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Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy beta and nuclear recoils in liquid argon with DEAP-1  [PDF]
M. G. Boulay,B. Cai,M. Chen,V. V. Golovko,P. Harvey,R. Mathew,J. J. Lidgard,A. B. McDonald,P. Pasuthip,T. Pollman,P. Skensved,K. Graham,A. L. Hallin,D. N. McKinsey,W. H. Lippincott,J. Nikkel,C. J. Jillings,F. Duncan,B. Cleveland,I. Lawson
Physics , 2009,
Abstract: The DEAP-1 low-background liquid argon detector has been used to measure scintillation pulse shapes of beta decays and nuclear recoil events and to demonstrate the feasibility of pulse-shape discrimination down to an electron-equivalent energy of 20 keVee. The relative intensities of singlet/triplet states in liquid argon have been measured as a function of energy between 15 and 500 keVee for both beta and nuclear recoils. Using a triple-coincidence tag we find the fraction of beta events that are mis-identified as nuclear recoils to be less than 6x10^{-8} between 43-86 keVee and that the discrimination parameter agrees with a simple analytic model. The discrimination measurement is currently limited by nuclear recoils induced by cosmic-ray generated neutrons, and is expected to improve by operating the detector underground at SNOLAB. The analytic model predicts a beta mis-identification fraction of 10^{-10} for an electron-equivalent energy threshold of 20 keVee. This reduction allows for a sensitive search for spin-independent scattering of WIMPs from 1000 kg of liquid argon with a WIMP-nucleon cross-section sensitivity of 10^{-46} cm^{2}.
Measurement of scintillation efficiency for nuclear recoils in liquid argon  [PDF]
D. Gastler,E. Kearns,A. Hime,L. C. Stonehill,S. Seibert,J. Klein,W. H. Lippincott,D. N. McKinsey,J. A. Nikkel
Physics , 2010, DOI: 10.1103/PhysRevC.85.065811
Abstract: The scintillation light yield of liquid argon from nuclear recoils relative to electronic recoils has been measured as a function of recoil energy from 10 keVr up to 250 keVr. The scintillation efficiency, defined as the ratio of the nuclear recoil scintillation response to the electronic recoil response, is 0.25 \pm 0.01 + 0.01(correlated) above 20 keVr.
Ionization and scintillation of nuclear recoils in gaseous xenon  [PDF]
J. Renner,V. M. Gehman,A. Goldschmidt,H. S. Matis,T. Miller,Y. Nakajima,D. Nygren,C. A. B. Oliveira,D. Shuman,V. álvarez,F. I. G. Borges,S. Cárcel,J. Castel,S. Cebrián,A. Cervera,C. A. N. Conde,T. Dafni,T. H. V. T. Dias,J. Díaz,R. Esteve,P. Evtoukhovitch,L. M. P. Fernandes,P. Ferrario,A. L. Ferreira,E. D. C. Freitas,A. Gil,H. Gómez,J. J. Gómez-Cadenas,D. González-Díaz,R. M. Gutiérrez,J. Hauptman,J. A. Hernando Morata,D. C. Herrera,F. J. Iguaz,I. G. Irastorza,M. A. Jinete,L. Labarga,A. Laing,I. Liubarsky,J. A. M. Lopes,D. Lorca,M. Losada,G. Luzón,A. Marí,J. Martín-Albo,A. Martínez,A. Moiseenko,F. Monrabal,M. Monserrate,C. M. B. Monteiro,F. J. Mora,L. M. Moutinho,J. Mu?oz Vidal,H. Natal da Luz,G. Navarro,M. Nebot-Guinot,R. Palma,J. Pérez,J. L. Pérez Aparicio,L. Ripoll,A. Rodríguez,J. Rodríguez,F. P. Santos,J. M. F. dos Santos,L. Seguí,L. Serra,A. Simón,C. Sofka,M. Sorel,J. F. Toledo,A. Tomás,J. Torrent,Z. Tsamalaidze,J. F. C. A. Veloso,J. A. Villar,R. C. Webb,J. White,N. Yahlali
Physics , 2014, DOI: 10.1016/j.nima.2015.04.057
Abstract: Ionization and scintillation produced by nuclear recoils in gaseous xenon at approximately 14 bar have been simultaneously observed in an electroluminescent time projection chamber. Neutrons from radioisotope $\alpha$-Be neutron sources were used to induce xenon nuclear recoils, and the observed recoil spectra were compared to a detailed Monte Carlo employing estimated ionization and scintillation yields for nuclear recoils. The ability to discriminate between electronic and nuclear recoils using the ratio of ionization to primary scintillation is demonstrated. These results encourage further investigation on the use of xenon in the gas phase as a detector medium in dark matter direct detection experiments.
Scintillation time dependence and pulse shape discrimination in liquid argon  [PDF]
W. H. Lippincott,K. J. Coakley,D. Gastler,A. Hime,E. Kearns,D. N. McKinsey,J. A. Nikkel,L. C. Stonehill
Physics , 2008, DOI: 10.1103/PhysRevC.81.039901
Abstract: Using a single-phase liquid argon detector with a signal yield of 4.85 photoelectrons per keV of electronic-equivalent recoil energy (keVee), we measure the scintillation time dependence of both electronic and nuclear recoils in liquid argon down to 5 keVee. We develop two methods of pulse shape discrimination to distinguish between electronic and nuclear recoils. Using one of these methods, we measure a background and statistics-limited level of electronic recoil contamination to be $7.6\times10^{-7}$ between 60 and 128 keV of nuclear recoil energy (keVr) for a nuclear recoil acceptance of 50% with no nuclear recoil-like events above 72 keVr. Finally, we develop a maximum likelihood method of pulse shape discrimination using the measured scintillation time dependence and predict the sensitivity to WIMP-nucleon scattering in three configurations of a liquid argon dark matter detector.
The scintillation and ionization yield of liquid xenon for nuclear recoils  [PDF]
P. Sorensen,A. Manzur,C. E. Dahl,J. Angle,E. Aprile,F. Arneodo,L. Baudis,A. Bernstein,A. Bolozdynya,P. Brusov,L. C. C. Coelho,L. DeViveiros,A. D. Ferella,L. M. P. Fernandes,S. Fiorucci,R. J. Gaitskell,K. L. Giboni,R. Gomez,R. Hasty,L. Kastens,J. Kwong,J. A. M. Lopes,N. Madden,A. Manalaysay,D. N. McKinsey,M. E. Monzani,K. Ni,U. Oberlack,J. Orboeck,G. Plante,R. Santorelli,J. M. F. dos Santos,P. Shagin,T. Shutt,S. Schulte,C. Winant,M. Yamashita,for the XENON10 Collaboration
Physics , 2008, DOI: 10.1016/j.nima.2008.12.197
Abstract: XENON10 is an experiment designed to directly detect particle dark matter. It is a dual phase (liquid/gas) xenon time-projection chamber with 3D position imaging. Particle interactions generate a primary scintillation signal (S1) and ionization signal (S2), which are both functions of the deposited recoil energy and the incident particle type. We present a new precision measurement of the relative scintillation yield \leff and the absolute ionization yield Q_y, for nuclear recoils in xenon. A dark matter particle is expected to deposit energy by scattering from a xenon nucleus. Knowledge of \leff is therefore crucial for establishing the energy threshold of the experiment; this in turn determines the sensitivity to particle dark matter. Our \leff measurement is in agreement with recent theoretical predictions above 15 keV nuclear recoil energy, and the energy threshold of the measurement is 4 keV. A knowledge of the ionization yield \Qy is necessary to establish the trigger threshold of the experiment. The ionization yield \Qy is measured in two ways, both in agreement with previous measurements and with a factor of 10 lower energy threshold.
Observation of the Dependence of Scintillation from Nuclear Recoils in Liquid Argon on Drift Field  [PDF]
T. Alexander,H. O. Back,H. Cao,A. G. Cocco,F. DeJongh,G. Fiorillo,C. Galbiati,C. Ghag,L. Grandi,C. Kendziora,W. H. Lippincott,B. Loer,C. Love,L. Manenti,C. J. Martoff,Y. Meng,D. Montanari,P. Mosteiro,D. Olvitt,S. Pordes,H. Qian,B. Rossi,R. Saldanha,W. Tan,J. Tatarowicz,S. Walker,H. Wang,A. W. Watson,S. Westerdale,J. Yoo
Physics , 2013, DOI: 10.1103/PhysRevD.88.092006
Abstract: We have exposed a dual-phase Liquid Argon Time Projection Chamber (LAr-TPC) to a low energy pulsed narrowband neutron beam, produced at the Notre Dame Institute for Structure and Nuclear Astrophysics to study the scintillation light yield of recoiling nuclei in a LAr-TPC. A liquid scintillation counter was arranged to detect and identify neutrons scattered in the LAr-TPC target and to select the energy of the recoiling nuclei. We report the observation of a significant dependence on drift field of liquid argon scintillation from nuclear recoils of 11 keV. This observation is important because, to date, estimates of the sensitivity of noble liquid TPC dark matter searches are based on the assumption that electric field has only a small effect on the light yield from nuclear recoils.
Study of nuclear recoils in liquid argon with monoenergetic neutrons  [PDF]
C. Regenfus,Y. Allkofer,C. Amsler,W. Creus,A. Ferella,J. Rochet,M. Walter
Physics , 2012, DOI: 10.1088/1742-6596/375/1/012019
Abstract: For the development of liquid argon dark matter detectors we assembled a setup in the laboratory to scatter neutrons on a small liquid argon target. The neutrons are produced mono-energetically (E_kin=2.45 MeV) by nuclear fusion in a deuterium plasma and are collimated onto a 3" liquid argon cell operating in single-phase mode (zero electric field). Organic liquid scintillators are used to tag scattered neutrons and to provide a time-of-flight measurement. The setup is designed to study light pulse shapes and scintillation yields from nuclear and electronic recoils as well as from {\alpha}-particles at working points relevant to dark matter searches. Liquid argon offers the possibility to scrutinise scintillation yields in noble liquids with respect to the populations of the two fundamental excimer states. Here we present experimental methods and first results from recent data towards such studies.
Scintillation efficiency and ionization yield of liquid xenon for mono-energetic nuclear recoils down to 4 keV  [PDF]
A. Manzur,A. Curioni,L. Kastens,D. N. McKinsey,K. Ni,T. Wongjirad
Physics , 2009, DOI: 10.1103/PhysRevC.81.025808
Abstract: Liquid Xenon (LXe) is an excellent material for experiments designed to detect dark matter in the form of Weakly Interacting Massive Particles (WIMPs). A low energy detection threshold is essential for a sensitive WIMP search. The understanding of the relative scintillation efficiency (Leff) and ionization yield of low energy nuclear recoils in LXe is limited for energies below 10 keV. In this paper, we present new measurements that extend the energy down to 4 keV, finding that Leff decreases with decreasing energy. We also measure the quenching of scintillation efficiency due to the electric field in LXe, finding no significant field dependence.
Measurements of Scintillation Efficiency and Pulse-Shape for Low Energy Recoils in Liquid Xenon  [PDF]
D. Akimov,A. Bewick,D. Davidge,J. Dawson,A. S. Howard,I. Ivaniouchenkov,W. G. Jones,M. Joshi,V. A. Kudryavtsev,T. B. Lawson,V. Lebedenko,M. J. Lehner,P. K. Lightfoot,I. Liubarsky,R. Luscher,J. E. McMillan,C. D. Peak,J. J. Quenby,N. J. C. Spooner,T. J. Sumner,D. R. Tovey,C. K. Ward
Physics , 2001, DOI: 10.1016/S0370-2693(01)01411-3
Abstract: Results of observations of low energy nuclear and electron recoil events in liquid xenon scintillator detectors are given. The relative scintillation efficiency for nuclear recoils is 0.22 +/- 0.01 in the recoil energy range 40 keV - 70 keV. Under the assumption of a single dominant decay component to the scintillation pulse-shape the log-normal mean parameter T0 of the maximum likelihood estimator of the decay time constant for 6 keV < Eee < 30 keV nuclear recoil events is equal to 21.0 ns +/- 0.5 ns. It is observed that for electron recoils T0 rises slowly with energy, having a value ~ 30 ns at Eee ~ 15 keV. Electron and nuclear recoil pulse-shapes are found to be well fitted by single exponential functions although some evidence is found for a double exponential form for the nuclear recoil pulse-shape.
Measurement of the ionization yield of nuclear recoils in liquid argon at 80 and 233 keV  [PDF]
A. Bondar,A. Buzulutskov,A. Dolgov,E. Grishnyaev,S. Polosatkin,L. Shekhtman,E. Shemyakina,A. Sokolov
Physics , 2014, DOI: 10.1209/0295-5075/108/12001
Abstract: The energy calibration of nuclear recoil detectors is of primary importance to rare-event experiments such as those of direct dark matter search and coherent neutrino-nucleus scattering. In particular, such a calibration is performed by measuring the ionization yield of nuclear recoils in liquid Ar and Xe detection media, using neutron elastic scattering off nuclei. In the present work, the ionization yield for nuclear recoils in liquid Ar has for the first time been measured in the higher energy range, at 80 and 233 keV, using a two-phase Cryogenic Avalanche Detector (CRAD) and DD neutron generator. The ionization yield in liquid Ar at an electric field of 2.3 kV/cm amounted to 7.8+/-1.1 and 9.7+/-1.3 e-/keV at 80 and 233 keV respectively. The Jaffe model for nuclear recoil-induced ionization, in contrast to that Thomas-Imel, can probably consistently describe the energy dependence of the ionization yield.
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