The first measurement of coherent ϒ(1S) meson photoproduction off heavy nuclei is performed using ultraperipheral lead-lead collisions collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The nuclear gluonic structure is probed at a nucleon momentum fraction of order x∼10^{-3}, determined by the kinematics of the process. Owing to the large ϒ(1S) mass, the measurement reaches the highest scale accessible so far through coherent vector-meson photoproduction, μ^{2}=22.4 GeV^{2}, where nonlinear quantum chromodynamics effects are expected to be minimal. In the ϒ(1S) rapidity range |y|<1, the ratio of the measured photoproduction cross section to a baseline model prediction that neglects nuclear effects is S_{ϒ(1S)}=0.25±0.06(stat)±0.02(syst), thereby demonstrating nuclear suppression in this process. Expressed in terms of a nuclear gluon suppression factor, the result yields R_{g}^{Pb}(x≈10^{-3},μ^{2}=22.4 GeV^{2})=0.55±0.12(stat)±0.02(syst). The measured S_{ϒ(1S)} is only slightly larger than the values previously reported for coherent ϕ photoproduction, despite the probed μ^{2} differing by approximately 2 orders of magnitude.
Observation of Nuclear Suppression in Coherent ϒ ( 1 S ) Photoproduction off Heavy Nuclei at the LHC
Abbrescia, M.;Barbieri, M.;Buonsante, M.;Colaleo, A.;De Palma, M.;Elmetenawee, W.;Louka, M.;Mastrapasqua, V.;My, S.;Nenna, F.;Nuzzo, S.;Pellecchia, A.;Pompili, A.;Radogna, R.;Stamerra, A.;Troiano, D.;Venditti, R.;Zaza, A.;D'Anzi, B.;
2026-01-01
Abstract
The first measurement of coherent ϒ(1S) meson photoproduction off heavy nuclei is performed using ultraperipheral lead-lead collisions collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The nuclear gluonic structure is probed at a nucleon momentum fraction of order x∼10^{-3}, determined by the kinematics of the process. Owing to the large ϒ(1S) mass, the measurement reaches the highest scale accessible so far through coherent vector-meson photoproduction, μ^{2}=22.4 GeV^{2}, where nonlinear quantum chromodynamics effects are expected to be minimal. In the ϒ(1S) rapidity range |y|<1, the ratio of the measured photoproduction cross section to a baseline model prediction that neglects nuclear effects is S_{ϒ(1S)}=0.25±0.06(stat)±0.02(syst), thereby demonstrating nuclear suppression in this process. Expressed in terms of a nuclear gluon suppression factor, the result yields R_{g}^{Pb}(x≈10^{-3},μ^{2}=22.4 GeV^{2})=0.55±0.12(stat)±0.02(syst). The measured S_{ϒ(1S)} is only slightly larger than the values previously reported for coherent ϕ photoproduction, despite the probed μ^{2} differing by approximately 2 orders of magnitude.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
