Properties of the hard pomeron with a running coupling constant and the high-energy scattering (original) (raw)
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Evidence for a super-hard pomeron structure
Physics Letters B, 1992
Results are presented from a study of jet production in p p interactions with p s = 630 GeV at the CERN Sp pS-Collider, which are tagged by a proton or antiproton which possesses more than 90% of the incident beam momentum. The hard scattering which occurs between a parton in a beam particle and another in the soft residual component (P omeron-dominated) of the tagged proton allows the Pomeron's partonic structure to be investigated. The observed jet distributions are in good agreement with expectations for hard parton-parton scattering in QCD. The Pomeron exhibits a hard structure like (1-x). However, there is an additional signicant (30%)-function-like component, in which the entire momentum of the Pomeron seems to participate in the hard scattering.
Expanding running coupling effects in the hard Pomeron
Physical Review D, 2002
We study QCD hard processes at scales of order k 2 ≫ Λ 2 in the limit in which the beta-function coefficient b is taken to be small, butᾱ s (k 2 ) is kept fixed. The (nonperturbative) Pomeron is exponentially suppressed in this limit, making it possible to define purely perturbative high-energy Green's functions. The hard Pomeron exponent acquires diffusion and running coupling corrections which can be expanded in the b parameter and turn out to be dependent on the effective coupling bᾱ 2 s Y . We provide a general setup for this b-expansion and we calculate the first few terms both analytically and numerically.
Probing the structure of the pomeron
The European Physical Journal C, 1999
We suggest that the pseudo-rapidity cut dependence of diffractive deep-inelastic scattering events at HERA may provide a sensitive test of models of diffraction. A comparison with the experimental cross section shows that the Donnachie-Landshoff model and a simple two-gluon exchange model of the pomeron model are disfavoured. However a model with a direct coupling of the pomeron to quarks is viable for a harder quark-pomeron form factor, as is a model based on the leading-twist operator contribution. We also consider a direct-coupling scalar pomeron model. We comment on the implications of these results for the determination of the partonic structure of the pomeron.
Photon contribution to the “super-hard” pomeron
Physics Letters B, 1996
It is shown that direct photons provide a leading twist mechanism for diffractive jet production in which the jets carry away all of the momentum lost by the proton. Two-photon processes are thus expected to asymptotically dominate "super-hard" pomeron events in ep collisions. We report the expected rates from these events for the recent ZEUS and H1 data cuts. We also estimate the direct photon contribution to the "super-hard" pomeron events observed by the CERN UA8 group for pp collisions.
Soft and hard Pomeron in the structure function of the proton at low x and low <img src="/ful
Eur Phys J C, 1999
We study inclusive electroproduction on the proton at low xxx and low Q2Q^2Q2 using a soft and a hard Pomeron. The contribution of the soft Pomeron is based on the Stochastic Vacuum Model, in which a nonperturbative dipole-dipole cross section can be calculated by means of a gauge invariant gluon field strength correlator. To model the hard Pomeron exchange we phenomenologically extend the leading order evolution of a power-behaved structure function, F2proptox−lambdaF_2 \propto x^{- \lambda}F2proptox−lambda, proposed by L\'opez and Yndur\'ain. This extension allows to consider both the case Q2=0Q^2 = 0Q2=0 and the region of higher Q2Q^2Q2 on the basis of the same parametrization. A good simultaneous fit to the data on F2F_2F2 and on the cross section sigmagammap\sigma_{\gamma p}sigmagammap of real photoproduction is obtained for lambda=0.37\lambda=0.37lambda=0.37. With four parameters we achieve a chi2/textrmd.o.f.=0.98\chi^2/\textrm{d.o.f.} = 0.98chi2/textrmd.o.f.=0.98 for 222 data points. In addition, we use our model of the inclusive gammaastp\gamma^{\ast} pgammaastp interaction to compute the longitudinal structure function FLF_LFL.
Soft and hard Pomeron in the structure function of the proton at low x and low Q2Q^2Q2
The European Physical Journal C, 1999
We study inclusive electroproduction on the proton at low x and low Q 2 using a soft and a hard Pomeron. The contribution of the soft Pomeron is based on the Stochastic Vacuum Model, in which a nonperturbative dipole-dipole cross section can be calculated by means of a gauge invariant gluon field strength correlator. To model the hard Pomeron exchange we phenomenologically extend the leading order evolution of a power-behaved structure function, F 2 ∝ x −λ , proposed by López and Ynduráin. This extension allows to consider both the case Q 2 = 0 and the region of higher Q 2 on the basis of the same parametrization. A good simultaneous fit to the data on F 2 and on the cross section σ γp of real photoproduction is obtained for λ = 0.37. With four parameters we achieve a χ 2 /d.o.f. = 0.98 for 222 data points. In addition, we use our model of the inclusive γ * p interaction to compute the longitudinal structure function F L .
Diffractive hard scattering with a coherent pomeron
Physics Letters B, 1993
Diffractive scattering involves exchange of a Pomeron to make a rapidity gap. It is normally assumed that to get a hard scattering in diffraction, one may treat the Pomeron as an ordinary particle, which has distributions of gluons and quarks. We show that this is not so: When we use perturbative QCD, there is a breakdown of the factorization theorem. The whole Pomeron can initiate the hard scattering, even though it is not point-like. Qualitatively, but not quantitatively, this gives the same effect as a delta function term in the gluon density in a Pomeron.
A quantitative investigation of the pomeron
Eur Phys J C, 1993
A comparative investigation of various pomeron models is carried out through the study of their predicted values of sigmatot, B, and{sigma _{el} }/{sigma _{tot }} in high energy pp andpbar p scattering. Our results strongly support a picture of the pomeron in which we have both moderate blackening and expansion of thep(bar p) - p amplitude in impact parameter space as a function of energy in the ISR-SSC domain. Our analysis shows the data is compatible with a hybrid eikonal model which combines the hard Lipatovlike QCD pomeron with the old fashioned soft pomeron and Regge terms. We show that the additive quark model, at least in the naive form, is not compatible with the data.
Nuclear Physics B - Proceedings Supplements, 2001
This talk is a brief presentation of our view on the Pomeron, as a non-perturbative QCD phenomenon but from sufficiently short distances. Our approach is based on the scale anomaly of QCD and emphasizes the rôle of semi-classical QCD vacuum fields. We show that both the intercept and the slope of Pomeron trajectory appear to be determined by the energy density of non-perturbative QCD vacuum. The particular example of semi-classical QCD vacuum fields is discussed based on a new type of instanton-induced interactions ("instanton ladder") that leads to the rising with energy cross section σ ∼ s ∆ P of Regge type (the Pomeron).