Coherent $$\mathrm{J}/\psi $$ and $${\uppsi '}$$ photoproduction at midrapidity in ultra-peripheral Pb–Pb collisions at $$\sqrt{s_{\mathrm {NN}}}~=~5.02$$ TeV
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<jats:title>Abstract</jats:title><jats:p>The coherent photoproduction of <jats:inline-formula><jats:alternatives><jats:tex-math>$$\mathrm{J}/\psi $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> and <jats:inline-formula><jats:alternatives><jats:tex-math>$${\uppsi '}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>ψ</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula> mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy <jats:inline-formula><jats:alternatives><jats:tex-math>$$\sqrt{s_{\mathrm {NN}}}~=~5.02$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msqrt> <mml:msub> <mml:mi>s</mml:mi> <mml:mi>NN</mml:mi> </mml:msub> </mml:msqrt> <mml:mspace /> <mml:mo>=</mml:mo> <mml:mspace /> <mml:mn>5.02</mml:mn> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The <jats:inline-formula><jats:alternatives><jats:tex-math>$$\mathrm{J}/\psi $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> is reconstructed using the dilepton (<jats:inline-formula><jats:alternatives><jats:tex-math>$$l^{+} l^{-}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>l</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>l</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula>) and proton–antiproton decay channels, while for the <jats:inline-formula><jats:alternatives><jats:tex-math>$${\uppsi '}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>ψ</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula> the dilepton and the <jats:inline-formula><jats:alternatives><jats:tex-math>$$l^{+} l^{-} \pi ^{+} \pi ^{-}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>l</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>l</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 <jats:inline-formula><jats:alternatives><jats:tex-math>$$\mu {\mathrm{b}}^{-1}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>μ</mml:mi> <mml:msup> <mml:mrow> <mml:mi>b</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula>. The results are compared with theoretical models for coherent <jats:inline-formula><jats:alternatives><jats:tex-math>$$\mathrm{J}/\psi $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> and <jats:inline-formula><jats:alternatives><jats:tex-math>$${\uppsi '}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>ψ</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula> 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-<jats:italic>x</jats:italic> of around <jats:inline-formula><jats:alternatives><jats:tex-math>$$6\times 10^{-4}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>6</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula>, such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent <jats:inline-formula><jats:alternatives><jats:tex-math>$$\mathrm{J}/\psi $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> cross section including ALICE measurements at forward rapidity. The ratio of <jats:inline-formula><jats:alternatives><jats:tex-math>$${\uppsi '}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>ψ</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula> to <jats:inline-formula><jats:alternatives><jats:tex-math>$$\mathrm{J}/\psi $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons.</jats:p>
収録刊行物
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- The European Physical Journal C
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The European Physical Journal C 81 (8), 2021-08
Springer Science and Business Media LLC
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詳細情報 詳細情報について
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- CRID
- 1360013168838575488
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- ISSN
- 14346052
- 14346044
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