G.L. Salmon

Vertex Triggering Using Time Difference Measurements in the ZEUS Central Tracking Detector

Abstract A method of vertex triggering which uses a time difference measurement to determine the z coordinate of a track is under development for the ZEUS Central Tracking Detector. This incorporates a pipelined readout system. We describe the system and report on its performance.

Statistical noise due to tunneling in superconducting tunnel junction detectors

We discuss the statistical noise associated with tunneling which is intrinsic to superconducting tunnel junctions. We deduce a simple expression for the noise in the general case where the tunneling probabilities may be dissimilar. The statistical tunneling noise exceeds the Fano‐factor limited statistical noise of the quasiparticle creation for most cases.

Development of the ZEUS central tracking detector

Abstract The design concept and development of the ZEUS central tracking detector is described. This is a cylindrical drift chamber designed for track reconstruction, electron identification and event triggering in a high-crossing-rate, high-magnetic-field environment.

Status and low background considerations for the CRESST dark matter search

Abstract 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.

Tunnel junction arrays on InSb: A high resolution cryogenic detector for X- and γ-rays

Abstract We have measured the response of a series array of superconducting tunnel junctions to the non-equilibrium phonons generated in single crystals of InSb by nuclear particle interactions at a temperature of 100 mK. The results demonstrate an energy resolution below 210±60 eV (FWHM) for photons of energy 22.1 keV after subtracting the electronic noise. The detector response has high linearity for the detection of photons with energies in the range 3 to 662 keV.

The design of a cryogenic dark matter detector based on the detection of the recoil direction of target nuclei

Abstract We discuss the design of a cryogenic detector for a WIMP dark matter search based on single crystal absorbers and using Series Arrays of Superconducting Tunnel Junctions (SASTJs). The distribution of recoil vectors of target nuclei from WIMP interactions are affected by the motion of the laboratory through the dark matter halo. The angular distribution of recoil directions is skewed due to the motion of the solar system around the galaxy and is modulated by the diurnal and annual rotation of the earth. We discuss the kinematics of the recoil events and how a directional signal might be identified in our cryogenic detectors using the fast response of SASTJs to the ballistic phonons arising in the absorber from WIMP interactions. We consider how the anisotropy of a dark matter recoil distribution can be used to place statistical limits on its component relative to the isotropic background signal. We also consider how the dark matter limit is altered if only the axis of the nuclear recoil, rather than the full recoil direction is available. We also briefly consider the effect of phonon focusing within single crystal absorbers. Focusing will modulate strongly the signal detected by the SASTJs, on the crystal surface, as the position of the interaction within the crystal varies. A comparison is made between the behaviour of phonons in strongly focusing crystals, such as Nb, Si and LiF, and their near isotropic propagation in BaF2.

Cryogenic detectors for experiments in elementary particle physics

Abstract The development of cryogenic detectors is largely motivated by the need for very good energy resolution in a number of particle physics experiments, and by the need to detect very small energy depositions. Good energy resolution can be obtained by utilizing the smallness of the superconducting energy gap or detecting the phonons which are produced by particle interactions. These detection schemes require low temperatures, where in addition the thermal fluctuations are small compared to the minute energies expected to be deposited in some experiments. Moreover, cryogenic detectors permit the tailoring of the target or absorber materials to match the particle physics goals. The basic physics behind the detection of excitations induced by particle interactions in bulk single crystal materials is reviewed, and recent results on the efficient detection of these excitations with series arrays of superconducting tunnel junctions are presented. Progress towards the implementation of particle physics experiments, such as the detection of low energy solar neutrinos, search for dark matter particles, search for neutrinoless double beta-decay and precision observation of a 17 keV neutrino in beta-decay, using cryogenic detectors is reviewed.

The technique of z-coordinate determination using a time-difference measurement for the zeus central tracking detector

A method to determine the z-coordinate of a track using a time-difference measurement has been developed for the ZEUS Central Tracking Detector. It has been demonstrated that a spatial resolution of 50 mm can be obtained under normal chamber operating conditions. This corresponds to a time-difference resolution of 330 ps. A method of minimizing nonlinearities in the time-to-distance response is described. This uses an inductor to form a matching network to achieve resistive termination of the chamber. Test beam measurements from a prototype chamber are presented, demonstrating the effects of the chamber surface field and beam incidence angle on the time-difference resolution.

Energy resolved X-ray detection in Al-Nb proximity layers

The authors report on their initial investigation of the response to 6 keV X-rays of composite aluminium/niobium films forming one side of a superconducting tunnel junction. The non-equilibrium state generated by the X-ray interactions that occur in the thick Nb layer is detected with high-resolution detectors. The choice of a smaller gap superconductor as a probe film permits detection of the phonons generated by quasiparticle trapping from the Nb and enhancement of the initial quasiparticle number.

The effect of hotspot formation on quasiparticle yields in superconducting aluminium films

Existing models show that any hotspot created in an Al film following a particle interaction is rapidly diluted. Quasiparticles and phonons decouple at high energies so that on short time-scales quasiparticle diffusion determines the energy transport. Few quasiparticles have energies near the energy gap and there is little gap suppression. We have measured the initial quasiparticle yields in very thin Al films and find somewhat surprisingly that this yield is reduced. It appears that a short time-scale quasiparticle loss mechanism, probably associated with localised over-injection, exists as quasiparticles scatter to low energies within the phonon hotspot.