Nuclear Physics Seminars

ics Special Colloquium
Tuesday, March 20, 2001
3:30 PM
Physics Building, Room 204
Ashot Gasparian [Host: Gordon Cates]
Jefferson Lab
"The Chiral Anomaly and Neutral Pion Lifetime"
ABSTRACT:
The system of the three light neutral mesons, pi-zero, eta eta-prime, contains fundamental information about chiral symmetry breaking in low energy QCD. In particular, SU(3)and isospin breaking by the light quark masses lead to important mixing effects among the mesons. Because of the small mass of the pion, the prediction of the chiral anomaly for the pi-zero To gamma - gamma decay width is more accurate and exact in the limit of massless quarks. In this limit the predicted decay width depends only on two fundamental constants: the number of colors in QCD,and the pion decay constant.The “PrimEx ” collaboration at Jefferson Lab will perform a high precision measurement of the neutral pion lifetime using the small angle coherent photoproduction of pi-zero's in the Coulomb field of a nucleus,i.e., the Primakoff effect. After giving a general overview of chiral symmetry breaking and the appearance of the chiral anomaly at low energies,this talk will present previous measurements and focus on the current experiment at JLab. The experimental program for the more massive eta and eta-prime mesons with the 12 GeV JLab energy upgrade will also be discussed.

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