arXiv subjects

Chung-Yi Wu

Publications and source records attributed to Chung-Yi Wu.

7 recordsLinked to original sources

arXiv2000

$B\to ϕK$ and $B\to ϕX_s$ in the Heavy Quark Limit

We study $B\to ϕK$ and $B\to ϕX_s$ decays in the heavy quark limit using perturbative QCD. The next leading order corrections introduce substantial modifications to the naive factorization results (more than 50%). The branching ratio $Br(B\to ϕK)$ is predicted to be in the range $(F^{B\to K}_1(m^2_ϕ)/0.33)^2(3.5\sim 4.2) \times 10^{-6}$ which is within the one $σ$ allowed region from the central value of $6.2\times 10^{-6}$ measured by CLEO, but outside the one $σ$ allowed region from the central value of $17.2\times 10^{-6}$ measured by BELLE for reasonable $F_1^{B\to K}$. For the semi-inclusive decay $B\to ϕX_s$ we also include initial bound state effect in the heavy quark limit which decreases the branching ratio by about 10%. $Br(B\to ϕX_s)$ is predicted to be in the range $(5.1\sim 6.3)\times 10^{-5}$.

hep-ph↗

arXiv1997

Asymmetry Effects in Polarized Hadron Scattering

We calculate the single-spin and double-spin asymmetry differential cross sections for the polarized hadron scattering $PP \to l^+ l^- + jet$ up to $O(α_s)$ by the helicity amplitude method. Numerical results of the differential cross sections, which can be used to probe the spin contents of the proton, are obtained with several sets of polarized parton distribution functions.

hep-ph↗

arXiv1996

Internal W-emmission and W-exchange Contributions to {\bf B}\to {{\bf D}^{(*)} Decays

We evaluate external $W$-emission, internal $W$-emission and $W$-exchange contributions to nonleptonic $B\to D^{(*)}$ decays based on the perturbative QCD formalism including Sudakov effects, whose ratio is found to be $1:+0.2:0.03i$ at the amplitude level. We observe that the internal $W$-emission contribution is additive to the external $W$-emission contribution, and that the $W$-exchange contribution is negligible and mainly imaginary, its real part being at least one order of magnitude smaller than the imaginary part. Our predictions are consistent with the CLEO data and with those obtained by the Bauer-Stech-Wirbel method.

hep-ph↗

arXiv1995

Polarized Parton Distribution Functions Reexamined

The hard-gluonic contribution to the first moment of the polarized proton structure function $g_1^p(x)$ is dependent of the factorization convention chosen in defining the quark spin density and the hard cross section for photon-gluon scattering. Two extremes of interest, namely gauge-invariant and chiral-invariant factorization schemes, are considered. We show that in order to satisfy the positivity constraint for sea and gluon polarizations, the polarized valence quark distributions should fully account for the observed $g_1^p(x)$ at $x\gsim 0.2\,$. This together with the first-moment and perturbative QCD constraints puts a pertinent restriction on the shape of $Δu_v(x)$ and $Δd_v(x)$. The spin-dependent sea distribution in the gauge-invariant factorization scheme is extracted from the data of $g_1^p(x)$. It is shown in the chiral invariant scheme that it is possible to interpret the $g_1^p(x)$ data with anomalous gluonic contributions, yet a best least $χ^2$ fit to the data implies a gluon spin distribution which violates the positivity condition $|ΔG(x)|\leq G(x)$. We then propose a more realistic set of parton spin distributions with sea polarization and with a moderate value of $ΔG$. The polarized parton distributions in this work are presented in the next-to-leading order of QCD at the scale $Q^2=10\,{\rm GeV}^2\,$. Predictions for the polarized structure functions $g_1^n(x)$ of the neutron and $g_1^d(x)$ of the deuteron are given.

hep-ph↗

arXiv1995

Perturbative QCD study of $B\to D^{(*)}$ decays

We compute various form factors involved in $B\to D^{(*)}$ transitions based on the perturbative QCD formalism, which includes Sudakov effects from the resummation of large radiative corrections in a heavy-light system. A two-parameter model wave function for $D^{(*)}$ mesons is fixed using data of the nonleptonic decays $B\to D^{(*)}π$, from which the ratio of the decay constants $f_{D^*}/f_D=0.92$ is obtained. We then derive the spectrum of the semileptonic decay $B\to D^{*}\ellν$ in the fast recoil region of the $D^*$ meson, and extract the CKM matrix element $|V_{cb}|=0.043\times(0.12 {\rm GeV}/f_B)\times(0.14 {\rm GeV}/f_D)$, $f_B$ and $f_D$ being the $B$ and $D$ meson decay constants, respectively. Here we adopt the convention with the pion decay constant $f_π=93$ MeV. With these outcomes, we evaluate the decay rate of $B\to DD_s$, and estimate the ratio $f_{D_s}/f_D=0.98$ from data. Contributions of internal $W$-emission and $W$-exchange diagrams are briefly discussed.

hep-ph↗

arXiv1995

Structural Aspects of the Proton in the Chiral Quark Model

We calculate with chiral symmetry the parton contents of the proton based on a two-component wave function. The calculation results give significant sea-quark contents and, especially, the intrinsic gluon polarization produced at a more fundamental level.

hep-ph↗

arXiv1994

Spin Structure of the Proton

By assuming that there is no significant intrinsic polarization of the gluon, we have computed the polarized quark contributions to the proton's spin under SU(3) flavor symmetry breaking for the polarized sea and have performed a global leading-order QCD fit to obtain the spin-dependent quark distributions, which could be used as input for analyzing lepton-hadron and hadron-hadron collisions.

hep-ph↗