The intense photon fluxes from relativistic nuclei provide an opportunity to study photonuclear interactions in ultraperipheral collisions. In particular, it allows for the investigations of excited, light-flavour vector mesons. The measurement of coherently photoproduced π+π−π+π− final states in ultraperipheral Pb–Pb collisions at sNN=5.02 TeV is presented for the first time. The cross section, d σ /d y , times the branching ratio (ρ→π+π+π−π−) is found to be 47.8 ± 2.3 (stat.) ± 7.7 (syst.) mb in the rapidity interval | y | < 0.5. The invariant mass distribution is not well described with a single Breit-Wigner resonance without an interference term. Including interference with a non-resonant contribution results in the mass and width values being too far from those reported in PDG, while the production of two interfering resonances, ρ (1450) and ρ (1700), also provides a good description of the data. The values of the masses ( m ) and widths (Γ) of the resonances extracted from the fit assuming two interfering resonances are m1=1385±14(stat.)±3(syst.) MeV/ c 2, Γ1=431±36(stat.)±82(syst.) MeV/ c 2, m2=1663±13(stat.)±22(syst.) MeV/ c 2 and Γ2=357±31(stat.)±49(syst.) MeV/ c 2, respectively. The measured cross sections times the branching ratios are compared to recent theoretical predictions.

Exclusive photoproduction of excited ρ mesons decaying to four pions in ultraperipheral Pb–Pb collisions at s_NN=5.02 TeV / Acharya, S., Adamová, D., Agarwal, A., Rinella, G.A., Aglietta, L., Agnello, M., Agrawal, N., Ahammed, Z., Ahmad, S., Ahn, S.U., Ahuja, I., Akindinov, A., Akishina, V., Al-Turany, M., Aleksandrov, D., Alessandro, B., Alfanda, H.M., Alfaro Molina, R., Ali, B., Alici, A., et al.. - In: PHYSICS LETTERS. SECTION B. - ISSN 0370-2693. - 872:(2026). [10.1016/j.physletb.2025.140006]

Exclusive photoproduction of excited ρ mesons decaying to four pions in ultraperipheral Pb–Pb collisions at s_NN=5.02 TeV

Bruno, G. E.;Colella, D.;Palasciano, A.;
2026

Abstract

The intense photon fluxes from relativistic nuclei provide an opportunity to study photonuclear interactions in ultraperipheral collisions. In particular, it allows for the investigations of excited, light-flavour vector mesons. The measurement of coherently photoproduced π+π−π+π− final states in ultraperipheral Pb–Pb collisions at sNN=5.02 TeV is presented for the first time. The cross section, d σ /d y , times the branching ratio (ρ→π+π+π−π−) is found to be 47.8 ± 2.3 (stat.) ± 7.7 (syst.) mb in the rapidity interval | y | < 0.5. The invariant mass distribution is not well described with a single Breit-Wigner resonance without an interference term. Including interference with a non-resonant contribution results in the mass and width values being too far from those reported in PDG, while the production of two interfering resonances, ρ (1450) and ρ (1700), also provides a good description of the data. The values of the masses ( m ) and widths (Γ) of the resonances extracted from the fit assuming two interfering resonances are m1=1385±14(stat.)±3(syst.) MeV/ c 2, Γ1=431±36(stat.)±82(syst.) MeV/ c 2, m2=1663±13(stat.)±22(syst.) MeV/ c 2 and Γ2=357±31(stat.)±49(syst.) MeV/ c 2, respectively. The measured cross sections times the branching ratios are compared to recent theoretical predictions.
2026
Exclusive photoproduction of excited ρ mesons decaying to four pions in ultraperipheral Pb–Pb collisions at s_NN=5.02 TeV / Acharya, S., Adamová, D., Agarwal, A., Rinella, G.A., Aglietta, L., Agnello, M., Agrawal, N., Ahammed, Z., Ahmad, S., Ahn, S.U., Ahuja, I., Akindinov, A., Akishina, V., Al-Turany, M., Aleksandrov, D., Alessandro, B., Alfanda, H.M., Alfaro Molina, R., Ali, B., Alici, A., et al.. - In: PHYSICS LETTERS. SECTION B. - ISSN 0370-2693. - 872:(2026). [10.1016/j.physletb.2025.140006]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11589/298220
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