arXiv subjects

Hsien-Hung Shih

Publications and source records attributed to Hsien-Hung Shih.

4 recordsLinked to original sources

arXiv2001

Λ_b \to ΛJ/ψdecay in perturbative QCD

We calculate the amplitudes involved in the heavy baryon nonleptonic decay $Λ_b \rar ΛJ/ψ$ using perturbative QCD factorization theorem, which are expressed as convolutions of hard $b$ quark decay amplitudes with the $Λ_b$ baryon, $Λ$ baryon and $J/ψ$ meson distribution amplitudes. It is found that nonfactorizable contributions dominate over factorizable ones. Because of soft cancellation in pairs of nonfactorizable diagrams, the $Λ_b \rar ΛJ/ψ$ decay is characterized by a large scale, such that perturbative QCD is applicable. Employing the distribution amplitudes determined in our previous works and from QCD sum rules, we derive the branching ratio $B(Λ_b \rar ΛJ/ψ)=(1.7 \sim 5.3)\times 10^{-4}$ in agreement with data. We predict an asymmetry parameter $α= -0.17 \sim -0.14$ associated with the anisotropic angular distribution of the $Λ$ baryons produced in polarized $Λ_b$ baryon decays.

hep-ph↗

arXiv2000

Polarized $Λ_b\to Λ_c l \barν$ decay in perturbative QCD

We study the polarized $Λ_b$ baryon semileptonic decay $Λ_b \to Λ_cl{\barν}$ using perturbative QCD factorization theorem. In this approach heavy baryon transition form factors are expressed as the convolutions of hard $b$ quark decay amplitudes with universal $Λ_b$ and $Λ_c$ baryon wave functions. With the heavy baryon wave functions determined in our previous work, we predict the asymmetry parameter $α({\hat e})\equiv (N_+-N_-)/(N_++N_-)=-0.31 {\bf P}\cdot{\hat e}$, where ${\bf P}$ is the $Λ_b$ baryon polarization, ${\hat e}$ a unit vector perpendicular to the $Λ_b$ baryon momentum, $N_+$ ($N_-$) the number of leptons whose momenta possess positive (negative) components along ${\hat e}$. This result is useful for extracting the transverse polarization of a $Λ_b$ baryon from data of exclusive semileptonic decays.

hep-ph↗

arXiv1999

Applicability of perturbative QCD to $Λ_b \to Λ_c$ decays

We develop perturbative QCD factorization theorem for the semileptonic heavy baryon decay $Λ_b \to Λ_c l\barν$, whose form factors are expressed as the convolutions of hard $b$ quark decay amplitudes with universal $Λ_b$ and $Λ_c$ baryon wave functions. Large logarithmic corrections are organized to all orders by the Sudakov resummation, which renders perturbative expansions more reliable. It is observed that perturbative QCD is applicable to $Λ_b \to Λ_c$ decays for velocity transfer greater than 1.2. Under requirement of heavy quark symmetry, we predict the branching ratio $B(Λ_b \to Λ_c l{\barν})\sim 2%$, and determine the $Λ_b$ and $Λ_c$ baryon wave functions.

hep-ph↗

arXiv1998

The $Λ_b\to pl{\barν}$ decay in perturbative QCD

We develop perturbative QCD factorization theorems for the exclusive semileptonic heavy baryon decay $Λ_b \to pl{\barν}$, in which the relevant hadronic form factor is expressed as the convolution of a hard subamplitude with the $Λ_b$ baryon wave function and the proton wave function. The specific evolution scale for the proton wave function, determined from the best fit to the data of the proton form factor, is adopted. The Sudakov resummation for a heavy-light system (the $Λ_b$ baryon) and the quark-level decay diagrams with at least one hard gluon attaching the $b$ quark, which were ignored in the literature, are incorporated. It turns out that these additional ingredients are important: the neglect of the former and the latter reduces the results of the form factor by factors 1.5 and 3, respectively. We present the predictions of the form factor and of the proton energy spectrum for the various choices of the parameter involved in the $Λ_b$ baryon wave function.

hep-ph↗