478 research outputs found

    Inclusive, prompt and non-prompt J/ψ production at midrapidity in p-Pb collisions at √sNN = 5.02 TeV

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    A measurement of inclusive, prompt, and non-prompt J/ψ production in p-Pb collisions at a nucleon-nucleon centre-of-mass energy sNN = 5.02 TeV is presented. The inclusive J/ψ mesons are reconstructed in the dielectron decay channel at midrapidity down to a transverse momentum pT = 0. The inclusive J/ψ nuclear modification factor RpPb 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 pT 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 Lint = 292 ± 11 μb−1, which is six times larger than the previous publications. The total uncertainty on the pT-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 RpPb are compared with theoretical models that include various combinations of cold nuclear matter effects. From the non-prompt J/ψ production cross section, the b b ̄ production cross section at midrapidity, d σbb ̄/dy, and the total cross section extrapolated over full phase space, σbb ̄, are derived. [Figure not available: see fulltext.

    First measurement of the vertical bar t vertical bar-dependence of coherent J/psi photonuclear production

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    The first measurement of the cross section for coherent J/Psi photoproduction as a function of vertical bar t vertical bar, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb-Pbcollisions at a centre-of-mass energy per nucleon pair root s(NN) = 5.02 TeV with the J/Psi produced in the central rapidity region vertical bar y vertical bar < 0.8, which corresponds to the small Bjorken-xrange (0.3 - 1.4) x 10(-3). The measured vertical bar t vertical bar-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky-Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken- x. (C) 2021 The Author(s). Published by Elsevier B.V

    Coherent J/psi and psi ' photoproduction at midrapidity in ultra-peripheral Pb-Pb collisions at root s(NN)=5.02 TeV

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    The coherent photoproduction of J / ψ and ψ ′ mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy sNN=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 J / ψ is reconstructed using the dilepton (l+l-) and proton–antiproton decay channels, while for the ψ ′ the dilepton and the l+l-π+π- decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 μb - 1. The results are compared with theoretical models for coherent J / ψ and 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 × 10 - 4, such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent J / ψ cross section including ALICE measurements at forward rapidity. The ratio of ψ ′ to J / ψ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons

    J/psi elliptic and triangular flow in Pb-Pb collisions at root s(NN)=5.02 TeV

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    The inclusive J/ψ elliptic (v2) and triangular (v3) flow coefficients measured at forward rapidity (2.5 &lt; y &lt; 4) and the v2 measured at midrapidity (|y| &lt; 0.9) in Pb-Pb collisions at sNN = 5.02 TeV using the ALICE detector at the LHC are reported. The entire Pb-Pb data sample collected during Run 2 is employed, amounting to an integrated luminosity of 750 μb−1 at forward rapidity and 93 μb−1 at midrapidity. The results are obtained using the scalar product method and are reported as a function of transverse momentum pT and collision centrality. At midrapidity, the J/ψ v2 is in agreement with the forward rapidity measurement. The centrality averaged results indicate a positive J/ψ v3 with a significance of more than 5σ at forward rapidity in the pT range 2 &lt; pT&lt; 5 GeV/c. The forward rapidity v2, v3, and v3/v2 results at low and intermediate pT (pT ≲ 8 GeV/c) exhibit a mass hierarchy when compared to pions and D mesons, while converging into a species-independent curve at higher pT. At low and intermediate pT, the results could be interpreted in terms of a later thermalization of charm quarks compared to light quarks, while at high pT, path-length dependent effects seem to dominate. The J/ψ v2 measurements are further compared to a microscopic transport model calculation. Using a simplified extension of the quark scaling approach involving both light and charm quark flow components, it is shown that the D-meson vn measurements can be described based on those for charged pions and J/ψ flow. [Figure not available: see fulltext.

    Inclusive J / ψ production at midrapidity in pp collisions at √s=13 TeV

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    We report on the inclusive J / ψ production cross section measured at the CERN Large Hadron Collider in proton–proton collisions at a center-of-mass energy s=13&nbsp;TeV. The J / ψ mesons are reconstructed in the e +e - decay channel and the measurements are performed at midrapidity (| y| &lt; 0.9) in the transverse-momentum interval 0 &lt; pT&lt; 40 GeV/c, using a minimum-bias data sample corresponding to an integrated luminosity Lint=32.2nb-1 and an Electromagnetic Calorimeter triggered data sample with Lint=8.3pb-1. The pT-integrated J / ψ production cross section at midrapidity, computed using the minimum-bias data sample, is dσ/dy|y=0=8.97±0.24(stat)±0.48(syst)±0.15(lumi)μb. An approximate logarithmic dependence with the collision energy is suggested by these results and available world data, in agreement with model predictions. The integrated and pT-differential measurements are compared with measurements in pp collisions at lower energies and with several recent phenomenological calculations based on the non-relativistic QCD and Color Evaporation models

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

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    Abstract The coherent photoproduction of J/ψ\mathrm{J}/\psi J / ψ and {\uppsi '} ψ ′ mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy sNN = 5.02\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 J/ψ\mathrm{J}/\psi J / ψ is reconstructed using the dilepton ( l+ll^{+} l^{-} l + l - ) and proton–antiproton decay channels, while for the {\uppsi '} ψ ′   the dilepton and the l+lπ+πl^{+} 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 μb1\mu {\mathrm{b}}^{-1} μ b - 1 . The results are compared with theoretical models for coherent J/ψ\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 6×1046\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 J/ψ\mathrm{J}/\psi J / ψ cross section including ALICE measurements at forward rapidity. The ratio of {\uppsi '} ψ ′ to J/ψ\mathrm{J}/\psi J / ψ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons

    J/psi production as a function of charged-particle multiplicity in p-Pb collisions at root s(NN)=8.16 TeV

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    Inclusive J/ψ yields and average transverse momenta in p-Pb collisions at a center-of-mass energy per nucleon pair sNN = 8.16 TeV are measured as a function of the charged-particle pseudorapidity density with ALICE. The J/ψ mesons are reconstructed at forward (2.03 &lt; ycms&lt; 3.53) and backward (−4.46 &lt; ycms&lt; −2.96) center-of-mass rapidity in their dimuon decay channel while the charged-particle pseudorapidity density is measured around midrapidity. The J/ψ yields at forward and backward rapidity normalized to their respective average values increase with the normalized charged-particle pseudorapidity density, the former showing a weaker increase than the latter. The normalized average transverse momenta at forward and backward rapidity manifest a steady increase from low to high charged-particle pseudorapidity density with a saturation beyond the average value. [Figure not available: see fulltext.

    Inclusive J / ψ production at midrapidity in pp collisions at √s=13 TeV

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    We report on the inclusive J / ψ production cross section measured at the CERN Large Hadron Collider in proton–proton collisions at a center-of-mass energy s=13 TeV. The J / ψ mesons are reconstructed in the e +e - decay channel and the measurements are performed at midrapidity (| y| TT-integrated J / ψ production cross section at midrapidity, computed using the minimum-bias data sample, is dσ/dy|y=0=8.97±0.24(stat)±0.48(syst)±0.15(lumi)μb. An approximate logarithmic dependence with the collision energy is suggested by these results and available world data, in agreement with model predictions. The integrated and pT-differential measurements are compared with measurements in pp collisions at lower energies and with several recent phenomenological calculations based on the non-relativistic QCD and Color Evaporation models

    J/psi elliptic and triangular flow in Pb-Pb collisions at root s(NN)=5.02 TeV

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    The inclusive J/psi (v(2)) and triangular (v(3)) flow coefficients measured at forward rapidity (2.5 < y < 4) and the v2 measured at midrapidity (vertical bar y vertical bar < 0.9) in Pb-Pb collisions at root s(NN) = 5.02TeV using the ALICE detector at the LHC are reported. The entire Pb-Pb data sample collected during Run 2 is employed, amounting to an integrated luminosity of 750 mu b(-1) at forward rapidity and 93 mu b(-1) at midrapidity. The results are obtained using the scalar product method and are reported as a function of transverse momentum p(T) and collision centrality. At midrapidity, the J psi v(2) is in agreement with the forward rapidity measurement. The centrality averaged results indicate a positive J/psi v(3) with a significance of more than 5 sigma at forward rapidity in the p(T) range 2 < p(T) < 5 GeV/c. The forward rapidity v(2), v(3), and v(3)/v(2) results at low and intermediate p(T) (p(T) < 8 GeV/c) exhibit a mass hierarchy when compared to pions and D mesons, while converging into a species-independent curve at higher p(T). At low and intermediate p(T), the results could be interpreted in terms of a later thermalization of charm quarks compared to light quarks, while at high p(T), path-length dependent effects seem to dominate. The J/psi v(2) measurements are further compared to a microscopic transport model calculation. Using a simplified extension of the quark scaling approach involving both light and charm quark flow components, it is shown that the D-meson vn measurements can be described based on those for charged pions and J/flow

    Forward rapidity J/ψ production as a function of charged-particle multiplicity in pp collisions at √s = 5.02 and 13 TeV

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    The production of J/ψ is measured as a function of charged-particle multiplicity at forward rapidity in proton-proton (pp) collisions at center-of-mass energies s = 5.02 and 13 TeV. The J/ψ mesons are reconstructed via their decay into dimuons in the rapidity interval (2.5 &lt; y &lt; 4.0), whereas the charged-particle multiplicity density (dNch/dη) is measured at midrapidity (|η| &lt; 1). The production rate as a function of multiplicity is reported as the ratio of the yield in a given multiplicity interval to the multiplicity-integrated one. This observable shows a linear increase with charged-particle multiplicity normalized to the corresponding average value for inelastic events (dNch/dη/〈dNch/dη〉), at both the colliding energies. Measurements are compared with available ALICE results at midrapidity and theoretical model calculations. First measurement of the mean transverse momentum (〈pT〉) of J/ψ in pp collisions exhibits an increasing trend as a function of dNch/dη/〈dNch/dη〉 showing a saturation towards high charged-particle multiplicities. [Figure not available: see fulltext.
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