Berlin 2005 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 31: Elektromagnetische und Hadronische Proben
HK 31.1: Vortrag
Dienstag, 8. März 2005, 16:30–16:45, TU MA004
Total cross section of the π− p → π0 n charge exchange reaction — •J. Breitschopf1, M. Bauer1, 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, we have measured total π− p → π0 n
cross sections at PSI in the energy range between 30 and 250 MeV with an
accuracy of about 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.
Experiment, data analysis and results will be presented and discussed.
This work is supported by BMBF (06TU201)and DFG (GRK683).