First observation of charmonium sequential suppression in heavy-ion collisions at Relativistic Heavy Ion Collider

Updated on Thu, 2024-11-14 03:19. Originally created by wy157543 on 2024-03-29 03:18.

First observation of charmonium sequential suppression in heavy-ion collisions at Relativistic Heavy Ion Collider

PAs: Rongrong Ma, Kaifeng Shen, Zebo Tang,Yan Wang, Qian Yang, Wangmei Zha

Target Journal: Phys. Rev. Lett.

Abstract:

We report on measurements of charmonium sequential suppression in high-energy Ru+Ru and Zr+Zr collisions with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The inclusive yield ratio of psi(2S) to J/psi as a function of transverse momentum is reported, along with the centrality dependence of the double ratio, defined as the psi(2S) to J/psi ratio in heavy-ion collisions to that in p+p collisions. In the 0-80% centrality class, such a double ratio is 0.41 $\pm$ 0.10 (stat) $\pm$ 0.02 (syst) $\pm$ 0.04 (norm), lower than unity with a significance of 5.3 standard deviations. This provides experimental evidence that psi(2S) is significantly more suppressed than Jpsi in heavy-ion collisions at RHIC. It is also observed that such a sequential suppression pattern is more profound at lower transverse momentum.

Figures:

Figure 1. psi(2S) and J/psi signal significances as a function of BDT cut in 0-80% Ru+Ru and Zr+Zr collisions. The solid markers represent significances extracted from data, while solid curves represent the expected significances from machine learning. Error bars around data points and bands around solid curves indicate statistical uncertainties. The measured and expected distributions are aligned at the BDT cut of 0.5, as indicated by the open boxes. The signal significance corresponding to the default BDT cut is indicated by stars.

Figure 2. Invariant mass distributions of psi(2S) and J/psi candidates for pT > 0.2 GeV/c reconstructed via the dielectron channel within |y| < 1 for 0-80% Ru+Ru and Zr+Zr collisions. Combinatorial background estimated using the mix-event technique is shown as triangles. Background-subtracted distributions (full circles) are fitted. Fit results are shown by the solid curves, while curves of other styles represent individual components included in the fit.

Figure 3. psi(2S) to Jpsi double ratio as a function of Npart. For measurements from heavy-ion collisions, the error bars indicate statistical uncertainties, while the boxes denote systematic uncertainties. Other results only display total uncertainties.

Figure 4. pT dependence of the psi(2S) to J/psi yield ratio in p+p and heavy-ion collisions. For Ru+Ru and Zr+Zr results, the vertical bars and boxes around data points represent statistical and systematic uncertainties, respectively, while the horizontal bars indicate the bin width. Other results only display the total uncertainties.

Summary:

In summary, we report the first measurements of psi(2S) production in Ru+Ru and Zr+Zr collisions at √s_NN = 200 GeV with the STAR detector at RHIC.

The pT-integrated double ratio, i.e., ratio of psi(2S) to J/psi yield ratio between heavy-ion and p+p collisions, in the 0–80% centrality class is lower than unity with a significance of 5.3 standard deviations, providing strong evidence that the psi(2S) is significantly more suppressed than J/psi in heavy-ion collisions at RHIC compared to p+p collisions.

The double ratio is also smaller than the interpolated value for p+Au collisions at 200 GeV, indicating additional suppression of psi2S relative to J/psi in the QGP beyond the CNM effects.

Hints of increasing relative suppression from peripheral to central collisions and with increasing pT are seen.

Paper draft:

https://drupal.star.bnl.gov/STAR/blog/wy157543/psi2s-paper

Analysis note:

https://drupal.star.bnl.gov/STAR/blog/wy157543/psi2snote

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First observation of charmonium sequential suppression in heavy-ion collisions at Relativistic Heavy Ion Collider