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Register a new userRecent developments on direct $CP$ violation in the kaon system and connection to $K to pi u bar{ u}$ measurements
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Teppei Kitahara
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The first lattice result from the RBC and UKQCD Collaborations and improved perturbative calculations of $varepsilon^{prime}_K / varepsilon_K$ have implied that the Standard-Model (SM) expectation deviates from measured values at the $2.8,sigma$ level. Since $varepsilon^{prime}_K / varepsilon_K$ comes from $CP$-violating FCNC and is significantly suppressed in the SM, the discrepancy can be explained easily in several new physics (NP) models. In this contribution, it is shown that correlations with the other rare decays, especially $Kto pi u overline{ u}$ and $K_S to mu^+ mu^-$, are crucial for discrimination of the NP models. These channels can be probed precisely in the future by the NA62 and KOTO experiments for $Kto pi u overline{ u}$ and LHCb experiment for $K_S to mu^+ mu^-$.
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The NA62 experiment will begin taking data in 2015. Its primary purpose is a 10% measurement of the branching ratio of the ultrarare kaon decay $K^+ to pi^+ u bar{ u }$, using the decay in flight of kaons in an unseparated beam with momentum 75 GeV/c.The detector and analysis technique are described here.
We have investigated the effects of unparticles in decays $B to l u$. It is found that the direct CP violation in the decays, which is zero in SM, can show up due to the CP conserving phase intrinsic in unparticle physics. For $l=tau$, the direct CP asymmetry can reach 30% for the scalar unparticle contribution, and 100% for the longitudinal vector unparticle contribution under the constraints of ${rm Br}(Btotau u)$ and $ u e$ elastic scattering. If both unparticle-lepton coupling universality and unparticle-quark coupling universality are assumed the constraint from $Br(pito mu u)$ leads that the direct CP violation in $Bto l u$ can only reach at most 8% and 1% for scalar and vector unparticle contributions respectively if $d_{cal U} < 2$. If the direct CP violation is observed in the future it would give strong evidence for the existence of unparticle stuff.
We apply QCD factorization to the quasi two-body B ->(K pi) pi decays where the (K pi)-pair effective mass is limited to 1.8 GeV. Our strong interaction phases constrained by theory and pi-K experimental data yield useful information for studies of CP violation
In order to explain the observed anomalies in the measurements of $R_{D^{(*)}}$ and $R_{J/psi}$, a variety of new-physics (NP) models that contribute to $bto ctau^-{bar u}$ have been proposed. In this paper, we show how CP-violating observables can be used to distinguish these NP models. Because ${vec p}_tau$ cannot be measured (the decay products of the $tau$ include the undetected $ u_tau$), obtaining the angular distribution of ${bar B}^0to D^{*+}tau^{-}{bar u}_tau$ is problematic. Instead, we focus here on ${bar B}^0to D^{*+}(to D^0 pi^+)mu^- {bar u}_mu$. This process may also receive contributions from the same NP, and LHCb intends to measure the CP-violating angular asymmetries in this decay. There are two classes of NP models that contribute to $bto cmu^-{bar u}_mu$. These involve (i) a $W$ (two types) or (ii) a leptoquark (LQ) (six types). The most popular NP models predict no CP-violating effects, so the measurement of nonzero CP-violating symmetries would rule them out. Furthermore these measurements allow one to distinguish the $W$ and LQ models, and to differentiate among several LQ models.
In this paper we investigate CP violation in charged decays of $D$ meson. Particularly, we study the direct CP asymmetry of the Cabibbo favored non-leptonic $D^+ rightarrow bar K^0 pi^+$ and the doubly Cabibbo-suppressed decay mode $D^+ rightarrow K^0 pi^+$ within standard model, two Higgs doublet model with generic Yukawa structure and left right symmetric models. In the standard model, we first derive the contributions from box and di-penguin diagrams contributing to their amplitudes which are relevant to the generation of the weak phases essential for non-vanishing direct CP violation. Then, we show that these phases are so tiny leading to a direct CP asymmetry of order $10^{-11}$ in both decay modes. Regarding the two Higgs doublet model with generic Yukawa structure and after taking into account all constraints on the parameter space of the model, we show that the enhanced direct CP asymmetries can be 6 and 7 orders of magnitudes larger than the standard model prediction for $D^+ rightarrow bar K^0 pi^+$ and $D^+ rightarrow K^0 pi^+$ respectively. Finally, within left right symmetric models, we find that sizable direct CP asymmetry of ${mathcal O } (10^{-3})$ can be obtained for the decay mode $D^+ rightarrow bar K^0 pi^+$ after respecting all relevant constraints.
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