Charged Jet Production Research Articles

Measurement of Inclusive Charged Jet Production in pp and Pb–Pb collisions at [formula omitted] with ALICE

In these proceedings, we report the ALICE measurements of inclusive charged jet production in pp and Pb-Pb collisions at the currently highest available centre-of-mass energy at the LHC of 5.02 TeV. Charged jet spectra are extracted after jet-area based soft background subtraction and unfolding. Charged jet production cross sections as well as nuclear modification factors (RAA) are presented. Furthermore, the inclusive charged jet production cross section in pp collisions is compared to QCD calculations. Our RAA results show a significant jet suppression in the most central Pb-Pb collisions at 5.02 TeV. A comparison to RAA measurements obtained at lower centre-of-mass energy is also presented.

Jets in Pb–Pb collisions at ALICE

We report results on jet production in Pb–Pb collisions at √sNN = 2.76 TeV from the ALICE collaboration. The nuclear modification factor of jets reconstructed with a resolution parameter R=0.2 shows a strong, centrality dependent suppression with respect to pp collisions. The azimuthal anisotropy of charged jet production relative to the event plane is studied. In semi-peripheral events, a significant υ 2 ch jet is observed, indicating path-length dependent in-medium parton energy loss. The measurement of jet shapes allows characterizing the intra-jet momentum flow of quenched jets. The measured radial moment and dispersion of the constituent transverse momentum distribution indicate a collimation and hardening of the jet core in Pb–Pb relative to pp collisions.

Azimuthal anisotropy of charged jet production in [formula omitted] Pb–Pb collisions: Quark Matter 2015

Measurements of charged jet production with respect to the second-order harmonic event plane, quantified as v2chjet, in sNN=2.76 TeV Pb–Pb collisions are presented. The contribution of hydrodynamic flow to the underlying event energy is corrected for on a jet-by-jet basis. Remaining effects from instrumental resolution and regional fluctuations in the energy density of the underlying event are corrected for by unfolding. Significant v2chjet is observed in semi-central collisions. Qualitative agreement is found with v2ch+emjet of jets reconstructed from charged and neutral fragments and v2 of single charged particles, as well as with predictions from the JEWEL Monte Carlo model.

Centrality dependence of charged jet production in p-Pb collisions at [Formula: see text] = 5.02 TeV.

Measurements of charged jet production as a function of centrality are presented for p–Pb collisions recorded at sqrt{s_mathrm {NN}}= 5.02 TeV with the ALICE detector. Centrality classes are determined via the energy deposit in neutron calorimeters at zero degree, close to the beam direction, to minimise dynamical biases of the selection. The corresponding number of participants or binary nucleon–nucleon collisions is determined based on the particle production in the Pb-going rapidity region. Jets have been reconstructed in the central rapidity region from charged particles with the anti-k_mathrm {T} algorithm for resolution parameters R = 0.2 and R = 0.4 in the transverse momentum range 20 to 120 GeV/c. The reconstructed jet momentum and yields have been corrected for detector effects and underlying-event background. In the five centrality bins considered, the charged jet production in p–Pb collisions is consistent with the production expected from binary scaling from pp collisions. The ratio of jet yields reconstructed with the two different resolution parameters is also independent of the centrality selection, demonstrating the absence of major modifications of the radial jet structure in the reported centrality classes.

Azimuthal anisotropy of charged jet production in [formula omitted] Pb–Pb collisions

We present measurements of the azimuthal dependence of charged jet production in central and semi-central sNN=2.76 TeV Pb–Pb collisions with respect to the second harmonic event plane, quantified as v2ch jet. Jet finding is performed employing the anti-kT algorithm with a resolution parameter R=0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero v2ch jet is observed in semi-central collisions (30–50% centrality) for 20<pTch jet<90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the v2 of single charged particles at high pT. Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions.

Measurement of charged jet production cross sections and nuclear modification in p–Pb collisions at [formula omitted

Charged jet production cross sections in p–Pb collisions at sNN=5.02 TeV measured with the ALICE detector at the LHC are presented. Using the anti-kT algorithm, jets have been reconstructed in the central rapidity region from charged particles with resolution parameters R=0.2 and R=0.4. The reconstructed jets have been corrected for detector effects and the underlying event background. To calculate the nuclear modification factor, RpPb, of charged jets in p–Pb collisions, a pp reference was constructed by scaling previously measured charged jet spectra at s=7 TeV. In the transverse momentum range 20≤pT,chjet≤120 GeV/c, RpPb is found to be consistent with unity, indicating the absence of strong nuclear matter effects on jet production. Major modifications to the radial jet structure are probed via the ratio of jet production cross sections reconstructed with the two different resolution parameters. This ratio is found to be similar to the measurement in pp collisions at s=7 TeV and to the expectations from PYTHIA pp simulations and NLO pQCD calculations at sNN=5.02 TeV.