[G12] Track Inefficiencies - Possible Drift Chamber Issue

Mon Jul 27 03:40:59 EDT 2015

Greetings,

If you are correct, and something is not simulated correctly, then 
wouldn't mapping the efficiencies of each particle in z, p, theta and 
phi for both MC and data suffice to correct for it?

BR
MK
----------------------------------------
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 7/27/15 12:28 AM, Volker Crede wrote:
> Michael,
>
> As much as I was hoping for g11a to be wrong, everything we have 
> observed so far is very consistent with g11a (normalization and 
> angular shape). At the moment, the g12 ω cross section in the forward 
> direction is lower than g11a … This cannot be correct. The g12 
> acceptance is better than in g11a (the target was moved backwards) and 
> reaching 0.9 is reasonable. Mike Williams was also close to that.
>
> The CBELSA/TAPS cross sections are generally higher than the CLAS 
> cross sections (across the entire angular range). This is likely an 
> issue with the absolute normalization and not with the angular shape. 
> Applying your trigger map unfortunately appears to pull up the forward 
> direction relative to the backward direction. If I remember correctly, 
> the CBELSA/TAPS γp → pπ^0 cross section was actually consistent with g1c.
>
> The reason for our lower ω cross section is that our acceptance is too 
> good in the forward direction and our suspicion is that dead detector 
> modules (drift chamber wires and perhaps also TOF paddles) are not 
> simulated correctly. I am afraid something is not right with g12.
>
> - Volker
>
>
>> On Jul 26, 2015, at 3:02 PM, Michael C. Kunkel <mkunkel at jlab.org 
>> <mailto:mkunkel at jlab.org>> wrote:
>>
>> 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
>> ----------------------------------------
>> 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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>>
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