199673512
Measuring QGP thermalization time with dileptons
We calculate leading-order dilepton production resulting from the annihilation process from a quark-gluon plasma which has a time-dependent anisotropy in the momentum-space. A phenomenological model for the hard momentum scale, Phard(τ) and the plasma anisotropy parameter, ξ(τ), is constructed. The model interpolates between free streaming behaviour at early times and ideal hydrodynamical behaviour at late times. Using this model, we show that for LHC energies, the medium dilepton production increases in the kinematic range 3 < PT < 8 GeV. As a result this observable is sensitive to the isotropization time of the system, τiso. Therefore high-energy dilepton production can be used to probe the degree of momentum-space isotropy of a quark-gluon plasma produced in relativistic heavy ion collisions and the time of onset of hydrodynamic expansion of the QGP.
36601565
Next-to-eikonal corrections in the CGC: gluon production and spin asymmetries in pA collisions
A bstractWe present a new method to systematically include corrections to the eikonal approximation in the background field formalism. Specifically, we calculate the subleading, power-suppressed corrections due to the finite width of the target or the finite energy of the projectile. Such power-suppressed corrections involve Wilson lines decorated by gradients of the background field — thus related to the density - of the target. The method is of generic applicability. As a first example, we study single inclusive gluon production in pA collisions, and various related spin asymmetries, beyond the eikonal accuracy.
118372212
Matching pre-equilibrium dynamics and viscous hydrodynamics
We demonstrate how to match pre-equilibrium dynamics of a $0+1$-dimensional quark-gluon plasma to second-order viscous hydrodynamical evolution. The matching allows us to specify the initial values of the energy density and shear tensor at the initial time of hydrodynamical evolution as a function of the lifetime of the pre-equilibrium period. We compare two models for pre-equilibrium quark-gluon plasma, longitudinal free streaming and collisionally broadened longitudinal expansion, and present analytic formulas that can be used to fix the necessary components of the energy-momentum tensor. The resulting dynamical models can be used to assess the effect of pre-equilibrium dynamics on quark-gluon plasma observables. Additionally, we investigate the dependence of entropy production on pre-equilibrium dynamics and discuss the limitations of the standard definitions of nonequilibrium entropy.
2553762
Boost-Invariant (2+1)-Dimensional Anisotropic Hydrodynamics
We present results of the application of the anisotropic hydrodynamics (aHydro) framework to (2+1)-dimensional boost-invariant systems. The necessary aHydro dynamical equations are derived by taking moments of the Boltzmann equation using a momentum-space anisotropic one-particle distribution function. We present a derivation of the necessary equations and then proceed to numerical solutions of the resulting partial differential equations using both realistic smooth Glauber initial conditions and fluctuating Monte Carlo Glauber initial conditions. For this purpose we have developed two numerical implementations: one that is based on straightforward integration of the resulting partial differential equations supplemented by a two-dimensional weighted Lax-Friedrichs smoothing in the case of fluctuating initial conditions and another that is based on the application of the Kurganov-Tadmor central scheme. For our final results we compute the collective flow of the matter via the laboratory-frame energy-momentum tensor eccentricity as a function of the assumed shear viscosity-to-entropy ratio, proper time, and impact parameter.
16251511
Proton to pion ratio at RHIC from dynamical quark recombination
We propose an scenario to study, from a dynamical point of view, the thermal recombination of quarks in the midsts of a relativistic heavy‐ion collision. We coin the term dynamical quark recombination to refer to the process of quark‐antiquark and three‐quark clustering, to form mesons and baryons, respectively, as a function of energy density. Using the string‐flip model we show that the probabilities to form such clusters differ. We apply these ideas to the calculation of the proton and pion spectra in a Bjorken‐like scenario that incorporates the evolution of these probabilities with proper time and compute the proton to pion ratio, comparing to recent RHIC data at the highest energy. We show that for a standard choice of parameters, this ratio reaches one, though the maximum is very sensitive to the initial evolution proper time.
13868349
Dilepton production as a measure of QGP thermalization time
We discuss dilepton production from a quark–gluon plasma which has a time-dependent anisotropy in momentum space. A phenomenological model for the hard momentum scale, phard(τ) and the plasma anisotropy parameter, ξ(τ), is presented. The model interpolates between early-time 1 + 1 free streaming behavior (τ τiso) and late-time ideal 1 + 1 hydrodynamical behavior (τ τiso). Using this model, we find that the dilepton rate arising from electromagnetic annihilations of quarks in the kinematic range 3 <pT< 8 GeV is sensitive to the assumed isotropization time of the system, τiso. Therefore high-energy dilepton production can be used to probe the degree of momentum-space isotropy of a quark–gluon plasma produced in relativistic heavy-ion collisions and the time of onset of hydrodynamic expansion of the QGP.
123410491
Z plus jets production at the tevatron
We present preliminary results on inclusive Z(→ee) boson plus jets production in pp collisions at s√ = 1.96 TeV, based on 1.7 fb-1 of data collected by the CDF experiment. Inclusive jet measurements are performed as function of pTjet and jet multiplicity for jets in the region of pTjet > 30 GeV/c and |yjet | < 2.1. Results are compared to NLO pQCD predictions and are found to be in good agreement.
111282417
The front-end system of the silicon drift detectors of ALICE
The ALICE experiment at CERN will have an inner tracker made of six barrels of semiconductor detectors. The two intermediate layers of the system will employ Silicon Drift Detectors (SDD) technology. The front-end electronics of the SDDs, which required the development of two full-custom integrated circuits, is reviewed in this paper. The design of the front-end hybrid is discussed and results obtained with full-size prototypes are presented.
19015103
Beam test results of the irradiated silicon drift detector for ALICE
The Inner Tracking System (ITS) of the ALICE experiment at LHC will use high precision Silicon Drift Detectors (SDD) in two of the six cylindrical layers. In this paper we report on the results of beam test of a SDD irradiated with 1 GeV electrons. The aim of this test was to verify the radiation tolerance of the device under an electron fluence equivalent to twice the particle fluence expected during 10 years of ALICE operation.
122001499
Experimental review of jet physics in hadronic collisions
In this contribution, a comprehensive review of the main aspects of high pT jet physics in Run II at the Tevatron is presented. Recent measurements on inclusive jet production are discussed using different jet algorithms and covering a wide region of jet transverse momentum and jet rapidity. Several measurements, sensitive to a proper description of soft gluon radiation and the underlying event in hadron collisions, are shown. Finally, high pT prompt photon measurements, and studies on the production of electroweak bosons in association with jets in the final state are discussed.
11938821
Search for new phenomena in events with a monojet and large missing transverse momentum at the LHC using the ATLAS detector
We report preliminary results on a search for new phenomena in an event sample with monojets and large missing transverse momentum in the final state. The analysis uses 1.00 fb−1 of data collected in 2011 with the ATLAS detector [1]. Good agreement is observed between the number of events in data and the Standard Model predictions. The results are translated into improved limits on a model with Large Extra Dimensions.