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 α_π and β_π of the beam pion, which may be used to test chiral pertubation theory. Under the assumption of α_π + β_π = 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^3π 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.