First analysis of the pPb pilot run data with LHCb

The paper is available here.

LHCb-CONF-2012-034

Abstract

A first analysis of the data taken during the proton-lead pilot run is presented. The data sample corresponds to an integrated luminosity of L_int = 0.93 ± 0.05 μb⁻¹. A first measurement of the inelastic pPb cross-section at a nucleon-nucleon centre-of-mass energy √s_{N N} = 5.02 TeV, with at least one charged particle in the region 2.5 <η_CM < 4.5 and p_T > 0.2 GeV/c, yields σ_inel = 2.09 ± 0.12 b, where the uncertainty is purely systematic. Clean signals of strange and charm flavour production are observed. In pPb interactions the average multiplicity in the proton hemisphere is found to be about a factor two larger than in pp interactions when extrapolating to the same nucleon-nucleon centre-of-mass energy.

Figures

(pdf and eps versions are available under attachments).

Caption	Figure
Figure 1: Distribution of the zPV positions of reconstructed primary vertices in pPb collisions without (left) and with (right) activated SMOG system. The distributions for only beam 1 (proton) and beam 2 (lead) are shown in red and blue, respectively. The magenta points are the weighted sums of the two, with weights adjusted to reproduce the integrals over the pPb distributions for |zPV | > 300 mm.
Figure 2: Distribution of the zPV positions of reconstructed primary vertices in pp collisions (left) and comparison of the luminous region between pp and beam-gas-subtracted pPb interactions (right). For comparison the histograms are normalised to unit area. The background subtracted pPb data with SMOG are shown in red, the one without SMOG in blue.
Figure 3: Transverse momentum versus pseudorapidity for charged particles originating from the luminous region. Distributions are shown for pPb interactions in the centre-of- mass system (left) and for pp collisions (right) in the laboratory frame, which is almost equivalent to the centre-of-mass frame. The boxes indicate the fiducial region used in the analysis.
Figure 4: Probability distributions of uncorrected beam-gas subtracted track multiplicities in 2.5 < ηCM < 4.5 and pT > 0.2 GeV/c. The probability P (n) to observe n ≥ 1 tracks within the fiducial cuts is shown as a function of n. The multiplicity distributions for data taken with (red) and without (blue) the SMOG system in operation show good agreement after beam-gas subtraction.
Figure 5: Probability distributions of uncorrected beam-gas subtracted track multiplicities of pp (black) and pPb interactions (red and blue) in 2.5 < ηCM < 4.5 and pT > 0.2 GeV/c. The probability P (n) to observe n tracks within the fiducial cuts is shown as a function of n. Only events with a single reconstructed primary vertex with at least five associated track segments contribute. The pPb distributions are shown for data taken with (red) and without (blue) the SMOG system in operation.
Figure 6: Production of KS0 -mesons in pPb collisions (left) and pp collisions (right). The points are the experimental data, the red line indicates the assumed background.
Figure 7: Production of Λ-hyperons in pPb collisions (left) and pp collisions (right). The points are the experimental data, the red line indicates the assumed background.
Figure 8: Production of Λbar-hyperons in pPb collisions (left) and pp collisions (right). The points are the experimental data, the red line indicates the assumed background.
Figure 9: Production of φ-mesons in pPb collisions (left) and pp collisions (right). The points are the experimental data, the red line indicates the assumed background.
Figure 10: Production of D0 -mesons in pPb collisions (left) and pp collisions (right). The points are the experimental data, the red indicates the assumed background. Inclusion of charge conjugate modes is assumed.
Figure 11: J/ψ-production in pPb collisions. The points are the experimental data, the green curve shows the assumed background, and the red curve the Crystal Ball function used to describe the signal. The sum of signal and background is given by the blue line. Also indicated are signal and background yields, NSig and NBkg, the fitted mass MJ/ψ of the signal and the width σmCB of the gaussian part of the Crystal ball function.
Figure 12: Fixed target production of strange particles, Ks0 (top, left) and φ (top, right), and Λ (bottom, left) and Λbar (bottom, right), in pNe collisions. The points are the experimental data, the red indicates the assumed background.

-- KatharinaMueller - 16 Jan 2014