Baryon Vertex Research Articles

Sum rules for baryonic vertex functions and the proton wave function in QCD

We consider light-cone sum rules for vertex functions involving baryon-meson couplings. These sum rules relate the non-pertubative, and experimentally known, coupling constants to the moments of the wave function of the proton state. Our results for these moments are consistent with those obtained from QCD sum rules for two-point functions.

More on the flux tube model of the deconfining transition

A recently proposed flux tube model describing the finite temperature deconfining transition in QCD is analysed in mean field theory. The phase structure is studied as a function of the baryonic vertex energy.

Superconvergence and the structure of current vertices

The vector and axial-vector form factors of the baryon vertices (B' mod Jmu mod B) (with B, B' denoting the nucleon or the Delta (1232) resonance) are predicted by means of superconvergence sum rules for momentum transfer satisfying mod K2 mod <1 GeV2. The existing experimental data confirm the numerical results for the form factors. It is a consequence of the high-energy constraints that these vertices are conserved or partially conserved, which is a necessary condition that CVC or PCAC, respectively, applies. Furthermore, it can be shown that no isotensor and second-class contributions of these vertices exist for K2 approximately=0 in the framework of these approximations. Internal symmetry predictions in the framework of broken U(6,6) theory can be reproduced.

A selection rule on angular momentum transfer in reactions of the type [formula omitted

An analysis of 50 experimental data on polarization and correlations of polarization in the reactions π N→ϱΔ, ωΔ and KN → K ∗Δ, ϱΣ ∗, ΦΣ ∗ strongly suggests a pure ΔJ=1 transition at the baryon vertex. A plot for testing graphically the linear constraints of the selection rule ΔJ=1 is proposed.

The s-Dependence of F/D Ratio and Universality of UR Amplitudes

The expenmental features of total cross sections up to FNAL region are analyzed systematically from the viewpomt of umversality of UR amplitudes. It is shown that p­ anel w-umversality relations wh1ch are independent of F/ D ratio are well satisfied. The relations among total cross section differences which reduce to the Johnson-Treiman relations and the Freund relations m the case of pure ftype coupling for baryon vertex are also :;atJsfied when the s-dependent F/D ratio F+=l+2.0(pdpo)0 • 75 (po=l GeV/c) is introduced. :Vloreover, the imaginary parts of the noncliffractive amplitudes and the cliffractive amplitudes are extracted. The rismg of total cross sections is bnefl.y discussed.

Partial-wave analyses of the (3π)-system in the reaction π−p → π−π−π+p at 11.2 GeV/ c

The results are presented of two partial-wave analyses of the (3π) − system in 30 000 events of the reaction π −p → π − π − π +p at 11.2 GeV/ c. Both techniques incorporate the assumptions of the isobar model and are (a) the University of Illinois program which fits in terms of the (3π) density matrix elements and (b) an amplitude parametrisaton including possible effects of both spin non-flip and spin flip at the baryon vertex. The results obtained with these independent programs are found to be very close. The proportions of contributing states, their t-dependence and the phases of off-diagonal density matrix elements are discussed for the mass range 0.9 M(3 π) 1.9 GeV/ c 2. The A 1 phenomenon is investigated in the context of a recent model; values of the mass, width and cross sections for the A 1, A 2, A 3 states are given, and an interesting variation in the 2 +P M=1 wave is observed at high masses.

Universality of Urbaryon Rearrangement Amplitudes

The concept of universality of urbaryon rearrangement amplitudes is introduced, in which the amplitudes of the same type of urbaryon rearrangement for meson-meson, meson-baryon and baryon- (anti) baryon scattering are described as common with each other and the ampli­ tudes of each type are counted even in the presence of the U (6) symmetry breaking, i.e., not pure f-type coupling. Relations for helicity non-flip and flip amplitudes are obtained on the basis of the concept of universality. Above all, it should be noticed that the following results are derived: (i) The relations which comprise the Johnson-Treiman relations and the Freund relations as special cases are obtained and in good agreement with experiments if one takes D/F ratio of helicity non-flip part as F+ =f+/ Cf+ +d+) =1.5. (ii) Universality relations for t-channel iso-scalar part in helicity non-flip and flip amplitudes hold independ­ ently of D/F ratios. (iii) Universality relations for t-channel iso-vector part depend on D/F ratios. (iv) The experimental ratio of polarizations for K+p-elastic scattering to that for pp­ one can be explained reasonably. These results give support to the view that the countable nature of constituent urbaryons reflects on the scattering amplitudes for hadronic reactions. Furthermore, the validity of the universality of urbaryon rearrangement amplitudes suggests that urbaryon rearrangement interaction shares a coupling strength independent of the num­ ber of spectator urbaryons (the universality of urbaryon rearrangement interaction). From the viewpoint of the urbaryon rearrangement (hereafter referred to as UR) it has been found that various characteristic features of hadronic reactions could be interpreted as a consequence of several properties of each UR amplitude. Presumptive evidence in support of the composite model of hadrons and UR model seems to be exhibited in the examination of hadronic reactions in terms of UR. 1 l~s) Especially the validity of the additivity of UR amplitudes seems to be closely related to existence of urbaryon and its dynamics. In view of the elucidation of dynamical properties of urbaryon, it is an interesting problem to ascertain more definitely whether the countable nature of constituent urbaryon reflects on the scattering amplitudes of hadronic reactions. The quark counting 7l in 1965 has been one of the first attempts on the above problem. In this model, however, the scattering amplitudes have not been classified according to the UR diagrams contributing to each process, and furthermore the countable nature of constituent urbaryons is indelibly associated with pure f-type coupling for baryon vertex which is also required by U(6) symmetry. As a result of quark count­ ing, for example, the following relations for total cross sections of high energy meson-baryon and baryon- (anti) baryon scattering have been obtained:

Experimental evidence for a violation of a quark model prediction at the baryon vertex

The matrix-elements of the reactions A + N → B + (Λ, Σ, Y ∗ (1385)) where A and B are hadrons and N is a nucleon, are related by quark model predictions or alternatively by baryon form-factors derived from SU(6) symmetry. Experimental results from various reactions at several energies are presented and found to be in disagreement with the prediction: the Σ and Y ∗ cross sections are consistently too large compared to the Λ cross section. Detailed analysis of vector-meson production in K −p and K −n interactions at 3 GeV/ c indicate that the violation is mainly due to the spin-flip contribution at the baryon vertex.

Behavior of Baryon-Baryon and Baryon-Antibaryon Total Cross Sections at High Energy

The energy-dependent parts of baryon-baryon and baryon-antibaryon total cross sections at high energies are obtained from (i) factorization of the residues of the leading meson trajectories, and (ii) the connection between the absence of resonances in "exotic" channels and the flatness of meson-meson and meson-baryon total cross sections in these channels. (Such a connection leads to exchange degeneracies, all of which are consistent with experiment.) The following is proven: (a) Nucleon-nucleon (and certain other $B=2$) total cross sections are flat whether or not trajectory couplings obey $\mathrm{SU}(3)$; (b) the remaining $B=2$ cross sections are flat if tensor and vector exchanges couple via $\mathrm{SU}(3)$, with equal $\frac{F}{D}$ ratios at the baryon vertex; (c) non-Pomeranchuk contributions to baryon-antibaryon total cross sections persist in the 10, $\overline{1}\overline{0}$, and 27 channels despite the relaxation of assumptions regarding $B=2$ systems. [Results similar to (a) and (b) have been assumed to hold in previous approaches.]

A Regge pole + cut model for two-body reactions dominated by ϱ exchange

The reactions π N → Ω N and π N → ΩΔ are analysed in terms of a model involving (a) reggeised ϱ exchange (b) the assumption that the ϱ coupling in the baryon vertex changes the baryon helicity by one and that the NϱΔ coupling is of dipole type (c) the cuts associated with the ϱ pole through absorption. Since the reactions πN → π 0n and πN → πΔ also can be described by this model we propose that it is valid for all two-body reactions dominated by ϱ exchange.

Possible Effects of Strong Interactions in the Feinberg-Pais Theory of Weak Interactions

We show that, in the simplest model where strong interaction effects are included in the baryon vertices and propagators only, the peratization of the nuclear vector $\ensuremath{\beta}$-decay coupling strength is no longer equal to the corresponding peratization of the $\ensuremath{\mu}$-decay coupling strength. This might suggest a vastly different role of strong interactions in the weak interaction (peratization) theory of Feinberg and Pais, in order to conform with the observed equality of nuclear vector $\ensuremath{\beta}$-decay and $\ensuremath{\mu}$-decay strengths.