J. Kwong

Search for light dark matter in XENON10 data.

We report results of a search for light (≲10  GeV) particle dark matter with the XENON10 detector. The event trigger was sensitive to a single electron, with the analysis threshold of 5 electrons corresponding to 1.4 keV nuclear recoil energy. Considering spin-independent dark matter-nucleon scattering, we exclude cross sections σ(n)>7×10(-42)  cm(2), for a dark matter particle mass m(χ)=7  GeV. We find that our data strongly constrain recent elastic dark matter interpretations of excess low-energy events observed by CoGeNT and CRESST-II, as well as the DAMA annual modulation signal.

Constraints on inelastic dark matter from XENON10

It has been suggested that dark matter particles which scatter inelastically from detector target nuclei could explain the apparent incompatibility of the DAMA modulation signal (interpreted as evidence for particle dark matter) with the null results from CDMS-II and XENON10. Among the predictions of inelastically interacting dark matter are a suppression of low-energy events, and a population of nuclear recoil events at higher nuclear recoil equivalent energies. This is in stark contrast to the well-known expectation of a falling exponential spectrum for the case of elastic interactions. We present a new analysis of XENON10 dark matter search data extending to E{sub nr} = 75 keV nuclear recoil equivalent energy. Our results exclude a significant region of previously allowed parameter space in the model of inelastically interacting dark matter. In particular, it is found that dark matter particle masses m{sub x} {approx}> 150 GeV are disfavored.

Simultaneous measurement of ionization and scintillation from nuclear recoils in liquid xenon for a dark matter experiment.

We report the first measurements of the absolute ionization yield of nuclear recoils in liquid xenon, as a function of energy and electric field. Independent experiments were carried out with two dual-phase time-projection chamber prototypes, developed for the XENON dark matter project. We find that the charge yield increases with decreasing recoil energy, and exhibits only a weak field dependence. These results are the first unambiguous demonstration of the capability of dual-phase xenon detectors to discriminate between electron and nuclear recoils down to 20 keV, a key requirement for a sensitive dark matter search.

The scintillation and ionization yield of liquid xenon for nuclear recoils

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 View the MathML source and the absolute ionization yield View the MathML source, for nuclear recoils in xenon. A dark matter particle is expected to deposit energy by scattering from a xenon nucleus. Knowledge of View the MathML source is therefore crucial for establishing the energy threshold of the experiment; this in turn determines the sensitivity to particle dark matter. Our View the MathML source measurement is in agreement with recent theoretical predictions above 15 keV nuclear recoil energy, and the energy threshold of the measurement is View the MathML source. A knowledge of the ionization yield View the MathML source is necessary to establish the trigger threshold of the experiment. The ionization yield View the MathML source is measured in two ways, both in agreement with previous measurements and with a factor of 10 lower energy threshold.

Liquefied Noble Gas (LNG) detectors for detection of nuclear materials

Liquefied noble gas (LNG) detectors have already been successfully employed in areas of fundamental particle physics research due to features such as their high energy resolution, fast response times, excellent discrimination between neutron and gamma-ray interactions, and relatively low cost. Such detectors are also attractive for nonintrusive inspection for the presence of special nuclear material (SNM) in large-scale objects such as cargo containers and trucks. An effective method of interrogation involves pulsing the object being interrogated with neutrons, which induces fission in the SNM. The fission reaction promptly releases gamma rays and neutrons. This reaction can be distinguished from background through the coincidence measurement of these particles striking multiple detectors. Rapiscan Laboratories, Yale University Physics Department, and Adelphi Technology have constructed two 18-L liquid argon prototype detectors to investigate the suitability of LNG detectors in performing this form of interrogation. The pulse shape, energy resolution, time resolution, detector efficiency, and the effects of doping with xenon were measured.