Studies on the RICH Velocity Reconstruction with a Likelihood Approach. Features and Variability Corrections

The Alpha Magnetic Spectrometer (AMS) is a particle physics detector operating on the International Space Station, designed for long-term precision measurements in space. A key objective of AMS is the isotopic separation of cosmic rays, providing crucial insight into their origin, propagation, and composition. Achieving accurate isotopic separation depends critically on the mass resolution, which is strongly determined by the velocity resolution at high energies.

The Ring Imaging Cherenkov Detector (RICH) is the AMS subdetector responsible for high-precision velocity measurements in the upper energy range. Improving its velocity resolution is therefore essential to extending AMS sensitivity to isotopic identification in previously unexplored energy domains.

The RICH determines particle velocities by reconstructing Cherenkov ring patterns produced as particles traverse one of its radiator materials, aerogel or sodium fluoride.

This work reports possible improvements to the velocity reconstruction performed by the LIP likelihood-based algorithm.

One enhancement involves exploiting Cherenkov photons emitted from the plastic foil support below the radiator. Jointly reconstructing the rings from both the foil and the radiator is expected to improve velocity resolution for high-charge particles.

A second improvement addresses time-dependent biases in reconstructed velocities. Periodicities of 60 days and one year, linked to the temperature dependence of radiator refractive indices, and a long-term drift from light guide and aerogel ageing are identified. Modeling these effects enables time- and temperature-dependent corrections to the refractive index and emission point used in reconstruction.