17318327
Hadronization via coalescence
We review the quark coalescence model for hadronization in relativistic heavy ion collisions and show how it can explain the observed large baryon to meson ratio at intermediate transverse momentum and scaling of the elliptic flows of identified hadrons. We also show its predictions on higher-order anisotropic flows and discuss how quark coalescence applied to open- and hidden-charm mesons can give insight to charm quark interactions in the quark–gluon plasma and J/Ψ production in heavy ion collisions.
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.
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.
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.
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 + .
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.
40642633
Level-3 calorimeter resolution available for the Level-1 and Level-2 CDF triggers
As the Tevatron luminosity increases more sophisticated selections are required to be efficient in selecting rare events from a very huge background. To cope with this problem, CDF has pushed the Level-3 calorimeter algorithm resolutions up to Level-2 and, when possible, at Level-1, increasing efficiency and, at the same time, keeping under control the rates. This strategy increases the purity of the Level-2 and Level-1 samples, produces free-bandwidth that allows to reduce the thresholds. The global effect is an increase of the signal efficiency of important Tevatron Standard Model Higgs search channels (H → WW, ZH, WH). The L2 upgrade improves the cluster finding algorithm, the resolution of the Missing Transverse Energy (MET) and the SUM Transverse Energy (SUMET) calculations. The same Level-2 MET and SUMET improved resolution has been made available to the Level-1 system, exploiting the same hardware used for the Level-2 upgrade. The upgrade is based on the Pulsar board, a general purpose VME board developed at CDF and already used for upgrading both the Level-2 tracking and the Level-2 global decision crate. The Level-2 upgrade has been designed, built, tested and commissioned in six months. It was accepted as the default system for CDF in August 2007. The same Level-2 hardware can be used in such a way to provide the Level-1 calorimeter system of the same MET, SUMET resolution provided to Level-2. While in the upgraded Level-2 system the algorithms are executed in a commercial CPU within the typical Level-2 processing timing of 20 μs, in the upgraded Level-1 system, MET and SUMET are calculated by powerful FPGAs within 5 μs. The Level-1 upgrade is currently ongoing and in commissioning phase.We describe the CDF Level-2 and the new Level-1 calorimeter upgrades, the architecture and the trigger performances, with particular emphasis on a new calorimeter MET_JET-based trigger performances used for CDF Higgs search.
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
22796813
Double diffractive cross-section measurement in the forward region at the LHC.
The first double diffractive cross-section measurement in the very forward region has been carried out by the TOTEM experiment at the LHC with a center-of-mass energy of sqrt[s]=7  TeV. By utilizing the very forward TOTEM tracking detectors T1 and T2, which extend up to |η|=6.5, a clean sample of double diffractive pp events was extracted. From these events, we determined the cross section σDD=(116±25)  μb for events where both diffractive systems have 4.7<|η|min<6.5.
118420745
Elastic Scattering and Total Cross-Section in p+p reactions measured by the LHC Experiment TOTEM at sqrt(s) = 7 TeV
Proton-proton elastic scattering has been measured by the TOTEM experiment at the CERN Large Hadron Collider at $\sqrt{s} = 7 $ TeV in special runs with the Roman Pot detectors placed as close to the outgoing beam as seven times the transverse beam size. The differential cross-section measurements are reported in the |t|-range of 0.36 to 2.5 GeV^2. Extending the range of data to low t values from 0.02 to 0.33 GeV^2,and utilizing the luminosity measurements of CMS, the total proton-proton cross section at sqrt(s) = 7 TeV is measured to be (98.3 +- 0.2(stat) +- 2.8(syst)) mb.
121659740
The CDF level 2 calorimetric trigger upgrade
Abstract CDF II upgraded the calorimeter trigger to cope with the higher detector occupancy due to the increased Tevatron instantaneous luminosity ( ∼ 2.8 × 10 32 cm - 2 s - 1 ) . While the original system was implemented in custom hardware and provided to the L2 trigger a limited-quality jet clustering performed using a reduced resolution measurement of the transverse energy in the calorimeter trigger towers, the upgraded system provides offline-quality jet reconstruction of the full resolution calorimeter data. This allows to keep better under control the dependence of the trigger rates on the instantaneous luminosity and to improve the efficiency and purity of the trigger selections. The upgraded calorimeter trigger uses the general purpose VME board Pulsar, developed at CDF II and already widely used to upgrade the L2 tracking and L2 decision systems. A battery of Pulsars is used to merge and send the calorimeter data to the L2 CPUs, where software-implemented algorithms perform offline-like clustering. In this paper we review the design and the performance of the upgraded system.