Direct extraction of hadronic form factors from elastic-scattering data

Non-forward elastic hadron-scattering data are collected and analysed within the Regge approach. Through an analysis of the data in small bins in $t$, we have directly extracted the pomeron trajectory and the hadronic form factors (or reggeon couplings). We found higher values than usually used for the intercept and for the slope of the soft pomeron trajectory. The presence of zeros in $t$ for the effective hadronic form factors is emphasised.Comment: 4 pages, 5 figures, talk given at Diffraction 2004, Cala Gonone, Sardinia, Italy, 18-23 September 200

Unitarisation of the hard pomeron and black-disk limit at the LHC

Recent models of soft diffraction include a hard pomeron pole besides the usual soft term. Such models violate the black-disk limit around Tevatron energies, so that they need to be supplemented by a unitarisation scheme. Several such schemes are considered in this letter, where we show that they lead to a large uncertainty at the LHC. We also examine the impact of unitarisation on various small-t observables, the slope in t of the elastic cross section, or the ratio of the real to imaginary parts of the scattering amplitude, leading to the conclusion that the existence of a hard pomeron in soft scattering may be confirmed by LHC data.Comment: 15 pages, 12 figures, late

Extrema bounds for the soft Pomeron intercept

By using an extended Regge parametrization and taking into account the discrepancies in the high-energy pp and p(bar)p total cross section data, in both accelerator and cosmic-ray regions, we estimate extrema bounds for the soft Pomeron intercept. First we consider two ensembles of data with either the CDF or the E710 and E811 results for the p(bar)p total cross section at 1.8 TeV, from which we obtain the bounds 1.102 and 1.081, respectively. These ensembles are then combined with the highest and lowest estimations for the pp total cross section from cosmic-ray experiments (6-40 TeV), leading to the upper and lower bounds 1.109 and 1.082, respectively. The effects of simultaneous fits to total cross sections and the rho parameter, individual fits to total cross sections, and the influence of the subtraction constant in the dispersion relations are also presented. Our global results favor the E710 and E811 data.Comment: 7 pages, 7 figures, aps-revtex, to be published in Physics Letters

The Total Cross Section at the LHC: Models and Experimental Consequences

I review the predictions of the total cross section for many models, and point out that some of them lead to the conclusion that the standard experimental analysis may lead to systematic errors much larger than expected.Comment: Contribution to the 13th International Conference on Elastic & Diffractive Scattering (13th "Blois Workshop"), CERN, 29th June - 3rd July 200

Saturation effects in pp scattering in the impact-parameter representation

The impact of unitarity is considered in different approaches to saturation in impact-parameter space. The energy and momentum-transfer dependence of the total and differential cross sections and of the ratio of the real to imaginary parts of the scattering amplitude are obtained in a model that includes soft and hard pomeron contributions, coupled to hadrons via the electromagnetic form factor. It is shown that the hard pomeron may significantly contribute to soft physics at the LHC. A similar conclusion can also be reached in the framework of non-linear approaches to unitarisation of the BFKL pomeron.Comment: 3 pages, 1 figure, uses espcrc2.sty. Contribution to ``Diffraction 2004'', International Workshop on Diffraction in High-Energy Physics, Cala Gonone, Sardinia, September 18-23, 200

A Review of the Soft Pomeron

Soft pomeron fits reproduce all zero-Q2 data for light quarks, but run into problems at HERA for heavy mesons and for high Q2, and at the Tevatron for W diffractive production. I review the basic properties of the soft pomeron, and outline the possibilities which have been considered to account for the new data.Comment: Latex document, 8 pages, no figures. Invited talk at the International Europhysics Conference on High Energy Physics (HEP 95), 27 Jul - 2 Aug 1995 , Brussels, Belgiu

Vector Meson Production at HERA

We show that the lowest-order QCD calculation in a simple model of elastic vector-meson production does reproduce correctly the ratios of cross sections for rho, phi and J/psi, both in photoproduction and in high-Q2 quasi-elastic scattering. The dependence of the slopes on the mass of the vector meson is reproduced as well. We examine the lower-energy data, and find that the energy dependence of the cross section does not depend on Q2, but may depend on the vector-meson mass.Comment: 12 pages, Latex, 6 figures. Shortened version of the previous paper, which also includes a clearer criticism of the work by Martin, Ryskin and Teubner, hep-ph/960944

Pseudoscalar Vertex and Quark Masses

We analyse available data on the quark pseudoscalar vertex and extract the contribution og the Goldstone boson pole. The strength of the pole is found to be quite large at presently accessible scales. We draw the important consequences of this finding for the various definitions of quark masses.Comment: LATTICE99 (Improvement and Renormalization), 3 p., 3 fi

Critical analysis of derivative dispersion relations at high energies

We discuss some formal and fundamental aspects related with the replacement of integral dispersion relations by derivative forms, and their practical uses in high energy elastic hadron scattering, in particular $pp$ and $\bar{p}p$ scattering. Starting with integral relations with one subtraction and considering parametrizations for the total cross sections belonging to the class of entire functions in the logarithm of the energy, a series of results is deduced and our main conclusions are the following: (1) except for the subtraction constant, the derivative forms do not depend on any additional free parameter; (2) the only approximation in going from integral to derivative relations (at high energies) concerns to assume as zero the lower limit in the integral form; (3) the previous approximation and the subtraction constant affect the fit results at both low and high energies and therefore, the subtraction constant can not be disregarded; (4) from a practical point of view, for single-pole Pomeron and secondary reggeons parametrizations and center-of-mass energies above 5 GeV, the derivative relations with the subtraction constant as a free fit parameter are completely equivalent to the integral forms with finite (non-zero) lower limit. A detailed review on the conditions of validity and assumptions related with the replacement of integral by derivative relations is also presented and discussed.Comment: Revised version, 30 pages, 16 eps-figures, elsart.cls (included), to appear in Nucl Phys.