Status of background studies (Michal Szleper)
Michal
studied the contributions from bbg, ccg, bbbb, cccc and bbcc
using
Whizard 1.24. The controversial bbg and ccg cross sections,
previously
calculated using MadGraph matrix elements, were cross
checked
using CompHEP matrix elements and still look quite the same.
It
is still not clear why they are so large comapred to bb and cc
(roughly
an order of magnitude larger), even in a spin-2
configuration.
Moreover, those cross sections do not converge at
all
unless a gluon energy cut is imposed in the calculation and
different
cut values yield different results. All the above is
true
also for channels with a gamma instead of a gluon, but their
contributions
are much smaller. The four fermion cross section
computations
have been cross checked in the past for 4e, 4mu and
eemumu
and look very reasonable. The bbbb cross section at 120
GeV
is about 300 fb (cf. 6770 fb for bb J=2, 1450 fb for bb J=0)
and
a provisory bb analysis (requiring 2 reconstructed jets, with
cosTheta
< 0.9 and being back to back within 0.1 rad) indicates
that
3-4% of these events are left after cuts. More four-fermion
results
are expected soon.
Status of resolved photon studies (David Asner)
David
has finally understood the difference between his
PYTHIA-Butterworth
estimates for the resolved photons and
Alberts
estimates. Albert estimates gives a cross section of
400
nbarn and are based on an extrapolation from the measurements
made
at LEP. David estimates gave values that where 6 times
larger.
By adjusting the PYTHIA parameters David manage to
reproduce
LEP results and get predictions close to Albert's.
David
will documment his finding and will make public the parameters
that
make PYTHIA compatible with LEP data larger.