1,575 research outputs found

### 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.Comment: 11 pages, 10 figure

### Charm production at HERA

The ZEUS data on the charm structure function F_2^c at small x fit well to a
single power of x, corresponding to the exchange of a hard pomeron that is
flavour-blind. When combined with the contribution from the exchange of a soft
pomeron, the hard pomeron gives a good description of elastic $J/\psi$
photoproduction.Comment: 6 pages, plain tex, with 3 figures embedded using epsf. Typos
corrected in equations (10) and (11

### Exclusive Vector Photoproduction: Confirmation of Regge Theory

Recent small-t ZEUS data for exclusive rho photoproduction are in excellent
agreement with exchange of the classical soft pomeron with slope alpha'=0.25
GeV^{-2}. Adding in a flavour-blind hard-pomeron contribution, whose magnitude
is calculated from the data for exclusive J/psi photoproduction, gives a good
fit also to the ZEUS data for rho photoproduction at larger values of t, and to
phi photoproduction.Comment: 6 pages, plain tex, with 5 figures embedded using eps

### The Interest of Large-t Elastic Scattering

Existing data for large-$t$ $pp$ elastic-scattering differential
cross-sections are energy-independent and behave as $t^{-8}$. This has been
explained in terms of triple-gluon exchange, or alternatively through
triple-singlet exchange. A discussion is given of the problems raised by each
of these explanations, and of the possibility that at RHIC or LHC energies the
exchange of three BFKL pomerons might result in a rapid rise with energy.Comment: 6 pages, plain tex, 3 figures embedded with eps

### Unusual high-pT jet events at HERA

We calculate the cross-section for events at HERA where the proton loses only
a minute fraction of its initial energy, all of which goes into producing a
single pair of transverse jets.Comment: 4 pages plus figure

### 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

### Pomeron physics: an update

Key issues in pomeron physics include whether the hard and soft pomerons are
distinct objects, and whether the hard pomeron is already present in amplitudes
at $Q^2=0$. It is urgent to learn how to combine perturbative and
nonperturbative concepts, and to construct a sound theory of perturbative
evolution at small $x$. Other questions are whether screening corrections are
small, and gap survival probabilities large. Finally, do diffractive processes
present a good way to discover the Higgs?Comment: 12 pages, 23 figures embedded with epsf Summary talk at
Diffraction2000, Calabria, September 200

### EFFECTS OF SHADOWING IN DOUBLE POMERON EXCHANGE PROCESSES

The effects of shadowing in double Pomeron exchange processes are
investigated within an eikonal approach with a Gaussian input. Damping factors
due to screening are calculated for this process and compared with the factors
obtained for total, elastic and single diffraction cross sections. Our main
conclusion is that counting rate calculations, of various double Pomeron
exchange processes (without screening corrections) such as heavy quark and
Higgs production are reduced by a factor of 5 in the LHC energy range, when
screening corrections are applied.Comment: 9 pages, latex, 5 figures obtainable from author

### Perturbative Evolution and Regge Behaviour

The known analytic properties of the Compton amplitude at small $Q^2$ place
significant constraints on its behaviour at large $Q^2$. This calls for a
re-evaluation of the role of perturbative evolution in past fits to data.Comment: Revised figures 4 and

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### Utopian designs: the Owenite communities

This article reviews the development of Robert Owen's community ideas with special reference to the architecture and physical arrangements. It highlights the importance of New Lanark, Scotland as a test-bed for Owen's ideal community and explores later designs for several of the communities that were built 1825-1845. Particular attention is paid to the ideas and plans of the Owenite architect, Stedman Whitwell, who produced descriptions, plans and a model of the ideal community. Many of the proposals greatly influenced later Utopian experiments

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