This paper presents the measurement of the iso- lated 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 √sNN = 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 momen- tum piso, ch T < 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 RpA for both collision energies is consistent with unity for pT > 20 GeV/c. However, devia- tions from unity (RpA < 1) of up to 20% are observed for pT < 20 GeV/c with limited significance, indicating the possi- ble presence of nuclear effects in the initial state of the col- lision. The suppression increases with decreasing pT with a significance of 2.3σ for a non-zero slope and yields RpA < 1 with a significance of 1.8σ at √sNN = 8.16 TeV for pT < 20 GeV/c. In addition, a significance of 1.1σ is observed for RpA < 1 at the lower collision energy √sNN = 5.02 TeV for pT < 14 GeV/c. The magnitude and shape of the sup- pression are consistent with pQCD predictions at NLO using nPDFs that incorporate nuclear shadowing effects in the Pb nucleus.
Measurement of isolated prompt photon production in pp and p–Pb collisions at the LHC
Cortese, P.;Jacazio, N.;Ramello, L.;Sitta, M.;
2025-01-01
Abstract
This paper presents the measurement of the iso- lated 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 √sNN = 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 momen- tum piso, ch T < 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 RpA for both collision energies is consistent with unity for pT > 20 GeV/c. However, devia- tions from unity (RpA < 1) of up to 20% are observed for pT < 20 GeV/c with limited significance, indicating the possi- ble presence of nuclear effects in the initial state of the col- lision. The suppression increases with decreasing pT with a significance of 2.3σ for a non-zero slope and yields RpA < 1 with a significance of 1.8σ at √sNN = 8.16 TeV for pT < 20 GeV/c. In addition, a significance of 1.1σ is observed for RpA < 1 at the lower collision energy √sNN = 5.02 TeV for pT < 14 GeV/c. The magnitude and shape of the sup- pression are consistent with pQCD predictions at NLO using nPDFs that incorporate nuclear shadowing effects in the Pb nucleus.| File | Dimensione | Formato | |
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