학술논문
First measurements of N-subjettiness in central Pb-Pb collisions at sNN = 2.76 TeV
Document Type
Original Paper
Author
Source
Journal of High Energy Physics. 2021(10)
Subject
Language
English
ISSN
1029-8479
Abstract
Abstract: The ALICE Collaboration reports the first fully-corrected measurements of the N-subjettiness observable for track-based jets in heavy-ion collisions. This study is performed using data recorded in pp and Pb-Pb collisions at centre-of-mass energies of ssNNss = 7 TeV and ssNNss = 2.76 TeV, respectively. In particular the ratio of 2-subjettiness to 1-subjettiness, τ2 /τ1 , which is sensitive to the rate of two-pronged jet substructure, is presented. Energy loss of jets traversing the strongly interacting medium in heavy-ion collisions is expected to change the rate of two-pronged substructure relative to vacuum. The results are presented for jets with a resolution parameter of R = 0.4 and charged jet transverse momentum of 40 ≤ pT,jet ≤ 60 GeV/c, which constitute a larger jet resolution and lower jet transverse momentum interval than previous measurements in heavy-ion collisions. This has been achieved by utilising a semi-inclusive hadron-jet coincidence technique to suppress the larger jet combinatorial background in this kinematic region. No significant modification of the τ2 /τ1 observable for track-based jets in Pb-Pb collisions is observed relative to vacuum PYTHIA6 and PYTHIA8 references at the same collision energy. The measurements of τ2 /τ1 , together with the splitting aperture angle ∆R, are also performed in pp collisions at ssNNss = 7 TeV for inclusive jets. These results are compared with PYTHIA calculations at ssNNss = 7 TeV, in order to validate the model as a vacuum reference for the Pb-Pb centre-of-mass energy. The PYTHIA references for τ2 /τ1 are shifted to larger values compared to the measurement in pp collisions. This hints at a reduction in the rate of two-pronged jets in Pb-Pb collisions compared to pp collisions.