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Register a new userAmplitude analysis of $D_{s}^{+} rightarrow pi^{+}pi^{0}eta$ and first observation of the pure $W$-annihilation decays $D_{s}^{+} rightarrow a_{0}(980)^{+}pi^{0}$ and $D_{s}^{+} rightarrow a_{0}(980)^{0}pi^{+}$
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We present the first amplitude analysis of the decay $D^{+}_{s} rightarrow pi^{+}pi^{0}eta$. We use an $e^{+}e^{-}$ collision data sample corresponding to an integrated luminosity of 3.19~${mbox{,fb}^{-1}}$ collected with the BESIII detector at a center-of-mass energy of $4.178$ GeV. We observe for the first time the pure $W$-annihilation decays $D_{s}^{+} rightarrow a_{0}(980)^{+}pi^{0}$ and $D_{s}^{+} rightarrow a_{0}(980)^{0}pi^{+}$. We measure the absolute branching fractions $mathcal{B}(D_{s}^{+} rightarrow a_{0}(980)^{+(0)}pi^{0^(+)}, a_{0}(980)^{+(0)} to pi^{+(0)}eta) = (1.46pm0.15_{{rm stat.}}pm0.23_{{rm sys.}})$%, which is larger than the branching fractions of other measured pure $W$-annihilation decays by at least one order of magnitude. In addition, we measure the branching fraction of $D_{s}^{+} rightarrow pi^{+}pi^{0}eta$ with significantly improved precision.
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Searches for $CP$ violation in the two-body decays $D_{(s)}^{+}rightarrow h^{+}pi^{0}$ and $D_{(s)}^{+} rightarrow h^{+}eta$ (where $h^{+}$ denotes a $pi^{+}$ 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 $pi^{0}$ and $eta$ mesons are reconstructed using the $e^{+}e^{-}gamma$ final state, which can proceed as three-body decays $pi^{0}rightarrow e^{+}e^{-}gamma$ and $eta rightarrow e^{+}e^{-}gamma$, or via the two-body decays $pi^{0}rightarrow gammagamma$ and $etarightarrowgammagamma$ followed by a photon conversion. The measurements are made relative to the control modes $D_{(s)}^{+}rightarrow K_{S}^{0} h^{+}$ to cancel the production and detection asymmetries. The $CP$ asymmetries are measured to be begin{align} mathcal{A}_{CP}(D^{+}rightarrow pi^{+}pi^{0}) &= (-1.3 pm 0.9 pm 0.6 )%, end{align} begin{align} mathcal{A}_{CP}(D^{+}rightarrow K^{+}pi^{0}) &= (-3.2 pm 4.7 pm 2.1 )%, end{align} begin{align} mathcal{A}_{CP}(D^{+}rightarrow pi^{+}eta) &= (-0.2 pm 0.8 pm 0.4 )%, end{align} begin{align} mathcal{A}_{CP}(D^{+}rightarrow K^{+}eta) &= (-6 pm 10 pm 4 )%, end{align} begin{align} mathcal{A}_{CP}(D_{s}^{+}rightarrow K^{+}pi^{0}) &= (-0.8 pm 3.9 pm 1.2 )%, end{align} begin{align} mathcal{A}_{CP}(D_{s}^{+}rightarrow pi^{+}eta) &= (0.8 pm 0.7 pm 0.5 )%, end{align} begin{align} mathcal{A}_{CP}(D_{s}^{+}rightarrow K^{+}eta) &= (0.9 pm 3.7 pm 1.1 )%, end{align} where the first uncertainties are statistical and the second systematic. These results are consistent with no $CP$ violation and mostly constitute the most precise measurements of $mathcal{A}_{CP}$ in these decay modes to date.
The decay $D^{+}_{s}rightarrow pi^{+}pi^{+}pi^{-}eta$ is observed for the first time, using $e^+e^-$ collision data corresponding to an integrated luminosity of 6.32 fb$^{-1}$, collected by the BESIII detector at center-of-mass energies between 4.178 and 4.226 GeV. The absolute branching fraction for this decay is measured to be $mathcal{B}(D^+_s to pi^+ pi^+ pi^- eta) = (3.12pm0.13_{rm stat.}pm0.09_{rm syst.})$%. The first amplitude analysis of this decay reveals the sub-structures in $D^{+}_{s}rightarrow pi^{+}pi^{+}pi^{-}eta$ and determines the relative fractions and the phases among these sub-structures. The dominant intermediate process is $D^{+}_{s}rightarrow a_1(1260)^+ eta, a_1(1260)^+ rightarrow rho(770)^0pi^+$ with a branching fraction of $(1.73 pm 0.14_{rm stat.} pm 0.08_{rm syst.})$%. We also observe the W-annihilation process $D^{+}_{s}rightarrow a_0(980)^+rho(770)^0$, $a_0(980)^+ to pi^+ eta$ with a branching fraction of $(0.21pm0.08_{rm stat.}pm0.05_{rm syst.})$%, which is larger than the branching fractions of other measured pure W-annihilation decays by one order of magnitude.
The decay $D^{+} rightarrow K_{S}^{0} pi^{+} pi^{+} pi^{-}$ is studied with an amplitude analysis using a data set of 2.93${mbox{,fb}^{-1}}$ of $e^+e^+$ collisions at the $psi(3770)$ peak accumulated by the BESIII detector. Intermediate states and non-resonant components, and their relative fractions and phases have been determined. The significant amplitudes, which contribute to the model that best fits the data, are composed of five quasi-two-body decays $ K_{S}^{0} a_{1}(1260)^{+}$, $ bar{K}_{1}(1270)^{0} pi^{+}$ $ bar{K}_{1}(1400)^{0} pi^{+}$, $ bar{K}_{1}(1650)^{0} pi^{+}$, and $ bar{K}(1460)^{0} pi^{+}$, a three-body decays $K_{S}^{0}pi^{+}rho^{0}$, as well as a non-resonant component $ K_{S}^{0}pi^{+}pi^{+}pi^{-}$. The dominant amplitude is $ K_{S}^{0} a_{1}(1260)^{+}$, with a fit fraction of $(40.3pm2.1pm2.9)%$, where the first and second uncertainties are statistical and systematic, respectively.
Based on a sample of $1.31 times 10^9$ $J/psi$ events collected with the BESIII detector, an amplitude analysis of the isospin-violating decays $eta^prime rightarrow pi^+pi^-pi^0$ and $eta^prime rightarrow pi^0pi^0pi^0$ is performed. A significant $P$-wave contribution from $eta^prime rightarrow rho^{pm} pi^{mp}$ is observed for the first time in $eta^prime rightarrow pi^+pi^-pi^0$. The branching fraction is determined to be ${mathcal B}(eta^prime rightarrow rho^{pm}pi^{mp})=(7.44pm0.60pm1.26pm1.84)times 10^{-4}$, where the first uncertainty is statistical, the second systematic, and the third model dependent. In addition to the nonresonant $S$-wave component, there is a significant $sigma$ meson component. The branching fractions of the combined $S$-wave components are determined to be ${mathcal B}(eta^prime rightarrow pi^+pi^-pi^0)_S=(37.63pm0.77pm2.22pm4.48)times 10^{-4}$ and ${mathcal B}(eta^prime rightarrow pi^0pi^0pi^0)=(35.22pm0.82pm2.54)times 10^{-4}$, respectively. The latter one is consistent with previous BESIII measurements.
Measurements of the effective lifetimes in the $B_{s}^{0} rightarrow K^{+}K^{-}$, $B^{0} rightarrow K^{+}pi^{-}$ and $B_{s}^{0} rightarrow pi^{+}K^{-}$ decays are presented using $1.0~mathrm{fb^{-1}}$ of $pp$ collision data collected at a centre-of-mass energy of 7 TeV by the LHCb experiment. The analysis uses a data-driven approach to correct for the decay time acceptance. The measured effective lifetimes are $tau_{B_{s}^{0} rightarrow K^{+}K^{-}}$ = $1.407~pm~0.016~pm~0.007~mathrm{ps}$, $tau_{B^{0} rightarrow K^{+}pi^{-}}$ = $1.524~pm~0.011~pm~0.004~mathrm{ps}$, $tau_{B_{s}^{0} rightarrow pi^{+}K^{-}}$ = $1.60~pm~0.06~pm~0.01~mathrm{ps}$. This is the most precise determination to date of the effective lifetime in the $B_{s}^{0} rightarrow K^{+}K^{-}$ decay and provides constraints on contributions from physics beyond the Standard Model to the $B_{s}^{0}$ mixing phase and the width difference $DeltaGamma_{s}$.
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