Observation of Bc+→J/ψDs+ and Bc+→J/ψDs*+ decays

The decays Bc+→J/ψDs+ and Bc+→J/ψDs*+ are observed for the first time using a dataset, corresponding to an integrated luminosity of 3  fb-1, collected by the LHCb experiment in proton-proton collisions at center-of-mass energies of √s=7 and 8 TeV. The statistical significance for both signals is in excess of 9 standard deviations. The following ratios of branching fractions are measured to be B(Bc+→J/ψDs+)/B(Bc+→J/ψπ+)=2.90±0.57±0.24, B(Bc+→J/ψDs*+)/B(Bc+→J/ψDs+)=2.37±0.56±0.10, where the first uncertainties are statistical and the second systematic. The mass of the Bc+ meson is measured to be mBc+=6276.28±1.44(stat)±0.36(syst)  MeV/c2, using the Bc+→J/ψDs+ decay mode

Measurements of the branching fractions of B+→ppK+ decays

The branching fractions of the decay B+ → pp̄K+ for different intermediate states are measured using data, corresponding to an integrated luminosity of 1.0 fb-1, collected by the LHCb experiment. The total branching fraction, its charmless component Mpp̄ < 2.85 GeV/c2 and the branching fractions via the resonant cc̄ states η c(1S) and ψ(2S) relative to the decay via a J/ψ intermediate state are [Equation not available: see fulltext.] Upper limits on the B + branching fractions into the η c(2S) meson and into the charmonium-like states X(3872) and X(3915) are also obtained

First Observation of a Baryonic B-c(+) Decay

A baryonic decay of the $B_c^+$ meson, $B_c^+\to J/\psi p\overline{p}\pi^+$, is observed for the first time, with a significance of $7.3$ standard deviations, in $pp$ collision data collected with the LHCb detector and corresponding to an integrated luminosity of $3.0$ fb$^{-1}$ taken at center-of-mass energies of $7$ and $8$ $\mathrm{TeV}$. With the $B_c^+\to J/\psi \pi^+$ decay as normalization channel, the ratio of branching fractions is measured to be \begin{equation*} \frac{\mathcal{B}(B_c^+\to J/\psi p\overline{p}\pi^+)}{\mathcal{B}(B_c^+\to J/\psi \pi^+)} = 0.143^{\,+\,0.039}_{\,-\,0.034}\,(\mathrm{stat})\pm0.013\,(\mathrm{syst}). \end{equation*} The mass of the $B_c^+$ meson is determined as $M(B_c^+)=6274.0\pm1.8\,(\mathrm{stat})\pm0.4\,(\mathrm{syst})\,\mathrm{MeV}/c^2$, using the $B_c^+\to J/\psi p\overline{p}\pi^+$ channel.Comment: 20 pages, 2 figure

Study of production and cold nuclear matter effects in pPb collisions at=5 TeV

Production of $\Upsilon$ mesons in proton-lead collisions at a nucleon-nucleon centre-of-mass energy $\sqrt{s_{NN}}=5 \mathrm{TeV}$ is studied with the LHCb detector. The analysis is based on a data sample corresponding to an integrated luminosity of $1.6 \mathrm{nb}^{-1}$. The $\Upsilon$ mesons of transverse momenta up to $15 \mathrm{GeV}/c$ are reconstructed in the dimuon decay mode. The rapidity coverage in the centre-of-mass system is $1.5<y<4.0$ (forward region) and $-5.0<y<-2.5$ (backward region). The forward-backward production ratio and the nuclear modification factor for $\Upsilon(1S)$ mesons are determined. The data are compatible with the predictions for a suppression of $\Upsilon(1S)$ production with respect to proton-proton collisions in the forward region, and an enhancement in the backward region. The suppression is found to be smaller than in the case of prompt $J/\psi$ mesons.Comment: 21 pages, 3 figures, published to JHE

Measurement of the Λb0, Ξb-, and Ωb- Baryon Masses

Bottom baryons decaying to a J/ψ meson and a hyperon are reconstructed using 1.0  fb-1 of data collected in 2011 with the LHCb detector. Significant Λb0→J/ψΛ, Ξb-→J/ψΞ- and Ωb-→J/ψΩ- signals are observed and the corresponding masses are measured to be M(Λb0)=5619.53±0.13(stat.)±0.45(syst.)  MeV/c2, M(Ξb-)=5795.8±0.9(stat.)±0.4(syst.)  MeV/c2, M(Ωb-)=6046.0±2.2(stat.)±0.5(syst.)  MeV/c2, while the differences with respect to the Λb0 mass are M(Ξb-)-M(Λb0)=176.2±0.9(stat.)±0.1(syst.)  MeV/c2, M(Ωb-)-M(Λb0)=426.4±2.2(stat.)±0.4(syst.)  MeV/c2. These are the most precise mass measurements of the Λb0, Ξb- and Ωb- baryons to date. Averaging the above Λb0 mass measurement with that published by LHCb using 35  pb-1 of data collected in 2010 yields M(Λb0)=5619.44±0.13(stat.)±0.38(syst.)  MeV/c2

Measurement of the forward energy flow in pp collisions at &#8730;<span style="text-decoration:overline">s</span>=7 TeV

The energy flow created in pp collisions at s√=7 TeV is studied within the pseudorapidity range 1.9&#60;η&#60;4.9 with data collected by the LHCb experiment. The measurements are performed for inclusive minimum-bias interactions, hard scattering processes and events with an enhanced or suppressed diffractive contribution. The results are compared to predictions given by Pythia-based and cosmic-ray event generators, which provide different models of soft hadronic interactions

Study of the kinematic dependences of Λ0b production in pp collisions and a measurement of the Λ0 b → Λ+c π− branching fraction

The kinematic dependences of the relative production rates, fΛ0 b /fd, of Λ0 b baryons and B0 mesons are measured using Λ0 b → Λ + c π − and B 0 → D+π − decays. The measurements use proton-proton collision data, corresponding to an integrated luminosity of 1 fb−1 at a centre-of-mass energy of 7 TeV, recorded in the forward region with the LHCb experiment. The relative production rates are observed to depend on the transverse momentum, pT, and pseudorapidity, η, of the beauty hadron, in the studied kinematic region 1.5 &#60; pT &#60; 40 GeV/c and 2 &#60; η &#60; 5. Using a previous LHCb measurement of fΛ0 b /fd in semileptonic decays, the branching fraction B Λ 0 b → Λ + c π − = 4.30±0.03 +0.12 −0.11±0.26± 0.21 ×10−3 is obtained, where the first uncertainty is statistical, the second is systematic, the third is from the previous LHCb measurement of fΛ0 b /fd and the fourth is due to the B 0 → D+π − branching fraction. This is the most precise measurement of a Λ0 b branching fraction to date

Observation of B ̄ (s) 0 → J / ψ f 1 (1285) decays and measurement of the f 1 (1285) mixing angle

Decays of B̄s0 and B̄0 mesons into J/ψ π+π-π+π- final states, produced in pp collisions at the LHC, are investigated using data corresponding to an integrated luminosity of 3 fb-1 collected with the LHCb detector. B̄(s)0→J/ψf1(1285) decays are seen for the first time, and the branching fractions are measured. Using these rates, the f1(1285) mixing angle between strange and nonstrange components of its wave function in the qq̄ structure model is determined to be ±(24.0-2.6-0.8+3.1+0.6). Implications on the possible tetraquark nature of the f1(1285) are discussed

Measurements of indirect CP asymmetries in D0→K−K+ and D0→π−π+ decays

A study of indirect CP violation in D0 mesons through the determination of the parameter AΓ is presented using a data sample of pp collisions, corresponding to an integrated luminosity of 1.0  fb−1, collected with the LHCb detector and recorded at the center-of-mass energy of 7 TeV at the LHC. The parameter AΓ is the asymmetry of the effective lifetimes measured in decays of D0 and D¯​0 mesons to the CP eigenstates K−K+ and π−π+. Fits to the data sample yield AΓ(KK)=(−0.35±0.62±0.12)×10−3 and AΓ(ππ)=(0.33±1.06±0.14)×10−3, where the first uncertainties are statistical and the second systematic. The results represent the world’s best measurements of these quantities. They show no difference in AΓ between the two final states and no indication of CP violation

Measurement of form-factor-independent observables in the decay B0→K*0μ+μ-

We present a measurement of form-factor-independent angular observables in the decay B0→K*(892)0μ+μ-. The analysis is based on a data sample corresponding to an integrated luminosity of 1.0  fb-1, collected by the LHCb experiment in pp collisions at a center-of-mass energy of 7 TeV. Four observables are measured in six bins of the dimuon invariant mass squared q2 in the range 0.1<q2<19.0  GeV2/c4. Agreement with recent theoretical predictions of the standard model is found for 23 of the 24 measurements. A local discrepancy, corresponding to 3.7 Gaussian standard deviations is observed in one q2 bin for one of the observables. Considering the 24 measurements as independent, the probability to observe such a discrepancy, or larger, in one is 0.5%