[Halld-cal] BCAL segmentation

[David Lawrence]

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
>>