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1. Energy dependence of coherent photonuclear production of J/ψ mesons in ultra-peripheral Pb-Pb collisions at $$ \sqrt{{\textrm{s}}_{\textrm{NN}}} $$ = 5.02 TeV

   https://doi.org/10.1007/JHEP10(2023)119  

   Acharya, S ; Adamová, D ; Adler, A ; Aglieri_Rinella, G ; Agnello, M ; Agrawal, N ; Ahammed, Z ; Ahmad, S ; Ahn, S U ; Ahuja, I ; et al ( October 2023 , Journal of High Energy Physics)

   The cross section for coherent photonuclear production of J/ψis presented as a function of the electromagnetic dissociation (EMD) of Pb. The measurement is performed with the ALICE detector in ultra-peripheral Pb-Pb collisions at a centre-of-mass energy per nucleon pair of$$ \sqrt{{\textrm{s}}_{\textrm{NN}}} $$$\sqrt{s_{\mathrm{NN}}}$= 5.02 TeV. Cross sections are presented in five different J/ψrapidity ranges within |y| < 4, with the J/ψreconstructed via its dilepton decay channels. In some events the J/ψis not accompanied by EMD, while other events do produce neutrons from EMD at beam rapidities either in one or the other beam direction, or in both. The cross sections in a given rapidity range and for different configurations of neutrons from EMD allow for the extraction of the energy dependence of this process in the range 17 <W_γPb,n< 920 GeV, whereW_γPb,nis the centre-of-mass energy per nucleon of theγPb system. This range corresponds to a Bjorken-xinterval spanning about three orders of magnitude: 1.1 × 10⁻⁵<x< 3.3 × 10⁻². In addition to the ultra-peripheral and photonuclear cross sections, the nuclear suppression factor is obtained. These measurements point to a strong depletion of the gluon distribution in Pb nuclei over a broad, previously unexplored, energy range. These results, together with previous ALICE measurements, provide unprecedented information to probe quantum chromodynamics at high energies.

    

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2. Coherent $$\mathrm{J}/\psi $$ and $${\uppsi '}$$ photoproduction at midrapidity in ultra-peripheral Pb–Pb  collisions at $$\sqrt{s_{\mathrm {NN}}}~=~5.02$$ TeV

   https://doi.org/10.1140/epjc/s10052-021-09437-6  

   Acharya, S. ; Adamová, D. ; Adler, A. ; Adolfsson, J. ; Rinella, G. Aglieri ; Agnello, M. ; Agrawal, N. ; Ahammed, Z. ; Ahmad, S. ; Ahn, S. U. ; et al ( August 2021 , The European Physical Journal C)

   Abstract The coherent photoproduction of $$\mathrm{J}/\psi $$ J / ψ and $${\uppsi '}$$ ψ ′ mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy $$\sqrt{s_{\mathrm {NN}}}~=~5.02$$ s NN = 5.02  TeV  with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The $$\mathrm{J}/\psi $$ J / ψ is reconstructed using the dilepton ( $$l^{+} l^{-}$$ l + l - ) and proton–antiproton decay channels, while for the $${\uppsi '}$$ ψ ′   the dilepton and the $$l^{+} l^{-} \pi ^{+} \pi ^{-}$$ l + l - π + π - decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 $$\mu {\mathrm{b}}^{-1}$$ μ b - 1 . The results are compared with theoretical models for coherent $$\mathrm{J}/\psi $$ J / ψ and $${\uppsi '}$$ ψ ′ photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.64 at a Bjorken- x of around $$6\times 10^{-4}$$ 6 × 10 - 4 , such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent $$\mathrm{J}/\psi $$ J / ψ cross section including ALICE measurements at forward rapidity. The ratio of $${\uppsi '}$$ ψ ′ to $$\mathrm{J}/\psi $$ J / ψ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons. 

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3. Measurement of exclusive $$\mathrm {\Upsilon }$$ photoproduction from protons in $$\mathrm {p}$$Pb collisions at $$\sqrt{\smash [b]{s_{_{\mathrm {NN}}}}} = 5.02\,\text {TeV} $$

   https://doi.org/10.1140/epjc/s10052-019-6774-8  

   Sirunyan, A. M. ; Tumasyan, A. ; Adam, W. ; Ambrogi, F. ; Asilar, E. ; Bergauer, T. ; Brandstetter, J. ; Brondolin, E. ; Dragicevic, M. ; Erö, J. ; et al ( March 2019 , The European Physical Journal C)

   Abstract The exclusive photoproduction of $$\mathrm {\Upsilon }\mathrm {(nS)} $$ Υ ( nS ) meson states from protons, $$\gamma \mathrm {p} \rightarrow \mathrm {\Upsilon }\mathrm {(nS)} \,\mathrm {p}$$ γ p → Υ ( nS ) p (with $$\mathrm {n}=1,2,3$$ n = 1 , 2 , 3 ), is studied in ultraperipheral $$\mathrm {p}$$ p Pb collisions at a centre-of-mass energy per nucleon pair of $$\sqrt{\smash [b]{s_{_{\mathrm {NN}}}}} = 5.02\,\text {TeV} $$ s NN = 5.02 TeV . The measurement is performed using the $$\mathrm {\Upsilon }\mathrm {(nS)} \rightarrow \mu ^+\mu ^-$$ Υ ( nS ) → μ + μ - decay mode, with data collected by the CMS experiment corresponding to an integrated luminosity of 32.6 $$\,\text {nb}^{-1}$$ nb - 1 . Differential cross sections as functions of the $$\mathrm {\Upsilon }\mathrm {(nS)} $$ Υ ( nS ) transverse momentum squared $$p_{\mathrm {T}} ^2$$ p T 2 , and rapidity y , are presented. The $$\mathrm {\Upsilon (1S)}$$ Υ ( 1 S ) photoproduction cross section is extracted in the rapidity range $$|y |< 2.2$$ | y | < 2.2 , which corresponds to photon–proton centre-of-mass energies in the range $$91 more » « less
4. Inclusive, prompt and non-prompt J/ψ production at midrapidity in p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 5.02 TeV

   https://doi.org/10.1007/JHEP06(2022)011  

   Acharya, S. ; Adamová, D. ; Adler, A. ; Adolfsson, J. ; Aglieri Rinella, G. ; Agnello, M. ; Agrawal, N. ; Ahammed, Z. ; Ahmad, S. ; Ahn, S. U. ; et al ( June 2022 , Journal of High Energy Physics)

   A bstract A measurement of inclusive, prompt, and non-prompt J/ ψ production in p-Pb collisions at a nucleon-nucleon centre-of-mass energy $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5 . 02 TeV is presented. The inclusive J/ ψ mesons are reconstructed in the dielectron decay channel at midrapidity down to a transverse momentum p T = 0. The inclusive J/ ψ nuclear modification factor R pPb is calculated by comparing the new results in p-Pb collisions to a recently measured proton-proton reference at the same centre-of-mass energy. Non-prompt J/ ψ mesons, which originate from the decay of beauty hadrons, are separated from promptly produced J/ ψ on a statistical basis for p T larger than 1.0 GeV/ c . These results are based on the data sample collected by the ALICE detector during the 2016 LHC p-Pb run, corresponding to an integrated luminosity $$ \mathcal{L} $$ L int = 292 ± 11 μ b − 1 , which is six times larger than the previous publications. The total uncertainty on the p T -integrated inclusive J/ ψ and non-prompt J/ ψ cross section are reduced by a factor 1.7 and 2.2, respectively. The measured cross sections and R pPb are compared with theoretical models that include various combinations of cold nuclear matter effects. From the non-prompt J/ ψ production cross section, the $$ \mathrm{b}\overline{\mathrm{b}} $$ b b ¯ production cross section at midrapidity, $$ {\mathrm{d}\sigma}_{\mathrm{b}\overline{\mathrm{b}}} $$ d σ b b ¯ / d y , and the total cross section extrapolated over full phase space, $$ {\sigma}_{\mathrm{b}\overline{\mathrm{b}}} $$ σ b b ¯ , are derived. 

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5. W±-boson production in p–Pb collisions at $$ \sqrt{s_{\textrm{NN}}} $$ = 8.16 TeV and Pb–Pb collisions at $$ \sqrt{s_{\textrm{NN}}} $$ = 5.02 TeV

   https://doi.org/10.1007/JHEP05(2023)036  

   Acharya, S. ; Adamová, D. ; Adler, A. ; Aglieri Rinella, G. ; Agnello, M. ; Agrawal, N. ; Ahammed, Z. ; Ahmad, S. ; Ahn, S. U. ; Ahuja, I. ; et al ( May 2023 , Journal of High Energy Physics)

   A bstract The production of the W ± bosons measured in p–Pb collisions at a centre-of-mass energy per nucleon–nucleon collision $$ \sqrt{s_{\textrm{NN}}} $$ s NN = 8 . 16 TeV and Pb–Pb collisions at $$ \sqrt{s_{\textrm{NN}}} $$ s NN = 5 . 02 TeV with ALICE at the LHC is presented. The W ± bosons are measured via their muonic decay channel, with the muon reconstructed in the pseudorapidity region − 4 < $$ {\eta}_{\textrm{lab}}^{\mu } $$ η lab μ < − 2 . 5 with transverse momentum $$ {p}_{\textrm{T}}^{\mu } $$ p T μ > 10 GeV /c . While in Pb–Pb collisions the measurements are performed in the forward (2 . 5 < $$ {y}_{\textrm{cms}}^{\mu } $$ y cms μ < 4) rapidity region, in p–Pb collisions, where the centre-of-mass frame is boosted with respect to the laboratory frame, the measurements are performed in the backward ( − 4 . 46 < $$ {y}_{\textrm{cms}}^{\mu } $$ y cms μ < − 2 . 96) and forward (2 . 03 < $$ {y}_{\textrm{cms}}^{\mu } $$ y cms μ < 3 . 53) rapidity regions. The W − and W + production cross sections, lepton-charge asymmetry, and nuclear modification factors are evaluated as a function of the muon rapidity. In order to study the production as a function of the p–Pb collision centrality, the production cross sections of the W − and W + bosons are combined and normalised to the average number of binary nucleon–nucleon collision 〈 N coll 〉. In Pb–Pb collisions, the same measurements are presented as a function of the collision centrality. Study of the binary scaling of the W ± -boson cross sections in p–Pb and Pb–Pb collisions is also reported. The results are compared with perturbative QCD calculations, with and without nuclear modifications of the Parton Distribution Functions (PDFs), as well as with available data at the LHC. Significant deviations from the theory expectations are found in the two collision systems, indicating that the measurements can provide additional constraints for the determination of nuclear PDFs and in particular of the light-quark distributions. 

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