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Nuclear Physics Seminars
| Special Colloquium
Tuesday, March 20, 2001
Physics Building, Room 204
[Host: Gordon Cates]
"The Chiral Anomaly and Neutral Pion Lifetime"
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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