Observation of Nuclear Suppression in Coherent; ; ; ; ϒ; ; (; 1; S; ); ; ; Photoproduction off Heavy Nuclei at the LHC
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; The first measurement of coherent; ; ; ϒ; (; 1; S; ); ; ; 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; (; 1; S; ); ; ; 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; (; 1; S; ); ; ; rapidity range; ; ; -; y; -; ; <; 1; ; , the ratio of the measured photoproduction cross section to a baseline model prediction that neglects nuclear effects is; ; ; ; ; S; ; ; ϒ; (; 1; S; ); ; ; =; 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; (; 1; S; ); ; ; ; 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.;
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September 30, 2026 5:43 AM
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Belyaev A; Hayrapetyan A; Tumasyan A; Adam W; Andrejkovic JW; Benato L; Bergauer T; Dragicevic M; Giordano C; Hussain PS
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