Low Mass DM Searches - Next Generation; Breaking The Solar Neutrino Floor

by Andrzej K. Drukier

at Physics Colloquium

Tue, 26 Feb 2019, 15:30
Nanotechnology institute building (#51) room 15

Abstract

There is a tension between different experiments attempting direct detection of Dark Matter candidates (DM). The DAMA-LIBRA experiment observed the annual modulation in count rate wherein other, both crogenic bolometers and l. Xenon detectors put impressive limits on DM in mass range of 15 GeV/c^2 < M_DM < 500 GeV/c^2 . Thus, if DM are Weakly Interacting Massive Particles (WIMPs) they may be either low mass, M_DM < 15 GeV/c^2 or very heavy (> 500 GeV/c^2). While large experimental programs are underway to extend sensitivity of current experiments, they are increasingly difficult to build and costly. They are probably unable to reach the “solar neutrino floor”.

We consider paleo-detectors, wherein one studies traces left by neutrino and/or DM interactions in ancient minerals. Kilogram size crystals are available with age of up to a few Gigayears (Gyr), which leads to exquisite capture rate many orders of magnitude larger than current, “real time” detectors. There is a reasonable understanding of mechanism(s) of radiation damage due to nuclear recoil in the very vertex of interactions, including the understanding of range of such recoil nuclei in detector material(s). In these new detectors, the target is multi-elemental (up to 10 elements) to provide the signature and improve signal to background noise ratio (S/B).

In recent papers we considered the possible performance of such “paleo-detectors” and concluded that they are critically dependent of material selection. We elucidate the principles of paleo-detectors and describe the two main sources of background, presence of U/Th impurities and “solar neutrino floor”. We comment on possibility of “mineral optimization”. The critical is ability of getting the minerals from significant depth, say > 5 km.

We focus on an important source of background, i.e. radioactive impurities such as U and Th. Especially difficult to reject are events of spontaneous fission which emit fast neutrons. Scattering of such fast neutrons in “paleo-detectors” may be the main source of background. Two types of minerals have lowest level of U/Th impurities, i.e. ultra-mafic minerals and marine evaporites(salts). Marine evaporates with X(U) < 0.01 ppb and X(Th) < 1 ppt are much better targets than even the best “rock forming minerals”, including ultra-mafic minerals with X(U) < 1 ppb and X(Th) < 3.5 ppb. The importance of selecting the minerals with perfect cleavage is stressed, and the availability of very old mineral samples, with age of about billion years is discussed.

We argue that “neutrino floor” is just due to imperfect knowledge of solar neutrinos fluxes, and suggest experiments in which both solar neutrinos (B-8 and hep branches) and LM-DM are detected. We provide the first estimates of sensitivities, which for LM-DM extend much below the current definition of the “neutrino floor”. We expect that over next few years, the paleo-detectors will reach and maybe breach the “solar neutrino floor”. Even better limits can be obtained by next generation of paleo-detectors based on meteorites.

Refreshments are served at 15:15.

Created on 22-02-2019 by Bar Lev, Yevgeny (ybarlev)
Updaded on 23-02-2019 by Kats, Yevgeny (katsye)