EJK has almost completed the work for absorption and decay correction in FS, and hopefully the parametrized curves will become available
tomorrow (Thursday)
I will though spend a few words on an issue that we found puzzling, but now understand.
Usually decay-correction for Kaons are very close to the simple expecation given by the ctau in the decay due to the rather large
q-value in the decay. The puzzle was that in the brag sim+digitization+requiring tofslat+-1 for track pointing the evaluated curve for
Kaon's were ~5-10% above the simple prediction. We looked at the sim in detail and found that at high momentum
the decay production (from K-> mu-pi-neutrino or mu-e-neutrine or pi-pi-pi) would hit very close to the slat as a non-decayed
K with same angle momentum (+-1 slats) and about the same TOF. Typical numbers are
FS 12 GeV Kaon+, 1000 kaon's thrown
no decay 1000 hitting a given tof slat
decay (no secondary == pure decay) 823
decay with secondary 859 ( 16 mu+ and 9 pi+)
So if PID is done by TOF one cannot distinguish primary from thecondary particle giving the tof hit (The decay usually takes place between T4 and TOF2)
If PID is done by the RICH on the other hand- the signal will be large i.e. looking as a pion/muon and the pure decay correction should be done
in the momentum range where Kaon's are well seperated from pi/mu ((up to 18 GeV or so).
In the range where the Kaon do not give signal and the Rich is used to define pion over Kaon/protons it shows that a fraction's
of kaon show up in the pion ID (order ~30/800) 5% and with K/pi~20% this is ~1% correction in the pion spectrum. The Kaon's
would be accounted for properly if the pure decay correction is used.
It is also true as you will see from EJ's curves that the pion is higher due to same focusing effect pi->mu-v;
The correction to be used depends if the final PID can distinguish between muon and pion's
which is only for a narrow range in the RICH.
The important message here is that what decay correction to use depends critically on the PID -method as well
as the momentm.um range
Flemming (+ Eun-Joo)
------------------------------------------------------
Flemming Videbaek
Physics Department
Brookhaven National Laboratory
tlf: 631-344-4106
fax 631-344-1334
e-mail: videbaek@bnl.gov
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