### Browsing by Subject "Hadrons"

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- ItemOpen AccessCentrality dependence of particle production in pāPb collisions at āsNN= 5.02 TeV(2015) Adam, J; AdamovĆ”, D; Aggarwal, M M; Aglieri Rinella, G; Agnello, M; Agostinelli, A; Agrawal, N; Ahammed, Z; Ahmed, I; Ahn, S U; Aimo, I; Aiola, S; Ajaz, M; Akindinov, A; Alam, S N; Aleksandrov, D; Alessandro, B; Alexandre, D; Alfaro Molina, R; Alici, A; Alkin, A; Alme, J; Alt, T; Altinpinar, S; Altsybeev, I; Alves Garcia Prado, C; Andrei, C; Andronic, A; Anguelov, V; Anielski, J; AntiÄiÄ, T; Antinori, FWe report measurements of the primary charged particle pseudorapidity density and transverse momentum distributions in pāPb collisions at āsNN = 5.02 TeV, and investigate their correlation with experimental observables sensitive to the centrality of the collision. Centrality classes are defined using different event activity estimators, i.e. charged particle multiplicities measured in three different pseudorapidity regions as well as the energy measured at beam rapidity (zero-degree). The procedures to determine the centrality, quantified by the number of participants (Npart), or the number of nucleon-nucleon binary collisions (Ncoll), are described. We show that, in contrast to PbāPb collisions, in pāPb collisions large multiplicity fluctuations together with the small range of participants available, generate a dynamical bias in centrality classes based on particle multiplicity. We propose to use the zero-degree energy, which we expect not to introduce a dynamical bias, as an alternative event-centrality estimator. Based on zero-degree energy centrality classes, the Npart dependence of particle production is studied. Under the assumption that the multiplicity measured in the Pb-going rapidity region scales with the number of Pb-participants, an approximate independence of the multiplicity per participating nucleon measured at midrapitity of the number of participating nucleons is observed. Furthermore, at high-pT the pāPb spectra are found to be consistent with the pp spectra scaled by Ncoll for all centrality classes. Our results represent valuable input for the study of the event activity dependence of hard probes in pāPb collision and, hence, help to establish baselines for the interpretation of the PbāPb data.
- ItemOpen AccessThe quark-hadron transition and hot hadronic matter in the early universe(1987) Von Oertzen, Detlof Wilhelm; Rafelski, Johann; Cleymans, JeanVarious calculationsĀ· of the evolution of the hadron gas in the early universe are carried out. To determine the starting point for the evolution equations a phase transition between the quark-gluon plasma phase and the hadron gas phase is constructed. A simple calculation leads to an estimate of the chemical potential of baryons at the quark-hadron phase transition in the early universe. We investigate how the transition temperature depends on the equations of state for the bagged quark and the hadron phase. A particle density evolution model is introduced which predicts the temperature at which particle species drop out of equilibrium (freeze-out) in an expanding universe. We then construct dynamical evolution equations to describe the reactions of interacting pions and photons. In order to model a more realistic hadron gas, we include kaons and finally nucleons and hyperons into the model universe. The results indicate that this type of model should be extended to include more interacting particle species and that a more realistic evolution model is dependent on obtaining accurate reaction cross-sections.
- ItemOpen AccessQuarks and hadrons on the lattice(1990) Boyd, Graham John; Cleymans, JeanThere is a short introduction to the ideas of lattice theory, followed by an equally brief look at pure gauge QCD on the lattice. More details for either of these may be found in the references cited in each section, as well as in [143]. The bulk of this work deals with the problems encountered in placing fermions on to the lattice, and the techniques used for this purpose. The Nielsen-Ninomiya theorem is introduced, with a detailed treatment thereof relegated to an appendix. The two main fermion techniques, due to Wilson (1974); and Kogut and Susskind (1975) are dealt with in some detail. This is followed by a discussion of the construction of hadrons on the lattice, using either Wilson or Kogut-Susskind fermions. There is a chapter covering the algorithms used in numerical simulations of lattice QCD, with some examples illustrating them. The thesis concludes with a discussion of the results obtained thus far on the hadron spectrum, in both the quenched approximation as well as those obtained using dynamical quarks.
- ItemOpen AccessA review and application of the Hadron gas model to heavy ion collisions(1996) Elliott, Duncan MarkA review and application of the Hadron Gas model to data gathered from heavy ion collision experiments in search of the Quark Gluon Plasma. The Hadron Gas model is extended by ensuring overall charge conservation of the collision system at freeze-out. Conclusions of thermal and chemical equilibrium at freeze-out are drawn from an analysis of the data of Si-Au collisions at BNL-AGS, and compared with the literature on thermal analyses of Si-Au collisions.