Graham Shaw

Extracting the dipole cross-section from photo- and electro-production total cross-section data

We report on a successful attempt to extract the cross-section for the high-energy scattering of colour dipoles of fixed transverse size off protons using electroproduction and photoproduction total cross-section data, subject to the constraint provided by the ratio of the overall photon dissociation cross-section to the total cross-section.

Color dipoles and ρ, Φ electroproduction

We present a detailed comparison of a variety of predictions for diffractive light vector meson production with the data collected at the HERA collider. All our calculations are performed within a dipole model framework and make use of different models for the meson light-cone wavefunction. There are no free parameters in any of the scenarios we consider. Generally we find good agreement with the data using rather simple Gaussian motivated wavefunctions in conjunction with dipole cross-sections which have been fitted to other data.

Further success of the colour dipole model

We confront a very wide body of HERA diffractive electroproduction data with the predictions of the colour dipole model. We focus upon three different parameterisations of the dipole scattering cross-section and find good agreement for all observables. There can be no doubting the success of the dipole scattering approach and more precise observations are needed in order to expose its limitations.

Gluon saturation in the colour dipole model

We use data on the deep inelastic structure function F2 in order to constrain the cross-section for scattering a colour dipole off a proton. The data seem to prefer parameterisations which include saturation effects. That is they indicate that the strong rise with energy of the dipole cross-section, which holds for small dipoles, pertains only for r < rs(x) where rs(x) decreases monotonically as x decreases. Subsequent predictions for the diffractive structure function F2D(3) also hint at saturation, although the data are not really sufficiently accurate.

Shadowing in Nuclear Photoabsorption

Abstract Shadowing in nuclear photoabsorption is studied using a generalised vector dominance model, and the simplifying assumptions of previous calculations shown to be inadequate. Less shadowing is found than hitherto, with possible anti-shadowing indicated for x′ ≳ 0.07. The results are compatible with experiment within the substantial systematic errors.

Low-energy pion-pion parameters from forward dispersion relations

Abstract Values of the ππ scattering lengths and low-energy phase shifts are tabulated corresponding to various assumptions on the mass and width of the sigma meson. The method uses forward and first derivative dispersion relations. The I = 0 S-wave scattering length a o comes out in the range −0.3 to 0.6 m π −1 . The P-and D-wave scattering lengths are relatively independent of the sigma parameters. Solutions are compared with results on Ke 4 decay and with the predictions of current algebra. Super broad sigmas seem to be preferred. Such solutions are also more self consistent in a bootstrap sense.

Predicting F2D(3) from the colour glass condensate model

Abstract We confront the colour glass condensate motivated dipole model parameterization of Iancu, Itakura and Munier with the available HERA data on the diffractive structure function F 2 D (3) and with existing dipole model parameterizations. Reasonably good agreement is found with only two adjustable parameters. We caution against interpreting the success of the model as compelling evidence for low- x perturbative saturation dynamics.

Predicting the diffractive structure function from the dipole cross-section

Abstract We employ a parameterisation of the proton dipole cross section previously extracted from electroproduction and photoproduction data to predict the diffractive structure function F 2 D (3) ( Q 2 , β , x P ). Comparison with HERA H1 data yields good agreement.We employ a parameterisation of the proton dipole cross section previously extracted from electroproduction and photoproduction data to predict the diffractive structure function F2D(3)(Q^2, beta, xpom). Comparison with HERA H1 data yields good agreement.

Magic moments in QCD2

Abstract The SVZ moment method of calculating resonance masses is studied in the context of two-dimensional QCD. It is shown to underestimate the appropriate parameter by about a factor of three.

Bound states of two gluinos at the Fermilab Tevatron and CERN LHC

We calculate the production cross-sections for the vector and pseudoscalar bound states of two gluinos. It is shown that existing and future colliders imply a realistic chance of observing gluinonium as a narrow peak in the two-jet invariant mass spectrum. With an integrated luminosity of 0.2 fb