Pion and photo-induced inelastic reactions off protons are studied in a multichannel partial-wave analysis. Properties of nucleon and ∆ resonances are derived and compared to previous analyses. Amplitudes are shown for transitions to N η, ΛK, and ΣK final states.

Abstract. Properties of nucleon and Δ resonances are derived from a multichannel partial wave analysis of pion and photo-induced reactions off protons. This paper summarizes the latest results on masses, widths, and decay properties of nucleon and Δ resonances.

Abstract. Cross sections, beam asymmetries, and recoil polarisations for the reactions γp → K + Λ; γp → K + Σ 0 , and γp → K 0 Σ + have been measured by the SAPHIR, CLAS, and LEPS collaborations with high statistics and good angular coverage for centre-of-mass energies between 1.6 and 2.3 GeV. The combined analysis of these data with data from π and η photoproduction reveals evidence for new baryon resonances in this energy region. A new P11 state with mass 1840 MeV and width 140 MeV was observed contributing to most of the fitted reactions. The data demand the presence of two D13 states at 1870 and 2170 MeV.

A combined analysis of photoproduction data on γp → πN, ηN was performed including the data on KΛ and KΣ. The data are interpreted in an isobar model with s-channel baryon resonances and π, ρ (ω), K, and K * exchange in the t-channel. Three baryon resonances have a substantial coupling to ηN, the well known N(1535)S11, N(1720)P13, and N(2070)D15. The inclusion of data with open strangeness reveals the presence of further new resonances, N(1840)P11, N(1875)D13 and N(2170)D13.

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Abstract.Nucleon and ∆ resonances in the fourth resonance region are studied in a multichannel partial-wave analysis which includes nearly all available data on pion-and photo-induced reactions off protons. In the high-mass range, above 1850 MeV, several alternative solutions yield a good description of the data. For these solutions, masses, widths, pole residues and photo-couplings are given. In particular, we find evidence for nucleon resonances with spin-paritiesFor one set of solutions, there are four resonances forming naturally a spin-quartet of resonances with orbital angular momentum L = 2 and spin S = 3/2 coupling to J = 1/2, · · · , 7/2. Just below 1.9 GeV we find a spin doublet of resonances with J P = 1/2 − and 3/2 − . Since a spin partner with J P = 5/2 − is missing at this mass, the two resonances form a spin doublet which must have a symmetric orbital-angular-momentum wave function with L = 1. For another set of solutions, the four positive-parity resonances are accompanied by mass-degenerate negativeparity partners -as suggested by the conjecture of chiral symmetry restoration. The possibility of a J P = 1/2 + , 3/2 + spin doublet at 1900 MeV belonging to a 20-plet is discussed.

BARYONS S y s t e m a t i z a t i o n a n d M e t h o d s o f A n a l y s i sMesons and Baryons Downloaded from www.worldscientific.com by 18.236.120.13 on 05/10/18. For personal use only. British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher. PrefaceThe notion of quarks appeared in the early sixties just as a tool for the systematisation of the growing number of experimentally observed particles. First it was understood as a mathematical formulation of the SU(3) properties of hadrons, but soon it became clear that hadrons have to be considered as bound states of quarks (objects which we call now "constituent quarks"). The next steps in understanding the quark-gluon structure of hadrons were made in the framework of Quantum Chromodynamics, a theory of coloured particles, as well as in the study of hard processes (i.e. in the study of hadron structure at small distances). We know that hadrons are, definitely, composed of large numbers of quarks, antiquarks and gluons. We have learned this from deep inelastic scattering experiments, and this picture is proven by many experiments on hard collisions and multiparticle production. At small distances quarks and gluons interact weakly, obeying the laws of QCD. An important fact is that a coloured quark or a gluon alone cannot leave the small region of the size of a hadron (i.e. that of the order of 10 −23 cm): they are confined -they can fly away only in groups which are colourless.In the fifties and sixties of the last century virtually the whole physics of "elementary particles" (at that time also hadrons were considered as such) was devoted to the consideration of these distances. With the progress of experimental physics very soon even smaller distances were reached at which hard processes were investigated, giving a strong basis to Quantum Chromodynamics -a theory in the framework of which coloured particles can be considered perturbatively. This, and the hope that the key for understanding the physics of strongly interacting quarks and gluons was hidden just here, initiated research towards smaller and smaller distances, skipping the region of strong (soft) interactions. We accumulated a very serious amount of knowledge on the hadron structure at extremely small distances. But looking back to the region of standard hadron sizes, 10 −24 -10 −23 cm, we realize now that, in fact, the physics at ∼ 10 −23 cm in its essential domains remains unknown [1, 2]. We left behind the hadron distances without really understanding all the observed phenomena. We have learned only a small part of what could be learned from the experimental results in that region, not to mention that experiments which could be easily carried out were also abandoned. The physics community just skipped some p...

We consider the pion structure in the region of low and moderately high momentum transfers: at low Q 2 , the pion is treated as a composite system of constituent quarks; at moderately high momentum transfers, Q 2 = 10 ÷ 25 GeV 2 , the pion form factor is calculated within perturbative QCD taking into account one-gluon hard exchange. Using the data on pion form factor at Q 2 < 3 GeV 2 and pion axial-vector decay constant, we reconstruct the pion wave function in the soft and intermediate regions. This very wave function combined with one-gluon hard scattering amplitude allows a calculation of the pion form factor in the hard region Q 2 = 10 ÷ 25 GeV 2 . A specific feature of the reconstructed pion wave function is a quasi-zone character of the qq-excitations. On the basis of the obtained pion wave function and the data on deep inelastic scattering off the pion, the valence quark distribution in a constituent quark is determined.