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Register a new userFirst observations of $bar{B}_s^0to D^+D^-$, $D_s^+D^-$ and $D^0bar{D}^0$ decays
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First observations and measurements of the branching fractions of the $bar{B}_s^0to D^+D^-$, $bar{B}_s^0to D_s^+D^-$ and $bar{B}_s^0to D^0bar{D}^0$ decays are presented using 1.0 fb$^{-1}$ of data collected by the LHCb experiment. These branching fractions are normalized to those of $bar{B}^0to D^+D^-$, $B^0to D_s^+D^-$ and $B^-to D^0D_s^-$, respectively. An excess of events consistent with the decay $bar{B}^0to D^0bar{D}^0$ is also seen, and its branching fraction is measured relative to that of $B^-to D^0D_s^-$. Improved measurements of the branching fractions ${cal{B}}(bar{B}_s^0to D_s^+D_s^-)$ and ${cal{B}}(B^-to D^0D_s^-)$ are reported, each relative to ${cal{B}}(B^0to D_s^+D^-)$. The ratios of branching fractions are {-0.2in} {center} {align*} {{cal{B}}(bar{B}_s^0to D^+D^-)over {cal{B}}(bar{B}^0to D^+D^-)} &= 1.08pm 0.20pm0.10, {{cal{B}}(bar{B}_s^0to D_s^+D^-)over {cal{B}}(B^0to D_s^+D^-)} &= 0.050pm 0.008pm0.004, {{cal{B}}(bar{B}_s^0to D^0bar{D}^0)over {cal{B}}(B^-to D^0D_s^-)} &= 0.019pm 0.003pm0.003, {{cal{B}}(bar{B}^0to D^0bar{D}^0)over {cal{B}}(B^-to D^0D_s^-)} &= 0.0014pm 0.0006pm0.0002,{{cal{B}}(bar{B}_s^0to D_s^+D_s^-)over {cal{B}}(B^0to D_s^+D^-)} &= 0.56pm 0.03pm0.04, {{cal{B}}(B^-to D^0D_s^-)over {cal{B}}(B^0to D_s^+D^-)} &= 1.22pm 0.02pm0.07, {align*} {center} oindent where the uncertainties are statistical and systematic, respectively.
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The first measurement of the effective lifetime of the $bar{B}_s^0$ meson in the decay $bar{B}_s^0to D_s^-D_s^+$ is reported using a proton-proton collision dataset, corresponding to an integrated luminosity of 3 fb$^{-1}$, collected by the LHCb experiment. The measured value of the $bar{B}_s^0to D_s^-D_s^+$ effective lifetime is $1.379pm0.026pm0.017$ ps, where the uncertainties are statistical and systematic, respectively. This lifetime translates into a measurement of the decay width of the light $bar{B}_s^0$ mass eigenstate of Gamma_L$=0.725pm0.014pm0.009$ ps$^{-1}$. The $bar{B}_s^0$ lifetime is also measured using the flavor-specific $bar{B}_s^0to D^-D_s^+$ decay to be $1.52pm0.15pm0.01 {rm ps}$.
The $CP$ asymmetry in $B^-to D_s^-D^0$ and $B^-to D^-D^0$ decays is measured using LHCb data corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. The results are $A^{CP}(B^-to D_s^-D^0)=(-0.4pm 0.5pm 0.5)%$ and $A^{CP}(B^-to D^-D^0)=( 2.3pm 2.7pm 0.4)%$, where the first uncertainties are statistical and the second systematic. This is the first measurement of $A^{CP}(B^-to D_s^-D^0)$ and the most precise determination of $A^{CP}(B^-to D^-D^0)$. Neither result shows evidence of $CP$ violation.
A measurement of four branching-fraction ratios for three-body decays of $B$ mesons involving two open-charm hadrons in the final state is presented. Run 1 and Run 2 $pp$ collision data are used, recorded by the LHCb experiment at centre-of-mass energies $7$, $8$, and $13$ TeV and corresponding to an integrated luminosity of $9$ fb$^{-1}$. The measured branching-fraction ratios are [ begin{eqnarray} frac{mathcal{B} (B^+to D^{*+}D^-K^+)}{mathcal{B} (B^+to kern 0.2emoverline{kern -0.2em D}{}^0 D^0 K^+)} &=& 0.517 pm 0.015 pm 0.013 pm 0.011 , frac{mathcal{B} (B^+to D^{*-}D^+K^+)}{mathcal{B} (B^+to kern 0.2emoverline{kern -0.2em D}{}^0 D^0 K^+)} &=& 0.577 pm 0.016 pm 0.013 pm 0.013 , frac{mathcal{B} (B^0to D^{*-}D^0K^+)}{mathcal{B} (B^0to D^- D^0 K^+)} &=& 1.754 pm 0.028 pm 0.016 pm 0.035 , frac{mathcal{B} (B^+to D^{*+}D^-K^+)}{mathcal{B} (B^+to D^{*-}D^+K^+)} &=& 0.907 pm 0.033 pm 0.014 ,end{eqnarray} ] where the first of the uncertainties is statistical, the second systematic, and the third is due to the uncertainties on the $D$-meson branching fractions. These are the most accurate measurements of these ratios to date.
Using $pp$ collision data corresponding to an integrated luminosity of $5.4,{rm fb}^{-1}$ collected with the LHCb detector at a center-of-mass energy of $13,{rm TeV}$, the $B^0to D^-D^+K^+pi^-$ decay is studied. A new excited $D_s^+$ meson is observed decaying into the $D^+K^+pi^-$ 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 $m_R=2591pm6pm7,{rm MeV}$, $Gamma_R=89pm16pm12,{rm MeV}$ and $J^P=0^-$, 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 $D_{s0}(2590)^+$, is a strong candidate to be the $D_s(2^1{S}_0)^+$ state, the radial excitation of the pseudoscalar ground-state $D_s^+$ meson.
Charm meson oscillations are observed in a time-dependent analysis of the ratio of $D^0to K^+pi^-pi^+pi^-$ to $D^0to K^-pi^+pi^-pi^+$ decay rates, using data corresponding to an integrated luminosity of $3.0,{rm fb}^{-1}$ recorded by the LHCb experiment. The measurements presented are sensitive to the phase-space averaged ratio of doubly Cabibbo-suppressed to Cabibbo-favoured amplitudes $r_{D}^{K3pi}$ and the product of the coherence factor $R_{D}^{K3pi}$ and a charm mixing parameter $y^{}_{K3pi}$. The constraints measured are $r_{D}^{K3pi}=(5.67 pm 0.12)times10^{-2}$, which is the most precise determination to date, and $R_{D}^{K3pi} cdot y^{}_{K3pi} = (0.3 pm 1.8)times 10^{-3}$, which provides useful input for determinations of the CP-violating phase $gamma$ in $B^pm to D K^pm, D to K^mppi^pmpi^mppi^pm$ decays. The analysis also gives the most precise measurement of the $D^0to K^+pi^-pi^+pi^-$ branching fraction, and the first observation of $D^0-bar D^0$ oscillations in this decay mode, with a significance of 8.2 standard deviations.
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