F. Halzen

Amplitude analysis of πN scattering at 6 GeV/c

Abstract The moduli and relative phases of the π N scattering amplitudes are extracted directly from 6 GeV/ c data. The resulting amplitude structure at the cross-over and at t = −0.6 GeV 2 is analyzed and compared with high-energy models. The helicity structure of the I t = 0 component is determined and predictions for R parameter measurements are given.

Evidence for multiple parton interactions from the observation of multi-muon events in Drell-Yan experiments

Abstract We calculate the production of two lepton pairs via the Drell-Yan mechanism. To establish the existence of multiple parton interactions in a single hadron collision, lepton pair production is superior to jet production from the theoretical, phenomenological and experimental points of view. The calculated rate agrees with the previously unexplained four-muon events observed in πp and pp interactions. Our results lend support to a recent analysis of ISR four-jet events and we discuss some implications of this study.

It is likely that mt<mW

Within the standard model with three generations, the experimental data on the rate of W versus Z events in pp collisions favour mt 3. The virtues as well as the shortcomings in the procedure to determine the t-quark mass from such data are discussed. Neutrino experiments sensitive to u(x)d(x) structure function ratios can help.

Bounds on polarization in πN scattering from isotopic spin invariance

Abstract Isotopic spin bounds on the polarization in π − p→ π o n scattering in terms of the polarizations in π + p→ π + p and π − p→ π − p scattering and the unpolarized differential cross-sections for π + p→ π + p, π − p→ π − p, and π − p→ π o n scattering are derived, and compared with recent experimental data. Similar bounds on the P , R and A parameters for elastic scattering are also given.

Regge poles with kinematic cuts in π N backward scattering

Abstract We investigate the effects of including kinematic cuts to suppress parity doublets in the Regge pole description of π N backward scattering.

Physics from Jψ-tags in p̄p collisions

Abstract We calculate J/ψ hadroproduction and emphasize the importance of the J ψ signal as a measure of bb production via the decay B→ψX and of the small-x gluon structure function via χ hadroproduction followed by χ→ψλ decay. Considering all sources of ψ events we predict that σ( p p →ψ) is in the range 30–60 nb at √s=630 GeV for p T (ψ)>5 GeV c . We identif distinctive features of ψ events of bb and χ origin which may allow their separation.

Broken exchange degeneracies and secondary trajectories in charge and hypercharge exchange reactions

Abstract A simple model is developed for the difference of K and K nucleon charge exchange cross-sections. In addition to a breaking of exchange degeneracy, the model requires secondary trajectories which are identified with the scalar meson trajectories. Hypercharge exchange reactions are also discussed.

Building meson-baryon scattering amplitudes from duality

Abstract We extend duality constraints to include the interrelation of the structure of the s-channel spectrum with that of u- and t-channels. Predictions for t-channel meson couplings are presented within an SU(3) framework.

The coupling of π and A1 trajectories by duality

Abstract Duality sum rules implied by the absence of resonances in the scattering of pseudoscalar-pseudoscalar, pseudoscalar-vector and vector-vector meson states in channels with exotic quantum numbers are studied. It is shown that the assumption of exact duality and SU(3) symmetry for the vertices leads inevitably to a decoupling of the π and the A 1 Regge trajectories. Next the view is taken that the experimental exchange degeneracy of the π and A 1 trajectories is not accidental and an alternative solution is proposed. It incorporates the normal degeneracy pattern for the leading vector and tensor trajectories but has a coupled triplet of exchange degenerate trajectories ( J PC = 0 ft ∓ , 1 ++ and 1 +− ) at the secondary level. The implications of this solution for (i) meson spectroscopy, (ii) meson-meson-reggeon coupling and (iii) the breaking of duality are investigated.

Interference of t and u channel amplitudes in pion nucleon scattering

Abstract We propose a Regge model for the full angular distribution in πN scattering. The pronounced dip near t = −2.8 (GeV/ c ) 2 is explained as a t − u channel exchange interference effect.