With the lowest background level ever reached by detectors searching for rare-events, XENON1T proved to be the most sensitive dark matter direct detection experiment on earth. The unprecedented low level of radioactivity reached, made the XENON1T experiment suitable also for other interesting rare-events searches including the neutrinoless double beta decay (0νßß) of 136Xe. Furthermore, in the context of the advancement of the XENON program, the next generation experiment, XENONnT, designed with a high level of background reduction aiming to increase the predecessor sensitivity in rare-events searches is currently under commissioning phase in the underground National Laboratory of Gran Sasso (LNGS): it will host 5.9 tonnes of liquid xenon as a target mass. In this talk I will present my contribution to the ongoing commissioning of XENONnT and to the 0νßß search in Large Scale LXe Dual phase Time Projection Chamber (TPC).

It is now known that a deconfined state of the strongly interacting matter can be formed under extreme conditions of temperature and density in heavy-ion collisions: the quark-gluon plasma (QGP). Intensive work has been done to understand its fascinating properties but many questions remain unanswered. Especially, theoretical studies suggest the existence of a critical point in the phase diagram of the QCD matter. For the moment, the supposed location of the critical point is outside the region accessible from first-principle lattice calculations (μB/T . 2). Therefore, we need to rely on understanding the experimental data obtained from heavy-ion collisions. Heavy-ion collisions are extremely fast and out-of-equilibrium phenomena. This has a huge impact on the observables that are supposed to carry information about the critical point such as the higher-order cumulants of the net-baryon density, net-charge density or net-strangeness density. A reliable study of the impact of the dynamics on the critical fluctuations is then required to fully address the following question : are we able to experimentally prove the existence of the critical point with heavy-ion collision ? We investigate the diffusive dynamics of the critical fluctuations of the conserved charges in the case of a relativistic heavy-ion collision undergoing a Bjorken-type expansion. The fluctuation observables are inferred from the study of coupled stochastic diffusion equations which incorporates both diffusive dynamics and intrinsic fluctuations. In the vicinity of the critical point, the critical behavior of the fluctuations is encoded in the Ginzburg-Landau free energy functional parametrized using a non-universal mapping to the 3D Ising model. Far from the critical region, the behavior of the fluctuations corresponds to lattice calculations of the susceptibilities in equilibrium. We present the coupling between the fluctuations of different conserved charges in heavy-ion collisions for trajectories passing near the critical point.