The European Physical Journal A

, Volume 39, Issue 3, pp 315–321 | Cite as

Unexpected features of e+e- \( \rightarrow\) p\( \overline{{p}}\) and e+e- \( \rightarrow\) \( \Lambda\) \( \overline{{\Lambda}}\) cross-sections near threshold

Regular Article - Theoretical Physics

Abstract

Unexpected features of the BaBar data on e + e - \( \rightarrow\) B \( \overline{{B}}\) cross-sections (B stands for baryon) are discussed. These data have been collected, with unprecedented accuracy, by means of the initial-state radiation technique, which is particularly suitable in giving good acceptance and energy resolution at threshold. A striking feature observed in the BaBar data is the non-vanishing cross-section at threshold for all these processes. This is the expectation due to the Coulomb enhancement factor acting on a charged fermion pair. In the case of e + e - \( \rightarrow\) p \( \overline{{p}}\) it is found that Coulomb final-state interactions largely dominate the cross-section and the form factor is | G p(4M 2 p)| ∼ 1 , which could be a general feature for baryons. In the case of neutral baryons an interpretation of the non-vanishing cross-section at threshold is suggested, based on quark electromagnetic interaction and taking into account the asymmetry between attractive and repulsive Coulomb factors. Besides strange baryon cross-sections are compared to U -spin invariance predictions.

PACS

11.30.Er Charge conjugation, parity, time reversal, and other discrete symmetries 13.40.Gp Electromagnetic form factors 13.40.Ks Electromagnetic corrections to strong- and weak-interaction processes 

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Copyright information

© SIF, Springer-Verlag Berlin Heidelberg 2009

Authors and Affiliations

  • R. Baldini
    • 1
    • 2
  • S. Pacetti
    • 1
    • 2
  • A. Zallo
    • 2
  • A. Zichichi
    • 1
    • 3
    • 4
  1. 1.Museo Storico della Fisica e Centro Studi e RicercheE. FermiRomeItaly
  2. 2.Laboratori Nazionali di FrascatiINFNFrascatiItaly
  3. 3.INFN and Department of PhysicsUniversity of BolognaBolognaItaly
  4. 4.CERNGenevaSwitzerland

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