Measurement of substructure-dependent jet suppression in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Pb</mml:mi><mml:mo>+</mml:mo><mml:mi>Pb</mml:mi></mml:mrow></mml:math> collisions at 5.02 TeV with the ATLAS detector
G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A. C. Abusleme Hoffman, B. S. Acharya, B. Achkar, L. Adam, C. Adam Bourdarios, L. Adamczyk, L. Adámek, S. V. Addepalli, J. Adelman, A. Adıgüzel, S. Adorni, T. Adye, A. A. Affolder, Y. Afik, M. N. Agaras, J. Agarwala, A. Aggarwal, C. Agheorghiesei, J. A. Aguilar–Saavedra, A. Ahmad, F. Ahmadov, W. S. Ahmed, S. Ahuja, X. Ai, G. Aielli, I. Aizenberg, M. Akbiyik, T. P. A. Åkesson, A. V. Akimov, K. Al Khoury, G. L. Alberghi, J. Albert, P. Albicocco, M. J. Alconada Verzini, S. Alderweireldt, M. Aleksa, I. N. Aleksandrov, C. Alexa, T. Alexopoulos, A. Alfonsi, F. Alfonsi, M. Alhroob, B. Ali, S. Ali, M. Aliev, G. Alimonti, C. Allaire, B. M. M. Allbrooke, P. P. Allport, A. Aloisio, F. Alonso, C. Alpigiani, E. Alunno Camelia, M. Alvarez Estevez, M. G. Alviggi, Y. Amaral Coutinho, A. Ambler, C. Amelung, C. G. Ames, D. Amidei, S. P. Amor Dos Santos, S. Amoroso, K. R. Amos, C. S. Amrouche, V. Ananiev, C. Anastopoulos, N. Andari, T. Andeen, J. K. Anders, S. Y. Andrean, A. Andreazza, S. Angelidakis, A. Angerami, A. V. Anisenkov, A. Annovi, C. Antel, M. T. Anthony, E. Antipov, M. Antonelli, D. J. A. Antrim, F. Anulli, M. Aoki, T. Aoki, J. A. Aparisi Pozo, M. A. Aparo, L. Aperio Bella, C. Appelt, N. Aranzabal, V. Araujo Ferraz, C. Arcangeletti, A. T. H. Arce
Abstract
The ATLAS detector at the Large Hadron Collider has been used to measure jet substructure modification and suppression in $\mathrm{Pb}+\mathrm{Pb}$ collisions at a nucleon--nucleon center-of-mass energy $\sqrt{{s}_{{}_{NN}}}=5.02\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$ in comparison with proton--proton ($pp$) collisions at $\sqrt{s}=5.02\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$. The $\mathrm{Pb}+\mathrm{Pb}$ data, collected in 2018, have an integrated luminosity of $1.72\phantom{\rule{0.16em}{0ex}}{\mathrm{nb}}^{\ensuremath{-}1}$, while the $pp$ data, collected in 2017, have an integrated luminosity of $260\phantom{\rule{0.16em}{0ex}}{\mathrm{pb}}^{\ensuremath{-}1}$. Jets used in this analysis are clustered using the anti-${k}_{t}$ algorithm with a radius parameter $R=0.4$. The jet constituents, defined by both tracking and calorimeter information, are used to determine the angular scale ${r}_{\mathrm{g}}$ of the first hard splitting inside the jet by reclustering them using the Cambridge--Aachen algorithm and employing the soft-drop grooming technique. The nuclear modification factor, ${R}_{AA}$, used to characterize jet suppression in $\mathrm{Pb}+\mathrm{Pb}$ collisions, is presented differentially in ${r}_{\mathrm{g}}$, jet transverse momentum, and in intervals of collision centrality. The ${R}_{AA}$ value is observed to depend significantly on jet ${r}_{\mathrm{g}}$. Jets produced with the largest measured ${r}_{\mathrm{g}}$ are found to be twice as suppressed as those with the smallest ${r}_{\mathrm{g}}$ in central $\mathrm{Pb}+\mathrm{Pb}$ collisions. The ${R}_{AA}$ values do not exhibit a strong variation with jet ${p}_{\mathrm{T}}$ in any of the ${r}_{\mathrm{g}}$ intervals. The ${r}_{\mathrm{g}}$ and ${p}_{\mathrm{T}}$ dependence of jet ${R}_{AA}$ is qualitatively consistent with a picture of jet quenching arising from coherence and provides the most direct evidence in support of this approach.