[Clas12_verystrange] Fwd: FT Timing and PiD taskforce!

[Eugene Pasyuk]

-Eugene

----- Forwarded Message -----
| From: "Derek Glazier" <Derek.Glazier at glasgow.ac.uk>
| To: "Raffaella De Vita" <devita at ge.infn.it>
| Cc: "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: Thursday, June 21, 2018 4:51:21 AM
| Subject: Re: FT Timing and PiD taskforce!
| 
| Hi Raffaella,
| 
|    Thanks for the clarifications. I mentioned the phi offset as I see
| this in the simulation of the order 0.5-1 degrees and had assumed a
| correction was still to be applied. I attach a plot of simulates FT
| e-
| phi - true value. Also shown is the phi of a pi- in the FD. There are
| actually significant deviations in reconstructed momentum of the FD
| particles (not shown), probably I should wait to test the new gemc
| before investigating further.
| 
|    Back to timing. I attach plot of the momentum dependence of the e-
| vertex time (RF bunch corrected). There is a reasonably strong
| dependence in the e- energy range 0.5-2. Also shown are the
| parameters
| of gaussian fits to slices in this distribution. The shift at low
| energy
| is of the order 0.5ns, also the sigma below 1GeV is considerably
| larger
| than high energies. This is probably the reason for the apparent
| decrease in resolution between run 3050 (open FT trigger) and the
| production runs which had the FT energy range restricted.
| 
|   Possibly a momentum dependent Ft timing calibration/correction
|   could
| be on a wish list.
| 
| Cheers
| 
| Derek
| 
| 
| On 21/06/18 00:42, Raffaella De Vita wrote:
| > Hi Derek,
| > thanks for compiling the list. I included some comments below.
| > Cheers,
| > Raffaella
| >
| >
| >> **  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?)
| > This is already done. Angles, both theta and phi, are already
| > corrected. For now, the cluster position from the calorimeter is
| > used
| > but, when tracking reconstruction will be implemented, we should
| > certainly use the fttrk position.
| >>
| >> -- Should be different for charged and neutrals
| > It is
| >>
| >> - 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.
| > Shower depth is already implemented. The depth was tuned based on
| > simulations.
| >
| >> ** 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.
| > I agree
| >
| >>
| >>
| >> -- 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
| > Mon12 can only display raw data while this kind of check requires
| > reconstruction. This is part in fact of the calibration suite. So
| > far,
| > calibrations were performed for 3-4 runs and no big changes were
| > seen.
| > Once pass0 will be done, we can do monitoring plots for all the
| > runs
| > and see when we need to recalibrate.
| >
| >>  --- 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]
| >> <RFVertexTime3050.pdf>
| >> <ExclusiveStartTimeDifference.pdf>
| 
| 
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