Threshold hyperon production in proton–proton collisions at COSY-11

Abstract

The Σ + hyperon production was measured at the COSY-11 spectrometer via the pp → nK + Σ + reaction at excess energies of Q = 13 MeV and Q = 60 MeV. These measurements continue systematic hyperon production studies via the pp → pK + Λ / Σ 0 reactions where a strong decrease of the cross section ratio close-to-threshold was observed. In order to verify models developed for the description of the Λ and Σ 0 production we have performed the measurement on the Σ + hyperon and found unexpectedly that the total cross section is by more than one order of magnitude larger than predicted by all anticipated models.After the reconstruction of the kaon and neutron four momenta, the Σ + is identified via the missing mass technique. Details of the method and the measurement will be given and discussed in view of theoretical models.

Reexamination of the role of theΔ*resonances in thepp→nK+Σ+reaction

“…What is worse, it is known that the close-tothreshold data are inconsistent between the COSY-11, HIRES and COSY-ANKE groups. The total cross section data from COSY-11 shows strong close-threshold enhancement [13], however, not confirmed by the measurement of other two groups. The COSY-ANKE data * Electronic address: xywang@impcas.ac.cn † Correspondent: caoxu@impcas.ac.cn ‡ Electronic address: xiejujun@impcas.ac.cn follow the behavior of three-body phase-space [14,15] and the values are about one order smaller than that of the COSY-11 at the same energy range [13].…”

“…At present, there are only a few experimental data on the total cross section of the pp → nK + Σ + reaction [12][13][14][15][16][17]. What is worse, it is known that the close-tothreshold data are inconsistent between the COSY-11, HIRES and COSY-ANKE groups.…”

Thepp→pΛK+andpp→pΣ0K+Xie1, Chen2, Oset3 2011Phys. Rev. C8080View full textAdd to dashboardCite

“…More recently the issue of the FSI in these reactions has been retaken in Refs. [5,6] using dispersion relations, and a further experimental research has given more support to the role of the Λp FSI in these reactions [7]. A further incursion into the problem looked for angular distribution as further observable that supported the importance of the Λp FSI [8].…”

Complementary studies on N* from e + e − , pp and pp̄ collisions

“…A recent study [40] on pp → nK + Σ + reaction suggests that the reaction is an excellent place for looking for those "missing" ∆ ++ * with large coupling to pρ + . data [41,42] and calculation (solid curve for sum of other curves) [40].…”

“…Experimentally there are only a few data points about its total cross section versus energy [41,42] . Theoretically a resonance model with an effective intermediate ∆ ++ * (1920) resonance [43] and the Jülich meson exchange model [44] reproduce the old data at higher beam energies [41] quite well, but their predictions for the cross sections close to threshold fail by order of magnitude compared with a recent COSY-11 measurement [42] . Recently this reaction was restudied [40] .…”