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.
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.
122019157
Transport approach to anisotropic flows from viscous hydro regime to high pT
We discuss the build up of the elliptic flow v2 in a transport approach at fixed viscosity. We point out that in the indermediate transverse momentum region flows are also sensitive to microscopic details of the cross section, while hydrodynamics suffers from large uncertainties due to the non-equilibrium correction to the distribution function. We show, exploring the temperature dependence of η/s, that a study of v2 in a wide pT range allows to understand the difference behind the collective flows at LHC respect to RHIC. In particular the transport approach provides a tool able to naturally describe the rise and fall and saturation of the v2(pT).
117486353
Elliptic Flow and Shear Viscosity in a Parton Cascade Approach
Within a parton cascade approach we investigate the scaling of the differential elliptic flow v2(pT ) with eccentricity ex and system size and its sensitivity to finite shear viscosity. A central issue we address here is the relation between v2(pT )/ex and v2(pT )/〈v2〉 scalings, as raised by recent experimental observations. We show that, with the inclusion of a freeze out condition, a cascade approach for a plasma at finite η/s can supply a reliable tool for the description of several observables on elliptic flow such as the breaking of v2(pT )/ex scaling and the persistence of v2(pT )/〈v2〉 scaling. Results are moreover compatible with a coalescence plus fragmentation hadronization mechanism acting at intermediate pT .
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.
118352755
Thermalization, Isotropization and Elliptic Flow from Nonequilibrium Initial Conditions with a Saturation Scale
In this article we report on our results about the computation of the elliptic flow of the quark-gluon-plasma produced in relativistic heavy ion collisions, simulating the expansion of the fireball by solving the relativistic Boltzmann equation for the parton distribution function tuned at a fixed shear viscosity to entropy density ratio $\eta/s$. Our main goal is to put emphasis on the role of a saturation scale in the initial gluon spectrum, which makes the initial distribution far from a thermalized one. We find that the presence of the saturation scale reduces the efficiency in building-up the elliptic flow, even if the thermalization process is quite fast $\tau_{therm} \approx 0.8 \,\rm fm/c$ and the pressure isotropization even faster $\tau_{isotr} \approx 0.3 \,\rm fm/c$. The impact of the non-equilibrium implied by the saturation scale manifests for non-central collisions and can modify the estimate of the viscosity respect to the assumption of full thermalization in $p_T$-space. We find that the estimate of $\eta/s$ is modified from $\eta/s \approx 2/4\pi$ to $\eta/s \approx 1/4\pi$ at RHIC and from $\eta/s \approx 3/4\pi$ to $\eta/s \approx 2/4\pi$ at LHC. We complete our investigation by a study of the thermalization and isotropization times of the fireball for different initial conditions and values of $\eta/s$ showing how the latter affects both isotropization and thermalization. Lastly, we have seen that the range of values explored by the phase-space distribution function $f$ is such that at $p_T<0.5\, \rm GeV$ the inner part of the fireball stays with occupation number significantly larger than unity despite the fast longitudinal expansion, which might suggest the possibility of the formation of a transient Bose-Einstein Condensate.
17472412
Heavy Flavor in the sQGP
We attempt a unified treatment of heavy quarkonia and heavy- quark diffusion in the Quark-Gluon Plasma. Our approach is based on finite- temperature T-matrices with interaction potentials estimated from the heavy- quark internal energy computed in thermal lattice QCD (lQCD). In the charmo- nium sectorS-wave bound states (J/ , �c) survive up to temperatures of ∼2Tc, not inconsistent with constraints from euclidean correlation functions in lQCD. In the open-heavy flavor sector, the T-matrix interaction reduces heavy-quark diffusion substantially, leading to fair agreement with single-electron spectra at RHIC and suggestive for a small viscosity-to-entropy ratio close to Tc.