2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008;
St. Louis, Missouri
Session X3: Topics In Nuclear Physics
1:30 PM–3:18 PM,
Tuesday, April 15, 2008
Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel),
Room: St. Louis E
Sponsoring
Unit:
DNP
Chair: Richard Casten, Yale University
Abstract ID: BAPS.2008.APR.X3.3
Abstract: X3.00003 : Test QCD symmetries via precision measurement of the neutral pion lifetime*
2:42 PM–3:18 PM
Preview Abstract
Abstract
Author:
Liping Gan
(University of North Carolina Wilmington)
Symmetries and their dynamical breaking effects play fundamental
roles in
the nature. In particular, the three light neutral pseudoscalar
mesons $\pi
^{0}$, $\eta $ and $\eta \prime $ contain fundamental information
about
QCD symmetries. While $\pi ^{0}$ and $\eta $ are Goldstone bosons
due to
spontaneous chiral symmetry breaking, the $\eta \prime $ is not
due to the
U(1)$_{A}$ anomaly. There is a second type of anomaly driving the
two-photon
decays of these mesons. Since $\pi ^{0}$ is the lightest meson in
the
hadron spectrum, the chiral anomaly prediction for the $\pi
^{0}$\textit{$\to \gamma \gamma $ }decay
width is more accurate and is exact in the limit of massless
quarks. In the
real world, the SU(3) and isospin breaking by the light quark
masses lead to
important mixing effects among these mesons. Theoretical
activities in this
field over the past several years have resulted in high precision
(1{\%}
level) predictions for the decay amplitude of the $\pi ^{0}$ into
two
photons. As a result, the experimental measurement on this
quantity with a
comparable precision will provide an important test on the
fundamental QCD
predictions. The present experimental uncertainty of the $\pi
^{0}$ decay
amplitude, according to the PDG average, is an order of magnitude
greater
than the theoretical uncertainties. The PrimEx collaboration at
Jefferson
Lab has recently developed and performed a new experiment to
measure the
neutral pion life time with high precision using the small angle
coherent
photoproduction of $\pi ^{0}$'s in the Coulomb field of nucleus,
$i.e.$, the
Primakoff effect. A new level of experimental precision ($\sim
$2.9{\%}
total error) has been achieved by implementing the new high
intensity and
high resolution photon tagging facility in Hall B at Jefferson
Lab and by
developing a novel high resolution electromagnetic hybrid
calorimeter
(HYCAL). The final result of this experiment will be presented.
The advent
of a 12 GeV electron beam at Jlab will make it possible to extend
the
program to $\eta $ and $\eta \prime $. A plan for future $\eta $
and $\eta
\prime $ program will be discussed.
*This project is supported by the U.S. National Science Foundation
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2008.APR.X3.3