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Abstract
In the framework of the search for dark matter in the form of WIMPs using superheated liquids, a study is conducted to establish a computational procedure aimed at determining how the thermodynamic conditions kept inside a particle detector affect the acoustic signal produced by bubble nucleation. It is found that the acoustic energy injected into the liquid by the growing vapour bubble increases as the liquid pressure is decreased and the superheat degree is increased, the former effect being crucial for the generation of a well-intelligible signal. A good agreement is met between the results of the present study and some experimental data available in the literature for the amplitude of the acoustic signal. Additionally, the higher loudness of the alpha-decay events compared with those arising from neutron-induced nuclear recoils is described in terms of multiple nucleations.
Highlights
The current approach to alpha background rejection is based on the fact that the radiation-induced nucleation of a vapour bubble in a superheated liquid is accompanied by sound emission, first observed by Glaser and Rahm [10], and that the alpha decays are normally louder than nuclear recoils
The computational procedure discussed earlier is applied to a number of refrigerants rich in Fluorine, which has by far the largest enhancement factor in the spin-dependent cross section for the scattering of WIMP particles, with the main aim to determine the effects of the thermodynamic conditions of metastability on the sound emission associated with a bubble nucleation
The use of superheated liquids in searches for dark matter in the form of WIMPs requires to know the effects of the thermodynamic operating conditions of the detector on the acoustic signature of bubble nucleation, which is useful both to carry out an acoustic bubble recognition additional to the visual inspection and to discriminate alpha-decay events from the events originating from nuclear recoils
Summary
The current approach to alpha background rejection is based on the fact that the radiation-induced nucleation of a vapour bubble in a superheated liquid is accompanied by sound emission, first observed by Glaser and Rahm [10], and that the alpha decays are normally louder than nuclear recoils. Acoustic signatures of bubble nucleations were originally measured by Martynyuk and Smirnova [11], and more recently recorded by a number of investigators - see, e.g., Aubin et al [12], Felizardo et al [13], Behnke et al [9], Mondal and Chatterjee [14], Archambault et al [15], Amole et al [16], and Sarkar et al [17] - , most of them being involved in dark matter searches According to these works, the amplitude of the acoustic signal - and its clarity - increases as the pressure of the sensitive liquid is decreased and its temperature is increased, yet no direct correlation between the thermodynamic operating conditions of the detector and the. A study is executed to establish a computational procedure aimed at determining in what measure the sound emission associated with a bubble nucleation occurrence is related to the thermodynamic state at which the superheated liquid is maintained, which could be helpful in defining the operating conditions of the detector and to provide a first-approach description of the higher loudness of the alpha-decay sound emission
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