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A large solid-angle apparatus consisting of a superconducting solenoid magnet, cylindrical drift chambers, and two arrays of lead-glass counters is used to examine particles associated with a high transverse momentum trigger in pp interactions at the CERN ISR. The trigger is given by energy deposition in the lead-glass arrays centered at 90/sup 0/. Results on particle correlations and on jets are presented for interactions at .sqrt.s = 62.4 GeV and in the trigger transverse momentum range 3
The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) in Geneva, Switzerland, is capable of accelerating beams of protons (pp) and heavy-ions (Pb+Pb) up to nearly the speed of light, which corresponds to center of mass energies of 7 TeV and 2.76 TeV, respectively. The goal of the pp program is to investigate physics of and beyond the standard model, while the heavy-ion program attempts to characterize the properties of a new state of matter, called the Quark Gluon Plasma. The main aim of this dissertation is to identify particle production mechanisms in pp collisions, also as a reference for possible modifications due to the plasma formation in heavy-ion collisions. Two-particle azimuthal correlation measurements were employed, which allow the study of high-pT parton fragmentation without full jet reconstruction. We present the results of correlations between charged trigger particles and associated strange baryons and mesons. Enhancements of the azimuthal correlations are seen at dphi= 0 and dphi= pi, resulting from back-to-back jet fragmentation in the parton center-of-mass system. Two model fit functions were introduced to characterize the properties of the jet peaks. Hard and soft yields were seperated using the ZYAM method and extracted yields were compared with pQCD inspired models and inclusive spectra. The analysis was performed in different multiplicity bins to detect possible enhancements of baryons or meson yields and the baryon/meson ratio. The latter was observed in high multiplicity Pb+Pb collisions and interpreted as a novel production mechanism in the deconfined medium produced at the LHC. A novel data-driven feeddown correction for Lambda is also introduced, which could allow a more accurate calculation of the primary Xi.
In relativistic heavy ion collisions at the Large Hadron Collider (LHC), a hot, dense and strongly interacting medium known as the Quark Gluon Plasma (QGP) is produced. Quarks and gluons from incoming nuclei collide to produce partons at high momenta early in the collisions. By fragmenting into collimated sprays of hadrons, these partons form 'jets'. Within the framework of perturbative Quantum Chromodynamics (pQCD), jet production is well understood in pp collisions. We can use jets measured in pp interactions as a baseline reference for comparing to heavy ion collision systems to detect and study jet quenching. The jet quenching mechanism can be studied through the angular correlations of trigger jets with charged hadrons and is examined in transverse momentum bins of the trigger jets, transverse momentum bins of the associated hadrons, and studied as a function of collision centrality. A highly robust and precise background subtraction method is used in this analysis to remove the complex, flow dominated, heavy ion background. The analysis of angular correlations for different orientations of the trigger jet relative to the event plane allows for the study of the path length dependence of medium modifications to jets. The event plane dependence of azimuthal angular correlations of charged hadrons with respect to the axis of an R=0.2 reconstructed 'trigger' full (charged + neutral) jet in Pb--Pb collisions at [square root s subscript NN] 2.76 TeV in ALICE will be discussed. Results will be compared for three angular bins of the trigger jet relative to the event plane in mid-peripheral events. The status of jet yields and widths relative to the event plane will be discussed. There is no significant event plane dependence within the current uncertainties. Path length dependence of energy loss is seen to be a secondary effect to statistical fluctuations and in-medium energy loss mechanisms.
The 1979 Cargese Summer Institute on Quarks and Leptons was organized by the Universite Pierre et Marie Curie, Paris (M. LEVY and J.-L. BASDEVANT), CERN (M. JACOB), the Universite Catholi~ue de Louvain (D. SPEISER and J. WEYERS), and the Katholieke Universiteit te Leuven (R. GASTMANS), who, like in 1975 and 1977, had joined their efforts and worked in common. It was the 20th Summer Institute held at Cargese and the 5th one organized by the two institutes of theoretical physics at Leuven and Louvain-la Neuve. This time, the school was dominated by the impressive advances which were made in the field of perturbative ~uantum chromodyna mics and its applications to high energy phenomena involving strongly interacting particles. The unification of weak and electromagnetic interactions being well established, a new picture in particle physics emerges wherein a possible unification of weak, electromagnetic, and strong forces is put forward. Its conse~uences were also discussed in detail. Finally, to complete the picture of the present status of high energy physics, experi mentalists from the major laboratories around the world reported on the latest developments in electron-positron scattering, neutrino induced reactions, and hadron collisions. We owe many thanks to all those who have made this Summer Institute possible! Thanks are due to the Scientific Committee of NATO and its President for a generous grant and especially to the head of the Scientific Affairs Division, Dr. M. DI LULLO for his constant help and encouragements.