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Register a new userJet measurements in the ALICE experiment at the LHC
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Authors
J.L. Klay
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Jet tomography probes provide a means to explore the properties of highly compressed and excited nuclear matter created in heavy ion collisions. The capabilities of the ALICE experiment, with its electromagnetic calorimeter (EMCal) upgrade, to trigger on and reconstruct jets in p+p and Pb+Pb collisions at $sqrt{s_{NN}}$=5.5 TeV are presented.
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The ALICE experiment at the Large Hadron Collider (LHC) at CERN consists of a central barrel, a muon spectrometer and additional detectors for trigger and event classification purposes. The low transverse momentum threshold of the central barrel gives ALICE a unique opportunity to study the low mass sector of central exclusive production at the LHC.
This article presents the basic idea of VHMPID, an upgrade detector for the ALICE experiment at LHC, CERN. The main goal of this detector is to extend the particle identification capabilities of ALICE to give more insight into the evolution of the hot and dense matter created in Pb-Pb collisions. Starting from the physics motivations and working principles the challenges and current status of development is detailed.
Results are presented from a phenomenological analysis of recent measurements of jet suppression and modifications of jet fragmentation functions in Pb+Pb collisions at the LHC. Particular emphasis is placed on the impact of the differences between quark and gluon jet quenching on the transverse momentum ($p_{T}^{jet}$) dependence of the jet $R_{AA}$ and on the fragmentation functions, $D(z)$. Primordial quark and gluon parton distributions were obtained from PYTHIA8 and were parameterized using simple power-law functions and extensions to the power-law function which were found to better describe the PYTHIA8 parton spectra. A simple model for the quark energy loss based on the shift formalism is used to model $R_{AA}$ and $D(z)$ using both analytic results and using direct Monte-Carlo sampling of the PYTHIA parton spectra. The model is capable of describing the full $p_{T}^{jet}$ , rapidity, and centrality dependence of the measured jet $R_{AA}$ using three effective parameters. A key result from the analysis is that the $D(z)$ modifications observed in the data, excluding the enhancement at low-$z$, may result primarily from the different quenching of the quarks and gluons. The model is also capable of reproducing the charged hadron $R_{AA}$ at high transverse momentum. Predictions are made for the jet $R_{AA}$ at large rapidities where it has not yet been measured and for the rapidity dependence of $D(z)$.
The ALICE experiment at LHC is mainly dedicated to heavy-ion physics. An overview of its performances, some predictions related to its first measurements and QGP observable measurements will be given.
We present new measurements related to spin alignment of $mathrm{K^{*0}}$ vector mesons at mid-rapidity for Pb-Pb collisions at $sqrt{s_{mathrm{NN}}}$ = 2.76 and 5.02 TeV. The spin alignment measurements are carried out with respect to production plane and second order event plane. At low $p_{mathrm{T}}$ the spin density matrix element $rho_{00}$ for $mathrm{K^{*0}}$ is found to have values slightly below 1/3, while it is consistent with 1/3, i.e. no spin alignment, at high $p_{mathrm{T}}$. Similar values of $rho_{00}$ are observed w.r.t. both production plane and event plane. Within statistical and systematic uncertainties, $rho_{00}$ values are also found to be independent of $sqrt{s_{mathrm{NN}}}$. $rho_{00}$ also shows centrality dependence with maximum deviation from 1/3 for mid-central collisions w.r.t. both the kinematic planes. The measurements for $mathrm{K^{*0}}$ in pp collisions at $sqrt{s}$ = 13 TeV and for $mathrm{K^{0}_{S}}$ (a spin 0 hadron) in 20-40% central Pb-Pb collisions at $sqrt{s_{mathrm{NN}}}$ = 2.76 TeV are consistent with no spin alignment.
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