[d2n-analysis-talk] DL.bit3 Analysis

[Brad Sawatzky]

Repost.

On Fri, 27 Aug 2010, Brad Sawatzky wrote:

> 
> On Thu, 26 Aug 2010, David Flay wrote:
> 
> > Looking at hits 0 and 1, I plotted their TDC histograms (see attached).  A
> > plot of hit 0 shows a self-timing peak at ~1000 channels.   We see a broad
> > peak at ~700 channels featured in hit 1, in addition to a large peak <=20
> > channels. I'm not quite sure why this is...
> 
> I presume it's because you are plotting DL.bit3[1] even when 
> NData.DL.bit3 == 1 (so DL.bit3[1] is really undefined).
> 
> > Also -- If I make a cut (DL.evtypebits&(1<<3))==(1<<3) on the DL.bit3
> > histogram, events still show up outside the cut range specified in the
> > source (THaDecD (see attached -- red line [dead time pulse + evtypebits
> > cut] overlaps exactly with black line [dead time pulse cut]).  Wouldn't
> > the evtypebits pick out only those events that are within the (200,1500)
> > cut window?
> 
> DL.evtypebits is a pretty trivial quantity and is defined quite explicitly
> in the DecData class.  You can only get into trouble (and get inconsistent
> results) if the number of actual hits (for DL.bitN in this case) is handled
> incorrectly.  (So, the inconsistent results suggest that there is an
> indexing problem associated with the histograms you're generating.)
> 
> You can also run into issues with when cutting on DL.evtypebits if
> mathematical operator precedence if you're not careful with parentheses.
> Your expression above looks good though, so I don't think that is the case
> here, but I thought I'd mention it just in case you're missing parentheses
> inside your actual code.
> 
> Please poke into the details and track down why you're seeing a
> discrepancy.  Then add this to next weeks report so the other students can
> learn to recognize and avoid the problem too.
> 
> -- Brad
> 
-- 
Brad Sawatzky, PhD <brads at jlab.org>  -<>-  Jefferson Lab / Hall C / C111
Ph: 757-269-5947  -<>-  Fax: 757-269-5235  -<>- Pager: brads-page at jlab.org
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