DOI: 10.1140/epjc/s2003-01134-4
The radiative return at
- and
B-factories:
small-angle photon emission at next-to-leading order
H. Czyz1, 2, A. Grzelinska1, 2, J.H. Kühn1 and G. Rodrigo3
1 Institut für Theoretische Teilchenphysik, Universität Karlsruhe, 76128 Karlsruhe, Germany
2 Institute of Physics, University of Silesia, 40007 Katowice, Poland
3 Theory Division, CERN, 1211 Geneva 23, Switzerland
(Received: 16 December 2002 / Published online: 26 February 2003 )
Abstract
The radiative return offers the
unique possibility for a measurement
of the cross section of electron-positron annihilation into
hadrons
over a wide range of energies. The large luminosity of present
- and
B-factories easily compensates for the additional
factor
of
due to the emission of a hard photon. Final states
with photons
at large angles can be easily identified. The rate for events
with
collinear photons, however, is enhanced by a large logarithm
and allows,
in particular at lower energies, for a complementary measurement.
The Monte Carlo generator PHOKHARA, which includes next-to-leading
order
corrections from virtual and real photon emission, has been extended
from large photon angles into the collinear region, using recent
results for the virtual corrections. In addition, the present
version
includes final state radiation for muon and pion pair production
and
final states with four pions. Implications for the experimental
analysis at three typical energies, 1.02, 4 and 10.6 GeV, are
presented:
the magnitude of these new corrections is studied, possibilities
for the separation of initial and final state radiation are proposed,
and the differences with respect to the previous treatment based
on structure
functions are investigated.
© Società Italiana di Fisica, Springer-Verlag 2003
