Non-spectator contributions to B->X_s eta'
We propose a nonspectator mechanism in which eta' is produced by two gluon fusion as the underlying process to explain the inclusive B-> X_s eta' as well as the exclusive B -> K^(*) eta' decays.
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arXiv subjects
M. R. Ahmady
Publications and source records attributed to M. R. Ahmady.
Non-spectator contribution: A mechanism for inclusive B-> X_s eta' and exclusive B-> K(*) eta' decays
We propose a mechanism which can explain the large BR(B-> X_s eta')~ 10^(-3) observed by CLEO. In this mechanism, eta' is produced by the fusion of two gluons, one from QCD penguin b->sg and the other one emitted by the light quark inside the B meson. The inclusive decay rate which is calculated via using the factorization assumption, can easily account for the observed branching ratio. We also estimate the exclusive branching ratio BR(B->K eta')=7.0X10^(-5) which is in good agreement with the experimental data and present our prediction for K* mode BR(B->K* eta')=3.4X10^(-5).
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Effective Higgs-to-Light-Quark Coupling Induced by Heavy Quark Loops
We study the coupling arising via perturbative QCD of zero 4-momentum Higgs bosons to light quarks inside the nucleon. Qualitative comparison with the results obtained from one-loop-order low energy theorems for the Higgs-nucleon interaction suggests the existence of a dynamical light-quark mass which falls off with momentum. Quantitative comparison leads to an estimate of $α_s$ at very low $q^2$ quite near unity.
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Induced Light-Quark Yukawa Couplings as a probe of Low-Energy Dynamics in QCD
We examine the heavy-quark-induced Yukawa interaction between light quarks and a light Higgs field, which is facilitated in the chiral limit by the dynamical mass of light quarks anticipated from the chiral-noninvariance of the QCD vacuum. A low-energy estimate of the strong coupling near unity can be obtained from a comparison of the explicit perturbative calculation of the induced Yukawa interaction at zero momentum to a Higgs-low-energy theorem prediction for the same interaction.
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Decay constants and mixing parameters in a relativistic model for q\barQ system
We extend our recent work, in which the Dirac equation with a ``(asymptotically free) Coulomb + (Lorentz scalar $γ_0σr$) linear '' potential is used to obtain the light quark wavefunction for $q\bar Q$ mesons in the limit $m_Q\to \infty$, to estimate the decay constant $f_P$ and the mixing parameter $B$ of the pseudoscalar mesons. We compare our results for the evolution of $f_P$ and $B$ with the meson mass $M_P$ to the non-relativistic formulas for these quantities and show that there is a significant correction in the subasymptotic region. For $σ=0.14{\rm ~GeV}^{-2}$ and $\lms =0.240{\rm ~GeV}$ we obtain: $f_D =0.371\; ,\; f_{D_s}=0.442\; ,\; f_B=0.301\; ,\; f_{B_s}=0.368 {\rm ~GeV}$ and $B_D=0.88\; ,\; B_{D_s}=0.89\; ,\; B_B=0.95\; ,\; B_{B_s}=0.96\; ,\;$ and $B_K=0.60$.
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Estimates of B-decays into K-Resonances and Dileptons
Short and long distance contributions to the exclusive B-decays into various K-resonances and dileptons, i.e. B --> Ki l l ( l = e, mu , nu ), are examined. The heavy quark effective theory has been used to calculate the hadronic matrix elements. Substantial branching fractions are obtained for the dileptonic B-decays into some higher excited states of K-mesons. The long distance (resonance) contributions to these exclusive rare B-decay modes dominate the short distance contributions mostly by two orders of magnitude. It is pointed out that, excluding the resonance contributions, the P-wave channels are dominant, accounting for about 50% of the inclusive B --> X_s l l branching fraction.
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The Decay $η_c \rightarrow γγ$ : A Test for Potential Models
We use a simple perturbation theory argument and measurements of charmonium leptonic widths $Γ(ψ_{NS} \rightarrow e^+e^-)$ to estimate the ratio \mbox{$R_\circ \equiv {\vert Ψ_{η_{c1S}}(0) \vert}^2 /{\vertΨ_{ψ_{1 S}}(0)\vert}^2$} in the general context of non- relativistic potential models. We obtain $R_\circ = 1.4 \pm 0.1$. We then apply well known potential model formulas, which include lowest order QCD corrections, to find $Γ(η_c \rightarrow γγ)/Γ(ψ_{1S} \rightarrow e^+e^-) \approx 2.2\pm 0.2$. The central value for $Γ(ψ_{1S} \rightarrow e^+ e^-)$in the 1992 Particle Data Tables then leads to a (non relativistic) prediction $Γ(η_c \rightarrow γγ)\approx 11.8\pm 0.8 $ keV. This prediction is in good agreement with a recent measurement by the ARGUS collaboration, is consistent with a recent measurement by the L3 collaboration but is significantly higher than several earlier measurements and than previous theoretical estimates, which usually assume $R_\circ =1$. The correction to $R_\circ =1$ is estimated to be smaller but nonnegligible for the $b\bar b$ system. Using the current central measurement for $Γ(Υ_{1S}\rightarrow e^+e^-)$ we find $Γ(η_b\rightarrow γγ)\approx 0.58\pm 0.03$ keV. A rough estimate of relativistic corrections reduces the expected two photon rates to about 8.8 keV and 0.52 keV for the $η_c$ and $η_b$ mesons respectively. Such corrections
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On-Mass-Shell Renormalization of the $\langle \bar{t}t \rangle$ Contribution to the $ΔI = 1/2$ $s \leftrightarrow d$ Self-Energy Transition
In $\langle \bar{t}t \rangle$-scenarios for dynamical electroweak symmetry breaking, the presence of a very large t-quark condensate necessarily generates an $s \leftrightarrow d$ self-energy transition which will contribute exclusively to $ΔI = 1/2$ strangeness-changing matrix elements. This contribution is calculated and compared to the purely perturbative contribution, which is well-known to be far too small to have an appreciable effect on $ΔI = 1/2$ strangeness-changing matrix elements after mass-shell renormalization subtractions are taken into account. The ratio between the t-quark condensate's contribution and the standard-model perturbative contribution to the mass-shell renormalized $s \leftrightarrow d$ self-energy transition is shown to be of order $\mid m_t \langle \bar{t} t \rangle \mid / M_W ^4$, suggesting that the large t-quark condensate proposed for electroweak symmetry breaking may also be responsible for the $Δ
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