Köln 2004 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 11: Poster Session: Electromagnetic and Hadronic Probes

HK 11.24: Poster

Tuesday, March 9, 2004, 13:30–15:30, Foyer

Measurement of elastic π^±p cross sections with CHAOS at low energy — •Holger Denz, Johannes Breitschopf, Heinz Clement, Rudolf Meier, Florian von Wrochem, and Gerhard J. Wagner — Universität Tübingen, Physikalisches Institut, Auf der Morgenstelle 14, 72076 Tübingen, Germany

From π^±p scattering data the πp sigma term can be extracted by phase shift analyses. This quantity is a measure of explicit breaking of chiral symmetry due to non-vanishing current quark masses. Recent analyses of πp data found very high values for the sigma term which lead to problems with the interpretation. A possible explanation for the high values could be the scarce and contradictory πN data base at low energies. Our program of measurements of cross section and polarisation observables aims at resolving these problems.
Differential cross sections in elastic π^±p scattering were measured for incident pion energies between 20 and 67 MeV using the CHAOS spectrometer at TRIUMF. In addition to the conventional detector setup a range telescope was placed in the forward scattering region to suppress the decay background which poses a major problem at low energies. This experiment provides a set of data measured simultanously over a large angular range and covering a wide energy range. The experimental setup, analysis and results for incident pion energies between 20 and 45 MeV will be discussed. This work is supported by BMBF(06TÜ987I) and DFG(GRK683).