The allowed parameter space for the lightest neutralino as the dark matter is explored using the minimal supersymmetric standard model as the low-energy effective theory without further theoretical constraints such as GUT. Selecting values of the parameters which are in agreement with present experimental limits and applying the additional requirement that the lightest neutralino is in a cosmologically interesting range, we give limits on the neutralino mass and composition. A similar analysis is also performed implementing the grand unification constraints. The elastic scattering cross section of the selected neutralinos on 27Al and on other materials for dark matter experiments is discussed.

We are preparing the CRESST experiment to search for dark matter WIMPs using cryogenic detectors with superconducting phase transition thermometers. In the first stage we plan to use four 250 g sapphire detectors with thresholds of 0.5 keV and resolutions of 0.2 keV at 1 keV. This will provide sensitivity to WIMP masses below 10 GeV, and is thus complementary to other dark matter searches.

The energy transport via thermal diffusion inside superheated superconducting granules (SSG) after nuclear recoils is discussed. The decay towards equilibrium of the initial disturbance is described by a set of coupled heat-flow equations for the effective quasiparticle and phonon temperatures. The solution is carried out analytically for a point source located anywhere inside the superconducting granule with the initial energy distributed in both quasiparticle and phonon systems. The calculated sensitivity to nuclear recoils and the decay in time between interaction and phase transition are compared with irradiation measurements performed on Sn and Zn granules. The derived expressions for the quasiparticle and phonon temperatures are useful to predict the sensitivity of SSG detectors to nuclear recoils produced in dark matter particle or neutrino interactions.

This work is part of an ongoing project to develop a superheated superconducting granule (SSG) detector for cold dark matter and neutrinos. The response of SSG devices to nuclear recoils has been explored irradiating SSG detectors with a 70 MeV neutron beam. The aim of the experiment was to test the sensitivity of Sn, Al and Zn SSG detectors to nuclear recoil energies down to a few keV. The detector consisted of a hollow teflon cylinder (0.1 cm3 inner volume) filled with tiny superconducting metastable granules embedded in a dielectric medium. The nuclear recoil energies deposited in the SSG were determined measuring the neutron scattering angles with a neutron hodoscope. Coincidences in time between the SSG and the hodoscope signals have been clearly established. In this paper the results of the neutron irradiation experiments at different SSG intrinsic thresholds are discussed and compared to Monte Carlo simulations. The results show that SSG are sensitive to recoil energies down to ∼ 1 keV. The limited angular resolution of the neutron hodoscope prevented us from measuring the SSG sensitivity to even lower recoil energies.

The presented results are part of a feasibility study of a Superheated Superconducting Granule (SSG) detector for weakly interacting massive particles (WIMPs). Using a 70 MeV neutron beam, the response of aluminum SSG to nuclear recoil energies of a few keV has been studied. The proved sensitivity of the detector to elastic scatterings will be discussed comparing the SSG performance at different detector thresholds with the theoretical expectations. The irradiation results allow to calibrate the detector energy threshold versus the magnetic threshold ΔHH and are in good agreement with the theoretical values. We are planning to start in the near future a dark matter search with a prototype SSG detector. The status of the project will be presented and the expected counting rate for spin-independent WIMP interactions will be discussed.

We investigated the phase transition time of single Sn, In and Al granules from 20 μm up to 50 μm in diameter. The transitions from the superconducting to the normal state were induced by ramping the external magnetic field above the superheating field or by irradiating the granules with X-ray or β sources at a constant magnetic field. The readout electronics was optimized to allow real-time measurements with a signal resolution of 11 ns. Within the experimental errors, the irradiation measurements revealed no difference between magnetically and thermally induced phase transitions. The dependence of the transition time on the temperature, the granule size and the orientation of the sample with respect to the magnetic field is discussed. The presented results are part of an ongoing project to develop a Superheated Superconducting Granule (SSG) detector for cold dark matter search and neutrino detection.

The propagation of the excess of quasiparticles and phonons produced by a nuclear recoil inside Sn and Zn superheated superconducting granules will be discussed. The decay towards equilibrium of the initial disturbance is assumed to be a thermal diffusion process described by a set of coupled heat flow equations for the effective quasiparticle and phonon temperatures. The solution is carried out analytically for a point source located anywhere inside the superconducting granule with the initial energy distributed in both quasiparticle and phonon systems. The calculated time delay between the neutron interaction and the nucleation of the phase transition will be compared to the time delay distributions obtained by irradiating Zn and Sn SSG detectors with a 70Me$\!$V neutron beam.

The response of Superheated Superconducting Granule (SSG) devices to nuclear recoils has been explored by irradiating SSG detectors with a 70Me$\!$V neutron beam. In the past we have tested Al SSG and more recently, measurements have been performed with Sn and Zn detectors. The aim of the experiments was to test the sensitivity of SSG detectors to recoil energies down to a few ke$\!$V. In this paper, the preliminary results of the neutron irradiation of a SSG detector made of Sn granules 15-20$\mu$m in diameter will be discussed. For the first time, recoil energy thresholds of $\sim$1ke$\!$V have been measured.

The presented results are part of a feasibility study of a Superheated Superconducting Granule (SSG) device for weakly interacting massive particles (WIMPs) detection. The sensitivity of SSG to nuclear recoils has been explored irradiating SSG detectors with a 70MeV neutron beam proving that energy thresholds of ∼1keV can be reached in 30µm Zn and 17µm Sn granules. The successful irradiation experiments with neutrons encouraged us to plan a prototype SSG dark matter detector. The status of the project will be presented and the expected counting rate for spin-independent WIMP interactions in SSG detectors will be discussed.

The interest in superconducting devices for particle detection is based on the very small quantum energies involved as compared to conventional ionization and semiconductor detectors. The use of superheated superconducting granules (SSG) as a particle detector is reviewed. Physical properties and experimental applications of SSG are discussed. The dynamic responses of the phase transition of superheated superconducting Sn, In, Al and Zn single granules (20-50mum in diameter) due to an applied magnetic field exceeding the superheating threshold are presented. A status report on further experimental development is given.

The presented results are part of a feasibility study of superheated superconducting microstructure detectors. The microstructures (dots) were fabricated using thin film patterning techniques with diameters ranging from50µm up to500µm and thickness of1µm. We used arrays and single dots to study the dynamics of the superheating and supercooling phase transitions in a magnetic field parallel to the dot surface. The phase transitions were produced by either varying the applied magnetic field strength at a constant temperature or changing the bath temperature at a constant field. Preliminary results on the dynamics of the phase transitions of arrays and single indium dots will be reported.

We present results of an irradiation of a Superheated Superconducting Granule (SSG) detector with a 70 MeV neutron beam. The aim of the experiment was to measure the sensitivity of the detector to nuclear recoil energies produced by elastically scattered neutrons. The detector consists of a small readout coil (diameter 5 mm, length 10 mm) filled with aluminum granules of average diameter 23 μm embedded in an Al2O3 granulate with a 6% volume filling factor. The neutron scattering angles were determined using a scintillator hodoscope. Coincidences in time between the SSG and the hodoscope signals have been clearly established. Data were taken at an operating temperature of 120 mK for different SSG intrinsic thresholds. The results prove the sensitivity of the detector to nuclear recoils in the energy range of a few keV. The data show good agreement with the global heating mechanism.

We report on improvements of the dc-SQUID instrumentation developed to study superheating-supercooling transitions of thin-film indium dots. In previous measurements on ordered arrays of dots with diameters larger than 100µm the flip signal of an individual dot in perpendicular magnetic field has been detected. In order to use these dots as superheated superconducting detectors it is necessary to reduce the dot diameter to lower the energy threshold and to avoid intermediate states. For these reasons, our effort has been to develop small and thick dots with diameter down to10 µm and thickness up to3.5 µm. At the same time the coupling with the dc-SQUID readout was improved using a thin-film niobium pickup coil integrated on the same chip containing the dots. Phase transitions of individual dots were observed. The superheating phase transition spread in temperature of the samples was about 0.15 %.

An analytic expression allowing to evaluate the spin-independent detection rate of weakly interacting massive particles as a function of the detector energy threshold for any dark matter mass and absorber material, is presented. The detection rate is calculated taking into account the dynamics of the dark matter particles and the loss of coherence in the neutral-current interactions due to the nuclear form factor. The amplitude of the seasonal modulation in the rate is discussed, showing that, in the case of detectors made of heavy nuclei, the sign of the modulation in the counting rate can be different from the amplitude of the modulation in the dark matter flux.

The ability of detectors to automatically recover (self-recovery) in a short period of time after sensing a particle is a very valuable advantage for their use as microvertex detectors at high energy particle colliders. Using a superconducting strip detector made of granular tungsten, we have observed such behavior with pulse amplitudes of few 100 μV and recovery times fo 10–50 ns. A 1.8 μm wide thin film was used to detect the superconducting-to-normal transitions induced by the absorption of 55Fe, 6 keV X-rays. For high bias currents the detector did not self-recover and a constant efficiency estimated to ∼65% was found, but with good indications that such a rate would persist in the self-recovery mode at lower bias currents. The threshold between self-recovering and propagating hotspots is discussed within the thermal propagation model, developed previously for normal regions which bridge the width of the strip. These results also confirm the potential applications of superconducting strips for high resolution X-rays detectors.

Irradiation of granular aluminum (g-Al) superconducting strips by betas with energies in the minimum-ionizing range has demonstrated a high detection efficiency. An efficiency of almost 70% was found for 0.5 μm wide g-Al strips operating at a temperature of 1.4–1.7 K. This is a very encouraging result for this new concept of a high-resolution tracking detector, which could be used in future colliding-beam accelerators such as the proposed Superconducting Super Collider or other large hadron colliders. As was found earlier with X-ray irradiation, the experiments are accurately described by our thermal-propagation model.

Two prototypes of silicon microstrip detectors, realized directly by our group either by ion implantation or by diffusion, are presented. The physical detector characteristics and their performances determined by exposing them to different radioactive sources are discussed, and a calculation of the different terms contributing to the total dark current is reported.