Baxter D, Chen C J, Crisler M, Cwiok T, Dahl C E, Grimsted A, Gupta J, Jin M, Puig R, Temples D, Zhang J
Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, USA.
Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA.
Phys Rev Lett. 2017 Jun 9;118(23):231301. doi: 10.1103/PhysRevLett.118.231301. Epub 2017 Jun 8.
A 30-g xenon bubble chamber, operated at Northwestern University in June and November 2016, has for the first time observed simultaneous bubble nucleation and scintillation by nuclear recoils in a superheated liquid. This chamber is instrumented with a CCD camera for near-IR bubble imaging, a solar-blind photomultiplier tube to detect 175-nm xenon scintillation light, and a piezoelectric acoustic transducer to detect the ultrasonic emission from a growing bubble. The time of nucleation determined from the acoustic signal is used to correlate specific scintillation pulses with bubble-nucleating events. We report on data from this chamber for thermodynamic "Seitz" thresholds from 4.2 to 15.0 keV. The observed single- and multiple-bubble rates when exposed to a ^{252}Cf neutron source indicate that, for an 8.3-keV thermodynamic threshold, the minimum nuclear recoil energy required to nucleate a bubble is 19±6 keV (1σ uncertainty). This is consistent with the observed scintillation spectrum for bubble-nucleating events. We see no evidence for bubble nucleation by gamma rays at any of the thresholds studied, setting a 90% C.L. upper limit of 6.3×10^{-7} bubbles per gamma interaction at a 4.2-keV thermodynamic threshold. This indicates stronger gamma discrimination than in CF_{3}I bubble chambers, supporting the hypothesis that scintillation production suppresses bubble nucleation by electron recoils, while nuclear recoils nucleate bubbles as usual. These measurements establish the noble-liquid bubble chamber as a promising new technology for the detection of weakly interacting massive particle dark matter and coherent elastic neutrino-nucleus scattering.
2016年6月和11月在西北大学运行的一个30克氙气泡室，首次观测到了过热液体中由核反冲导致的气泡同时成核和闪烁现象。该气泡室配备了用于近红外气泡成像的电荷耦合器件（CCD）相机、用于探测175纳米氙闪烁光的日盲光电倍增管以及用于探测正在生长气泡发出的超声波的压电声换能器。根据声信号确定的成核时间用于将特定的闪烁脉冲与气泡成核事件关联起来。我们报告了该气泡室在4.2至15.0千电子伏特的热力学“塞茨”阈值下的数据。当暴露于²⁵²Cf中子源时观测到的单气泡和多气泡速率表明，对于8.3千电子伏特的热力学阈值，使气泡成核所需的最小核反冲能量为19±6千电子伏特（1σ不确定度）。这与气泡成核事件观测到的闪烁光谱一致。在任何研究的阈值下，我们都没有发现伽马射线导致气泡成核的证据，在4.2千电子伏特的热力学阈值下，设定了每伽马相互作用产生气泡数的90%置信水平上限为6.3×10⁻⁷个气泡。这表明其伽马分辨能力比CF₃I气泡室更强，支持了这样的假设：闪烁产生抑制了电子反冲导致的气泡成核，而核反冲则像往常一样使气泡成核。这些测量结果确立了惰性液体气泡室作为探测弱相互作用大质量粒子暗物质和相干弹性中微子 - 核散射的一种有前景的新技术。
