Jerome C. Barton

NaI dark matter limits and the NAIAD array – a detector with improved sensitivity to WIMPs using unencapsulated NaI

Re-analysis of published data from the UKDMC NaI Tl dark matter experiment is presented using latest spin factors and comparison is made with the sensitivity predicted for NAIAD, a 100 kg NaI detector concept based on unencapsulated . NaI Tl . We present experimental results and Monte Carlo simulations for NAIAD and show that a factor of 1.5-2 improvement in energy threshold is achievable over conventional NaI dark matter detectors with consequent ; 50% improvement in nuclear recoil discrimination at 10 keV. An overall improvement in sensitivity to spin dependent WIMP interactions of factor 50, based on 100 kg = yrs of data, is predicted relative to previous UKDMC limits. q 2000 Published by Elsevier Science B.V. All rights reserved.

CsI(Tl) for WIMP dark matter searches

Abstract We report a study of CsI(Tl) scintillator to assess its applicability in experiments to search for dark matter particles. Measurements of the mean scintillation pulse shapes due to nuclear and electron recoils have been performed. We find that, as with NaI(Tl), pulse shape analysis can be used to discriminate between electron and nuclear recoils down to 4 keV. However, the discrimination factor is typically 10–15% better than in NaI(Tl) above 4 keV. The quenching factor for caesium and iodine recoils was measured and found to increase from 11% to ∼17% with decreasing recoil energy from 60 to 12 keV. Based on these results, the potential sensitivity of CsI(Tl) to dark matter particles in the form of neutralinos was calculated. We find an improvement over NaI(Tl) for the spin-independent WIMP–nucleon interactions up to a factor of 5 assuming comparable electron background levels in the two scintillators.

Dark matter experiments at the UK Boulby Mine UK Dark Matter Collaboration

Abstract The current status is summarised of dark matter searches at the UK Boulby Mine based on pulse shape discrimination in NaI, together with further plans for international collaboration on detectors based on nuclear recoil discrimination in liquid and gaseous xenon.

Results from the first stage of a UK Galactic dark matter search using low background sodium iodide detectors

Abstract Low-energy background spectra from 1.3 kg and 6.2 kg NaI(TI) crystal scintillators operating in the shielded Boulby underground facility were measured. Upper limits to the scattering interaction rates and cross-sections of Galactic dark matter in the form of Weakly Interacting Massive Particles (WIMPs) are calculated from these data. This work provides an improved limit for spin-dependent interactions for WIMP masses above 10 GeV.

Current limits on the cold dark matter interaction cross section obtained by the UK collaboration

Abstract The UK Dark Matter Collaboration has run a 5–6 kg NaI detector in a well-shielded underground environment for about a year. Signatures of Cold Dark Matter (CDM) interactions are sought using pulse shape discrimination techniques by searching for the relatively short scintillation pulses arising from nuclear recoils among the residual, longer, background events from residual radioactivity in the detector and its environment. Here we report on an improvement to the limits on the CDM cross section for spin dependent interactions using our latest data from a crystal with improved detection efficiency and taking into account recent improved estimates of the spin factor correction between the nucleus and nucleon-supersymmetric particle cross sections.

New limits to Galactic cold dark matter interaction rates

Abstract Analysis is reported of a 6 month run with a 6.2 kg NaI detector deployed in a well shielded underground laboratory to search for signatures of cold dark matter interactions. By using pulse shape information to reject most background events, a significant improvement is obtained on existing upper limits to the cold dark matter spin-dependent interaction rates.

Progress report from the UK Dark Matter search at Boulby Mine

Abstract The UK Dark Matter Collaboration is currently running a series of scintillation devices at the Boulby mine in North Yorkshire to search for the neutralino, the hypothetical WIMP solution to the dark matter problem. Results of the current NaI(T1) detector array will be discussed, illustrating a population of events of unknown origin. Diagnostic tests performed to investigate the origin of these anomalous events will be outlined, including alpha, beta and neutron calibrations.

Current Status of the DRIFT Project and UKDMC Dark Matter Search

Three new projects are being prepared to run in the Boulby Mine Dark Matter Facility within the next year. The first of these, NAIAD, is an array of NaI scintillation crystals with 50 kg of total target mass. Second, the ZEPLIN project, in its first incarnation, is a 4 kg single phase liquid Xenon detector. Finally, the DRIFT project is a low-pressure gas chamber designed to be sensitive to the directions of WIMP-induced nuclear recoils as well as their energies. In this paper we will mainly discuss the DRIFT experiment, and short reports on the status of ZEPLIN and NAIAD will be given at the end.