$V^0$ production ratios at LHCb and the alignment of its RICH detectors

Abstract

The strangeness production ratios $\overline{\Lambda}/\Lambda$ and $\overline{\Lambda}/K^0_S$ are measured by the LHCb detector from \mbox{$0.3$\,nb$^{-1}$} of proton-proton collisions delivered by the Large Hadron Collider (LHC) at CERN with centre-of-mass energy $\sqrt{s}=0.9$\,TeV and \mbox{$1.8$\,nb$^{-1}$} at $\sqrt{s}=7$\,TeV. Both ratios are presented as a function of transverse momentum, $p_\mathrm{T}$, and rapidity, $y$, in the ranges \mbox{$0.15 < p_\mathrm{T} < 2.50$\,GeV/$c$} and \mbox{$2.0 < y < 4.5$}. The ratios measured at the two energies are in good agreement in an overlapping region of rapidity loss, $\Delta y = y_\mathrm{beam} - y$, and are consistent with previous measurements. A review of the Standard Model is presented with emphasis on the difficulties in its application for predictions of physics at the LHC. Phenomenological models are introduced as the current state of the art for such predictions. Accurate models are required as an essential benchmark for future discoveries of physics beyond the Standard Model. LHCb's results represent a powerful test for these models in the soft QCD regime for processes including hadronisation. The ratio $\overline{\Lambda}/\Lambda$, measuring the transport of baryon number from the collision into the detector, is smaller in data than predicted, particularly at high rapidity. The ratio $\overline{\Lambda}/K^0_S$, measuring the baryon-to-meson suppression in strange quark hadronisation, is significantly larger than expected. The LHCb experiment is introduced, with particular focus on its Ring Imaging Cherenkov (RICH) detectors. The development and successful implementation of a method to align those RICH detectors is presented, using proton-proton collision data from the early running period of the Large Hadron Collider, which began in November 2009. The performance of the RICH detectors is investigated with preliminary analysis of the Cherenkov photon yield. The RICH mirror positions are monitored using an automated software control system, which has been running successfully since October 2008.