Measurement of mixing and CP violation parameters in two-body charm decays

A study of mixing and indirect CP violation in D 0 mesons through the determination of the parameters y CP and A Γ is presented. The parameter y CP is the deviation from unity of the ratio of effective lifetimes measured in D 0 decays to the CP eigenstate K + K − with respect to decays to the Cabibbo favoured mode K −π+. The result measured using data collected by LHCb in 2010, corresponding to an integrated luminosity of 29 pb−1, is y CP = (5.5 ± 6.3stat ± 4.1syst) × 10−3. The parameter A Γ is the asymmetry of effective lifetimes measured in decays of D 0 and D¯¯¯¯0 mesons to K + K −. The result is A Γ = (−5.9 ± 5.9stat ± 2.1syst) × 10−3. A data-driven technique is used to correct for lifetime-biasing effects

Study of B0(s)→K0Sh+h′− decays with first observation of B0s→K0SK±π∓ and B0s→K0Sπ+π

A search for charmless three-body decays of B 0 and B0s mesons with a K0S meson in the final state is performed using the pp collision data, corresponding to an integrated luminosity of 1.0 fb−1, collected at a centre-of-mass energy of 7 TeV recorded by the LHCb experiment. Branching fractions of the B0(s)→K0Sh+h′− decay modes (h (′) = π, K), relative to the well measured B0→K0Sπ+π− decay, are obtained. First observation of the decay modes B0s→K0SK±π∓ and B0s→K0Sπ+π− and confirmation of the decay B0→K0SK±π∓ are reported. The following relative branching fraction measurements or limits are obtained $ B(B0→K0SK±π∓)B(B0→K0Sπ+π−)=0.128±0.017(stat.)±0.009(syst.),B(B0→K0SK+K−)B(B0→K0Sπ+π−)=0.385±0.031(stat.)±0.023(syst.),B(B0s→K0Sπ+π−)B(B0→K0Sπ+π−)=0.29±0.06(stat.)±0.03(syst.)±0.02(fs/fd),B(B0s→K0SK±π∓)B(B0→K0Sπ+π−)=1.48±0.12(stat.)±0.08(syst.)±0.12(fs/fd)B(B0s→K0SK+K−)B(B0→K0Sπ+π−)∈[0.004;0.068]at90%CL

A study of the Z production cross-section in pp collisions at s√=7 TeV using tau final states

A measurement of the inclusive Z → ττ cross-section in pp collisions at s√=7TeV is presented based on a dataset of 1.0 fb−1 collected by the LHCb detector. Candidates for Z → τ τ decays are identified through reconstructed final states with two muons, a muon and an electron, a muon and a hadron, or an electron and a hadron. The production cross-section for Z bosons, with invariant mass between 60 and 120 GeV/c 2, which decay to τ leptons with transverse momenta greater than 20 GeV/c and pseudorapidities between 2.0 and 4.5, is measured to be σ pp→Z→ττ = 71.4 ± 3.5 ± 2.8 ± 2.5 pb; the first uncertainty is statistical, the second is systematic, and the third is due to the uncertainty on the integrated luminosity. The ratio of the cross-sections for Z → τ τ to Z → μμ is determined to be 0.93 ± 0.09, where the uncertainty is the combination of statistical, systematic, and luminosity uncertainties of the two measurements

Differential branching fraction and angular analysis of the decay B 0 → K ∗0 μ + μ -

The angular distribution and differential branching fraction of the decay B 0→ K ∗0 μ + μ − are studied using a data sample, collected by the LHCb experiment in pp collisions at s√=7 TeV, corresponding to an integrated luminosity of 1.0 fb−1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions

Angular analysis of charged and neutral B → Kμ + μ − decays

The angular distributions of the rare decays B + → K + μ + μ − and B0→K0Sμ+μ− are studied with data corresponding to 3fb−1 of integrated luminosity, collected in proton-proton collisions at 7 and 8 TeV centre-of-mass energies with the LHCb detector. The angular distribution is described by two parameters, F H and the forward-backward asymmetry of the dimuon system A FB, which are determined in bins of the dimuon mass squared. The parameter F H is a measure of the contribution from (pseudo)scalar and tensor amplitudes to the decay width. The measurements of A FB and F H reported here are the most precise to date and are compatible with predictions from the Standard Model

First measurement of time-dependent CP violation in B0s→K+K− decays

Direct and mixing-induced CP-violating asymmetries in B0s→K+K− decays are measured for the first time using a data sample of pp collisions, corresponding to an integrated luminosity of 1.0 fb−1, collected with the LHCb detector at a centre-of-mass energy of 7 TeV. The results are C KK  = 0.14 ± 0.11 ± 0.03 and S KK  = 0.30 ± 0.12 ± 0.04, where the first uncertainties are statistical and the second systematic. The corresponding quantities are also determined for B 0 → π + π − decays to be C ππ  = −0.38 ± 0.15 ± 0.02 and S ππ  = −0.71 ± 0.13 ± 0.02, in good agreement with existing measurements

Search for CP violation in the decay D+→π−π+π+

A search for CP violation in the phase space of the decay $D^+\to\pi^-\pi^+\pi^+$ is reported using $pp$ collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. The Dalitz plot distributions for $3.1\times 10^6$ $D^+$ and $D^-$ candidates are compared with binned and unbinned model-independent techniques. No evidence for CP violation is found

Measurement of the differential branching fraction of the decay Λ0b → Λμ+ μ−

The differential branching fraction of the decay $\Lambda_b^0\rightarrow\Lambda\mu^+\mu^-$ is measured as a function of the square of the dimuon invariant mass, $q^2$. A yield of $78\pm12$ $\Lambda_b^0\rightarrow\Lambda\mu^+\mu^-$ decays is observed using data, corresponding to an integrated luminosity of 1.0\,fb$^{-1}$, collected by the LHCb experiment at a centre-of-mass energy of 7\,TeV. A significant signal is found in the $q^2$ region above the square of the $J/\psi$ mass, while at lower-$q^2$ values upper limits are set on the differential branching fraction. Integrating the differential branching fraction over $q^2$, while excluding the $J/\psi$ and $\psi(2S)$ regions, gives a branching fraction of \BF(\Lambda_b^0\rightarrow\Lambda\mu^+\mu^-)=(0.96\pm 0.16\stat\pm 0.13\syst\pm 0.21 (\mathrm{norm}))\times 10^{-6}, where the uncertainties are statistical, systematic and due to the normalisation mode, $$\Lambda_b^0\rightarrow J/psi\Lambda$, respectively

Measurement of the ηc(1S) production cross-section in p p collisions at s√=13 TeV

Using a data sample corresponding to an integrated luminosity of 2.0 fb−1, collected by the LHCb experiment, the production of the ηc(1S) state in proton–proton collisions at a centre-of-mass energy of s√=13 TeV is studied in the rapidity range 2.0<y<4.5 and in the transverse momentum range 6.5<pT<14.0GeV. The cross-section for prompt production of ηc(1S) mesons relative to that of the J/ψ meson is measured using the p p¯¯¯ decay mode and is found to be σηc(1S)/σJ/ψ=1.69±0.15±0.10±0.18. The quoted uncertainties are, in order, statistical, systematic and due to uncertainties on the branching fractions of the J/ψ→pp¯¯¯ and ηc→pp¯¯¯ decays. The prompt ηc(1S) production cross-section is determined to be σηc(1S)=1.26±0.11±0.08±0.14μb, where the last uncertainty includes that on the J/ψ meson cross-section. The ratio of the branching fractions of b-hadron decays to the ηc(1S) and J/ψ states is measured to be Bb→ηcX/Bb→J ψX=0.48±0.03±0.03±0.05, where the last uncertainty is due to those on the branching fractions of the J/ψ→pp¯¯¯ and ηc→pp¯¯¯ decays. The difference between the J/ψ and ηc(1S) masses is also determined to be 113.0±0.7±0.1MeV, which is the most precise single measurement of this quantity to date

Search for direct CP violation in D0 → h−h+ modes using semileptonic B decays

A search for direct CP violation in D0 -> h- h+ (where h=K or pi) is presented using data corresponding to an integrated luminosity of 1.0 fb^-1 collected in 2011 by LHCb in pp collisions at a centre-of-mass energy of 7 TeV. The analysis uses D0 mesons produced in inclusive semileptonic b-hadron decays to the D0 mu X final state, where the charge of the accompanying muon is used to tag the flavour of the D0 meson. The difference in the CP-violating asymmetries between the two decay channels is measured to be Delta A_CP = A_CP(K-K+) - A_CP(pi-pi+) = (0.49 +- 0.30 (stat) +- 0.14 (syst)) % . This result does not confirm the evidence for direct CP violation in the charm sector reported in other analyses