Speaker
Description
There are ample convincing evidences based on gravitational effects point to the existence of dark matter (DM) though the particle properties of DM is unknown. Many theories suggest that Weakly Interacting Massive Particles (WIMPs) are one of the most promising candidates for DM with masses varies from few MeV to few hundred of TeV. It could be observed directly via direct detection of DM search experiments, which are aimed at detecting the nuclear recoils caused by WIMPs-nucleus elastic scattering. The most challenging part of any DM direct search experiment is identifying and suppressing the backgrounds, therefore the experiments are conducted deep down to minimise the cosmic ray-induced backgrounds. The current most sensitive direct detection experiments are sensitive in the 25–40 GeV WIMP mass range and the null results of these experiments have piqued curiosity in the low WIMP mass region, particularly below 10 GeV. Low threshold energy and a target with low mass nuclei are required for the detector to be sensitive to low WIMP mass.
Here, we have investigated the potentiality of C$_{2}$H$_{2}$F$_{4}$ (b.p. -26.3 $^{\rm o}$C) superheated liquid detector (SLD) (containing low mass nuclei) to probe the low mass WIMPs. SLD provides an excellent rejection to the backgrounds by adjusting the operating temperature and pressure of the liquid such that it can detect heavy ionizing particles (e.g. neutrons) at a certain temperature and pressure range while remaining insensitive to low ionizing radiation (e.g. gamma-rays and muons). Due to the presence of $^{12}$C and $^{19}$F recoil nuclei, the detector operating at 35.0 $^{\rm o}$C (gamma-ray insensitive zone) with 100$\%$ thermodynamic efficiency can detect WIMPs with masses as low as 2.2 GeV, whereas the $^{1}$H recoil nucleus is insensitive in this temperature range. At zero background environment, WIMPs in the few GeV mass range could be explored with a C$_{2}$H$_{2}$F$_{4}$ SLD with a WIMP-nucleon spin-independent cross-section sensitivity of about 2.10$\times$10$^{-41}$ cm$^2$ at WIMP masses as low as 4.0 GeV and a total exposure of 1000 kg.day, assuming a thermodynamic efficiency to be 50$\%$ or more. Sensitivity to sub-GeV WIMP masses usually demands sensitivity to the WIMP produced $^{1}$H recoil nucleus, which involves the detector working at 50.0 $^{\rm o}$C temperature and thermodynamic efficiency > 50$\%$. From the calculation, it is found that C$_{2}$H$_{2}$F$_{4}$ SLD operating at 60.0 $^{\rm o}$C temperature (gamma-ray sensitive zone) with 100$\%$ thermodynamic efficiency, the bubble nucleation threshold energy of 0.1 keV can be achieved for all three nuclei which is found to be sensitive to 140 MeV, 430 MeV, and 540 MeV WIMP masses due to $^{1}$H, $^{12}$C, and $^{19}$F recoil nuclei, respectively.
The experiment in steps with increasing exposure with C$_{2}$H$_{2}$F$_{4}$ SLD has been started at 555m deep Jaduguda Underground Science Laboratory (JUSL), UCIL, Jharkhand, India for the hunt for low mass WIMPs. It is necessary to investigate the noise and background levels at JUSL before run the SLD for WIMPs search. It is observed with a small mass SLD at JUSL that the 20Hz-20 kHz region is dominated by the noises and the background event rate is reduced at underground. The detector with increased active mass is under construction and DAQ and related instrumentation have developed. Signals at higher frequencies will be measured in future to better understand the background induced events as well as the noise with increased active mass and longer run time with a goal to search for the low mass WIMPs.
| What is your experiment? | R & D works for dark matter search |
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