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 sqrt(s_NN) = 5.02 TeV

Aglietta, L.
Membro del Collaboration Group
;
Alocco, G.
Membro del Collaboration Group
;
Beole, S.
Membro del Collaboration Group
;
Bianchi, L.
Membro del Collaboration Group
;
Botta, E.
Membro del Collaboration Group
;
Cerri, R.
Membro del Collaboration Group
;
Ferretti, A.
Membro del Collaboration Group
;
Gagliardi, M.
Membro del Collaboration Group
;
Masera, M.
Membro del Collaboration Group
;
Pennisi, M.
Membro del Collaboration Group
;
Perciballi, S.
Membro del Collaboration Group
;
Politano, S.
Membro del Collaboration Group
;
Pucillo, S.
Membro del Collaboration Group
;
Quaglia, L.
Membro del Collaboration Group
;
Terlizzi, L.
Membro del Collaboration Group
;
Vercellin, E.
Membro del Collaboration Group
;
2026-01-01

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
872
140006
140006
Exclusive photoproduction; Ultraperipheral collisions; Vector mesons
Acharya, S.; Adamová, D.; Agarwal, A.; Rinella, G. Aglieri; Aglietta, L.; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S.U.; Ahuja, I.; Akin...espandi
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/2121088
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