Joao M. Soares

CP violation in radiative b decays

Abstract According to the standard CKM model, the rare decays of the B-mesons can produce CP -violating asymmetries that may be accessible to experiment. I investigate the radiative decays b → sγ and b → dγ , at the quark level, and I find asymmetries of the order (0.1–1)% and (1–10)%, respectively. I use a modified formalism to calculate the as the relevant contributions, and simplifies handling the important QCD corrections to the amplitudes.

More on direct CP violation in b-->dJ/ psi decays.

Direct CP violation can occur in B-meson decays of the type b -> d+c+cbar, where the charm-anticharm pair forms a J/psi. The CP asymmetry requires the contribution to the amplitude from decays into other states, which rescatter into d+J/psi via final state interactions. In particular, states with the same quark content as d+J/psi can contribute. A perturbative calculation, based on a quark level description of the rescattering process, gives an asymmetry of about 1%, due to this effect. This makes it the dominant contribution to the asymmetry, as suggested by an earlier estimate, based on an hadronic picture.

Constraints on extended technicolor models from [ital B][r arrow][mu][sup +][mu][sup [minus]][ital X]

A recent study by Randall and Sundrum shows that models of Extended Technicolor (ETC) have interesting implications on rare B decays. We extend their study to the decay B → μ+μ−X. ETC models with a GIM mechanism predict a decay rate that is a factor of order 30 above the Standard Model, violating the experimental upper bound by a factor of 2–4. “Traditional” ETC models predict a decay rate that is a factor of order 4 above the Standard Model, and will be probed when an improvement in the sensitivity of experiments by a factor of order 2–4 is achieved. In a recent paper, Randall and Sundrum [1] studied the contributions to the decays b → sγ and Bs → μμ from various classes of Extended Technicolor (ETC) models. Models with and without a GIM mechanism were considered. In both cases, the radiative decay has roughly the same rate as in the Standard Model (SM). However, ETC contributions enhance the rate for Bs → μμ by one to two orders of magnitude. In this paper, we point out that a similar enhancement occurs for the decay b → sμμ. This is particularly interesting because there exists an upper bound on this rate [2] which is only an order of magnitude above the SM rate and, furthermore, near term experiments are expected to further improve this bound [3]. In this brief note, we estimate BR(b → sμμ) in the two classes of ETC models discussed in ref. [1], and compare it to the present experimental upper bound. The first class of models considered in ref. [1], or “traditional” ETC models, contains the minimal set of interactions necessary for quark mass generation. (The study is restricted to models where neither composite nor fundamental scalars are involved in the quark mass generation.) It is this very minimal set of interactions that are considered in the generation of flavor changing neutral currents (FCNC). As such, it is safe to assume that predictions based on these can be considered as lower bounds. The caveat, of course, is the possibility of cancellations once additional interactions are incorporated. The rates that we find strongly deviate from the SM ones and, therefore, unless these additional cancellations are rather precise, one may conceivably rule out this class of models in the near future. The second class of models, those with a “techni-GIM” mechanism, incorporate interactions beyond the minimal set of traditional models. They are theoretically appealing since, unlike traditional ETC, the massive vector bosons of the ETC interactions are nearly degenerate, with masses of a few TeV. Although these are rather light by traditional ETC standards, this class of models avoids many dangerous low energy FCNC interactions by incorporating an automatic techni-GIM cancellation mechanism. In the absence of masses, the quark sector has a large SU(3) flavor symmetry. If the only parameters that break this symmetry are the quark mass matrices (in the weak eigenstate basis), all of the flavor changing interactions must be proportional to them. Techni-GIM cancellations occur when one rotates to

Direct CP violation in b ---> d J / psi decays

We investigate the possibility of observing direct CP violation in self-tagging B-meson decays of the type b -> d J/\psi. The CP asymmetry can be generated due to strong or electromagnetic scattering in the final state, or due to long distance effects. The first two contributions give asymmetries of a few 10^(-3), in the standard model. The long distance effects are hard to estimate, but it cannot be excluded that they yield asymmetries of about 1%.

Comment on `Annihilation, rescattering, and CP asymmetries in B meson decays'

A Comment on the Letter by Boris Blok, Michael Gronau, Jonathan L. Rosner, Phys.Rev.Lett.{bold 78}, 3999 (1997). {copyright} {ital 1997} {ital The American Physical Society}

Comment on “Annihilation, Rescattering, andCPAsymmetries inBMeson Decays”

A Comment on the Letter by Boris Blok, Michael Gronau, Jonathan L. Rosner, Phys.Rev.Lett.{bold 78}, 3999 (1997). {copyright} {ital 1997} {ital The American Physical Society}

QCD corrections to B ---> J / psi + anything

We calculate the branching ratio for B -> J/psi + anything, within the color-singlet approximation for J/psi production, but including perturbative QCD corrections beyond the leading logarithm approximation. Such higher order corrections are necessary, in order to obtain a result that is not strongly dependent on the renormalization scale. As in the earlier work of Bergstrom and Ernstrom, we use a double expansion in alpha_s and in the small ratio of Wilson coefficients L_0/L_2, to identify the dominant terms in the decay amplitude. We complete their work by calculating all the leading order terms in this double expansion. The predicted branching ratio is then BR(B -> J/psi + anything) = 0.09 (+1.1)(-0.3) %, which is well below the experimental value BR(experimental) = 0.80 (+-0.08) %. This confirms the suspicion that non-perturbative corrections to the color-singlet approximation for J/psi production in B decays are important.

Direct [ital CP] violation in [ital b][r arrow][ital dJ]/[psi] decays

We investigate the possibility of observing direct CP violation in self-tagging B-meson decays of the type b -> d J/\psi. The CP asymmetry can be generated due to strong or electromagnetic scattering in the final state, or due to long distance effects. The first two contributions give asymmetries of a few 10^(-3), in the standard model. The long distance effects are hard to estimate, but it cannot be excluded that they yield asymmetries of about 1%.

Testing the superweak theory of CP violation in neutral B decays

In order to rule out the superweak theory for CP violation, future experiments will try to find a difference between the CP-violating asymmetries in the decays B{sup 0} {yields} {psi} K{sub s} and B{sup 0} {yields} {pi}{sup +}{pi}{sup {minus}}. However, Winstein recently noted that, for some acceptable values of the CKM parameters, the standard model would give equal asymmetry parameters for these decays just as the superweak theory does. In this paper we show that, by considering both tree and penguin contributions to the decay amplitudes, the test can still be effective if a third asymmetry is measured with enough precision.