Medium modification of the shape of small-radius jets in central Pb-Pb collisions at √sN-N-=2.76 TeV
Acharya, Shreyasi; Acosta, Fernando T.; Adamová, Dagmar; Adler, Clemens; Adolfsson, Jonatan; Aggarwal, Madan M.; Aglieri Rinella, Gianluca; Agnello, Michelangelo; Agrawal, Nikita; Ahammed, Zubayer; Alme, Johan; Altenkaemper, Lucas; Djuvsland, Øystein; Ersdal, Magnus Rentsch; Fionda, Fiorella Maria Celeste; Nystrand, Joakim; Rehman, Attiq ur; Røhrich, Dieter; Tambave, Ganesh Jagannath; Ullaland, Kjetil; Wagner, Boris; Zhou, Zhuo; Arsene, Ionut Cristian; Bätzing, Paul Christoph; Dordic, Olja; Lardeux, Antoine Xavier; Lindal, Svein; Mahmood, Sohail Musa; Malik, Qasim Waheed; Richter, Matthias; Røed, Ketil; Skaali, Toralf Bernhard; Tveter, Trine Spedstad; Wikne, Jon Christopher; Zhao, Chengxin; Helstrup, Håvard; Hetland, Kristin Fanebust; Kileng, Bjarte; Nesbø, Simon Voigt; Storetvedt, Maksim Melnik; Langøy, Rune; Lien, Jørgen André; Ahn, Sang Un; Aiola, Salvatore; Akindinov, Alexander; Al-Turany, Mohammed; Alam, Sk Noor; De Albuquerque, Danilo Silva; Aleksandrov, Dimitry; Alessandro, Bruno; ALICE, Collaboration
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Original versionAcharya, S., Acosta, F. T., Adamová, D., Adler, A., Adolfsson, J., Aggarwal, M. M., . . . Zmeskal, J. (2018). Medium modification of the shape of small-radius jets in central Pb-Pb collisions at √sN-N-=2.76 TeV. Journal of High Energy Physics, 2018(10) 10.1007/JHEP10(2018)139
We present the measurement of a new set of jet shape observables for trackbased jets in central Pb-Pb collisions at √sNN = 2.76 TeV. The set of jet shapes includesthe first radial moment or angularity, g; the momentum dispersion, pTD; and the difference between the leading and sub-leading constituent track transverse momentum, LeSub.These observables provide complementary information on the jet fragmentation and canconstrain different aspects of the theoretical description of jet-medium interactions. The jetshapes were measured for a small resolution parameter R = 0.2 and were fully corrected toparticle level. The observed jet shape modifications indicate that in-medium fragmentationis harder and more collimated than vacuum fragmentation as obtained by PYTHIA calculations, which were validated with the measurements of the jet shapes in proton-protoncollisions at √s = 7 TeV. The comparison of the measured distributions to templates forquark and gluon-initiated jets indicates that in-medium fragmentation resembles that ofquark jets in vacuum. We further argue that the observed modifications are not consistentwith a totally coherent energy loss picture where the jet loses energy as a single colourcharge, suggesting that the medium resolves the jet structure at the angular scales probedby our measurements (R = 0.2). Furthermore, we observe that small-R jets can help toisolate purely energy loss effects from other effects that contribute to the modifications ofthe jet shower in medium such as the correlated background or medium response.