Semileptonic CP Asymmetry Research Articles

Taming new physics in b → cūd(s) with τ(B+)/τ(Bd) and asld\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {a}_{sl}^d $$\\end{document}

Inspired by the recently observed tensions between the experimental data and the theoretical predictions, based on QCD factorisation, for several colour-allowed non-leptonic B-meson decays, we study the potential size of new physics (NP) effects in the decay channels b → cūd(s). Starting from the most general effective Hamiltonian describing the b → cūd(s) transitions, we compute NP contributions to the theoretical predictions of B-meson lifetime and of B-mixing observables. The well-known lifetime ratio τ(B+)/τ(Bd) and the experimental bound on the semi-leptonic CP asymmetry asld\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {a}_{sl}^d $$\\end{document}, provide strong, complementary constraints on some of the NP Wilson coefficients.

Charming new B-physics

We give a comprehensive account of the flavour physics of Beyond-Standard-Model (BSM) effects in b → c overline{c} cs transitions, considering the full set of 20 four-quark operators. We discuss the leading-order structure of their RG mixing with each other as well as the QCD-penguin, dipole, and FCNC semileptonic operators they necessarily mix with, providing compact expressions. We also provide the first complete results for BSM effects in the lifetime observables ∆Γs and τ (Bs)/τ(Bd), as well as for the semileptonic CP-asymmetry {a}_{sl}^s . From a global analysis, we obtain stringent constraints on 16 of the 20 BSM operators, including the 10 operators {Q}_{1dots 10}^{cprime } involving a right-handed strange quark. Focussing on CP-conserving new physics, the constraints correspond to NP scales of order 10 TeV in most cases, always dominated by exclusive and/or radiative B-decays via RGE mixing. For the remaining four operators, including the two Standard-Model (SM) ones, larger effects are experimentally allowed, as previously noted in [1]. We extend that paper’s scope to the CP-violating case, paying attention to the impact on the decay rate and time-dependent CP-violation in Bd → J/ψKS. Contrary to common lore, we show that quantifiable constraints arise for new physics in either of the two SM operators, with the uncertain non-perturbative matrix element of the colour-suppressed (or equivalently, colour-octet) operator determined from the data. For new physics in the coefficient {C}_1^c , suppressed in the SM, we find (in addition to CP-conserving new physics) two perfectly viable, narrow bands of complex Wilson coefficients. Somewhat curiously, one of them contains a region where the fitted matrix element for the colour-suppressed operator is in agreement with naive factorization, contrarily to a widely held belief that large non- factorizable contributions to Bd → J/ψKS are implied by experimental data.

CP violation in the Bs0 system

Experimental and theoretical studies of CP violation in the B0s system are reviewed. Updated predictions for the mixing parameters of the B0s mesons expected in the standard model (SM) are given, namely, the mass difference ΔMSMs=18.3±2.7 ps−1, the decay rate difference ΔΓSMs=0.085±0.015 ps−1, and the flavor-specific CP asymmetry as,SMfs=(2.22±0.27)×10−5 and the equivalent quantities in the B0 sector. Current experimental values of ΔMs and ΔΓs agree with remarkable precision with theoretical expectations. This agreement supports the applicability of theoretical tools such as the heavy quark expansion to these decays. CP-violating studies in the B0s system provide essential information to test the SM expectations and to unveil a possible contribution of the new physics (NP). NP effects on ΔMs of the order of 15% are still possible. The CP phase ϕs due to CP violation in interference of decays and mixing can accommodate effects of the order of O(100%). The semileptonic CP asymmetry assl due to CP violation in mixing could still be a factor of 130 larger than its robust SM expectation and thus provides a very clean observable for NP searches. Theoretical improvements that are necessary to make full use of the experimental precision are discussed.

B→sdecays in a model withZ-mediated flavor changing neutral current

In the scenario with Z mediated flavor changing neutral current occurring at the tree level due to the addition of a vector-like isosinglet down-type quark d' to the SM particle spectrum, we perform a chi square fit using the flavor physics data and obtain the best fit value along with errors of the tree level Zbs coupling, U_{sb}. The fit indicates that the new physics coupling is constrained to be small: we obtain |U_{sb}| <= 3.40 X 10^{-4} at 3 sigma. Still this does allow for the possibility of new physics signals in some of the observables such as semileptonic CP asymmetry in Bs decays.

ConstrainingCPviolation in neutralBmeson mixing with theory input

There has been a lot of recent interest in the experimental hints of CP violation in B_{d,s}^0 mixing, which would be a clear signal of beyond the standard model physics (with higher significance). We derive a new relation for the mixing parameters, which allows clearer interpretation of the data in models in which new physics enters in M_12 and/or \Gamma_12. Our results imply that the central value of the D\O\ measurement of the semileptonic CP asymmetry in B_{d,s}^0 decay is not only in conflict with the standard model, but in a stronger tension with data on \Delta\Gamma_s than previously appreciated. This result can be used to improve the constraint on \Delta\Gamma or A_SL, whichever is less precisely measured.

Simple relation forBsmixing

We reinvestigate a simple relation between the semileptonic CP asymmetry a_{sl}^s, the decay rate difference \Delta \Gamma_s, the mass difference \Delta M_s and S_{\psi \phi} extracted from the angular analysis of the decay B_s \to \psi \phi, which is regularly used in the literature. We find that this relation is not suited to eliminate the theory prediction for \Gamma_{12}, it can, however be used to determine the size of the penguin contributions to the decay B_s \to \psi \phi. Moreover we comment on the current precision of the theory prediction for \Gamma_{12}.

CP violation inD0−D̄0oscillations: general considerations and applications to the Littlest Higgs model with T-parity

The observed D0 - anti-D0 oscillations provide a new stage in our search for New Physics in heavy flavour dynamics. The theoretical verdict on the observed values of x_D and y_D remains ambiguous: while they could be totally generated by Standard Model dynamics, they could also contain a sizable or even leading contribution from New Physics. Those oscillations are likely to enhance the observability of CP violation as clear manifestations of New Physics. We present general formulae for D0 - anti-D0 oscillations, concentrating on the case of negligible direct CP violation. In particular we derive a general formula for the time-dependent mixing-induced CP asymmetry in decays to a CP eigenstate and its correlation with the semileptonic CP asymmetry a_SL(D0) in D0(t) -> l nu K. We apply our formalism to the Littlest Higgs model with T-parity, using the time-dependent CP asymmetry in D -> K_S phi as an example. We find observable effects at a level well beyond anything possible with CKM dynamics. Comparisons with CP violation in the K and B systems offer an excellent test of this scenario and reveal the specific pattern of flavour and CP violation in the D0 - anti-D0 system predicted by this model. We discuss a number of charm decays that could potentially offer an insight in the dynamics of CP violation in D decays. We also apply our formalism to B_s - anti-B_s mixing.

CP asymmetries at D0

Using two independent measurements of the semileptonic CP asymmetry in the Bs system, we constrain the CP-violating phase of the Bs system to be ϕs = -0.70-0.39+0.47. The data sample corresponds to an integrated luminosity of 1.1 fb− accumulated with D0 detector at the Fermilab Tevatron Collider. We also measure the direct CP violating asymmetry in the decay B+ → J/ψK+ to be ACP(B+ → J/ψK+) = +0.0067 ± 0.0074(stat)±0.0026(syst). The data corresponds to an integrated luminosity of 1.6 fb−.

Constraining the Phase ofBs−B¯sMixing

New physics contributions to B_s-\bar{B}_s mixing can be parametrized by the size (r_s^2) and the phase (2\theta_s) of the total mixing amplitude relative to the Standard Model amplitude. The phase has so far been unconstrained. We first use the D0 measurement of the semileptonic CP asymmetry A_SL to obtain the first constraint on the semileptonic CP asymmetry in B_s decays, A_SL^s=-0.008 \pm 0.011. Then we combine recent measurements by the CDF and D0 collaborations - the mass difference (\Delta M_s), the width difference (\Delta\Gamma_s) and A_SL^s - to constrain 2\theta_s. The errors on \Delta\Gamma_s and A_SL^s should still be reduced to have a sensitive probe of the phase, yet the central values are such that the regions around 2\theta_s ~ 3\pi/2 and, in particular, 2\theta_s ~ \pi/2, are disfavored.