Neutral bremsstrahlung and excimer electroluminescence in noble gases and its relevance to two-phase dark matter detectors

Abstract

Proportional electroluminescence (EL) is the physical effect used in two-phase detectors for dark matter searches, to optically record (in the gas phase) the ionization signal produced by particle scattering in the liquid phase. In our previous work the presence of a new EL mechanism, namely that of neutral bremsstrahlung (NBrS), was demonstrated in two-phase argon detectors both theoretically and experimentally, in addition to the ordinary EL mechanism due to excimer emission. In this work the similar theoretical approach is applied to all noble gases, i.e. overall to helium, neon, argon, krypton and xenon, to calculate the EL yields and spectra both for NBrS and excimer EL. The relevance of the results obtained to the development of two-phase dark matter detectors is discussed.

Bremsstrahlung on noble gases at low energies

“…The bremsstrahlung spectra on argon and xenon, obtained by means of the exact (3) and approximate (15) formulas, are shown in Fig. 2 for energies ε = 0.5 ÷ 10 eV.…”

“…In recent years, search for particles of dark matter has stimulated the development of detectors with increased sensitivity to registration of such particles [1][2][3][4][5]. One of the fundamental processes, that determine the properties of new detectors, is bremsstrahlung on noble gases, in particular on argon or xenon.…”

“…(15) expressed via σ el . Experimental data for argon are taken from Ref [3],. and data for xenon are recalculated from that in Ref [5]…”

Study of visible-light emission in pure and methane-doped liquid argon

“…2). Secondly, if the spectrum is indeed determined by the NBrS effect, its shape should not depend much on which species the electron is scattered on (Ar or CH 4 ), since numerous NBrS spectra of various origins presented in the literature look very flat and therefore very similar to each other [15,22,23].…”

“…So far, the NBrS emission in the form of electroluminescence (secondary scintillation) in noble gases has been experimentally and theoretically studied in [15][16][17][18][19][20][21] and [15,[22][23][24] respectively, with predicted continuous spectrum in the visible and NIR range. It is known that secondary scintillations in the VUV in gaseous Ar due to the excimer effect are associated with primary scintillations in the VUV in liquid Ar due to the same excimer effect.…”