Semileptonic and Exclusive Rare B Decays

The exclusive rare decay B \ra K^\ast \gamma takes place in a region of maximum recoil, $q^{2}=0$, posing a problem for nonrelativistic quark models which are usually thought to be most reliable at zero recoil. The Bauer--Stech--Wirbel (BSW) model, formulated in the infinite--momentum--frame (IMF) formalism, is designed to work at $q^2=0$. We show in this model that the ratio relating the decay B \ra K^\ast \gamma and the $q^2$--spectrum of the semileptonic decay B\ra \rho e {\bar \nu}, becomes independent of the wave function in the SU(3) flavor symmetry limit. We show that this feature is also true in relativistic quark models formulated in the IMF or light--cone formalism, if the $b$ quark is infinitely heavy. In fact, these relativistic models, which have a different spin structure from the BSW case, reduce to the BSW model in the heavy $b$--quark limit. A direct measurement of the $q^2$--spectrum of the semileptonic decay can therefore provide accurate information for the exclusive rare decay.Comment: 13 pages, Latex, no figure, UTPT--94--0

Constraining the CKM Parameters using CP Violation in semi-leptonic B Decays

We discuss the usefulness of the CP violating semi-leptonic asymmetry a_{SL} not only as a signal of new physics, but also as a tool in constraining the CKM parameters. We show that this technique could yield useful results in the first years of running at the B factories. We present the analysis graphically in terms of M_{12}, the dispersive part of the B-Bbar mixing amplitude. This is complementary to the usual unitarity triangle representation and often allows a cleaner interpretation of the data.Comment: 15 pages REVTEX, 7 figure

Radiative B decays to the axial KK mesons at next-to-leading order

We calculate the branching ratios of $B\to K_1\gamma$ at next-to-leading order (NLO) of $\alpha_s$ where $K_1$ is the orbitally excited axial vector meson. The NLO decay amplitude is divided into the vertex correction and the hard spectator interaction part. The one is proportional to the weak form factor of $B\to K_1$ transition while the other is a convolution between light-cone distribution amplitudes and hard scattering kernel. Using the light-cone sum rule results for the form factor, we have \calB(B^0\to K_1^0(1270)\gamma)=(0.828\pm0.335)\times 10^{-5} and \calB(B^0\to K_1^0(1400)\gamma)=(0.393\pm0.151)\times 10^{-5}.Comment: 17pages, 4 figures. Minor changes, typos corrected. PRD accepted versio

Potential Models for Radiative Rare B Decays

We compute the branching ratios for the radiative rare decays of B into K-Meson states and compare them to the experimentally determined branching ratio for inclusive decay b -> s gamma using non relativistic quark model, and form factor definitions consistent with HQET covariant trace formalism. Such calculations necessarily involve a potential model. In order to test the sensitivity of calculations to potential models we have used three different potentials, namely linear potential, screening confining potential and heavy quark potential as it stands in QCD.We find the branching ratios relative to the inclusive b ->s gamma decay to be (16.07\pm 5.2)% for B -> K^* (892)gamma and (7.25\pm 3.2)% for B -> K_2^* (1430)gamma for linear potential. In the case of the screening confining potential these values are (19.75\pm 5.3)% and (4.74\pm 1.2)% while those for the heavy quark potential are (11.18\pm 4.6)% and (5.09\pm 2.7)% respectively. All these values are consistent with the corresponding present CLEO experimental values: (16.25\pm 1.21)% and (5.93\pm 0.46)%.Comment: RevTeX, 6 pages, 1 eps figur

Measuring the Photon Helicity in Radiative B Decays

We propose a way of measuring the photon polarization in radiative B decays into K resonance states decaying to K\pi\pi, which can test the Standard Model and probe new physics. The photon polarization is shown to be measured by the up-down asymmetry of the photon direction relative to the K\pi\pi decay plane in the K resonance rest frame. The integrated asymmetry in K_1(1400)\to K\pi\pi, calculated to be 0.34\pm 0.05 in the Standard Model, is measurable at currently operating B factories.Comment: 4 pages, final version to appear in Physical Review Letter

Heavy Quark Symmetry Violation in Semileptonic Decays of D Mesons

The decays of $D$ mesons to $K l \nu$ and $K^* l \nu$ final states exhibit significant deviations from the predictions of heavy-quark symmetry, as one might expect since the strange quark's mass is of the same order as the QCD scale. Nonetheless, in order to understand where the most significant effects might lie for heavier systems (such as $B \to D l\nu$ and $B \to D^* l\nu$), the pattern of these deviations is analyzed from the standpoint of perturbative QCD and ${\cal O}(1/m_s)$ corrections. Two main effects are noted. First, the perturbative QCD corrections lead to an overall decrease of predicted rates, which can be understood in terms of production of excited kaonic states. Second, ${\cal O}(1/m_s)$ effects tend to cancel the perturbative QCD corrections in the case of $Kl\nu$ decay, while they have minimal effect in $K^*l\nu$ decay.Comment: 25 pages (LaTeX) + 7 pages of Postscript figures (included at end), EFI-92-3

Factorization and Nonfactorization in B Decays

Using NLL values for Wilson coefficients and including the contributions from the penguin diagrams, we estimate the amount of nonfactorization in two-body hadronic B decays. Also, we investigate the model dependence of the nonfactorization parameters by performing the calculation using different models for the form factors. The results support the universality of nonfactorizable contributions in both Cabibbo-favored and Cabibbo-suppressed B decays.Comment: 17 pages, 5 figures, revte

Constraints on the minimal supergravity model from the b->s+\gamma decay

The constraints on the minimal supergravity model from the b->s+\gamma decay are studied. A large domain in the parameter space for the model satisfies the CLEO bound, BR(b->s+\gamma)<5.4X10^{-4}. However, the allowed domain is expected to diminish significantly with an improved bound on this decay. The dependence of the b->s+\gamma branching ratio on various parameters is studied in detail. It is found that, for A_t<0 and the top quark mass within the vicinity of the center of the CDF value, m_t^{pole}=174\pm17 GeV, there exists only a small allowed domain because the light stop is tachyonic for most of the parameter space. A similar phenomenon exists for a lighter top and A_t negative when the GUT coupling constant is slightly reduced. For A_t>0, however, the branching ratio is much less sensitive to small changes in m_t, and \alpha_G.Comment: 12 pages, plain tex file, three figures avaliable upon request, CTP-TAMU-03/94, NUB-TH.7316/94, and CERN-TH.3092/9

Heavy Mesons in Two Dimensions

The large mass limit of QCD uncovers symmetries that are not present in the QCD lagrangian. These symmetries have been applied to physical (finite mass) systems, such as B and D mesons. We explore the validity of this approximation in the 't Hooft model (two-dimensional QCD in the large-N approximation). We find that the large mass approximation is good, even at the charm mass, for form factors, but it breaks down for the pseudoscalar decay constant.Comment: 4 pages, 3 figures inc

Probing SUSY-induced CP violations at B factories

In the minimal supersymmetric standard model (MSSM), the \mu-parameter and the trilinear coupling A_t may be generically complex and can affect various observables at B factories. Imposing the edm constraints, we find that there is no new large phase shift in the B^0 - \bar{B^0} mixing, CP violating dilepton asymmetry is smaller than 0.1 %, and the direct CP violation in B\to X_s \gamma can be as large as \sim \pm 16 %.Comment: 4 pages, 2 figures. Version to appear in Phys. Rev. Let