Narrow Results

The highlights and conflicts at the B factories are briefly reviewed. CP violation was established in 2001 in B⁰→J/ψK_S and related modes, which has now become a precision measurement of CP violation in mixing. However, the situation for the B⁰→π⁺π^- and charmless b→s modes, which also probe CP violation in the decay amplitude, are not quite settled yet. They could be hinting at the presence of both strong (CP conserving) and new physics (CP violating) phases. We critically assess the developments and discuss some related discrepancies and highlights, such as observation of direct CP violation, and make a projection towards the next few years.

Recent experimental measurements and lattice QCD calculations are now reaching the precision (and accuracy) needed to over-constrain the CKM parameters and . In this brief review, we discuss the current status of lattice QCD calculations needed to connect the experimental measurements of B meson properties to quark flavor-changing parameters. Special attention is given to B→πℓν, which is becoming a competitive way to determine |V_ub|, and to mixings, which now include reliable extrapolation to the physical light quark mass. The combination of the recent measurement of the B_s mass difference and current lattice calculations dramatically reduces the uncertainty in |V_td|. We present an outlook for reducing dominant lattice QCD uncertainties entering CKM fits and remark on lattice calculations for other decay channels.

In this short review we present the history, an overview of the analysis, and some personal comments on the anomalous like-sign dimuon charge asymmetry measurements by the DØ collaboration.

Results on $B\to {\mu }^{+}{\mu }^{-}$ decays with the CMS experiment are reported, using 61 fb${}^{-1}$ of data recorded during LHC Run 1 and 2016. With an improved muon identification algorithm and refined unbinned maximum likelihood fitting methods, the decay $B_s^0\to {\mu }^{+}{\mu }^{-}$ is observed with a significance of 5.6 standard deviations. Its branching fraction is measured to be $\overline{{ℬ}}(B_s^0\to {\mu }^{+}{\mu }^{-})=[2.9\pm 0.7(exp)\pm 0.2(\mathrm{\text{frag}})]\times 10^{-9}$, where the first error is the combined statistical and systematic uncertainty and the second error quantifies the uncertainty of the $B_s^0$ and $B^{+}$ fragmentation probability ratio. The $B_s^0\to {\mu }^{+}{\mu }^{-}$ effective lifetime is ${\tau }_{{\mu }^{+}{\mu }^{-}}=1.70_{-0.44}^{+0.61}\mathrm{\text{ps}}$. No evidence for the decay $B^0\to {\mu }^{+}{\mu }^{-}$ is found and an upper limit of ${ℬ}(B^0\to {\mu }^{+}{\mu }^{-})<3.6\times 10^{-10}$ (at 95% confidence level) is determined. All results are consistent with the standard model of particle physics.

We present recent results on CP violation in the B meson system from the BABAR experiment at the PEP II asymmetric e⁺e^- collider. We discuss the study of CP violation in B-mixing and present measurements of unitarity-triangle angles α, β, and constraints on γ.

We review some of the key 2006 measurements constraining the Unitarity Triangle and probing New Physics at B factory experiments BELLE and BABAR.

We report recent measurements of the three CKM angles of the Unitarity Triangle using about 383 millions pairs collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC.

mixing offers a profound probe into the effects of new physics beyond the Standard Model. In this paper, and mass differences are considered taking the effect of both Z- and Z′-mediated flavor-changing neutral currents in the mixing (q = d, s). Our estimated mass of Z′ boson is accessible at the experiments LHC and B-factories in near future.

In recent years, B_s →τ⁺τ^- rare decay has attracted a lot of attention since it is very sensitive to the structure of standard model (SM) and potential source of new physics beyond SM. In this paper, we study the effect of both Z and Z′-mediated flavor-changing neutral currents on the B_s →τ⁺τ^- decay. We find the branching ratio B(B_s→τ⁺τ^-) is enhanced relative to SM prediction, which would help to explain the recently observed CP-violation from like-sign dimuon charge asymmetry in the B system.

The recent observation of the same-sign dimuon charge asymmetry in the B system by the D0 collaboration has 3.9σ deviation from the standard model prediction. However, the recent LHCb data on B_s neutral-meson mixing do not accommodate the D0 collaboration result. In this paper, considering the effect of Z′-mediated flavor-changing neutral currents in the mixing, the same-sign dimuon charge asymmetry is calculated. We find the same-sign dimuon charge asymmetry is enhanced from its SM prediction and provides signals for new physics beyond the SM.

The rare decays $B_{s,d}^{\ast }\to l^{+}{l}^{-}$ are important to probe the flavor sector of the standard model and to search new physics beyond the SM. Unlike pseudoscalar $B$ meson, the leptonic decays of vector $B_{s,d}^{\ast }$ mesons are not chirally suppressed which compensates for their short lifetimes, and results in significant branching ratios. In this paper, we estimate the branching ratios of $B_{s,d}^{\ast }\to l^{+}{l}^{-}$$(l=e,\mu )$ rare decays in $Z^{\prime }$ model which is an extension of the SM with an extra $U{(1)}^{\prime }$ gauge symmetry. We find that the branching ratios are increased from their corresponding standard model values and vary with the mass of $Z^{\prime }$ boson. The lower the mass of $Z^{\prime }$ boson, the higher is the branching ratio.

We investigate $B_s^0\to {\ell }^{+}{\ell }^{-}\gamma$ decays in a nonuniversal $Z^{\prime }$ model derived from the extension of the Standard Model (SM). Considering the $Z^{\prime }$-mediated flavor-changing neutral current (FCNC) effects, we calculate the branching ratio and forward–backward asymmetry $(A_{\mathrm{\text{FB}}})$ for $B_s^0\to {\ell }^{+}{\ell }^{-}\gamma$ decay processes. We compare the obtained results with predictions of the SM and discuss the sensitivity of the observables to $Z^{\prime }$ boson coupling parameters. We find that the branching ratios are enhanced by one order from SM predictions in $Z^{\prime }$ model scenario. We also observe that the variation of forward–backward asymmetry with the $Z^{\prime }$ boson coupling parameters portrays discrimination between NP effects and SM results.

In this paper we present a phenomenological analysis of the Partially Aligned Two Higgs Doublet Model (PA-2HDM) by using leptonic decays of mesons and $B_{d,s}^0$–${\bar{B}}_{d,s}^0$ mixing. We focus our attention in a scenario where the leading contribution to FCNC is given by the tree-level interaction with the light pseudoscalar $A^0$ ($M_{A^0}\sim 250$ GeV). We show how an underlying flavor symmetry controls FCNC in the quark and lepton couplings with the pseudoscalar, without alignment between Yukawa matrices. Upper bounds on the free parameters are calculated in the context of the leptonic decays $B_{s,d}^0\to {\mu }^{+}{\mu }^{-}$ and $K_L^0\to {\mu }^{+}{\mu }^{-}$ and $B_{s,d}^0$ mixing. Also, our assumptions imply that bounds on New Physics contribution in the quark sector coming from $B_{s,d}^0$ mixing impose an upper bound on the parameters for the leptonic sector. Finally we give predictions of branching ratios for leptonic decay of mesons with FCNC and LFV.

In a version of the PA-2HDM where only mixing between third and second fermion generations is allowed, we propose a mechanism to generate the second Yukawa matrix through a Unitary V-spin flavor transformation on the mass matrix for quarks and leptons. This flavor structure is constrained to be universal, that is, we use the same parameters to generate Yukawa matrix elements in the quark and leptonic sectors, reducing drastically the number of free parameters of the PA-2HDM.

As a consequence of this restrictive condition, we obtain relations between the Yukawa matrix elements, that we call the Universal Texture Constraint (UTC). We obtained an interval of values for the second Yukawa matrix elements, expressed in terms of the Cheng and Sher ansatz, for $\tau \to \mu {\mu }^{+}{\mu }^{-}$ and $\tau \to \gamma \mu$ coming from the UTC and experimental bounds for light scalar masses. Finally, we find the allowed parameter region when the experimental bounds and values for $B_s\to \mu \mu$ decays, $B_s^0-{\bar{B}}_s^0$ mixing, $\tau \to \mu {\mu }^{+}{\mu }^{-}$ and $\tau \to \gamma \mu$ are considered.