First measurements of N-subjettiness in central Pb-Pb collisions at √sNN = 2.76 TeV
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aglieri Rinella, Gianluca; Agnello, Michelangelo; Agrawal, Nikita; Ahammed, Zubayer; Ahmad, Shafiq F.; Ahn, Sang Un; Alme, Johan; Altenkaemper, Lucas; Djuvsland, Øystein; Eikeland, Viljar Nilsen; Ersdal, Magnus Rentsch; Fionda, Fiorella Maria Celeste; Grøttvik, Ola Slettevoll; Lofnes, Ingrid Mckibben; Nystrand, Joakim Ingemar; Rehman, Attiq Ur; Röhrich, Dieter; Sætre, Jon-Are; Tambave, Ganesh Jagannath; Ullaland, Kjetil; Wagner, Boris; Yang, Shiming; Yuan, Shiming; Arsene, Ionut Cristian; Dordic, Olja; Malik, Qasim Waheed; Neagu, Alexandra; Richter, Matthias; Røed, Ketil; Skaali, Toralf Bernhard; Storehaug, Ida Torkjellsdatter; Tveter, Trine Spedstad; Wikne, Jon Christopher; Helstrup, Håvard; Hetland, Kristin Fanebust; Kileng, Bjarte; Nesbø, Simon Voigt; Reme-Ness, Haakon André; Storetvedt, Maksim Melnik; Langøy, Rune; Lien, Jørgen André; Ahuja, Ishaan; Akbar, Zaenai; Akindinov, Alexander; Al-Turany, Mohammed; Alam, Sk Noor; ALICE, Collaboration
Peer reviewed, Journal article
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Original versionAcharya, S., Adamová, D., Adler, A., Adolfsson, J., Aglieri Rinella, G., Agnello, M., . . . Zurlo, N. (2021). First measurements of N-subjettiness in central Pb-Pb collisions at √sNN = 2.76 TeV. Journal of High Energy Physics, 2021(10):3. 10.1007/JHEP10(2021)003
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 √s = 7 TeV and √sNN = 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 √s = 7 TeV for inclusive jets. These results are compared with PYTHIA calculations at √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 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.