T. A. Girard

Final Analysis and Results of the Phase II SIMPLE Dark Matter Search

We report the final results of the Phase II SIMPLE measurements, comprising two run stages of 15 superheated droplet detectors each, with the second stage including an improved neutron shielding. The analyses include a refined signal analysis, and revised nucleation efficiency based on a reanalysis of previously reported monochromatic neutron irradiations. The combined results yield a contour minimum of σp=5.7×10(-3)  pb at 35  GeV/c2 in the spin-dependent sector of weakly interacting massive particle (WIMP) proton interactions, the most restrictive to date for MW}≤60  GeV/c2 from a direct search experiment and overlapping, for the first time, with results previously obtained only indirectly. In the spin-independent sector, a minimum of 4.7×10(-6)  pb at 35  GeV/c2 is achieved, with the exclusion contour challenging a significant part of the light mass WIMP region of current interest.

SIMPLE dark matter search results

We report an improved SIMPLE experiment comprising four superheated droplet detectors with a total exposure of 0.42 kgd. The result yields similar to factor 10 improvement in the previously-reported results, and-despite the low exposure-is seen to provide restrictions on the allowed phase space of spin-dependent coupling strengths almost equivalent to those from the significantly larger exposure NAIAD-CDMS/ZEPLIN searches. (c) 2005 Elsevier B.V. All rights reserved.

First Results of the Phase II SIMPLE Dark Matter Search

We report results of a 14.1   kg d measurement with 15 superheated droplet detectors of total active mass 0.208 kg, comprising the first stage of a 30 kg d Phase II experiment. In combination with the results of the neutron-spin sensitive XENON10 experiment, these results yield a limit of |a(p)|<0.32 for M(W)=50 GeV/c² on the spin-dependent sector of weakly interacting massive particle-nucleus interactions with a 50% reduction in the previously allowed region of the phase space, formerly defined by XENON, KIMS, and PICASSO. In the spin-independent sector, a limit of 2.3×10⁻⁵ pb at M(W)=45 GeV/c² is obtained.

Model-independent limits from spin-dependent WIMP dark matter experiments

Spin-dependent weakly interacting massive particle (WIMP) searches have traditionally presented results within an odd group approximation and by suppressing one of the spin-dependent interaction cross sections. We here elaborate on a model-independent analysis in which spin-dependent interactions with both protons and neutrons are simultaneously considered. Within this approach, equivalent current limits on the WIMP-nucleon interaction at WIMP mass of 50 GeV/c{sup 2} are either {sigma}{sub p}{<=}0.7 pb, {sigma}{sub n}{<=}0.2 pb or vertical bar a{sub p} vertical bar {<=}0.4, vertical bar a{sub n} vertical bar {<=}0.7 depending on the choice of cross section or coupling strength representation. These limits become less restrictive for either larger or smaller masses; they are less restrictive than those from the traditional odd group approximation regardless of WIMP mass. Combinations of experimental results are seen to produce significantly more restrictive limits than those obtained from any single experiment. Experiments traditionally considered spin-independent are moreover found to severely limit the spin-dependent phase space. The extension of this analysis to the case of positive signal experiments is explored.

Exclusion limits on spin dependent WIMP-nucleon couplings from the SIMPLE experiment

The SIMPLE experiment is reanalyzed within the context of the WIMP model independent framework of Tovey et al. The results are compared with those of the UK NAIAD and NaF experiments as recently reported by the Tokyo group, together with those of the latest UK NAIAD results in 2003, and further constrain the allowed parameter space.

Expulsion of magnetic flux in a type-I superconducting strip

Abstract Flux expulsion in a type-I superconducting strip, induced by decrease of a perpendicular magnetic field following field increase-induced flux penetration, is observed by real time detection of the flux-induced voltage pulses. Three different expulsion regimes are identified, corresponding in general to the three initial regimes of flux penetration. The crossover field between two expulsion regimes is found to be associated with the change of nucleation mechanism at Hc2. Possible association of the expulsion onset with surface superconductivity and Hc3 is discussed. The results support the idea of existence of an energy barrier against flux expulsion.

Recent results from the SIMPLE dark matter search

We present the results of the recent Phase II SIMPLE search effort, comprising two stages each of ~14 kgd exposure of 15 Superheated Droplet Detectors with ~0.2 kg active mass and recoil energy threshold of 8 keV. In the second stage, the neutron shielding was increased to reduce the on-detector rate by a factor 3.5. Combined with an improved nucleation efficiency and analysis of the detector pressure evolution during the measurements, the results yield improved results in the phase space of both spin -dependent and -independent WIMP interactions.

On the direct search for spin-dependent WIMP interactions

We examine the current directions in the search for spin-dependent dark matter. We discover that, with few exceptions, the search activity is concentrated towards constraints on the WIMP-neutron spin coupling, with significantly less impact in the WIMP-proton sector. We review the situation of those experiments with WIMP-proton spin sensitivity, toward identifying those capable of reestablishing the balance.

MCNP optimization of filtered neutron beams for calibration of the SIMPLE detector

We report an MCNP study of filtered monochromatic neutron beams of energies 25, 54 and 149 keV for response studies of a superheated droplet detector for the SIMPLE experiment. The results identify the importance of the detector temperature stabilizing water bath and the aqueous gel of the detector on the beam quality, in general agreement with recent measurements made on the thermal port of the Portuguese research reactor.

The cern axion solar telescope (CAST)

A decommissioned LHC test magnet is being prepared as the CERN Axion Solar Telescope (CAST) experiment. The magnet has a field of 9.6 Tesla and length of 10 meters. It is being mounted on a platform to track the sun over ±8° vertically and ±45°, horizontally. A sensitivity in axion-photon coupling gαγγ < 5 × 10−11GeV−1 can be reached for mα ≤ 10−2eV, and with a gas filled tube-can reach gαγγ ≤ 10−10GeV−1 for axion masses mα < 2eV.