[Clas12_verystrange] Fwd: FT Timing and PiD taskforce!

[Eugene Pasyuk]

-Eugene

----- Forwarded Message -----
| From: "Eugene Pasyuk" <pasyuk at jlab.org>
| To: "Derek Glazier" <Derek.Glazier at glasgow.ac.uk>
| Cc: "Lei Guo" <lguo at jlab.org>, "Achyut Khanal" <akhanal at jlab.org>, "Raffaella De Vita" <Raffaella.Devita at ge.infn.it>,
| "Raffaella De Vita" <devita at ge.infn.it>
| Sent: Thursday, June 21, 2018 10:42:18 AM
| Subject: Re: FT Timing and PiD taskforce!
| 
| Perhaps we should consider option of using the FTHODO time for
| charged particles in FT. It should be independent on the FTCAL
| threshold and shower profile. For neutrals we still use FTCAL time.
| 
| -Eugene
| 
| ----- Original 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>
| | 
| | 
|