Abstract
The cross-section for inelastic proton-proton collisions at a centre-of-mass energy of 13 TeV is measured with the LHCb detector. The fiducial cross-section for inelastic interactions producing at least one prompt long-lived charged particle with momentum p > 2 GeV/c in the pseudorapidity range 2 < η < 5 is determined to be σacc = 62.2 ± 0.2 ± 2.5 mb. The first uncertainty is the intrinsic systematic uncertainty of the measurement, the second is due to the uncertainty on the integrated luminosity. The statistical uncertainty is negligible. Extrapolation to full phase space yields the total inelastic proton-proton cross-section σinel = 75.4 ± 3.0 ± 4.5 mb, where the first uncertainty is experimental and the second due to the extrapolation. An updated value of the inelastic cross-section at a centre-of-mass energy of 7 TeV is also reported.
Highlights
Analysis methodThe primary measurement is a fiducial cross-section, defined as the cross-section for protonproton collisions with at least one prompt, long-lived charged particle with momentum p > 2 GeV/c and pseudorapidity in the range 2 < η < 5
A measurement is presented of the inelastic proton-proton cross-section with at least one prompt long-lived charged particle with momentum p > 2 GeV/c in the pseudorapidity range 2 < η < 5
The new value of the reference cross-section for the integrated luminosity of the data analysed for the previous measurement is 2.7% larger than the initial estimate and the uncertainty has been reduced from 3.5% to 1.7%
Summary
The primary measurement is a fiducial cross-section, defined as the cross-section for protonproton collisions with at least one prompt, long-lived charged particle with momentum p > 2 GeV/c and pseudorapidity in the range 2 < η < 5. From a parametrisation of the PV density by a threedimensional Gaussian function, the estimated point of origin is determined as that point on the particle trajectory, parametrised by a straight line, where the PV density is highest With this selection all events can be used in the analysis, independently of whether a PV was reconstructed. The determination of the empty-event probability p0 takes into account that, because of inefficiencies, events may be wrongly tagged as empty, and that events which have no prompt long-lived charged particle inside the fiducial region can be classified as non-empty because of misreconstructed tracks. For the measurement presented here, the detector related effects are accounted for by an approach that relates p0 to the observed charged track multiplicity distribution inside the fiducial region. In this case p0 can be determined from the observed multiplicity distribution of long-lived prompt charged tracks in the detector acceptance. With a typical value α ≈ −0.6 the values of p0 are on average only about 3% smaller than their leading-order estimates q0, which results in robust cross-section measurements even in case of sizeable systematic uncertainties on α
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