# Measurement of the inelastic $pp$ cross-section at a centre-of-mass energy of $\sqrt{s}=7$ TeV

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## Abstract

The cross-section for inelastic proton-proton collisions, with at least one prompt long-lived charged particle of transverse momentum $p_{\rm T}>0.2$ GeV/$c$ in the pseudorapidity range $2.0<\eta<4.5$, is measured by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=7$ TeV. The cross-section in this kinematic range is determined to be $\sigma_{\rm inel}^{\rm acc} = 55.0 \pm 2.4$ mb within the spectrometer acceptance with an experimental uncertainty that is dominated by systematic contributions. Extrapolation to the full phase space, using PYTHIA 6, yields $\sigma_{\rm inel} = 66.9 \pm 2.9 \pm 4.4$ mb, where the first uncertainty is experimental and the second is due to the extrapolation.

## Figures and captions

 Normalized track multiplicity distributions with $n\geq 1$\/ tracks in the fiducial region for the field-down configuration and tight cut settings in data and simulation. The superimposed function is an exponential with the same average as the simulation. The right hand plot with a linear scale shows a zoom of the low-multiplicity region. The vertical error bars are smaller than the symbol sizes. Fig1a.pdf [8 KiB] HiDef png [180 KiB] Thumbnail [55 KiB] *.C file Fig1b.pdf [4 KiB] HiDef png [117 KiB] Thumbnail [35 KiB] *.C file Inelastic cross-section measured by LHCb compared to the existing data on the total {{\cite{Nakamura:2010zzi}}} and inelastic cross-sections {{\cite{Achilli:2011}}} in $pp$\/ and $p\bar{p}$\/ collisions as a function to the centre-of-mass energy. The full (dashed) line is a phenomenological fit {{\cite{Fagundes:2013}}} of the energy dependence of the inelastic (total) cross-section. The main plot only shows the LHCb measurement. The inset is a zoom, comparing all inelastic cross-section measurements by the LHC experiments ALICE \cite{ALICEcs:2013}, ATLAS \cite{ATLAScs:2011,ATLASxs:2014}, CMS \cite{CMScs:2011} and TOTEM \cite{TOTEMcs:2011,Antchev:2013iaa}. The horizontal line represents the value of the phenomenological fit at $\sqrt{s}=7$ TeV. The error bars give the total uncertainties of the measurements. When an inner error bar is shown, it represents the experimental uncertainties added in quadrature, while the full error bar also covers an extrapolation uncertainty. Fig2.pdf [9 KiB] HiDef png [202 KiB] Thumbnail [62 KiB] *.C file Animated gif made out of all figures. PAPER-2014-057.gif Thumbnail

## Tables and captions

 Numbers of interactions and events, in multiples of $10^6$, in simulation and data for different magnetic field configurations and analysis cuts, and the resulting cross-sections in the kinematic acceptance. Table_0.pdf [43 KiB] HiDef png [167 KiB] Thumbnail [25 KiB] tex code Summary of the relative systematic uncertainties, expresses as a percentage, for the measurement of the inelastic $pp$\/ cross-section measurement, separately for the two magnet polarities and the combined value. Table_1.pdf [18 KiB] HiDef png [91 KiB] Thumbnail [14 KiB] tex code Properties of soft QCD tunes in Pythia 8.201. For non-diffractive, single-diffractive and double-diffractive interactions, mean value and standard deviation over the tunes considered in this study are given for average multiplicities inside the kinematic acceptance, visibilities and interaction type fractions. Table_2.pdf [30 KiB] HiDef png [53 KiB] Thumbnail [9 KiB] tex code

## Supplementary Material [file]

 Supplementary material full pdf supple[..].pdf [129 KiB] Supplementary material for LHCB-PAPER-2014-057 ---------------------------------------------- Supplementary material is provided for the cross-section extrapolation factor and the plot of the final cross-section results. For the cross-section extrapolation the results of the MC-approach to estimate its uncertainty are shown for the extrapolation factor and the corresponding interaction-type frcations. The cross-section plots are the same as in the paper, but main plot and inset splitted into two independent plots. Figures and tables are numbered as if tey appeared in a continuation of the paper. The following files are provided: Fig3.[C,png,eps,pdf] : distributions of the extrapolation factor and interaction type fractions consistent with the PYTHIA 8 tunes and the LHCb data Fig4a.[C,png,eps,pdf] : energy dependence of total and inelastic cross-section Fig4b.[C,png,eps,pdf] : LHC cross-section measurements table4.tex : properties of the specific PYTHIA8 tunes used in the study table5.tex : allowed ranges for the interaction-type fractions for the PYTHIA 8 tunes used in the study supplementary.tex : TeX-file with a coherent presentation of the supplementary material supplementary.pdf : pdf-file with a coherent presentation of the supplementary material README : this file Fig3.pdf [32 KiB] HiDef png [155 KiB] Thumbnail [48 KiB] *C file Fig4a.pdf [8 KiB] HiDef png [159 KiB] Thumbnail [49 KiB] *C file Fig4b.pdf [4 KiB] HiDef png [150 KiB] Thumbnail [63 KiB] *C file

Created on 16 February 2019.Citation count from INSPIRE on 16 February 2019.