Performance of large area CsI-RICH prototypes for ALICE at LHC

We present the performances of large area CsI-RICH prototypes obtained in single particle events. The differential quantum efficiency of the photocathodes has been deduced from Cherenkov rings by means of two different procedures: a direct measurement with a thin NaF radiator and a Monte Carlo based estimation for a C$_6$F$_{14}$ radiator. A factor of merit of 45 cm$^{-1}$ has been found for the typical detector configuration. Two angle reconstruction algorithms have been used and the different errors affecting the Cherenkov angle resolution have been estimated combining the analytical treatment and the Monte Carlo simulation. Also the dependence on radiator thickness, Cherenkov ring radius, chamber voltage and particle incidence angle has been studied

Final tests of the CsI-based ring imaging detector for the ALICE experiment

We report on the final tests performed on a CsI-based RICH detector equipped with 2 C$_6$F$_{14}$ radiator trays and 4 photocathodes, each of 64$\times$38 cm$^2$ area. The overall performance of the detector is described, using different gas mixtures, in view of optimizing the photoelectron yield and the pad occupancy. Test results under magnetic field up to 0.9 T, photocathode homogeneity and stability are presented

A pattern recognition method for the RICH-based HMPID detector in ALICE

A pattern recognition method developed for the High Momentum Particle IDentification (HMPID) detector in the ALICE experiment at CERN is presented. The algorithm is based on the Hough transform with a mapping of the pad coordinate space directly to the Cherenkov angle parameter space. Cherenkov angle reconstruction has been studied as a function of different particle densities in the photodetector using real data taken in the ALICE tests at the CERN SPS: a satisfactory resolution can be achieved even in events where the occupancy reaches more than 12, which is the situation we may be confronted with in central Pb-Pb interactions at LHC. (9 refs)

High-resolution coherency functionals for improving the velocity analysis of ground-penetrating radar data

We aim at verifying whether the use of high-resolution coherency functionals could improve the signal-to-noise ratio (S/N) of Ground-Penetrating Radar data by introducing a variable and precisely picked velocity field in the migration process. After carrying out tests on synthetic data to schematically simulate the problem, assessing the types of functionals most suitable for GPR data analysis, we estimated a varying velocity field relative to a real dataset. This dataset was acquired in an archaeological area where an excavation after a GPR survey made it possible to define the position, type, and composition of the detected targets. Two functionals, the Complex Matched Coherency Measure and the Complex Matched Analysis, turned out to be effective in computing coherency maps characterized by high-resolution and strong noise rejection, where velocity picking can be done with high precision. By using the 2D velocity field thus obtained, migration algorithms performed better than in the case of constant or 1D velocity field, with satisfactory collapsing of the diffracted events and moving of the reflected energy in the correct position. The varying velocity field was estimated on different lines and used to migrate all the GPR profiles composing the survey covering the entire archaeological area. The time slices built with the migrated profiles resulted in a higher S/N than those obtained from non-migrated or migrated at constant velocity GPR profiles. The improvements are inherent to the resolution, continuity, and energy content of linear reflective areas. On the basis of our experience, we can state that the use of high-resolution coherency functionals leads to migrated GPR profiles with a high-grade of hyperbolas focusing. These profiles favor better imaging of the targets of interest, thereby allowing for a more reliable interpretation