Evidence of Spin-Interference Effects in Exclusive $J/ψ\to e^+e^-$ Photoproduction in Ultraperipheral Heavy-Ion Collisions
Fuente:
arXiv
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| Natura: | Preprint |
| Pubblicazione: |
2025
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| _version_ | 1866915648986152960 |
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| author | The STAR Collaboration |
| author_facet | The STAR Collaboration |
| contents | We report the first evidence of spin interference in exclusive $J/ψ\to e^+e^-$ photoproduction in ultraperipheral Au+Au and isobar (Ru+Ru, Zr+Zr) collisions ($\sqrt{s_{NN}} = 200$~GeV) at STAR. A negative $\cos(2ϕ)$ modulation is observed for $p_T < 100$ MeV/$c$, opposite in sign to that in $ρ^{0}\!\to\!π^+π^-$ photoproduction. This establishes for the first time that the interference sign is controlled by the spin structure of the final-state daughters, resolving the ambiguity present in the all-boson $ρ^0$ channel. The compact $J/ψ$ probes gluon distributions at perturbative scales, resulting in a weaker modulation and providing stringent constraints on Color Glass Condensate calculations. These findings demonstrate that spin-dependent interference in heavy vector mesons provides a new, experimentally accessible handle on gluon structure beyond traditional cross-section measurements. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2512_02865 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Evidence of Spin-Interference Effects in Exclusive $J/ψ\to e^+e^-$ Photoproduction in Ultraperipheral Heavy-Ion Collisions The STAR Collaboration Nuclear Experiment High Energy Physics - Experiment High Energy Physics - Phenomenology Nuclear Theory We report the first evidence of spin interference in exclusive $J/ψ\to e^+e^-$ photoproduction in ultraperipheral Au+Au and isobar (Ru+Ru, Zr+Zr) collisions ($\sqrt{s_{NN}} = 200$~GeV) at STAR. A negative $\cos(2ϕ)$ modulation is observed for $p_T < 100$ MeV/$c$, opposite in sign to that in $ρ^{0}\!\to\!π^+π^-$ photoproduction. This establishes for the first time that the interference sign is controlled by the spin structure of the final-state daughters, resolving the ambiguity present in the all-boson $ρ^0$ channel. The compact $J/ψ$ probes gluon distributions at perturbative scales, resulting in a weaker modulation and providing stringent constraints on Color Glass Condensate calculations. These findings demonstrate that spin-dependent interference in heavy vector mesons provides a new, experimentally accessible handle on gluon structure beyond traditional cross-section measurements. |
| title | Evidence of Spin-Interference Effects in Exclusive $J/ψ\to e^+e^-$ Photoproduction in Ultraperipheral Heavy-Ion Collisions |
| topic | Nuclear Experiment High Energy Physics - Experiment High Energy Physics - Phenomenology Nuclear Theory |
| url | https://arxiv.org/abs/2512.02865 |