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G. Shaw

Publications and source records attributed to G. Shaw.

31 records · Page 2Linked to original sources
arXiv2004

Colour dipoles and rho, phi 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.

hep-ph↗
arXiv2003

Effects of hydrostatic pressure on the magnetic susceptibility of ruthenium oxide Sr3Ru2O7: Evidence for pressure-enhanced antiferromagnetic instability

Hydrostatic pressure effects on the temperature- and magnetic field dependencies of the in-plane and out-of-plane magnetization of the bi-layered perovskite Sr3Ru2O7 have been studied by SQUID magnetometer measurements under a hydrostatic helium-gas pressure. The anomalously enhanced low-temperature value of the paramagnetic susceptibility has been found to systematically decrease with increasing pressure. The effect is accompanied by an increase of the temperature Tmax of a pronounced peak of susceptibility. Thus, magnetization measurements under hydrostatic pressure reveal that the lattice contraction in the structure of Sr3Ru2O7 promotes antiferromagnetism and not ferromagnetism, contrary to the previous beliefs. The effects can be explained by the enhancement of the inter-bi-layer antiferromagnetic spin coupling, driven by the shortening of the superexchange path, and suppression, due to the band-broadening effect, of competing itinerant ferromagnetic correlations.

cond-mat.mtrl-sci↗
arXiv2001

Colour dipoles and virtual Compton scattering

An analysis of Deeply Virtual Compton Scattering (DVCS) is made within the colour dipole model. We compare and contrast two models for the dipole cross-section which have been successful in describing structure function data. Both models agree with the available cross section data on DVCS from HERA. We give predictions for various azimuthal angle asymmetries in HERA kinematics and for the DVCS cross section in the THERA region.

hep-ph↗
arXiv2000

Introduction to Diffractive Photoprocesses

The objectives of my talk are to provide a very brief introduction to diffractive photoprocesses in general and the colour dipole model in particular; and to comment on possible gluon saturation effects at HERA and beyond.

hep-ph↗
arXiv2000

Rho Electroproduction and the Hadronic Contribution to Deeply Virtual Compton Scattering

A two-gluon-exchange model incorporating perturbative and non-perturbative effects is presented for rho electroproduction which provides an excellent description of all current data. This is then used to calculate the contribution from the rho to deeply virtual Compton scattering via the vector-meson-dominance transition rho -> gamma. This is found to be sufficiently large to provide a significant contribution through interference with the perturbative QCD term.

hep-ph↗
arXiv2000

Colour Dipoles and Saturation

We employ values of the colour dipole cross section extracted from electroproduction and photoproduction data to show that gluon saturation effects are not required by the current HERA data but will become important in the THERA energy region.

hep-ph↗
arXiv1999

Predicting F2D(3) from the dipole cross-section

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.

hep-ph↗
arXiv1999

Jacobi evolution of structure functions: convergence and stability

The Jacobi evolution method has been widely used in the QCD analysis of structure function data. However a recent paper claims that there are serious problems with its convergence and stability. Here we briefly review the evidence for the adequate convergence of the method; and show that there are errors in the above paper which undermine its conclusions.

hep-ph↗
arXiv1997

Nuclear shadowing and rho photoproduction

Rho photoproduction on complex nuclei is re-examined using a generalised vector dominance model which succesfully predicts the observed nuclear shadowing in real photoabsorption and deep inelastic scattering. This model is shown to give a good fit to rho photoproduction data on both nucleons and complex nuclei, in which the well-known disagreement between the measured gamma-rho coupling and the gamma-rho coupling required by the simple vector dominance model is eliminated. The rho N total cross-sections required are similar to those predicted by the additive quark model; and the magnitude of the correction to simple vector dominance is consistent with that inferred from the analysis of real photoabsorption and deep inelastic scattering.

hep-ph↗
arXiv1997

From Deep Inelastic Scattering to Photoproduction: A Unified Approach

The strikingly different high energy behaviours of real photoabsorption cross-sections with Q^2 = 0 and the low x proton structure function at large Q^2 are studied from a laboratory frame viewpoint, in which the x and Q^2 dependence reflects the space-time structure of the interaction. This is done using a simple model which incorporates hadron dominance, but attributes the striking enhancement observed at HERA at very low x and high Q^2 to contributions from heavy long-lived fluctuations of the incoming photon. Earlier published predictions of the model for the then unknown behaviour of the structure function at small x and intermediate Q^2 are shown to be strikingly confirmed by recent experimental data. A simultaneous analysis of real photoabsorption data and structure function data for 0 <= x < 0.1 and 0 <= Q^2 <= 15 GeV^2 is then reported. An excellent fit is obtained, with all parameters in the restricted ranges allowed by other physical requirements.

hep-ph↗
arXiv1996

Pion Polarisability and Hadronic Tau Decays

Recent experimental data on tau decays are used to reconstruct the difference in hadronic spectral densities with vector and axial-vector quantum numbers. The saturation of Das-Mathur-Okubo and Weinberg sum rules is studied. Two methods of improving convergence and decreasing errors are applied, and good agreement with the predictions of current algebra and chiral perturbation theory is observed. The resulting value of the pion polarisability is (2.64 +/- 0.36) 10^-4 fm^3.

hep-ph↗
arXiv1996

Bound States of Two Gluinos at the Tevatron and 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$^{-1}$ at the Tevatron, and the high efficiency for tagging heavy quark jets at CDF, one should be able to detect vector gluinonium for gluino masses up to about 170 GeV; or up to about 260 GeV for an upgraded Tevatron with a centre of mass energy of 2 TeV and an integrated luminosity of 1 fb$^{-1}$. The significantly higher energy and luminosity of LHC should allow pseudoscalar gluinonium to be detected for gluino masses up to about 1500 GeV for an assumed luminosity of 200 fb$^{-1}$. These results are insensitive to the details of supersymmetry models, provided that R-parity is conserved and the gluinos are lighter than the squarks. In addition, gluinonium detection implies a relatively accurate measure of the gluino mass, which is difficult to determine by other means.

hep-ph↗