Academic literature on the topic 'Montecarlo for heavy-ion collisions'

The results of the full next-to-leading-order calculation of open charm production cross section, via hard parton scattering, for both hadronic and heavy-ion collisions at RHIC and LHC energies are presented. In addition to the total cross section, the transverse momentum and rapidity distributions are included. An effective K-factor which encapsulates the next-to-leading-order corrections and the nuclear effects is presented. The open charm yield will be measured through the correlated dileptons produced when the charm decays. An important background comes from the decay of bottom quarks. Therefore, the open bottom yield from hard parton scatterings is presented. The first next-to-leading-order calculation of the thermal heavy quark production is presented, as well as the dimuon spectrum from both the thermal and the initial fusion charm and bottom production at RHIC energies.

In this dissertation, the phenomenology of electromagnetic radiation and high transverse momentum jets in relativistic heavy ion collisions is investigated. These are two very important probes to study the strongly interacting matter at extreme temperatures and/or densities and to investigate the possibility of a phase transition between hadronic matter and quark-gluon plasma (QGP). First, a new channel of direct photon production from a charge-asymmetric QGP is explored in the effective theory of quantum chromodynamics (QCD) at high temperature. The photon production from this new channel is found to be suppressed compared to QCD annihilation process and Compton scattering at low baryon density, but might assume significance in baryon-rich matter. Second, the radiative jet energy loss in a three-dimensional ideal hydrodynamical medium is studied for Au+Au collisions at Relativistic Heavy Ion Collider (RHIC). A systematic analysis of the nuclear modification factor RAA is presented for pi0 production at high pT in central and non-central collisions, at mid and forward rapidity. Third, jet energy loss by elastic collisions is consistently incorporated in the same formalism and applied to the study of jet quenching at RHIC. It is found that the nuclear modification factor RAA for pi0 in relativistic heavy ion collisions is sensitive to both collisional and radiative energy loss, while the average energy loss is less affected by the inclusion of collisional energy loss. Last, the nuclear suppression of photon-tagged jets at high pT is studied by incorporating not only direct photons, but the additional sources from fragmentation and jet-plasma interaction. We find that these additional sources are very important for a complete study of the correlations between hard photons and hadrons and even dominate in some kinetic regime.

<p> Fluctuations are one of the main probes of the physics of the new state of hot and dense nuclear matter called the Quark Gluon Plasma (QGP) which is created in the ultra-relativistic heavy ion collisions. In this dissertation we extend and improve upon the existing descriptions of heavy ion collisions in three different directions: we study the new signatures of initial state fluctuations, the propagation of perturbations in the early stages of the collision, and the effect of thermal fluctuations on the hydrodynamic expansion of the QGP. </p><p> First, in Chapter 3 we study initial state fluctuations by examining the complete statistical information contained in the two-particle correlation measurements in hydrodynamic simulations of Pb+Pb collisions at the CERN Large Hadron Collider (&radic;<i>s_NN</i> = 2.76 TeV). We use Principal Component Analysis (PCA) to decompose the spectrum of harmonic flow, v_n(p_T) for <i>n</i> = 0&ndash;5, into dominant components. The leading component is identified with the standard event plane <i> v_n</i>(<i>p_T</i>), while the subleading component describes additional fluctuations in the two-particle correlation function. We find good geometric predictors for the orientation and the magnitude of the leading and the subleading flows. The subleading <i>v</i>₀, <i>v</i>₁, and <i>v</i>₃ flow harmonics are shown to be a response to the radial excitation of the corresponding eccentricity &epsiv;<i>_n</i>. In contrast, for <i>v</i>₂ the subleading flow in peripheral collisions is dominated by the nonlinear mixing between the leading elliptic flow and radial flow fluctuations. Nonlinear mixing also plays a significant role in generating subleading <i>v</i>₄ and <i>v</i>₅ harmonics. The PCA gives a systematic way of studying the full information of the two-particle correlation matrix and identifying the subleading flows, which we show are responsible for factorization breaking in hydrodynamics. </p><p> Second, in Chapter 4 we study the thermalization and hydrodynamization of fluctuations at the early stages of heavy ion collisions. We use leading order effective kinetic theory, accurate at weak coupling, to simulate the pre-equilibrium evolution of transverse energy and flow perturbations. For the short evolution we can use a linear response theory to construct the pre-equilibrium Green functions. Then the energy-momentum tensor at a time when hydrodynamics becomes applicable can be expressed as a linear convolution of response functions with the initial perturbations. We propose combining effective kinetic theory with weak coupling initial state models, such as IP-Glasma, to model the complete pre-thermal evolution from saturated nuclei to hydrodynamics in a weak coupling framework. </p><p> Last, in Chapter 5 we consider out-of-equilibrium hydrodynamic fluctuations in the expanding QGP. We develop a set of kinetic equations for a correlator of thermal fluctuations which are equivalent to nonlinear hydrodynamics with noise. We first show that the kinetic response precisely reproduces the one-loop renormalization of the shear viscosity for a static fluid. We then use the hydro-kinetic equations to analyze thermal fluctuations for a Bjorken expansion. The steady state solution to the kinetic equations determine the coefficient of the first fractional power of the gradient expansion (&infin; 1/(&tau;<i> T</i>)^3/2), which was computed here for the first time. The formalism of hydro-kinetic equations can be applied to more general background flows and coupled to existing viscous hydrodynamic codes to incorporate the physics of hydrodynamic fluctuations.</p><p>

We investigate and compare two field theoretical formalisms, namely, the former state-of-the-art but noncovariant Ruckl formula-based formalism developed by K. Haglin and C. Gale, and a more recent covariant formalism developed by P. Lichard, for lepton pair production via soft virtual bremsstrahlung in hadronic reactions. A quantitative study of the discrepancy between both formalisms with regard to rates and total yields of $e sp{+}e sp{-}$ and $ mu sp{+} mu sp{-}$ pair production from radiative pion and quark (antiquark) scattering in ultrarelativistic heavy-ion collisions is made. Dilepton production rates are calculated using the independent particle approximation from kinetic theory, and total dilepton yields are obtained by integrating these rates over the space-time evolution of the heavy-ion collision as dictated by Bjorken's longitudinal hydrodynamic model. All rates and total yields of $e sp{+}e sp{-}$ and $ mu sp{+} mu sp{-}$ pair production with invariant masses less than 300 MeV turn out to be overestimated in the Ruckl formula-based formalism.