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Köln 2004 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 11: Poster Session: Electromagnetic and Hadronic Probes

HK 11.23: Poster

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

Total cross section of the π p → π0 n charge exchange reaction — •J. Breitschopf1, H. Clement1, M. Cröni1, H. Denz1, E. Friedman2, E. Gibson3, P. Jesinger1, R. Meier1, and G. J. Wagner11Physikalisches Institut, Universität Tübingen — 2Racah Institute of Physics, The Hebrew University, Jerusalem, Israel — 3California State University, Sacramento, USA

The origin of isospin violation in the strong interaction is the mass difference of the up- and down-quarks. Pion-nucleon elastic scattering and single charge exchange (SCX) offers access to the amount of isospin breaking. Recent analyses of existing data have found unexpectedly large (7%) violations for pion energies around 50 MeV. However, these analyses are probably affected by the limited SCX data base.
Therefore, at PSI we have measured total π p → π0 n cross sections for energies between 30 and 250 MeV aiming at an accuracy of 1-2%. We used a 4π scintillator box to measure the transmission of negatively charged pions through accurately manufactured CH2 and C targets of about 4 mm thickness. The difference of the transmissions corresponds to reactions on hydrogen with outgoing neutral particles and yields the SCX cross sections. Non-vanishing detector sensitivities for photons and neutrons, effects of detector geometry, radiative pion capture pion decay etc lead to corrections of up to 8%. These were determined by extensive Monte Carlo simulations. Data were recorded event by event yielding about 2.5 TB of data. Detector, data taking procedure, status of the analysis and preliminary results will be presented.
This work is supported by BMBF (06TÜ987I)and DFG (GRK683).

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