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Register a new userImplications of $D^0-overline{D^0}$ on the rare top quark decays $tto ugamma$ and $tto ug$
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J. I. Aranda
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The recently observed mass difference of the $D^0-overline{D^0}$ mixing is used to predict the branching ratios of the rare top quark decays $tto ugamma$ and $tto ug$ in a model independent way using the effective Lagrangian approach. It is found that $Br(tto ugamma)<4times 10^{-4}$ and $Br(tto ug)<2times 10^{-3}$, which still may be within reach of the LHC collider.
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The first observation of the $B_s^0 to overline{D}^{*0} phi$ 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 centre-of-mass energies of $7$ and $8$ TeV. The branching fraction is measured relative to that of the topologically similar decay $B^0 to overline{D}^0 pi^+pi^-$ and is found to be $mathcal{B}(B_s^0 to overline{D}^{*0} phi) = (3.7 pm 0.5 pm 0.3 pm 0.2) times 10^{-5}$, where the first uncertainty is statistical, the second systematic, and the third from the branching fraction of the $B^0 to overline{D}^0 pi^+pi^-$ decay. The fraction of longitudinal polarisation in this decay is measured to be ${f_{rm L} =(73 pm 15 pm 3)%}$. The most precise determination of the branching fraction for the $B_s^0 to overline{D}^{0} phi$ decay is also obtained, $mathcal{B}(B_s^0 to overline{D}^{0} phi) = (3.0 pm 0.3 pm 0.2 pm 0.2) times 10^{-5}$. An upper limit, $mathcal{B}(B^0 to overline{D}^{0} phi) < 2.0 (2.2) times 10^{-6}$ at $90%$ (95%) confidence level is set. A constraint on the $omega-phi$ mixing angle $delta$ is set at $|delta| < 5.2^circ~ (5.5^circ)$ at $90%$ ($95%$) confidence level.
The flavor-changing top-quark decay $tto c h$, where $h$ is the lightest CP-even Higgs boson in the minimal supersymmetric standard model, is examined in the R-parity-violating supersymmetric model. Within the existing bounds on the relevant R-parity-violating couplings, the branching fraction for $tto c h$ can be as large as about $10^{-5}$ in some part of the parameter space.
We present an observation and rate measurement of the decay D0 -> K+pi-pi0 produced in 9/fb of e+e- collisions near the Upsilon(4S) resonance. The signal is inconsistent with an upward fluctuation of the background by 4.9 standard deviations. We measured the rate of D0 -> K+pi-pi0 normalized to the rate of D0bar -> K+pi-pi0 to be 0.0043 +0.0011 -0.0010 (stat) +/- 0.0007 (syst). This decay can be produced by doubly-Cabibbo-suppressed decays or by the D0 evolving into a D0bar through mixing, followed by a Cabibbo-favored decay to K+pi-pi0. We also found the CP asymmetry A=(8 +25 -22)% to be consistent with zero.
The decay of the narrow resonance $overline{B}{}_{s2}^{*0}!rightarrow B^- K^+$ can be used to determine the $B^-$ momentum in partially reconstructed decays without any assumptions on the decay products of the $B^-$ meson. This technique is employed for the first time to distinguish contributions from $D^0$, $D^{*0}$, and higher-mass charmed states ($D^{**0}$) in semileptonic $B^-$ decays by using the missing-mass distribution. The measurement is performed using a data sample corresponding to an integrated luminosity of 3.0 fb${}^{-1}$ collected with the LHCb detector in $pp$ collisions at center-of-mass energies of 7 and 8 TeV. The resulting branching fractions relative to the inclusive $B^- !rightarrow D^0 X mu^- overline{ u}_mu$ are $f_{D^0} = mathcal{B}( B^- rightarrow D^0mu^-overline{ u}_mu )/mathcal{B}( B^- rightarrow D^0 X mu^- overline{ u}_mu ) = 0.25 pm 0.06$, $f_{D^{**0}} = mathcal{B}( B^- rightarrow ( D^{**0} rightarrow D^0 X)mu^-overline{ u}_mu )/mathcal{B}( B^- rightarrow D^0 X mu^- overline{ u}_mu ) = 0.21 pm 0.07$, with $f_{D^{*0}} = 1 - f_{D^0} - f_{D^{**0}}$ making up the remainder.
We report measurements of charm-mixing parameters based on the decay-time-dependent ratio of $D^0to K^+pi^-$ to $D^0to K^-pi^+$ rates. The analysis uses a data sample of proton-proton collisions corresponding to an integrated luminosity of $5.0$ fb$^{-1}$ recorded by the LHCb experiment from 2011 through 2016. Assuming charge-parity (CP) symmetry, the mixing parameters are determined to be $x^2=(3.9 pm 2.7) times10^{-5}$, $y=(5.28 pm 0.52) times 10^{-3}$, and $R_D=(3.454 pm 0.031)times10^{-3}$. Without this assumption, the measurement is performed separately for $D^0$ and $overline{D}{}^0$ mesons, yielding a direct CP-violating asymmetry $A_D =(-0.1pm9.1)times10^{-3}$, and magnitude of the ratio of mixing parameters $1.00< |q/p| <1.35$ at the $68.3%$ confidence level. All results include statistical and systematic uncertainties and improve significantly upon previous single-measurement determinations. No evidence for CP violation in charm mixing is observed.
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