CMS-HIN-16-015

CMS-HIN-16-015 ; CERN-EP-2018-056
Measurement of prompt $\psi (\mathrm{2S})$ production cross sections in proton-lead and proton-proton collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV
CMS Collaboration
6 May 2018
Phys. Lett. B 790 (2019) 509
Abstract: Measurements of prompt $\psi (\text{2S})$ meson production cross sections in proton-lead (pPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV are reported. The results are based on pPb and pp data collected by the CMS experiment at the LHC, corresponding to integrated luminosities of 34.6 nb $^{-1}$ and 28.0 pb $^{-1}$ , respectively. The nuclear modification factor ${R_{\mathrm{pPb}}}$ is measured for prompt $\psi (\text{2S})$ in the transverse momentum range 4 $< {p_{\mathrm{T}}} <$ 30 GeV/ $c$ and the center-of-mass rapidity range $-2.4 < {y_{\text{CM}}} < 1.93$ . The results on $\psi (\text{2S})$ ${R_{\mathrm{pPb}}}$ are compared to the corresponding modification factor for prompt $\mathrm{J}/\psi$ mesons and are found to be more suppressed than the $\mathrm{J}/\psi$ states over the entire kinematic range studied.
Links: e-print arXiv:1805.02248 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Dimuon invariant mass distribution showing the $\mathrm{J}/\psi$ and $\psi (\text{2S})$ peaks in pPb data, after applying the ${\ell _{\mathrm{J}/\psi}}$ selection, for $-2.4 < {y_{\text {CM}}} < -1.93$ and {4 $< {p_{\mathrm {T}}} < 6.5$ GeV/ $c$ (left panel), and $0 < {y_{\text {CM}}} < 0.9$ and 10 $< {p_{\mathrm {T}}} <$ 30 GeV/ $c$ (right panel). The fits to the distributions are also shown.
png pdf	Figure 1-a: Dimuon invariant mass distribution showing the $\mathrm{J}/\psi$ and $\psi (\text{2S})$ peaks in pPb data, after applying the ${\ell _{\mathrm{J}/\psi}}$ selection, for $-2.4 < {y_{\text {CM}}} < -1.93$ and {4 $< {p_{\mathrm {T}}} < 6.5$ GeV/ $c$ . The fits to the distributions are also shown.
png pdf	Figure 1-b: Dimuon invariant mass distribution showing the $\mathrm{J}/\psi$ and $\psi (\text{2S})$ peaks in pPb data, after applying the ${\ell _{\mathrm{J}/\psi}}$ selection, for $0 < {y_{\text {CM}}} < 0.9$ and 10 $< {p_{\mathrm {T}}} <$ 30 GeV/ $c$ . The fits to the distributions are also shown.
png pdf	Figure 2: Differential cross section (multiplied by the dimuon branching fraction and divided by A = 208) of prompt $\psi (\text{2S})$ production in pPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV, as a function of ${p_{\mathrm {T}}}$ , in several rapidity bins and separately for backward (left panel) and forward (right panel) rapidity regions. Statistical and systematic uncertainties are represented with error bars and boxes, respectively. The fully correlated luminosity uncertainty of 3.5% is not included in the point-by-point uncertainties.
png pdf	Figure 2-a: Differential cross section (multiplied by the dimuon branching fraction and divided by A = 208) of prompt $\psi (\text{2S})$ production in pPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV, as a function of ${p_{\mathrm {T}}}$ , in several rapidity bins and separately for the backward rapidity region. Statistical and systematic uncertainties are represented with error bars and boxes, respectively. The fully correlated luminosity uncertainty of 3.5% is not included in the point-by-point uncertainties.
png pdf	Figure 2-b: Differential cross section (multiplied by the dimuon branching fraction and divided by A = 208) of prompt $\psi (\text{2S})$ production in pPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV, as a function of ${p_{\mathrm {T}}}$ , in several rapidity bins and separately for the forward rapidity region. Statistical and systematic uncertainties are represented with error bars and boxes, respectively. The fully correlated luminosity uncertainty of 3.5% is not included in the point-by-point uncertainties.
png pdf	Figure 3: Differential cross section (multiplied by the dimuon branching fraction) of prompt $\psi (\text{2S})$ production in ${{{\mathrm {p}} {\mathrm {p}}}}$ collisions at { ${\sqrt {s}} =$ 5.02 TeV} as a function of ${p_{\mathrm {T}}}$ , in four ${y_{\text {CM}}}$ bins. Statistical and systematic uncertainties are represented with error bars and boxes, respectively. The fully correlated luminosity uncertainty of 2.3% is not included in the point-by-point uncertainties.
png pdf	Figure 4: Rapidity dependence of the prompt $\psi (\text{2S})$ ${R_{{{\mathrm {p}}\text {Pb}}}}$ in three ${p_{\mathrm {T}}}$ ranges. For comparison, the prompt $\mathrm{J}/\psi$ nuclear modification factor [31] is also shown. Statistical and systematic uncertainties are represented with error bars and boxes, respectively. The fully correlated global uncertainty of 4.2% (that affects both charmonia) is displayed as a box around ${R_{{{\mathrm {p}}\text {Pb}}}} =$ 1.
png pdf	Figure 4-a: Rapidity dependence of the prompt $\psi (\text{2S})$ ${R_{{{\mathrm {p}}\text {Pb}}}}$ in ${p_{\mathrm {T}}}$ range 4 $< {p_{\mathrm {T}}} <$ 6.5 GeV/ $c$ . For comparison, the prompt $\mathrm{J}/\psi$ nuclear modification factor [31] is also shown. Statistical and systematic uncertainties are represented with error bars and boxes, respectively. The fully correlated global uncertainty of 4.2% (that affects both charmonia) is displayed as a box around ${R_{{{\mathrm {p}}\text {Pb}}}} =$ 1.
png pdf	Figure 4-b: Rapidity dependence of the prompt $\psi (\text{2S})$ ${R_{{{\mathrm {p}}\text {Pb}}}}$ in ${p_{\mathrm {T}}}$ range 6.5 $< {p_{\mathrm {T}}} <$ 10 GeV/ $c$ . For comparison, the prompt $\mathrm{J}/\psi$ nuclear modification factor [31] is also shown. Statistical and systematic uncertainties are represented with error bars and boxes, respectively. The fully correlated global uncertainty of 4.2% (that affects both charmonia) is displayed as a box around ${R_{{{\mathrm {p}}\text {Pb}}}} =$ 1.
png pdf	Figure 4-c: Rapidity dependence of the prompt $\psi (\text{2S})$ ${R_{{{\mathrm {p}}\text {Pb}}}}$ in ${p_{\mathrm {T}}}$ range 10 $< {p_{\mathrm {T}}} <$ 30 GeV/ $c$ . For comparison, the prompt $\mathrm{J}/\psi$ nuclear modification factor [31] is also shown. Statistical and systematic uncertainties are represented with error bars and boxes, respectively. The fully correlated global uncertainty of 4.2% (that affects both charmonia) is displayed as a box around ${R_{{{\mathrm {p}}\text {Pb}}}} =$ 1.
png pdf	Figure 5: Transverse momentum dependence of the prompt $\psi (\text{2S})$ ${R_{{{\mathrm {p}}\text {Pb}}}}$ in four rapidity ranges. Statistical and systematic uncertainties are represented with error bars and boxes, respectively. The fully correlated global uncertainty of 4.2% is displayed as a box around ${R_{{{\mathrm {p}}\text {Pb}}}} =$ 1.
png pdf	Figure 5-a: Transverse momentum dependence of the prompt $\psi (\text{2S})$ ${R_{{{\mathrm {p}}\text {Pb}}}}$ in rapidity range $-2.4 < {y_{\text {CM}}} < -1.93$ . Statistical and systematic uncertainties are represented with error bars and boxes, respectively. The fully correlated global uncertainty of 4.2% is displayed as a box around ${R_{{{\mathrm {p}}\text {Pb}}}} =$ 1.
png pdf	Figure 5-b: Transverse momentum dependence of the prompt $\psi (\text{2S})$ ${R_{{{\mathrm {p}}\text {Pb}}}}$ in rapidity range $-1.93 < {y_{\text {CM}}} < -1.5$ and $1.5 < {y_{\text {CM}}} < 1.93$ . Statistical and systematic uncertainties are represented with error bars and boxes, respectively. The fully correlated global uncertainty of 4.2% is displayed as a box around ${R_{{{\mathrm {p}}\text {Pb}}}} =$ 1.
png pdf	Figure 5-c: Transverse momentum dependence of the prompt $\psi (\text{2S})$ ${R_{{{\mathrm {p}}\text {Pb}}}}$ in rapidity range $-1.5 < {y_{\text {CM}}} < -0.9$ and $0.9 < {y_{\text {CM}}} < 1.5$ . Statistical and systematic uncertainties are represented with error bars and boxes, respectively. The fully correlated global uncertainty of 4.2% is displayed as a box around ${R_{{{\mathrm {p}}\text {Pb}}}} =$ 1.
png pdf	Figure 5-d: Transverse momentum dependence of the prompt $\psi (\text{2S})$ ${R_{{{\mathrm {p}}\text {Pb}}}}$ in rapidity range $-0.9 < {y_{\text {CM}}} < 0$ and $0 < {y_{\text {CM}}} < 0.9$ . Statistical and systematic uncertainties are represented with error bars and boxes, respectively. The fully correlated global uncertainty of 4.2% is displayed as a box around ${R_{{{\mathrm {p}}\text {Pb}}}} =$ 1.

Summary

The data collected by CMS in pp and pPb collisions at

${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV are used to investigate prompt

$\psi (\text{2S})$ meson production. The results are based on data samples corresponding to integrated luminosities of 28.0 pb

$^{-1}$ for pp collisions and 34.6 nb

$^{-1}$ for pPb collisions. The nuclear modification factor (

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

$\psi (\text{2S})$ , in the kinematic range 4

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

$c$ and

$-2.4 < {y_{\text{CM}}} < 1.93$ , is determined and compared to that of prompt

$\mathrm{J}/\psi$ mesons, reported in Ref. [31]. In the ranges 4

$< {p_{\mathrm{T}}} <$ 6.5 and 6.5

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

$c$ the value

${R_{\mathrm{pPb}}}$ for prompt

$\psi (\text{2S})$ production remains below unity independent of rapidity, while in the highest

${p_{\mathrm{T}}}$ bin (10

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

$c$ ) it is consistent with unity (although systematically smaller). The

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

$\mathrm{J}/\psi$ lie systematically above those of prompt

$\psi (\text{2S})$ mesons, indicating different nuclear effects in the production of the two states. The effects of nuclear parton distribution functions or coherent energy loss are expected to affect the

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

$\mathrm{J}/\psi$ and

$\psi (\text{2S})$ by a similar amount, thus the results hint the presence of final-state interactions with the medium produced in pPb collisions.

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