Measurement of the flavour-specific CP-violating asymmetry a(sl)(s) in B-s(0) decays (original) (raw)
Related papers
2018
This thesis presents the results of a time-dependent analysis of B 0 Ñ D¯⇡˘decays using 3 fb´1 of proton-proton collision data collected with the LHCb detector at CERN's Large Hadron Collider during Run 1 with a centre-of-mass energy of 7 (2011) and 8 (2012) TeV. The LHCb experiment is dedicated to the study of the properties of b-flavoured hadrons, in particular CP violation in the B meson system. The Standard Model of Particle Physics describes very precisely the mechanism and the amount of CP violation expected in the Universe. However, the observed matter-antimatter asymmetry is larger by several order of magnitude compared to the predictions. This could be explained by the existence of a new source of CP violation, originating in New Physics beyond the Standard Model. The time-dependent analysis of B 0 Ñ D¯⇡˘decays provides constraints on the angle of the Unitarity Triangle, one of the fundamental parameters of the Standard Model related to CP violation. Since no sizeable high-order Standard Model processes are expected to contribute, any deviation from the predictions would be an unambiguous signature of New Physics. The current experimental precision on is significantly lower than that of theoretical predictions. This motivates the effort for new experimental determinations of in order to reduce its uncertainty. The analysis of B 0 Ñ D¯⇡˘decays, although not as sensitive as that obtained from decays of charged B mesons into D p˚q0 K p˚q`fi nal states, represents an independent and uncorrelated estimation of that contributes to the global combination of all measurements. The result obtained in this thesis is more precise than previous determinations from other experiments (BaBar, Belle) using B 0 Ñ D¯⇡d ecays. Although based on a very large sample of about half a million signal events, it is still dominated by statistical uncertainties, indicating good prospects for future improvements in precision with more data from Run 2 and beyond. In addition to the B 0 Ñ D¯⇡˘analysis, this thesis also summarizes the studies to improve the performances of the flavour tagging algorithms used by the LHCb collaboration to infer the flavour of neutral B mesons in time-dependent analyses. The performance of these algorithms, being correlated with the kinematics of the reconstructed particles as well as the complexity of the event (number of tracks and primary vertices), showed a significant decrease on Run 2 data (2015-2018), which were collected at a centre-of-mass energy of 13 TeV. Thanks to new implementations, these algorithms now have a performance similar to that obtained with Run 1 data.
Investigation of inclusive CP asymmetries in decays
2001
Abstract. A search for CP violating effects in the mixing of neutral B mesons is performed using a sample of 4.1 million hadronic Z decays collected with the ALEPH detector from 1991 to 1995. By studying time-dependent asymmetries in flavour-tagged samples of semileptonic and fully inclusive b-hadron decays, two measurements of the semileptonic asymmetry are extracted. No evidence for CP violation is observed, and the combined value is obtained.
Study of time-dependent CP-violating asymmetries in b→sq¯q decays
Physical Review D, 2003
We present a measurement of time-dependent CP-violating asymmetries in neutral B meson decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at the Stanford Linear Accelerator Center. The data sample consists of 29.7 fb −1 recorded at the Υ (4S) resonance and 3.9 fb −1 off-resonance. One of the neutral B mesons, which are produced in pairs at the Υ (4S), is fully reconstructed in the CP decay modes J/ψ K 0 S , ψ(2S)K 0 S , χc1K 0 S , J/ψ K * 0 (K * 0 → K 0 S π 0) and J/ψ K 0 L , or in flavor-eigenstate modes involving D (*) π/ρ/a1 and J/ψ K * 0 (K * 0 → K + π −). The flavor of the other neutral B meson is tagged at the time of its decay, mainly with the charge of identified leptons and kaons. A neural network tagging algorithm is used to recover events without a clear lepton or kaon tag. The proper time elapsed between the decays is determined by measuring the distance between the decay vertices. Wrong-tag probabilities, the time-difference resolution function, and the B 0-B 0 oscillation frequency ∆m d are measured with a sample of about 6350 fully-reconstructed B 0 decays in hadronic flavor-eigenstate modes. A maximum-likelihood fit to this flavor eigenstate sample finds ∆m d = 0.516 ± 0.016 (stat) ± 0.010 (syst) ps −1. The value of the asymmetry amplitude sin2β is determined from a simultaneous maximum-likelihood fit to the time-difference distribution of the flavor-eigenstate sample and about 642 tagged B 0 decays in the CP-eigenstate modes. We find sin2β = 0.59 ± 0.14 (stat) ± 0.05 (syst), demonstrating that CP violation exists in the neutral B meson system. We also determine the value of the CP violation parameter |λ| = 0.93 ± 0.09 (stat) ± 0.03 (syst), which is consistent with the expectation of |λ| = 1 for no direct CP violation.
Measurement of the CP Asymmetry in B^{+}→K^{+}μ^{+}μ^{-} Decays
Physical Review Letters, 2013
A measurement of the CP asymmetry in B þ ! K þ þ À decays is presented using pp collision data, corresponding to an integrated luminosity of 1:0 fb À1 , recorded by the LHCb experiment during 2011 at a center-of-mass energy of 7 TeV. The measurement is performed in seven bins of þ À invariant mass squared in the range 0:05 < q 2 < 22:00 GeV 2 =c 4 , excluding the J=c and c ð2SÞ resonance regions. Production and detection asymmetries are corrected for using the B þ ! J=c K þ decay as a control mode. Averaged over all the bins, the CP asymmetry is found to be A CP ¼ 0:000 AE 0:033 ðstatÞ AE 0:005 ðsystÞ AE 0:007 (J=c K), where the third uncertainty is due to the CP asymmetry of the control mode. This is consistent with the standard model prediction.
Journal of High Energy Physics, 2015
Time-dependent CP asymmetries in the decay rates of the singly Cabibbosuppressed decays D 0 → K − K + and D 0 → π − π + are measured in pp collision data corresponding to an integrated luminosity of 3.0 fb −1 collected by the LHCb experiment. The D 0 mesons are produced in semileptonic b-hadron decays, where the charge of the accompanying muon is used to determine the initial state as D 0 or D 0. The asymmetries in effective lifetimes between D 0 and D 0 decays, which are sensitive to indirect CP violation, are determined to be A Γ K − K + = −0.134 ± 0.077 +0.026 −0.034 % , A Γ π − π + = −0.092 ± 0.145 +0.025 −0.033 % , where the first uncertainties are statistical and the second systematic. This result is in agreement with previous measurements and with the hypothesis of no indirect CP violation in D 0 decays.
Measurement of the CP asymmetry in B0 -> K*0 mu+ mu- decays
2012
A measurement of the CP asymmetry in B 0 → K * 0 µ + µ − decays is presented, based on 1.0 fb −1 of pp collision data recorded by the LHCb experiment during 2011. The measurement is performed in six bins of invariant mass squared of the µ + µ − pair, excluding the J/ψ and ψ(2S) resonance regions. Production and detection asymmetries are removed using the B 0 → J/ψK * 0 decay as a control mode. The integrated CP asymmetry is found to be −0.072 ± 0.040 (stat.) ± 0.005 (syst.), consistent with the Standard Model.
Measurement of time-dependent CP asymmetries in B0→D(*)±π∓ and B0→D±ρ∓ decays
Physical Review D, 2006
The first measurement of decay-time-dependent CP asymmetries in the decay B 0 s → J/ψ K 0 S and an updated measurement of the ratio of branching fractions B(B 0 s → J/ψ K 0 S)/B(B 0 → J/ψ K 0 S) are presented. The results are obtained using data corresponding to an integrated luminosity of 3.0 fb −1 of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The results on the CP asymmetries are A ∆Γ B 0 s → J/ψ K 0 S = 0.49 ± 0.77 0.65 (stat) ± 0.06 (syst) , C dir B 0 s → J/ψ K 0 S = −0.28 ± 0.41 (stat) ± 0.08 (syst) , S mix B 0 s → J/ψ K 0 S = −0.08 ± 0.40 (stat) ± 0.08 (syst). The ratio B(B 0 s → J/ψ K 0 S)/B(B 0 → J/ψ K 0 S) is measured to be 0.0431 ± 0.0017 (stat) ± 0.0012 (syst) ± 0.0025 (f s /f d) , where the last uncertainty is due to the knowledge of the B 0 s and B 0 production fractions.
Investigation of inclusive CP asymmetries in rmB0\rm B^0rmB0 decays
The European Physical Journal C, 2001
A search for CP violating effects in the mixing of neutral B mesons is performed using a sample of 4.1 million hadronic Z decays collected with the ALEPH detector from 1991 to 1995. By studying time-dependent asymmetries in flavour-tagged samples of semileptonic and fully inclusive b-hadron decays, two measurements of the semileptonic asymmetry a CP are extracted. No evidence for CP violation is observed, and the combined value a CP = −0.013 ± 0.026 is obtained.
Measurement of CP Violation in B^{0}→D^{+}D^{-} Decays
Physical review letters, 2016
The CP violation observables S and C in the decay channel B^{0}→D^{+}D^{-} are determined from a sample of proton-proton collisions at center-of-mass energies of 7 and 8 TeV, collected by the LHCb experiment and corresponding to an integrated luminosity of 3 fb^{-1}. The observable S describes CP violation in the interference between mixing and the decay amplitude, and C parametrizes direct CP violation in the decay. The following values are obtained from a flavor-tagged, decay-time-dependent analysis: S=-0.54_{-0.16}^{+0.17}(stat)±0.05(syst), C=0.26_{-0.17}^{+0.18}(stat)±0.02(syst). These values provide evidence for CP violation at a significance level of 4.0 standard deviations. The phase shift due to higher-order standard model corrections is constrained to a small value of Δϕ=-0.16_{-0.21}^{+0.19} rad.