The ratios of branching fractions $R(D*)$ ≡ $B(\overline{B} → D*τ^-\overline{ν}_μ$)/$B$($\overline{B}$ → $D*μ^-\overline{ν}_μ$) and $R$($D$0) ≡ $B$($B$- → $D^0τ^-\overline{v}_τ$)/$B$($B$- → ...$D^0μ^-\overline{v}_μ$) are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb-1 of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode $τ^-$ → $μ^-ν_τ\overline{ν}_μ$. The measured values are $R$($D$*) = 0.281 ± 0.018 ± 0.024 and $R$($D$0) = 0.441 ± 0.060 ± 0.066, where the first uncertainty is statistical and the second is systematic. The correlation between these measurements is $ρ$ = -0.43. The results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the standard model.
The only anticipated resonant contributions to B^{+}→D^{+}D^{-}K^{+} decays are charmonium states in the D^{+}D^{-} channel. A model-independent analysis, using LHCb proton-proton collision data ...taken at center-of-mass energies of sqrts=7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb^{-1}, is carried out to test this hypothesis. The description of the data assuming that resonances only manifest in decays to the D^{+}D^{-} pair is shown to be incomplete. This constitutes evidence for a new contribution to the decay, potentially one or more new charm-strange resonances in the D^{-}K^{+} channel with masses around 2.9 GeV/c^{2}.
Results are reported from an amplitude analysis of the B+ → D+D− K+ decay. The analysis is carried out using LHCb proton-proton collision data taken at √s = 7, 8, and 13 TeV, corresponding to a total ...integrated luminosity of 9 fb−1. In order to obtain a good description of the data, it is found to be necessary to include new spin-0 and spin-1 resonances in the D−K+ channel with masses around 2.9 GeV/c2, and a new spin-0 charmonium resonance in proximity to the spin-2 χc2(3930) state.
An improved measurement of the decay $B^0_S$ → $μ^+μ^-$ and searches for the decays $B^0$ → $μ^+μ^+$ and $B^0_S$ → $μ^+μ^-γ$ are performed at the LHCb experiment using data collected in proton-proton ...collisions at $\sqrt{s}$ = 7, 8 and 13 TeV. corresponding to integrated luminosities of 1, 2 and 6 fb-1, respectively. The $B^0_S$ → $μ^+μ^-$ branching fraction and effective lifetime are measured to be $\mathscr{B}$($B^0_S$ → $μ^+μ^-$) = (3.09$^{(+0.46+0.15)}_{(-0.43-0.11)}$) x 10-9 and $τ(B^0_s →μ^+μ^-)$ = (2.07 ± 0.29 ± 0.03) ps, respectively, where the uncertainties include both statistical and systematic contributions. No significant signal for $B^0$ → $μ^+μ^-$ and $B^0_S$ → $μ^+μ^-γ$ decays is found and the upper limits $\mathscr{B}$($B^0$ → $μ^+μ^-$) < 2.6 x 10-10 and $B^0_S$ → $μ^+μ^-γ$ < 2.0 x 10-9 at 95% confidence level are determined, where the latter is limited to the range $m_{μμ}$ > 4.9 GeV/c2. Additionally, the ratio between the $B^0$ → $μ^+μ^-$ and $B^0_S$ → $μ^+μ^-$ branching fractions is measured to be $\mathscr{R}_{μ+μ-}$ < 0.095 at 95% confidence level. The results are in agreement with the Standard Model predictions.
A study of the lineshape of the χc1 ( 3872 ) state is made using a data sample corresponding to an integrated luminosity of 3 fb−1 collected in p p collisions at center-of-mass energies of 7 and ...8 TeV with the LHCb detector. Candidate χc1 ( 3872 ) and ψ ( 2S ) mesons from b -hadron decays are selected in the J / ψ π+ π− decay mode. Describing the lineshape with a Breit-Wigner function, the mass splitting between the χc1 ( 3872 ) and ψ ( 2S ) states, Δm, and the width of the χc1 ( 3872 ) state, ΓBW, are determined to be ..., where the first uncertainty is statistical and the second systematic. Using a Flatté-inspired model, the mode and full width at half maximum of the lineshape are determined to be ... . An investigation of the analytic structure of the Flatté amplitude reveals a pole structure, which is compatible with a quasibound D0 D*0 state but a quasivirtual state is still allowed at the level of 2 standard deviations. (ProQuest: ... denotes formulae omited.).
Branching fraction and effective lifetime measurements of the rare decay B_{s}^{0}→μ^{+}μ^{-} and searches for the decays B^{0}→μ^{+}μ^{-} and B_{s}^{0}→μ^{+}μ^{-}γ are reported using proton-proton ...collision data collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a luminosity of 9 fb^{-1}. The branching fraction B(B_{s}^{0}→μ^{+}μ^{-})=(3.09_{-0.43-0.11}^{+0.46+0.15})×10^{-9} and the effective lifetime τ(B_{s}^{0}→μ^{+}μ^{-})=2.07±0.29±0.03 ps are measured, where the first uncertainty is statistical and the second systematic. No significant signal for B^{0}→μ^{+}μ^{-} and B_{s}^{0}→μ^{+}μ^{-}γ decays is found and upper limits B(B^{0}→μ^{+}μ^{-})<2.6×10^{-10} and B(B_{s}^{0}→μ^{+}μ^{-}γ)<2.0×10^{-9} at the 95% C.L. are determined, where the latter is limited to the range m_{μμ}>4.9 GeV/c^{2}. The results are in agreement with the standard model expectations.
Observation of a new Ξb0 state Ackernley, T.; Alessio, F.; Amato, S. ...
Physical review. D,
01/2021, Letnik:
103, Številka:
1
Journal Article
Recenzirano
Using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 8.5 fb-1, the observation of a new excited $Ξ^{0}_{b}$ resonance decaying to ...the $Ξ^{-}_{b}$$π$+ final state is presented. The state, referred to as $Ξ_b$(6227)0, has a measured mass and natural width of $m$$(Ξ_b$(6227)0) = $6227.1^{+1.4}_{-1.5}$ ± 0.5 MeV and Γ($Ξ_b$(6227)0) = $18.6^{+5.0}_{-4.1}$ ± 1.4 MeV, where the uncertainties are statistical and systematic. The production rate of the $Ξ_b$(6227)0 state relative to that of the $Ξ^{-}_{b}$ baryon in the kinematic region 2 < $η$ < 5 and pT < 30 GeV is measured to be $\frac{f_{Ξ_b}(6227)^0}{f_{Ξ_b^-}}$ $\mathscr{B}$($Ξ_b$(6227)0 → $Ξ^-_b$$π^+$) = 0.045 ± 0.008 ± 0.004; where $\mathscr{B}$($Ξ_b$(6227)0 → $Ξ^-_b$$π^+$) is the branching fraction of the decay, and $f$$Ξ$$_{b}$$_{(6227)^0}$ and $f$$Ξ$$_{b}^-$ represent fragmentation fractions. Improved measurements of the mass and natural width of the previously observed $Ξ_b$$(6227)^-$ state, along with the mass of the $Ξ^{-}_{b}$ baryon, are also reported. Both measurements are significantly more precise than, and consistent with, previously reported values.
The fraction of $χ$c1 and $χ$c2 decays in the prompt $J/ψ$ yield, $F$χc→J/ψ = σχc→J/ψ/σJ/ψ, is measured by the LHCb detector in $p$ Pb collisions at $\sqrt{^sNN}$ = 8.16 $TeV$. The study covers the ...forward (1.5 < y* < 4.0) and backward (-5.0 < y* < - 2.5) rapidity regions, where y* is the $J/ψ$ rapidity in the nucleon-nucleon center-of-mass system. Forward and backward rapidity samples correspond to integrated luminosities of 13.6 ± 0.3 and 20.8 ± 0.5 nb-1, respectively. The result is presented as a function of the $J/ψ$ transverse momentum $p$T,J/ψ in the range 1 < $p$T,J/ψ < 20 $GeV$ /c. The $F$χc→J/ψ fraction at forward rapidity is compatible with the LHCb measurement performed in $pp$ collisions at $\sqrt{s}$ = 7 $TeV$, whereas the result at backward rapidity is $2.4σ$ larger than in the forward region for 1 < $p$T,J/ψ < 3 $GeV$ /c. The increase of $F$χc→J/ψ at low pT,J/ψ at backward rapidity is compatible with the suppression of the $ψ$ ($2S$) contribution to the prompt $J/ψ$ yield. The lack of in-medium dissociation of $χ$c states observed in this study sets an upper limit of 180 MeV on the free energy available in these $pPb$ collisions to dissociate or inhibit charmonium state formation.
The production rate of $B^{0}_{s}$ mesons relative to $B^0$ mesons is measured by the LHCb experiment in $pp$ collisions at a center-of-mass energy $\sqrt{s}$ = 13 TeV over the forward rapidity ...interval 2 < $y$ < 4.5 as a function of the charged particle multiplicity measured in the event. Evidence at the 3.4$σ$ level is found for an increase of the ratio of $B^{0}_{s}$ to $B^0$ cross sections with multiplicity at transverse momenta below 6 GeV /$c$, with no significant multiplicity dependence at higher transverse momentum. Comparison with data from $e^+$ $e^–$ collisions implies that the density of the hadronic medium may affect the production rates of $B$ mesons. This is qualitatively consistent with the emergence of quark coalescence as an additional hadronization mechanism in high-multiplicity collisions.