Updated measurement of time-dependent $$CP$$-violating observables in $${{B} ^0_{s}} \rightarrow J/\psi K^+ K^-$$ decays

Abstract

The decay-time-dependent CP asymmetry in B 0 s → J/ψ K + K − decays is measured using proton-proton collision data, corresponding to an integrated luminosity of 1.9 fb −1 , collected with the LHCb detector at a centre-ofmass energy of 13 TeV in 2015 and 2016. Using a sample of approximately 117 000 signal decays with an invariant K + K − mass in the vicinity of the φ(1020) resonance, the CP-violating phase φ s is measured, along with the difference in decay widths of the light and heavy mass eigenstatesThe values obtained are φ s = −0.083 ± 0.041 ± 0.006 rad, s = 0.077 ± 0.008 ± 0.003 ps −1 and s − d = −0.0041 ± 0.0024 ± 0.0015 ps −1 , where the first uncertainty is statistical and the second systematic. These are the most precise single measurements of these quantities to date and are consistent with expectations based on the Standard Model and with a previous LHCb analysis of this decay using data recorded at centre-of-mass energies 7 and 8 TeV. Finally, the results are combined with recent results from B 0 s → J/ψ π + π − decays obtained using the same dataset as this analysis, and with previous independent LHCb results. Detector and simulationThe LHCb detector [35,36] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, designed for the study of particles containing b or c quarks. The detector includes a high-precision tracking system consisting of a silicon-strip vertex detector surrounding the pp interaction region, a large-area silicon-strip detector located upstream of a dipole magnet with a bending power of about 4 Tm, and three stations of silicon-strip detectors and straw drift tubes placed downstream of the magnet. The tracking system provides a measurement of the momentum, p,

Beauty 2019 — Conference summary

“…In parallel there has been progress on precision measurement of CP asymmetries in B decays. The weak B 0 s mixing phase, φ s , was measured with similar precision by ATLAS and LHCb [38][39][40]. The latest HFLAV average [35] is shown in Fig.…”

“…3. The improvement is particularly striking when comparing the performance of LHCb's analyses of B 0 s → J/ψφ published this year [38] and B 0 → J/ψK 0 S , which dates from 2015 [37]. More developments in flavour tagging are still in the pipeline.…”

“…-0. Tagging efficiency, εtag [35] and (right) comparison of tagging efficiency and mistag fraction for selected CP violation measurements [36][37][38][39].…”

$\phi_{s}$ status and prospects at LHCb

“…Two recent measurements of the CP-violating phase φ s using B 0 s mesons at the LHCb experiment are presented. One analysis explores the B 0 s → J/ψK + K − decay mode [7], while the other studies the B 0 s → J/ψπ + π − decay [8]. Since the analysis strategies are very similar, the baseline strategy adopted by both is covered and relevant differences between the two are highlighted.…”

Search for new physics in CP violation with beauty and charm decays at LHCb

“…Global fits to experimental data, assuming unitarity of the CKM matrix, give a precise prediction of this value [10]. LHCb has recently released a new measurement of φ s using data from pp collisions corresponding to an integrated luminosity of 1.9 fb −1 and collected at a centre-of-mass energy of 13 TeV analyzing the decays B 0 s → J/ψπ + π − [11] and B 0 s → J/ψK + K − [12]. The mass distributions of the selected B 0 s candidates are shown in Fig.…”