Browsing by Author "Yeh, TW"

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Applicability of perturbative QCD and NLO power corrections for the pion form factor
(2002-04-01)
Yeh, TW
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物理研究所
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Institute of Physics
As is well recognized, the asymptotic of the perturbative QCD prediction for the pion form factor is much smaller than the upper end of the data. We investigate this problem. We first evaluate the next-to-leading-order (NLO) power correction for the pion form factor. The corrected form factor contains nonperturbative parameters which are determined from a chi(2) fit to the data. Interpreting these parameters leads to the fact that the involved strong interaction coupling constant should be identified as an effective coupling constant under a nonperturbative QCD vacuum. If the scale associated with the effective coupling constant is identified as (2)Q(2), then Q(2), the momentum transfer square for the pion form factor to be measured, can have a value about 1 GeV2, and , the averaged momentum fraction variable, can locate around 0.5. This circumstance is consistent with the asymptotic model for the pion wave function.
Energy spectrum of tau leptons induced by the high energy Earth-skimming neutrinos
(2003-09-15)
Tseng, JJ
;
Yeh, TW
;
Athar, H
;
Huang, MA
;
Lee, FF
We present a semianalytic calculation of the tau-lepton flux emerging from the Earth induced by incident high energy neutrinos interacting inside the Earth for 10(5)less than or equal toE(nu)/GeVless than or equal to10(10). We obtain results for the energy dependence of the tau-lepton flux coming from the Earth-skimming neutrinos, because of the neutrino-nucleon charged-current scattering as well as the resonant (nu) over bar (e)e(-) scattering. We illustrate our results for several anticipated high energy astrophysical neutrino sources such as the active galactic nuclei, the gamma-ray bursts, and the Greisen-Zatsepin-Kuzmin neutrino fluxes. The tau-lepton fluxes resulting from rock-skimming and ocean-skimming neutrinos are compared. Such comparisons can render useful information about the spectral indices of incident neutrino fluxes.
eta-eta ' mixing and the next-to-leading-order power correction
(2002-05-01)
Yeh, TW
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物理研究所
;
Institute of Physics
The next-to-leading-order O(1/Q(4)) power corrections for etagamma and eta(')gamma form factors are evaluated and employed to explore the eta-eta(') mixing. The parameters of the two-mixing-angle scheme are extracted from the data for form factors, two-photon decay widths, and radiative J/psi decays. The chi(2) analysis gives the result f(eta1)=(1.16+/-0.06)f(pi),f(eta8)=(1.33+/-0.23)f(pi),theta(1)=-9degrees+/-3degrees,theta(8)=-21.3degrees+/-2.3degrees, where f(eta1(8)) and theta(1(8)) are the decay constants and the mixing angles for the singlet (octet) state. In addition, we arrive at a stringent range for f(eta)('c):-10 MeVless than or equal tof(eta)('c)less than or equal to-4 MeV.
Next-to-leading-order power correction to photon-pion transition form factor
(2002-07-01)
Yeh, TW
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物理研究所
;
Institute of Physics
We propose an approach to calculate the next-to-leading-order power corrections to the photon-pion transition form factor F-pigamma(Q(2)). The effects of the next-to-leading-order power corrections are analyzed.
Polarization and distribution function of the Lambda(b) baryon
(2002-08-01)
Yeh, TW
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物理研究所
;
Institute of Physics
The polarization of the Lambda(b) baryon has been measured in ALEPH, OPAL, and DELPHI experiments. A significant loss on the transfer of the b quark polarization to the Lambda(b) baryon polarization has been noticed. This implies that the hadronization effects cannot be neglected. Therefore we may make use of the polarization measurements to look for a suitable model for the Lambda(b) distribution function. To investigate the Lambda(b) polarization, we construct four models based on a perturbative QCD factorization formula. The models are the quark model, the modified quark model, the parton model, and the modified parton model. The modified models mean the models having transverse degrees of freedom and the associated soft radiative corrections having been resummed. The quark and parton models cannot describe all experiments at the same time. On the other hand, the modified models can have the power to explain all data in the same formalism.
PQCD analysis of atmospheric tau neutrino
(2003)
Yeh, TW
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物理研究所
;
Institute of Physics
We calculate the flux of v, produced in the atmosphere by cosmic ray-air collisions. The production channels of v, from the process pA -> X -> v(T)((v) over bar (T))Y with X = D-s W-+/-, Z, h(b), t (t) over bar, are considered. The calculations are performed by employing perturbative QCD (PQCD). The predicted v(T) flux phi v(T)(E) is given for energy range 10(3)GeV <= E <= 10(8)GeV.
Revisited reparameterization invariance of HQET
(2003-08-01)
Yeh, TW
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物理研究所
;
Institute of Physics
The heavy quark effective theory is invariant under reparameterization. The specific form of the reparameterization transformation is not unique; and it is closely related to the effective theory. The theory invariant under Luke and Manohar's reparameterization transformation is derived.