$pp$ and $\bar pp$ total cross sections and elastic scattering
It is shown that $p p$ and $p\bar p$ data, including those from the TOTEM experiment, agree well with Regge theory.
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arXiv subjects
P. V. Landshoff
Publications and source records attributed to P. V. Landshoff.
Central soft production of hadrons in $pp$ collisions
The high-energy behaviour of soft scattering observables such as total cross sections, elastic scattering at small momentum transfer, diffractive dissociation and central production have been described successfully in the context of Regge theory, with the same basic structure holding as energies have increased. For elastic scattering and diffraction dissociation the defining energies were those of the ISR, the $Sp\bar{p}S$ collider and the Tevatron. The elastic scattering data from the LHC demonstrate the continuing applicability of Regge theory. Preliminary data on diffraction dissociation promise to add to our understanding and now, for the first time, we can expect to test fully these concepts in central production. Although the latter is the principal objective of this discussion, understanding the first two is an essential prerequisite as they define the formalism and establish parameters.
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Elastic Scattering at the LHC
The first data from the TOTEM experiment agree well with Regge theory, and demand a hard-pomeron contribution.
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Frozen ghosts in thermal gauge field theory
We review an alternative formulation of gauge field theories at finite temperature where unphysical degrees of freedom of gauge fields and the Faddeev-Popov ghosts are kept at zero temperature.
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Successful description of exclusive vector meson electroproduction
Data for the differential cross sections for $γ^* p\toρ^0 p$, $γ^* p \to ϕp$ and $γ^* p\to J/ψp$, at all available values of $Q^2$, fit very well to a combination of soft pomeron, hard pomeron and $f_2$ exchange.
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The total cross section at the LHC
We do not have the ability to perform precise calculations of long-range strong interaction effects, because the effective QCD coupling is not small and so we cannot use perturbation theory. Nevertheless, I show that we know a lot, though not nearly enough. As a measure of our lack of knowledge, the best prediction for the total cross section at LHC energy is 125 +/- 25 mb.
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Does the hard pomeron obey Regge factorisation?
While data for the proton structure function demand the presence of a hard-pomeron contribution even at quite small Q^2, previous fits to the pp and p\bar p total cross sections have found that in these there is little or no room for such a contribution. We re-analyse the data and show that itmay indeed be present and that, further, it probably obeys Regge factorisation: sigma^{gamma p}(s,Q_1^2)sigma^{gamma p}(s,Q_2^2)= sigma^{pp}(s)sigma^{gamma gamma}(s,Q_1^2,Q_2^2) for all values of Q_1^2 and Q_2^2.
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Evolution at small x
At present there is no correct theory of evolution of F_2(x,Q^2) at small x. It is a mixture of hard and soft pomeron exchange and perturbative QCD very successfully describes the evolution of the hard-pomeron component. This allows the gluon density to be calculated. It is somewhat different from what is conventionally supposed, but it leads to a clean PQCD description of the data for the charm structure function. Perturbative QCD breaks down for the evolution of the soft-pomeron component of F_2(x,Q^2).
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The proton's gluon structure
The proton's gluon structure function at small x is larger than nowadays is commonly believed
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The Challenge of Small x
We review the current understanding of the behaviour of inclusive cross sections at small x and large Q^2 in terms of Altarelli-Parisi evolution, the BFKL equation, and Regge theory, asking in particular to what extent they are mutually consistent.
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Some Remarks on the Pomeron and the Odderon in Theory and Experiment
On March 19-21, 1998, a workshop devoted to questions of the pomeron and the odderon in high energy scattering was held in Heidelberg. This note gives a personal account of some of the issues discussed at this workshop. Of course, misconceptions and misunderstandings are to be blamed on us, not on the other participants of the workshop. A puzzle of odderon physics is identified and a convenient reaction for its experimental study is discussed.
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Elastic Meson Production - Factorisation and Gauge Invariance
The factorisation of the hard amplitude for exclusive meson production in deep inelastic scattering is considered in the framework of a simple model. It is demonstrated explicitly how gauge invariance ensures the cancellation of non-factorising contributions.
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Eliminating Infrared Divergences in the Pressure
The pressure of a system in thermal equilibrium is expressed as a mass integral over a sum of thermal propagators. This allows a Dyson resummation and is used to demonstrate that potential infrared divergences are rendered harmless.
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Vector Meson production in ep -> epV
The diffractive production of vector mesons in ep interactions at low x is a subject of heated debates. This chapter consists of four contributions written by the original authors and expresses the possible scenarios which are to be investigated experimentally.
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Some tests for the helicity structure of the pomeron in $ep$ collisions
We discuss the reaction $e p \to e \tilde{p} X$ in the one-photon exchange approximation, where it is in essence the reaction $γ^{*} p \to \tilde{p} X$. A large rapidity gap is required between the particle or particles of the proton remnant $\tilde{p}$ and those of $X$. We define a suitable azimuthal angle $φ$ between a leptonic and a hadronic plane. The dependence of the cross section on $φ$ is given explicitly and can be used to extract cross sections and interference terms for the reaction $γ^{*} p \to \tilde{p} X$ corresponding to the various helicities of the virtual photon $γ^{*}$. The interference terms can be used to test models for the large rapidity gap events in a sensitive way. We discuss in detail models with factorizing Pomeron exchange and in particular the Donnachie-Landshoff Pomeron model. We make some remarks on soft colour exchange models and on possible effects of QCD background vacuum fields. We conclude with a suggestion to look for Odderon exchange in exclusive deep inelastic high energy reactions like $γ^{*} p \to \tilde{p} π^{0}$ and $γ^{*} p \to \tilde{p} η$.
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