Modification of jet shapes in PbPb collisions at sNN=2.76 TeV

Abstract

The first measurement of jet shapes, defined as the fractional transverse momentum radial distribution, for inclusive jets produced in heavy-ion collisions is presented. Data samples of PbPb and pp collisions, corresponding to integrated luminosities of 150 µb −1 and 5.3 pb −1 respectively, were collected at a nucleon-nucleon centre-ofmass energy of √ s NN = 2.76 TeV with the CMS detector at the LHC. The jets are reconstructed with the anti-k T algorithm with a distance parameter R = 0.3, and the jet shapes are measured for charged particles with transverse momentum p T > 1 GeV/c. The jet shapes measured in PbPb collisions in different collision centralities are compared to reference distributions based on the pp data. A centrality-dependent modification of the jet shapes is observed in the more central PbPb collisions, indicating a redistribution of the energy inside the jet cone. This measurement provides information about the parton shower mechanism in the hot and dense medium produced in heavy-ion collisions.

Vector boson tagged jets and jet substructure

“…The green band correspond to the full calculation the green band is the full calculation and adds the event-by-event broadening. It is evident that the jet shape modification is highly nontrivial and we find that it compares well to the data from CMS [36] with jet radius R = 0.3.…”

Novel subjet observables for jet quenching in heavy-ion collisions

“…Considerations of the RSD distributions show that the R IQR[ΔS 12 ] carries the largest discrimination power for highp T jets, although there is an associated uncertainty of [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]% due to hadronization effects. For low-p T jets ( p T 120 GeV/c) and/or recoil-jets in dijet systems the use of the R Q 1 [ΔS 12 ] and/or the median R Q 2 [ΔS 12 ] may prove more advantageous, with hadronization uncertainties that are smaller than 5% for the chosen subjet parameters.…”

“…Experiments at RHIC and the LHC observed a strong suppression of high transverse momentum particle yields [9][10][11][12][13][14][15], suppression of inclusive and semi-inclusive yields of fully reconstructed jets [16][17][18][19][20], and, more recently, the internal structure of the jets [21][22][23][24][25] for detailed studies of jet quenching. However, in all these measurements the treatment of the background originating from the copiously produced particles not associated to hard scatterings poses an experimental challenge for precise and unbiased measurements.…”

Early hydrodynamisation, energy loss and small systems in holographic heavy ion collisions

“…As can be seen, in this model either effect can dominate depending on the free parameters (a, b). Interestingly, it is hence entirely possible that the mean value of C (1) 1 in a specified energy range decreases (as experiments indicate [25]), even though every individual jet in the ensemble widens in angle.…”