Journal Article

Measurement of isolated prompt photon production in pp and p–Pb collisions at the LHC

Weiglhofer, F. T, Ahammed, Z, Isidori, T, Fabbietti, L, Závada, P, Wenzel, S. C, Fuchs, U, Goswami, K, Gaardhøje, J. J, Caliva, A, Bok, J, Malik, N. M, Humanic, T. J, Herrmann, S, Kundu, S, Martínez García, G, Buhler, P, Islam, M. S, Seger, J. E, Evans, D, Nepeivoda, R, Agrawal, N, Conesa Balbastre, G, Gautam, A, Scapparone, E, Xu, R, Buckland, M. D, Borquez Carcamo, A. G, Gwizdziel, K, Monira, S, Khuranova, Z, Pestov, Y, Vargas Torres, P, Keul, J, Saramela, T. B, Gotovac, S, Wilk, G, Chujo, T, Manso, F, Lömker, J, Ciacco, M, Majerz, E. M, Gay Ducati, M. B, Batyunya, B, Gernhaeuser, R. A, Hamagaki, H, Altsybeev, I, Zardoshti, N, Plociennik, D. K, Suaide, A. A. P, Palasciano, A, Germain, M, Panasenko, I, Röhrich, D, Koster, C, Šerkšnytė, L, Kalweit, A, Tabares, L. H, Scheid, H. S, Kweon, M. J, Shangaraev, A, Schweda, K, Grelli, A, Kluge, A, Krizkova Gajdosova, K, Janik, M. A, Lee, H, Verma, R, Yadav, A, Giubellino, P, Gahlaut, T, Samitz, D, Lambert, S, Read, K. F, Krupova, D. M, Płoskoń, M, Alizadehvandchali, N, Riffero, A. G, Rudolph, J. A, Elia, D, Cantway, S. L, Shirinkin, S, Sultanov, R, Glässel, P, Poljak, N, Gonzalez, V, Jusko, A, Karavichev, O, Radhakr

2025

Overview

This paper presents the measurement of the isolated prompt photon inclusive production cross section in pp and p–Pb collisions by the ALICE Collaboration at the LHC. The measurement is performed in p–Pb collisions at centre-of-mass energies per nucleon pair of s NN = 5.02 TeV and 8.16 TeV, as well as in pp collisions at s = 5.02 TeV and 8 TeV. The cross section is obtained at midrapidity ( | y | < 0.7 ) using a charged-track based isolation momentum p T iso, ch < 1.5 GeV / c in a cone with radius R = 0.4 . The data for both collision systems are well reproduced by perturbative QCD (pQCD) calculations at next-to-leading order (NLO) using recent parton distribution functions for free (PDF) and bound (nPDF) nucleons. Furthermore, the nuclear modification factor R pA for both collision energies is consistent with unity for p T > 20 GeV / c . However, deviations from unity ( R pA < 1 ) of up to 20% are observed for p T < 20 GeV / c with limited significance, indicating the possible presence of nuclear effects in the initial state of the collision. The suppression increases with decreasing p T with a significance of 2.3 σ for a non-zero slope and yields R pA < 1 with a significance of 1.8 σ at s NN = 8.16 TeV for p T < 20 GeV / c . In addition, a significance of 1.1 σ is observed for R pA < 1 at the lower collision energy s NN = 5.02 TeV for p T < 14 GeV / c . The magnitude and shape of the suppression are consistent with pQCD predictions at NLO using nPDFs that incorporate nuclear shadowing effects in the Pb nucleus.

• Publisher: Springer Berlin Heidelberg,Springer Nature B.V,SpringerOpen
• Subject: Astronomy / Astrophysics and Cosmology / Atoms & subatomic particles / Charged particles / Collisions / Cross-sections / Distribution functions / Elementary Particles / Gluons / Hadrons / Heavy Ions / Measurement Science and Instrumentation / Nuclear Energy / Nuclear Physics / Nucleons / Partons / Photons / Physics / Physics and Astronomy / Quantum Field Theories / Quantum Field Theory / Regular Article - Experimental Physics / Sensors / Silicon / String Theory / Unity