A new model forN $$\bar N$$ annihilation

Abstract

A new quark model for Nb7 annihilation is proposed. It is argued that a linear superposition of the so-called SP 0 and SS t models is more consistent with QCD and the inclusion of quark degrees of freedom in NN scattering, and is also suggested by the data. A comparison is made, in Born approximation, with the angular distribution for p~AA. PACS" 25.10+ 5; 12.40.Qq Applications of QCD to low energy hadronic interactions require numerical calculations on a lattice or models. Among the latter are bag models, topological and nontopological soliton models, and flux-tube type models. It has been shown that the so-called SP o model [1,2] in which a quark(q)-antiquark(~) pair are created from, or annihilated into, the vacuum is related to QCD and flux-tube approximations thereto [3]. In recent years an effective perturbative approach [4] or "3S1" model [5,2] 1 has also been shown to be effective in describing reactions in which a q ~ pair is annihilated or created. Reactions in which these models have been applied include nucleon-antinucleon (NbT) annihilation [2].A number of recent letters and papers argue that one model (e.g. 3P0) is superior to the other (e.g. "3S 1 ") [6]. We wish to argue in this short article that such comparisons should not be made, but rather, that these two models emphasize different aspects of QCD. Furthermore a description consistent with NN scattering models also leads to a superposition of the 3P 0 and "sst" models as components of an overall scheme. We show that this is also suggested by the data.Almost all models which incorporate quark-gluon degrees of freedom in the description of the NN inter-1 The name sS 1 is a misnomer because the virtual gluon exchanged between quarks/antiquarks has both transverse (je = 1 -) and longitudinal (JP=0 +) or Coulomb components. It thus is not a pure (qO) sS1 model, and we use quotes for that reason action [7] require two parts: (1) a short distance one gluon exchange force and (2) a long distance scalar confining force. Indeed the combination of the one gluon exchange and a linear confining force reproduces the spectra of heavy quarkonia systems such as c g, b b, and those of one light and one heavy quark such as D ~ D ~ [8]. For light quark (u, d, s) systems the confining forces are often taken to be harmonic (~ r 2) in potential models [7]. If we begin with a field theory and use crossing symmetry, then consistency requires that similar forces should be present in the NN system, i.e. a short range one gluon exchange and a long range scalar interaction.The important features which appear to be present in both nuclear and quark systems is that they are dominated by scalar (or pseudoscalar) and vector interactions. In the NN system these are described, at large distances, by ~, a, p, and co exchanges. In q q and q c~ systems they arise from gluon exchange and the confining force. There is good evidence [9] that the confining force is a scalar one which is independent of flavor, whereas the one gluon force is clearly a colored-vector exchange one.In ...

Observables in high-statistics measurements of the reactionp¯p→Λ¯Λ

“…transition have been studied in many theoretical papers [34]{ [61]. These descriptions have been of three general types: the strangeness production originates from the t-channel exchange of K mesons [34]{ [40]; the process originates from the s-channel annihilation of a uu pair and the subsequent production of an ss pair that is accompanied by four`spectator' quarks [41]{ [51] (other work has focused on quark descriptions via quark counting rules [52]); model-independent analyses of the low-momentum data, which are based on a partial-wave amplitude decomposition [53]{ [55]. Since only a few partial waves contribute here, it may be possible to learn more about the underlying reaction mechanism.…”

The potential of $$\varLambda $$ and $$\varXi ^-$$ studies with PANDA at FAIR

“…From this, conclusions about the Λ quark structure can be drawn: the spin of the Λ is carried by the strange quark, while the light u and d quarks form a spin-0 di-quark. Theoretical investigations based on the aforementioned quark-gluon approach [25][26][27][28][29], kaon exchange [30][31][32][33][34] and a combined approach [35], reproduced this finding. However, no model so far describes the complete spin structure of the reaction.…”

“…Therefore, the relevant degrees of freedom in processes involving strange quarks are unclear: quarks and gluons, or hadrons? Single-strange hyperon production inp p →Ȳ Y has been modeled using quark-gluon degrees of freedom [25][26][27][28][29], meson exchange [30][31][32][33][34] and a combination of the two [35]. The production of double-strange hyperons requires interactions at shorter distances, since it either implies annihilation of two quark-antiquark pairs [36][37][38][39], or exchange of two kaons [40].…”

“…(ΩB, Ω B ) = (ΩB) • (Ω B ). (29) We then define the following matrices of efficiency weighted moments A μ,ν ≡ cos θB μ cos θB ν (ΩB)dΩB (30)…”

PANDA Phase One

“…Exclusive hyperon-antihyperon production provides the cleanest environment to constrain these models. Phenomenological models based on quark-gluon degrees of freedom [114][115][116][117][118], meson exchange [119][120][121][122][123] and a combination of the two [124] have been developed for single-strange hyperons. The quark-gluon approach and the meson exchange approach have also been extended to the multi-strange sector [125][126][127][128][129].…”