Dark matter-electron scattering from aromatic organic targets

Abstract

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 de-excitation process leads to a photon which propagates until it is absorbed and re-emitted 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.

Dark matter interpretation of excesses in multiple direct detection experiments

“…We note that a recent result using phototube readout of EJ-301 scintillator reports a total single photoelectron rate of 3.8 Hz, corresponding to a mass-normalized single scintillation photon production rate of 14 Hz=kg[25,26], much larger than the noble liquid rates and comparable to the semiconductor rates. However, since this experiment was the first demonstration of a new technique for light DM searches and was run with minimal overburden, we regard this result as qualitatively interesting and await further data from an underground run 3.…”

Atomic responses to general dark matter-electron interactions

“…From the experimental side, a number of different ap-arXiv:2105.02233v1 [hep-ph] 5 May 2021 proaches has been pushed forward to search for sub-GeV DM particles. These involve the use of dual-phase argon [15] and xenon [16][17][18] targets, silicon and germanium semiconductors [13,[19][20][21][22][23][24][25][26][27], sodium iodide crystals [28], graphene [29,30], 3D Dirac materials [31,32], polar crystals [33], scintillators [34,35] and superconductors [36][37][38].…”

The Low-Mass Dark Matter Frontier

“…These interactions often allow the transfer of a sizable fraction of the particle's kinetic energy to the target, thus leading to a signal that is, in principle, measurable. Dark matter particles can interact inelastically with an electron in, for example, atoms [2,3], crystals [2, 4-8] molecules [9], superconductors [10], or Dirac materials [11,12]. They can also interact with nuclei in atoms [13,14], molecular systems [2,15], crystals [7, 8, 13, 14, 16], or superfluid helium [17].…”