The scintillation and ionization yield of liquid xenon for nuclear recoils

Abstract

a b s t r a c t XENON10 is an experiment designed to directly detect particle dark matter. It is a dual phase (liquid/ gas) xenon time-projection chamber with 3D position imaging. Particle interactions generate a primary scintillation signal (S1) and ionization signal (S2), which are both functions of the deposited recoil energy and the incident particle type. We present a new precision measurement of the relative scintillation yield L eff and the absolute ionization yield Q y , for nuclear recoils in xenon. A dark matter particle is expected to deposit energy by scattering from a xenon nucleus. Knowledge of L eff is therefore crucial for establishing the energy threshold of the experiment; this in turn determines the sensitivity to particle dark matter. Our L eff measurement is in agreement with recent theoretical predictions above 15 keV nuclear recoil energy, and the energy threshold of the measurement is $4 keV.A knowledge of the ionization yield Q y is necessary to establish the trigger threshold of the experiment. The ionization yield Q y is measured in two ways, both in agreement with previous measurements and with a factor of 10 lower energy threshold.

Lowering the low-energy threshold of xenon-based detectors

“…The neutron calibration experiment and general analysis technique are both described in a previous study by the XENON10 collaboration [9]. Note that here we circumvent the false single scatter pathology described in [3], since our calibration technique relies only on the S2 signal.…”

“…Lowering the low-energy threshold of xenon detectors P. Sorensen previous analyses [4,5,3,9] in that it considers the full ∆z = 15 cm active target (8.6 kg target mass), rather than just the central ∆z = 9.3 cm (5.4 kg target mass).…”

“…This background is assessed by counting the number of events within ±2σ of the electron recoil centroid, in the region around 30 − 35 keVee. The chosen energy window is above the tail of the elastic nuclear recoil distribution, and below the 40 keVee inelastic scatters [9]. The electromagnetic background spectrum below about 50 keVee is predicted and observed to be flat with energy.…”

A novel source of tagged low-energy nuclear recoils

“…The largest non-background signals may be attributed to the largest nuclear recoil energy produced by the selected fluorescence state in an end-point measurement. Going one step further, the theoretical distribution of nuclear recoil energies produced by the target resonance could be folded into analysis of the non-background signals in a similar manner to broad-spectrum neutron scatter measurements [6]. High efficiency background rejection would require detailed background characterization with beam on-and off-resonance in addition to selective triggering of the DAQ and post-processing cuts on quantities such as energy, position, and event shape.…”

“…For this purpose the scintillation efficiency (L e f f ) and ionization yield (I.Y.) of nuclear recoils have been reported in candidate detector materials [4][5][6][7][8][9][10][11][12] (see Table I). Of the reported measurements only two [11,12], have probed recoils below one keV, both in Ge.…”