Cerenkov angle and charge reconstruction with the RICH detector for the AMS experiment

F.Barao, J.Borges, M.Pimenta, L.Arruda, P.Gonalves

Av. Elias Garcia, 14 1-andar, 1000-Lisboa


Campo Grande,, 1749-Lisboa


     The Alpha Magnetic Spectrometer (AMS) experiment to be installed on the International Space Station (ISS) will be equipped with a proximity focusing Ring Imaging Cerenkov (RICH) detector, for measurement of particle electric charge and velocity. The detector is made of an aerogel radiator and a photomultiplier matrix, enveloped by a large reflectivity conical shape mirror in order to increase the geometrical acceptance.
     Reconstruction of particle velocity has to deal with an essentially flat background from photomultipliers noise and photon scattering on aerogel radiator. Additionally, complex photon patterns can occur at the detector plane due to mirror reflected photons. A Likelihood method for the cerenkov angle reconstruction was developed leading to a velocity determination for protons with a resolution of around 0.1%.
     Charge Reconstruction with the Rich detector is also envisaged. The existence of a large fraction of background photons which can be different from event to event due to the detector geometrical acceptance and then event kinematics implied a charge reconstruction method based on an overall efficiency estimation on a event by event basis. A typical signal resolution on charge of the order of 20% is obtained for protons.

Preprint submitted to Elsevier Science                                                                 21 March 2002