[G12] Track Inefficiencies - Possible Drift Chamber Issue

[Michael C. Kunkel]

Greetings,

 From what I see there are 2 things,

1) cos\theta 0.9 is very forward, I do not even think we have good 
events past cos\theta 0.8. Especially with a 3 prong trigger.

2) The mapping I created does pull most distributions high in the 
cos\theta > 0.67, but as I said to Zulkaida and g12 members, this is a 
known effect. I do not think g11 nor g1c was actually all that accurate 
in the forward direction. You, Volker, are the person who put me onto 
the fact that CLAS might have a forward acceptance issue, since your 
analysis of the gp->ppi0 with TAPS showed a higher XSection in the 
forward direction, which also matched that of GRAAL and LEPS.
When I compare gp->ppi0 with g1c, yes g12 is higher in the forward 
direction, but so is the rest of the world. Therefore unless there are 
other measurements to coincide with g11's or g12's measurement, I would 
not say that g11 is the "set in stone" measurement.

BR
MK
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Michael C. Kunkel, PhD
Forschungszentrum Jülich
Nuclear Physics Institute and Juelich Center for Hadron Physics
Experimental Hadron Structure (IKP-1)
www.fz-juelich.de/ikp

On 7/26/15 8:00 PM, Volker Crede wrote:
> Hi Everybody,
>
> I know that we are all working on finalizing various g12 analyses. 
> However, we found a serious issue with our γp →pω cross section that 
> currently prevents us from moving on. We are somewhat stuck and it may 
> affect the whole run group.
>
> The attached pictures show the 3π invariant mass for the energy range 
> 1650 - 1700 MeV and for forward angles of the 3π system. A nice ω peak 
> is visible and a massive hole on the right side of the peak. This hole 
> is not supposed to be there (unless somebody has a good physics 
> argument). The energy range is probably very low for most of the g12 
> analyses. However, the hole will slowly move to higher masses with 
> increasing photon energy but it will not disappear. The other two 
> pictures show the same distribution if one (1) uses events where only 
> sectors 1, 3, 5 triggered or alternatively, (2) only sectors 2, 4, 6 
> triggered.
>
> We assume the effect is based on track inefficiencies, perhaps dead 
> regions in the drift chamber. In principle, Michael Kunkel’s "trigger 
> map" should account for this since his approach is based on comparing 
> two- and three-track events, i.e. it combines trigger and track 
> inefficiencies; the idea is good. In our analysis however, this 
> trigger map leads to an overall disagreement with the g11 ω cross 
> section, whereas Zulkaida's current cross section is in fair agreement 
> with g11 but exhibits certain problematic regions, e.g. the forward 
> direction. These holes in the mass distributions are not accounted for 
> by the Monte Carlo simulations and we assume the effect is not in the MC.
>
> We have a few questions we would like some help with (and need to find 
> an answer for).
>
> 1) Since it is still possible that the problem is at our end, would 
> anybody be able to reproduce this problem for us? The effect is so big 
> that even a quick and dirty look at it, will probably work.
>
> 2) We tried to knock out dead TOF paddles as suggested in the analysis 
> note. The paddle numbers are available in the data. However in the 
> Monte Carlo, the numbers appear to be available only for the proton 
> and not for the pions. Has anybody else noticed this issue? How do 
> others knock out the paddles in the MC? Or is this done automatically? 
> It is difficult to do this based on measured angles since two 
> particles with the same polar and azimuthal angles, one produced at 
> the beginning of the target and one at the end, may hit different TOF 
> paddles. The g12 target was very long.
>
> 3) The Monte Carlo “gpp" options given in the analysis note do not 
> reproduce the holes in the mass distributions. For this reason, we do 
> not know if dead wires are actually simulated and to what extent. Can 
> anybody comment on this?
>
> This problem shows up in the γp → pω channel but we are concerned that 
> it may also affect the two-pion channel we are analyzing, perhaps not 
> as holes in mass distributions but as general track inefficiencies in 
> certain regions of the drift chamber. In the latter case, it would 
> extremely difficult to notice. If so, it can potentially affect any 
> reaction that uses Monte Carlo for the acceptance correction. My 
> understanding is that we partially use the pω and the KΛ cross 
> sections to make sure that the g12 MC, trigger, etc. is working correctly.
>
> Best wishes,
>
> Volker
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