Spin-dependent azimuthal asymmetry of coherent J/$ψ$ photoproduction in hadronic PbPb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.36 TeV
Year: 2026
Type: preprint
Abstract: We report a measurement of the azimuthal asymmetry of muons from the decay of coherently photoproduced J/$ψ$ mesons with respect to the second-order event plane in hadronic lead-lead (PbPb) collisions. The analysis is based on data collected by the CMS experiment at the LHC at a nucleon-nucleon center-of-mass energy of 5.36 TeV, corresponding to an integrated luminosity of 1.26 nb$^{-1}$. The asymmetry is quantified using the amplitude $A_{2}$ of the second-order harmonic modulation of the decay-muon azimuthal distribution. A negative $A_{2}$ = $-$0.194 $\pm$ 0.022 (stat.) $\pm$ 0.018 (syst.) is observed with a significance greater than five standard deviations for the first time. The $A_{2}$ values show no significant dependence on the J/$ψ$ meson rapidity or the degree of overlap of the colliding ions. A theoretical model in which the coherently photoproduced J/$ψ$ meson inherits the linear polarization of the incident photon is consistent with the data. When considered together with recent measurements of coherent $ρ^0$ $\to$ $π^+π^-$ photoproduction in ultraperipheral collisions, these results provide a direct observation of spin dependence in the azimuthal asymmetry of decay products from coherently photoproduced vector mesons. In addition, the observed correlation with the event plane may enable a novel approach to reaction plane determination in the future.
Source: arXiv (Cornell University)
Author: CMS Collaboration
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, U.S. Department of Energy, CERN, Türkiye Enerji, Nükleer ve Maden Araştırma Kurumu, Department of Science and Technology, Ministry of Science and Technology, India, Science Foundation Ireland, Deutsche Forschungsgemeinschaft, Fundação de Amparo à Pesquisa do Estado de São Paulo, National Natural Science Foundation of China, National Science Council, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Austrian Science Fund, Fonds De La Recherche Scientifique - FNRS, Fonds Wetenschappelijk Onderzoek, Ministerio de Economía y Competitividad, Bulgarian National Science Fund, Conselho Nacional de Desenvolvimento Científico e Tecnológico, Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul, Secretaría de Educación Superior, Ciencia, Tecnología e Innovación, Türkiye Bilimsel ve Teknolojik Araştırma Kurumu, Ministry of Education, India, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, National Academy of Sciences of Ukraine, Centre National de la Recherche Scientifique, Shota Rustaveli National Science Foundation, Universidad Autónoma de San Luis Potosí, Benemérita Universidad Autónoma de Puebla, Pakistan Atomic Energy Commission, Ministry of Science,Technology and Research, Nemzeti Kutatási Fejlesztési és Innovációs Hivatal, Ministry of Science and ICT, South Korea, Narodowa Agencja Wymiany Akademickiej, Ministry of Higher Education, Science, Research and Innovation, Thailand, Science and Technology Facilities Council, Fundação para a Ciência e a Tecnologia, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Agencia Estatal de Investigación, Institut National de Physique Nucléaire et de Physique des Particules
Awards: G196419191, G6024799018, G6649312515
OpenAlex ID: W7211892630