Browsing by Author "Lin, GL"

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A new look at the pair-production width in a strong magnetic field
(2000-12-07)
Kao, WF
;
Lin, GL
;
Tseng, JJ
;
物理研究所
;
Institute of Physics
We reexamine the process gamma --> e(+) + e(-) in a background magnetic field comparable to B-c equivalent to m(e)(2)/e male. This process is known to be non-perturbative in the magnetic-field strength. However, it can be shown that the moments of the above pair production width are proportional to the derivatives of photon polarization function at the zero energy, which is perturbative in B. Hence, the pair-production width can be easily obtained from the latter by the inverse Mellin transform. The implications of our approach are discussed. (C) 2000 Published by Elsevier Science B.V.
A semi-analytic calculation on the atmospheric tau neutrino flux in the GeV to TeV energy range
(2006-02-01)
Lee, FF
;
Lin, GL
;
物理研究所
;
Institute of Physics
We present a semi-analytic calculation on the atmospheric tau neutrino flux in the GeV to TeV energy range. The atmospheric v, flux is calculated for the entire zenith angle range. This flux is contributed by the oscillations of muon neutrinos coming from the two-body pi and K decays and the three-body mu(+/-) decays, and the intrinsic tau neutrino flux surviving the oscillations. The uncertainties in our calculations are discussed in detail. The implications of our result are also discussed. (c) 2005 Elsevier B.V. All rights reserved.
B -> eta ' X-s in the standard model
(1999-05-13)
He, XG
;
Lin, GL
;
物理研究所
;
Institute of Physics
We study B --> eta'X-s within the framework of the Standard Model. Several mechanisms such as b --> eta'sg through the QCD anomaly, and b --> eta's and B --> eta's (q) over bar arising from four-quark operators are treated simultaneously. Using QCD equations of motion, we relate the effective Hamiltonian for the first mechanism to that for the latter two. By incorporating next-to-leading-logarithmic(NLL) contributions, the first mechanism is shown to give a significant branching ratio for B --> eta'X-s, while the other two mechanisms account for about 15% of the experimental value. The Standard Model prediction for B --> eta'X-s is consistent with the CLEO data. (C) 1999 Elsevier Science B.V. All rights reserved.
Comparison of high-energy galactic and atmospheric tau neutrino flux
(2003-01-01)
Athar, H
;
Cheung, KM
;
Lin, GL
;
Tseng, JJ
;
物理研究所
We compare the tau neutrino flux arising from the galaxy and the earth atmosphere for 10(3) <= E/GeV <= 10(11). The intrinsic and oscillated tau neutrino fluxes from both sources are calculated. The intrinsic galactic v(tau) flux (E >= 10(3) GeV) is calculated by considering the interactions of high-energy cosmic-rays with the matter present in our galaxy, whereas the oscillated galactic v, flux is coming from the oscillation of the galactic v(mu), flux. For the intrinsic atmospheric v, flux, we extend the validity of a previous calculation from E <= 10(6) GeV up to E <= 10(11) GeV. The oscillated atmospheric v, flux is, on the other hand, rather suppressed. We find that, for 10(3) <= E/GeV <= 5.10(7), the oscillated v(tau) flux along the galactic plane dominates over the maximal intrinsic atmospheric v(tau) flux, i.e., the flux along the horizontal direction.
Comparison of high-energy galactic and atmospheric tau neutrino flux
(2003-03-01)
Athar, H
;
Cheung, K
;
Lin, GL
;
Tseng, JJ
;
物理研究所
We compare the tau neutrino flux arising from the galaxy and the earth atmosphere for 10(3) less than or equal to E/GeV less than or equal to 10(11). The intrinsic and oscillated tau neutrino fluxes from both sources are calculated. The intrinsic galactic nu(tau) flux (E greater than or equal to 10(3) GeV) is calculated by considering the interactions of high-energy cosmic-rays with the matter present in our galaxy, whereas the oscillated galactic nu(tau) flux is coming from the oscillation of the galactic nu(mu) flux. For the intrinsic atmospheric nu(tau) flux, we extend the validity of a previous calculation from E less than or equal to 10(6) GeV up to E less than or equal to 10(11) GeV. The oscillated atmospheric nu(tau) flux is, on the other hand, rather suppressed. We find that, for 10(3) less than or equal to E/GeV less than or equal to 5 x 10(7), the oscillated nu(tau) flux along the galactic plane dominates over the maximal intrinsic atmospheric nu(tau) flux, i.e., the flux along the horizontal direction. We also briefly mention the presently envisaged prospects for observing these high-energy tau neutrinos. (C) 2002 Elsevier Science B.V. All rights reserved.
Detecting earth-skimming and mountain-penetrating tau neutrinos
(2005-02-01)
Lin, GL
;
物理研究所
;
Institute of Physics
In this talk, we discuss issues relevant to the detections of Earth-skimming/mountain-penetrating tau neutrinos. We first argue that there are non-negligible astrophysical tau neutrino fluxes due to neutrino flavor oscillations. We then discuss the rationale for detecting Earth-skimming and mountain-penetrating tau neutrinos. The nu(tau) --> tau conversion efficiencies and the tau-lepton event rate are presented.
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.
Flavor-changing neutral Higgs boson couplings and top-quark-charm-quark production at the Next Linear Collider
(1997-12-01)
Hou, WS
;
Lin, GL
;
Ma, CY
;
電子物理學系
;
物理研究所
We explore the possibility of detecting flavor-changing neutral Higgs boson couplings at the Next Linear Collider (NLC) through e(+)e(-)->nu(e)<(nu)over bar>(e)t (c) over bar. In the framework of a general two-Higgs-doublet model, we perform a complete calculation and find that sigma(e(+)e(-)-->nu(e) nu(e)t (c) over bar nu(e)<(nu)over bar>(e) (t) over bar c) could reach similar to 9 fb for root s=2 TeV. This amounts to an annual production of 500 t (c) over bar plus (t) over bar c pairs at the NLC with an integrated luminosity of 50 fb(-1). The dependence of the tc-production rate on the neutral scalar mixing angle is mild except when sin(2) alpha-->0 or 1. The nu nu W+W- background should be manageable after b tagging, while vvt (t) over bar background should not be a problem when the signal event rate is still interesting. The process, together with e(+)e(-)-->nu(e)<(nu(e))over bar>W+W-,nu(e)<(nu(e))over bar>ZZ studies, offer the chance of measuring the t-c-Higgs-bsson coupling.
Flavor-changing neutral Higgs boson couplings and top-quark-charm-quark production at the Next Linear Collider
(1997-12-01)
Hou, WS
;
Lin, GL
;
Ma, CY
;
電子物理學系
;
物理研究所
We explore the possibility of detecting flavor-changing neutral Higgs boson couplings at the Next Linear Collider (NLC) through e(+)e(-)->nu(e)<(nu)over bar>(e)t (c) over bar. In the framework of a general two-Higgs-doublet model, we perform a complete calculation and find that sigma(e(+)e(-)-->nu(e) nu(e)t (c) over bar nu(e)<(nu)over bar>(e) (t) over bar c) could reach similar to 9 fb for root s=2 TeV. This amounts to an annual production of 500 t (c) over bar plus (t) over bar c pairs at the NLC with an integrated luminosity of 50 fb(-1). The dependence of the tc-production rate on the neutral scalar mixing angle is mild except when sin(2) alpha-->0 or 1. The nu nu W+W- background should be manageable after b tagging, while vvt (t) over bar background should not be a problem when the signal event rate is still interesting. The process, together with e(+)e(-)-->nu(e)<(nu(e))over bar>W+W-,nu(e)<(nu(e))over bar>ZZ studies, offer the chance of measuring the t-c-Higgs-bsson coupling.
Gauge independent effective potential and the Higgs boson mass bound
(1999-07-01)
Lin, GL
;
Chyi, TK
;
物理研究所
;
Institute of Physics
We introduce the Vilkovisky-DeWitt formalism for deriving the lower bound of the Higgs boson mass. We illustrate the formalism with a simplified version of the standard electroweak model, where all charged boson fields as well as the bottom-quark field are disregarded. The effective potential obtained in this approach is gauge independent. We derive from the effective potential the mass bound of the Higgs boson. The result is compared to its counterpart obtained from the ordinary effective potential. [S0556-2821(99)06211-6].
Heavy quark effective theory on the light front
(1996-07-20)
Zhang, WM
;
Cheung, CY
;
Lin, GL
;
物理研究所
;
Institute of Physics
The light front heavy quark effective theory is derived to all orders in 1/m(Q). In the limit m(Q)-->infinity, the theory exhibits the familiar heavy quark spin-flavor symmetry. This new formalism permits a straightforward canonical quantization to all orders in 1/m(Q); moreover, higher order terms have rather simple operator structures. The light front heavy quark effective theory can serve as a useful framework for the study of nonperturbative QCD dynamics of heavy hadron bound states.
Heavy quark effective theory on the light front
(1996-07-20)
Zhang, WM
;
Cheung, CY
;
Lin, GL
;
物理研究所
;
Institute of Physics
The light front heavy quark effective theory is derived to all orders in 1/m(Q). In the limit m(Q)-->infinity, the theory exhibits the familiar heavy quark spin-flavor symmetry. This new formalism permits a straightforward canonical quantization to all orders in 1/m(Q); moreover, higher order terms have rather simple operator structures. The light front heavy quark effective theory can serve as a useful framework for the study of nonperturbative QCD dynamics of heavy hadron bound states.
Like sign top pair production at LHC
(1997)
Lin, GL
;
物理研究所
;
Institute of Physics
Having a mass comparable to the weak scale, the top quark may have a sizable flavor changing couplings to Higgs bosons. We show that such couplings can be probed at the LHC through the parton subprocess c((c) over bar)g --> t((t) over bar)A(0), where the pseudoscalar A(0) subsequently decays into t (c) over bar or (t) over bar c, giving rise to the intriguing final state of like sign top quark pairs. We also discuss major backgrounds to the above signal, in particular the QCD-Weak process q (q) over bar' --> W+(W-)t (t) over bar. The issue of background reduction is briefly discussed.
Like sign top quark pair production at linear colliders
(1996-06-27)
Hou, WS
;
Lin, GL
;
物理研究所
;
Institute of Physics
In the general two Higgs doublet model with flavor changing neutral Higgs couplings, neutral Higgs bosons may decay dominantly via or <(t)over bar c> final states. At the linear collider, e(+)e(-) --> h(0)A(0) or H(0)A(0) production processes may result in , W+W- t (c) over bar or tt (c) over bar (c) over bar (or (t) over bar (t) over bar cc) final states. The process yy --> h(0), A(0) --> t (c) over bar is also promising, but e(+)e(-) --> (h(0), H-0)Z(0) --> is relatively suppressed. The possibility of observing like sign lepton pairs, usually the hallmark for neutral meson mixing, is quite interesting since T-0 mesons do not even form.
Muon pair production by electron-photon scatterings
(2001-10-01)
Athar, H
;
Lin, GL
;
Tseng, JL
;
物理研究所
;
Institute of Physics
The cross section for muon pair productions by electrons scattering over photons, sigma (MPP), is calculated analytically in the leading order. It is pointed out that for the center-of-mass energy range s greater than or equal to 5m(mu)(2), the cross section sigma (MPP) is less than 1 mub. The differential energy spectrum for either of the resulting muons is given for the purpose of high-energy neutrino astronomy. An implication of our result for a recent suggestion concerning the high-energy cosmic neutrino generation through this muon pair is discussed.
Neutrino-photon scattering and its crossed processes in a background magnetic field
(1999-11-04)
Chyi, TK
;
Hwang, CW
;
Kao, WF
;
Lin, GL
;
Ng, KW
We study the neutrino-photon processes such as gamma gamma --> , v gamma --> v gamma, and --> gamma gamma in a background magnetic field smaller than the critical magnetic field Bc + m(e)(2)/e. Using Schwinger's formalism, we extract leading magnetic-field contributions to the above processes. Our result is valid throughout the kinematic regime where both neutrino and photon energies are significantly smaller than m(w). We briefly discuss the astrophysical implications of our result. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
On analytic properties of the photon polarization function in a background magnetic field
(2001-12-13)
Kao, WF
;
Lin, GL
;
Tseng, JJ
;
物理研究所
;
Institute of Physics
We examine the analytic properties of the photon polarization function in a background magnetic field, using the technique of inverse Mellin transform. The photon polarization function is first expressed as a power series of the photon energy omega with omega < 2m(e). Based upon this energy expansion and the branch cut of the photon polarization function in the complex omega plane. we compute the absorptive part of the polarization function with the inverse Mellin transform. Our results are valid for arbitrary photon energies and magnetic-fieid strengths. The applications of our approach are briefly discussed. (C) 2001 Published by Elsevier Science B.V.
On analytic properties of the photon polarization function in a background magnetic field (vol B 522, pg 257, 2001)
(2002-08-15)
Kao, WF
;
Lin, GL
;
Tseng, HJ
;
物理研究所
;
Institute of Physics
On possibility of the tau neutrino astronomy in GeV energies
(2005-06-01)
Athar, H
;
Lee, FF
;
Lin, GL
;
物理研究所
;
Institute of Physics
We discuss the possibility of searching the galactic-plane tau neutrinos in GeV energies.
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].