Browsing by Author "Li, HN"

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A modified BFKL equation with Q dependence
(1999-06-01)
Lim, JL
;
Li, HN
;
電子物理學系
;
Department of Electrophysics
We propose a modified Balitsky-Fadin-Kuraev-Lipatov (BFKL) equation for the summation of large ln(1/x), x being the Bjorken variable, which contains an extra dependence on the momentum transfer Q compared to the conventional BFKL equation. This Q dependence comes from the phase space constraint for soft real gluon emissions in the derivation of the BFKL kernel. The modified equation gives a slower rise of the gluon distribution function with 1/x for smaller Q, such that the predictions for the structure functions F-2,F-L(x, Q(2)) involved in deep inelastic scattering match the HERA data. These results are similar to those obtained from the Ciafaloni-Catani-Fiorani-Marchesini equation, which embodies both the ln Q and 1a(1/x) summations. The reason that the conventional BFKL equation can not be applied to the low Q (soft pomeron dominant) region is given.
New unified evolution equation
(2000-08-01)
Lim, JL
;
Li, HN
;
電子物理學系
;
Department of Electrophysics
We propose a new unified evolution equation for parton distribution functions appropriate for both large and small Bjorken variables x, which is an improved version of the Ciafaloni-Catani-Fiorani-Marchesini equation. In this new equation the cancellation of soft divergences between virtual and real gluon emissions is explicit without introducing infrared cutoffs and next-to-leading contributions to the Sudakov resummation can be included systematically. It is shown that the new equation reduces to the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi equation at large x, to the Balitsky-Fadin-Kuraev-Lipatov (BFKL) equation at small x, and to the modified BFKL equation with a dependence on momentum transfer Q, if hard virtual gluon contributions are retained.
Perturbative QCD study of the B -> K* gamma decay
(1999-09-01)
Li, HN
;
Lin, GL
;
物理研究所
;
Institute of Physics
We apply the perturbative QCD factorization theorem developed recently for nonleptonic heavy meson decays to the radiative decay B-->K* gamma. In this formalism the evolution of the Wilson coefficients from the W boson mass down to the characteristic scale of the decay process is governed by the effective weak Hamiltonian. The evolution from the characteristic scale to a lower hadronic scale is formulated by the Sudakov resummation. In addition to computing the dominant contribution arising from the magnetic-penguin operator O-7. We also calculate the contributions of four-quark operators. By fitting our prediction for the branching ratio of the B-->K* gamma decay to the CLEO data, we determine the B meson wave function that possesses a sharp peak at a low momentum fraction. [S0556-2821(99)01015-2].