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[Mathias Labonte <mlabonte AT ucdavis.edu>]

Hi Gene,

Thank you for the explanation. I was not aware of this particular effect. 
I’ll take a look at the postXTracks in the muDst. 

Mathias 

> On Oct 31, 2024, at 11:45 PM, Van Buren, Gene <gene AT bnl.gov> wrote:
> 
> Hi, Mathias
> 
> The "last hit at z = -40 cm" tracks are dominated by pile-up from 
> post-trigger-crossing collisions & backgrounds.... Either they are 
> completely pile-up tracks, or potentially they are tracks with many pile-up 
> hits and a few non-pile-up hits.
> 
> I do want to make sure you are aware (though maybe you already are?) that 
> we read out the TPC for longer than the full drift time, specifically so 
> that tracks are more easily identified as being from post-trigger-crossings 
> because they include hits that are reconstructed "beyond" the central 
> membrane (i.e. they have the wrong sign z for the side of the TPC from 
> which they were detected). These tracks are called PCTs (post-crossing 
> tracks. In FXT data, the last hit on PCTs should be between approximately 
> -40 cm < z < 0, and should be visible in your plots as an excess of such 
> hits.
> 
> Likewise, PCTs in FXT should have a first hit excess for 0 < z < +40 cm.
> 
> It is not obvious to me why there would be an excess specifically at last z 
> = -40 cm or first z = +40 cm, without an excess between there and zero.
> 
> -Gene
> 
> p.s. I see no flag for PCTs in either StMuTrack or StPicoTrack. It's there 
> in StEvent/StTrack, but I guess no one thought it worth a single bit in 
> DSTs  :-(
>  bool StTrack::isPostXTrack()
> I also see no count of PCT daughters in the StPicoDst vertex information, 
> but this count is in StEvent and StMuDst (which just re-uses StEvent's 
> StPrimaryVertex):
>  UShort_t StPrimaryVertex::numPostXTracks()
> This leaves you with no handle on PCTs and vertices that use them at the 
> PicoDst level.
> 
> 
> 
> 
>> On Oct 31, 2024, at 8:22 PM, Mathias Labonte <Star-tpc-l AT lists.bnl.gov> 
>> wrote:
>> 
>> Hi Everyone,
>> 
>> Here are comparisons between gene’s production, and the TFG24e production. 
>> Please see the slides below.
>> 
>> 
>> Some things to highlight:
>> 
>> 
>> 
>> I observe that the change in the vertexer cuts do not resolve the DCA y 
>> distributions. I include a slide explaining why we may have initially 
>> thought this.
>> 
>> There are differences between there two productions in the first and last 
>> hit distributions that I find hard to explain.
>> 
>> 
>> 
>> 
>> 
>> Any comments, suggestions, or otherwise are welcome and I look forward to 
>> a discussion on these studies. If you have any ideas to explore further 
>> before the TPC meeting, I would like to hear those too.
>> 
>> Mathias
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> <latest_test_production_comparisons.pdf>
>