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Exclusive proton-antiproton annihilation into two photons at large s ( approximately 10 GeV2) and /t/,/u/ approximately s can be described by a generalized parton picture analogous to the "soft mechanism" in wide-angle real Compton scattering. The two photons are emitted in the annihilation of a single fast quark and antiquark. The matrix element describing the transition of the pp system to a qq pair can be related to the timelike proton elastic form factors as well as to the quark/antiquark distributions measured in inclusive deep-inelastic scattering. The reaction could be studied with the proposed 1.5-15 GeV high-luminosity antiproton storage ring (HESR) at GSI. 相似文献
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Within the framework of a holographic dual model of QCD, we develop a formalism for calculating form factors of vector mesons. We show that the holographic bound states can be described not only in terms of eigenfunctions of the equation of motion, but also in terms of conjugate wave functions that are close analogues of quantum-mechanical bound state wave functions. We derive a generalized VMD representation for form factors, and find a very specific VMD pattern, in which form factors are essentially given by contributions due to the first two bound states in the Q2-channel. We calculate electric radius of the ρ-meson, finding the value . 相似文献
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A. V. Radyushkin 《Physics letters. [Part B]》1996,380(3-4):417-425
I outline a perturbative QCD approach to the analysis of the deeply virtual Compton scattering process γ*p → γp′ in the limit of vanishing momentum transfer t = (p′ − p)2. The DVCS amplitude in this limit exhibits a scaling behavior described by two-argument distributions F(x,y) which specify the fractions of the initial momentum p and the momentum transfer r ≡ p′ − p carried by the constituents of the nucleon. The kernel R(x,y;ξ,η) governing the evolution of the non-forward distributions F(x,y) has a remarkable property: it produces the GLAPD evolution kernel P(x/ξ) when integrated over y and reduces to the Brodsky-Lepage evolution kernel V(y,η) after the x-integration. This property is used to construct the solution of the one-loop evolution equation for the flavor non-singlet part of the non-forward quark distribution. 相似文献
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L. Mankiewicz G. Piller A. Radyushkin 《The European Physical Journal C - Particles and Fields》1999,10(2):307-312
We investigate the exclusive electroproduction of mesons from nucleons. To leading-twist, leading-order accuracy, the corresponding production amplitude can be decomposed into pseudovector and pseudoscalar parts. Both can be
expressed in terms of quark double distribution functions of the nucleon. While the pseudovector contribution is connected
to ordinary polarized quark distributions, the pseudoscalar part can be related to one-pion t-channel exchange. We observe that the pseudovector part of the production amplitude is important at . On the other hand, for , contributions from one-pion exchange dominate.
Received: 4 January 1999 / Published online: 15 July 1999 相似文献
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We propose a new method of calculating gluonic power corrections in QCD based on the Schwinger gauge xμAμ(x) = 0. Results of the calculation of the O(mc−6)-correction to the QCD charmonium sum rules are presented and discussed. 相似文献
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R Nirmala V Sankaranarayanan K Sethupathi AV Morozkin T Geethakumary Y Hariharan 《Pramana》2002,58(5-6):1101-1104
New R
2Ti3Ge4 (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac
magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize
in the parent, Sm5Ge4-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series.
The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales
with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays
a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects. 相似文献
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