The cross section for coherent J/ψphotoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, Xn0n, is measured with the CMS experiment in ultra-peripheral PbPb collisions at √sNN=2.76TeV. The analysis is based on a data sample corresponding to an integrated luminosity of 159μb−1, collected during the 2011 PbPb run. The J/ψmesons are reconstructed in the dimuon decay channel, while neutrons are detected using zero degree calorimeters. The measured cross section is dσcohXn0n/dy(J/ψ) =0.36 ±0.04 (stat)±0.04 (syst)mbin the rapidity interval 1.8 <|y| <2.3. Using a model for the relative rate of coherent photoproduction processes, this Xn0nmeasurement gives a total coherent photoproduction cross section of dσcoh/dy(J/ψ) =1.82 ±0.22 (stat)±0.20 (syst)±0.19 (theo)mb. The data strongly disfavorthe impulse approximation model prediction, indicating that nuclear effects are needed to describe coherent J/ψphotoproduction in γ+Pbinteractions. The data are found to be consistent with the leading twist approximation, which includes nuclear gluon shadowing.
(2017). Coherent J/ψ photoproduction in ultra-peripheral PbPb collisions at √sNN=2.76 TeVwith the CMS experiment [journal article - articolo]. In PHYSICS LETTERS. SECTION B. Retrieved from http://hdl.handle.net/10446/142668
Coherent J/ψ photoproduction in ultra-peripheral PbPb collisions at √sNN=2.76 TeVwith the CMS experiment
Re, V.;Vai, I.;
2017-01-01
Abstract
The cross section for coherent J/ψphotoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, Xn0n, is measured with the CMS experiment in ultra-peripheral PbPb collisions at √sNN=2.76TeV. The analysis is based on a data sample corresponding to an integrated luminosity of 159μb−1, collected during the 2011 PbPb run. The J/ψmesons are reconstructed in the dimuon decay channel, while neutrons are detected using zero degree calorimeters. The measured cross section is dσcohXn0n/dy(J/ψ) =0.36 ±0.04 (stat)±0.04 (syst)mbin the rapidity interval 1.8 <|y| <2.3. Using a model for the relative rate of coherent photoproduction processes, this Xn0nmeasurement gives a total coherent photoproduction cross section of dσcoh/dy(J/ψ) =1.82 ±0.22 (stat)±0.20 (syst)±0.19 (theo)mb. The data strongly disfavorthe impulse approximation model prediction, indicating that nuclear effects are needed to describe coherent J/ψphotoproduction in γ+Pbinteractions. The data are found to be consistent with the leading twist approximation, which includes nuclear gluon shadowing.File | Dimensione del file | Formato | |
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