Measurement of isolated prompt photon production in pp and p-Pb collisions at the LHC
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2025
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| _version_ | 1866918343373488128 |
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| author | ALICE Collaboration |
| author_facet | ALICE Collaboration |
| contents | 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 $\sqrt{s_{\rm{NN}}} = 5.02$ TeV and $8.16$ TeV, as well as in pp collisions at $\sqrt{s} = 5.02$ TeV and $8$ TeV. The cross section is obtained at midrapidity $(|y|<0.7)$ using a charged-track based isolation momentum $p_{\rm T}^{\rm{iso, ch}} < 1.5$ 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 $R_{\text{pA}}$ for both collision energies is consistent with unity for $p_{\rm T} > 20$ GeV/$c$. However, deviations from unity ($R_{\rm pA}<1$) of up to 20% are observed for $p_{\rm T} < 20$ GeV/$c$ with limited significance, indicating the possible presence of nuclear effects in the initial state of the collision. The suppression increases with decreasing \pt with a significance of $2.3σ$ for a non-zero slope and yields $R_{\rm pA}<1$ with a significance of $1.8σ$ at $\sqrt{s_{\rm NN}} = 8.16$ TeV for $p_{\rm T} < 20$ GeV/$c$. In addition, a significance of $1.1σ$ is observed for $R_{\rm pA}<1$ at the lower collision energy $\sqrt{s_{\rm NN}} = 5.02$ TeV for $p_{\rm T} < 14$ 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. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2502_18054 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Measurement of isolated prompt photon production in pp and p-Pb collisions at the LHC ALICE Collaboration Nuclear Experiment High Energy Physics - Experiment 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 $\sqrt{s_{\rm{NN}}} = 5.02$ TeV and $8.16$ TeV, as well as in pp collisions at $\sqrt{s} = 5.02$ TeV and $8$ TeV. The cross section is obtained at midrapidity $(|y|<0.7)$ using a charged-track based isolation momentum $p_{\rm T}^{\rm{iso, ch}} < 1.5$ 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 $R_{\text{pA}}$ for both collision energies is consistent with unity for $p_{\rm T} > 20$ GeV/$c$. However, deviations from unity ($R_{\rm pA}<1$) of up to 20% are observed for $p_{\rm T} < 20$ GeV/$c$ with limited significance, indicating the possible presence of nuclear effects in the initial state of the collision. The suppression increases with decreasing \pt with a significance of $2.3σ$ for a non-zero slope and yields $R_{\rm pA}<1$ with a significance of $1.8σ$ at $\sqrt{s_{\rm NN}} = 8.16$ TeV for $p_{\rm T} < 20$ GeV/$c$. In addition, a significance of $1.1σ$ is observed for $R_{\rm pA}<1$ at the lower collision energy $\sqrt{s_{\rm NN}} = 5.02$ TeV for $p_{\rm T} < 14$ 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. |
| title | Measurement of isolated prompt photon production in pp and p-Pb collisions at the LHC |
| topic | Nuclear Experiment High Energy Physics - Experiment |
| url | https://arxiv.org/abs/2502.18054 |