45 research outputs found
Measurement of the cross-section for Z → e<sup>+</sup>e<sup>-</sup> production in pp collisions at √<span style="text-decoration:overline">s</span>=7 TeV
No full textA measurement of the cross-section for pp → Z → e+e− is presented using data at s√=7 TeV corresponding to an integrated luminosity of 0.94 fb−1. The process is measured within the kinematic acceptance p T > 20 GeV/c and 2 < η < 4.5 for the daughter electrons and dielectron invariant mass in the range 60–120 GeV/c 2. The cross-section is determined to be σ(pp→Z→e+e−)=76.0±0.8±2.0±2.6pb where the first uncertainty is statistical, the second is systematic and the third is the uncertainty in the luminosity. The measurement is performed as a function of Z rapidity and as a function of an angular variable which is closely related to the Z transverse momentum. The results are compared with previous LHCb measurements and with theoretical predictions from QCD
Measurement of the B0→K∗0e+e− branching fraction at low dilepton mass
No full textThe branching fraction of the rare decay B 0 → K ∗0 e + e − in the dilepton mass region from 30 to 1000 MeV/c 2 has been measured by the LHCb experiment, using pp collision data, corresponding to an integrated luminosity of 1.0 fb−1, at a centre-of-mass energy of 7 TeV. The decay mode B 0 → J/ψ (e + e −)K ∗0 is utilized as a normalization channel. The branching fraction B(B0→K∗0e+e−) is measured to be B(B0→K∗0e+e−)30−1000MeV/c2 =(3.1+0.9−0.8+0.2−0.3±0.2)×10−7, where the first error is statistical, the second is systematic, and the third comes from the uncertainties on the B 0 → J/ψ K ∗0 and J/ψ → e + e − branching fractions
Measurement of the time-dependent CP asymmetry in B0 -> J/ψ KS0 decays
No full textThis Letter reports a measurement of the CP violation observables SJ/ψK0S and CJ/ψK0S in the decay channel B0→J/ψK0S performed with 1.0 fb−1 of pp collisions at s√=7 TeV collected by the LHCb experiment. The fit to the data yields SJ/ψK0S=0.73±0.07(stat)±0.04(syst) and CJ/ψK0S=0.03±0.09(stat)±0.01(syst). Both values are consistent with the current world averages and within
expectations from the Standard Model
Differential branching fraction and angular analysis of the decay B0→K*0μ+μ-
No full textThe angular distributions and the partial branching fraction of the decay B0→K *0μ +μ - are studied by using an integrated luminosity of 0.37fb -1 of data collected with the LHCb detector. The forward-backward asymmetry of the muons, A FB, the fraction of longitudinal polarization, F L, and the partial branching fraction dB/dq2 are determined as a function of the dimuon invariant mass. The measurements are in good agreement with the standard model predictions and are the most precise to date. In the dimuon invariant mass squared range 1.00-6.00GeV2/c4, the results are A FB=-0.06-0.14+0.13±0.04, F L=0.55±0.10±0.03, and dB/dq2=(0.42±0. 06±0.03)×10 -7c4/GeV2. In each case, the first error is statistical and the second systematic
First evidence for the two-body charmless baryonic decay B0→pp−
No full textThe results of a search for the rare two-body charmless baryonic decays B0→pp− and B0s→pp− are reported. The analysis uses a data sample, corresponding to an integrated luminosity of 0.9 fb−1, of pp collision data collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. An excess of B0→pp− candidates with respect to background expectations is seen with a statistical significance of 3.3 standard deviations. This is the first evidence for a two-body charmless baryonic B 0 decay. No significant B0s→pp− signal is observed, leading to an improvement of three orders of magnitude over previous bounds. If the excess events are interpreted as signal, the 68.3% confidence level intervals on the branching fractions are B(B0→pp−)=1.47+0.62+0.35−0.51−0.14×10−8,\hfillB(Bs→pp−)=2.84+2.03+0.85−1.68−0.18×10−8,\hfill where the first uncertainty is statistical and the second is systematic
Measurement of the fragmentation fraction ratio fs/fd and its dependence on B meson kinematics
No full textThe relative production rate of B0s and B 0 mesons is determined with the hadronic decays B0s→D−sπ+ and B 0 → D − K +. The measurement uses data corresponding to 1.0 fb−1 of pp collisions at a centre-of-mass energy of s√=7 TeV recorded in the forward region with the LHCb experiment. The ratio of production rates, f s /f d , is measured to be 0.238 ± 0.004 ± 0.015 ± 0.021, where the first uncertainty is statistical, the second systematic, and the third theoretical. This is combined with a previous LHCb measurement to obtain f s /f d = 0.256 ± 0.020. The dependence of f s /f d on the transverse momentum and pseudorapidity of the B meson is determined using the decays B0s→D−sπ+ and B 0 → D −π+. There is evidence for a decrease with increasing transverse momentum, whereas the ratio remains constant as a function of pseudorapidity. In addition, the ratio of branching fractions of the decays B 0 → D − K + and B 0 → D −π+ is measured to be 0.0822 ± 0.0011 (stat) ± 0.0025 (syst)
First observation of the decays B0 -> D+K-π+π- and B- -> D0K-π+π-
No full textFirst observations of the Cabibbo-suppressed decays B0→D+K-π+π- and B-→D0K-π+π- are reported using 35pb -1 of data collected with the LHCb detector. Their branching fractions are measured with respect to the corresponding Cabibbo-favored decays, from which we obtain B(B0→D+K-π+π-)/B(B0→D+π-π+π-)=(5.9±1.1±0.5) ×10-2 and B(B-→D0K-π+π-)/B(B-→D0π-π+π-)=(9.4±1.3±0.9) ×10-2, where the uncertainties are statistical and systematic, respectively. The B-→D0K-π+π- decay is particularly interesting, as it can be used in a similar way to B-→D0K- to measure the Cabibbo-Kobayashi-Maskawa phase γ
Differential branching fraction and angular analysis of the decay → ϕμ + μ −
No full textThe determination of the differential branching fraction and the first angular analysis of the decay B0s → ϕμ + μ − are presented using data, corresponding to an integrated luminosity of 1.0 fb−1, collected by the LHCb experiment at s√=7 TeV. The differential branching fraction is determined in bins of q 2, the invariant dimuon mass squared. Integration over the full q 2 range yields a total branching fraction of B(B0s→ϕμ+μ−)=(7.07+0.64−0.59±0.71±0.71) × 10−7, where the first uncertainty is statistical, the second systematic, and the third originates from the branching fraction of the normalisation channel. An angular analysis is performed to determine the angular observables F L, S 3, A 6, and A 9. The observables are consistent with Standard Model expectations
Measurements of the branching fractions of the decays B0s→D∓sK± and B0s→D−sπ+
No full textThe decay mode B0s→D∓sK± allows for one of the theoretically cleanest measurements of the CKM angle γ through the study of time-dependent CP violation. This paper reports a measurement of its branching fraction relative to the Cabibbo-favoured mode B0s→D−sπ+ based on a data sample corresponding to 0.37 fb−1 of proton-proton collisions at s√=7TeV collected in 2011 with the LHCb detector. In addition, the ratio of B meson production fractions f s /f d , determined from semileptonic decays, together with the known branching fraction of the control channel B 0 → D −π+, is used to perform an absolute measurement of the branching fractions: B(B0s→D−sπ+)=(2.95±0.05±0.17+0.18−0.22)×10−3,\hfillB(B0s→D∓sK±)=(1.90±0.12±0.13+0.12−0.14)×10−4,\hfill where the first uncertainty is statistical, the second the experimental systematic uncertainty, and the third the uncertainty due to f s /f d
Precision measurement of D meson mass differences
No full textUsing three- and four-body decays of D mesons produced in semileptonic b-hadron decays, precision measurements of D meson mass differences are made together with a measurement of the D 0 mass. The measurements are based on a dataset corresponding to an integrated luminosity of 1.0 fb−1 collected in pp collisions at 7 TeV. Using the decay D 0 → K + K − K − π +, the D 0 mass is measured to be M(D0)=1864.75±0.15(stat)±0.11(syst)MeV/c2.
The mass differences
M(D+)−M(D0)=4.76±0.12(stat)±0.07(syst)MeV/c2,M(Ds)−M(D+)=98.68±0.03(stat)±0.04(syst)MeV/c2
are measured using the D 0 → K + K − π + π − and D+(s)→K+K−π+ mode
