Hi all,
I would like to bring to your attention to the yields from recent unpol
runs.
since 22nd, we v been running with unpol gas with Mass Flow Controller
dialed at different values, and I analyzed the yield from these run.
Again I present the yield by equivalent gas flow assuming 100% detection
efficiency:
gas flow dialed flow from edelastic yield runs
-------------------------------------------------------------
4.48 atoms/sec (0.05sccm) 1.67+-0.17 atoms/sec 1262-1277(June)
9.96 atoms/sec (0.1sccm) 7.82+-0.21 atoms/sec 1642-1725(7/22-
7.97 atoms/sec (0.08sccm) 3.69+-0.36 atoms/sec 1726-1730
4.48 atoms/sec (0.05sccm) 2.83+-0.09 atoms/sec 1731-1799
the errors on the yield are estimated from the number of counts in the
fastest counting bin Q^2 = 0.125-0.185 GeV^2
yield/(dialed gas flow) varries from 37%(0.05sccm runs: 1262-1277) to
79%(0.1sccm runs: 1642-1725) and the two series of 0.05sccm runs one month
apart produce rather different yields.
Detection efficiency could well be varying during these days, due to the
raise and lower of left box 6, however, there is definitely no evidence
that the efficiency changed by a factor of 2.
Again, this indicates the limit of the current flow control system. these
1sccm controlers provides errors of 1% full scale, calibrated with N2 gas.
for D2 gas which has smaller mass, the uncertainty is 0.025sccm. when
working at 0.05sccm, the error could be as large as 50%.
It may be possible to calibrate the linear relation between real gas
output and dialed value, but seems the validity of such a calibration over
a long period of time is still questionable.
It demonstrates again the need for a reliable and accuate gas flow system.
Otherwise, calibration and monitoring of detector efficiency and target
density would always be entangled and hard to resolve independantly and
definitively.
Chi
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