[G12] Track Inefficiencies - Possible Drift Chamber Issue

Mon Jul 27 12:50:40 EDT 2015

Greetings,

I am not attending today's meeting. Please fill me in on this discussion.

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 4:09 PM, Volker Crede wrote:
> Michael,
>
> I agree that the idea sounds correct, we have already discussed this 
> here. For this reason, Zulkaida applied your "map" but unfortunately, 
> it does not reproduce the holes in the mass distributions.
>
> - Volker
>
>
> On Jul 27, 2015, at 3:40 AM, Michael C. Kunkel <mkunkel at jlab.org 
> <mailto:mkunkel at jlab.org>> wrote:
>
>> 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
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> G12 mailing list
>>>>> G12 at jlab.org
>>>>> https://mailman.jlab.org/mailman/listinfo/g12
>>>>
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>
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