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HK: Physik der Hadronen und Kerne
HK 11: Poster Session: Electromagnetic and Hadronic Probes
HK 11.23: Poster
Dienstag, 9. März 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. Wagner1 — 1Physikalisches 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).