Limits on WIMP dark matter

Abstract

Abstract:The current state searches for dark matter in the form of Weakly Interacting Massive Particles (WIMPs) using both direct and indirect techniques is reviewed. Advances in recent years by various direct search experiments, utilising technology able to record the nuclear recoil events expected from elastic scattering by WIMPs, have allowed progress towards lower limits to be made. In particular, the Edelweiss and CDMS collaborations are achieving sensitiviy able to challenge data from DAMA interpreted as evidence for WIMPs of mass in the region of 60 GeV. Meanwhile, indirect searches, based on observing the annihilation products of neutralino-neutralino interactions in the Earth, Sun and Galaxy, have produced intriguing results. For instance, analysis by Superkamiokande now suggests limits comparable with the best direct search results. WIMP Direct SearchesWIMPs interact with normal matter by elastic scattering off nuclei. The energy deposited by the resulting recoil nuclei or atoms has a characteristic exponential spectrum. This is determined mainly by the kinematics of the interaction, the WIMP mass relative to that of the recoiling nuclei and the velocity of the WIMP, determined by the velocity of the Earth through the galactic halo. The favoured range of WIMP masses, velocities and likely cross sections (for instance for MSSM) lead to recoil spectra expected to have energy ranging from a few keV upto a few hundred keV with rate <1 kg −1 day −1 . The latter rate is typically a factor of 10 6 lower than the ambient rate from background gammas due to surrounding natural radioactivity [1].These characteristics determine basic requirements of direct detection technology, the need for low energy threshold and some means of identifying genuine recoils from the much higher rate of background electron recoils. The latter is feasible in principle because the * Speaker.

The NAIAD experiment for WIMP searches at Boulby mine and recent results

“…upper limits on the nuclear recoil rate for various energy bins. The limit on the nuclear recoil rate at 4-5 keV for our statistics is typically about (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)% of the background rate due to the discrimination power of PSA. Note that the limit on the nuclear recoil rate presented in Figure 6, when analysed in terms of WIMP-nucleon interactions, is the convolution of the expected rate from WIMP interactions and the detector response function.…”

“…[7,8,9,10], and Ref. [11] for recent review), they use other techniques and other target materials. This leaves room for speculation about possible uncertainties in the comparison of results.…”