Dear Friends,
Andrei has made a first look at EM dissociation
for sqrt{s}=200GeV. He takes -40<Z<40 and requires that there
be zero hits
in both the left and right beam-beam counters. He then has
79K events below 600GeV. He then fits the spectrum to a set of
5 gaussians centered at 100, 200 ... 500 GeV with widths of
sigma, sqrt(2)*sigma, sqrt(3)*sigma etc where sigma is a fit
parameter. The other 5 parameters are the normalisations of the
gausians. For the ratio of 2/1 neutrons he gets .38+-.01 where I would
guess a systematic error of .04. He cannot yet use the tiles in
his veto. We will contact Hiro about using the silicon as an
additional veto on charged particle multiplicity.
The value of 0.38+-.04 is slightly higher than we observed at
130GeV. RELDIS predicted very little change between the two
energies since we are well above threshold for 2 neutron production.
. For what it is worth the ratio 3N/1N=.18 +- 0.3(stat) compared to
0.12 at 130GeV. So the fraction of
3 neutron events seems to be rising more rapidly with energy
than that of 2 neutrons. I will send out a revised summary
plot shortly.
Yours Michael
Michael Murray, Cyclotron TAMU, 979 845 1411 x 273, Fax 1899
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