Because the cross section for neutrino-electron scattering increases at small kinetic energy tran... more Because the cross section for neutrino-electron scattering increases at small kinetic energy transfer for magnetic scattering, a large gain in sensitivity to the neutrino magnetic moment can be obtained with a massive ultra-low energy ( ˜10 eV) threshold detector. Such detectors are being evaluated for possible use with an intense tritium source of low energy neutrinos. Silicon particle detectors developed for the Cryogenic Dark Matter Search (CDMS) have been used as prototypes to evaluate the Nagonov-Trofimov-Luke (NTL) Effect at charge bias voltages up to 200 V/cm. Quasiparticle-assisted electrothermal feedback transition-edge sensors are lithographically patterned onto the surface of 100 g Si wafers (3-inch diameter, 1-cm thick) to create Z-sensitive Ionization and Phonon detectors (ZIPs). Energy is collected from electron recoil events in the wafer in both athermal phonon and ionization channels. The ionization signal output remains stable against applied voltage, while the accelerated ionization electrons and holes inelastically scatter from the Si crystal lattice, pumping energy into the phonon channel (NTL Effect). Evaluations conducted at Case Western Reserve University show that noise in the athermal phonon channel is not significantly affected by the ionization channel voltage bias. A factor of 50 gain in the phonon channel has been observed through study of gamma events from ^241Am sources, resulting in an effective Si ZIP energy threshold of approximately 30 eV. The favorable results from these prototype detectors make feasible further development toward an antineutrino magnetic moment experiment with sensitivity two orders of magnitude better than present limits.
The Cryogenic Dark Matter Search experiment uses cooled germanium and silicon detectors for a dir... more The Cryogenic Dark Matter Search experiment uses cooled germanium and silicon detectors for a direct search for weakly interacting massive particles in our Galaxy. The novel detectors allow a high degree of background rejection by discriminating between electron and nuclear recoils through the simultaneous measurement of the energy deposited in phonons and ionization. Exposures on the order of one kilogram-day
Material screening for low-energy betas and alphas is necessary for rare-event-search experiments... more Material screening for low-energy betas and alphas is necessary for rare-event-search experiments, such as dark matter and neutrinoless double-beta decay searches where surface radiocontamination has become a significant background. The BetaCage, a gaseous neon time-projection chamber, has been proposed as a screener for emitters of low-energy betas and alphas to which existing screening facilities are insufficiently sensitive. The expected sensitivity is 0.1 betas / (keV m^2 day) and 0.1 alphas / (m^2 day). Expected backgrounds are dominated by Compton scattering of external photons in the sample to be screened; radioassays and simulations indicate backgrounds from detector materials and radon daughters should be subdominant. We will report on details of the background simulations and the detector design that allows discrimination to reach these sensitivity levels.
ABSTRACT . The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weak... more ABSTRACT . The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on the spinindependent WIMP-nucleon elastic-scattering cross section that exclude unexplored parameter space above 10 GeV c 2 WIMP mass and, at > 75% CL, the entire 3 allowed region for the WIMP signal reported by the DAMA experiment. 1 Introduction Weakly Interacting Massive Particles (WIMPs) are an excellent candidate for the universe's nonbaryonic, cold dark matter [1]. WIMPs in our Galaxy would scatter o nuclei via the weak interaction, potentially allowing their direct detection. The expected spectrum of the resulting nuclei recoil energies is exponential with a characteristic energy of a few to tens of keV [2]. The expected event rate is model-dependent but is generic...
Cosmo-2000 - Proceedings of the Fourth International Workshop on Particle Physics and the Early Universe, 2001
The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for WIMPs via their... more The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for WIMPs via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on ...
We report on the results of a search for a Weakly Interacting Massive Particle (WIMP) signal in l... more We report on the results of a search for a Weakly Interacting Massive Particle (WIMP) signal in low-energy data of the Cryogenic Dark Matter Search (CDMS II) experiment using a maximum likelihood analysis. A background model is constructed using GEANT4 to simulate the surface-event background from 210 Pb decaychain events, while using independent calibration data to model the gamma background. Fitting this background model to the data results in no statistically significant WIMP component. In addition, we perform fits using an analytic ad hoc background model proposed by Collar and Fields, who claimed to find a large excess of signallike events in our data. We confirm the strong preference for a signal hypothesis in their analysis under these assumptions, but excesses are observed in both single-and multiple-scatter events, which implies the signal is not caused by WIMPs, but rather reflects the inadequacy of their background model. PACS numbers: 95.35.+d, 95.30.Cq, 29.40.Wk
Many current and future dark matter and neutrino detectors are designed to measure scintillation ... more Many current and future dark matter and neutrino detectors are designed to measure scintillation light with a large array of photomultiplier tubes (PMTs). The energy resolution and particle identification capabilities of these detectors depend in part on the ability to accurately identify individual photoelectrons in PMT waveforms despite large variability in pulse amplitudes and pulse pileup. We describe a Bayesian technique that can identify the times of individual photoelectrons in a sampled PMT waveform without deconvolution, even when pileup is present. To demonstrate the technique, we apply it to the general problem of particle identification in single-phase liquid argon dark matter detectors. Using the output of the Bayesian photoelectron counting algorithm described in this paper, we construct several test statistics for rejection of backgrounds for dark matter searches in argon. Compared to simpler methods based on either observed charge or peak finding, the photoelectron counting technique improves both energy resolution and particle identification of low energy events in calibration data from the DEAP-1 detector and simulation of the larger MiniCLEAN dark matter detector.
BetaCage, a gaseous neon time-projection chamber, has been proposed as a viable screener for emit... more BetaCage, a gaseous neon time-projection chamber, has been proposed as a viable screener for emitters of low-energy alphas and electrons to which commercial radioactivity counting techniques are insensitive. Using radiopure materials for construction, active and passive shielding from extrinsic backgrounds, large counting area and minimal detector mass, BetaCage will be able to achieve sensitivities of 10−5 counts keV−1 kg−1 day−1 in a few days of running time. We report on progress in prototype development work since the last meeting of this workshop.
While the standard model of particle physics does not include free particles with fractional char... more While the standard model of particle physics does not include free particles with fractional charge, experimental searches have not ruled out their existence. We report results from the Cryogenic Dark Matter Search (CDMS II) experiment that give the first direct-detection limits for cosmogenically produced relativistic particles with electric charge lower than e/6. A search for tracks in the six stacked detectors of each of two of the CDMS II towers finds no candidates, thereby excluding new parameter space for particles with electric charges between e/6 and e/200.
Modest improvements in the level and/or discrimination of backgrounds are needed to keep backgrou... more Modest improvements in the level and/or discrimination of backgrounds are needed to keep backgrounds negligible during the three phases of SuperCDMS. By developing production designs that require only modest testing, detector production rates may be improved sufficiently to allow an exposure of 500 ton d within a reasonable time and budget. Overall, the improvement estimates described above are conservative. Previous
As part of the Snowmass process, the Cosmic Frontier WIMP Direct Detection subgroup (CF1) has dra... more As part of the Snowmass process, the Cosmic Frontier WIMP Direct Detection subgroup (CF1) has drawn on input from the Cosmic Frontier and the broader Particle Physics community to produce this document. The charge to CF1 was (a) to summarize the current status and projected sensitivity of WIMP direct detection experiments worldwide, (b) motivate WIMP dark matter searches over a broad parameter space by examining a spectrum of WIMP models, (c) establish a community consensus on the type of experimental program required to explore that parameter space, and (d) identify the common infrastructure required to practically meet those goals.
The CDMS and EDELWEISS collaborations have combined the results of their direct searches for dark... more The CDMS and EDELWEISS collaborations have combined the results of their direct searches for dark matter using cryogenic germanium detectors. The total data set represents 614 kg·days equivalent exposure. A straightforward method of combination was chosen for its simplicity before data were exchanged between experiments. The results are interpreted in terms of limits on spinindependent WIMP-nucleon cross-section. For a WIMP mass of 90 GeV/c 2 , where this analysis is most sensitive, a cross-section of 3.3 × 10 −44 cm 2 is excluded at 90% CL. At higher WIMP masses, the combination improves the individual limits, by a factor 1.6 above 700 GeV/c 2 . Alternative methods of combining the data provide stronger constraints for some ranges of WIMP masses and weaker constraints for others. PACS numbers: 95.35.+d, 14.80.Ly, 29.40.Wk, 98.80.Es
The Cryogenic Dark Matter Search experiment uses cooled germanium and silicon detectors for a dir... more The Cryogenic Dark Matter Search experiment uses cooled germanium and silicon detectors for a direct search for weakly interacting massive particles in our Galaxy. The novel detectors allow a high degree of background rejection by discriminating between electron and nuclear recoils through the simultaneous measurement of the energy deposited in phonons and ionization. Exposures on the order of one kilogram-day
We report results of a search for Weakly Interacting Massive Particles (WIMPS) with the silicon d... more We report results of a search for Weakly Interacting Massive Particles (WIMPS) with the silicon detectors of the CDMS II experiment. This blind analysis of 140.2 kg-days of data taken between July 2007 and September 2008 revealed three WIMP-candidate events with a surface-event background estimate of 0.41 +0.20 −0.08 (stat.) +0.28 −0.24 (syst.). Other known backgrounds from neutrons and 206 Pb are limited to < 0.13 and < 0.08 events at the 90% confidence level, respectively. The exposure of this analysis is equivalent to 23.4 kg-days for a recoil energy range of 7-100 keV for a WIMP of mass 10 GeV/c 2 . The probability that the known backgrounds would produce three or more events in the signal region is 5.4%. A profile likelihood ratio test of the three events that includes the measured recoil energies gives a 0.19% probability for the known-background-only hypothesis when tested against the alternative WIMP+background hypothesis. The highest likelihood occurs for a WIMP mass of 8.6 GeV/c 2 and WIMP-nucleon cross section of 1.9×10 −41 cm 2 .
SuperCDMS is an experiment designed to directly detect Weakly Interacting Massive Particles (WIMP... more SuperCDMS is an experiment designed to directly detect Weakly Interacting Massive Particles (WIMPs), a favored candidate for dark matter ubiquitous in the Universe. In this paper, we present WIMP-search results using a calorimetric technique we call CDMSlite, which relies on voltageassisted Luke-Neganov amplification of the ionization energy deposited by particle interactions. The data were collected with a single 0.6 kg germanium detector running for 10 live days at the Soudan Underground Laboratory. A low energy threshold of 170 eVee (electron equivalent) was obtained, which allows us to constrain new WIMP-nucleon spin-independent parameter space for WIMP masses below 6 GeV/c 2 .
We report results of a search for Weakly Interacting Massive Particles (WIMPs) with the Si detect... more We report results of a search for Weakly Interacting Massive Particles (WIMPs) with the Si detectors of the CDMS II experiment. This report describes a blind analysis of the first data taken with CDMS II's full complement of detectors in 2006-2007; results from this exposure using the Ge detectors have already been presented. We observed no candidate WIMP-scattering events in an exposure of 55.9 kg-days before analysis cuts, with an expected background of ∼1.1 events. The exposure of this analysis is equivalent to 10.3 kg-days over a recoil energy range of 7-100 keV for an ideal Si detector and a WIMP mass of 10 GeV/c 2 . These data set an upper limit of 1.7 × 10 −41 cm 2 on the WIMP-nucleon spin-independent cross section of a 10 GeV/c 2 WIMP. These data exclude parameter space for spin-independent WIMP-nucleon elastic scattering that is relevant to recent searches for low-mass WIMPs.
Because the cross section for neutrino-electron scattering increases at small kinetic energy tran... more Because the cross section for neutrino-electron scattering increases at small kinetic energy transfer for magnetic scattering, a large gain in sensitivity to the neutrino magnetic moment can be obtained with a massive ultra-low energy ( ˜10 eV) threshold detector. Such detectors are being evaluated for possible use with an intense tritium source of low energy neutrinos. Silicon particle detectors developed for the Cryogenic Dark Matter Search (CDMS) have been used as prototypes to evaluate the Nagonov-Trofimov-Luke (NTL) Effect at charge bias voltages up to 200 V/cm. Quasiparticle-assisted electrothermal feedback transition-edge sensors are lithographically patterned onto the surface of 100 g Si wafers (3-inch diameter, 1-cm thick) to create Z-sensitive Ionization and Phonon detectors (ZIPs). Energy is collected from electron recoil events in the wafer in both athermal phonon and ionization channels. The ionization signal output remains stable against applied voltage, while the accelerated ionization electrons and holes inelastically scatter from the Si crystal lattice, pumping energy into the phonon channel (NTL Effect). Evaluations conducted at Case Western Reserve University show that noise in the athermal phonon channel is not significantly affected by the ionization channel voltage bias. A factor of 50 gain in the phonon channel has been observed through study of gamma events from ^241Am sources, resulting in an effective Si ZIP energy threshold of approximately 30 eV. The favorable results from these prototype detectors make feasible further development toward an antineutrino magnetic moment experiment with sensitivity two orders of magnitude better than present limits.
The Cryogenic Dark Matter Search experiment uses cooled germanium and silicon detectors for a dir... more The Cryogenic Dark Matter Search experiment uses cooled germanium and silicon detectors for a direct search for weakly interacting massive particles in our Galaxy. The novel detectors allow a high degree of background rejection by discriminating between electron and nuclear recoils through the simultaneous measurement of the energy deposited in phonons and ionization. Exposures on the order of one kilogram-day
Material screening for low-energy betas and alphas is necessary for rare-event-search experiments... more Material screening for low-energy betas and alphas is necessary for rare-event-search experiments, such as dark matter and neutrinoless double-beta decay searches where surface radiocontamination has become a significant background. The BetaCage, a gaseous neon time-projection chamber, has been proposed as a screener for emitters of low-energy betas and alphas to which existing screening facilities are insufficiently sensitive. The expected sensitivity is 0.1 betas / (keV m^2 day) and 0.1 alphas / (m^2 day). Expected backgrounds are dominated by Compton scattering of external photons in the sample to be screened; radioassays and simulations indicate backgrounds from detector materials and radon daughters should be subdominant. We will report on details of the background simulations and the detector design that allows discrimination to reach these sensitivity levels.
ABSTRACT . The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weak... more ABSTRACT . The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on the spinindependent WIMP-nucleon elastic-scattering cross section that exclude unexplored parameter space above 10 GeV c 2 WIMP mass and, at &gt; 75% CL, the entire 3 allowed region for the WIMP signal reported by the DAMA experiment. 1 Introduction Weakly Interacting Massive Particles (WIMPs) are an excellent candidate for the universe&#39;s nonbaryonic, cold dark matter [1]. WIMPs in our Galaxy would scatter o nuclei via the weak interaction, potentially allowing their direct detection. The expected spectrum of the resulting nuclei recoil energies is exponential with a characteristic energy of a few to tens of keV [2]. The expected event rate is model-dependent but is generic...
Cosmo-2000 - Proceedings of the Fourth International Workshop on Particle Physics and the Early Universe, 2001
The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for WIMPs via their... more The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for WIMPs via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on ...
We report on the results of a search for a Weakly Interacting Massive Particle (WIMP) signal in l... more We report on the results of a search for a Weakly Interacting Massive Particle (WIMP) signal in low-energy data of the Cryogenic Dark Matter Search (CDMS II) experiment using a maximum likelihood analysis. A background model is constructed using GEANT4 to simulate the surface-event background from 210 Pb decaychain events, while using independent calibration data to model the gamma background. Fitting this background model to the data results in no statistically significant WIMP component. In addition, we perform fits using an analytic ad hoc background model proposed by Collar and Fields, who claimed to find a large excess of signallike events in our data. We confirm the strong preference for a signal hypothesis in their analysis under these assumptions, but excesses are observed in both single-and multiple-scatter events, which implies the signal is not caused by WIMPs, but rather reflects the inadequacy of their background model. PACS numbers: 95.35.+d, 95.30.Cq, 29.40.Wk
Many current and future dark matter and neutrino detectors are designed to measure scintillation ... more Many current and future dark matter and neutrino detectors are designed to measure scintillation light with a large array of photomultiplier tubes (PMTs). The energy resolution and particle identification capabilities of these detectors depend in part on the ability to accurately identify individual photoelectrons in PMT waveforms despite large variability in pulse amplitudes and pulse pileup. We describe a Bayesian technique that can identify the times of individual photoelectrons in a sampled PMT waveform without deconvolution, even when pileup is present. To demonstrate the technique, we apply it to the general problem of particle identification in single-phase liquid argon dark matter detectors. Using the output of the Bayesian photoelectron counting algorithm described in this paper, we construct several test statistics for rejection of backgrounds for dark matter searches in argon. Compared to simpler methods based on either observed charge or peak finding, the photoelectron counting technique improves both energy resolution and particle identification of low energy events in calibration data from the DEAP-1 detector and simulation of the larger MiniCLEAN dark matter detector.
BetaCage, a gaseous neon time-projection chamber, has been proposed as a viable screener for emit... more BetaCage, a gaseous neon time-projection chamber, has been proposed as a viable screener for emitters of low-energy alphas and electrons to which commercial radioactivity counting techniques are insensitive. Using radiopure materials for construction, active and passive shielding from extrinsic backgrounds, large counting area and minimal detector mass, BetaCage will be able to achieve sensitivities of 10−5 counts keV−1 kg−1 day−1 in a few days of running time. We report on progress in prototype development work since the last meeting of this workshop.
While the standard model of particle physics does not include free particles with fractional char... more While the standard model of particle physics does not include free particles with fractional charge, experimental searches have not ruled out their existence. We report results from the Cryogenic Dark Matter Search (CDMS II) experiment that give the first direct-detection limits for cosmogenically produced relativistic particles with electric charge lower than e/6. A search for tracks in the six stacked detectors of each of two of the CDMS II towers finds no candidates, thereby excluding new parameter space for particles with electric charges between e/6 and e/200.
Modest improvements in the level and/or discrimination of backgrounds are needed to keep backgrou... more Modest improvements in the level and/or discrimination of backgrounds are needed to keep backgrounds negligible during the three phases of SuperCDMS. By developing production designs that require only modest testing, detector production rates may be improved sufficiently to allow an exposure of 500 ton d within a reasonable time and budget. Overall, the improvement estimates described above are conservative. Previous
As part of the Snowmass process, the Cosmic Frontier WIMP Direct Detection subgroup (CF1) has dra... more As part of the Snowmass process, the Cosmic Frontier WIMP Direct Detection subgroup (CF1) has drawn on input from the Cosmic Frontier and the broader Particle Physics community to produce this document. The charge to CF1 was (a) to summarize the current status and projected sensitivity of WIMP direct detection experiments worldwide, (b) motivate WIMP dark matter searches over a broad parameter space by examining a spectrum of WIMP models, (c) establish a community consensus on the type of experimental program required to explore that parameter space, and (d) identify the common infrastructure required to practically meet those goals.
The CDMS and EDELWEISS collaborations have combined the results of their direct searches for dark... more The CDMS and EDELWEISS collaborations have combined the results of their direct searches for dark matter using cryogenic germanium detectors. The total data set represents 614 kg·days equivalent exposure. A straightforward method of combination was chosen for its simplicity before data were exchanged between experiments. The results are interpreted in terms of limits on spinindependent WIMP-nucleon cross-section. For a WIMP mass of 90 GeV/c 2 , where this analysis is most sensitive, a cross-section of 3.3 × 10 −44 cm 2 is excluded at 90% CL. At higher WIMP masses, the combination improves the individual limits, by a factor 1.6 above 700 GeV/c 2 . Alternative methods of combining the data provide stronger constraints for some ranges of WIMP masses and weaker constraints for others. PACS numbers: 95.35.+d, 14.80.Ly, 29.40.Wk, 98.80.Es
The Cryogenic Dark Matter Search experiment uses cooled germanium and silicon detectors for a dir... more The Cryogenic Dark Matter Search experiment uses cooled germanium and silicon detectors for a direct search for weakly interacting massive particles in our Galaxy. The novel detectors allow a high degree of background rejection by discriminating between electron and nuclear recoils through the simultaneous measurement of the energy deposited in phonons and ionization. Exposures on the order of one kilogram-day
We report results of a search for Weakly Interacting Massive Particles (WIMPS) with the silicon d... more We report results of a search for Weakly Interacting Massive Particles (WIMPS) with the silicon detectors of the CDMS II experiment. This blind analysis of 140.2 kg-days of data taken between July 2007 and September 2008 revealed three WIMP-candidate events with a surface-event background estimate of 0.41 +0.20 −0.08 (stat.) +0.28 −0.24 (syst.). Other known backgrounds from neutrons and 206 Pb are limited to < 0.13 and < 0.08 events at the 90% confidence level, respectively. The exposure of this analysis is equivalent to 23.4 kg-days for a recoil energy range of 7-100 keV for a WIMP of mass 10 GeV/c 2 . The probability that the known backgrounds would produce three or more events in the signal region is 5.4%. A profile likelihood ratio test of the three events that includes the measured recoil energies gives a 0.19% probability for the known-background-only hypothesis when tested against the alternative WIMP+background hypothesis. The highest likelihood occurs for a WIMP mass of 8.6 GeV/c 2 and WIMP-nucleon cross section of 1.9×10 −41 cm 2 .
SuperCDMS is an experiment designed to directly detect Weakly Interacting Massive Particles (WIMP... more SuperCDMS is an experiment designed to directly detect Weakly Interacting Massive Particles (WIMPs), a favored candidate for dark matter ubiquitous in the Universe. In this paper, we present WIMP-search results using a calorimetric technique we call CDMSlite, which relies on voltageassisted Luke-Neganov amplification of the ionization energy deposited by particle interactions. The data were collected with a single 0.6 kg germanium detector running for 10 live days at the Soudan Underground Laboratory. A low energy threshold of 170 eVee (electron equivalent) was obtained, which allows us to constrain new WIMP-nucleon spin-independent parameter space for WIMP masses below 6 GeV/c 2 .
We report results of a search for Weakly Interacting Massive Particles (WIMPs) with the Si detect... more We report results of a search for Weakly Interacting Massive Particles (WIMPs) with the Si detectors of the CDMS II experiment. This report describes a blind analysis of the first data taken with CDMS II's full complement of detectors in 2006-2007; results from this exposure using the Ge detectors have already been presented. We observed no candidate WIMP-scattering events in an exposure of 55.9 kg-days before analysis cuts, with an expected background of ∼1.1 events. The exposure of this analysis is equivalent to 10.3 kg-days over a recoil energy range of 7-100 keV for an ideal Si detector and a WIMP mass of 10 GeV/c 2 . These data set an upper limit of 1.7 × 10 −41 cm 2 on the WIMP-nucleon spin-independent cross section of a 10 GeV/c 2 WIMP. These data exclude parameter space for spin-independent WIMP-nucleon elastic scattering that is relevant to recent searches for low-mass WIMPs.
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Papers by Richard Schnee