[Halld-offline] possible problems with DChargedTrackHypothesis

[Paul Mattione]

You do not need a google account.  I will forward you the email with the instructions.  

 - Paul

On Apr 26, 2016, at 6:35 PM, semenov at jlab.org wrote:

> Paul:
> 
> You suggestion to use the google group is not good for me because I do not
> have google account, and I do not want create it because of the google
> demand to share my cell phone number. I do believe that we are working for
> JLab (not for the Google corporation), so we should use JLab computer
> resources. I would suggest to use "halld-offline" e-mail list. Sorry and
> thank you for understanding. (Alternatively, some shared "gluex" account
> for google might be a solution, but in this case it will be not obvious
> why's actually the author of the specific communication.)
> 
> Talking of "t0 is set to the chosen RF time, propagated to the vertex-z of
> the track": Am I correct that in this case, "t0" should be exactly the
> same as "T" value from the DVertex class? (If yes, it's strange because
> "t0" is close to the "T" from DVertex, but not exactly the same.)
> 
> By the way, how the "t1" value is produced? Is it some estimation from the
> chambers timing, or it came from the "t1_detector" (which is in my case
> always =4; I hope that it corresponds to BCAL). If the last is correct,
> how good this "t1" value is? (Meaning time-walk corrections, channels
> alignment etc.)
> 
> My plot contains all PIDs.
> 
> Talking of multiple hypotheses, I do believe that "PID" in this class is
> not a vector but one number. Does it mean that "DChargedTrackHypothesis"
> vector size is always bigger than the size of the correspondent
> "DTrackTimeBased" vector (that contains one record per one "real" track, I
> hope)?
> 
> I do not agree that the right-column plots do not help. In the case of
> multiple hypotheses (viz., unknown particle mass), the right-column plot
> (which presents the TOF minus the time needed to travel the pathLength
> distance with the speed-of-light) shows that we have a lot of tracks with
> TOF that suggests that the particle travels much faster than
> speed-of-light (negative values in the histogram). If we do not consider
> tachyons seriously, it means that the "TOF" value has some problems.
> 
> I'll produce the "(TOF-L/(beta*C)) vs momentum" 2-dim plots you suggested,
> but it will require a few hours on our computers; I hope that it will be
> ready tomorrow. (I'm not quite sure why you want to see "momentum
> dimension": most probably, it will be just horizontal bands. But OK, no
> problem. Note that I can not just plot "TOF vs momentum" because different
> pathLengths.)
> 
> Thank you,
> Andrei
> 
> 
> 
> 
>> 
>> On Apr 25, 2016, at 8:26 PM, pmatt at jlab.org wrote:
>> 
>> You may know this, but for the record, when you call
>> DKinematicData::TOF(), it is subtracting t1 - t0. In the
>> DChargedTrackHypothesis factory, t0 is set to the chosen RF time,
>> propagated to the vertex-z of the track.
>> 
>> Are you histogramming this for all PID hypotheses?  Or are you always
>> picking the ones with the same PID? (e.g. proton)  Remember, each
>> physical track has multiple hypotheses, for different PIDs.  If you chose
>> all hypotheses, then only one can be correct, and you will see funny
>> structures.  Although yes, they would not give rise to the right-column
>> plots.  However, the tracks certainly aren’t going at beta = 1, so the
>> right plots don’t help much.
>> 
>> You should have separate plots for each PID, and then you should make this
>> a 2D plot vs. track momentum, and you will see a mass dependence that
>> will give rise to the structures.  You should see distinct pion, proton,
>> etc. bands.
>> 
>> - Paul
>> 
>> ************************************************************************
>> 
>> We now have a new method of asking software questions, a google group:
>> gluex-software at googlegroups.com
>> 
>> I am about to forward this message to there, and then will try to answer
>> it there when I have time.  If you are not part of the group yet, please
>> sign up:
>> 
>> https://groups.google.com/forum/#!forum/gluex-software
>> 
>> - Paul
>> 
>> On Apr 25, 2016, at 6:46 PM, semenov at jlab.org wrote:
>> 
>>> Paul, Mark and Simon:
>>> 
>>> I'm trying to use the information from DChargedTrackHypothesis, and I
>>> see
>>> the things I do not understand. If I plot "TOF" (from the class) minus
>>> the
>>> time-of-flight "pathLength*sqrt(mass*mass+pmag*pmag)/pmag/c" (that I
>>> calculated from the variables in the class) for the charged tracks that
>>> are matched with the showers in BCAL, I see some interesting structure
>>> (see the top-left panel in the attached file) instead of expected
>>> centered-at-zero peak with the RMS of the order of the uncertainty on
>>> TOF
>>> (0.4-0.5ns). The bottom-left panel shows the same-variable histogram
>>> with
>>> the requirement to have 3 or more charged tracks in the event (to be
>>> sure
>>> that we have a good start time).
>>> 
>>> For the "mass", I used the "PID" hypothesis in the class. To be sure
>>> that
>>> this structure is not affected much by PID hypothesis, I plotted also
>>> the
>>> histograms for "TOF-pathLength/c" (see the right column in the file);
>>> everything that is visibly below zero are "tachyons" :) that means that
>>> the problem is probably with the "TOF" variable which is the difference
>>> between "t1" (stop time) and "t0" (start time) variables. "t0" is pretty
>>> close to the "vertex" time "T" from DVertex class.
>>> 
>>> As you can see from the plot, the peaks in the structure are not
>>> separated
>>> with 4-ns intervals, so I would not blame "wrong-RF-bucket" reason.
>>> 
>>> For this plot, I used run 3180, and my version of sim-recon is 1.10 .
>>> 
>>> Most probably, I just using something incorrectly, and you already have
>>> a
>>> good explanation for the plots I see. Could you please help me?
>>> 
>>> Thank you,
>>> Andrei<tdiff-160423.pdf>
>> 
>> 
> <tdiff-160423.pdf>