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Abstract
We study the sensitivity of multi ton-scale time projection chambers using a liquid xenon target, e.g., the proposed DARWIN instrument, to spin-independent and spin-dependent WIMP-nucleon scattering interactions. Taking into account realistic backgrounds from the detector itself as well as from neutrinos, we examine the impact of exposure, energy threshold, background rejection efficiency and energy resolution on the dark matter sensitivity. With an exposure of 200 t × y and assuming detector parameters which have been already demonstrated experimentally, spin-independent cross sections as low as 2.5 × 10−49 cm2 can be probed for WIMP masses around 40 GeV/c2. Additional improvements in terms of background rejection and exposure will further increase the sensitivity, while the ultimate WIMP science reach will be limited by neutrinos scattering coherently off the xenon nuclei.
Highlights
Pp-neutrino flux [19, 20], supernova neutrinos [21], axions and axion-like particles [22, 23], as well as rare nuclear processes such as the neutrinoless double beta decays of 136Xe [19] and 134Xe, 126Xe and 124Xe [24]
We mainly focus on spin-independent interactions and take into account backgrounds, background rejection efficiency, exposure, thresholds and energy resolution
We have studied the sensitivity of a DARWIN-like multi-ton scale LXe detector to spinindependent WIMP-nucleon interactions by means of toy Monte Carlo experiments, which take into account all known backgrounds and a realistic detector response
Summary
In order to simulate the detection process of signal and background events in a realistic fashion, we employ a signal generation model following Ref. [26]. Based on the energy and the type of interaction, ERs measured in keVee (electronic recoil equivalent energy) or NRs measured in keVnr (nuclear recoil equivalent), the mean number of generated quanta nγ (scintillation photons) and ne (ionization electrons) is calculated for a drift field of 500 V/cm, a typical number for dual-phase TPCs. For ERs, charge and light yields are taken from NEST v0.98 [26], while for NRs, Qy and Leff are taken from XENON100, using Refs. The signal quanta observed in the detector, nS1 and nS2, are drawn from a Poisson or a Gaussian distribution, respectively, with the means n0S1 and n0S2 and resolutions tuned to match existing experimental data. This takes into account additional effects from the photoelectron detection process (“single photoelectron resolution”). Throughout this study, the charge signal (S2) is given in electrons, and we do not consider charge losses during the drift of the electrons through the LXe, which requires an effective gas cleaning system and 100% charge extraction into the gas phase (as achieved by XENON100 [30])
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