Production of inclusive charmonia in pp collisions at center-of-mass energy of $\sqrt{s}$ = 13 TeV and p-Pb collisions at center-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}}$ = 8.16 TeV is studied as a function of charged-particle pseudorapidity density with ALICE. Ground and excited charmonium states (J/$\psi$, $\psi$(2S)) are measured from their dimuon decays in the interval of rapidity in the center-of-mass frame $2.5 <~ y_{\rm cms} <~ 4.0$ for pp collisions, and $2.03 <~ y_{\rm cms} <~ 3.53$ and $-4.46 <~ y_{\rm cms} <~ -2.96$ for p-Pb collisions. The charged-particle pseudorapidity density is measured around midrapidity ($|\eta|<~1.0$). In pp collisions, the measured charged-particle multiplicity extends to about six times the average value, while in p-Pb collisions at forward (backward) rapidity a multiplicity corresponding to about three (four) times the average is reached. The $\psi$(2S) yield increases with the charged-particle pseudorapidity density. The ratio of $\psi$(2S) over J/$\psi$ yield does not show a significant multiplicity dependence in either colliding system, suggesting a similar behavior of J/$\psi$ and $\psi$(2S) yields with respect to charged-particle pseudorapidity density. Results for the $\psi$(2S) yield and its ratio with respect to J/$\psi$ agree with available model calculations.
JHEP 06 (2023) 147
HEP Data
e-Print: arXiv:2204.10253 | PDF | inSPIRE
CERN-EP-2022-064
Figure group
Figure 1
Invariant-mass distribution of opposite-sign muon pairs in (a) forward p-Pb, (b) backward p-Pb, and (c) pp data, integrated in multiplicity. Superimposed is a typical fit function, shown as a solid blue line (see text on details regarding the fit components). The J$/\psi$ and $\psi$(2S) contributions are shown as red and yellow shaded areas, respectively. Finally the background is depicted as a dashed gray line. The inset shows the region of the $\psi$(2S) mass. |    |
Figure 2
The normalized $\psi$(2S) yield as a function of the normalized charged-particle pseudorapidity density in pp collisions at $\sqrt{s}$ = 13 TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16 TeV. Quoted is the correlated event-class normalization uncertainty. The pp results are normalized to the INEL$>$0 event class, whereas the p-Pb ones refer to the NSD one. |  |
Figure 3
Ratio of normalized $\psi{\rm (2S)}\mbox{-over-}{\rm J}/\psi$ yield as a function of the normalized charged-particle pseudorapidity density in pp collisions at $\sqrt{s}$ = 13 TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16 TeV. The pp results are normalized to the INEL$>$0 event class, whereas the p-Pb ones refer to the NSD one. |  |
Figure 4
The normalized $\psi$(2S) yield and the ratio of normalized $\psi{\rm (2S)}\mbox{-over-}{\rm J}/\psi$ yields at $2.5 < y_{\rm cms} <4.0$ as a function of the normalized charged-particle pseudorapidity density in pp collisions at $\sqrt{s}$ = 13 TeV. Measurements are compared with the following models: PYTHIA 8.2, PYTHIA 8.2 without color reconnection (no CR), comovers. Quoted is the correlated event-class normalization uncertainty. |   |
Figure 5
The normalized $\psi$(2S) yield and the ratio of normalized $\psi{\rm (2S)}\mbox{-over-}{\rm J}/\psi$ yields at $2.03<y_{\rm cms}<3.53$ as a function of the normalized charged-particle pseudorapidity density in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16 TeV. Measurements are compared with the percolation calculation coupled with comover model and EPS09 nPDF. Quoted is the correlated event-class normalization uncertainty. |   |
Figure 6
The normalized $\psi$(2S) yield and the ratio of normalized $\psi{\rm (2S)}\mbox{-over-}{\rm J}/\psi$ yields at $-4.46<y_{\rm cms}<-2.96$ as a function of the normalized charged-particle pseudorapidity density in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16 TeV. Measurements are compared with the percolation calculation coupled with comover model and EPS09 nPDF. Quoted is the correlated event-class normalization uncertainty. |   |