共查询到20条相似文献,搜索用时 15 毫秒
1.
Estimates for electroproduction of pseudoscalar mesons at small values of skewness are presented. Cross-sections and asymmetries
for these processes are calculated within the handbag approach which is based on factorization in hard parton subprocesses
and soft generalized parton distributions (GPDs). The latter are constructed from double distributions. Transversity GPDs
are taken into account; they are accompanied by twist-3 meson wave functions. For most pseudoscalar-meson channels a combination
of ˜T and [`(E)]T \bar{{E}}_{T}^{} plays a particularly prominent role. This combination of GPDs, which we constrain by moments obtained from lattice QCD, leads,
with the exception of the p+ \pi^{+}_{} and h¢ \eta^{\prime}_{} channels, to large transverse cross-sections. 相似文献
2.
3.
F. Caporale A. Papa A. Sabio Vera 《The European Physical Journal C - Particles and Fields》2008,53(4):525-532
The use of the BFKL kernel improved by the inclusion of subleading terms generated by renormalization group (RG) analysis
has been suggested to cure the instabilities in the behavior of the BFKL Green’s function in the next-to-leading approximation
(NLA). We test the performance of a RG-improved kernel in the determination of the amplitude of a physical process, the electroproduction
of two light vector mesons, in the BFKL approach in the NLA. We find that a smooth behavior of the amplitude with the center-of-mass
energy can be achieved, setting the renormalization and energy scales appearing in the subleading terms to values much closer
to the kinematical scales of the process than in the approaches based on the unimproved kernel. 相似文献
4.
The large t behavior of the helicity amplitudes of diffractive photoproduction is estimated relying on models of the photon and meson light-cone wave functions and on the double-logarithmic approximation to the exchanged gluon interaction. The role of large-size color dipole contributions to the photon-meson transition impact factor is discussed.Received: 17 November 2003, Revised: 10 March 2004, Published online: 23 June 2004A. Ivanov: Corresponding author. 相似文献
5.
M. Battaglieri 《Acta Physica Hungarica A》2002,16(1-4):193-202
The total and differential cross section for exclusive electro- and photoproduction of vector mesons in the resonance region and above (1.6 < W < 2.9 GeV) was measured at Jefferson Laboratory in a wide kinematic range (0 < Q 2 < 4 GeV2 and 0 < —t < 5 GeV2). The measurement of the total and differential cross section down to 100 pb/GeV2 with the full kinematic coverage, was possible for the first time thanks to the combination of the 100% duty cycle of CEBAF and the large acceptance of the CLAS detector. The main results from the CLAS Collaboration activity in this field will be presented and discussed. 相似文献
6.
We discuss various aspects of vector meson production, first analysing the interplay between perturbative and nonperturbative
aspects of the QCD calculation. Using a general method adapted to incorporate both perturbative and nonperturbative aspects,
we show that nonperturbative effects are important for all experimentally available values of the photon virtuality Q2. We compare the huge amount of experimental information now available with our theoretical results obtained using a specific
nonperturbative model without free parameters, showing that quite simple features are able to explain the data. 相似文献
7.
Photoproduction ofρ andω mesons on nucleons is considered in the peripheral model. The interaction mechanism is assumed to be pseudoscalar and scalar exchange. Absorptive final-state interactions are taken into account. The differential cross section and the angular distribution for the decay are calculated and compared with experimental data. 相似文献
8.
Virtual radiative corrections due to the long-range Coulomb forces of heavy nuclei with charge Z may lead to sizeable corrections to the Born cross-section usually used for lepton-nucleus scattering processes. An introduction and presentation of the most important issues of the eikonal approximation is given. We present calculations for forward electroproduction of rho-mesons in a framework suggested by the VDM (vector dominance model), using the eikonal approximation. It turns out that Coulomb corrections may become relatively large. Some minor errors in the literature are corrected.Received: 3 October 2003, Revised: 2 December 2003, Published online: 6 July 2004PACS:
25.30.-c Lepton-induced reactions - 25.30.Rw Electroproduction reactions - 13.40.-f Electromagnetic processes and properties - 25.30.Bf Elastic electron scattering 相似文献
9.
R. M. Davidson 《Czechoslovak Journal of Physics》1994,44(4-5):365-403
The lecture provides an elementary introduction to photo and electroproduction of pseudoscalar mesons in the resonance region. After discussing the general structure of the elementary production amplitude and its symmetry properties the formalism is applied to some interesting physical problems.Lecture presented at the Indian-Summer School on Interaction in Hadronic Systems, Praha (The Czech Republic), 25–31 August 1993.I would like to thank the organizers of the school for the invitation and congratulate them on the success of the school. This work was supported by the Deutsche Forschungsgemeinschaft (SFB 201). 相似文献
10.
V.A. Korotkov W.-D. Nowak K.A. Oganessyan 《The European Physical Journal C - Particles and Fields》2001,18(4):639-644
A method is discussed to determine the hitherto unknown u-quark transversity distribution from a planned HERMES measurement of a single target-spin asymmetry in semi-inclusive pion electroproduction off a transversely
polarized target. Assuming u-quark dominance, the measurement yields the shapes of the transversity distribution and of the ratio , of polarized and unpolarized u-quark fragmentation functions. The unknown relative normalization can be obtained by identifying the transversity distribution
with the well-known helicity distribution at large x and small . The systematic uncertainty of the method is dominated by the assumption of u-quark dominance.
Received: 18 June 2000 / Revised version: 20 November 2000 / Published online: 5 February 2001 相似文献
11.
Eta photo- and electroproduction off the nucleon is investigated in an effective lagrangian approach that contains Born terms and both vector meson and nucleon resonance contributions. In particular, we review and develop the formalism for coincidence experiments with polarization degrees of freedom. The different response functions appearing in single and double polarization experiments have been studied. We will present calculations for structure functions and kinematical conditions that are most sensitive to details of the lagrangian, in particular with regard to contributions of nucleon resonances beyond the dominantS
11(1535) resonance.This work has been supported by the Deutsche Forschungsgemeinschaft (SFB 201) 相似文献
12.
G. Preparata 《Physics letters. [Part B]》1974,49(4):374-376
We discuss the problem of exclusive electroproduction in the framework a massive quark model (MQM). An interesting scaling law for the production of vector mesons is derived and compared with experiments. 相似文献
13.
J. Nemchik N.N. Nikolaev E. Predazzi B.G. Zakharov 《Zeitschrift fur Physik C Particles and Fields》1997,75(1):71-87
We develop the color dipole phenomenology of diffractive photo- and electroproduction γ* N → V(V′)N of light vector mesons (V(1S) = ?0, ω0, ρ0) and their radial excitations (V′(2S) ?′, ω′, ρ′). The node of the radial wave function of the 2S states in conjunction with the energy dependence of the color dipole cross section is shown to lead to a strikingly different Q 2 and ν dependence of diffractive production of the V(1S) and V′(2S) vector mesons. We discuss the restoration of flavor symmetry and universality properties of production of different vector mesons as a function of Q 2 + m V 2 . The color dipole model predictions for the ρ 0 and ? 0 production are in good agreement with the experimental data from the EMC, NMC, ZEUS and H1 collaborations. We present the first direct evaluation of the dipole cross section from these data. 相似文献
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15.
Assuming the proton's light-cone wave function to be dominated by small parton virtualities and small intrinsic transverse
momenta, we show that the electroproduction amplitudes at large momentum transfer factorize into parton-level subprocess amplitudes
and form factors representing 1/x-moments of skewed parton distributions. On the basis of a wave function overlap model for the form factors we present detailed
predictions for the electroproduction cross sections. We also comment on large momentum transfer photoproduction.
Received: 9 June 2000 / Revised version: 27 July 2000 / Published online: 25 September 2000 相似文献
16.
J. Breitweg et al. 《The European Physical Journal C - Particles and Fields》2000,14(2):213-238
Elastic and proton–dissociative photoproduction of , and vector mesons (, , respectively) have been measured in interactions at HERA up to GeV, where t is the four-momentum transfer squared at the photon–vector–meson vertex. The analysis is based on a data sample in which
photoproduction reactions were tagged by detection of the scattered positron in a special-purpose calorimeter. This limits
the photon virtuality, , to values less than 0.01 GeV, and selects a average center-of-mass energy of = 94 GeV. Results for the differential cross sections, , for , and mesons are presented and compared to the results of recent QCD calculations. Results are also presented for the t-dependence of the pion-pair invariant-mass distribution in the mass region and of the spin-density matrix elements determined from the decay-angle distributions. The Pomeron trajectory
has been derived from measurements of the W dependence of the elastic differential cross sections for both and mesons.
Received: 16 October 1999 / Revised version: 17 January 2000 / Published online: 6 April 2000 相似文献
17.
J. Nemchik 《The European Physical Journal C - Particles and Fields》2001,18(4):711-718
Within the color dipole gBFKL phenomenology of the diffraction slope we predict an anomalous t-dependence of the differential cross section as a function of energy and for the production of radially excited light vector mesons. The pattern we found for the t-dependence for is in contradiction with the well-known standard monotonical t-behavior for theV(1S) vector mesons. The origin of this phenomenon lies in the interplay of the nodal structure of the V'(2S) radial wave function and the energy and dipole size dependence of the color dipole cross section and the diffraction slope.
We show how a different position of the node in the V'(2S) wave function leads to a different pattern of anomalous t-behavior of and discuss the possibility to determine this position from the low energy and HERA data.
Received: 5 September 2000 / Revised version: 24 November 2000 / Published online: 23 January 2001 相似文献
18.
On the slope of the differential cross section for the photo- and electroproduction of vector mesons
Victor Snell 《Nuclear Physics B》1974,73(3):497-508
The photo- and electroproduction of ? mesons at high energy is examined in a simple Regge-pole model with q2 dependent residues. The behaviour of the differential cross section at t=0 and of its slope, as a function of the q2 and of the photon energy, are correlated, and good fits to the data are obtained. 相似文献
19.
E.R. Berger A. Donnachie H.G. Dosch W. Kilian O. Nachtmann M. Rueter 《The European Physical Journal C - Particles and Fields》1999,9(3):491-501
We investigate the reaction where PS denotes a pseudoscalar meson , , , or and X either a proton or resonance or continuum state into which the proton can go by diffractive excitation. At high energies
photon and odderon exchange contribute to the reaction. The photon exchange contribution is evaluated exactly using data for
the total virtual photon-proton absorption cross section. The odderon exchange contribution is calculated in nonperturbative
QCD, using functional integral techniques and the model of the stochastic vacuum. For the proton we assume a quark-diquark
structure as suggested by the small odderon amplitude in pp and forward scattering. We show that odderon exchange leads to a much larger inelastic than elastic PS production cross section.
Observation of our reaction at HERA would establish the soft odderon as an exchange object on an equal footing with the soft
pomeron and would give us valuable insight into both the nucleon structure and the mechanism of high energy diffractive scattering.
Received: 2 February 1999 / Revised version: 22 March 1999 / Published online: 28 May 1999 相似文献
20.
On the basis of the dynamical dual model of strong interactions followed from the parton model of hadrons as discussed in an earlier paper, we study here the photo-production of pseudoscalar and vector mesons in the high energy region. To incorporate the concept of duality, it is taken that any two spin pointlike constituents (partons) can form a π-meson cluster in the structure of a nucleon and the basic interaction involved in MB scattering is the interaction of the incident meson with the π meson in the structure of the nucleon. In this scheme, the amplitudes for the photoproduction of mesons such as γN → Nπ, γN → N?, and γN → Nω in the high energy region can be related with the amplitudes for the process γπ → ππ, γπ → π?, and γπ → πω, respectively. To calculate the amplitudes for the relevant process we also consider a factor corresponding to the structural rearrangement of partons involved in duality diagrams. To obtain the cross sections, we take into account the photon-vector meson analogy, though the naive form of the vector dominance model (VDM) has not been considered here. From a knowledge of the coupling constants , , , and we obtain the differential cross sections which are in excellent agreement with experimental results. Also we obtain a good fit for the scattering process γN → Nπ at backward angles. For the vector meson production processes, we have contributions from the diffraction mechanism also apart from the amplitudes considered here. In the region where the contribution from the diffraction part is negligible, we obtain the relation which is in nice agreement with experiments. Finally, it is shown that, though the vector meson dominance is not considered here, the universality of the vector meson coupling with hadrons follows directly from the present model. 相似文献