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| CMS-BPH-14-009 ; CERN-EP-2020-075 | ||
| Investigation into the event-activity dependence of $\Upsilon(\text{nS})$ relative production in proton-proton collisions at $\sqrt{s} = $ 7 TeV | ||
| CMS Collaboration | ||
| 9 July 2020 | ||
| JHEP 11 (2020) 001 | ||
| Abstract: The ratios of the production cross sections between the excited $\Upsilon\text{(2S)}$ and $\Upsilon\text{(3S)}$ mesons and the $\Upsilon\text{(1S)}$ ground state, detected via their decay into two muons, are studied as a function of the number of charged particles in the event. The data are from proton-proton collisions at $\sqrt{s} = $ 7 TeV, corresponding to an integrated luminosity of 4.8 fb$^{-1}$, collected with the CMS detector at the LHC. Evidence of a decrease in these ratios as a function of the particle multiplicity is observed, more pronounced at low transverse momentum ${{p_{\mathrm{T}}}^{\mu\mu}} $. For $\Upsilon(\text{nS})$ mesons with ${{p_{\mathrm{T}}}^{\mu\mu}} > $ 7 GeV, where most of the data were collected, the correlation with multiplicity is studied as a function of the underlying event transverse sphericity and the number of particles in a cone around the $\Upsilon(\text{nS})$ direction. The ratios are found to be multiplicity independent for jet-like events. The mean ${{p_{\mathrm{T}}}^{\mu\mu}} $ values for the $\Upsilon(\text{nS})$ states as a function of particle multiplicity are also measured and found to grow more steeply as their mass increases. | ||
| Links: e-print arXiv:2007.04277 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The $\mu^{+} \mu^{-}$ invariant mass distributions for dimuon candidates with $ {{p_{\mathrm {T}}} ^{\mu \mu}} > $ 7 GeV and $ {{| y^{\mu \mu} |}} < $ 1.2, in two intervals of charged particle multiplicity, 0-6 (left) and 110-140 (right). The result of the fit is shown by the solid lines, with the various dotted lines giving the different components. The lower panel displays the pull distribution. |
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Figure 1-a:
The $\mu^{+} \mu^{-}$ invariant mass distributions for dimuon candidates with $ {{p_{\mathrm {T}}} ^{\mu \mu}} > $ 7 GeV and $ {{| y^{\mu \mu} |}} < $ 1.2, in the 0-6 interval of charged particle multiplicity. The result of the fit is shown by the solid lines, with the various dotted lines giving the different components. The lower panel displays the pull distribution. |
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Figure 1-b:
The $\mu^{+} \mu^{-}$ invariant mass distributions for dimuon candidates with $ {{p_{\mathrm {T}}} ^{\mu \mu}} > $ 7 GeV and $ {{| y^{\mu \mu} |}} < $ 1.2, in the 110-140 interval of charged particle multiplicity. The result of the fit is shown by the solid lines, with the various dotted lines giving the different components. The lower panel displays the pull distribution. |
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Figure 2:
The ratios ${\Upsilon(\text{2S})/\Upsilon(\text{1S})}$ and ${\Upsilon(\text{3S})/\Upsilon(\text{1S})}$ with $ {{p_{\mathrm {T}}} ^{\mu \mu}} > $ 7 GeV (left) and $ {{p_{\mathrm {T}}} ^{\mu \mu}} > $ 0 GeV (right) as a function of ${N_{\text {track}}}$. The lines are fits to the data with an exponential function. The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}} {>} $ in each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}} {>} $. The results of Ref. [7] are shown in the right plot for comparison, and a small correction is applied to the present results to account for the different rapidity ranges in the measurements, $ {{| y^{\mu \mu} |}} < $ 1.20 here and $ {{| y^{\mu \mu} |}} < $ 1.93 in Ref. [7]. |
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Figure 2-a:
The ratios ${\Upsilon(\text{2S})/\Upsilon(\text{1S})}$ and ${\Upsilon(\text{3S})/\Upsilon(\text{1S})}$ with $ {{p_{\mathrm {T}}} ^{\mu \mu}} > $ 7 GeV $ {{p_{\mathrm {T}}} ^{\mu \mu}} > $ 0 GeV as a function of ${N_{\text {track}}}$. The lines are fits to the data with an exponential function. The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}} {>} $ in each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}} {>} $. The results of Ref. [7] are shown in the right plot for comparison, and a small correction is applied to the present results to account for the different rapidity ranges in the measurements, $ {{| y^{\mu \mu} |}} < $ 1.20 here and $ {{| y^{\mu \mu} |}} < $ 1.93 in Ref. [7]. |
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Figure 2-b:
The ratios ${\Upsilon(\text{2S})/\Upsilon(\text{1S})}$ and ${\Upsilon(\text{3S})/\Upsilon(\text{1S})}$ with $ {{p_{\mathrm {T}}} ^{\mu \mu}} > $ 7 GeV $ {{p_{\mathrm {T}}} ^{\mu \mu}} > $ 0 GeV as a function of ${N_{\text {track}}}$. The lines are fits to the data with an exponential function. The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}} {>} $ in each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}} {>} $. The results of Ref. [7] are shown in the right plot for comparison, and a small correction is applied to the present results to account for the different rapidity ranges in the measurements, $ {{| y^{\mu \mu} |}} < $ 1.20 here and $ {{| y^{\mu \mu} |}} < $ 1.93 in Ref. [7]. |
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Figure 3:
Mean ${{p_{\mathrm {T}}} ^{\mu \mu}}$ values for the three $\Upsilon(\text{nS})$ states as a function of ${N_{\text {track}}}$ for $ {{p_{\mathrm {T}}} ^{\mu \mu}} > $ 7 GeV (left) and $ > $ 0 GeV (right). The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}} {>} $ in each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}} {>} $. |
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Figure 3-a:
Mean ${{p_{\mathrm {T}}} ^{\mu \mu}}$ values for the three $\Upsilon(\text{nS})$ states as a function of ${N_{\text {track}}}$ for $ {{p_{\mathrm {T}}} ^{\mu \mu}} > $ 7 GeV. The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}} {>} $ in each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}} {>} $. |
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Figure 3-b:
Mean ${{p_{\mathrm {T}}} ^{\mu \mu}}$ values for the three $\Upsilon(\text{nS})$ states as a function of ${N_{\text {track}}}$ for $ {{p_{\mathrm {T}}} ^{\mu \mu}} > $ 0 GeV. The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}} {>} $ in each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}} {>} $. |
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Figure 4:
The ratios ${\Upsilon(\text{2S})/\Upsilon(\text{1S})}$ (left) and ${\Upsilon(\text{3S})/\Upsilon(\text{1S})}$ (right) as a function of ${N_{\text {track}}}$, for different ${{p_{\mathrm {T}}} ^{\mu \mu}}$ intervals. The interval 0-5 GeV corresponds to an integrated luminosity of 0.3 fb$^{-1}$, the interval 5-7 GeV to 1.9 fb$^{-1}$, and the rest to the full integrated luminosity of 4.8 fb$^{-1}$. The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}} {>} $ in each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}} {>} $. |
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Figure 4-a:
The ratio ${\Upsilon(\text{2S})/\Upsilon(\text{1S})}$ as a function of ${N_{\text {track}}}$, for different ${{p_{\mathrm {T}}} ^{\mu \mu}}$ intervals. The interval 0-5 GeV corresponds to an integrated luminosity of 0.3 fb$^{-1}$, the interval 5-7 GeV to 1.9 fb$^{-1}$, and the rest to the full integrated luminosity of 4.8 fb$^{-1}$. The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}} {>} $ in each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}} {>} $. |
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Figure 4-b:
The ratio ${\Upsilon(\text{3S})/\Upsilon(\text{1S})}$ as a function of ${N_{\text {track}}}$, for different ${{p_{\mathrm {T}}} ^{\mu \mu}}$ intervals. The interval 0-5 GeV corresponds to an integrated luminosity of 0.3 fb$^{-1}$, the interval 5-7 GeV to 1.9 fb$^{-1}$, and the rest to the full integrated luminosity of 4.8 fb$^{-1}$. The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}} {>} $ in each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}} {>} $. |
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Figure 5:
Left: A schematic view in the azimuthal plane of the three $\Delta \phi $ regions with respect to the $\Upsilon(\text{nS})$ momentum direction. Right: The ratios ${\Upsilon(\text{2S})/\Upsilon(\text{1S})}$ and ${\Upsilon(\text{3S})/\Upsilon(\text{1S})}$, as a function of ${N_{\text {track}}^{\Delta \phi}}$ for the three $\Delta \phi $ regions shown in the left plot. The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}}^{\Delta \phi} {>}$ for each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}}^{\Delta \phi} {>}$. |
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Figure 5-a:
A schematic view in the azimuthal plane of the three $\Delta \phi $ regions with respect to the $\Upsilon(\text{nS})$ momentum direction. |
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Figure 5-b:
The ratios ${\Upsilon(\text{2S})/\Upsilon(\text{1S})}$ and ${\Upsilon(\text{3S})/\Upsilon(\text{1S})}$, as a function of ${N_{\text {track}}^{\Delta \phi}}$ for the three $\Delta \phi $ regions shown in the left plot. The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}}^{\Delta \phi} {>}$ for each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}}^{\Delta \phi} {>}$. |
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Figure 6:
The ratios ${\Upsilon(\text{2S})/\Upsilon(\text{1S})}$ and ${\Upsilon(\text{3S})/\Upsilon(\text{1S})}$ are shown as a function of the track multiplicity ${N_{\text {track}}}$ : in four categories based on the number of charged particles produced in a $\Delta \mathrm {R} < $ 0.5 cone around the $\Upsilon$ direction (left), and in different intervals of charged particle transverse sphericity, ${S_{\mathrm {T}}}$ (right). The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}} {>} $ in each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}} {>} $. |
png pdf |
Figure 6-a:
The ratios ${\Upsilon(\text{2S})/\Upsilon(\text{1S})}$ and ${\Upsilon(\text{3S})/\Upsilon(\text{1S})}$ are shown as a function of the track multiplicity ${N_{\text {track}}}$, in four categories based on the number of charged particles produced in a $\Delta \mathrm {R} < $ 0.5 cone around the $\Upsilon$ direction. The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}} {>} $ in each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}} {>} $. |
png pdf |
Figure 6-b:
The ratios ${\Upsilon(\text{2S})/\Upsilon(\text{1S})}$ and ${\Upsilon(\text{3S})/\Upsilon(\text{1S})}$ are shown as a function of the track multiplicity ${N_{\text {track}}}$, in different intervals of charged particle transverse sphericity, ${S_{\mathrm {T}}}$. The outer vertical bars represent the combined statistical and systematic uncertainties in the ratios, while the horizontal bars give the uncertainty in $ {<} N_{\text {track}} {>} $ in each bin. Inner tick marks show only the statistical uncertainty, both in the ratio and in $ {<} N_{\text {track}} {>} $. |
| Tables | |
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Table 1:
Efficiency-corrected multiplicity bins used in the $\Upsilon(\text{nS})$ ratio analysis and the corresponding mean number of charged particle tracks with $ {{p_{\mathrm {T}}} ^{\text {track}}} > $ 0.4 GeV in the data sample. The most probable values of the two half-Gaussian fit to the corresponding ${N^{\text {true}}_{\text {track}}}$ in simulation, for $ {{p_{\mathrm {T}}} ^{\text {track}}} > $ 0.4 GeV and $ {{p_{\mathrm {T}}} ^{\text {track}}} > $ 0 GeV, are also indicated. The uncertainties shown are statistical, except for $ {<} N_{\text {track}} {>} $, where the systematic uncertainties are also reported. In the last column, the percentage of minimum bias (MB) events in the different multiplicity bins is also indicated. |
| Summary |
| The measurement of ratios of the $\Upsilon(\text{nS}) \to \mu^{+} \mu^{-}$ yields in proton-proton collisions at $\sqrt{s} = $ 7 TeV, corresponding to an integrated luminosity of 4.8 fb$^{-1}$, collected with the CMS detector at the LHC, are reported as a function of the number of charged particles produced with pseudorapidity ${|{\eta^{\text{track}}}|} < $ 2.4 and transverse momentum ${{p_{\mathrm{T}}}^{\text{track}}} > $ 0.4 GeV. A significant reduction of the $\Upsilon\text{(2S)}/\Upsilon\text{(1S)}$ and $\Upsilon\text{(3S)}/\Upsilon\text{(1S)}$ production ratios is observed with increasing multiplicity. This result confirms the observation made in proton-proton and proton-lead collisions at lower centre-of-mass energy [7], with increased precision. The effect is present in different ranges of ${{p_{\mathrm{T}}}^{\mu\mu}} $, but decreases with increasing ${{p_{\mathrm{T}}}^{\mu\mu}} $. For ${{p_{\mathrm{T}}}^{\mu\mu}} > $ 7 GeV, different observables are studied in order to obtain a better description of the phenomenon in connection with the underlying event. No variation in the decrease of the ratios is found by changing the azimuthal angle separation of the charged particles with respect to the $\Upsilon$ momentum direction. The same applies when varying the number of tracks in a restricted cone around the Y momentum direction. However, the ratios are observed to be multiplicity independent for jet-like events. The presented results give for the first time a comprehensive review of the connection between $\Upsilon(\text{nS})$ production and the underlying event, stressing the need for an improved theoretical description of quarkonium production in proton-proton collisions. |
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