DOI: 10.1140/epjc/s2003-01146-0
Measuring the FSR-inclusive
cross section
J. Gluza1, 2, A. Hoefer3, S. Jadach3 and F. Jegerlehner2
1 Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, Poland
2 DESY Zeuthen, Platanenallee 6, 15738 Zeuthen, Germany
3 Institute of Nuclear Physics, Radzikowskiego 152, 31-342 Krakow, Poland
(Received: 2 January 2003 / Published online: 24 March 2003 )
Abstract
Final state radiation (FSR) in pion pair production cannot be
calculated reliably because of the composite structure of the
pions.
However, FSR corrections have to be taken into account for a
precise
evaluation of the hadronic contribution to
g-2 of the muon.
The role
of FSR in both energy scan and radiative return experiments is
discussed. It is shown how FSR influences the pion form factor
extraction from experimental data and, as a consequence, the
evaluation of
. In fact the
FSR
corrections should be included to reach the precision we are
aiming
at. We argue that for an extraction of the desired FSR-inclusive
cross section
a photon-inclusive
scan
measurement of the "
"
cross
section is needed. For exclusive scan and radiative return
measurements in contrast we have to rely on ad hoc FSR models
if we
want to obtain either
or
the
FSR-exclusive cross section
. We
thus
advocate to consider seriously precise photon-inclusive energy
scan
measurements at present and future low energy
e+e--facilities.
Then together with radiative return measurements from DA
NE
and
BABAR and forthcoming scan measurements at VEPP-2000 we have
a good
chance to substantially improve the evaluation of
in the future.
© Società Italiana di Fisica, Springer-Verlag 2003
