Collisionneur d'ions lourds relativistes

Résumé

vignette|Une section du collisionneur. Le Collisionneur d'ions lourds relativistes, ou RHIC (de l'anglais Relativistic Heavy Ion Collider), est un accélérateur de particules, construit au Laboratoire national de Brookhaven (situé à sur Long Island). Il est spécialisé dans des collisions entre ions lourds à vitesses relativistes (d’où son nom), afin d’étudier la forme primordiale de la matière qui existait dans l'Univers peu après le Big Bang. Il peut également produire des collisions entre protons pour l’étude de leur structure. Constitution Le RHIC est un collisionneur constitué de deux tubes indépendants concentriques, formant un anneau légèrement hexagonal d’une circonférence de 3834 mètres. Ces tubes sont équipés d’électroaimants supraconducteurs à base de niobium, et accélèrent des particules en sens inverse l’un par rapport à l’autre. Cette installation peut accélérer soit des noyaux lourds (de cuivre, d’or, ou d’uranium ) avec une énergie allant jusqu’à 100&

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Contribution of next-to-leading order and Landau-Pomeranchuk-Migdal corrections to thermal dilepton emission in heavy-ion collisions

Yannis Burnier, Chiara Gastaldi

Recently lots of effort has been made to obtain the next-to-leading-order and Landau-Pomeranchuk-Migdal corrections to the thermal dilepton emission rate in perturbative QCD. Here we apply these results to the plasma created in heavy-ion collisions and see whether these corrections improve the comparison between theoretical calculations and experimental results for the invariant mass dependence of the dilepton emission rate. In particular, we simulate the quark-gluon plasma produced at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory and the Large Hadron Collider at CERN using 2 + 1-dimensional viscous hydrodynamical simulations. We compare our results to those of the STAR experiment and comment on the need for a nonperturbative determination of the dilepton rate at low invariant mass.

Amer Physical Soc2016

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A particle beam is a collection of a large number of charges and represents an electromagnetic potential for other charges, therefore exerting forces on itself (space charge) and other beams (Beam-Beam Interactions, BBIs). The control of the BBIs in particle colliders is fundamental to preserve beam stability and achieve the optimum collider performance. In the case of the Large Hadron Collider (LHC) at CERN, these forces are experienced as localized periodic distortions when the two beams cross each other in the four experimental areas. The forces are most important for high density beams, i.e. high intensity and small beam sizes. Each LHC beam is composed of 2808 bunches, each containing 1011 protons and with a transverse size of 16 µm at the interaction points. These extreme parameters are the key to obtain high "luminosity", i.e. the number of collisions per second needed to study \rare" physics phenomena. The BBI is therefore often the limiting factor for the luminosity of colliders. Within all BB effects, this thesis covers coherent and incoherent beam-beam effects in hadron colliders with particular emphasis on those with a large number of bunches, like the LHC. Complementary numerical tools have been developed to study the effects of BBIs on the particle beams. The use of new parallel algorithms was fundamental to allow the scale of the calculations. The objectives are a better understanding of these effects and if necessary to propose changes to the LHC beam parameters to keep detrimental effects small. We have demonstrated the numerical predictibility of bunch to bunch differences and for the first time compared the results to analytical predictions and experimental data from the Relativistic Heavy Ion Collider (RHIC). Beam-beam transfer function measurements had been reproduced and understood in terms of coherent beam-beam modes. An implementation of the measurement devices had been suggested in order to avoid misinterpreted diagnostics. An emittance growth caused by the BBIs had been observed and characterized with numerical studies and explained with a simple physical picture. A study of the parametrical dependency of this effect defines qualitatively the expected limiting factors to avoid detrimental deterioration of the beams. The variation of the LHC tune spectra for different collision symmetries and in the presence of long range as well as head-on collisions had been presented and explained. This will be of fundamental importance to correctly interprete the observations of single bunch measurements during the operation of the collider and to improve the performances.

EPFL2008

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In-medium P-wave quarkonium from the complex lattice QCD potential

Yannis Burnier

We extend our lattice QCD potential based study [1] of the in-medium properties of heavy quark bound states to P-wave bottomonium and charmonium. Similar to the behavior found in the S-wave channel their spectra show a characteristic broadening, as well as mass shifts to lower energy with increasing temperature. In contrast to the S-wave states, finite angular momentum leads to the survival of spectral peaks even at temperatures, where the continuum threshold reaches below the bound state remnant mass. We elaborate on the ensuing challenges in de fining quarkonium dissolution and present estimates of melting temperatures for the spin averaged chi(b) and chi(c) states. As an application to heavy-ion collisions we further estimate the contribution of feed down to S-wave quarkonium through the P-wave states after freezeout.

Springer2016

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EPFL2008