Measurement of the inelastic proton-proton cross section at sqrt(s) = 7 TeV

Abstract

A measurement is presented of the inelastic proton-proton cross section at a centre-of-mass energy of sqrt(s) = 7 TeV. Using the CMS detector at the LHC, the inelastic cross section is measured through two independent methods based on information from (i) forward calorimetry (for pseudorapidity 3 < abs(eta) < 5), in collisions where at least one proton loses more than 5E-6 of its longitudinal momentum, and (ii) the central tracker (abs(eta) < 2.4), in collisions containing an interaction vertex with more than 1, 2, or 3 tracks with transverse momenta pT > 200 MeV. The measurements cover a large fraction of the inelastic cross section for particle production over about 9 units of pseudorapidity and down to small transverse momenta. The results are compared with those of other experiments, and with models used to describe high-energy hadronic interactions.

Figures (6)

• Figure 1: The normalized $\xi$ distributions for $E_{\mathrm{HF}} > 4$ and $E_{\mathrm{HF}} > 5$$\,\text{Ge\spaceV}$ from MC simulation of inelastic pp collisions using (a) pythia6, (c) pythia8, and (e) Phojet, are shown for the full range of $\xi$. The corresponding efficiencies are shown in (b), (d), and (f), respectively. The cut value of $\xi$ used in this analysis of $5\times10^{-6}$ is shown on the plots as a dashed vertical line.
• Figure 2: Fraction of reconstructed events with more than one track, corrected for efficiency, measured as a function of the number of vertices, in data (dots) and in Monte Carlo (histogram), for instantaneous bunch-crossing luminosities between $0.05\times 10^{30}$ and $0.7\times 10^{30}\,\text{cm}^\text{$-$2}\,\text{s}^\text{$-$1}\xspace$.
• Figure 3: Fraction of pp events with $n$ pileup vertices, for $n = 0$ to 8, containing more than one charged particle, as a function of instantaneous bunch-crossing luminosity. The dashed lines are the fits described in the text. The data points are plotted at the mean of the differential distribution in each bin.
• Figure 4: (a) Values of the inelastic pp cross section $\sigma_\text{inel}$ and (b) their associated goodness of fit $\chi^2/\mathrm{NDOF}$, obtained for each of the fits in Fig. \ref{['fig:final']}, as a function of the number of pileup vertices, in interactions with $>1$ track with $p_{\mathrm{T}}\xspace > 200$${\,\text{Me\spaceV\space/\space}c}$ and $|\eta| < 2.4$. The line in (a) is the result of a fit to the 9 individual values of $\sigma_\text{inel}$, while the dashed line in (b) indicates $\chi^2/\mathrm{NDOF} = 1$.
• Figure 5: The two types of CMS measurements of the inelastic pp cross section (red filled circle and squares) compared to predictions from several Monte Carlo models for different criteria, as labelled below the abscissa axis. The MC predictions have an uncertainty of 1$\text{\,mb}$ (not shown). The label pythia6 (tunes D6T, Z1_LEP, AMBT1, DW-Pro, and Pro-PT0) and pythia8 (versions 8.127--8.139, Tunes 2C 8.140 Cor10a, Tune 2M 8.140 Cor10a, and Tune 4C 8.145 Cor10a) indicates several versions that give equivalent results. Other LHC experimental results are also included for comparison.