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Darmstadt 2008 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 2: Elektromagnetische und Hadronische Sonden

HK 2.4: Talk

Monday, March 10, 2008, 15:00–15:15, 1C

Measurement of Pion Polarizability and Chiral Anomaly in Primakoff Reactions at COMPASS — •Thiemo Nagel1, Anna-Maria Dinkelbach2, Jan Michael Friedrich1, Sergei Gerassimov1, Stefanie Grabmüller1, Florian Haas1, Bernhard Ketzer1, Igor Konorov1, Roland Kuhn1, Sebastian Neubert1, Stephan Paul1, and Quirin Weitzel1 for the COMPASS collaboration — 1TU München, Physik-Department E18 — 2Prüftechnik Alignment Systems, 85737 Ismaning

In a pilot run in 2004, the COMPASS experiment at CERN observed the scattering of negative pions of 190 GeV/c off various nuclear targets, measuring soft processes. Primakoff reactions, i.e. interactions between the beam particle and a quasi-real photon from the Coulomb field of the nucleus, are used to study the physics of strong interaction at small momentum transfer.

The inverse Compton scattering reaction π + Z —→ π + γ + Z gives access to the polarizabilities απ and βπ of the beam pion, which may be used to test chiral pertubation theory. Under the assumption of απ + βπ = 0 a preliminary result has been extracted which is in agreement with calculations of χPT.

The π0 production reaction π + Z —→ π + π0 + Z permits determination of the F coupling constant of the γ → 3π vertex, a measurement crucial for the confirmation of the chiral anomaly hypothesis. Here, the current status of analysis will be shown.

This work is supported by BMBF, Maier-Leibnitz-Labor München and Cluster of Excellence 153.

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