arXiv subjects
Publications and source records attributed to David London.
The decays B_{d,s}^0 --> K^{(*)} K-bar^{(*)} can be used to measure the angle alpha of the CKM unitarity triangle. The theoretical error from SU(3) breaking is expected to be small, so that the determination of alpha is clean. Moreover, since B_{d,s}^0 --> K^{(*)} K-bar^{(*)} are pure penguin decays, they are particularly sensitive to the presence of new physics
We describe a new method for obtaining the CP phase alpha via measurements of B_{d,s} -> K(*) Kbar(*) decays. This method is particularly appropriate for hadron colliders since some of the branching ratios are small [O(10^{-6})], and since B_s decays are involved. By comparing the value of alpha extracted from this method with that obtained in B -> pi pi or B -> rho pi decays, one can detect the presence of new physics in the b -> d penguin amplitude. The method does require theoretical input, but model calculations suggest that the theoretical uncertainty is at most 5%, and might well be even smaller. These estimates can be tested experimentally. The method is therefore quite clean.
Using factorization, we compute, within the standard model, the T-violating triple-product correlations in the charmless decays Lambda_b -> F_1 F_2, where F_1 is a light spin-1/2 baryon and F_2 is a pseudoscalar (P) or vector (V) meson. We find a large triple-product asymmetry of 18% for the decay Lambda_b -> p K^-. However, for other classes of Lambda_b -> F_1 P decays, the asymmetry is found to be at most at the percent level. For Lambda_b -> F_1 V decays, we find that all triple-product asymmetries are small (at most O(1%)) for a transversely-polarized V, and are even smaller for longitudinal polarization. Our estimates of the nonfactorizable contributions to these decays show them to be negligible, and we describe ways of testing this.
We re-examine a recent proposal for obtaining βusing the measurements of the b -> d penguin decays B_d(t) -> K^0 \kbar and B_s(t) -> ϕK_S, along with a theoretical assumption. We show that there are in fact three assumptions one can make, so that the method can in principle be used to extract α, βor γ. We also show that it is the assumption which yields γwhich is the best. However, the theoretical error on this assumption is still 25-30%, which leads to an error on γof at least 20-25%. Given our current understanding of hadronic physics, it does not seem possible to reduce this error.
We present a new method for measuring the CP phase α. It requires the measurement of the pure penguin decays Bd(t) -> K(*) Kbar(*) and B_s -> K(*) Kbar(*). The method is quite clean: we estimate the theoretical uncertainty to be at most 5%. By applying the method to several K(*) Kbar(*) final states, αcan be extracted with a fourfold ambiguity. An additional assumption reduces this ambiguity to twofold: {α, α+ π}. Since no \pi0 detection is needed, this method can be used at hadron colliders.
In this talk we show that, unlike other pure $b\to d$ penguin processes, the decay $\bs(t)\toϕ\ks$ is dominated by a single amplitude, that of the internal $t$-quark. Thus, the indirect CP asymmetry in this decay probes $\sin 2β$. This cancellation holds for most part of the parameter space and error on $\sin 2β$ is less than 10%. By measuring the direct CP asymmetry, one can get a better idea of the probable error on $\sin 2β$.
Leptophobic Z' gauge bosons can appear in models with an E_6 gauge symmetry. We show that flavour-changing neutral currents can be generated in some of these models due to the mixing of the ordinary d_R, s_R and b_R quark fields with the exotic h_R. Because the Z' does not couple to charged leptons, the constraints on the flavour-changing couplings U^{Z'}_{db} and U^{Z'}_{sb} are relatively weak. Indeed, B_q--Bbar_q mixing (q=d,s) can be dominated by Z' exchange, which will affect CP-violating rate asymmetries in B decays. Rare hadronic B decays can also be affected, while decays involving charged leptons will be unchanged.
In the presence of penguin contributions, the indirect CP asymmetry in B0(t) -> pi+ pi- measures sin(2α+ 2θ), where 2θparametrizes the size of the penguin ``pollution.'' We derive a new upper bound on |2θ|, requiring the measurement of of BR(B+ -> pi+ pi0) and an upper bound on B00 \equiv {1\over 2} [BR(B0 -> pi0 pi0) + BR(B0bar -> pi0 pi0)]. The new bound is stronger than those previously discussed in the literature. We also present a lower bound on B00. Current data may suggest that it is not very small, in which case θcan be determined using a complete isospin analysis.
We show that, unlike other pure b -> d penguin processes, the decay Bs(t) -> phi K_s is dominated by a single amplitude, that of the internal t-quark. The contributions of the u- and c-quark operators each vanish due to a cancellation between the (V-A) \otimes (V-A) and (V-A) \otimes (V+A) matrix elements. Thus, the indirect CP asymmetry in this decay probes sin 2β. Although this cancellation is complete only for certain values of the s- and b-quark masses, the theoretical uncertainty on sin 2βis still less than 10% over most (~80%) of the parameter space. By measuring the direct CP asymmetry, one can get a better idea of the probable error on sin 2β.
We describe a new method for extracting weak, CP-violating phase information, with no hadronic uncertainties, from an angular analysis of B -> V_1 V_2 decays, where V_1 and V_2 are vector mesons. The quantity $\sin^2 (2β+ γ)$ can be cleanly obtained from the study of decays such as B_d^0(t) -> D^{*\pm} ρ^\mp, D^{*\pm} a_1^{\mp}, D^{*0} K^{*0}, etc. Similarly, one can use B_s^0(t) -> D_s^{*\pm} K^{*\mp} to extract $\sin^2 γ$. There are no penguin contributions to these decays. It is possible that $\sin^2 (2β+ γ)$ will be the second function of CP phases, after $\sin 2β$, to be measured at B-factories.
The first measurements of CP violation in the B system will probably extract $\sin 2α$, $\sin 2β$ and $\cos 2γ$. Assuming that the CP angles $α$, $β$ and $γ$ are the interior angles of the unitarity triangle, this determines the angle set $(α,β,γ)$ up to a twofold discrete ambiguity. The presence of this discrete ambiguity can make the discovery of new physics difficult: if only one of the two solutions is consistent with constraints from other measurements in the B and K systems, one is not sure whether new physics is present or not. I present examples of this situation, and discuss ways to resolve the discrete ambiguity.
Measurements of CP asymmetries in B decays will soon be made at $B$ factories and hadron machines. In light of this, we review and update the profile of the CKM unitarity triangle and the resulting CP asymmetries in B decays. This is done both in the standard model and in several variants of the minimal supersymmetric standard model (MSSM), which are characterized by a single phase in the quark flavour mixing matrix. After imposing present constraints on the parameters of these models, the predicted ranges of $\sin 2 β$ in the standard model and in the MSSM are found to be similar. However, these theories may be distinguished by future precise measurements of the other two CP-violating phases $α$ and $γ$.
We review the salient features of a comparative study of the profile of the CKM unitarity triangle, and the resulting CP-violating phases $α$, $β$ and $γ$ in B decays, in the standard model and in several variants of the minimal supersymmetric standard model (MSSM), reported recently by us. These theories are characterized by a single phase in the quark flavour mixing matrix and give rise to well-defined contributions in the flavour-changing-neutral-current transitions in K and B decays. We analyse the supersymmetric contributions to the mass differences in the Bd-Bd(bar) and Bs-Bs(bar) systems, $ΔM_d$ and $ΔM_s$, respectively, and to the CP-violating quantity $|epsilon|$ in K decays. Our analysis shows that the predicted ranges of $β$ in the standard model and in MSSM models are very similar. However, precise measurements at B-factories and hadron machines may be able to distinguish these theories in terms of the other two CP-violating phases $α$ and $γ$. (Contribution to the Festschrift for L.B. Okun, to appear in a special issue of Physics Reports, eds. V.L. Telegdi and K. Winter)
After reviewing the present experimental constraints on the unitarity triangle, I discuss the various ways in which new physics can manifest itself in measurements of the parameters of the unitarity triangle. Apart from one exception, which I describe, new physics enters principally through new contributions to B0-B0(bar) mixing. Different models of new physics can be partially distinguished by looking at their effects on rare, flavour-changing $B$ penguin decays. (Invited talk given at the Symposium Twenty Beautiful Years of Bottom Physics, Chicago, IL, USA, June 29 -- July 2, 1997.)
Asymmetric e^+e^- colliders running on the Υ(4S) (B factories) will much more readily measure CP-violating asymmetries in the decays of B_d^0 and B^\pm mesons than in the decays of B_s^0 mesons. As such, they will seemingly not be able to probe new phases in Bs-Bs(bar) mixing, i.e. in b\to s transitions. However, by measuring the CP angle βvia b \to s hadronic penguin decays such as B_d^0 \to η'\ks and B_d^0 \toϕ\ks, and comparing its value to that obtained in B_d^0 \toΨ\ks, it is possible to detect the presence of new physics in the b\to s flavour-changing neutral current. Recent CLEO results are encouraging in this regard. They suggest that the branching ratio of the b\to s penguin decay B_d^0 \to η'\ks is anomalously large, about 4 \times 10^{-5}, which will make it much easier to search for new physics in b\to s transitions.
I review several topics involving CP violation with heavy hadrons. In particular, I discuss (i) Hyperons: CP violation in the decay $Λ^0 \to p π^-$, (ii) Charm: indirect CP violation in the D^0 system, both within and beyond the SM, and (iii) Beauty: indirect CP violation in the neutral B-meson system beyond the SM. Talk presented at the 2nd International Conference on Hyperons, Charm and Beauty Hadrons, Montréal, Canada, August 1996.
The decays of $B$ mesons to two-body hadronic final states are analyzed within the context of broken flavor SU(3) symmetry, extending a previous analysis involving pairs of light pseudoscalars to decays involving one or two charmed quarks in the final state. A systematic program is described for learning information {}from decay rates regarding (i) SU(3)-violating contributions, (ii) the magnitude of exchange and annihilation diagrams (effects involving the spectator quark), and (iii) strong final-state interactions. The implication of SU(3)-breaking effects for the extraction of weak phases is also examined. The present status of data on these questions is reviewed and suggestions for further experimental study are made.
We discuss the role of electroweak penguins in $B$ decays to two light pseudoscalar mesons. We confirm that the extraction of the weak phase $α$ through the isospin analysis involving $B\toππ$ decays is largely unaffected by such operators. However, the methods proposed to obtain weak and strong phases by relating $B\toππ$, $B\toπK$ and $B\to KK$ decays through flavor SU(3) will be invalidated if electroweak penguins are large. We show that, although the introduction of electroweak penguin contributions introduces no new amplitudes of flavor SU(3), there are a number of ways to experimentally measure the size of such effects. Finally, using SU(3) amplitude relations we present a new way of measuring the weak angle $γ$ which holds even in the presence of electroweak penguins.