Göttingen 1997 – scientific programme

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HK: Hadronen und Kerne

HK 26: Hadronisch wechselwirkende Sonden I

HK 26.4: Talk

Tuesday, March 25, 1997, 15:15–15:45, HS H

The dynamics of particle annihilation and production at low energies^* — •K. Röhrich, for the PS185 Collaboration — Inst. f. Kernphysik, Forschungszentrum KFA, D-52425 Jülich

Threshold production of YY pairs in pp annihilations has special features which make the study of these processes unique. The final state particles contain strangeness and thus tag the creation of a new qq pair. Near threshold they are produced with very small momenta and therefore only small orbital angular momenta contribute. The hyperons/antihyperons decay weakly. Their asymmetric two body decay is used to determine the spin configuration of the final state. Our experiment has measured angular distributions of cross sections for ΛΛ, ΛΣ^o+cc and Σ^±Σ^± and polarisations for those reactions involving Λ and Σ^o (anti)hyperons. The data have been taken at momenta from the reaction threshold up to almost 200 MeV above and allow a comprehensive study of the reaction dynamics. The pheripheral character of the reaction, indicated by the strong forward peeking of the cross section, underlines the importance of the annihilation in the process. Polarizations are supposedly more sensitive to initial and final state interactions. They are found to be positiv at small, and large and negativ at larger momentum transfer values. Spin correlations for the final state particles are determined. It turns out that ΛΛ is always produced in triplet configuration, while for ΛΣ^o+cc a sizeable singlet contribution is found.

^* work supported in part by BMBF
The PS185 Collaboration at LEAR/CERN: B.Bassalleck¹, B.Bunker⁸, H.Dennert⁴, H.Dutz², B.Eisenstein⁸, W.Eyrich⁴, D.Fields¹, H.Fischer⁵, G.Franklin³, J.Franz⁵, R.Geier⁶, R.Gering², J.Hauffe⁴, D.Hertzog⁸, T.Johansson⁷, K.Kilian⁶, P.Kingsberry¹, K.Königsmann⁵, E.Kriegler⁵, J.Lowe¹, C.Meyer³, W.Meyer⁹, W.Oelert⁶, K.Paschke³, M.Plückthun², S.Pomp⁷, B.Quinn³, G.Reicherz⁹, K.Röhrich⁶, M.Ruh⁵, H.Schmitt⁵, T.Sefzick⁶, F.Stinzing⁹, D.Wolfe^1
1University of New Mexico Albuquerque, ²Universität Bonn, ³Carnegie Mellon University, ⁴Universität Erlangen-Nürnberg, ⁵Universität Freiburg, ⁶IKP, Forschungszentrum Jülich, ⁷University of Uppsala, ⁸University of Illinois Urbana-Champaign, ⁹Universität Bochum