The first observation of the B 0 s → η ′ η ′ decay is reported. The study is based on a sample of proton-proton collisions corresponding to 3.0 fb − 1 of integrated luminosity collected with the ...LHCb detector. The significance of the signal is 6.4 standard deviations. The branching fraction is measured to be 3.31 ± 0.64 ( stat ) ± 0.28 ( syst ) ± 0.12 ( norm ) × 10 − 5 , where the third uncertainty comes from the B ± → η ′ K ± branching fraction that is used as a normalization. In addition, the charge asymmetries of B ± → η ′ K ± and B ± → ϕ K ± , which are control channels, are measured to be ( − 0.2 ± 1.3 ) % and ( + 1.7 ± 1.3 ) % , respectively. All results are consistent with theoretical expectations.
The steadily increasing luminosity of the LHC requires an upgrade with high-rate and high-resolution detector technology for the inner end cap of the ATLAS muon spectrometer: the New Small Wheels ...(NSW). In order to achieve the goal of precision tracking at a hit rate of about 15 kHz/cm2 at the inner radius of the NSW, large area Micromegas quadruplets with 100µm spatial resolution per plane have been produced. IRFU, from the CEA research center of Saclay, is responsible for the production and validation of LM1 Micromegas modules. The construction, production, qualification and validation of the largest Micromegas detectors ever built are reported here. Performance results under cosmic muon characterization will also be discussed.
Measurements are presented of the C P violation observables S and C in the decays of B 0 and ¯ B 0 mesons to the J / ψ K 0 S final state. The data sample corresponds to an integrated luminosity of ...3.0 fb − 1 collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, and contains a total of 41 560 selected B 0 and ¯ B 0 decays. The analysis of the time evolution of these decays yields S = 0.731 ± 0.035 ( stat ) ± 0.020 ( syst ) and C = − 0.038 ± 0.032 ( stat ) ± 0.005 ( syst ) . In the standard model, S equals sin ( 2 β ) to a good level of precision. The values are consistent with the current world averages and with the standard model expectations.
An angular analysis and a measurement of the differential branching fraction of the decay B0s→ϕμ+μ− are presented, using data corresponding to an integrated luminosity of 3.0fb−1 of pp collisions ...recorded by the LHCb experiment at s√=7 and 8TeV. Measurements are reported as a function of q2, the square of the dimuon invariant mass and results of the angular analysis are found to be consistent with the Standard Model. In the range 1
A study of $B^0$~and $B^0_s$ meson decays into $J/\psi\eta$~and $J/\psi\eta^{\prime}$ final states is performed using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8TeV, ...collected by the LHCb experiment and corresponding to 3.0fb$^{-1}$ of integrated luminosity. The decay $B^0 \rightarrow J/\psi \eta^{\prime}$ is observed for thefirst time. The following ratios of branching fractions are measured: $$ \frac{\mathcal{B}(B^0 \rightarrow J/\psi \eta^{\prime})}{\mathcal{B}(B^0_s \rightarrow J/\psi \eta^{\prime})} = (2.28\pm0.65\,(stat)\,\pm0.10\,(syst)\,\pm0.13\,(f_{s}/f_{d}))\times10^{-2},$$ $$ \frac{\mathcal{B}(B^0 \rightarrow J/\psi \eta)}{\mathcal{B}(B^0_s \rightarrow J/\psi \eta)} = (1.85\pm0.61\,(stat)\,\pm0.09\,(syst)\,\pm0.11\,(f_{s}/f_{d}))\times10^{-2},$$ where the third uncertainty is related to the present knowledge of $f_{s}/f_{d}$, the ratio between the probabilities for a $b$ quark to form a $B^0_s$ or $B^0$ meson. The branching fraction ratios are used to determine the parameters of $\eta-\eta^{\prime}$ meson mixing. In addition, the first evidence for the decay $B^0_s \rightarrow \psi(2S) \eta^{\prime}$ is reported, and the relative branching fraction is measured,$$\frac{\mathcal{B}(B^0_s \rightarrow \psi(2S) \eta^{\prime})}{\mathcal{B}(B^0_s \rightarrow J/\psi \eta^{\prime})} = (38.7\pm9.0\,(stat)\,\pm1.3\,(syst)\,\pm0.9(\mathcal{B}))\times10^{-2},$$where the third uncertainty is due to the limited knowledge of the branching fractions of $J/\psi$ and $\psi(2S)$~mesons.
The time-dependent C P asymmetry in B 0 s → J / ψ K + K − decays is measured using p p collision data, corresponding to an integrated luminosity of 3.0 fb − 1 , collected with the LHCb detector ...at center-of-mass energies of 7 and 8 TeV. In a sample of 96 000 B 0 s → J / ψ K + K − decays, the C P -violating phase ϕ s is measured, as well as the decay widths Γ L and Γ H of the light and heavy mass eigenstates of the B 0 s - ¯ B 0 s system. The values obtained are ϕ s = − 0.058 ± 0.049 ± 0.006 rad , Γ s ≡ ( Γ L + Γ H ) / 2 = 0.6603 ± 0.0027 ± 0.0015 ps − 1 , and Δ Γ s ≡ Γ L − Γ H = 0.0805 ± 0.0091 ± 0.0032 ps − 1 , where the first uncertainty is statistical and the second, systematic. These are the most precise single measurements of those quantities to date. A combined analysis with B 0 s → J / ψ π + π − decays gives ϕ s = − 0.010 ± 0.039 rad . All measurements are in agreement with the standard model predictions. For the first time, the phase ϕ s is measured independently for each polarization state of the K + K − system and shows no evidence for polarization dependence.
The first observation of the B0s→D∗∓sK± decay is reported using 3.0fb−1 of proton-proton collision data collected by the LHCb experiment. The D∗∓s mesons are reconstructed through the decay chain ...D∗∓s→γD∓s(K∓K±π∓). The branching fraction relative to that for B0s→D∗−sπ+ is measured to be 0.068±0.005+0.003−0.002, where the first uncertainty is statistical and the second is systematic. Using a recent measurement of BR(B0s→D∗−sπ+) the absolute branching fraction of B0s→D∗∓sK± is measured as ( 16.3 ± 1.2 (stat) +0.7−0.5 (syst) ± 4.8 (norm) ) × 10−5, where the third uncertainty is due to the uncertainty on the branching fraction of the normalisation channel.
An angular analysis of the decay B0s→K∗0K¯∗0 is performed using pp collisions corresponding to an integrated luminosity of 1.0 fb−1 collected by the LHCb experiment at a centre-of-mass energy s√=7 ...TeV. A combined angular and mass analysis separates six helicity amplitudes and allows the measurement of the longitudinal polarisation fraction fL=0.201±0.057(stat.)±0.040(syst.) for the B0s→K∗(892)0K¯∗(892)0 decay. A large scalar contribution from the K∗0(1430) and K∗0(800) resonances is found, allowing the determination of additional CP asymmetries. Triple product and direct CP asymmetries are determined to be compatible with the Standard Model expectations. The branching fraction B(B0s→K∗(892)0K¯∗(892)0) is measured to be (10.6±1.8(stat.)±1.0(syst.)±0.6(fd/fs))×10−6.
The first measurement of decay-time-dependent CP asymmetries in the decay B0s→J/ψK0S and an updated measurement of the ratio of branching fractions B(B0s→J/ψK0S)/B(B0d→J/ψK0S)} 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 AΔΓ(B0s→J/ψK0S)=0.49+0.77−0.65(stat)±0.06(syst), Cdir(B0s→J/ψK0S)=−0.28±0.41(stat)±0.08(syst) and Smix(B0s→J/ψK0S)=−0.08±0.40(stat)±0.08(syst). The ratio B(B0s→J/ψK0S)/B(B0d→J/ψK0S) is measured to be 0.0431±0.0017(stat)±0.0012(syst)±0.0025(fs/fd), where the last uncertainty is due to the knowledge of the B0s and B0d production fractions.
A measurement of the cross-section for Z-boson production in the forward region of pp collisions at 8TeV centre-of-mass energy is presented. The measurement is based on a sample of Z→e+e− decays ...reconstructed using the LHCb detector, corresponding to an integrated luminosity of 2.0fb−1. The acceptance is defined by the requirements 2.0<η<4.5 and pT>20GeV for the pseudorapidities and transverse momenta of the leptons. Their invariant mass is required to lie in the range 60--120GeV. The cross-section is determined to beσ(pp→Z→e+e−)=93.81±0.41(stat)±1.48(syst)±1.14(lumi)pb,where the first uncertainty is statistical and the second reflects all systematic effects apart from that arising from the luminosity, which is given as the third uncertainty. Differential cross-sections are presented as functions of the Z-boson rapidity and of the angular variable ϕ∗, which is related to the Z-boson transverse momentum.
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