Hello, some propaganda plots for the collimator. These are all normalized
yields (to charge) vs the vertex position in cm, positive is downstream
and this time they should be ok..
attach #1 blue is before, red after collimator insertion. And Ion pol
removal. This is a plot of z-left, for "all" tracks, i.e.
irregardless of physics, trigger type and/or tracking on
opposite sector
Comparing data where you only have the cell clearly shows a significant
improvement. Note that the "peak" downstream was seen also before the ion
pol lens. Please check runs 300-400 and so
attach #2 As above but now minimal ep cuts have been applied: a track for
one negative and one positive charge, z-range is +- 15 cm and
(z-left-z-right) < 1 cm. THere is no "physics" cuts however on
angle, moment or coplanarity.
attach #3 As above but the green curve is the normalized yield for 0.05
sccm hydrogen. As you can see there is a factor 10 reduction in
the empty target yield whihc is now 1% of an expected ABS flow
(new ABS)
attach #4 as 3, in linear scale.
In these last two plots the ratios of the total normalized yields for 0.05
sccm gas, empty before collimator, empty after collimator become 23.3 vs
3.0 vs 0.36 respectively
Things eventually get even better with realistic hydrogen cuts, when the
ratios becme 9.26 vs 0.22 vs 0.014, respectively, with a total empty
rate of 0.5 % of the 0.05 sccm rate (note, this was done for a cold cold target
of ca 70 K), as shown - vs Q2 - in attch #5.
The last plot really makes me think that we have to account for beam
blow-up properly, which we still have to characterize. The Q2 distribution
of these data does not seem very natural (soon compared to mc...) Surely the
collimator reduces backgrounds, but we may be limited by beam blow up.
Regards
-- tancredi
________________________________________________________________________________
Tancredi Botto, phone: +1-617-253-9204 mobile: +1-978-490-4124
research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949
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