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Register a new userDirect CP violation of $B to l u$ in unparticle physics
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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.
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According to the standard model, the Cabibbo-favored (CF) decays are $CP$ conserve at tree level. Observation of any finite $CP$ asymmetry can be received as a signal of new physics. In CF charm meson decays, $ D^0 rightarrow K^- pi^+ $ and $ D^+ rightarrow K_s^0 pi^+ $, the following experimental values for their $CP$ asymmetry are reported, respectively: ($0.3 pm 0.7$) % and ($-0.41 pm 0.09$) %. The value of the later can be attributed to the mixing of $ K^0 $ and $ overline{K^0} $, however, its contribution is about ($-0.332 pm 0.006 $) %. In this paper, we use these experimental results to constrain the unparticle stuff as a new physics which may contribute to these $CP$ asymmetries.
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.
A rare decay $K_L to mu^+ mu^- $ has been measured precisely, while a rare decay $K_S to mu^+ mu^- $ will be observed by an upgrade of the LHCb experiment. Although both processes are almost CP-conserving decays, we point out that an interference contribution between $K_L$ and $K_S$ in the kaon beam emerges from a genuine direct CP violation. It is found that the interference contribution can change $K_S to mu^+ mu^-$ standard-model predictions at $mathcal{O}(60%)$. We also stress that an unknown sign of $mathcal{A}(K_L to gamma gamma)$ can be determined by a measurement of the interference, which can much reduce a theoretical uncertainty of $mathcal{B}(K_L to mu^+ mu^-)$. We also investigate the interference in a new physics model, where the $epsilon_K / epsilon_K$ tension is explained by an additional $Z$-penguin contribution.
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 $K_S to mu^+ mu^-$.
It is well known that one can use B -> pi pi decays to probe the CP-violating phase alpha. In this paper we show that these same decays can be used to search for new physics. This is done by comparing two weak phases which are equal in the standard model: the phase of the t-quark contribution to the b -> d penguin amplitude, and the phase of Bd-Bd(bar) mixing. In order to make such a comparison, we require one piece of theoretical input, which we take to be a prediction for |P/T|, the relative size of the penguin and tree contributions to Bd -> pi^+ pi^-. If independent knowledge of alpha is available, the decay Bd(t) -> pi^+ pi^- alone can be used to search for new physics. If a full isospin analysis can be done, then new physics can be found solely through measurements of B -> pi pi decays. The most promising scenario occurs when the isospin analysis can be combined with independent knowledge of alpha. In all cases, the prospects for detecting new physics in B -> pi pi decays can be greatly improved with the help of additional measurements which will remove discrete ambiguities.
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