Dark matter particles gravitationally bound to our Galaxy should exhibit a characteristic speed distribution limited by their escape velocity at the position of Earth (vesc≃550 km/s). An ongoing ...search for anomalous cosmic rays at Earth, kinematically similar to cold dark matter, is described. The technique can discriminate between these and known slow-moving particles such as neutrons, would be sensitive to telltale signatures from presently unexplored candidates, and offers the possibility of identifying the mediating type of interaction (nuclear vs electron recoils). Studies of background identification and abatement in a shallow underground site are presented. The expected reach of the method is discussed, and illustrated by obtaining the first limits for dark matter particles lighter than 100 MeV/c2 interacting via nuclear recoils.
Sub-GeV dark matter (DM) which interacts with electrons can excite electrons occupying molecular orbitals in a scattering event. In particular, aromatic compounds such as benzene or xylene have an ...electronic excitation energy of a few eV, making them sensitive to DM as light as a few MeV. These compounds are often used as solvents in organic scintillators, where the deexcitation process leads to a photon which propagates until it is absorbed and reemitted by a dilute fluor. The fluor photoemission is not absorbed by the bulk, but is instead detected by a photon detector such as a photomultiplier tube. We develop the formalism for DM–electron scattering in aromatic organic molecules, calculate the expected rate in p-xylene, and apply this calculation to an existing measurement of the single photo-electron emission rate in a low-background EJ-301 scintillator cell. Despite the fact that this measurement was performed in a shallow underground laboratory under minimal overburden, the DM–electron scattering limits extracted from these data are already approaching leading constraints in the 3–100 MeV DM mass range. We discuss possible next steps in the evolution of this direct detection technique, in which scalable organic scintillators are used in solid or liquid crystal phases and in conjunction with semiconductor photodetectors to improve sensitivity through directional signal information and potentially lower dark rates.
Germanium is the detector material of choice in many rare-event searches looking for low-energy nuclear recoils induced by dark matter particles or neutrinos. We perform a systematic exploration of ...its quenching factor for sub-keV nuclear recoils, using multiple techniques: photoneutron sources, recoils from gamma-emission following thermal neutron capture, and a monochromatic filtered neutron beam. Our results point to a marked deviation from the predictions of the Lindhard model in this mostly unexplored energy range. We comment on the compatibility of our data with low-energy processes such as the Migdal effect, and on the impact of our measurements on upcoming searches.
Certain strongly interacting dark matter candidates could have evaded detection, and much work has been done on constraining their parameter space. Recently, it was shown theoretically that the ...scattering cross section for mχ≳1 GeV pointlike dark matter with a nucleus cannot be significantly larger than the geometric cross section of the nucleus. This realization closes the parameter space for pointlike strongly interacting dark matter. However, strongly interacting dark matter is still theoretically possible for composite particles, with much parameter space open. We set new, wide-ranging limits based on data from a novel detector at the University of Chicago. Backgrounds are greatly suppressed by requiring coincidence detection between two spatially separated liquid-scintillator modules. For dark matter (v∼10−3 c), the time of flight would be ∼2 μs, whereas for cosmic rays, it would be ∼2 ns. We outline ways to greatly increase sensitivity at modest costs.
A new measurement of the quenching factor for low-energy nuclear recoils in CsINa is presented. Past measurements are revisited, identifying and correcting several systematic effects. The resulting ...global data are well described by a physics-based model for the generation of scintillation by ions in this material, in agreement with phenomenological considerations. The uncertainty in the new model is reduced by a factor of four with respect to an energy-independent quenching factor initially adopted as a compromise by the COHERENT Collaboration. A significantly improved agreement with Standard Model predictions for the first measurement of coherent elastic neutrino-nucleus scattering (CEνNS) is generated. We emphasize the critical impact of the quenching factor on the search for new physics via CEνNS experiments.
Experiments looking for a lepton-flavor-violating decay μ+ → e+ X0 are reviewed in light of present-day germanium detector technology, with an eye on scenarios where a long-lived, slow-moving massive ...boson X0 might have a cosmological impact. A broad swath of interesting, unexplored parameter space very close to the kinematic limit of the decay is found to be within the reach of a new proposed search. A number of possible roles for X 0 in past and present epochs can be investigated.
We report a measurement of the ionization efficiency of silicon nuclei recoiling with sub-keV kinetic energy in the bulk silicon of a charge-coupled device (CCD). Nuclear recoils are produced by ...low-energy neutrons (<24 keV) from a Sb124−Be9 photoneutron source, and their ionization signal is measured down to 60 eV electron equivalent. This energy range, previously unexplored, is relevant for the detection of low-mass dark matter particles. The measured efficiency is found to deviate from the extrapolation to low energies of the Lindhard model. This measurement also demonstrates the sensitivity to nuclear recoils of CCDs employed by DAMIC, a dark matter direct detection experiment located in the SNOLAB underground laboratory.
The deployment of a low-noise 3 kg p-type point contact germanium detector at the Dresden-II power reactor, 8 meters from its 2.96 GWth core, is described. This location provides an unprecedented ...(anti)neutrino flux of ... . When combined with the 0.2 keVee detector threshold achieved, a first measurement of CE ν NS from a reactor source appears to be within reach. We report on the characterization and abatement of backgrounds during initial runs, deriving improved limits on extensions of the Standard Model involving a light vector mediator, from preliminary data. (ProQuest: … denotes formula omitted.)
PDF
