[Halld-tracking-hw] [CDC] preAmp follow up on todays meeting

[Beni Zihlmann]

Hi Yves,
I have one question about the 2-dim histograms in

http://www.jlab.org/Hall-D/software/wiki/index.php/Energy/Amplitude_as_a_function_of_drift_time

the vertical bands clearly visible at channel 2000 and beyond are equidistant. on the right plot
one even sees hints for this bands below 2000. Do you know what that is?

cheers,
Beni 


> Hi Lubomir,
>
>   
>> - the maximum amplitude of the first peak (this is what you mean by 
>> amplitude, right?)
>>     
> Yes
>
>   
>> is almost constant, except at the extreme  track 
>> positions. One expects this because this amplitude is related the cluster (or 
>> few clusters) that is closest to the wire and should not depend on the path 
>> length. To make sure that this correct, could you make a profile plot: the 
>> mean amplitude vs drift time, excluding the overflow channels.
>>     
> I added this plot (non-tracked and tracked version) on
> http://www.jlab.org/Hall-D/software/wiki/index.php/Energy/Amplitude_as_a_function_of_drift_time
>
> It is fairly constant, there is a slow trend downwards.
>
> Cheers,
>  	Yves
>
>
>
>   
>> Thanks,
>> Lubomir
>>
>>
>>
>> On Wed, 7 Jul 2010, Yves Van Haarlem wrote:
>>
>>     
>>> Hi All,
>>>
>>> This is to follow up on the discussion we had on todays meeting.
>>>
>>> After watching Germany lose I locked myself up the lab and noticed that:
>>>
>>> 1/ That weird noise peak, mentioned in the meeting, is caused by the 
>>> thermo-couple. If I switch off the T-controller that peak disappears.  It 
>>> makes sense because after we fixed a gas leak the thermocouple must have 
>>> moved closer to the straws, it is around this time this noise appeared. -- 
>>> problem solved at the moment by switching off the T monitoring. Also, the 
>>> noise is higher in amplitude on straws close to the T-couple.
>>>
>>> 2/ By comparing drift time spectra of the old preamp (as in the published 
>>> paper) with the new preAMp at 2100V and 50-50 gas. It can be seen:
>>>
>>> http://www.jlab.org/Hall-D/software/wiki/index.php/Drift_time_comparison_(gas_check)
>>>
>>> that the new preAmp shows that the longest drift times are 100~ns shorter 
>>> compared to the old measurement, this means that the gas mixtures are 
>>> different. L'histoire se r?p?te: mysteries with the old pre-amp were 
>>> explained by wrong settings of the gas flow controllers. Now the mystery of 
>>> the new preAmp has again something to do with the gas mixture. Indeed Beni, 
>>> it looks like a 60/40 Ar/CO2 gas: both drift-time as efficiency-curve wise. 
>>> Back then the problem with the gas mixer was easily fixed because some 
>>> settings were wrong, now it has to be something else.
>>>
>>> Personally I do NOT think it is worth to send the preAmps back before we 
>>> solve this gas problem. If you still want me to send them to J-lab please 
>>> ask me to do so.
>>>
>>> The way we can solve/avoid the gas problem is to compare with pre-mixed 
>>> gas: we have 90-10 Ar-CO2 premixed. This will take time... Or we can order 
>>> 50-50 premixed and repeat our studies, or we just put the 90-10 premixed in 
>>> and compare with the measurements done for the paper and track down 
>>> problems with the gas mixer later. Personally I would go with the last 
>>> options because this produces results concerning the new preAmp faster.
>>>
>>>
>>> 3/ The plots requested by Lubomir with Energy/amplitude as a function of 
>>> energy (using cosmics) can be found here:
>>>
>>> http://www.jlab.org/Hall-D/software/wiki/index.php/Energy/Amplitude_as_a_function_of_drift_time
>>>
>>> Expected behavior can be seen, this data is not tracked (to save time), so 
>>> some noise hits are present. Let me know if you want the tracked version 
>>> too.
>>>
>>> Cheers,
>>> 	Yves
>>>