Study of the doubly charmed tetraquark Tcc+

Quantum chromodynamics, the theory of the strong force, describes interactions of coloured quarks and gluons and the formation of hadronic matter. Conventional hadronic matter consists of baryons and mesons made of three quarks and quark-antiquark pairs, respectively. Particles with an alternative quark content are known as exotic states. Here a study is reported of an exotic narrow state in the (DD0)-D-0 pi(+) mass spectrum just below the D*+D-0 mass threshold produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. The state is consistent with the ground isoscalar T-cc(+), tetraquark with a quark content of cc (u) over bar(d) over bar and spin-parity quantum numbers J(P) =1(+). Study of the DD mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell D*(+) mesons is consistent with the observed D-0 pi(+) mass distribution. To analyse the mass of the resonance and its coupling to the DID system, a dedicated model is developed under the assumption of an isoscalar axial-vector T-cc(+), state decaying to the D*D channel. Using this model, resonance parameters including the pole position, scattering length, effective range and compositeness are determined to reveal important information about the nature of the T-cc(+), state. In addition, an unexpected dependence of the production rate on track multiplicity is observed

Observation of a New Ξ−b Resonance

From samples of pp collision data collected by the LHCb experiment at √s=7, 8 and 13 TeV, corresponding to integrated luminosities of 1.0, 2.0 and 1.5  fb−1, respectively, a peak in both the Λ0bK− and Ξ0bπ− invariant mass spectra is observed. In the quark model, radially and orbitally excited Ξ−b resonances with quark content bds are expected. Referring to this peak as Ξb(6227)−, the mass and natural width are measured to be mΞb(6227)−=6226.9±2.0±0.3±0.2  MeV/c2 and ΓΞb(6227)−=18.1±5.4±1.8  MeV/c2, where the first uncertainty is statistical, the second is systematic, and the third, on mΞb(6227)−, is due to the knowledge of the Λ0b baryon mass. Relative production rates of the Ξb(6227)−→Λ0bK− and Ξb(6227)−→Ξ0bπ− decays are also reported

Measurement of CP asymmetries in two-body B0(s)-meson decays to charged pions and kaons

The time-dependent CP asymmetries in B0→π+π− and B0s→K+K− decays are measured using a data sample of p p collisions 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. The same data sample is used to measure the time-integrated CP asymmetries in B0→K+π− and B0s→π+K− decays. The results are Cπ+π−=−0.34±0.06±0.01, Sπ+π−=−0.63±0.05±0.01, CK+K−=0.20±0.06±0.02, SK+K−=0.18±0.06±0.02, AΔΓK+K−=−0.79±0.07±0.10, AB0CP=−0.084±0.004±0.003, and AB0sCP=0.213±0.015±0.007, where the first uncertainties are statistical and the second systematic. Evidence for CP violation is found in the B0s→K+K− decay for the first time

Observation of B0s→¯D*0ϕ and search for B0→¯D0ϕ decays

The first observation of the B0s→¯D*0ϕ decay is reported, with a significance of more than seven standard deviations, from an analysis of pp collision data corresponding to an integrated luminosity of 3  fb−1, collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. The branching fraction is measured relative to that of the topologically similar decay B0→¯D0π+π− and is found to be B(B0s→¯D*0ϕ)=(3.7±0.5±0.3±0.2)×10−5, where the first uncertainty is statistical, the second systematic, and the third from the branching fraction of the B0→¯D0π+π− decay. The fraction of longitudinal polarization in this decay is measured to be fL=(73±15±4)%. The most precise determination of the branching fraction for the B0s→¯D0ϕ decay is also obtained, B(B0s→¯D0ϕ)=(3.0±0.3±0.2±0.2)×10−5. An upper limit, B(B0→¯D0ϕ)<2.0 (2.3)×10−6 at 90% (95%) confidence level is set. A constraint on the ω−ϕ mixing angle δ is set at |δ|<5.2° (5.5°) at 90% (95%) confidence level

Observation of the decay B0s→¯D0K+K−

The first observation of the B0s→¯D0K+K− decay is reported, together with the most precise branching fraction measurement of the mode B0→¯D0K+K−. The results are obtained from an analysis of pp collision data corresponding to an integrated luminosity of 3.0  fb−1. The data were collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. The branching fraction of the B0→¯D0K+K− decay is measured relative to that of the decay B0→¯D0π+π− to be B(B0→¯D0K+K−)B(B0→¯D0π+π−)=(6.9±0.4±0.3)%, where the first uncertainty is statistical and the second is systematic. The measured branching fraction of the B0s→¯D0K+K− decay mode relative to that of the corresponding B0 decay is B(B0s→¯D0K+K−)B(B0→¯D0K+K−)=(93.0±8.9±6.9)%. Using the known branching fraction of B0→¯D0π+π−, the values of B(B0→¯D0K+K−)=(6.1±0.4±0.3±0.3)×10−5 and B(B0s→¯D0K+K−)=(5.7±0.5±0.4±0.5)×10−5 are obtained, where the third uncertainties arise from the branching fraction of the decay modes B0→¯D0π+π− and B0→¯D0K+K−, respectively

Evidence for the decay B0S→K¯∗0μ+μ−

A search for the decay B0S→K¯¯∗0μ+μ−BS0→K¯∗0μ+μ− is presented using data sets corresponding to 1.0, 2.0 and 1.6 fb−1 of integrated luminosity collected during pp collisions with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, respectively. An excess is found over the background-only hypothesis with a significance of 3.4 standard deviations. The branching fraction of the B0S→K¯¯∗0μ+μ−BS0→K¯∗0μ+μ− decay is determined to be B(B0s→K¯¯∗0μ+μ−)=[2.9±1.0(stat)±0.2(syst)±0.3(norm)]×10−8B(Bs0→K¯∗0μ+μ−)=[2.9±1.0(stat)±0.2(syst)±0.3(norm)]×10−8, where the first and second uncertainties are statistical and systematic, respectively. The third uncertainty is due to limited knowledge of external parameters used to normalise the branching fraction measurement

Measurement of ϒ production in pp collisions at √ s =13 TeV

The production cross-sections of ϒ(1S), ϒ(2S) and ϒ(3S) mesons in proton-proton collisions at s√=13s=13 TeV are measured with a data sample corresponding to an integrated luminosity of 277 ± 11 pb−1 recorded by the LHCb experiment in 2015. The ϒ mesons are reconstructed in the decay mode ϒ → μ+μ−. The differential production cross-sections times the dimuon branching fractions are measured as a function of the ϒ transverse momentum, pT, and rapidity, y, over the range 0 < pT < 30 GeV/c and 2.0 < y < 4.5. The ratios of the cross-sections with respect to the LHCb measurement at s√=8s=8 TeV are also determined. The measurements are compared with theoretical predictions based on NRQCD

Measurement of the Ω0c Baryon Lifetime

We report a measurement of the lifetime of the Ω0c baryon using proton-proton collision data at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0  fb−1 collected by the LHCb experiment. The sample consists of about 1000  Ω−b→Ω0cμ−¯νμX signal decays, where the Ω0cbaryon is detected in the pK−K−π+ final state and X represents possible additional undetected particles in the decay. The Ω0c lifetime is measured to be τΩ0c=268±24±10±2  fs, where the uncertainties are statistical, systematic, and from the uncertainty in the D+ lifetime, respectively. This value is nearly four times larger than, and inconsistent with, the current world-average value

Measurement of Angular and CP Asymmetries in D0→π+π−μ+μ− and D0→K+K−μ+μ− Decays

The first measurements of the forward-backward asymmetry of the dimuon pair (AFB), the triple-product asymmetry (A2ϕ), and the charge-parity-conjugation asymmetry (ACP), in D0→π+π−μ+μ−and D0→K+K−μ+μ− decays are reported. They are performed using data from proton-proton collisions collected with the LHCb experiment from 2011 to 2016, corresponding to a total integrated luminosity of 5  fb−1. The asymmetries are measured to be AFB(D0→π+π−μ+μ−)=(3.3±3.7±0.6)%, A2ϕ(D0→π+π−μ+μ−)=(−0.6±3.7±0.6)%, ACP(D0→π+π−μ+μ−)=(4.9±3.8±0.7)%, AFB(D0→K+K−μ+μ−)=(0±11±2)%, A2ϕ(D0→K+K−μ+μ−)=(9±11±1)%, ACP(D0→K+K−μ+μ−)=(0±11±2)%, where the first uncertainty is statistical and the second systematic. The asymmetries are also measured as a function of the dimuon invariant mass. The results are consistent with the standard model predictions

Observation of the decay Λ b 0 → ψ(2S)pπ−

The Cabibbo-suppressed decay Λ b 0  → ψ(2S)pπ− is observed for the first time using a data sample collected by the LHCb experiment in proton-proton collisions corresponding to 1.0, 2.0 and 1.9 fb−1 of integrated luminosity at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The ψ(2S) mesons are reconstructed in the μ+μ− final state. The branching fraction with respect to that of the Λ b 0  → ψ(2S)pK− decay mode is measured to beB(Λ0b→ψ(2S)pπ−)B(Λ0b→ψ(2S)pK−)=(11.4±1.3±0.2)%,B(Λb0→ψ(2S)pπ−)B(Λb0→ψ(2S)pK−)=(11.4±1.3±0.2)%,where the first uncertainty is statistical and the second is systematic. The ψ(2S)p and ψ(2S)π−mass spectra are investigated and no evidence for exotic resonances is found