Observation of tau neutrinos and absolute orientation measurement in KM3NeT/ORCA.

• Luc Cerisy (KM3Net)

To better understand the properties of each neutrino flavor, one has to learn how to distinguish them. This can be achieved by using the characteristics of the signal induced by the neutrino interaction. The similarities between tau and electron neutrino interactions allow to separate them from the muon neutrino interaction, using the track-shower distinction. From that separation, a sample with an enhanced ratio of tau neutrinos can be isolated and used to measure their properties. The configuration and size of KM3NeT/ORCA allow to observe one of the largest samples of tau neutrinos in the world, which helps to further constrain the tau normalization. A deviation from one would indicate inconsistencies in the modeling of tau neutrinos that could be related to the cross section or the unitarity of the flavor mixing matrix . While KM3NeT/ARCA is built to explore the high-energy neutrinos sky, it has the ambitious goal of reaching the 0.05° angular resolution for muon neutrino track reconstruction, to provide the most accurate worldwide measurement of point source neutrino emission. However to reach such a precise measurement a good knowledge of the absolute orientation of the detector is required. Two distinct methods are being exploited to perform this absolute calibration of the detector, considering that neutrino telescopes do not have any known neutrino point source to calibrate on.

Simulation based modeling of galaxy clustering and peculiar velocities for growth rate measurements

• Tyann Dumerchat (CPPM)

Galaxies are tracers of the underlying dark matter distribution and evolution through the history of our universe. Therefore, it is a powerful probe to study the physical laws of large scale structures, and more generally our cosmological model. The main observables are the two-point functions of the galaxy density field, namely the correlation function in configuration space or the power spectrum in Fourier space. While large scales (typically above tens of Mpc/h) are well modelled by linear theory, small scales are highly non-linear and harder to model though they also contain cosmological information. Standard perturbative theories attempt to model mildly non-linear scales analytically but ultimately those perturbative approaches are limited as the density perturbations on small scales are not small. This is especially true at low redshift. An alternative is to build a simulation based model to extract the full information from the unexploited small scales in the standard two point statistics observables. A recent approach consists in running several N-body simulations for different cosmological models, compute the summary statistics for each and use them to predict the clustering for a new set of cosmological parameters. This process is commonly referred to as emulation. Brute iterative solving of dynamical equations in N-body simulations provide the high fidelity description of the matter non-linear clustering, although they are computationally expensive to produce.