Tools for physics with LHC and RIB

Abstract

My thesis consists of two parts. T0, the fast timing and trigger detector for the ALICE experiment at CERN LHC, is the subject of the first part. My contribution included simulations, design, construction, tests, installation and commissioning of the detector. We hope that the T0 will play a noticeable role in extracting the first physics results and providing the beam diagnostics during the restart of LHC in autumn 2009. This part of my thesis concludes with how T0 can be used for ALICE luminosity and multiplicity measurements as well as for a verification of the position of the interaction along the longitudinal and transverse axis already during the runs in the LHC commissioning period. The outcome of the first LHC injection and extraction tests performed in August 2008 and July 2009 is presented. The results indicate that T0 is functioning well and is ready for the first collisions at the LHC. The development and construction of the T0 detector as a part of the ALICE experiment is discussed. In essence all hardware and software parts of the T0 system, including all the electronics, Offline, Detector Control System, Databases, and so on are described. The consequences of the T0 detector tests including that with a mixted beam of 6 GeV/c negative pions and kaons at CERN PS when the time resolution of 28 ps r.m.s., a world record at that time, was reached, are discussed. The results of simulations of the T0 detector performance for p + p collisions at p s = 900 GeV 14 TeV using Pythia and Phojet event generators, and for p sNN = 5.5 TeV Pb + Pb collisions using Hijing prove that, despite the small acceptance (the T0 efficiency for p + p minimum bias events is about 40%), the shape of the charged particle density can be estimated based on T0 data alone. The physics framework is outlined in the introductory part, introducing the heavy ion physics concept and formalism with special emphasis on luminosity, particle production in the ultra-relativistic heavy ion collision and QGP signatures. The introductory part is concluded with the role of the ALICE experiment in the LHC scientific program and the description of the ALICE detector. The second part of my thesis focuses on the measurements of neutron yields by the activation and TOF method performed for SPES and SPIRAL 2 radioactive beam facilities. The work involved several experiments carried out during the years 2004 2008 at JYFL. The results are compared with Monte Carlo calculations and are discussed in the framework of a converter method for the SPES and SPIRAL 2. Our results have indicated that at 20 MeV the p+13C reaction proposed for SPES is not competitive. Consequently the converter method has been abandoned in favour of the direct method. Measurements for SPIRAL 2 show that the neutron yield has been overestimated during the modelling of the converter fission target ensemble, so that the expected number of fissions with a carbon converter is of order 2 2.5 · 1013 and not 5 · 1013 fissions/s, as was initially expected. Measurements also show that the number of fissions achievable with a heavy water converter is only about 1.4 1.5 × higher than with a carbon converter. It was hoped that a gain close to 2 could be achieved. Following the outcome of the measurements, a re evaluation of the converter + fission target module has been recommended by the SPIRAL 2 Technical Advisory Committee.