Dielectron production in central Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV
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2023
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| _version_ | 1866917196665454592 |
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| author | ALICE Collaboration |
| author_facet | ALICE Collaboration |
| contents | The first measurement of the e$^+$e$^-$ pair production at midrapidity and low invariant mass in central Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV at the LHC is presented. The yield of e$^+$e$^-$ pairs is compared with a cocktail of expected hadronic decay contributions in the invariant mass ($m_{\rm ee}$) and pair transverse momentum ($p_{\rm T,ee}$) ranges $m_{\rm ee} < 3.5$ GeV$/c^2$ and $p_{\rm T,ee} < 8$ GeV$/c$. For $0.18 < m_{\rm ee} < 0.5$ GeV$/c^2$ the ratio of data to the cocktail of hadronic contributions amounts to $1.40 \pm 0.11 \ ({\rm stat.}) \pm 0.23 \ ({\rm syst.}) \pm 0.16 \ ({\rm cocktail})$ and $1.42 \pm 0.11 \ ({\rm stat.}) \pm 0.23 \ ({\rm syst.}) ^{+0.24}_{-0.29} \ ({\rm cocktail})$, including or not including medium effects in the estimation of the heavy-flavor background, respectively. It is consistent with predictions from two different models for an additional contribution of thermal e$^+$e$^-$ pairs from the hadronic and partonic phases. In the intermediate-mass range ($1.2 < m_{\rm ee} < 2.6$ GeV$/c^2$), the pair transverse impact parameter of the e$^+$e$^-$ pairs (DCA$_{\rm ee}$) is used for the first time in Pb$-$Pb collisions to separate displaced dielectrons from heavy-flavor hadron decays from a possible (thermal) contribution produced at the interaction point. The data are consistent with a suppression of e$^+$e$^-$ pairs from ${\rm c\overline{c}}$ and an additional prompt component. Finally, the first direct-photon measurement in the 10\% most central Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV is reported via the study of virtual direct photons in the transverse momentum range $1 < p_{\rm T} < 5$ GeV$/c$. A model including prompt photons, as well as photons from the pre-equilibrium and fluid-dynamic phases, can reproduce the result, while being at the upper edge of the data uncertainties. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2308_16704 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Dielectron production in central Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV ALICE Collaboration Nuclear Experiment High Energy Physics - Experiment The first measurement of the e$^+$e$^-$ pair production at midrapidity and low invariant mass in central Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV at the LHC is presented. The yield of e$^+$e$^-$ pairs is compared with a cocktail of expected hadronic decay contributions in the invariant mass ($m_{\rm ee}$) and pair transverse momentum ($p_{\rm T,ee}$) ranges $m_{\rm ee} < 3.5$ GeV$/c^2$ and $p_{\rm T,ee} < 8$ GeV$/c$. For $0.18 < m_{\rm ee} < 0.5$ GeV$/c^2$ the ratio of data to the cocktail of hadronic contributions amounts to $1.40 \pm 0.11 \ ({\rm stat.}) \pm 0.23 \ ({\rm syst.}) \pm 0.16 \ ({\rm cocktail})$ and $1.42 \pm 0.11 \ ({\rm stat.}) \pm 0.23 \ ({\rm syst.}) ^{+0.24}_{-0.29} \ ({\rm cocktail})$, including or not including medium effects in the estimation of the heavy-flavor background, respectively. It is consistent with predictions from two different models for an additional contribution of thermal e$^+$e$^-$ pairs from the hadronic and partonic phases. In the intermediate-mass range ($1.2 < m_{\rm ee} < 2.6$ GeV$/c^2$), the pair transverse impact parameter of the e$^+$e$^-$ pairs (DCA$_{\rm ee}$) is used for the first time in Pb$-$Pb collisions to separate displaced dielectrons from heavy-flavor hadron decays from a possible (thermal) contribution produced at the interaction point. The data are consistent with a suppression of e$^+$e$^-$ pairs from ${\rm c\overline{c}}$ and an additional prompt component. Finally, the first direct-photon measurement in the 10\% most central Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV is reported via the study of virtual direct photons in the transverse momentum range $1 < p_{\rm T} < 5$ GeV$/c$. A model including prompt photons, as well as photons from the pre-equilibrium and fluid-dynamic phases, can reproduce the result, while being at the upper edge of the data uncertainties. |
| title | Dielectron production in central Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV |
| topic | Nuclear Experiment High Energy Physics - Experiment |
| url | https://arxiv.org/abs/2308.16704 |