First measurement of the inclusive Φ meson production cross-section in pp collisions at √s = 7 TeV and search for CP violation in the Bs→φφ decay at LHCb

Abstract

Several studies towards the measurement of CP violation in the Bs0→ΦΦ decay channel with the LHCb experiment at the Large Hadron Collider at CERN are presented in this thesis. An important input to this analysis is precise knowledge of the detector performance and the Φ meson production in proton-proton collisions. As a study targeting both goals, the first measurement of the inclusive Φ meson production cross-section in pp collisions at a center-of-mass energy of √s = 7 TeV is carried out.

The CP violating phase in the Bs0→ΦΦ decay is predicted to vanish in the Standard Model of particle physics, but it could adopt finite values in some models beyond the Standard Model. Hereby this phase can distinguish different models and be a direct hint of “New Physics” in the case that a non-vanishing phase is measured.

The first step to an analysis of the Bs0→ΦΦ decay is the implementation of a signal pre-selection. The experimental techniques to extract the CP violating phase in this decay channel are developed and tested on samples simulated by event generators. Furthermore, the projective performance of the LHCb detector is determined from simulated samples and the signal and background yield expectation is extrapolated from data. Based on these analyses, the statistical uncertainty on the CP violating phase is predicted as 0.23 ± 0.04 for one nominal year (2 fb-1) of LHCb data taking.

As premise for CP violation studies, the detector performance needs to be understood. Further, since simulated samples are part of the analysis process, good agreement between the predictions and the real data is necessary. The Φ meson production in pp collision is governed by the non-perturbative QCD regime, which event generators describe by phenomenological models that need to be tuned to data. The measurement of the inclusive Φ meson production cross-section is an important probe of strangeness production in the context of this tuning effort.

The differential Φ meson production cross-section is determined as a function of the Φ transverse momentum pT and rapidity y in the region 0.6 < pT < 5.0 GeV/c and 2.44 < y < 4.06. The total Φ meson production cross-section in this range is σ(pp→ΦX) = 1758 ± 19(stat) +43/-14 (syst) ±182(syst) µb, where the first systematic uncertainty depends on the pT and y region and the second is related to the overall scale. Predictions based on the P YTHIA 6.4 generator underestimate the cross-section.