共查询到20条相似文献,搜索用时 156 毫秒
1.
Using the asymptotic conformal invariance of perturbative QCD we derive the expression of the coupling of external states
to all conformal spin p components of the forward elastic amplitude. Using the wave function formalism for structure functions at small x, we derive the perturbative coupling of the virtual photon for , which is maximal for linear transverse polarization. The non-perturbative coupling to the proton is discussed in terms of
“azimuthal matching” between the proton color dipoles and the configurations of the photon. As an application, the recent conjecture of a second QCD pomeron related to the conformal spin-1
component is shown to rely upon a strong azimuthal matching of the component in –proton scattering.
Received: 25 October 1999 / Revised version: 19 January 2000 / Published online: 14 April 2000 相似文献
2.
N.G. Stefanis W. Schroers H.-Ch. Kim 《The European Physical Journal C - Particles and Fields》2000,18(1):137-156
We develop and discuss in technical detail an infrared-finite factorization and optimized renormalization scheme for calculating
exclusive processes, which enables the inclusion of transverse degrees of freedom without entailing suppression of calculated
observables, like form factors. This is achieved by employing an analytic, i.e., infrared stable, running strong-coupling
which removes the Landau singularity at by a minimum power-behaved correction. The ensuing contributions to the cusp anomalous dimension – related to the Sudakov
form factor – and to the quark anomalous dimension – which controls evolution – lead to an enhancement at high of the hard part of exclusive amplitudes, calculated in perturbative QCD, while simultaneously improving its scaling behavior.
The phenomenological implications of this framework are analyzed by applying it to the pion's electromagnetic form factor,
including the NLO contribution to the hard-scattering amplitude, and also to the pion–photon transition at LO. For the pion
wave function, an improved ansatz of the Brodsky–Huang–Lepage type is employed, which includes an effective (constituent-like)
quark mass, GeV. Predictions for both form factors are presented and compared to the experimental data, applying Brodsky–Lepage–Mackenzie
commensurate scale setting. We find that the perturbative hard part prevails at momentum transfers above about 20 GeV, while at lower values the pion form factor is dominated by Feynman-type contributions. The theoretical prediction for the form factor indicates that the true pion distribution amplitude may be somewhat broader than the asymptotic one.
Received: 19 May 2000 / Revised version: 16 August 2000 / Published online: 13 November 2000 相似文献
3.
E. Basso M. B. Gay Ducati E. G. de Oliveira J. T. de Santana Amaral 《The European Physical Journal C - Particles and Fields》2008,58(1):9-15
Among the dipole models of deep inelastic scattering at small values of the Bjorken variable x, one has been recently proposed which relates the virtual photon–proton cross section to the dipole–proton forward scattering
amplitude in momentum space. The latter is parametrized by an expression which interpolates between its behavior at saturation
and the travelling wave, ultraviolet, amplitudes predicted by perturbative QCD from the Balitsky–Kovchegov equation. Inspired
by recent developments in coordinate space, we use this model to parametrize the structure function of the proton and confront
it with HERA data on ep deep inelastic scattering. Both event-by-event and physical amplitudes are considered, the latter being used to investigate
the effect of gluon number fluctuations, beyond the mean-field approximation. We conclude that fluctuations are not present
in DIS at HERA energies. 相似文献
4.
5.
We extract the B, D, and meson wave functions from the CLEO data of the decays and in the perturbative QCD framework. In this formalism, various logarithmic corrections are organized to give the Wilson evolution
from the W boson mass down to the characteristic scale of a decay process, which is of order of the b quark mass, and the Sudakov evolution from the characteristic scale to a lower factorization scale of order . With large logarithms organized, the b quark decay amplitudes are evaluated reliably in perturbation theory. Below the factorization scale, QCD dynamics is regarded
as being nonperturbative, and absorbed into meson wave functions. Because of their universality, the heavy-meson wave functions
determined in this work, can be employed to make predictions of other decay modes. We also observe that the dependence of
heavy meson wave functions on intrinsic parton transverse momenta plays an important role in the explanation of data.
Received: 18 February 1999 / Revised version: 24 June 1999 / Published online: 3 November 1999 相似文献
6.
Jiunn-Wei Chen Hiroaki Kohyama Kazuaki Ohnishi Udit Raha Yue-Long Shen 《Physics letters. [Part B]》2010
We present a combined analysis of the space- and time-like electromagnetic pion form factors in light-cone perturbative QCD with transverse momentum dependence and Sudakov suppression. Including the genuine non-perturbative “soft” QCD and the power suppressed twist-3 corrections to the standard twist-2 perturbative QCD result, the experimental form factor data available at moderate energies/momentum transfers can be explained reasonably well. To this end, the bulk of the existing discrepancy between the space- and time-like experimental data is ostensibly reconciled. 相似文献
7.
We calculate the , (P is the light pseudoscalar meson, V the light vector meson) form factors in the large-recoil limit in the perturbative QCD approach, including both the vector
(axial vector) and tensor operators. In general there are two leading components and for the B meson wave functions. We consider both contributions of them. Sudakov effects ( and threshold resummation) are included to regulate the soft end-point singularity. By choosing the hard scale as the maximum
virtualities of the internal particles in the hard b quark decay amplitudes, Sudakov factors can effectively suppress the long-distance soft contribution. The hard contribution
can be dominant in these approaches.
Received: 27 December 2002 / Published online: 5 May 2003
RID="a"
ID="a" e-mail: lucd@mail.ihep.ac.cn
RID="b"
ID="b" e-mail: yangmz@mail.ihep.ac.cn 相似文献
8.
We obtain perturbative expressions for jet distributions using soft-collinear effective theory (SCET). By matching SCET onto QCD at high energy, tree level matrix elements and higher order virtual corrections can be reproduced in SCET. The resulting operators are then evolved to lower scales, with additional operators being populated by required threshold matchings in the effective theory. We show that the renormalization group evolution and threshold matchings reproduce the Sudakov factors and splitting functions of QCD, and that the effective theory naturally combines QCD matrix elements and parton showers. The effective theory calculation is systematically improvable and any higher order perturbative effects can be included by a well-defined procedure. 相似文献
9.
We derive a full set, and determine the twist, of helicity amplitudes for diffractive production of light to heavy vector
mesons in deep inelastic scattering. For large Q
2 all helicity amplitudes but the double-flip are calculable in perturbative QCD and are proportional to the gluon structure
function of the proton at a similar hardness scale. We find a substantial breaking of the s-channel helicity conservation, which must persist in real photoproduction also.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 9, 667–673 (10 November 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
10.
A.L. Ayala Filho M.B. Gay Ducati E.M. Levin 《The European Physical Journal C - Particles and Fields》1999,8(1):115-120
We study the value of shadowing corrections (SC) in the HERA kinematic region in the Glauber–Mueller approach. Since the
Glauber–Mueller approach was proven in perturbative quantum chromodynamics (QCD) in the double-logarithmic approximation (DLA),
we develop the DLA approach for the deep inelastic structure function which takes into account the SC. Our estimates show
small SC for in the HERA kinematic region while they turn out to be sizable for the gluon structure function. We compare our estimates
with those for gluon distribution in leading order (LO) and next to leading order (NLO) in the DGLAP evolution equations.
Received: 21 September 1998 /Published online: 14 January 1999 相似文献
11.
12.
C.-D. Lü 《The European Physical Journal C - Particles and Fields》2002,24(1):121-126
The rare decay can occur only via annihilation-type diagrams in the standard model. We calculated this decay in the perturbative QCD approach
with Sudakov resummation. We found that the branching ratio of is of order ; this may be measured in the near future by the KEK and SLAC B factories. The small branching ratio predicted in the standard model makes this channel sensitive to new physics contributions.
Received: 16 January 2002 / Published online: 5 April 2002 相似文献
13.
The possibilities to determine the flavor structure of the polarized sea (antiquark) distributions of the nucleon via vector
boson production at high energy polarized hadron–hadron colliders, such as the Relativistic Heavy–Ion Collider (RHIC), are studied
in detail. In particular the perturbative stability of the expected asymmetries in two representative models for the (un)broken
flavor structure are investigated by confronting perturbative QCD leading order predictions of the expected asymmetries with
their next–to–leading order counterparts.
Received: 28 November 2000 / Published online: 5 February 2001 相似文献
14.
《Nuclear Physics B》1995,456(3):497-530
Using a recent calculation of the perturbative hard part for dilepton production that sums large threshold corrections to all orders in perturbative QCD, we compute the corresponding cross sections. The hard part has been evaluated using principal value resummation and contains all singular momentum-dependent corrections. We also include a resummation of large Sudakov terms, which are independent of parton momenta. We give predictions for the dilepton-mass distribution, the rapidity distribution and the rapidity-integrated K-factor at fixed-target energies and compare with various experimental results in several kinematic regimes. We find that principal value resummation produces cross sections that are finite and well-behaved. For both protons and anti-protons on fixed targets, the resummed cross sections are, in general, in excellent agreement with the data. 相似文献
15.
We study the possible effect of QCD in the proton wave function in a quark model for inclusive processesA+B→C+X pursued by us. The assumption is the validity of the conjecture of Lepage and Brodsky in QCD on such effects. Our results
obey the perturbative expectation, |R
g
tan2
φ|<1. Symmetric version of the model is, however, found to be at variance with most of the inclusive data as well as with some
known phenomenology. If the dynamics of the underlying theory generate Regge-like symmetry breaking approximately, the model
is phenomenologically viable, and the non-leading QCD effects become reasonable in size. Phenomenological necessity of the
admixtures of (56, 0+)*, (70, 0+) and (56, 2+) in the nucleon wave function is also discussed in the present analysis. 相似文献
16.
N.N. Nikolaev J. Speth V.R. Zoller 《The European Physical Journal C - Particles and Fields》2002,22(4):637-646
High-energy virtual photon–virtual photon scattering can be viewed as an interaction of small size color dipoles from the
beam and target photons, which makes scattering at high energies (LEP, LEP200 and NLC) an indispensable probe of the short distance properties of the QCD pomeron
exchange. Based on the color dipole representation, we investigate the consequences for the scattering of the incorporation of asymptotic freedom into the BFKL equation which makes the QCD pomeron a series of isolated
poles in the angular momentum plane. The emerging color dipole BFKL–Regge factorization allows us to relate in a model-independent
way the contributions of each BFKL pole to scattering and DIS off protons. Numerical predictions based on our early works on the color dipole BFKL phenomenology of
DIS on protons are in good agreement with the experimental data on the photon structure function and the most recent data on the cross section from the OPAL and L3 experiments at LEP200. We discuss the role of non-perturbative dynamics and predict a pronounced effect
of the Regge-factorization breaking due to large unfactorizable non-perturbative corrections to the perturbative vacuum exchange.
We comment on the salient features of the BFKL–Regge expansion for scattering including the issue of the decoupling of subleading BFKL poles and the soft plus rightmost hard BFKL pole dominance.
Received: 9 January 2001 / Revised version: 25 September 2001 / Published online: 7 December 2001 相似文献
17.
P. Aurenche Rahul Basu M. Fontannaz 《The European Physical Journal C - Particles and Fields》2008,57(4):681-688
We discuss, in the framework of perturbative QCD at next to leading order, two related observables which are usually considered
to provide tests of the BFKL dynamics: jet–jet correlations at Tevatron energies and forward particle–jet correlations at
HERA. In the first case we study the rapidity gap dependence of the azimuthal correlations and find slightly too strong correlations
at large gap. In the second case we discuss the cross section as well as the azimuthal correlations over a rapidity gap range
of 5 units. We find that the requirement of a forward particle imposes strong kinematical constraints which distort the distributions,
notably at small rapidity gaps. We also show that the decorrelation is stronger in electroproduction than in hadron–hadron
collisions. Unfortunately data are not yet available for comparison. 相似文献
18.
Ji-huan PAN 《Frontiers of Physics》2009,4(4):534
Based on the generalized vector meson dominance model in QCD, we study the photoproduction of vector meson Υ off the proton by use of the QCD-inspired model in which the contributions from quark–quark, gluon–gluon and quark–gluon interference term to observable are taken into consideration. Calculations are performed for total cross section σtot, differential cross section dσ/dt, ratio of the real part to imaginary part of forward scattering amplitude ρ and nuclear slop parameter function β. We analyze the individual contributions from quark gluon degrees of freedom and the QCD Odderon to the total cross section σtot (s), differential cross section dσ/dt, ratio of the real part to imaginary part of the forward scattering amplitude ρ, and nuclear slop parameter function β. The mediators of interactions between projectiles (the quark and antiquark pair fluctuated from the real photon) and the proton target (three quark system) are the tensor Glueball and Odderon instead of using the usual Pomeron exchange. The theoretical predictions for σtot(s) are consistent with the experimental data within error bars of the data. The data for dσ/dt, β and ρ are urgently needed. The gluon–gluon interaction makes a significant contribution to the observables while the Odderon contribution is negligibly small. Therefore, we may conclude that it is impossible to find the QCD Odderon in the γ+p→Υ+p process as suggested before. 相似文献
19.
C. Adloff et al. 《The European Physical Journal C - Particles and Fields》2001,19(2):289-311
Jet production is studied in the Breit frame in deep-inelastic positron-proton scattering over a large range of four-momentum transfers and transverse jet energies GeV. The analysis is based on data corresponding to an integrated luminosity of taken in the years 1995–1997 with the H1 detector at HERA at a center-of-mass energy GeV. Dijet and inclusive jet cross sections are measured multi-differentially using and angular ordered jet algorithms. The results are compared to the predictions of perturbative QCD calculations in next-to-leading order in the strong coupling constant . QCD fits are performed in which and the gluon density in the proton are determined separately. The gluon density is found to be in good agreement with results obtained in other analyses using data from different processes. The strong coupling constant is determined to be . In addition an analysis of the data in which both and the gluon density are determined simultaneously is presented. 相似文献
20.
Measurements of at low x and low are expected to provide a sensitive probe of the transition from Regge to perturbative QCD dynamics, offering a new testing
ground for models of small x physics. We discuss the potential of polarized ep colliders (Polarized HERA and eRHIC) to investigate this physics – varying between 0.01 and 1 GeV– and to constrain the high-energy part of the Drell-Hearn-Gerasimov sum-rule for polarized photoproduction.
Received: 28 August 2000 / Revised version: 9 November 2000 / Published online: 21 December 2000 相似文献