The presented thesis is dedicated to particle identification in COMPASS RICH-1 experiment which is located in European Organization for Nuclear Research (CERN). For particle identification Cherenkov radiation is used, which is described in the thesis together with detection principles. Current aim in detector upgrade is replacing a part of Multi Wire Proportional Chambers (MWPC) in peripheral regions of the detection surface by a suitable photon detector so as to guarantee one-photon detection. For this purpose the hybrid photon detector based on THGEM and MicroMegas technologies was developed. The hybrid detector test results are presented in the thesis.

LHCb est l'une des quatre grandes expériences installées sur l'anneau du LHC. Le détecteur a pour but la mesure précise de la violation de CP et de canaux rares de désintégration dans le secteur des mésons B. Le calorimètre de l'expérience est un ensemble de quatre sous-systèmes : le détecteur de pied de gerbe, le ''preshower'' et les calorimètres électromagnétique (ECAL) et hadronique (HCAL). Il est essentiel pour la reconstruction des événements, pour le déclenchement de l'expérience et pour l'identification des électrons et des photons. Après une revue du détecteur LHCb, l'électronique des calorimètres est décrite dans la première partie de ce mémoire. Dans un premier temps l'électronique de lecture des voies des photomultiplicateurs des ECAL et HCAL est présentée en mettant l'accent sur ses performances, puis la carte de contrôle de l'ensemble du système calorimétrique de l'expérience est détaillée. Les chapitres trois et quatre concernent les programmes de test de cette électronique, les choix technologiques permettant de la rendre suffisamment tolérante aux radiations et les mesures quantifiant cette tolérance. La seconde partie de ce mémoire porte d'abord sur l'identification des photons avec les calorimètres de LHCb. La méthode est présentée avec ses performances. Enfin, l'étalonnage absolu en énergie des PRS et ECAL, basée sur les données enregistrées avec le détecteur en 2010, est décrite dans le dernier chapitre de cette même seconde partie.

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Fusion reactions between 12C nuclei are among the most important in stellar evolution since they determine the destiny of massive stars (> 8 M). At thermonuclear energies (Ecm=1.5 ± 0.3 MeV), the 12C+12C reactions mainly proceed through 20Ne+α and 23Na+p channels. Since these energies are much lower than the height of the Coulomb barrier (Ecm= 6.1 MeV), the direct measurements of the 12C+12C reactions are very challenging because of the extremely small cross sections involved and the high beam-induced background originating from impurities in the targets. In addition, the 12C+12C reaction forms 24Mg at relatively high excitation energies (above the 12C 13.93 MeV thresholds) where molecular configurations are possible. Theoretical models fail to reproduce such structures and as a result, the extrapolation of high-energy cross section data towards the energy of astrophysical interest remain uncertain by 2-3 orders of magnitude. Further experimental efforts to measure at the lowest accessible energies are therefore in need. However, additionally to the extremely low cross sections and the resonant structure, the measurements at stellar energies of the 12C+12C reactions are troublesome due to natural hydrogen and deuterium contamination in the carbon targets. These target contaminants hamper the measurement of the 12C+12C process in all exit channels given that the 12C+1,2H reactions cross sections are considerably higher than that of the reaction of interest. In consequence, the use of ultra-low H content graphite targets and a study of the target behaviour under beam bombardment are necessary. This work focused on the experimental measurements of the 12C(12C,p)23Na and 12C(12C,α)20Ne reactions using charge particle detection. Although both channels were measured, only the proton channel was analysed and discussed in this thesis due to time constrains. The experiment was performed at the 3 MV pelletron tandem accelerator of the CIRCE (Centre for Isotopic Research on the Cultural and Environmental heritage) laboratory in Caserta, Italy. The experimental approach involved the development of optical calculations for optimal beam transportation (using the software COSY), the use of a four ΔE-Erest detectors system (a variable pressure CF4 ionization chamber used as the ΔE detector and a 300 mm2 Si detector used as the Erest) called GASTLY (GAs Silicon Two-Layer sYstem) and a study of the deuterium (hydrogen does not contribute to the beam-induced background at the detection angles and beam energies used here) contamination in graphite targets. The GASTLY detectors were placed at backward angles (121, 143 and 156o respect to the beam axis) and the 12C+12C reactions were investigated using carbon beams of Ecm=4.30 - 2.52 MeV with intensities of the order of μA. Highly Ordered Pyrolytic Graphite (HOPG) and highly pure (99.8%) natural graphite targets were used for the deuterium contamination study. A thermocamera was used to constantly monitor the target temperature during beam bombardment, allowing the investigation of target's deuterium content as a function of target temperature. Results showed a decrease in target's deuterium content of 53-80% in the target's temperature range of 200-1200 °C, depending on the type of target and detection angle. Furthermore, it was found that surrounding the scattering chamber with a nitrogen atmosphere while measuring low counting rate reactions (such as 12C+12C at low energies), the HOPG target's deuterium content decreases to about half its original value for a target temperature in the range between 800-1100 °C. For the 12C+12C reactions measurements, the HOPG target was used, maintaining high target temperatures. The p0-6 proton groups of the 12C(12C,p)23Na reaction were analysed and their yields, cross sections and astrophysical S-factors were obtained and are presented in this thesis. A comparison with previous data available in the literature is also presented, together with an indication for possible improvements in future investigations.

The CEBAF Large Acceptance Spectrometer for the 12 GeV era, known as CLAS12, uses the time of flight (TOF) system to identify charged particles from scattering events between the beam and target. The TOF system is divided into two parts: The Forward time of flight system, and the Central time of flight system. These two sub-systems subtend different polar angles of the detector geometry for wide acceptance of scattered particles. Reconstruction is the service used to identify particles from the interactions between the beam and target, called as a vertex or the point where the interaction occurs. The vertex position is traced back using the tracking system and the TOF system. The resolution of the detector affects the accuracy of the reconstructed vertex location. This paper’s goal will be to develop software for validation suite for CLAS12, which will include central and forward tracking plots. Plots will be developed to check the precision of the reconstructed vertices in both the central and forward detectors. This will be done assuming a target with zero dimension at 𝑣𝑧 = 0, and an extended target of 5 cm at 𝑣𝑧 = 0. This paper will also look at the TOF resolution, and identify particles using the TOF detectors and the effect of the vertex correction on the velocity vs. momentum plots.

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Two measurements have been made, addressing gaps in knowledge for 235U(n,f) and 238U(n,f). The energy distribution for prompt fission neutrons is not well-understood below 1 MeV in 235U(n,f). To measure the 235U(n,f) prompt fission neutron distribution, a pulsed neutron beam at the WNR facility in Los Alamos National Laboratory was directed onto a 235U target with neutron detectors placed 1 m from the target. These neutron detectors were designed specifically for this experiment and employed a unique geometry of scintillating plastic material that was designed to reject backgrounds. Fission fragments were detected using an avalanche counter. Coincidences between fission fragment production and neutron detector events were analyzed, using a double time-of-flight technique to determine the energy of the prompt fission neutrons. A separate measurement was made, investigating the neutron-induced fission cross section for 238U(n,f). This measurement also used the pulsed neutron beam at the WNR facility. The neutron flux was normalized to the well-known hydrogen standard and the fission rate was observed for beam neutrons in the energy range of 130-300 MeV. Using an extrapolation technique, the energy dependence of the cross section was determined. These new data filled a sparsely populated energy region that was not well-studied and were measured relative to the hydrogen standard, unlike the majority of available data. These data can be used to constrain the fission cross section, which is considered a nuclear reaction standard.