Observation of an Excited Bc+ State

Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+π+π- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc∗(2S31)+ state reconstructed without the low-energy photon from the Bc∗(1S31)+→Bc+γ decay following Bc∗(2S31)+→Bc∗(1S31)+π+π-. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date

Observation of a New Excited Ds+ Meson in B0 →d-D+K+π-Decays

Using pp collision data corresponding to an integrated luminosity of 5.4 fb−1 collected with the LHCb detector at a center-of-mass energy of 13 TeV, the B0 → D−DþKþπ− decay is studied. A new excited Dþ s meson is observed decaying into the DþKþπ− final state with large statistical significance. The pole mass and width, and the spin parity of the new state are measured with an amplitude analysis to be mR ¼ 2591 6 7 MeV, ΓR ¼ 89 16 12 MeV, and JP ¼ 0−, where the first uncertainty is statistical and the second systematic. Fit fractions for all components in the amplitude analysis are also reported. The new resonance, denoted as Ds0ð2590Þþ, is a strong candidate to be the Dsð21 S0Þþ state, the radial excitation of the pseudoscalar ground-state Dþ s meson

Measurement of CP observables in B± → D(*)K± and B± → D(*) π ± decays using two-body D final states

Measurements of CP observables in B± → D(∗)K± and B± → D(∗)π ± decays are presented, where D(∗) indicates a neutral D or D∗ meson that is an admixture of meson and anti-meson states. Decays of the D(∗) meson to the Dπ0 and Dγ final states are partially reconstructed without inclusion of the neutral pion or photon. Decays of the D meson are reconstructed in the K±π ∓, K+K−, and π +π − final states. The analysis uses a sample of charged B mesons produced in proton-proton collisions and collected with the LHCb experiment, corresponding to integrated luminosities of 2.0, 1.0, and 5.7 fb−1 taken at centre-of-mass energies of 7, 8, and 13 TeV, respectively. The measurements of partially reconstructed B± → D(∗)K± and B± → D(∗)π ± with D → K∓π ± decays are the first of their kind, and a first observation of the B± → (Dπ0 )D∗ π ± decay is made with a significance of 6.1 standard deviations. All CP observables are measured with world-best precision, and in combination with other LHCb results will provide strong constraints on the CKM angle

Observation of Multiplicity Dependent Prompt χc1 (3872) and ψ (2S) Production in pp Collisions

The production of χc1(3872) and ψ(2S) hadrons is studied as a function of charged particle multiplicity in pp collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2 fb−1 . For both states, the fraction that is produced promptly at the collision vertex is found to decrease as charged particle multiplicity increases. The ratio of χc1(3872) to ψ(2S) cross-sections for promptly produced particles is also found to decrease with multiplicity, while no significant dependence on multiplicity is observed for the equivalent ratio of particles produced away from the collision vertex in b-hadron decays. This behavior is consistent with a calculation that models the χc1(3872) structure as a compact tetraquark. Implications for the binding energy of the χc1(3872) state are discussed

Observation of the decay Λb0 → χc1pπ−

The Cabibbo-suppressed decay Λ 0 b → χc1pπ − is observed for the first time using data from proton-proton collisions corresponding to an integrated luminosity of 6 fb−1 , collected with the LHCb detector at a centre-of-mass energy of 13 TeV. Evidence for the Λ 0 b → χc2pπ − decay is also found. Using the Λ 0 b → χc1pK− decay as normalisation channel, the ratios of branching fractions are measured to be B Λ 0 b → χc1pπ − B Λ0 b → χc1pK− = (6.59 ± 1.01 ± 0.22) × 10−2 , B Λ 0 b → χc2pπ − B Λ0 b → χc1pπ− = 0.95 ± 0.30 ± 0.04 ± 0.04 , B Λ 0 b → χc2pK− B Λ0 b → χc1pK− = 1.06 ± 0.05 ± 0.04 ± 0.04 , where the first uncertainty is statistical, the second is systematic and the third is due to the uncertainties in the branching fractions of χc1,2 → J/ψγ decays. Keywords: B physics, Branching fraction, Hadron-Hadron scattering (experiments), QCD, Qua

Search for CP violation in D(s)+→h+π0 and D(s)+→h+η decays

Searches for CP violation in the two-body decays D + (s) → h +π 0 and D + (s) → h +η (where h + denotes a π + or K+ meson) are performed using pp collision data collected by the LHCb experiment corresponding to either 9 fb−1 or 6 fb−1 of integrated luminosity. The π 0 and η mesons are reconstructed using the e +e −γ final state, which can proceed as three-body decays π 0 → e +e −γ and η → e +e −γ, or via the two-body decays π 0 → γγ and η → γγ followed by a photon conversion. The measurements are made relative to the control modes D + (s)→ K0 S h + to cancel the production and detection asymmetries. The CP asymmetries are measured to b

Measurement of the CKM angle γ and Bs0‐B¯s0 mixing frequency with Bs0→Ds∓h±π±π∓ decays

The CKM angle γ is measured for the first time from mixing-induced CP violation between B0 s → D∓ s K±π ±π ∓ and B 0 s → D± s K∓π ∓π ± decays reconstructed in proton-proton collision data corresponding to an integrated luminosity of 9 fb−1 recorded with the LHCb detector. A time-dependent amplitude analysis is performed to extract the CP-violating weak phase γ − 2βs and, subsequently, γ by taking the B0 s -B 0 s mixing phase βs as an external input. The measurement yields γ = (44±12)◦ modulo 180◦ , where statistical and systematic uncertainties are combined. An alternative model-independent measurement, integrating over the five-dimensional phase space of the decay, yields γ = (44 + 20 − 13) ◦ modulo 180◦ . Moreover, the B0 s -B 0 s oscillation frequency is measured from the flavour-specific control channel B0 s → D− s π +π +π − to be ∆ms = (17.757 ± 0.007(stat) ± 0.008(syst)) ps−1 , consistent with and more precise than the current world-average value

Searches for 25 rare and forbidden decays of D + and Ds+ mesons

A search is performed for rare and forbidden charm decays of the form D + (s)→ h ±` +` (0)∓, where h ± is a pion or kaon and ` ( 0 )± is an electron or muon. The measurements are performed using proton-proton collision data, corresponding to an integrated luminosity of 1.6 fb−1 , collected by the LHCb experiment in 2016. No evidence is observed for the 25 decay modes that are investigated and 90 % confidence level limits on the branching fractions are set between 1.4 × 10−8 and 6.4 × 10−6 . In most cases, these results represent an improvement on existing limits by one to two orders of magnitude

Search for the doubly charmed baryon Ξ+cc in the Ξ+cπ−π+ final state

A search for the doubly charmed baryon Ξ+ cc is performed in the Ξ+ c π −π + invariant-mass spectrum, where the Ξ+ c baryon is reconstructed in the pK−π + final state. The study uses proton-proton collision data collected with the LHCb detector at a centreof-mass energy of 13 TeV, corresponding to a total integrated luminosity of 5.4 fb−1 . No significant signal is observed in the invariant-mass range of 3.4-3.8 GeV/c 2 . Upper limits are set on the ratio of branching fractions multiplied by the production cross-section with respect to the Ξ++ cc → (Ξ+ c → pK−π +)π + decay for different Ξ+ cc mass and lifetime hypotheses in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 2.5 to 25 GeV/c. The results from this search are combined with a previously published search for the Ξ+ cc → Λ + c K−π + decay mode, yielding a maximum local significance of 4.0 standard deviations around the mass of 3620 MeV/c 2 , including systematic uncertainties. Taking into account the look-elsewhere effect in the 3.5-3.7 GeV/c 2 mass window, the combined global significance is 2.9 standard deviations including systematic uncertainties