sci. 54 (2004) 315-359 Known Unknown - Direct Detection - Nov 2005 Rick Gaitskell, Brown University 4

Signature of Signal vs Background Detectors must effectively discriminate between Nuclear Recoils (Neutrons, WIMPs) Electron Recoils (gammas, betas) Much of dark matter detector effort is being focused on techniques that can discriminate between these two types of backgrounds Attisha (Brown) Known Unknown - Direct Detection - Nov 2005 Rick Gaitskell, Brown University 5

Within the xenon target: XENON Event Discrimination: Electron or Nuclear Recoil? Neutrons, WIMPs => Slow nuclear recoils => strong columnar recombination => Primary Scintillation (S1) preserved, but Ionization (S2) strongly suppressed γ, e-, µ, (etc) => Fast electron recoils => => Weaker S1, Stronger S2 Ionization signal from nuclear recoil too small to be directly detected => extract charges from liquid to gas and detect much larger proportional scintillation signal => dual phase Simultaneously detect (array of UV PMTs) primary (S1) and proportional (S2) light => Distinctly different S2 / S1 ratio for e / n recoils provide basis for event-by-event discrimination. Challenge: ultra pure liquid and high drift field to preserve small electron signal (~20 electrons) ; efficient extraction into gas; efficient detection of small primary light signal (~ 200 photons) associated with 16 kevr Gaitskell Time Proportiona l ~1 µs width 0 150 µs depending on depth Primary ~40 ns width Light Signal UV ~175 nm photons e - e - e - - e - e - e - - e - e - e - - Gas phase Electron Drift ~2 mm/µs Liquid phase PMT Array (not all tubes shown) E AG E GC Anode Liq. Surface Grid Cathod e E AG > E GC Interaction (WIMP or Electron) 6

New Highlights Nuclear Recoil Scintillation (Primary Light) Efficiency Determined Low energy recoil calibration 10-50 kevr (QF 12-20% rel to zero field kevee signal) (~6-10 primary photons per kevr) Aprile at al., Phys. Rev. D 72 (2005) 072006 Nuclear Recoil Ionization Efficiency Determined Electron signal from NR higher than expected 20-100 kevr ~3-5 electron in liquid per kevr (~250 secondary photons per liquid electron extracted into gas) Aprile et al., PRL, astro-ph/0601552 XENON3 (6 kg target) LXe (40 PMT) - Test systems for 10 Full checkout of cryogenics, HV, DAQ systems Fall 2005 Operated with PMT arrays located above and below LXe Position reconstruction/discrimination verified Verified photoelectron/kevee & /kevr numbers Using γ sources and neutron scattering at defined angles XENON10 (14 kg target) LXe (90 PMT) - Underground Deployment Dec/Jan - Upgraded chamber to full complement of PMTs at Nevis Labs (Columbia) Currently performance testing prior to shipping to LNGS this month 7

Nuclear Recoil Scintillation Efficiency Columbia RARAF p(t,3he)n 2.4 MeV neutrons Borated Polyethylene Pb LXe L=20 cm BC501A Time of (ToF) and PSD used to resolve neutron/gamma Scintillation efficiency at low nuclear recoil energy was measured, which supports a bi-excitonic collision model At higher energy recoils, our results are consistent with most of the other results 10.4 kev nuclear recoils Lindhard Hitachi [Columbia/Yale] Aprile et al., Phys. Rev. D 72 (2005) 072006 8

Gamma Events 1 kg LXe Tests Nuclear Recoil Aprile et al., PRL, astro-ph/0601552 Columbia/Brown Columbia/Brown Case Western Case Western 9

Event Discrimination Nuclear Recoil Discrimination Aprile et al., PRL, astro-ph/0601552 Non gaussian tails due to edge effects which can be eliminated with multipmt xy cuts Data taken with 2 kv/cm drift field electron recoils nuclear recoils 10

XENON3 3D position sensitive dual phase detector Hamamatsu R8520 PMT: Compact metal channel: 2.5 cm square x 3.5 cm Low background: 3 mbq U-238/Th-232 Quantum Efficiency: >20% @ 178 nm Drift 10 cm (50μs) background events mostly happen near the edge (maximum r) and surface (top/bottom) efficiently reduce them by fiducial volume cut electric field lines near the edge are not uniform and straight those events mimic nuclear recoils and have to be removed WIMPs do not multiply scatter. (Multiple scattering of neutrons can be used as tag on background) 11

XENON3 Event XENON3 Event 100 kev nucl recoil evt Σ Top PMTs: Blue trace (gas) Σ Bottom PMTs: Red trace (liq) First Signal, S1 Primary Scintillation S1 phe ~50 ns wide Bottom PMTs see most phe (Top suffer loss at liq. surf.) Second Signal, S2 Electron Drift liq. ~30 µs -> extract into gas -> Electroluminescence z position S2 phe ~1.5 us wide See Hot Spot position x-y position [Luiz de Viveiros, Brown] 12

XENON3 Neutron Scattering at Fixed Angles XENON Collaboration Direct Calibration of Nuclear Recoils Er = 22 and 55 kevr 0.75 phe/kevr 55 kevr d(d, 3 He)n 22 kevr LXe BC501A BC501A [Luiz de Viveiros, Brown] 13

XENON3 Position Reconstruction edge events well reconstructed Preliminary Algorithms already achieving <1 cm position resolution. Simulations suggest σxy~2 mm should be possible at 20 kevr. direct light collection is not uniform along Z a small fraction of charges lost [Kaixuan Ni, Columbia] Z Lifetime 280 +/- 53 μs 14

XENON10 detector 14 kg LXe XENON10 now running above ground at Nevis Columbia Lab Testing prior to shipping to LNGS 48 PMTs on top, 41 on bottom, 20 cm diameter, 15 cm drift length, 14 kg LXe 15

XENON10 R&D Milestones: Summary + PMTs operation in LXe + > 1 meter λ e in LXe + Operating ~1 kv/cm electric field + Electron extraction to gas phase + Efficient & Reliable Cryogenic System + Nuclear recoil Scintillation Efficiency (10-55 kevr) + Nuclear recoil Ionization Efficiency + Electron/Nuclear recoil discrimination + Kr removal for XENON10 + Electric Field / Light Collection Simulations + Background Simulations + Materials Screening for XENON10 + Assembly of XENON10 System + Low Activity PMTs and Alternatives Readouts Achieved Achieved Achieved Achieved Achieved Achieved Achieved Achieved 1 kg purification achieved Tools Developed_Done for XENON10 Tools Developed_Done for XENON10 All major components screened Achieved Verified Hamamatsu # s 16

XENON10 at LNGS: Gran Sasso National Laboratory Ex-LUNA Building 5 x 7 m (h 4 m) Detector + 2.5 x 8 m Box Assembly Space + 2.5 x 6 m Box Analysis XENON10 Main Halls ~100 m long x 15 m high 17

XENON10 Intrinsic Backgrounds (Monte Carlos) dru == /kev/kg/day Effect of Position Cuts on Upper (gas) PMT Backgrounds Event Rates 10-50 kevee Hamamatsu R8520 <3 mbq/pmt Stainless from inner + outer vessel + PMT 0.11 dru in 10.3 kg fiducial LXe 0-50 kevee (17.3 kg gross volume) [Luiz de Viveiros, Brown] [Joerg Oberlach, U. FLORIDA] 18

DM Mass From Direct Detection WIMP Mass Spectroscopy 10 events above threshold 1000 events above threshold Comparisons above assume same # of events in each experiment, (not constant cross section). Also we assume WIMP velocity v0=230 km/s. At all masses, more events -> Better sensitivity to M D Undergraduate Senior Thesis, Brown Review of XENON Thesis Research April 2005 D SILVERMAN 19

Homestake for Dark Matter Experiments Depth is critical, because of muon generating high energy neutrons that are able to punch-through conventional shielding. D.M. Mei and A. Hime, (astro-ph/0512125) 20

Homestake Water Shield (see T Shutt Talk) MRI Proposal submitted (Jan 06) for high purity water shield (16m x 11m x h10 m) capable of housing multiple dark matter and other low background experiments at Homestake Achieves γ backgrounds of better than 0.01 /kevee/kg/day at low energies (thickness > 3 m) Crucially combination of depth of Homestake 4850 ft and water will ensure that background due to high energy punch-through neutrons is reduced well below levels required for 1 tonne dm experiments to measure WIMP spectra (σ<~10-46 cm2) Very cost effective way of achieving shield for multiple LXe modules to achieve 1 tonne fiducial (XENON1T) 21

Proposed Homestake Water Shield (Side) (Top) 22

Homestake Water Shield - Davis Solar Neutrino Cavity (Side) (Top) Ray Davis taking a dip 24

Conclusion XENON10 Basic Xenon detector physics now fully characterized XENON10 now being operated at Columbia Labs -> LNGS this month To exceed current best dm sensitivity will require <1 week running Goal is for factor 10 improvement over current sensitivity 3D Event reconstruction will be crucial to assist characterizing backgrounds XENON LOI (Elena Aprile) XENON1T will require multiple module deployment Homestake Water Shield (Tom Shutt) There is an opportunity to establish a multi-user low background facility Provide a strong incentive for locating at Homestake Very cost effective way of providing ultra low bg environment Radioactive backgrounds low enough to satisfy dm experiments for at least next 5 years (1 tonne scale) 25

XENON1T Multi-module Requirements The total volume for the 1000 kg of fiducial LXe is relatively modest at ~0.35 m 3. The space requirements will be dominated by the low background shielding required to reduce the external gamma and neutron fluxes incident on the fiducial detector volumes. With current detector designs a single 100 kg detector would be enclosed by a 2.5 m x 2.5 m x 2.5 m shield (external dimensions) constructed of Pb and Polyethylene. (Additional LXe adjacent to the fiducial region, and plastic scintillator surrounding the passive shielding are also employed for background rejection, acting as anti-coincidence vetoes.) The building for housing a single 100 kg detector and shield would be 6 m x 6 m x 7 m. One way of achieving a 1000 kg fiducial mass would be to replicate 100 kg detector modules within a single shielded volume. The total footprint of a Pb/Poly shield would be ~10 m x 8 m x 3 m height. The building (which would permit environment control ~ class 2000-5000) in which a shield that could accommodate 10x100 kg modules would be housed would be ~14 m x 12 m x 7 m height. A crane of ~5 tonnes rating would be required to manipulate the shield components. An alternative is the use of a water shield (instead of Pb/Poly). This could be constructed at lower cost than the conventional Pb/Poly shield, - MRI Proposal Submitted. In this case, cavern of the order of 12 m linear, with a depth of 10 m would be required to house up to 10 detectors. Additional staging areas below ground would be required for detector assembly, servicing, and xenon gas recirculation (purification and krypton removal). Also huts for electronics, cryogenics and analysis huts. This would require an addition 150 m2 of space. Backup systems would be in place to ensure that the LXe (-100 degc) could be recovered and kept in liquid form, in the event of a power outage. However, a full safety analysis would be necessary focusing on the possibility of a significant fraction of Xe liquid being released into the caverns. 100 kg of liquid Xe corresponds to ~20 m3 of heavier-than-air gas. Timescale: The existing XENON10 detector is expected to be operated through 2006 and possibly part of 2007. Funding proposals for future XENON experiments would be expected to be submitted before Sept. 2006, and so construction could begin in 2007, with operation expected in 2008. 26