The low-background, VUV-sensitive 3-inch diameter photomultiplier tube R11410 has been developed ... more The low-background, VUV-sensitive 3-inch diameter photomultiplier tube R11410 has been developed by Hamamatsu for dark matter direct detection experiments using liquid xenon as the target material. We present the results from the joint effort between the XENON collaboration and the Hamamatsu company to produce a highly radio-pure photosensor (version R11410-21) for the XENON1T dark matter experiment. After introducing the photosensor and its components, we show the methods and results of the radioactive contamination measurements of the individual materials employed in the photomultiplier production. We then discuss the adopted strategies to reduce the radioactivity of the various PMT versions. Finally, we detail the results from screening 216 tubes with ultra-low background germanium detectors, as well as their implications for the expected electronic and nuclear recoil background of the XENON1T experiment. a
We have searched for periodic variations of the electronic recoil event rate in the (2-6) keV ene... more We have searched for periodic variations of the electronic recoil event rate in the (2-6) keV energy range recorded between February 2011 and March 2012 with the XENON100 detector, adding up to 224.6 live days in total. Following a detailed study to establish the stability of the detector and its background contributions during this run, we performed an unbinned profile likelihood analysis to identify any periodicity up to 500 days. We find a global significance of less than 1σ for all periods, suggesting no statistically significant modulation in the data. While the local significance for an annual modulation is 2.8σ, the analysis of a multiple-scatter control sample and the phase of the modulation disfavor a dark matter interpretation. The DAMA/LIBRA annual modulation interpreted as a dark matter signature with axial-vector coupling of weakly interacting massive particles to electrons is excluded at 4.8σ.
Liquid xenon detectors are one of the leading technologies in direct dark matter searches. In ord... more Liquid xenon detectors are one of the leading technologies in direct dark matter searches. In order to improve the precision of their energy scales, it is important to characterize the scintillation and ionization of liquid xenon at low energies, where measurements with applied electric field are few or nonexistent. At Columbia University we have built a dual-phase detector, neriX, capable of simultaneously measuring the light and charge deposits from low-energy interactions in liquid xenon. The detector was designed to optimize event vertex reconstruction while maintaining a high light detection efficiency. Far detector coincidence techniques (Compton or neutron elastic scattering) are employed to extract the light and charge yields of liquid xenon as a function of energy for different particle types. In this talk we will discuss the detector calibration and performance, and will present some preliminary results.
We have searched for periodic variations of the electronic recoil event rate in the (2−6) keV ene... more We have searched for periodic variations of the electronic recoil event rate in the (2−6) keV energy range recorded between February 2011 and March 2012 with the XENON100 detector, adding up to 224.6 live days in total. Following a detailed study to establish the stability of the detector and its background contributions during this run, we performed an un-binned profile likelihood analysis to identify any periodicity up to 500 days. We find a global significance of less than 1 σ for all periods suggesting no statistically significant modulation in the data. While the local significance for an annual modulation is 2.8 σ, the analysis of a multiple-scatter control sample and the phase of the modulation disfavor a dark matter interpretation. The DAMA/LIBRA annual modulation interpreted as a dark matter signature with axial-vector coupling of WIMPs to electrons is excluded at 4.8 σ.
Laboratory experiments searching for galactic dark matter particles scattering off nuclei have so... more Laboratory experiments searching for galactic dark matter particles scattering off nuclei have so far not been able to establish a discovery. We use data from the XENON100 experiment to search for dark matter interacting with electrons. With no evidence for a signal above the low background of our experiment, we exclude a variety of representative dark matter models that would induce electronic recoils. For axial-vector couplings to electrons, we exclude cross sections above 6 × 10(-35) cm(2) for particle masses of m(χ) = 2 GeV/c(2). Independent of the dark matter halo, we exclude leptophilic models as an explanation for the long-standing DAMA/LIBRA signal, such as couplings to electrons through axial-vector interactions at a 4.4σ confidence level, mirror dark matter at 3.6σ, and luminous dark matter at 4.6σ.
We have developed an efficient cryogenic system with heat exchange and associated gas purificatio... more We have developed an efficient cryogenic system with heat exchange and associated gas purification system as a prototype for the XENON1T experiment. The XENON1T detector will use about 3 tons of liquid xenon (LXe) at a temperature of 175K as target and detection medium for a dark matter search. In this paper we report results on the cryogenic system performance focusing on the dynamics of the gas circulation-purification through a heated getter, at flow rates above 50 Standard Liter per Minute (SLPM). A maximum flow of 114 SLPM has been achieved, and using two heat exchangers in series, a heat exchange efficiency better than 96% has been measured.
ABSTRACT Proportional scintillation in liquid xenon has a promising application in the field of d... more ABSTRACT Proportional scintillation in liquid xenon has a promising application in the field of direct dark matter detection, potentially allowing for simpler, more sensitive detectors. However, knowledge of the basic properties of the phenomenon as well as guidelines for its practical use are currently limited. We report here on measurements of proportional scintillation light emitted in liquid xenon around thin wires. The maximum proportional scintillation gain of $287^{+97}_{-75}$ photons per drift electron was obtained using 10 $\mu$m diameter gold plated tungsten wire. The thresholds for electron multiplication and proportional scintillation are measured as $725^{+48}_{-139}$ and $412^{+10}_{-133}$ kV/cm, respectively. The threshold for proportional scintillation is in good agreement with a previously published result, while the electron multiplication threshold represents a novel measurement. A complete set of parameters for the practical use of the electron multiplication and proportional scintillation processes in liquid xenon was also obtained for the first time.
Vacuum ultraviolet light sensitive photomultiplier tubes directly coupled to liquid xenon are bei... more Vacuum ultraviolet light sensitive photomultiplier tubes directly coupled to liquid xenon are being used to efficiently detect the 178 nm scintillation light in a variety of liquid xenon based particle detectors. Good knowledge of the performance of these photomultipliers under cryogenic conditions is needed to properly characterize these detectors. Here, we report on measurements of the quantum efficiency of Hamamatsu R8520 photomultipliers, used in the XENON Dark Matter Experiments. The quantum efficiency measurements at room temperature agree with the values provided by Hamamatsu. At low temperatures, between 160K and 170K, the quantum efficiency increases by ∼ 5 − 11% relative to the room temperature values.
We have measured the energy dependence of the liquid xenon (LXe) scintillation yield of electrons... more We have measured the energy dependence of the liquid xenon (LXe) scintillation yield of electrons with energy between 2.1 and 120.2 keV, using the Compton coincidence technique. A LXe scintillation detector with a very high light detection efficiency was irradiated with 137 Cs γ rays and the energy of the Compton-scattered γ rays was measured with a high-purity germanium (HPGe) detector placed at different scattering angles. The excellent energy resolution of the HPGe detector allows the selection of events with Compton electrons of known energy in the LXe detector. We find that the scintillation yield initially increases as the electron energy decreases from 120 keV to about 60 keV but then decreases by about 30% from 60 keV to 2 keV. The measured scintillation yield was also measured with conversion electrons from the 32.1 keV and 9.4 keV transitions of the 83m Kr isomer, used as an internal calibration source. We find that the scintillation yield of the 32.1 keV transition is compatible with that obtained from the Compton coincidence measurement. On the other hand, the yield for the 9.4 keV transition is much higher than that measured for a Compton electron of the same energy. We interpret the enhancement in the scintillation yield as due to the enhanced recombination rate in the presence of Xe ions left from the 32.1 keV transition, which precedes the 9.4 keV one by 220 ns, on average.
XENON100 is the current phase of the XENON dark matter program, which aims for the direct detecti... more XENON100 is the current phase of the XENON dark matter program, which aims for the direct detection of WIMPs with liquid xenon time-projection chambers. We present the status of the experiment after 224.6 live days taken in 2011 and 2012 during which the detector successfully improved in terms of more calibration data, higher xenon purity, lower threshold and better background removal. The analysis has yielded no evidence for dark matter interactions. The status of the next generation XENON1T detector will be briefly described.
The worldwide race towards direct dark matter detection in the form of Weakly Interacting Massive... more The worldwide race towards direct dark matter detection in the form of Weakly Interacting Massive Particles (WIMPs) has been dramatically accelerated by the remarkable progress and evolution of liquid xenon time projection chambers (LXeTPCs). With a realistic discovery potential, XENON100 has already reached a sensitivity of $7\times10^{-45}\,\n{cm}^2$, and continues to accrue data at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy towards its ultimate sensitivity reach at the $\sigma_{\n{SI}}\sim 2\times10^{-45}\,\n{cm}^2$ level for the spin-independent WIMP-nucleon cross-section. To fully explore the favoured parameter space for WIMP dark matter in search of a first robust and statistically significant discovery, or to confirm any hint of a signal from \Xehund, the next phase of the XENON program will be a detector at the ton scale - XENON1T. The XENON1T detector, based on 2.2 ton of LXe viewed by low radioactivity photomultiplier tubes and housed in a water Cherenkov muon...
XENON100 is a liquid xenon (LXe) time projection chamber built to search for rare collisions of h... more XENON100 is a liquid xenon (LXe) time projection chamber built to search for rare collisions of hypothetical, weakly interacting massive particles (WIMPs). Operated in a low-background shield at the Gran Sasso underground laboratory in Italy, XENON100 has reached the unprecedented background level of $<$0.15 events/day/\kevr in the energy range below 100 \kevr in 30 kg of target mass, before electronic/nuclear recoil discrimination. It found no evidence for WIMPs during a dark matter run lasting for 100.9 live days in 2010, excluding with 90% confidence scalar WIMP-nucleon cross sections above 7x10$^{-45}$ cm$^{2}$ at a WIMP mass of 50 GeV/c$^{2}$. A new run started in March 2011, and more than 200 live days of WIMP-search data have been acquired. Results of this second run are expected to be released in summer 2012.
We present the first results of searches for axions and axion-like-particles with the XENON100 ex... more We present the first results of searches for axions and axion-like-particles with the XENON100 experiment. The axion-electron coupling constant, gAe, has been tested by exploiting the axioelectric effect in liquid xenon. A profile likelihood analysis of 224.6 live days × 34 kg exposure has shown no evidence for a signal. By rejecting gAe larger than 7.7 × 10 −12 (90% CL) in the solar axion search, we set the best limit to date on this coupling. In the frame of the DFSZ and KSVZ models, we exclude QCD axions heavier than 0.3 eV/c 2 and 80 eV/c 2 , respectively. For axion-like-particles, under the assumption that they constitute the whole abundance of dark matter in our galaxy, we constrain gAe to be lower than 1 × 10 −12 (90% CL) for masses between 5 and 10 keV/c 2 .
The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy,... more The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, was designed to search for evidence of dark matter interactions inside a volume of liquid xenon using a dual-phase time projection chamber. This paper describes the Slow Control System (SCS) of the experiment with emphasis on the distributed architecture as well as on its modular and expandable nature. The system software was designed according to the rules of Object-Oriented Programming and coded in Java, thus promoting code reusability and maximum flexibility during commissioning of the experiment. The SCS has been continuously monitoring the XENON100 detector since mid 2008, remotely recording hundreds of parameters on a few dozen instruments in real time, and setting emergency alarms for the most important variables.
XENON10 is an experiment to directly detect weakly interacting massive particle (WIMPs), which ma... more XENON10 is an experiment to directly detect weakly interacting massive particle (WIMPs), which may comprise the bulk of the non-baryonic dark matter in our Universe. We report new results for spin-dependent WIMP-nucleon interactions with 129 Xe and 131 Xe from 58.6 live-days of operation at the Laboratori Nazionali del Gran Sasso (LNGS). Based on the non-observation of a WIMP signal in 5.4 kg of fiducial liquid xenon mass, we exclude previously unexplored regions in the theoretically allowed parameter space for neutralinos. We also exclude a heavy Majorana neutrino with a mass in the range of ∼10 GeV/c 2 -2 TeV/c 2 as a dark matter candidate under standard assumptions for its density and distribution in the galactic halo. PACS numbers: 95.35.+d, 29.40.Mc, 95.55.Vj
Results from the nuclear recoil calibration of the XENON100 dark matter detector installed underg... more Results from the nuclear recoil calibration of the XENON100 dark matter detector installed underground at the Laboratori Nazionali del Gran Sasso (LNGS), Italy are presented. Data from measurements with an external 241 AmBe neutron source are compared with a detailed Monte Carlo simulation which is used to extract the energy dependent charge-yield Qy and relative scintillation efficiency L eff . A very good level of absolute spectral matching is achieved in both observable signal channels -scintillation S1 and ionization S2 -along with agreement in the 2-dimensional particle discrimination space. The results confirm the validity of the derived signal acceptance in earlier reported dark matter searches of the XENON100 experiment.
Particle detectors that use liquid xenon (LXe) as detection medium are among the leading technolo... more Particle detectors that use liquid xenon (LXe) as detection medium are among the leading technologies in the search for dark matter weakly interacting massive particles (WIMPs). A key enabling element has been the low-energy detection threshold for recoiling nuclei produced by the interaction of WIMPs in LXe targets. In these detectors, the nuclear recoil energy scale is based on the LXe scintillation signal and thus requires knowledge of the relative scintillation efficiency of nuclear recoils, L eff . The uncertainty in L eff at low energies is the largest systematic uncertainty in the reported results from LXe WIMP searches at low masses. In the context of the XENON Dark Matter project, a new LXe scintillation detector has been designed and built specifically for the measurement of L eff at low energies, with an emphasis on maximizing the scintillation light detection efficiency to obtain the lowest possible energy threshold. We report new measurements of L eff at low energies performed with this detector. Our results suggest a L eff which slowly decreases with decreasing energy, from 0.144 ± 0.009 at 15 keV down to 0.088 +0.014 −0.015 at 3 keV. PACS numbers: 95.35.+d, 14.80.Ly, 29.40.-n, 95.55.Vj
Journal of Physics G: Nuclear and Particle Physics, 2013
The XENON100 experiment, installed underground at the Laboratori Nazionali del Gran Sasso (LNGS),... more The XENON100 experiment, installed underground at the Laboratori Nazionali del Gran Sasso (LNGS), aims to directly detect dark matter in the form of Weakly Interacting Massive Particles (WIMPs) via their elastic scattering off xenon nuclei. This paper presents a study on the nuclear recoil background of the experiment, taking into account neutron backgrounds from (α,n) and spontaneous fission reactions due to natural radioactivity in the detector and shield materials, as well as muon-induced neutrons. Based on Monte Carlo simulations and using measured radioactive contaminations of all detector components, we predict the nuclear recoil backgrounds for the WIMP search results published by the XENON100 experiment in 2011 and 2012, 0.11 +0.08 −0.04 events and 0.17 +0.12 −0.07 events, respectively, and conclude that they do not limit the sensitivity of the experiment. PACS numbers: 95.35.+d, 29.40.-n, 34.80.Dp
Journal of Physics G: Nuclear and Particle Physics, 2014
The XENON100 dark matter experiment uses liquid xenon in a time projection chamber (TPC) to measu... more The XENON100 dark matter experiment uses liquid xenon in a time projection chamber (TPC) to measure xenon nuclear recoils resulting from the scattering of dark matter Weakly Interacting Massive Particles (WIMPs). In this paper, we report the observation of single-electron charge signals which are not related to WIMP interactions. These signals, which show the excellent sensitivity of the detector to small charge signals, are explained as being due to the photoionization of impurities in the liquid xenon and of the metal components inside the TPC. They are used as a unique calibration source to characterize the detector. We explain how we can infer crucial parameters for the XENON100 experiment: the secondary-scintillation gain, the extraction yield from the liquid to the gas phase and the electron drift velocity.
In a recent manuscript (arXiv:1208.5046) Peter Sorensen claims that XENON100's upper limits on sp... more In a recent manuscript (arXiv:1208.5046) Peter Sorensen claims that XENON100's upper limits on spin-independent WIMP-nucleon cross sections for WIMP masses below 10 GeV "may be understated by one order of magnitude or more". Having performed a similar, though more detailed analysis prior to the submission of our new result (arXiv:1207.5988), we do not confirm these findings. We point out the rationale for not considering the described effect in our final analysis and list several potential problems with his study.
The low-background, VUV-sensitive 3-inch diameter photomultiplier tube R11410 has been developed ... more The low-background, VUV-sensitive 3-inch diameter photomultiplier tube R11410 has been developed by Hamamatsu for dark matter direct detection experiments using liquid xenon as the target material. We present the results from the joint effort between the XENON collaboration and the Hamamatsu company to produce a highly radio-pure photosensor (version R11410-21) for the XENON1T dark matter experiment. After introducing the photosensor and its components, we show the methods and results of the radioactive contamination measurements of the individual materials employed in the photomultiplier production. We then discuss the adopted strategies to reduce the radioactivity of the various PMT versions. Finally, we detail the results from screening 216 tubes with ultra-low background germanium detectors, as well as their implications for the expected electronic and nuclear recoil background of the XENON1T experiment. a
We have searched for periodic variations of the electronic recoil event rate in the (2-6) keV ene... more We have searched for periodic variations of the electronic recoil event rate in the (2-6) keV energy range recorded between February 2011 and March 2012 with the XENON100 detector, adding up to 224.6 live days in total. Following a detailed study to establish the stability of the detector and its background contributions during this run, we performed an unbinned profile likelihood analysis to identify any periodicity up to 500 days. We find a global significance of less than 1σ for all periods, suggesting no statistically significant modulation in the data. While the local significance for an annual modulation is 2.8σ, the analysis of a multiple-scatter control sample and the phase of the modulation disfavor a dark matter interpretation. The DAMA/LIBRA annual modulation interpreted as a dark matter signature with axial-vector coupling of weakly interacting massive particles to electrons is excluded at 4.8σ.
Liquid xenon detectors are one of the leading technologies in direct dark matter searches. In ord... more Liquid xenon detectors are one of the leading technologies in direct dark matter searches. In order to improve the precision of their energy scales, it is important to characterize the scintillation and ionization of liquid xenon at low energies, where measurements with applied electric field are few or nonexistent. At Columbia University we have built a dual-phase detector, neriX, capable of simultaneously measuring the light and charge deposits from low-energy interactions in liquid xenon. The detector was designed to optimize event vertex reconstruction while maintaining a high light detection efficiency. Far detector coincidence techniques (Compton or neutron elastic scattering) are employed to extract the light and charge yields of liquid xenon as a function of energy for different particle types. In this talk we will discuss the detector calibration and performance, and will present some preliminary results.
We have searched for periodic variations of the electronic recoil event rate in the (2−6) keV ene... more We have searched for periodic variations of the electronic recoil event rate in the (2−6) keV energy range recorded between February 2011 and March 2012 with the XENON100 detector, adding up to 224.6 live days in total. Following a detailed study to establish the stability of the detector and its background contributions during this run, we performed an un-binned profile likelihood analysis to identify any periodicity up to 500 days. We find a global significance of less than 1 σ for all periods suggesting no statistically significant modulation in the data. While the local significance for an annual modulation is 2.8 σ, the analysis of a multiple-scatter control sample and the phase of the modulation disfavor a dark matter interpretation. The DAMA/LIBRA annual modulation interpreted as a dark matter signature with axial-vector coupling of WIMPs to electrons is excluded at 4.8 σ.
Laboratory experiments searching for galactic dark matter particles scattering off nuclei have so... more Laboratory experiments searching for galactic dark matter particles scattering off nuclei have so far not been able to establish a discovery. We use data from the XENON100 experiment to search for dark matter interacting with electrons. With no evidence for a signal above the low background of our experiment, we exclude a variety of representative dark matter models that would induce electronic recoils. For axial-vector couplings to electrons, we exclude cross sections above 6 × 10(-35) cm(2) for particle masses of m(χ) = 2 GeV/c(2). Independent of the dark matter halo, we exclude leptophilic models as an explanation for the long-standing DAMA/LIBRA signal, such as couplings to electrons through axial-vector interactions at a 4.4σ confidence level, mirror dark matter at 3.6σ, and luminous dark matter at 4.6σ.
We have developed an efficient cryogenic system with heat exchange and associated gas purificatio... more We have developed an efficient cryogenic system with heat exchange and associated gas purification system as a prototype for the XENON1T experiment. The XENON1T detector will use about 3 tons of liquid xenon (LXe) at a temperature of 175K as target and detection medium for a dark matter search. In this paper we report results on the cryogenic system performance focusing on the dynamics of the gas circulation-purification through a heated getter, at flow rates above 50 Standard Liter per Minute (SLPM). A maximum flow of 114 SLPM has been achieved, and using two heat exchangers in series, a heat exchange efficiency better than 96% has been measured.
ABSTRACT Proportional scintillation in liquid xenon has a promising application in the field of d... more ABSTRACT Proportional scintillation in liquid xenon has a promising application in the field of direct dark matter detection, potentially allowing for simpler, more sensitive detectors. However, knowledge of the basic properties of the phenomenon as well as guidelines for its practical use are currently limited. We report here on measurements of proportional scintillation light emitted in liquid xenon around thin wires. The maximum proportional scintillation gain of $287^{+97}_{-75}$ photons per drift electron was obtained using 10 $\mu$m diameter gold plated tungsten wire. The thresholds for electron multiplication and proportional scintillation are measured as $725^{+48}_{-139}$ and $412^{+10}_{-133}$ kV/cm, respectively. The threshold for proportional scintillation is in good agreement with a previously published result, while the electron multiplication threshold represents a novel measurement. A complete set of parameters for the practical use of the electron multiplication and proportional scintillation processes in liquid xenon was also obtained for the first time.
Vacuum ultraviolet light sensitive photomultiplier tubes directly coupled to liquid xenon are bei... more Vacuum ultraviolet light sensitive photomultiplier tubes directly coupled to liquid xenon are being used to efficiently detect the 178 nm scintillation light in a variety of liquid xenon based particle detectors. Good knowledge of the performance of these photomultipliers under cryogenic conditions is needed to properly characterize these detectors. Here, we report on measurements of the quantum efficiency of Hamamatsu R8520 photomultipliers, used in the XENON Dark Matter Experiments. The quantum efficiency measurements at room temperature agree with the values provided by Hamamatsu. At low temperatures, between 160K and 170K, the quantum efficiency increases by ∼ 5 − 11% relative to the room temperature values.
We have measured the energy dependence of the liquid xenon (LXe) scintillation yield of electrons... more We have measured the energy dependence of the liquid xenon (LXe) scintillation yield of electrons with energy between 2.1 and 120.2 keV, using the Compton coincidence technique. A LXe scintillation detector with a very high light detection efficiency was irradiated with 137 Cs γ rays and the energy of the Compton-scattered γ rays was measured with a high-purity germanium (HPGe) detector placed at different scattering angles. The excellent energy resolution of the HPGe detector allows the selection of events with Compton electrons of known energy in the LXe detector. We find that the scintillation yield initially increases as the electron energy decreases from 120 keV to about 60 keV but then decreases by about 30% from 60 keV to 2 keV. The measured scintillation yield was also measured with conversion electrons from the 32.1 keV and 9.4 keV transitions of the 83m Kr isomer, used as an internal calibration source. We find that the scintillation yield of the 32.1 keV transition is compatible with that obtained from the Compton coincidence measurement. On the other hand, the yield for the 9.4 keV transition is much higher than that measured for a Compton electron of the same energy. We interpret the enhancement in the scintillation yield as due to the enhanced recombination rate in the presence of Xe ions left from the 32.1 keV transition, which precedes the 9.4 keV one by 220 ns, on average.
XENON100 is the current phase of the XENON dark matter program, which aims for the direct detecti... more XENON100 is the current phase of the XENON dark matter program, which aims for the direct detection of WIMPs with liquid xenon time-projection chambers. We present the status of the experiment after 224.6 live days taken in 2011 and 2012 during which the detector successfully improved in terms of more calibration data, higher xenon purity, lower threshold and better background removal. The analysis has yielded no evidence for dark matter interactions. The status of the next generation XENON1T detector will be briefly described.
The worldwide race towards direct dark matter detection in the form of Weakly Interacting Massive... more The worldwide race towards direct dark matter detection in the form of Weakly Interacting Massive Particles (WIMPs) has been dramatically accelerated by the remarkable progress and evolution of liquid xenon time projection chambers (LXeTPCs). With a realistic discovery potential, XENON100 has already reached a sensitivity of $7\times10^{-45}\,\n{cm}^2$, and continues to accrue data at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy towards its ultimate sensitivity reach at the $\sigma_{\n{SI}}\sim 2\times10^{-45}\,\n{cm}^2$ level for the spin-independent WIMP-nucleon cross-section. To fully explore the favoured parameter space for WIMP dark matter in search of a first robust and statistically significant discovery, or to confirm any hint of a signal from \Xehund, the next phase of the XENON program will be a detector at the ton scale - XENON1T. The XENON1T detector, based on 2.2 ton of LXe viewed by low radioactivity photomultiplier tubes and housed in a water Cherenkov muon...
XENON100 is a liquid xenon (LXe) time projection chamber built to search for rare collisions of h... more XENON100 is a liquid xenon (LXe) time projection chamber built to search for rare collisions of hypothetical, weakly interacting massive particles (WIMPs). Operated in a low-background shield at the Gran Sasso underground laboratory in Italy, XENON100 has reached the unprecedented background level of $<$0.15 events/day/\kevr in the energy range below 100 \kevr in 30 kg of target mass, before electronic/nuclear recoil discrimination. It found no evidence for WIMPs during a dark matter run lasting for 100.9 live days in 2010, excluding with 90% confidence scalar WIMP-nucleon cross sections above 7x10$^{-45}$ cm$^{2}$ at a WIMP mass of 50 GeV/c$^{2}$. A new run started in March 2011, and more than 200 live days of WIMP-search data have been acquired. Results of this second run are expected to be released in summer 2012.
We present the first results of searches for axions and axion-like-particles with the XENON100 ex... more We present the first results of searches for axions and axion-like-particles with the XENON100 experiment. The axion-electron coupling constant, gAe, has been tested by exploiting the axioelectric effect in liquid xenon. A profile likelihood analysis of 224.6 live days × 34 kg exposure has shown no evidence for a signal. By rejecting gAe larger than 7.7 × 10 −12 (90% CL) in the solar axion search, we set the best limit to date on this coupling. In the frame of the DFSZ and KSVZ models, we exclude QCD axions heavier than 0.3 eV/c 2 and 80 eV/c 2 , respectively. For axion-like-particles, under the assumption that they constitute the whole abundance of dark matter in our galaxy, we constrain gAe to be lower than 1 × 10 −12 (90% CL) for masses between 5 and 10 keV/c 2 .
The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy,... more The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, was designed to search for evidence of dark matter interactions inside a volume of liquid xenon using a dual-phase time projection chamber. This paper describes the Slow Control System (SCS) of the experiment with emphasis on the distributed architecture as well as on its modular and expandable nature. The system software was designed according to the rules of Object-Oriented Programming and coded in Java, thus promoting code reusability and maximum flexibility during commissioning of the experiment. The SCS has been continuously monitoring the XENON100 detector since mid 2008, remotely recording hundreds of parameters on a few dozen instruments in real time, and setting emergency alarms for the most important variables.
XENON10 is an experiment to directly detect weakly interacting massive particle (WIMPs), which ma... more XENON10 is an experiment to directly detect weakly interacting massive particle (WIMPs), which may comprise the bulk of the non-baryonic dark matter in our Universe. We report new results for spin-dependent WIMP-nucleon interactions with 129 Xe and 131 Xe from 58.6 live-days of operation at the Laboratori Nazionali del Gran Sasso (LNGS). Based on the non-observation of a WIMP signal in 5.4 kg of fiducial liquid xenon mass, we exclude previously unexplored regions in the theoretically allowed parameter space for neutralinos. We also exclude a heavy Majorana neutrino with a mass in the range of ∼10 GeV/c 2 -2 TeV/c 2 as a dark matter candidate under standard assumptions for its density and distribution in the galactic halo. PACS numbers: 95.35.+d, 29.40.Mc, 95.55.Vj
Results from the nuclear recoil calibration of the XENON100 dark matter detector installed underg... more Results from the nuclear recoil calibration of the XENON100 dark matter detector installed underground at the Laboratori Nazionali del Gran Sasso (LNGS), Italy are presented. Data from measurements with an external 241 AmBe neutron source are compared with a detailed Monte Carlo simulation which is used to extract the energy dependent charge-yield Qy and relative scintillation efficiency L eff . A very good level of absolute spectral matching is achieved in both observable signal channels -scintillation S1 and ionization S2 -along with agreement in the 2-dimensional particle discrimination space. The results confirm the validity of the derived signal acceptance in earlier reported dark matter searches of the XENON100 experiment.
Particle detectors that use liquid xenon (LXe) as detection medium are among the leading technolo... more Particle detectors that use liquid xenon (LXe) as detection medium are among the leading technologies in the search for dark matter weakly interacting massive particles (WIMPs). A key enabling element has been the low-energy detection threshold for recoiling nuclei produced by the interaction of WIMPs in LXe targets. In these detectors, the nuclear recoil energy scale is based on the LXe scintillation signal and thus requires knowledge of the relative scintillation efficiency of nuclear recoils, L eff . The uncertainty in L eff at low energies is the largest systematic uncertainty in the reported results from LXe WIMP searches at low masses. In the context of the XENON Dark Matter project, a new LXe scintillation detector has been designed and built specifically for the measurement of L eff at low energies, with an emphasis on maximizing the scintillation light detection efficiency to obtain the lowest possible energy threshold. We report new measurements of L eff at low energies performed with this detector. Our results suggest a L eff which slowly decreases with decreasing energy, from 0.144 ± 0.009 at 15 keV down to 0.088 +0.014 −0.015 at 3 keV. PACS numbers: 95.35.+d, 14.80.Ly, 29.40.-n, 95.55.Vj
Journal of Physics G: Nuclear and Particle Physics, 2013
The XENON100 experiment, installed underground at the Laboratori Nazionali del Gran Sasso (LNGS),... more The XENON100 experiment, installed underground at the Laboratori Nazionali del Gran Sasso (LNGS), aims to directly detect dark matter in the form of Weakly Interacting Massive Particles (WIMPs) via their elastic scattering off xenon nuclei. This paper presents a study on the nuclear recoil background of the experiment, taking into account neutron backgrounds from (α,n) and spontaneous fission reactions due to natural radioactivity in the detector and shield materials, as well as muon-induced neutrons. Based on Monte Carlo simulations and using measured radioactive contaminations of all detector components, we predict the nuclear recoil backgrounds for the WIMP search results published by the XENON100 experiment in 2011 and 2012, 0.11 +0.08 −0.04 events and 0.17 +0.12 −0.07 events, respectively, and conclude that they do not limit the sensitivity of the experiment. PACS numbers: 95.35.+d, 29.40.-n, 34.80.Dp
Journal of Physics G: Nuclear and Particle Physics, 2014
The XENON100 dark matter experiment uses liquid xenon in a time projection chamber (TPC) to measu... more The XENON100 dark matter experiment uses liquid xenon in a time projection chamber (TPC) to measure xenon nuclear recoils resulting from the scattering of dark matter Weakly Interacting Massive Particles (WIMPs). In this paper, we report the observation of single-electron charge signals which are not related to WIMP interactions. These signals, which show the excellent sensitivity of the detector to small charge signals, are explained as being due to the photoionization of impurities in the liquid xenon and of the metal components inside the TPC. They are used as a unique calibration source to characterize the detector. We explain how we can infer crucial parameters for the XENON100 experiment: the secondary-scintillation gain, the extraction yield from the liquid to the gas phase and the electron drift velocity.
In a recent manuscript (arXiv:1208.5046) Peter Sorensen claims that XENON100's upper limits on sp... more In a recent manuscript (arXiv:1208.5046) Peter Sorensen claims that XENON100's upper limits on spin-independent WIMP-nucleon cross sections for WIMP masses below 10 GeV "may be understated by one order of magnitude or more". Having performed a similar, though more detailed analysis prior to the submission of our new result (arXiv:1207.5988), we do not confirm these findings. We point out the rationale for not considering the described effect in our final analysis and list several potential problems with his study.
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Papers by L. Goetzke