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Register a new userThe hidden strangeness mechanism in Ds^+ -> omega pi^+ and Ds^+ -> rho^0 pi^+ decays
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Svjetlana Fajfer
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We study possible contributions to the Ds^+ -> omega pi^+ and Ds^+ -> rho^0 pi^+ decay amplitudes. The Ds^+ -> omega pi^+ decay amplitude vanishes when the naive factorization is used, while the Ds^+ -> rho^0 pi^+ decay amplitude arises due to the annihilation contribution. We find that amplitudes for both decays might be a result of the internal K, K^* exchange. The Ds^+ -> omega pi^+ amplitude might obtain additional contribution from Ds^+ -> rho^0 eta (eta) re-scattering. The low experimental bound on the Ds^+ -> rho^0 pi^+ rate can be understood as a result of combination of the pi(1300) pole dominated annihilation contribution and the K,K^* internal exchanges. The calculated branching fractions for Ds^+ -> omega pi^+ and Ds^+ -> rho^0 pi^+ are in agreement with the current experimental results.
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A search for CP violation in D+ -> phi pi+ decays is performed using data collected in 2011 by the LHCb experiment corresponding to an integrated luminosity of 1.0 fb^{-1} at a centre of mass energy of 7 TeV. The CP-violating asymmetry is measured to be (-0.04+/-0.14+/-0.14)% for candidates with K-K+ mass within 20 MeV/c^{2} of the phi meson mass. A search for a CP-violating asymmetry that varies across the phi mass region of the D+ -> K-K+pi+ Dalitz plot is also performed, and no evidence for CP violation is found. In addition, the CP asymmetry in the Ds+ -> Ks pi+ decay is measured to be (0.61+/-0.83+/-0.14)%.
Proton-proton collision data recorded in 2011 and 2012 by the lhcb experiment, co-rres-pon-ding to an integrated luminosity of 3.0invfb, are a-na-lysed to search for the charmless ${B^0 to rho^0 rho^0}$ decay. More than 600 ${B^0 to (pi^+pi^-)(pi^+pi^-)}$ signal decays are selected and used to perform an amplitude analysis from which the ${B^0 to rho^0 rho^0}$ decay is observed for the first time with 7.1 standard deviations significance. The fraction of ${B^0 to rho^0 rho^0}$ decays yielding a longitudinally polarised final state is measured to be $fL = 0.745^{+0.048}_{-0.058} ({rm stat}) pm 0.034 ({rm syst})$. The ${B^0 to rho^0 rho^0}$ branching fraction, using the ${B^0 to phi K^*(892)^{0}}$ decay as reference, is also reported as ${BF(B^0 to rho^0 rho^0) = (0.94 pm 0.17 ({rm stat}) pm 0.09 ({rm syst}) pm 0.06 ({rm BF})) times 10^{-6}}$.
We present a detailed study of direct CP violation and branching ratios in the channels $B^{0,pm} to pi^{+}pi^{-} V^{0,pm}$, where $V$ is a vector meson ($K^{* 0,pm}$ or $rho^{pm}$). Emphasis is placed upon the important role played by ${{rho}^{0}}-{omega}$ mixing effects in the estimation of the CP-violating asymmetry parameter, $a_{cp}$, associated with the difference of $B$ and $bar B$ decay amplitudes. A thorough study of the helicity amplitudes is presented as a function of the pion-pion invariant mass. All of the calculations and simulations considered correspond to channels which will be analyzed at the LHCb facility.
Simulation methods for the decays $ B to {pi}^+ {pi}^- V$, where $V$ is a $1^{--}$ vector-meson, are presented in detail. Emphasis is put on the use of the helicity formalism and the use of effective Lagrangians. We show the importance of ${{rho}^{0}}-{omega}$ mixing in enhancing the direct $CP$ violation (DCPV) when the pion-pion invariant mass is near the mass of the $omega$.
We study the effect of the sigma(600) and a_1(1260) resonances in the rho^0 -> pi^+ pi^- gamma decay, within the meson dominance model. Major effects are driven by the mass and width parameters of the sigma(600), and the usually neglected contribution of the a_1(1260), although small by itself, may become sizable through its interference with pion bremsstrahlung, and the proper relative sign can favor the central value of the experimental branching ratio. We present a procedure, using the gauge invariant structure of the resonant amplitudes, to kinematically enhance the resonant effects in the angular and energy distribution of the photon. We also elaborate on the coupling constants involved.
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