118150495
Quarks production in the quark–gluon plasma created in relativistic heavy ion collisions
Abstract In this article we report our results about quark production and chemical equilibration of quark–gluon plasma. Our initial condition corresponds to a classic Yang–Mills spectrum, in which only gluon degrees of freedom are considered; the initial condition is then evolved to a quark–gluon plasma by means of relativistic transport theory with inelastic processes which permit the conversion of gluons to q q ¯ pairs. We then compare our results to the ones obtained with a standard Glauber model initialization. We find that regardless of the initial condition the final stage of the system contains an abundant percentage of q q ¯ pairs; moreover spanning the possible coupling from weak to strong we find that unless the coupling is unrealistically small, both production rate and final percentage of fermions are quite large.
119459213
Pentaquark baryon production at the relativistic heavy ion collider
Abstract Production of pentaquark Θ + baryons in central relativistic heavy ion collisions is studied in a kinetic model. Assuming that a quark–gluon plasma is produced in the collisions, we first determine the number of Θ + produced from the quark–gluon plasma using a parton coalescence model, and then take into consideration its production and absorption in subsequent hadronic matter via the reactions K N ↔ Θ , K N ↔ π Θ and π N ↔ K ¯ Θ . We find that although the final Θ + number is affected by hadronic interactions, it remains sensitive to the initial number of Θ + produced from the quark–gluon plasma, particularly in the case of a small Θ + width as imposed by the K + N and K + d scattering data. Because of small baryon chemical potential in the hot dense matter produced in these collisions, the number of produced anti- Θ is only slightly smaller than that of Θ + .
118564693
Renormalized vs. nonrenormalized chiral transition in a magnetic background
A bstractWe study analytically the chiral phase transition for hot quark matter in presence of a strong magnetic background, focusing on the existence of a critical point at zero baryon chemical potential and nonzero magnetic field. We build up a Ginzburg-Landau effective potential for the chiral condensate at finite temperature, computing the coefficients of the expansion within a chiral quark-meson model. Our conclusion is that the existence of the critical point at finite B is very sensitive to the way the ultraviolet divergences of the model are treated. In particular, we find that after renormalization, no chiral critical point is present in the phase diagram. On the other hand, such a critical point there exists when the ultraviolet divergences are not removed by a proper renormalization of the thermodynamic potential.
119235890
Shear viscosity and chemical equilibration of the QGP
We have investigated, in the frame work of the transport approach, different aspects of the QGP created in Heavy Ion Collisions at RHIC and LHC energies. The shear viscosityhas been calculated by using the Green-Kubo relation at the cascade level. We have compared the numerical results forobtained from the Green-Kubo correlator with the analytical formula in both the Relaxation Time Approximation (RTA) and the Chapman-Enskog approximation (CE). From this comparison we show that in the range of temperature explored in a Heavy Ion collision the RTA underestimates the viscosity by about a factor of 2, while a good agreement is found between the CE approximation and Gree-Kubo relation already at first order of approximation. The agreement with the CE approximation supplies an analytical formula that allows to develop kinetic transport theory at fixed shear viscosity to entropy density ratio, ´/s. We show some results for the build up of anisotropic flows v2 in a transport approach at fixed shear viscosity to entropy density ratio, ´/s. We study the impact of a T-dependent ´/s(T ) on the generation of the elliptic flows at both RHIC and LHC. We show that the transport approach provides, in a unified way, a tool able to naturally describe the v2(pT ) in a wide range of pT , including also the description of the rise and fall and saturation of the v2(pT ) observed at LHC. Finally, we have studied the evolution of the quark-gluon composition employing a Boltzmann-Vlasov transport approach that include: the mean fields dynamics, associated to the quasi-particle model, and the elastic and inelastic collisions for massive quarks and gluons. Following the chemical evolution from an initial gluon dominated plasma we predict a quark dominance close to TC paving the way to an hadronization via quark coalescence.
119263837
Heavy Flavor Suppression: Boltzmann vs Langevin
The propagation of heavy flavor through the quark gluon plasma has been treated commonly within the framework of Langevin dynamics, i.e. assuming the heavy flavor momentum transfer is much smaller than the light one. On the other hand a similar suppression factor RAA has been observed experimentally for light and heavy flavors. We present a thorough study of the approximations involved by Langevin equation by mean of a direct comparison with the full collisional integral within the framework of Boltzmann transport equation. We have compared the results obtained in both approaches which can differ substantially for charm quark leading to quite different values extracted for the heavy quark diffusion coefficient. In the case of bottom quark the approximation appears to be quite reasonable.
23741379
Effects of symmetry energy on two-nucleon correlation functions in heavy-ion collisions induced by neutron-rich nuclei.
Using an isospin-dependent transport model, we study the effects of nuclear symmetry energy on two-nucleon correlation functions in heavy-ion collisions induced by neutron-rich nuclei. We find that the density dependence of the nuclear symmetry energy affects significantly the nucleon emission times in these collisions, leading to larger values of two-nucleon correlation functions for a symmetry energy that has a stronger density dependence. Two-nucleon correlation functions are thus useful tools for extracting information about the nuclear symmetry energy from heavy-ion collisions.
120345606
The TOTEM GEM Telescope (T2) at the LHC
The TOTEM T2 telescope will measure inelastically produced charged particles in the forward region of the LHC Interaction Point 5. Each arm of the telescope consists in a set of 20 triple-GEM (Gas Electron Multiplier) detectors with tracking and trigger capabilities. The GEM technology has been considered for the design of TOTEM very forward T2 telescopes thanks to its characteristics: large active areas, good position and timing resolution, excellent rate capability and radiation hardness. Each of the four T2 half arms has been fully assembled and equipped with electronics at CERN and systematically tested in the SPS beam line H8 in 2008/09. After some optimization, the operation of the GEM chambers was fully satisfactory and the T2 telescopes were installed and commissioned in their final positions at the LHC interaction point. During the first LHC run (December 2009) the T2 telescopes have collected data, at 900 GeV and 2.36 TeV. We will present here the performances of the detector and the preliminary results obtained using the data collected.
67834315
Luminosity-independent measurements of total, elastic and inelastic cross-sections at $\sqrt{s}$ = 7 TeV
The TOTEM experiment at the LHC has performed the first luminosity-independent determination of the total proton-proton cross-section at . This technique is based on the optical theorem and requires simultaneous measurements of the inelastic rate – accomplished with the forward charged-particle telescopes T1 and T2 in the range 3.1 < |η| < 6.5 – and of the elastic rate by detecting the outcoming protons with Roman Pot detectors. The data presented here were collected in a dedicated run in 2011 with special beam optics (β* = 90 m) and Roman Pots approaching the beam close enough to register elastic events with squared four-momentum transfers |t| as low as 5·10−3 GeV2. The luminosity-independent results for the elastic, inelastic and total cross-sections are σel = (25.1 ± 1.1) mb, σinel = (72.9 ± 1.5) mb and σtot = (98.0 ± 2.5) mb, respectively. At the same time this method yields the integrated luminosity, in agreement with measurements by CMS. TOTEM has also determined the total cross-section in two complementary ways, both using the CMS luminosity measurement as an input. The first method sums the elastic and inelastic cross-sections and thus does not depend on the ρ parameter. The second applies the optical theorem to the elastic-scattering measurements only and therefore is free of the T1 and T2 measurement uncertainties. The methods, having very different systematic dependences, give results in excellent agreement. Moreover, the ρ-independent measurement makes a first estimate for the ρ parameter at possible: |ρ| = 0.145 ± 0.091.
117874201
First Results from the TOTEM Experiment
Visitor from an external Institution.The ﬁrst physics results from the TOTEM experiment are here reported,concerning the measurements of the total, diﬀerential elastic, elastic and in-elastic pp cross-section at the LHC energy of√s = 7 TeV, obtained using theluminosity measurement from CMS. A preliminary measurement of the forwardcharged particle η distribution is also shown.PRESENTED AT
47564335
Level-2 Calorimeter Trigger Upgrade at CDF
The CDF Run II level-2 calorimeter trigger is implemented in hardware and is based on a simple algorithm used in Run I. This system has worked well for Run II at low luminosity. However, as the Tevatron instantaneous luminosity increases, the limitation due to the simple algorithm starts to become clear. In this paper, we will present an upgrade path to the level-2 calorimeter trigger system at CDF. This upgrade approach is based on the Pulsar board, a general purpose VME board developed at CDF and used for upgrading both the level-2 tracking and the Level-2 global decision crate. This paper will describe the design, hardware and software implementation, as well as the advantages of this approach over the existing system.
122038644
The TOTEM T2 telescope based on triple-GEM chambers
Abstract The TOTEM experiment at LHC has chosen the triple Gas Electron Multiplier (GEM) technology for its T2 telescope which will provide charged track reconstruction in the pseudorapidity range 5.3 | η | 6.5 and a fully inclusive trigger for inelastic events. GEMs are gas filled detectors which combine good spatial resolution with very high rate capability and a good resistance to radiation. Preliminary results of cosmic ray tests performed at CERN on final T2 modules before installation are here presented. Comparisons between real and simulated detector performance are also shown.