[Halld-cal] BCAL segmentation

[semenov at jlab.org]

David:

2 comments:

1. Irina's name is "Irina" and not some other ancient-Greek versions (with
all my respect to the Greek culture :)

2. About to use the fitting function instead calculating RMS: I do agree
that the fitting procedure (with Breit-Wigner convoluted with Gaussian or
just sum of 2 Gaussians or Gaussian core and some tails) will provide more
stable result; but we need agreement about what value to use as the
numerical estimator of the resolution. If we use "1-sigma" analog (viz.,
sixty-something percent confidence interval), we will catch the "core"
structure only and will not be sensitive much to the tails, and definitely
we don't want to do such a thing. I do believe that 95%-confidence
interval will be much more appropriate, but we all should be aware that it
corresponds to "2-sigma-resolution" if we will make any comparisons with
the "1-sigma" resolutions from Gaussian-shaped spectra.

So, do we all agree to use from now the 95%-confidence interval as the
resolution?

Thank you,
Andrei







> Hi Irinia,
>
>      Please find my responses below.
>
> On 3/31/11 9:20 PM, stepi at jlab.org wrote:
>> Hi David,
>>
>> plots on the 2nd slide were calculated for the range of z  from -34cm to
>> 30 cm (Near part of BCal).
> OK. This would make things seem more consistent. Your plots looked
> similar to my ~90 degree plot which I believe corresponds to z=0 in your
> coordinate system.
>
>> For the RMS calculation I used the same method : TH1D :: GetRMS().
>> For the histogram presented on this slide limits for RMS are:
>> (-15 to 15)  for the histogram "Fine-Segmented" and
>> (-30 to 30)  for the histogram "Summed-in-Towers".
>>
> Looking at the documentation for TH1, it looks like we should be calling
> TH1::StatOverflows() prior to filling the histogram if we want the RMS
> to include the tails. I did not do this myself, but will correct that.
> If that is not done, then the RMS will be a (possibly strong) function
> of the histogram limits.
>
>> For the comparison consistency :
>> All these results ( energy resolution, polar angle and azimuthal angle)
>> were obtained under the following conditions:
>> ( "nTrue == 1&&  prim == 1&&  nShow == 1" )
>> that were created as:
>> ......
>>     m_rootTree->Branch( "nTrue",&m_nTrue, "nTrue/I" );
>>     m_rootTree->Branch( "prim", m_primary, "prim[nTrue]/F" );
>>     m_rootTree->Branch( "nShow",&m_numShowers, "nShow/I" );
>>
>> I have few questions to you:
>>
> OK, that may explain part of the discrepancy. In my RMS plot I'm not
> cutting on having only 1 reconstructed shower and I have no cut to
> ensure the primary particle makes it to the BCAL. My events will
> therefore, not be as clean so the tails will be a little larger which
> would blow up my RMS.
>
>> 1. You didn't put the numbers for the RMS on your plots. It's good to
>> know
>> how big the difference really is.
>>
> I can do this, but I don't trust the RMS as a good indicator since it is
> so sensitive to the tails. I think we we need to find an appropriate
> fitting function.
>
>> 2. What version of reconstruction code did you use? As I mentioned
>> before,
>> I am using tag version sim-recon-2011-02-02 . Matt recently found the
>> bug
>> in the smear.cc that included in this release.
>> To fix this bug,  the opening lines of SmearBCal should be changed to:
>> ......
>>    for( int m = 1; m<= 48; ++m ){
>>      for( int l = 1; l<= 10; ++l ){
>>        for( int s = 1; s<= 4; ++s ){
>> ............
>> (the l and s loop limits were swapped).
>> For the plots presented on the meeting, the "bagged" version was used.
>> After fixing the bug, the change in the angle and the energy resolutions
>> is not big.
>>
> I used revision 7602 from the repository which looks to still have the
> bug. I'll fix that as well.
>
>
> Regards,
> -Dave
>
>
>> Thank you,
>> Irina
>>
>>> Hi Andrei and Irina,
>>>
>>>       I've start trying to look at the splitoffs issue for the course
>>> vs.
>>> finely segmented readout options in the BCAL. One of my first steps was
>>> to try and compare resolutions to some plots you showed at the meeting
>>> this week as a check that I've got the course segmentation set up
>>> correctly. I've not gotten results that seem completely consistent with
>>> yours. I'd like find the source of the discrepancy. I've put a couple
>>> of
>>> the plots into a PDF that I uploaded to the wiki here:
>>>
>>> http://www.jlab.org/Hall-D/software/wiki/images/7/7f/20110405_bcal_segmentation.pdf
>>>
>>> My first question is if the resolution plots shown on your 2nd slide
>>> were for the full range of z or, just for some range around 90 degrees.
>>>
>>> Also, how did you calculate the RMS? In my plots, I just used ROOT's
>>> TH1D::GetRMS() method which I believe is limited by the defined
>>> histogram range (-20 to +20 in my case). I would think that by cutting
>>> off the tails, I would get a *smaller* RMS than the actual, but mine
>>> seems bigger than yours. Any clues as to why?
>>>
>>> Regards,
>>> -David
>>>
>