arXiv subjects
Publications and source records attributed to A. Grau.
We discuss models for total cross-sections, show their predictions for photon-photon collisions and compare them with the recent LEP measurements. We show that the extrapolations to high center of mass energies within various models differ by large factors at high energies and discuss the precision required from future measurements at the proposed Linear Collider which would allow to distinguish between them.
We present here a brief overview of recent models describing the photon-photon cross-section into hadrons. We shall show in detail results from the eikonal minijet model, with and without soft gluon summation.
The Bloch-Nordsieck model for the parton distribution of hadrons in impact parameter space, constructed using soft gluon summation, is investigated in detail. Its dependence upon the infrared structure of the strong coupling constant $α_s$ is discussed, both for finite as well as singular, but integrable, $α_s$. The formalism is applied to the prediction of total proton-proton and proton-antiproton cross-sections, where screening, due to soft gluon emission from the initial valence quarks, becomes evident.
A model for the parton distributions of hadrons in impact parameter space has been constructed using soft gluon summation. This model incorporates the salient features of distributions obtained from the intrinsic transverse momentum behaviour of hadrons. Under the assumption that the intrinsic behaviour is dominated by soft gluon emission stimulated by the scattering process, the b-spectrum becomes softer and softer as the scattering energy increases. In minijet models for the inclusive cross-sections, this will counter the increase from $σ_{jet}$ .
Predictions for total inelastic cross-sections for photon induced processes are discussed in the context of the QCD-inspired minijet model. Large theoretical uncertainties exist, some of them related to the parton distributions of hadrons in impact parameter space. A model for such distribution is presented, based on soft gluon summation. This model incorporates (the salient features of distributions obtained from) the intrinsic transverse momentum behaviour of hadrons. Under the assumption that the intrinsic behaviour is dominated by soft gluon emission stimulated by the scattering process, the b-spectrum becomes softer and softer as the scattering energy increases. In minijet models for the inclusive cross-sections, this will counter the increase from $σ_{jet}$ .
The accuracy of effective chiral lagrangians including vector-mesons as (hidden symmetry) gauge fields is shown to be improved by taking into account SU(3)-breaking in the vector-meson sector. The masses, $M_V$, and couplings to the photon field and pseudoscalar pairs, $f_{Vγ}$ and $g_{VPP}$, are all consistently described in terms of two parameters, which also fit the values for the pseudoscalar decay-constants, $f_P$, and charge radii, $ $. The description of the latter is further improved when working in the context of chiral perturbation theory.
If a new $Z'$ is discovered with a mass $\sim 1 \ TeV$ at LHC/SSC, its (rare) decays into two charged leptons plus missing transverse energy will probe the $Z'$ coupling to the lepton doublet $(ν,e)_L$ and to $W^+W^-$, allowing further discrimination among extended electroweak models.