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Title: First measurements of N-subjettiness in central Pb-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 2.76 TeV
A bstract 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 $$ \sqrt{s} $$ s = 7 TeV and $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 2 . 76 TeV, respectively. In particular the ratio of 2-subjettiness to 1-subjettiness, τ 2 /τ 1 , 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 ≤ p T , 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 τ 2 /τ 1 observable for track-based jets in Pb-Pb collisions is observed relative to vacuum PYTHIA6 more » and PYTHIA8 references at the same collision energy. The measurements of τ 2 /τ 1 , together with the splitting aperture angle ∆ R , are also performed in pp collisions at $$ \sqrt{s} $$ s = 7 TeV for inclusive jets. These results are compared with PYTHIA calculations at $$ \sqrt{s} $$ s = 7 TeV, in order to validate the model as a vacuum reference for the Pb-Pb centre-of-mass energy. The PYTHIA references for τ 2 /τ 1 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. « less
Authors:
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Award ID(s):
2012154 1719759
Publication Date:
NSF-PAR ID:
10338975
Journal Name:
Journal of High Energy Physics
Volume:
2021
Issue:
10
ISSN:
1029-8479
Sponsoring Org:
National Science Foundation
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