Measurement of inelastic, single- and double-diffraction cross sections in proton-proton collisions at the LHC with ALICE

Abstract

Measurements of cross sections of inelastic and diffractive processes in proton--proton collisions at LHC energies were carried out with the ALICE detector. The fractions of diffractive processes in inelastic collisions were determined from a study of gaps in charged particle pseudorapidity distributions: for single diffraction (diffractive mass \(M_X < 200\) GeV/\(c^2\)) \(\sigma_{\rm SD}/\sigma_{\rm INEL} = 0.21 \pm 0.03, 0.20^{+0.07}_{-0.08}\), and \(0.20^{+0.04}_{-0.07}\), respectively at centre-of-mass energies \(\sqrt{s} = 0.9, 2.76\), and 7 TeV; for double diffraction (for a pseudorapidity gap \(\Delta\eta > 3\)) \(\sigma_{\rm DD}/\sigma_{\rm INEL} = 0.11 \pm 0.03, 0.12 \pm 0.05\), and \(0.12^{+0.05}_{-0.04}\), respectively at \(\sqrt{s} = 0.9, 2.76\), and 7 TeV. To measure the inelastic cross section, beam properties were determined with van der Meer scans, and, using a simulation of diffraction adjusted to data, the following values were obtained: \(\sigma_{\rm INEL} = 62.8^{+2.4}_{-4.0} (model) \pm 1.2 (lumi)\) mb at \(\sqrt{s} =\) 2.76 TeV and \(73.2^{+2.0}_{-4.6} (model) \pm 2.6 (lumi)\) mb at \(\sqrt{s}\) = 7 TeV. The single- and double-diffractive cross sections were calculated combining relative rates of diffraction with inelastic cross sections. The results are compared to previous measurements at proton--antiproton and proton--proton colliders at lower energies, to measurements by other experiments at the LHC, and to theoretical models.