[Clas12_verystrange] Fwd: FT Timing and PiD taskforce!

[Eugene Pasyuk]

-Eugene

----- Forwarded Message -----
| From: "Derek Glazier" <Derek.Glazier at glasgow.ac.uk>
| To: "Lei Guo" <lguo at jlab.org>, "Eugene Pasyuk" <pasyuk at jlab.org>, "Achyut Khanal" <akhanal at jlab.org>, "Raffaella De
| Vita" <Raffaella.Devita at ge.infn.it>
| Sent: Wednesday, June 20, 2018 6:28:05 AM
| Subject: FT Timing and PiD taskforce!
| 
| Hi folks,
| 
|    From the meeting minutes I see we are officially forced to perform
| some tasks. Here are my thoughts on the issues, please comment, add,
| remove,...It would be good to come up with a list of specific tasks
| assigned to a responsible person.
| 
| **  FT time **
| 
| - Need to include full swimming to get correct path
| 
|    (  --related to this but not specific to time, the e- in the FT
|    have
| a phi offset due to the solenoid. Perhaps this can be corrected at
| the
| same time as the path. Perhaps this also need FTTrack info?)
| 
|   -- Should be different for charged and neutrals
| 
| 
| - Need to account for shower profile/depth
| 
|   --Probably this can just be a constant offset (~1cm) which can be
| determined once the path is corrected.
| 
| 
| ** FT time for Start Time**
| 
| 
| - Should the FT time be used to detemine the start time for
| time-based
| tracking?
| 
|   --This is distinct from should the FT time be used to determine the
| start time for PID. In general it should be for PID as not all
| reactions
| will have a start time from the FD and those that do will not be as
| reliable as the FT if the resolution we have seen for the FT holds
| up.
| 
| 
| -- For time based tracking,
| 
| case e- in FD : use FD based start time
| 
| case pion in FD and FT hit : I attach a plot of the vertex time- RF
| time
| , for the FT and for different PID in the FD. The FT time looks
| better
| than pion times. Although as I mention the FT time resolution is not
| so
| good for run 3432.
| 
|    --- How often is the FT timing alignment performed, should this be
| done for every run/week/run period? Probably someone should monitor
| the
| resolution for the cooked data files, is this done in CLAS12 mon ?
| 
|    --- In general an algorithm could determine the RF based start
|    time
| for FD and FT, if these are the same then everything is fine and the
| tracking can proceed. If these are different then a choice needs to
| be made.
| 
|   --- I also attach a plot of my own RF based starttime - EB
|   starttime
| for background subtracted 2 pion events. I sent this to Raffaella
| yesterday and include the explanation below +++. But basically it
| looks
| like for good pion events the 2 agree 99.9% of the time.
| 
| --- If I understand this should be equivalent to the plot Achyut
| showed
| yesterday, but I did not understand why that plot did not have spikes
| but rather Gaussian distribution.
| 
| --- One complication may be random background events which I have
| subtracted. It may be that a different beam bucket track is selected
| to
| give the start time for all tracks if it has the highest momentum.
| 
| ---- Is this an actual issue? In general the event multiplicity is
| very
| high (I think mostly from tracking artefacts rather then real random
| events)
| 
| 
| ** PID **
| 
| --Event Builder already provides a PID, why do we need something
| else?
| 
| --- PID not 100% particularly pi/K > 2GeV . For exclusive reactions
| we
| can take both hypothesis and use energy and momentum conservation to
| decide. This is essentially what GLUEX do with their kinematic fit.
| 
| --- Can try additional information (e.g. DeltaE)  and use correlated
| information between different tracks, rather than 1 track on its own.
| 
| --- Can try additional methods like machine learning (I have a couple
| of
| summer students looking into this)
| 
| -- I think we still need to monitor/control what PID is being
| developed
| and have (strict) guidlines for validating it before the working
| group
| can accept it.
| 
| Cheers
| 
| Derek
| 
| +++ For events which have a start time (~28% do not) I find very
| little
| difference between the EB starttime and the one that I find (using
| FTCAL::clusters::time, and I think this is the time that should go in
| the EB for the FT rather than FT::particles::time; or
| REC::scintillator::time for the FD e-). This is when I select
| exclusive
| e,p,pi+,pi- topology and perform a background subtraction i.e. it
| should
| be pure signal events. The plot is attached which shows the startime
| difference between my code and the EB for e- in the FT and e- in FD.
| At the moment I am only looking at events where all particles have a
| measured time, so I think that ensures there is a valid start time
| too.
| 
| 
| 
| [University of Glasgow: The Times Scottish University of the Year
| 2018]
| 
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