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Measurement of charged particle multiplicities and densities in $pp$ collisions at $\sqrt{s}$ = 7 TeV in the forward region

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Abstract

Charged particle multiplicities are studied in proton-proton collisions in the forward region at a centre-of-mass energy of $\sqrt{s} = 7\;$TeV with data collected by the LHCb detector. The forward spectrometer allows access to a kinematic range of $2.0<\eta<4.8$ in pseudorapidity, momenta down to $2\;$GeV/$c$ and transverse momenta down to $0.2\;$GeV/$c$. The measurements are performed using minimum-bias events with at least one charged particle in the kinematic acceptance. The results are presented as functions of pseudorapidity and transverse momentum and are compared to predictions from several Monte Carlo event generators.

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Charged particle density as a function of $\eta$. The LHCb data are shown as points with statistical error bars (smaller than the marker size) and combined systematic and statistical uncertainties as the grey band. The measurement is compared to several Monte Carlo generator predictions, (a) Pythia 6 and Phojet , (b) Pythia 8 and Herwig++ . Both plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis.

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Charged particle density as a function of $p_{\rm T}$ . The LHCb data are shown as points with statistical error bars (smaller than the marker size) and combined systematic and statistical uncertainties as the grey band. The measurement is compared to several Monte Carlo generator predictions, (a) Pythia 6 and Phojet , (b) Pythia 8 and Herwig++ . Both plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis.

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Observed charged particle multiplicity distribution in the full kinematic range of the analysis. The error bars represent the statistical uncertainty, the error band shows the combined statistical and systematic uncertainties. The data are compared to several Monte Carlo predictions, (a) Pythia 6 and Phojet , (b) Pythia 8 and Herwig++ . Both plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis.

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Observed charged particle multiplicity distribution in different $\eta$ bins. Error bars represent the statistical uncertainty, the error bands show the combined statistical and systematic uncertainties. The data are compared to Monte Carlo predictions, (a,b) Pythia 6 and Phojet , (c,d) Pythia 8 and Herwig++ . All plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis.

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Observed charged particle multiplicity distribution in different $\eta$ bins. Error bars represent the statistical uncertainty, the error bands show the combined statistical and systematic uncertainties. The data are compared to Monte Carlo predictions, (a-c) Pythia 6 and Phojet , (d-f) Pythia 8 and Herwig++ . All plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis.

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Observed charged particle multiplicity distribution in different $p_{\rm T}$ bins. Error bars represent the statistical uncertainty, the error bands show the combined statistical and systematic uncertainties. The data are compared to Monte Carlo predictions, (a,b) Pythia 6 and Phojet , (c,d) Pythia 8 and Herwig++ . All plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis.

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Observed charged particle multiplicity distribution in different $p_{\rm T}$ bins. Error bars represent the statistical uncertainty, the error bands show the combined statistical and systematic uncertainties. The data are compared to Monte Carlo predictions, (a-c) Pythia 6 and Phojet , (d-f) Pythia 8 and Herwig++ . All plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis.

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Example of the parametrized detector response matrix in the full kinematic range. The matrix is obtained from fully simulated events showing the relation between the true charged particle multiplicity and the reconstructed and background subtracted track multiplicity.

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Animated gif made out of all figures.

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Tables and captions

Charged particle density as a function of pseudorapidity. The first quoted uncertainty is statistical and the second systematic.

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Charged particle density as a function of transverse momentum. The first quoted uncertainty is statistical and the second systematic.

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Truncated mean value and root-mean-square deviation for charged particle multiplicities in different $\eta$-bins. The range is from 0 to 20 particles. The first quoted uncertainty is statistical and the second systematic.

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Truncated mean value and root-mean-square deviation for charged particle multiplicities in different $p_{\rm T}$ -bins. The range is from 0 to 20 particles. The first quoted uncertainty is statistical and the second systematic.

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Created on 27 April 2024.