Proton-antiproton annihilation at rest into two mesons is analysed in a model describing annihilation by quark lines. The model allows to fit existing data with two parameters. The parameters describe the amplitudes for diagrams with and without rearrangement of quark lines.PACS: 12.35Ht; 13.75CsUnderstanding long-range strong interactions at the level of the underlying quark dynamics is a major challenge in present medium and low-energy physics. Yet even though the existence of quarks was originally deduced from low-energy hadron spectroscopy, it is not at all clear that quarks and gluons are really needed to describe low-energy strong interaction dynamics. Models of NN interactions based on meson exchange potentials are, e.g., very successful and provide a very good description of experimental data [1].The extension of meson exchange models to Nb7 interactions is in principle straightforward [2][3][4]. In these models antiproton-proton annihilation is described by baryon exchange [5][6][7]. But even though this approach seems to be well founded, many authors have attempted to describe Nb7 interactions within the quark model approach [8][9][10][11][12][13][14][15][16][17][18][19]. These groups emphasize the importance of the following two questions: Is there a dominance of "annihilation" or "rearrangement" type of diagrams (Fig. l a, b)? Are In this letter we present further evidence that NN annihilation at rest into two mesons seems to require a description in terms of quarks. The argument is based on SU(3) invariance and the validity of the OZI rule. There are no dynamical calculations involved. In particular no assumption is made concerning the spin and angular momentum of annihilating q ~ pairs.Most data on i0p annihilation at rest stem from bubble chamber experiments [20]. Antiprotons stopping in liquid H2 form protonium atoms; due to Stark mixing these annihilate dominantly from S wave orbitals [21]. (The principle quantum number n is not known; presumably n~5... 20). The contribution of annihilations from P states was estimated to be less than 6% [22]; it is mostly neglected in the analysis of the data. Hence two protonium states supposedly contribute to annihilations in liquid H2, the 2S+IL s =13S1) and ]1S0) states with quantum numbers jec= 1--and 0-+, respectively. Both states can annihilate into even and odd numbers of pions (n~). Since the G parity is G=(-1)"==( -1) L+s+I, the protonium wave function must have two isospin components. The isospin decomposition can be written as
12S+Isj)= {as l as+ 1S j; I = 0,13 = 0) +bjI 2s+lSJ;I= 1, I 3=0)} with lasl 2 + IbjI 2 = 1.(1)
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