Simultaneous measurement of the light and charge response of liquid xenon to low-energy nuclear recoils at multiple electric fields

Dual-phase liquid xenon (LXe) detectors lead the direct search for particle dark matter. Understanding the signal production process of nuclear recoils in LXe is essential for the interpretation of LXe based dark matter searches. Up to now, only two experiments have simultaneously measured both the light and charge yield at different electric fields, neither of which attempted to evaluate the processes leading to light and charge production. In this paper, results from a neutron calibration of liquid xenon with simultaneous light and charge detection are presented for nuclear recoil energies from 3–74 keV, at electric fields of 0.19, 0.49, and $1.02\mathrm{kV}/\mathrm{cm}$. No significant field dependence of the yields is observed.

Figure 1

Schematic drawing of neriX TPC. Plot from Ref. [18].

Figure 2

The deposit energy spectra of the neutron scatters with scattering angles of 30° (red), 35° (blue), 45° (green), and 53° (orange) in the detector fiducial volume. The spectra are derived using the Geant4 simulation toolkit [24]. The nuclear recoil energy spectrum of neutron scatters with the coincidence requirement between the TPC and LS detector trigger inhibited is also shown as a dashed blue line.

Figure 3

The trigger efficiency (red) as a function of the number of electrons and the peak-finding efficiency (blue) as a function of the number of photons. The solid lines are the median efficiencies. The shaded regions show the uncertainty (15.4% to 84.6% credible region).

Figure 4

Coincidence data taken with a drift field of $190\mathrm{V}/\mathrm{cm}$ for scattering angles of 30°, 35°, 45°, and 53°, from left to right and top to bottom. Panel I shows the data distribution on ${\log }_{10}(\mathrm{S}2/\mathrm{S}1)$ vs S1 space, overlaid with the 68% ($1\sigma$, solid) and 95% ($2\sigma$, dashed) red contour lines derived from the median of the two-dimensional marginalized posterior from the MCMC sampling of the likelihood. Panel II shows the S1 spectrum of data (black circles) compared to the one-dimensional marginalized posterior (blue). The dashed line represents the median of the posterior, and the shaded region is the 15.4% to 84.6% credible region. Panel III shows the S2 spectra in different S1 ranges. The data spectra are shown with the error bars, and the posterior medians and credible regions (15.4%–84.6%) are shown in dashed lines and shaded regions, respectively.

Figure 5

Coincidence data taken with a drift field of $490\mathrm{V}/\mathrm{cm}$. The figure description is the same as in Fig. 4.

Figure 6

Coincidence data taken with a drift field of $1.02\mathrm{kV}/\mathrm{cm}$. The figure description is the same as in Fig. 4.

Figure 7

Band data taken with scanned drift fields of $190\mathrm{V}/\mathrm{cm}$, $490\mathrm{V}/\mathrm{cm}$, and $1.02\mathrm{kV}/\mathrm{cm}$, from left to right. The figure description is the same as in Fig. 4.

Figure 8

The comparison of the light and charge yield results from this work to previous measurements [6, 7, 8, 9, 10, 11, 12, 14, 35]. Panels II and III show the light and charge yields, respectively. The red, blue, and green diamonds with error bars correspond to electric fields of 0.19, 0.49, and $1.02\mathrm{kV}/\mathrm{cm}$, respectively, using the previous fixed-angle measurement interpretation as described in the text. The red, blue, and green solid lines are the results (medians of the posteriors) from the simultaneous fit of all available data with the MC simulation-based model. The dashed lines serve as reference light and charge yields, which are the best-fit results from nest1.0 [15] at $490\mathrm{V}/\mathrm{cm}$. Panels I and IV show the deviations of the light and charge yield posteriors at the three fields to the reference nest light and charge yields. An energy cutoff of 3 keV (shown in gray) is chosen as this represents an approximately 10% detection efficiency assuming a light yield of $5.5\mathrm{photons}/\mathrm{keV}$ and charge yield of $7.5\mathrm{electrons}/\mathrm{keV}$. Note that all measurements of light yield, with the exception of this work and of Ref. [14], are extrapolations from ${\mathcal{L}}_{\mathrm{eff}}$ using a light yield of $63\mathrm{photons}/\mathrm{keV}$ for 122 keV electronic recoils. For reference, light and charge yields from nest2.0 [36] at 0.19, 0.49, and $1.02\mathrm{kV}/\mathrm{cm}$ are shown in blue, green, and red dashed lines, respectively.