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| Natura: | Preprint |
| Pubblicazione: |
2023
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| Accesso online: | https://arxiv.org/abs/2304.10928 |
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| _version_ | 1866916738436694016 |
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| author | ALICE Collaboration |
| author_facet | ALICE Collaboration |
| contents | The first measurement of the polarisation of coherently photoproduced J$/ψ$ mesons in ultra-peripheral Pb-Pb collisions, using data at $\sqrt{s_{\rm NN}}$ = 5.02 TeV, is presented. The J/$ψ$ meson is measured via its dimuon decay channel in the forward rapidity interval $-4.0 < y < -2.5$ using the ALICE detector at the CERN LHC. An event sample corresponding to an integrated luminosity of 750 $μ\text{b}^{-1}$ $\pm$ 5% (syst) is analysed. Hadronic activity is highly suppressed since the interaction is mediated by a photon. The polar and azimuthal angle distributions of the decay muons are measured, and the polarisation parameters $\mathbf{λ_θ}$, $\mathbf{λ_φ}$, $\mathbf{λ_{θφ}}$ are extracted. The analysis is carried out in the helicity frame. The results are found to be consistent with a transversely polarised J/$ψ$. These values are compared with previous measurements by the H1 and ZEUS experiments. The polarisation parameters of coherent J/$ψ$ photoproduction in Pb-Pb collisions are found to be consistent with the $s$-channel helicity conservation hypothesis. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2304_10928 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | First polarisation measurement of coherently photoproduced J/$ψ$ in ultra-peripheral Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV ALICE Collaboration Nuclear Experiment High Energy Physics - Experiment The first measurement of the polarisation of coherently photoproduced J$/ψ$ mesons in ultra-peripheral Pb-Pb collisions, using data at $\sqrt{s_{\rm NN}}$ = 5.02 TeV, is presented. The J/$ψ$ meson is measured via its dimuon decay channel in the forward rapidity interval $-4.0 < y < -2.5$ using the ALICE detector at the CERN LHC. An event sample corresponding to an integrated luminosity of 750 $μ\text{b}^{-1}$ $\pm$ 5% (syst) is analysed. Hadronic activity is highly suppressed since the interaction is mediated by a photon. The polar and azimuthal angle distributions of the decay muons are measured, and the polarisation parameters $\mathbf{λ_θ}$, $\mathbf{λ_φ}$, $\mathbf{λ_{θφ}}$ are extracted. The analysis is carried out in the helicity frame. The results are found to be consistent with a transversely polarised J/$ψ$. These values are compared with previous measurements by the H1 and ZEUS experiments. The polarisation parameters of coherent J/$ψ$ photoproduction in Pb-Pb collisions are found to be consistent with the $s$-channel helicity conservation hypothesis. |
| title | First polarisation measurement of coherently photoproduced J/$ψ$ in ultra-peripheral Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV |
| topic | Nuclear Experiment High Energy Physics - Experiment |
| url | https://arxiv.org/abs/2304.10928 |