Measurement of $ψ$(2S) production as a function of charged-particle pseudorapidity density in pp collisions at $\sqrt{s}$ = 13 TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16 TeV with ALICE at the LHC

Charmonium production 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. The results are also compared with model calculations.

 

Submitted to: JHEP
e-Print: arXiv:2204.10253 | PDF | inSPIRE
Figure group

Figure 1

The normalized $\psip$ yield as a function of the normalized charged-particle pseudorapidity density in \pp collisions at \thirteen and \pPb collisions at \eightnn. Quoted is the correlated event-class normalization uncertainty. The \pp results are normalized to the INEL$>$0 event class, whereas the \pPb ones refer to the NSD one. .

Figure 2

Ratio of normalized $\psipOJpsi$ yield as a function of the normalized charged-particle pseudorapidity density in \pp collisions at \thirteen and \pPb collisions at \eightnn The \pp results are normalized to the INEL$>$0 event class, whereas the \pPb ones refer to the NSD one. .

Figure 3

The normalized ψ(2S) yield and the ratio of normalized ψ(2S)-over-J/ ψ yields at 2.5 < ycms < 4.0 as a function of the normalized charged-particle pseudorapidity density in pp collisions at √s = 13 TeV. Measurements are compared with the following models: PYTHIA 8.2 [43], PYTHIA 8.2 without color reconnection (no CR) [43], comovers [5]. Quoted is the correlated event-class normalization uncertainty.

Figure 4

The normalized ψ(2S) yield and the ratio of normalized ψ(2S)-over-J/ ψ yields at 2.03 < ycms < 3.53 as a function of the normalized charged-particle pseudorapidity density in p–Pb collisions at √sNN = 8.16 TeV. Measurements are compared with the percolation calculation [53] coupled with comover model [5] and EPS09 nPDF [58]. Quoted is the correlated event-class normalization uncertainty

Figure 5

The normalized ψ(2S) yield and the ratio of normalized ψ(2S)-over-J/ ψ yields at −4.46 < ycms < −2.96 as a function of the normalized charged-particle pseudorapidity density in p–Pb collisions at √sNN = 8.16 TeV. Measurements are compared with the percolation calculation [53] coupled with comover model [5] and EPS09 nPDF [58]. Quoted is the correlated event-class normalization uncertainty.