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Register a new userMeasurement of $y_{CP}$ in $D^0-overline{D}^0$ oscillation using quantum correlations in $e^+e^-to D^0overline{D}^0$ at $sqrt{s}$ = 3.773,GeV
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We report a measurement of the parameter $y_{CP}$ in $ensuremath{D^0}xspace-ensuremath{overline{D}^{0}}xspace$ oscillations performed by taking advantage of quantum coherence between pairs of $ensuremath{D^0}xspace ensuremath{overline{D}^{0}}xspace$ mesons produced in $e^+e^-$ annihilations near threshold. In this work, doubly-tagged $ensuremath{D^0}xspace ensuremath{overline{D}^{0}}xspace$ events, where one $D$ decays to a $CP$ eigenstate and the other $D$ decays in a semileptonic mode, are reconstructed using a data sample of 2.92,fb$^{-1}$ collected with the BESIII detector at the center-of-mass energy of $sqrt{s}$ = 3.773,GeV. We obtain $y_{CP} = (-2.0pm1.3pm0.7)%$, where the first uncertainty is statistical and the second is systematic. This result is compatible with the current world average.
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We observe $D^0-bar{D}^0$ mixing in the decay $D^0rightarrow K^+pi^-$ using a data sample of integrated luminosity 976 fb$^{-1}$ collected with the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. We measure the mixing parameters ${x}^2 = (0.09pm0.22)times 10^{-3}$ and $y = (4.6pm3.4)times 10^{-3}$ and the ratio of doubly Cabibbo-suppressed to Cabibbo-favored decay rates $R_D = (3.53pm0.13)times 10^{-3}$, where the uncertainties are statistical and systematic combined. Our measurement excludes the no-mixing hypothesis at the 5.1 standard deviation level.
Charm physics has played all along a central role in particle physics, however the level of attention on it has tremendously increased in the last years because of the observation of fast $D^0-bar{D}^0$ flavour oscillations and because of very recent observed hints of CP violation. While in the past these would have been unambiguously interpreted as signs of New Physics, the revisitation of theoretical expectations, prompted by the latest experimental measurements, makes the picture not clear. This brief review covers the current status of CP-violating measurements in the $D^0-bar{D}^0$ system, both on the experimental and theoretical side.
Using 1.8 million DDbar pairs and a neutrino reconstruction technique, we have studied the decays D^0 -> K^- e^+ nu_e, D^0 -> pi^- e^+ nu_e, D^+ -> Kbar^0 e^+ nu_e, and D^+ -> pi^0 e^+ nu_e. We find B(D^0 -> pi^- e^+ nu_e) = 0.299(11)(9)%, B(D^+ -> pi^0 e^+ nu_e) = 0.373(22)(13)%, B(D^0 -> K^- e^+ nu_e) = 3.56(3)(9)%, and B(D^+ -> Kbar^0 e^+ nu_e) = 8.53(13)(23)%. In addition, form factors are studied through fits to the partial branching fractions obtained in five q^2 ranges. By combining our results with recent unquenched lattice calculations, we obtain |Vcd| = 0.217(9)(4)(23) and |Vcs| = 1.015(10)(11)(106).
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.
Using a sample of 1.8 million DDbar meson pairs collected at the psi(3770) with the CLEO-c detector, we study the semileptonic decays D^0 -> pi^- e^+ nu_e, D^+ -> pi^0 e^+ u_e, D^0 -> K^- e^+ u_e, and D^+ -> Kbar^0 e^+ nu_e. For the total branching fractions we find B(D^0 -> pi^- e^+ u_e) = 0.299(11)(9)%, B(D^+ -> pi^0 e^+ u_e) = 0.373(22)(13)%, B(D^0 -> K^- e^+ nu_e) = 3.56(3)(9)%, and B(D^+ -> Kbar^0 e^+ nu_e) = 8.53(13)(23)%, where the first error is statistical and the second systematic. In addition, form factors are studied through fits to the partial branching fractions obtained in five q^2 ranges. By combining our results with recent unquenched lattice calculations, we obtain |Vcd| = 0.217(9)(4)(23) and |Vcs| = 1.015(10)(11)(106), where the final error is theoretical.
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