Searching for Light Dark Matter with a Spherical Proportional Counter

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F68407700%3A90107%2F21%3A00357745" target="_blank" >RIV/68407700:90107/21:00357745 - isvavai.cz</a>

Result on the web

<a href="https://www.theses.fr/2021UPASP035" target="_blank" >https://www.theses.fr/2021UPASP035</a>

DOI - Digital Object Identifier

—

Result language

angličtina

Original language name

Searching for Light Dark Matter with a Spherical Proportional Counter

Original language description

The NEWS-G collaboration is conducting experiments that search for dark matter down to sub-GeV candidate masses with a gaseous detector, the spherical proportional counter. The next-generation detector, SNOGLOBE, a 140 cm-diameter spherical proportional counter, has been constructed, and plans for experiments beyond this are underway. The presented work has enabled SNOGLOBE, developing the understanding of the detector, the properties of gases, background suppression techniques and the physics potential of future experiments. The understanding of the detector electric field is essential to detector operation. Finite element method calculations were used to guide the development of read-out sensors, as was a dedicated simulation framework for spherical proportional counters, based on Geant4 and Garfield++. The use of a high-resistivity secondary correction electrode with the single-anode sensor improved detector operational stability and energy resolution by shaping the electric field. The use of a DLC coated, 3D-printed central electrode for the multi-anode sensor, ACHINOS, provided a breakthrough in detector stability and robustness. ACHINOS provides a means of operating with increasingly large and high-pressure detectors, which is essential for the operation of SNOGLOBE and future spherical proportional counter rare-event searches. The fraction of deposited energy dissipated as ionization must be understood to infer the energy of a recoiling nucleus induced by dark matter elastic scattering. A method has been developed to compute this from precision measurements of the W-value in gases, which have been conducted for several decades. These experimental provide estimates of the ionization quenching factor (QF) in several gases. The QF in CH₄ is ​​of particular importance to the NEWS-G collaboration and is estimated to sub-keV recoil energies. The construction of dark matter detectors places extremely rigorous constraints on the radiopurity of materials used. In the case of NEWS-G, (2)(2)(2)Rn introduced into the detector copper during manufacturing leads to a (2)¹⁰Pb contamination, which is the dominant experimental background. A method of suppressing this background in copper is electroforming, which has been used by experiments to produce detector components due to the significant improvement in radiopurity. The technique has been scaled up and applied to apply a highly-pure copper layer to the inner surface of SNOGLOBE, reducing the background below 1 keV by a factor of 2.6. This is the largest deep-underground electroforming ever performed and has demonstrated the feasibility of the technique on large, spherical surfaces deep underground. The enhancement in radiopurity that can be achieved with electroforming has motivated future fully electroformed spherical proportional counters directly in an underground laboratory. The ECUME facility in SNOLAB will produce a 140 cm detector for NEWS-G, and is beginning operation this year. When installed in the shielding of SNOGLOBE, the fully electroformed detector will increase NEWS-G's sensitivity. Beyond this, DarkSPHERE is proposed as the next-generation detector. The 3 m fully underground electroformed detector, installed in an improved radiopurity shielding composed mainly of water, would have the potential to explore the dark matter candidate mass-cross section parameter space close to the solar neutrino floor in the sub-GeV dark matter mass range. The physics potential of such a detector has been explored.

Czech name

—

Czech description

—

Type

O - Miscellaneous

CEP classification

—

OECD FORD branch

10304 - Nuclear physics

Project

—

Continuities

—

Publication year

2021

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů