Precision measurements of the scintillation pulse shape for low-energy recoils in liquid xenon

Abstract

A: We present measurements of the scintillation pulse shape in liquid xenon for nuclear recoils (NR) and electronic recoils (ER) at electric fields of 0 to 0.5 kV/cm for energies <15 keV and <70 keV electron-equivalent, respectively. The average pulse shapes are well-described by an effective model with two exponential decay components, where both decay times are fit parameters. We find significant broadening of the pulse for ER due to delayed luminescence from the recombination process. In addition to the effective model, we fit a model describing the recombination luminescence for ER at zero field and obtain good agreement. We estimate the best performance of a combined S2/S1 and pulse shape ER/NR discrimination and show that even with 2 ns time resolution, the improvement over S2/S1 discrimination alone is marginal, so that pulse shape discrimination will likely not be useful for future dual-phase liquid xenon experiments looking for elastic dark matter recoil interactions. K: Noble liquid detectors (scintillation, ionization, double-phase); scintillators, scintillation and light emission processes (solid, gas and liquid scintillators); particle identification methods; Time Projection Chambers (TPC) A X P : 1803.07935

A measurement of the scintillation decay time constant of nuclear recoils in liquid xenon with the XMASS-I detector

“…The singlet fraction obtained in this work agrees with the results of Ref. [13,14], however, the τ T is about 5 ns longer than those values. The τ T discrepancy might stem from a time delay introduced by the recombination process, which is suppressed under an electric field.…”

“…The scintillation timing information can be used for position reconstruction of an event in the detector [6] as well as for particle identification [7]. Studies on the scintillation process in LXe has been conducted in various experiments [8][9][10][11][12][13][14][15][16][17][18][19]. A scintillation photon is produced by two mechanisms.…”

“…While the recombination process has a longer decay time constant of more than 30 ns, measured with 1 MeV electrons from a 207 Bi source [10,11]. In the case of neutron induced NR events, the decay time constant of the triplet state was reported to be ∼20 ns both with an applied electric field (0.1-0.5 kV/cm) [13,14] and without [15,19]. The decay time constants of the singlet and triplet states depend weakly on the density of the excited species, whereas the ratio of the singlet to triplet state as well as the recombination time depends on the deposited energy density [20].…”

Direct detection of WIMP dark matter: concepts and status

“…However, the need for a large number of detected photons for pulse shape discrimination increases the analysis threshold to ∼30 keV nr . For xenon, the two time constants are too similar to be exploited for ER rejection in a meaningful way [114]. Bubble chambers operated at the right temperature regime are almost immune (at the 10 −9 level) to interactions from particles producing ERs with a low ionization density as these do not create detectable bubbles.…”

Field dependence of electronic recoil signals in a dual-phase liquid xenon time projection chamber

“…The drift velocity, electron lifetime, diffusion constant, and light and charge yields are determined for all measured fields and are compared to NEST where possible. In addition, we fit the scintillation pulse shape using a model with two exponential decay components [17], where we allow the effective triplet lifetime component to vary.…”