Martin J. Savage

Strong and electromagnetic decays of the baryon decuplet

Abstract To explore further the role that QCD symmetries play on hadron dynamics, we discuss the radiative decay of the baryon decuplet to the baryon octet and compute the leading non-analytic SU(3) violating corrections induced at the one-loop level. In the limit of exact flavour SU(3) symmetry two of the possible decay modes are forbidden and the rates for these two decays are dominated by loop corrections. There is only one SU(3) conserving contact term at leading order in chiral perturbation theory for the radiative decays. We determine its coefficient from the observed branching ratio for Δ → Nγ and from the present upper limit on Ξ ∗0 → Ξ 0 γ . We then predict the branching fractions for Σ ∗− → Σ − γ, Σ ∗0 → Λγ, Σ ∗0 → Σ 0 γ, Σ ∗+ → Σ + γ, Ξ ∗0 γ → Ξ 0 γ and Ξ ∗− → Ξ − γ . Some of the decay modes are predicted to have branching fractions near the current experimental upper limit and could possibly be observed in the near future. The leading corrections to the octet-decuplet-meson strong coupling constant, C , are computed at one-loop and the strong decay rates of the Δ, Σ ∗ and Ξ ∗ allow us to determine | C | = 1.2 ± 0.1 and H = −2.2 ± 0.6 , in remarkable agreement with predictions based on spin-flavour symmetry. We calculate the Δ pole graph contribution to the polarisability of the nucleon to order 1 Λ χ 2 in chiral perturbation theory.

Radiative D* decay using heavy quark and chiral symmetry

Abstract The implications of chiral SU(3) L ×SU(3) R symmetry and heavy quark symmetry for the radiative decays D ∗0 →D 0 γ , D ∗+ →D + γ , and D s ∗ →D s γ are discussed. Particular attention is paid to SU(3) violating contributions of order m q 1 2 . Experimental data on these radiative decays provide constraints on the D ∗ Dπ coupling.

Chiral perturbation theory analysis of the baryon magnetic moments

Abstract Nonanalytic m q 1 2 and mq ln mq chiral corrections to the baryon magnetic moments are computed. The calculation includes contributions from both intermediate octet and decuplet baryon states. Unlike the one-loop contributions to the baryon axial currents and masses, the contribution from decuplet intermediate states does not partially cancel that from octet intermediate states. The fit to the observed magnetic moments including m q 1 2 corrections is found to be much worse than the tree level SU(3) fit if values for the baryon-pion axial coupling constants obtained from a tree level extraction are used. Using the axial coupling constant values extracted at one loop results in a better fit to the magnetic moments than the tree level SU(3) fit. There are three linear relations amongst the magnetic moments when m q 1 2 corrections are included, and one relation including m q 1 2 , mqln mq and mq corrections. These relations are independent of the axial coupling constant of the baryons and agree well with experiment.

A QCD calculation of the interaction of quarkonium with nuclei

Abstract The interaction of quarkonium with nuclei is studied in the m Q →∞ limit of QCD, where the binding energy is found to be exactly computable. The dominant contribution to the interaction is from two-gluon operators. The forward matrix elements of these two-gluon operators can be determined from the QCD scale anomaly, and from deep inelastic scattering. We apply our results to the υ and J ψ treating the Q Q interaction as purely coulombic. We find the υ binds in nuclear matter with a binding energy of a few MeV, while for the J ψ binding is of order 10 MeV. For the J ψ in particular we expect confinement effects to produce large corrections to this result.

Hadron spectra for semileptonic heavy quark decay

We calculate the leading perturbative and power corrections to the hadronic invariant mass and energy spectra in semileptonic heavy hadron decays. We apply our results to the {ital B} system. Moments of the invariant mass spectrum, which vanish in the parton model, probe gluon bremsstrahlung and nonperturbative effects. Combining our results with recent data on {ital B} meson branching ratios, we obtain a lower bound {bar {Lambda}}{approx_gt}410MeV and an upper bound {ital m}{sub {ital b}}{sup pole}{lt}4.89 GeV. The Brodsky-Lepage-Mackenzie scale-setting procedure suggests that higher order perturbative corrections to the first moment of the hadronic invariant mass spectrum are small for bottom decay, and even tractable for charm decay. {copyright} {ital 1996 The American Physical Society.}

Flavour Changing Neutral Currents, Weak-Scale Scalars and Rare Top Decays

Abstract We examine the decays t → cγ and cZ 0 in the Standard Model with an extra scalar doublet and no discrete symmetry preventing tree-level flavour changing neutral currents. The Yukawa couplings of the new scalars are assumed to be proportional to fermion masses, evading bounds on FCNCs from the light quark sector. These rare top decays may be visible at the SSC.

An analysis of parity-violating pion-nucleon couplings

Abstract We construct to all orders in the pion field and to one power of pion momentum the most general lagrangian for parity-violating pion-nucleon interactions that can arise from weak interactions. In particular, we show that in addition to the previously discussed P-violating πNN vertex, there are independent ππNN, and πγNN interactions. All three may be relevant for nuclear and atomic parity-violation experiments, as well as P-violating elastic nucleon scattering. We give numerical estimates for the interactions, and show that there is reason to believe that the Z°-induced strange-quark operator ( s γ μ γ 5 s)( u γ μ u− d γ μ d) contributes significantly in the ΔI = 1 channel.

The Spin flavor dependence of nuclear forces from large n QCD

Abstract We show that nuclear interactions are SU (4) symmetric at leading order in chiral perturbation theory in the large- N limit of QCD. The nucleons and delta resonances form a 20-dimensional representation of SU (4) and we show how Wigners supermultiplet symmetry SU (4) sm , under which the nucleons transform as a 4-dimensional representation, follows as an accidental low energy symmetry. Exploiting SU (4) symmetry allows one to express the 18 independent leading N , Δ interaction operators invariant under SU (2) I × SU (2) J in terms of only two couplings. The three flavor analogue allows one to express the 28 leading octet, decuplet interactions in terms of only two couplings, which has implications for hypernuclei and strangeness in “neutron” stars.

Semileptonic Bc decay and heavy quark spin symmetry

Semileptonic decay of the Bc meson is studied in the heavy quark limit. The six possible form factors for Bc → Bs(B0), Bs∗(B∗0) semileptonic decay are determined by two invariant functions. Only one of these functions contributes at zero recoil, where it is calculable to lowest order in an operator product expansion in terms of the meson decay constant ƒB and the Bc wave function. A similar result is found for Bc → D0, D∗0 and for Bc → ηc, J/ψ semileptonic decay for a restricted kinematic region. Semileptonic Bc decay provides a means for determining the KM mixing angle |ub|.

Chiral perturbation theory for fDSFD and BBSBB

The decay constants for D and Ds mesons, denoted fD and fDS respectively, are equal in the SU(3)V limit, as are the hadronic amplitudes for BS−BS and B0−B0 mixing. The leading SU(3)V violating contribution to (FDS/FD) and to the ration of hadronic matrix elements relevant for BS − BS and B0 − B0 mixing amplitudes are calculated in chiral perturbatiion theory. We discuss the formalism needed to include both meson and anti-meson fields in the heavy quark effective theory.