Wolfgang Ochs

ππ Phase‐Shift Analysis from 600 to 1900 MeV

Wa have performed an energy‐dependent and an energy‐independent analysis of elastic ππ scattering, using data for the reaction π−p ⇒ π−π+n at 17.2 GeV/c. The ππ energy covers the range from 600 MeV to 1900 MeV. Apart from the well‐known resonances ρ, f and g, we find a strong S‐wave in the ρ and also in the f‐meson region. A P‐wave resonance occurs in both analyses at ∼ 1600 MeV with a total width of 180 MeV and an elasticity of 0.25, which can be identified with the ρ′ meson in its ππ decay mode. The zeros in the complex cos Θ plane of the scattering amplitude are studied as a function of the energy. The position of the real parts of the zeros are in qualitative agreement with the prediction of the Veneziano model. Furthermore, we show that an analogous relation holds also for the imaginary parts of the zero trajectories.

High statistics study of the reaction π−p→π−π+n: Apparatus, method of analysis, and general features of results at 17 GeV/c

Abstract A detailed account is given of a high statistics experiment measuring the reaction π−p→π−π+n at 17.2 GeV/c. The spark chamber and counter triggering system are desribed. The methods of data analysis are described, in particular the determination of angular distributions from apparatus with limited acceptance. Experimental data and their interpretation are presented.

Perturbative-QCD Approach to Multiparticle Production

In this review we discuss the analytical perturbative approach, based on perturbative QCD and local parton hadron duality (LPHD), and its application to multiparticle production in jets in the semisoft region. Analytical formulae are presented for various observables within the accuracy of the modified leading logarithmic approximation (MLLA), i.e. with terms of relative order taken into account systematically, and in some cases with even higher accuracy. These predictions are confronted with existing experimental data. Many details of the perturbative approach to multiple hadroproduction have been consolidated in recent years, and the overall picture is remarkably healthy. The prospects of future studies of the semisoft jet physics are also discussed.

Intermittency and jets

Abstract We show that intermittency, i.e. unlimited growth of multiplicity fluctuations with increasing resolution, is obtained in hadron cascade models with scale invariant branching structure. Strong effects are expected if in a multiparticle event not only the rapidity but simultaneously the azimuthal angle around the beam axis is analysed. The occurrence of narrow jets (“pencil jets”) is expected. The relevance of this type of study for models of hadronization is pointed out.

The Status of Glueballs

Calculations within QCD (lattice and sum rules) find the lightest glueball to be a scalar with mass in the range of about 1000–1700 MeV. Several phenomenological investigations are discussed which aim at the identification of the scalar meson nonets of lowest mass and the super-numerous states if any. Results on the flavour structure of the light scalars f0(500), f0(980) and f0(1500) are presented; the evidence for f0(1370) is scrutinized. A significant surplus of leading clusters of neutral charge in gluon jets is found at LEP in comparison with MCs, possibly a direct signal for glueball production; further studies with more energetic jets at LHC are suggested. As a powerful tool in the identification of the scalar nonets or other multiplets, along with signals from glueballs we propose the exploration of symmetry relations for decay rates of C = +1 heavy quark states like χc or χb. Results from χc decays are discussed; they are not in support of a tetra-quark substructure of f0(980). A minimal scenario for scalar quarkonium-glueball spectroscopy is presented.

The importance of phase space dimension in the intermittency analysis of multi hadron production

Abstract It is shown for a simple model (“α-model”) realizing a self-similar random cascade process in d=2 (or d=3) dimensions of momentum space that intermittency of the multiplicity distribution occurs in the d-dimensional analysis but disappears in the one-dimensional projection. This demonstrates the importance of multidimensional analysis for the interpretation of data in terms of intermittency. However, in a variety of two- and three-dimensional cascade models a power-type relation between moments remains for the one dimensional projection into rapidity space and these relations are supported by data from all collision processes in the full rapidity range. The difference to the negative binomial description is pointed out.

A study of the ππ phase-shift solutions in the mass region 1.0 to 1.8 GeV from π−p → π−π+n at 17.2 GeV

Abstract The ππ phase shifts from 1 to 1.8 GeV are presented. The method used was an essentially energy-independent parametrization of the amplitudes fitted simultaneously to the M ππ and t -dependence of the moments of the dipion angular distribution from the reaction π − p → π − π + n at 17.2 GeV. The various ambiguous solutions are discussed.

Multidimensional intermittency analysis

We propose a method to perform the intermittency analysis of multi hadron production in up to three momentum space dimensions. The analysis of realistic (approximately) selfsimilar cascade models shows that the strongest rise of multiplicity moments with decreasing phase space intervals and the closest approach to a power law occurs in three dimensions. Moments of higher orderF(q) are related to the second momentF(2) by a power law in good approximation. These powers are found independent of the dimensions in the models and in available data; furthermore, they are only weakly dependent on the reaction type. The relevance to the quark gluon plasma search is discussed.

On the strength of absorption in single pion production reactions

From data on the reactions π−p → π− π+n and K+n → K+π−p we determine the strength of absorptive corrections to the pion exchange Bornterm as a function of the ππ and Kπ mass and angular momentum.

Multiparton correlations in QCD jets

Abstract We derive a scheme to solve the integral equations for inclusive multiparton densities in the double logarithmic approximation of QCD. We present the explicit solution for the angle dependent two parton correlation function, in the case of constant α s . The normalised angular correlation function has a singularity at small angle caused by gluon bremsstrahlung; at larger angles both the normalised and the unnormalised distributions reveal the self-similar behaviour of the QCD cascade with known exponents of the power law.