The performance of ALICE-Diffractive detector in a beam-test.

The ALICE Diffractive (AD) detector is a forward detector that was added to ALICE to extend the acceptance of the experiment in the forward rapidity region in order to improve the sensitivity for diffraction physics. The AD detector will contribute to measure the inelastic proton-proton cross-section and to provide additional measurements of centrality in Pb-Pb, proton-Pb and Xe-Xe collisions. The AD is used as a trigger as well as a beam quality monitor at Point 2 of the LHC. AD consists of two assemblies, ADA and ADC, each station consist of two layers of scintillators. Two detector modules identical to those installed in the experiment were tested in the Proton Synchrotron T10 secondary beam at CERN, at four different momenta: 1, 1.5, 2 and 6 GeV/c. The modules were scanned using the beam along the scintillator pad, which is the biggest part of the detector, and additionally the other components, such as optical connectors, optical fibres, photomultiplier and the wavelength shifting bars. The experimental setup used for this study allow us to identify pions and protons coming from the beam. An additional setup to measure cosmic rays was mounted to have a reference. With those measurements, we prove that the efficiency along the plastic scintillators pads is homogeneous, which is an important requirement for a good performance in the experiment. The plastic scintillators pads were extensively analyzed to obtain the timing and charge properties for the different particles species and momenta, obtaining a suitable time resolution and charge response for a minimum ionization particle. It is worth to mention that the timing correction technique was successfully implemented for a MIP and was obtained the correlation between the energy deposited by a particle in the detector and the measurement of the charge. All those studies made for the plastic scintillator were also done for the rest of components (with exception of the correlation of the energy deposition and the charge). The results show that the efficiencies and charges of those sections are low in comparison with the scintillator pad, except for the photomultiplier that have an important contribution when a particle hits its photocathode. Additionally, the wavelength shifting bar was studied in detail by using a pixel detector. Finally, the time resolution and charge were correlated to compare them with the obtained in proton-proton collisions in the ALICE experiment. Also is presented an overview of the diffractive physics and the experiments, which attempt to study and understand the physics related to diffraction in high energy physics.