erenkov angle and charge reconstruction with the RICH detector of the AMS experiment

The Alpha Magnetic Spectrometer (AMS) experiment to be installed on the International Space Station (ISS) will be equipped with a proximity focusing Ring ImagingČerenkov (RICH) detector, for measurements of particle electric charge and velocity. In this note, two possible methods for reconstructing thě Cerenkov angle and the electric charge with the RICH, are discussed. A Likelihood method for thě Cerenkov angle reconstruction was applied leading to a velocity determination for protons with a resolution of around 0.1%. The existence of a large fraction of background photons which can vary from event to event, implied a charge reconstruction method based on an overall efficiency estimation on an event-by-event basis. The Alpha Magnetic Spectrometer (AMS) [1] is a precision spectrometer to be installed by 2005 in the International Space Station (ISS), where it will operate for a period of three years. Its main goals are the search for cosmic anti-matter, the search for dark matter and the measurement of the relative abundance of elements and isotopes in primary cosmic rays. The future installation of AMS in the ISS was preceded by a 10 days engineering test flight aboard the Space Shuttle Discovery in June 1998, at a mean altitude of 370 km. Although the purpose of this experimental flight was the test of the spectrometer design principles, about 100 million events were collected enabling precise measurements of the spectra of high energy protons, electrons , positrons and helium nuclei [2]. The AMS spectrometer capabilities were extended with respect to those of the experimental flight, through the inclusion of new subdetec-tor systems and the completion of others. The spectrometer design includes a superconducting magnet, a Time-of-Flight system (TOF), a Silicon Tracker, Veto Counters, a Transition Radiation Detector (TRD), an Electromagnetic Calorimeter (ECAL) and a Ring ImagingČerenkov Detector (RICH). It will be capable of measuring the rigidity (R ≡ pc/|Z|e), the charge (Z), the velocity (β) and the energy (E) of cosmic rays within a geometrical acceptance of ∼ 0.5 m 2 .sr. The tracking system, with a cylindrical shape, is made of 8 double sided silicon planes embedded inside a magnetic field of about 0.9 Tesla and will provide both charge measurements and momentum measurements with a resolution ∆p/p of at most 2% up to 100 GeV/c/nucleon. The TOF system, made of four scintillator planes placed at the magnet end-caps, will provide a fast trigger, charge and velocity measurements for charged particles as …