LUX-ZEPLIN

Abstract:

Identifying the nature and origin of dark matter is one of the major challenges for modern astro and particle physics. Direct dark-matter searches aim at an observation of dark-matter particles interacting within detectors. The focus of several such searches is on interactions with nuclei as provided e.g. byWeakly Interacting Massive Particles. However, there is a variety of dark-matter candidates favoring interactions with electrons rather than with nuclei. One example are dark photons, i.e., long-lived vector particles with a kinetic mixing to standard-model photons. In this work we present constraints on this kinetic mixing based on data from CRESST-II Phase 2 corresponding to an exposure before cuts of 52 kg-days. These constraints improve the existing ones for dark-photon masses between 0.3 and 0.7 keV/c2.

Abstract:

Temperature is a very important parameter when aiming to minimize radiation damage to biological samples during experiments that utilise intense ionising radiation. A novel technique for remote, non-contact, in situ monitoring of the protein crystal temperature has been developed for the new I23 beamline at the Diamond Light Source, a facility dedicated to macromolecular crystallography (MX) with long-wavelength X-rays. The temperature is derived from the temperature-dependant decay time constant of luminescence from a minuscule scintillation sensor (<0.05 mm3 ) located in very close proximity to the sample under test. In this work we present the underlying principle of cryogenic luminescence lifetime thermometry, discuss the features of the detection method, the choice of temperature sensor and demonstrate how the temperature monitoring system was integrated within the viewing system of the end-station used for the visualisation of protein crystals. The thermometry system was characterised using a Bi4Ge3O12 (BGO) crystal scintillator that exhibits good responsivity of the decay time constant as function of temperature over a wide range (8 – 270 K). The scintillation sensor was calibrated and the uncertainty of the temperature measurements over the primary operation temperature range of the beamline (30 – 150 K) was assessed to be ±1.6 K. It has been shown that the temperature of the sample holder, measured using the luminescence sensor, agrees well with the expected value. The technique was applied to characterise the thermal performance of different sample mounts that have been used in MX experiments at the I23 beamline. The thickness of the mount is shown to have the greatest impact upon the temperature distribution across the sample mount. Altogether these tests and findings demonstrate the usefulness of the thermometry system in highlighting the challenges that remain to be addressed for the in-vacuum MX experiment to become a reliable and indispensable tool for structural biology.