Measurement of muon pairs produced via <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>γ</mml:mi><mml:mi>γ</mml:mi></mml:mrow></mml:math> scattering in nonultraperipheral <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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msqrt><mml:msub><mml:mi>s</mml:mi><mml:mrow><mml:mi>N</mml:mi><mml:mi>N</mml:mi></mml:mrow></mml:msub></mml:msqrt><mml:mo>=</mml:mo><mml:mn>5.02</mml:mn></mml:mrow></mml:math> 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, 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, J. A. Aparisi Pozo, M. A. Aparo, L. Aperio Bella, C. Appelt, N. Aranzabal, V. Araujo Ferraz, C. Arcangeletti, A. T. H. Arce, E. Arena, J-F. Arguin
Abstract
In ultrarelativistic heavy-ion collisions the Lorentz-contracted electromagnetic fields of the nuclei are a source of high-energy quasireal photons which can produce muon pairs via the process $\ensuremath{\gamma}+\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}+{\ensuremath{\mu}}^{\ensuremath{-}}$. In hadronic Pb+Pb collisions the two leptons in the final state provide a sensitive probe of the quark-gluon plasma created in the Pb+Pb collision or the strong magnetic fields that the plasma generates. This work presents new measurements by the ATLAS collaboration at the LHC of the Pb+Pb collision centrality dependence of the angular decorrelation of muon pairs created via the $\ensuremath{\gamma}\phantom{\rule{0}{0ex}}\ensuremath{\gamma}$ process. Comparisons of the results to theoretical calculations suggest that the observed decorrelation in more central collisions results from an initial-state broadening of the photon transverse momenta and not from the interaction of the muons with the plasma or its magnetic field.