Beam-beam counters and charged particle multiplicity in the BRAHMS experiment at RHIC

The Relativistic Heavy Ion Collisions are considered to be the only method to condense and to heat up a nuclear matter in the laboratory conditions. It is believed, that at high temperature (T ≥ 200 MeV) and high density (ρ/ρ_o ∼ 5 ÷ 20), quarks and gluons, which are one of the smallest bricks of nature and are confined to each other under the regular conditions, will break the confinement and create a new form of matter, called the Quark Gluon Plasma (QGP). This new form of the nuclear matter is of the great interest, since it is believed to resemble the state of matter just a few microseconds after the Big Bang.; The Relativistic Heavy Ion Collider (RHIC), presently operating at the Brookhaven National Lab, is designed to collide two beams of gold ions at energies of 100A GeV. Broad RAnge Hadron Magnetic Spectrometer (BRAHMS) is one of the four experiments, operating at RHIC and is trying to search for the Quark Gluon Plasma. The Beam-Beam Counters are one of the global detectors at BRAHMS and are designed to characterize collisions from the global perspective; to form a level0 trigger for the BRAHMS experiment and to identify the space-time location of the collision vertex. The Beam-Beam Counters are a set of the photomultipliers with a Cherenkov radiators attached to their face. They are designed to detect charged particles, and, thus, are able to characterize the collision from the perspective of the charged particles production.; The Beam-Beam Counters are the main object of this thesis. Different theoretical models, predicting the QGP creation in the relativistic heavy ion collisions will be discussed through the mechanisms of the charged particles production. The Beam-Beam Counters design and performance will be shown in great detail. It will be demonstrated how the Beam-Beam Counters are able to provide the level0 trigger and to locate the collision vertex with the designed precision. First experimental results of the charged particle multiplicity distribution in the relativistic heavy ion collisions at RHIC will be presented and compared with the known theoretical models.; This is a great thesis, enjoy!...