CMS-PAS-HIN-16-015

CMS-PAS-HIN-16-015
Measurement of $\psi(2S)$ production in proton-lead and proton-proton collisions at $\sqrt{ s _{\mathrm{NN}} } =$ 5.02 TeV
CMS Collaboration
February 2017

Abstract: This note reports the measurement of prompt $\psi$ (2S) production in proton-lead (pPb) and proton-proton (pp) collisions at $\sqrt{ s _{\mathrm{NN}} } =$ 5.02 TeV. The results are based on pPb and pp data samples collected by CMS at the LHC corresponding to an integrated luminosity of 34.6 nb $^{-1}$ and 28.0 pb $^{-1}$ respectively. The nuclear modification factor, $R_{\rm pPb}$ , is calculated for prompt $\psi$ (2S) in the kinematic interval 4 $< p_{\mathrm{T}} <$ 30 GeV/ $c$ and $-2.4 < y_{\rm CM} < 1.93$ , and compared to the $R_{\rm pPb}$ of prompt $J/\psi$ . The $R_{\rm pPb}$ of the excited state is found to be smaller than the $R_{\rm pPb}$ of the ground state, over the whole kinematic range studied. The suppression is more pronounced in the region of negative rapidity and $p_{\mathrm{T}} <$ 10 GeV/ $c$ .
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 790 (2019) 509. The superseded preliminary plots can be found here.

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: (Left) Fit of the dimuon mass distribution both to the $\mathrm{J} / \psi$ and $\psi$ (2S) peaks of the pPb data in the kinematical bin $-2.4 < y_{\rm CM} < -1.93$ and 4 $< {p_{\mathrm {T}}} <$ 6.5 GeV/ $c$ . The signal is fitted with Crystal Ball and Gaussian functions and background is described with a Chebyshev polynomial of degree 3. (Right) Fit of the dimuon mass distribution both to the $\mathrm{J} / \psi$ and $\psi$ (2S) peaks of the pPb data in the kinematical bin 0 $< y_{\rm CM} <$ 0.9 and 10 $< {p_{\mathrm {T}}} <$ 30 GeV/ $c$ . The signal is fitted with Crystal Ball and Gaussian functions and background is described with a Chebyshev polynomial of degree 3.
png pdf	Figure 1-a: Fit of the dimuon mass distribution both to the $\mathrm{J} / \psi$ and $\psi$ (2S) peaks of the pPb data in the kinematical bin $-2.4 < y_{\rm CM} < -1.93$ and 4 $< {p_{\mathrm {T}}} <$ 6.5 GeV/ $c$ . The signal is fitted with Crystal Ball and Gaussian functions and background is described with a Chebyshev polynomial of degree 3.
png pdf	Figure 1-b: Fit of the dimuon mass distribution both to the $\mathrm{J} / \psi$ and $\psi$ (2S) peaks of the pPb data in the kinematical bin 0 $< y_{\rm CM} <$ 0.9 and 10 $< {p_{\mathrm {T}}} <$ 30 GeV/ $c$ . The signal is fitted with Crystal Ball and Gaussian functions and background is described with a Chebyshev polynomial of degree 3.
png pdf	Figure 2: Rapidity dependence of ${R_{ \mathrm{pPb} }}$ for prompt $\psi$ (2S) in three ${p_{\mathrm {T}}}$ ranges. The error bars represent the statistical uncertainties, and the boxes show the quadratic sum of systematic uncertainties. The fully correlated global uncertainty of 4.2% is displayed as a grey box arround ${R_{ \mathrm{pPb} }} =$ 1.
png pdf	Figure 2-a: Rapidity dependence of ${R_{ \mathrm{pPb} }}$ for prompt $\psi$ (2S) in the 4 $< {p_{\mathrm {T}}} <$ 6.5 GeV/ $c$ range. The error bars represent the statistical uncertainties, and the boxes show the quadratic sum of systematic uncertainties. The fully correlated global uncertainty of 4.2% is displayed as a grey box arround ${R_{ \mathrm{pPb} }} =$ 1.
png pdf	Figure 2-b: Rapidity dependence of ${R_{ \mathrm{pPb} }}$ for prompt $\psi$ (2S) in the 6.6 $< {p_{\mathrm {T}}} <$ 10 GeV/ $c$ range. The error bars represent the statistical uncertainties, and the boxes show the quadratic sum of systematic uncertainties. The fully correlated global uncertainty of 4.2% is displayed as a grey box arround ${R_{ \mathrm{pPb} }} =$ 1.
png pdf	Figure 2-c: Rapidity dependence of ${R_{ \mathrm{pPb} }}$ for prompt $\psi$ (2S) in the 10 $< {p_{\mathrm {T}}} <$ 30 GeV/ $c$ range. The error bars represent the statistical uncertainties, and the boxes show the quadratic sum of systematic uncertainties. The fully correlated global uncertainty of 4.2% is displayed as a grey box arround ${R_{ \mathrm{pPb} }} =$ 1.
png pdf	Figure 3: Transverse momentum ${p_{\mathrm {T}}}$ dependence of ${R_{ \mathrm{pPb} }}$ for prompt $\psi$ (2S) in four rapidity ranges. The error bars represent the statistical uncertainties, and the shaded boxes show the quadratic sum of systematic uncertainties. The fully correlated global uncertainty of 4.2% is displayed as a grey box arround ${R_{ \mathrm{pPb} }}$ = 1.
png pdf	Figure 3-a: Transverse momentum ${p_{\mathrm {T}}}$ dependence of ${R_{ \mathrm{pPb} }}$ for prompt $\psi$ (2S) in rapidity range $-2.4 < y_{\rm CM} < -1.93$ . The error bars represent the statistical uncertainties, and the shaded boxes show the quadratic sum of systematic uncertainties. The fully correlated global uncertainty of 4.2% is displayed as a grey box arround ${R_{ \mathrm{pPb} }}$ = 1.
png pdf	Figure 3-b: Transverse momentum ${p_{\mathrm {T}}}$ dependence of ${R_{ \mathrm{pPb} }}$ for prompt $\psi$ (2S) in rapidity ranges $-1.93 < y_{\rm CM} < -1.5$ and $1.5 < y_{\rm CM} < 1.93$ . The error bars represent the statistical uncertainties, and the shaded boxes show the quadratic sum of systematic uncertainties. The fully correlated global uncertainty of 4.2% is displayed as a grey box arround ${R_{ \mathrm{pPb} }}$ = 1.
png pdf	Figure 3-c: Transverse momentum ${p_{\mathrm {T}}}$ dependence of ${R_{ \mathrm{pPb} }}$ for prompt $\psi$ (2S) in rapidity ranges $-1.5 < y_{\rm CM} < -0.9$ and $0.9 < y_{\rm CM} < 1.5$ . The error bars represent the statistical uncertainties, and the shaded boxes show the quadratic sum of systematic uncertainties. The fully correlated global uncertainty of 4.2% is displayed as a grey box arround ${R_{ \mathrm{pPb} }}$ = 1.
png pdf	Figure 3-d: Transverse momentum ${p_{\mathrm {T}}}$ dependence of ${R_{ \mathrm{pPb} }}$ for prompt $\psi$ (2S) in rapidity ranges $-0.9 < y_{\rm CM} < 0$ and $0 < y_{\rm CM} < 0.9$ . The error bars represent the statistical uncertainties, and the shaded boxes show the quadratic sum of systematic uncertainties. The fully correlated global uncertainty of 4.2% is displayed as a grey box arround ${R_{ \mathrm{pPb} }}$ = 1.

Summary

The pPb and pp collision data at

${\sqrt{s_{_{\text{NN}}}}} =$ 5.02 TeV taken by the CMS detector are used to investigate the production of prompt

$\psi$ (2S). The results are based on pPb and pp data samples collected by CMS at the LHC corresponding to an integrated luminosity of 34.6 nb

$^{-1}$ and 28.0 pb

$^{-1}$ respectively. The nuclear modification factor of prompt

$\psi$ (2S) is determined in the kinematic interval 4

$< p_{\mathrm{T}} <$ 30 GeV/

$c$ and

$-2.4 < y_{\rm CM} <$ 1.93, and compared to the

$R_{\rm pPb}$ of prompt

$\mathrm{J}/ \psi$ . The suppression is more pronounced in the region of negative rapidity and at

$p_{\mathrm{T}} <$ 10 GeV/

$c$ . The

${R_{\mathrm{pPb}}}$ of

$\psi$ (2S) is also found to be smaller to that of the

$\mathrm{J}/ \psi$ measured in Ref. [18], over the whole kinematic range studied. The different nuclear dependence of

$\mathrm{J}/ \psi$ and

$\psi$ (2S) reported here cannot be attributed to nPDF or coherent energy loss effects which predict a similar suppression in both channels. It may however be consistent with the picture of final state inelastic interaction of

$\psi$ (2S) mesons in the medium produced in pPb collisions at

${\sqrt{s_{_{\text{NN}}}}} =$ 5 TeV.

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