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| CMS-PAS-HIN-23-009 | ||
| The Bjorken-$ x $ evolution of gluon fields probed via incoherent $ \mathrm{J}/\psi $ photoproduction in ultraperipheral PbPb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 5.02 TeV | ||
| CMS Collaboration | ||
| 23 September 2024 | ||
| Abstract: The cross section for incoherent $ \mathrm{J}/\psi $ photoproduction off lead nuclei is measured to probe the event-by-event fluctuations of the gluon field density within heavy nuclei across a broad range of Bjorken-$ x $. Results are obtained using PbPb ultraperipheral collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV collected by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 1.52 nb$^{-1}$. The dependence of the cross section on the photon-nucleus center-of-mass energy per nucleon ($ W^{\mathrm{Pb}}_{\gamma\mathrm{N}} $) is studied from $ W^{\mathrm{Pb}}_{\gamma\mathrm{N}} \approx $ 40 GeV up to 400 GeV, corresponding to a Bjorken-$ x $ interval of 5.8 $ \times $ 10$^{-3}$ $ > x > $ 6.5 $\times$ 10$^{-5} $. The ratio of incoherent to coherent $ \mathrm{J}/\psi $ cross sections is found to be independent of $ W^{\mathrm{Pb}}_{\gamma\mathrm{N}} $ and $ x $ over the range studied. Significant nuclear suppression of incoherent $ \mathrm{J}/\psi $ photoproduction is observed. For $ x < $ 10$^{-4} $, the suppression is comparable to that observed in coherent $ \mathrm{J}/\psi $ photoproduction, becoming more pronounced as $ x $ increases. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, Submitted to PRL. The superseded preliminary plots can be found here. |
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Compact Muon Solenoid LHC, CERN |
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