Browsing by Author "Cleymans, Jean"
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- ItemOpen AccessApplications of extensive and non-extensive statistics to high energy physics(2021) Paradza, Masimba Welligton; Cleymans, Jean; Dominguez CesareoHeavy ion collisions produce nuclear matter at high temperatures and densities, to gain insights into this nuclear matter, we make use of statistical and thermal models to analyse the matter in the final state. A significant number of recent publications have shown that fits based on the Tsallis distribution give a good description of transverse momentum distributions measured at the Large Hadron Collider in p − p collisions. We set out to determine systematic behaviour of the parameters obtained and to gain theoretical insight in these. A detailed analysis is presented of the precise values of the Tsallis parameters obtained in p − p collisions for identified particles, pions, kaons and protons at the LHC at three beam energies √ s = 0.9, 2.76 and 7 TeV. Interpolated data at √ s = 5.02 TeV have also been included. It is shown that the Tsallis formula provides reasonably good fits to the pT distributions in p − p collisions at the LHC using three parameters dN/dy, T0 and q. However, the parameters T0 and q depend on the particle species and are different for pions, kaons and protons. As a consequence there is no mT scaling and also no universality of the parameters for different particle species. The thermodynamic parameters like energy density, pressure, entropy density, temperature and particle density are determined from the transverse momentum distributions of charged particles in Pb-Pb and Xe-Xe collisions at the LHC. The results show a clear increase with the centrality and the beam energy in all parameters. It is determined that in the final freeze-out stage the energy density reaches a value of about 0.039 GeV/fm3 for the most central collisions at √ sNN = 5.02 TeV. This is less than that at chemical freeze-out where the energy density is about 0.36 GeV/fm3 . This decrease approximately follows a T 4 law. The results for the pressure and entropy density are presented for each centrality class at √ sNN = 2.76 and 5.02 TeV for Pb-Pb collisions as well as at √ sNN = 5.44 TeV for Xe-Xe collisions. An analysis is made of the particle composition (hadrochemistry) of the final state in proton-proton p − p, proton-lead p−Pb and lead-lead Pb-Pb collisions as a function of the charged particle multiplicity (dNch/dη). The thermal model is used to determine the chemical freeze-out temperature as well as the radius and strangeness saturation factor γs . Abstract Three different ensembles are used in the analysis namely, the grand canonical ensemble, the canonical ensemble with exact strangeness conservation and the canonical ensemble with exact baryon number, strangeness and electric charge conservation. It is shown that for high multiplicities (at least 20 charged hadrons in the mid-rapidity interval considered) the three ensembles lead to the same results. Finally, most of the results discussed in this thesis have been published before in [1, 2, 3, 4, 5], in addition, results on Xe-Xe and chemical potential analysis are new in this thesis. I read and reviewed over 200 articles of which 130 made it into the final thesis. This extensive literature review allowed me to gain a broad overview of the basics of high energy physics, extensive and non-extensive statistics together with their applications in this field. I also became well-informed of the current research and this helped me to conceptualise and formulate the various research questions in his thesis. I searched for data using the references from the various articles and came up with a large data set covering as much scope as possible, representative enough to adequately address the questions I have raised. From the literature, I developed several macros to fit the data. To derive insights and to make a meaningful analysis of the data, I developed a methodology to systematically organize the data in pursuit of the research objectives, and to plot the relevant graphs from this large sample of data. From this, I prepared results tables together with the many relevant graphs presented in this thesis. I analysed the results in the tables and the figures and critically reflected on their meaning and finally derived the conclusions. After conducting the analysis, interpreting the results, I prepared the text for the draft manuscripts for all articles published. This thesis is written in a traditional way, so that I can expand on the details than in the articles. In the publications, I included tables and graphs depending on what I needed to highlight, and this thesis brings everything together. All this work was achieved under the guidance of my supervisors. The names on the articles do not appear in alphabetical order.
- ItemOpen AccessThe development and application of THERMUS : a statistical-thermal model analysis package for ROOT(2005) Wheaton, Spencer Miles; Cleymans, JeanA statistical-thermal model package, THERMUS, developed for incorporation into the ROOT framework of analysis, is presented. THERMUS, designed with applications to relativistic heavy-ion and elementary collisions of the baryon, strangeness and charge contents of he fireballs resulting from such collisions.
- ItemOpen AccessDevelopment of a high-level trigger for the dimuon spectrometer of the ALICE experiment at the large hadron collider(2006) Becker, Bruce; Vilakazi, Zeblon; Cleymans, JeanThe ALICE experiment at CERN's Large Hadronic Collider will mark the beginning of a new phase in the study of ultra-relativistic heavy ion-collisions. It will be possible to explore in great detail phenomena discovered or hinted at in the course of experiments at the Relativistic Heavy Ion Collider, in particular the signals of the quark-gluon plasma. One of the most promising signals of the creation of this new state of matter is the anomalous suppression of the Υ (bb) and J/v(cc) families. One of the main decay channels of these mesons is into dimuons and ALICE has a dedicated dimuon spectrometer in order to study the spectra of these interesting particles. The signal is, however, swamped by a large background from several other muonic sources. Due to the large data rate expected for ALICE and the limited bandwidth, a highly efficient and selective trigger is required for the experiment - the dimuon high-level trigger (dHLT). This thesis concerns the context, development and implementation of the ALICE dimuon high-level trigger. The physics context ot the experimentation is described, as well as the technical requirements of the system. The performance of the prototype is investigated with the use of Monte-Carlo simulations. An investigation into the performance estimates of system in the expected physics environment was performed, which validated the benchmarks, as well as investigation of the effect of possible modifications of quarkonia yields due to QGP formation on the response of the dHLT.
- ItemOpen AccessFinite-temperature quantum field theory and the structure functions of the nucleon(1992) Joubert, Jean; Cleymans, JeanThe deep inelastic scattering of leptons off a proton in the statistical model is considered. The interior of the nucleon is viewed as a thermalized assembly of up and down quarks and gluons. This enables the incorporation of features which are absent in the parton model. These include the presence of identical quarks and gluons in initial and final states and of quantum statistical correlations which have a role to play in the propagation of particles when considering Feynman diagrams containing internal lines in next-to-leading-order calculations. These features are incorporated through the use of Fermi-Dirac and Bose-Einstein distributions for quarks and gluons, respectively. Stimulated emission factors for final-state gluons and Pauli-blocking factors for final-state quarks are incorporated. The propagation of particles through a many-body medium is taken into account by using thermal Feynman rules for propagators and vertices. The statistical model could also be seen as an attempt to describe the interior of the nucleon at a more fundamental level than that attained through the use of arbitrary parton distributions containing many parameters in the parton model.
- ItemOpen AccessFlux corrected transport applied to hydrodynamics for heavy ion collisions(2008) Adams, Rory Montague; Cleymans, Jean; Muronga, AzwinndiniThis thesis presents FCTHydro, a ROOT package, and its application to hydrodynamic simulations through the packages RelHydro and Nonideal xy. These packages aim to provide the broader heavy ion collision community with access to hydrodynamic simulation software which is now accessible from within the primary analysis framework, ROOT. Tests are performed and show how well the high-order, monotone, conservative, positivity preserving routines within FCTHydro simulate hydrodynamic systems with harsh initial conditions. RelHydro illustrates the application of FCTHydro to relativistic systems and Nonideal xy the application to causal non-ideal hydrodynamic systems. Nonideal xy is also used to obtain a first order understanding of the effects of the relaxation times in causal non-ideal hydrodynamics. In addition, a semi-analytic solution for the particle rapidity spectra obtained by combining Landau hydrodynamics and the Cooper-Frye freezeout formalism is given. The results are compared with the Landau Gaussian and a known approximation for midrapidies. The Landau Gaussian provides the best approximation to experimental data. Furthermore, the chemical freezeout results for preliminary data from AGS for central Au-Au collisions at nominal beam energies 2, 4, 6 and 8 AGeV are shown to agree with the E/N = 1 GeV freezeout criteria. These data allow access to a previously unexplored region in the T-μB phase space.
- ItemOpen AccessHadronic gas description of relativistic heavy ion collisions incorporating exact conservation of quantum numbers(1997) Muronga, Azwinndini; Cleymans, JeanThe hadron production (especially kaon production) and the hadronic ratios (especially K/π) in heavy ion collisions are studied assuming that particles are produced in a hadron gas at both thermal and chemical equilibrium. The final state in relativistic ion collision is described by a hadronic gas model which is governed by two freeze out parameters, namely, temperature T and baryon density B/V. It is found that for large interaction volumes and/or large net baryon number, a description using the grand canonical ensemble could be justified. For a small system however, corrections arising solely from exact strangeness and baryon number conservation cannot be neglected. Analytic results for the partition function and the particle numbers are presented. A detailed numerical evaluation is made. A comparison of the behaviour of the results with the experimental information is made. A review of kaon production and K/π ratio and the comparisons of the hadron gas model with recent experimental results is made.
- ItemOpen AccessHeavy-flavour production at forward rapidity as a function of charged-particle multiplicity with ALICE at the LHC(2020) Mhlanga, Sibaliso; Cleymans, Jean; Buthelezi, ZinhleHeavy-flavour hadrons are hadrons made up of at least a charm or beauty heavy quark. They are produced in the early stages of ultra-relativistic collisions via hard scatterings and are important tools for studying different aspects of Quantum Chromodynamics (QCD) in hadronic collisions. Charged-particle multiplicity gives information on the global characteristics of the event and could be used to characterize particle production mechanisms. In hadronic collisions at Large Hadron Collider (LHC) energies, there is a significant contribution of Multiple Parton Interactions (MPI), i.e. several hard partonic interactions occurring in a single collision between nucleons. Therefore, the measurement of heavy-flavour hadrons as a function of charged-particle multiplicity gives insight into the mechanisms influencing their production in hadronic collisions at these energies and is a tool to test the influence of MPIs. Furthermore, charged-particle multiplicity dependence of heavy-flavour hadron production is used to test the ability of QCD theoretical models to reproduce data. In this thesis we investigate the production of heavy flavours via the single muon decay channel at forward rapidity as a function of the charged-particle multiplicity measured at central rapidity in proton-lead (p–Pb) collisions at √ sNN = 8.16 TeV using ALICE (A Large Ion Collider Experiment) at the LHC. ALICE is a dedicated detector optimized to study ultra-relativistic heavy-ion collisions in which the Quark-Gluon Plasma (QGP - the state of matter which prevailed in the Early Universe shortly after the Big Bang) is created. ALICE also studies proton-proton (pp) and p–Pb collisions. In pp collisions, production cross sections obtained from data provide information used to test pQCD theories while in p–Pb collisions, where the energy density is believed to be too low to produce the QGP, the presence of additional nuclear matter can alter the wavefunction of the nucleus leading to modified observables - the so-called cold nuclear matter (CNM) effects. The study of the multiplicity dependence of heavy-flavour production in p-Pb collisions may give important information regarding initial-state effects in CNM. Both pp and p– Pb collisions provide reference for comparison with heavy-ion (Pb–Pb) collisions. ALICE measures hadrons, leptons, and photons up to very high transverse momentum (pT) ≈100 GeV/c. The detector consists of a central barrel, which covers a rapidity of |y| < 1 and a Muon Spectrometer which covers the forward rapidity, -4 < y < -2.5. In this thesis, the production of heavy flavours via the contribution of their muonic decays to the inclusive pT-differential muon yield at forward (2.03 < ycms < 3.53) and backward (-4.46 < ycms < -2.96) rapidity reconstructed with the Muon Spectrometer and charged-particle multiplicity using the Silicon Pixel Detector located in the central barrel (|y| <1) in p-Pb collisions at √ sNN = 8.16 TeV in the forward and backward rapidity are studied. The aim of the study is to probe the role of MPIs in the production of heavy flavours focusing on the contribution of hard and soft processes as well as to investigate effects of the presence of multiple binary nucleon-nucleon interactions and the initial state effects modified by CNM in particle production.
- ItemOpen AccessIntroduction to lattice gauge theories(1988) La Cock, Pierre; Cleymans, JeanThe thesis is organized as follows. Part I is a general introduction to LGT. The theory is discussed from first principles, so that for the interested reader no previous knowledge is required, although it is assumed that he/she will be familiar with the rudiments of relativistic quantum mechanics. Part II is a review of QCD on the lattice at finite temperature and density. Monte Carlo results and analytical methods are discussed. An attempt has been made to include most relevant data up to the end of 1987, and to update some earlier reviews existing on the subject. To facilitate an understanding of the techniques used in LGT, provision has been made in the form of a separate Chapter on Group Theory and Integration, as well as four Appendices, one of which deals with Grassmann variables and integration.
- ItemOpen AccessJ / ( ) production in heavy ion collisions at the STAR detector at RHIC(2012) Powell, Christopher Beresford; Cleymans, Jean; Peshier, AndreThe success of the Standard Model of particle physics in describing a large variety of experimental results has been supported by the prediction and subsequent discovery of the charm, bottom, and top quarks, and the Z, W±, and Higgs bosons. The theory of Quantum Chromodynamics (QCD), which describes the strong interaction between quarks and gluons in the Standard Model, predicts a phase transition from hadronic matter to a deconfined Quark Gluon Plasma (QGP) at high temperature and energy density. The Relativistic Heavy Ion Collider (RHIC) was built to achieve these conditions to test the predictions of QCD and understand the properties of a deconfined medium. Charm (c) quarks have been suggested as ideal probes of the medium created in heavy ion collisions, as they are created primarily in the initial hard scattering of the collision because of their large mass.
- ItemOpen AccessThe quark-hadron transition and hot hadronic matter in the early universe(1987) Von Oertzen, Detlof Wilhelm; Rafelski, Johann; Cleymans, JeanVarious calculations· 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 AccessThe reconstruction of high-pt photons with the electromagnetic calorimeter of the ALICE experiment at the LHC.(2005) Gray, Heather M; Cleymans, JeanCareful jet and jet quenching analyses require calibration with the parton energy prior to its passage though the nuclear matter. This can only be obtained via analysis of y-jet processes because photons, once produced, are essentially unaffected by a colour-charged medium, and pass through the medium retaining their original energy. The experimental challenges include identifying photons within the high multiplicity heavy-ion environment and reducing the background from the photonic decays of neutral pions. This thesis details algorithms developed for photon reconstruction in the heavy-ion environment for the electromagnetic calorimeter (EMCal) of the ALICE experiment. Shower shape analysis was used to optimise cuts to discriminate between the direct photon signal and the background from the photonic decays of neutral pions.
- ItemOpen AccessA review of the Landau-Pomeranchuk-Migdal effect(1995) Roscherr, Bruce; Cleymans, JeanThe Bethe-Heitler formula is the correct expression for the energy radiated in the form of bremsstrahlung when a charged particle interacts in isolation with the Coulomb field of a nucleus. When the effects of multiple scattering are taken into account, however, the formula needs modification. This is the Landau-Pomeranchuk-Migdal effect. We review here several approaches for the calculation of the revised spectrum and compare the results with experiment.
- ItemOpen AccessStatistical distributions in the thermal model(2006) Hauer, Michael; Cleymans, JeanAn attempt is made to use the thermal model to determine statistical particle number fluctuations in the presence of exact conservation laws. A basis is provided, which will be useful to extend the range of applications of the thermal model with both a large number of conserved charges as well as quantum statistics. The central limit theorem and its related expansions provide a flexible mathematical tool for calculation of statistical fluctuations, and allows for application of the canonical ensemble to high energy particle collision data. A first analysis of the NA49 CC data suggests that statistical multiplicity fluctuations can be understood within the statistical hadronization model.
- ItemOpen AccessStatistical models to describe nuclear matter at high temperatures and densities(2011) Worku, Dawit Solomon; Cleymans, JeanIn order to understand nuclear matter at high temperatures and densities formed in heavy ion collisions, it is useful to use statistical-thermal models to analyse the final state. We apply different types of statistical distributions and discuss their effects. We discuss the hadron resonance gas model and its extension to include the Hagedorn spectrum [1, 2, 3]. The Hagedorn temperature, TH is determined from the number of hadronic resonances including all mesons and baryons. This leads to the result TH = 174±1l MeV consistent with the critical and the chemical freeze-out temperatures at zero chemical potential. We apply this result to calculate the speed of sound and other thermodynamic quantities in the resonance hadron gas model for a wide range of baryon chemical potentials using the chemical freeze-out curve [4, 5]. We compare some of our results to those obtained previously [6, 7]. We have also made additions to THERMUS [8] by including charm and bottom hadrons from the particle data table . Then, we analyze and discussthe hadronic abundances measured in proton-proton (p-p), gold-gold (Au-Au) and lead-lead (Pb-Pb) collisions at Relativistic Heavy-Ion Collider (RHIC) [10] and Large Hadron Collider (LHC) [11, 12, 13] experiments using THERMUS. The THERMUS results obtained with the 2002 particle data table and new particle data table (2008 particle data table) and their differences are discussed. In particular, the data from the RHIC experiment for Au-Au collisions at 130 GeV and 200 GeV [10] are discussed and analyzed. Similarly, using the preliminary particle yield results of p-p collisions at 0.9 TeV and 7 TeV as well as Pb-Pb collision at 2.76 TeV [11, 12, 13l are presented and the thermodynamic parameters are obtained from the fit are discussed.
- ItemOpen AccessStatistical-thermodynamical analysis, using Tsallis statistics, in high energy physics(2014) Whitehead, Andile; Cleymans, JeanObtained via the maximisation of a modified entropy, the Tsallis distribution has been used to fit the transverse momentum distributions of identified particles from several high energy experiments. We propose a form of the distribution described in Cleymans and Worku, 2012, and show it to be thermodynamically consistent. Transverse momenta distributions and fits from ALICE, ATLAS, and CMS using both Tsallis and Boltzmann distributions are presented.
- ItemOpen AccessStrangeness excitation functions and transition from baryonic to mesonic freeze-out(2009) Cleymans, Jean; Oeschler, Helmut; Redlich, Krzysztof; Wheaton, SpencerThe sharp peak in the K+/π+ ratio in relativistic heavy-ion collisions is discussed in the framework of the Statistical Model. In this model a rapid change is expected as the hadronic gas undergoes a transition from a baryon-dominated to a meson-dominated gas. The maximum in the Λ/π ratio is well reproduced by the Statistical Model, but the change in the K+/π+ ratio is somewhat less pronounced than the one observed by the NA49 collaboration. The calculated smooth increase of the K−/π− ratio and the shape of the Ξ−/π+ and Ω−/π+ ratios exhibiting maxima at different incident energies is consistent with the presently available experimental data. We conclude that the measured particle ratios with 20 − 30% deviations agree with a hadronic freeze-out scenario. These deviations seem to occur just in the transition from baryon-dominated to meson-dominated freeze-out.
- ItemOpen AccessThermal modelling of ultrarelativistic heavy ion collisions conserving strangeness exactly(2003) Marais, Mark; Cleymans, Jean[ pg 56-60,87,88 missing] Thermal modelling of particle production in ultrarelativistic heavy ion collisions incorporating appropriate conservation principles with respect to the relevant quantum numbers, has been highly successful in determining chemical freeze-out conditions across a wide range of beam energies. This is done for heavy-ion collisions in the broad range of energy from SIS/GSI through AGS/BNL up to BPS/CERN and RHIC/BNL, assuming that particles can be described by a hadron gas in thermal and chemical equilibrium. The role of strangeness conservation and strangeness equilibration is a central feature in our considerations. Fits to the data from collaborations at the above facilities, and, comparisons with analysis done by other authors, are made. Energy dependence of the chemical freeze-out parameters is studied and, recently proposed criteria for freeze-out in terms of energy per particle and total baryon density are investigated. The chemical freeze-out trajectory is compared with the phase boundary between the hadron gas phase and the quark-gluon plasma in the temperature versus baryochemical potential plane.
- ItemOpen AccessTransport coefficients in quantum chromodynamics(1990) Von Oertzen, Detlof Wilhelm; Cleymans, JeanRelativistic kinetic theory provides a transport equation for classical, spinless, colored particles in a non-Abelian external field. We review the methods of solution used in the literature to find the transport coefficients for quark and gluon systems. Most authors use the relaxation time approximation of the Boltzmann equation to compute the transport coefficients, but this method has shortcomings in mixtures. We use the Chapman Enskog (CE) method to solve the classical transport equations for quarks and gluons for the transport coefficients. The differential crosssections describing the particle interaction are obtained from the lowest order scattering diagrams of quantum chromodynamics. We study a pure quark system, a pure gluon system and a quark antiquark (qq) mixture. For mixtures of quarks, antiquarks and gluons, we find the shear viscosity, heat conductivity and cross-coefficients. The coefficients pertaining to qq mixtures, namely the thermal diffusion, diffusion and Dufour coefficient, the viscosities and heat conductivity are obtained and the conductivity of a qq mixture in an external field is computed. We compare our transport coefficients to others in the literature by rewriting them in terms of characteristic relaxation times. Although our results are generally larger than others, they are of the same order of magnitude, with important implications for quark-gluon (QG) plasma signatures. The quark to gluon shear viscosity ratio is found to be ~5 times the number of quark flavors, emphasising the importance of quarks in dynamical QG calculations. The coefficients for a field-free qq mixture indicate no qq separation in the presence of a temperature gradient. In the CE method, the transport coefficients depend naturally on a logarithmic factor due to the divergent scattering cross-sections, reflecting the plasma shielding effects. This logarithm is evaluated by relating it to typical plasma parameters. We apply our results to the QG phase in the early universe and ultra-relativistic heavy ion collisions. A comparison of the QG to pion transport coefficients at the quark-hadron phase transition shows that the latter are ~10³ smaller. Dissipative effects increase the plasma lifetime, resulting in a longer high energy density and temperature plasma phase.
- ItemOpen AccessTsallis Statistics in High Energy Physics: Chemical and Thermal Freeze-Outs(2020-12-04) Cleymans, Jean; Paradza, Masimba WellingtonWe present an overview of a proposal in relativistic proton-proton (pp) collisions emphasizing the thermal or kinetic freeze-out stage in the framework of the Tsallis distribution. In this paper we take into account the chemical potential present in the Tsallis distribution by following a two step procedure. In the first step we used the redudancy present in the variables such as the system temperature, T, volume, V, Tsallis exponent, q, chemical potential, µ, and performed all fits by effectively setting to zero the chemical potential. In the second step the value q is kept fixed at the value determined in the first step. This way the complete set of variables T, q, V and µ can be determined. The final results show a weak energy dependence in pp collisions at the centre-of-mass energy √ s = 20 TeV to 13 TeV. The chemical potential µ at kinetic freeze-out shows an increase with beam energy. This simplifies the description of the thermal freeze-out stage in pp collisions as the values of T and of the freeze-out radius R remain constant to a good approximation over a wide range of beam energies.