Ccgen Darkside

Abstract: Building on the successful experience in operating the DarkSide-50 detector,the DarkSide Collaboration is going to construct DarkSide-20k, a direct WIMPsearch detector using a two-phase Liquid Argon Time Projection Chamber (LArTPC)with an active (fiducial) mass of 23 t (20 t). The DarkSide-20k LArTPC will bedeployed within a shield/veto with a spherical Liquid Scintillator Veto (LSV)inside a cylindrical Water Cherenkov Veto (WCV). Operation of DarkSide-50demonstrated a major reduction in the dominant $^{39}$Ar background when usingargon extracted from an underground source, before applying pulse shapeanalysis. Data from DarkSide-50, in combination with MC simulation andanalytical modeling, shows that a rejection factor for discrimination betweenelectron and nuclear recoils of $gt3times10^9$ is achievable. This, alongwith the use of the veto system, is the key to unlocking the path to largeLArTPC detector masses, while maintaining an 'instrumental background-free'experiment, an experiment in which less than 0.1 events (other than$nu$-induced nuclear recoils) is expected to occur within the WIMP searchregion during the planned exposure. DarkSide-20k will have ultra-lowbackgrounds than can be measured in situ. This will give sensitivity toWIMP-nucleon cross sections of $1.2times10^{-47}$ cm$^2$ ($1.1times10^{-46}$cm$^2$) for WIMPs of $1$ TeV$/c^2$ ($10$ TeV$/c^2$) mass, to be achieved duringa 5 yr run producing an exposure of 100 t yr free from any instrumentalbackground. DarkSide-20k could then extend its operation to a decade,increasing the exposure to 200 t yr, reaching a sensitivity of$7.4times10^{-48}$ cm$^2$ ($6.9times10^{-47}$ cm$^2$) for WIMPs of $1$TeV$/c^2$ ($10$ TeV$/c^2$) mass.