Study of Quark Gluon Plasma by Heavy Ion Collision

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In this research work, production characteristics of charm particles in 200 A.GeV/c^<32>S - nucleus central interactions has been studied. A hybrid experimental apparatus of 2 layers of emulsion tape and electronic counters has been developed for this work and used successfully. This is a first time in the world when 2 layers of emulsion tape has been used successfully. Currently, central interactions of ultra relativistic nucleus is the best way to explore the state of quarks and gluons. We tried to explore such a state through production characteristics of charm charm quarks in that state.200 A.GeV/c^<32>S beam accelerated at the CERN SPS was exposed to 100 mum thick target, Ag and Pb, to produce central interactions. AS a fraction of central interactions is only 10% of total, the ring counter was used to select central interactions effectively. PSD was used to measure beam position and a fiducial mark was printed on the emulsion tape to know the position of a selected interaction on … More the emulsion tape. Specially developed PSD was used to increase radiation hardness. The exposure was performed in 1990 August and we succeeded to recored 2 X 10^4 central interactions. About 500 events with charm production are expected in this sample by extraporating our result in ^<16>O - nucleus central interactions.In this experiment, charm decays between the target and the upstream emulsion tape are detected. About 400 charged secondary particles are produced in ^<32>S central interactions. It is not practical to examine all tracks if they are from decay vertecies because a lot of fake second vertecies due to the inaccuracy of measurement could be produced. Thus, as the decay daughters of charm particles has the impact parameter of the order of 100mum, reconstruction of decay vertecies is done only with tracks which have the impact parameter greater than the accuracy of the measurement. But, unfortunately, our ordinal micro scope stage could not be used because its accuracy of few micron was not enough to keep high detection efficiency of charm decays. Thus we developed much more accurate micro scope stage of about 0.3 mum accuracy for almost 1 year. The standard deviation of the impact parameter of tracks from the primary interaction is about 4 mum with this new microscope stage. Thus tracks with the impact parameter > 20 mum can be used to search decay vertecies. The efficiency to detect events with charm production is estimated to be 40 % in this case. It takes about 2.5 hours to finish 1 event with this stage.Systematic analysis with 2 micro scope stage was continued for 1 year. About 600 central interactions were measured and 11 events with charm candidate were found. This means that the production cross section per nucleon - nucleon interaction in ^<32>S - nucleus central interactions is about 15 mub and no statistically significant deviation from the nucleon - nucleon interaction was seen up tp now. A technical paper on the PSD has already been published. A technical paper on the emulsion tape is now under preparation and will soon be submitted to the Nuclear Instuments and Methods. Physics results will be published when we correct 2 time more statistics. Technical Knowledge and experience we obtained in the development of the accurate stage is now being adoped to the D_S * gamma detection in E653 experiments etc. Less