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Re: Fwd: Kfit with timing
Hall D PID Mail List:
On Mon, 24 Mar 2008, Alex Dzierba wrote:
Dear all,
I totally agree all the work is very nice.
The only thing which still worries me a bit is the assumptions on the
error matrix for the tracking. I think we should show one or 2 example for
the kinematic fits, but should clearly point out that this is still a
point of concern.
cheers elke
> Date: Mon, 24 Mar 2008 07:17:20 -0400
> From: Alex Dzierba <dzierba@indiana.edu>
> To: Eugene Chudakov <gen@jlab.org>
> Cc: halld-pid@jlab.org, bellis@ernest.phys.cmu.edu,
> cmeyer@ernest.phys.cmu.edu
> Subject: Re: Fwd: Kfit with timing
>
> Hall D PID Mail List:
>
> Dear Eugene, Matt et al
>
> Matt indeed did a nice job and I find his results almost too good to
> be true. But to first order they are consistent with bubble chamber
> data at these energies.
>
> Most of information about photoproduction at 9 GeV comes from a SLAC
> bubble chamber experiment (Bingham et al, Phys Rev 8 (1973) 1277).
> They employed kinematic fitting to identify the reactions with 4pi-p
> final state and 2pi-2K-p final state (in the 5-prong topology) and
> found these to be in the ratio of 10:1. They were able to identify
> the proton in the bubble chamber by dE/dx. There was no way to
> separate pions from Kaons. They did studies to look at how many
> simulated events had an incorrect kinematic identification. These
> were not very clearly described in the paper but it seems that the
> level of misidentification was of order 1%. That same experiment
> also looked at the 7-prong events and identified the 6pi-p and
> 4pi-2K-p final states and found these in the ratio 15:1.
>
> A note regarding Pythia backgrounds: When I did Pythia studies in
> September (see GlueX-doc-856) I found that for the 4pi-p and
> 2pi-2K-p reactions the effective mass distribution for all four
> mesons in both reactions showed no structure - it rose nearly
> linearly with mass from threshold and rolled over to zero at the
> kinematic limit. In the 4pi-p sample there was no structure in the
> 2pi masses (no rho's) but in the K-pi mass distributions - it seemed
> to be largely K*(890).
>
> Are there 5-prong events with a clearly identified proton in the CLAS
> data? And have these been analyzed with kinematic fitting and if so
> what are the results?
>
> Cheers
> Alex
>
> >Hall D PID Mail List:
> >
> >Hi all,
> >
> >after messing around a bit with the event fitting I came to an agreement
> >with the points made by Matt Belis. Indeed, using the chi2 of the 4C fit,
> >(or a reasonably tight Delta(E) separation after the 3C fit) reduces
> >the BG dramatically. With a loose cut of CL>1% along with the PID
> >cuts, practically
> >no BG from p2pi+2pi- is left.
> >
> >For the PYTHIA data, the same cuts lead to a signal/all ratio
> >of about 90%. After the kin. cut, the proton PID reduces the BG
> >by a factor of 3 and the kaon PID - by a factor of 2.
> >For twice larger errors on the tracks and beam, the ratio
> >becomes 70%, while for 4-times larger errors it becomes 30%.
> >
> >If only the 3-mom chi2 is used, the signals/all is about 0.2,
> >with the PID suppression factor of about 25.
> >
> >Thanks to Matt for a nice piece of work and for making his point.
> >
> >I will change this part of the talk. One may summarize with smth like:
> >
> >- identification of fully reconstructed events with charged kaons
> > should be feasible, providing the expected quality of pattern
> > recognition, levels of the background, and understanding of the
> > resolutions of the track parameters.
> >- Identification of kaon events with a missing particle (a neutron
> > recoil, for example), will most likely require an additional PID.
> >
> >
> >Eugene
> >
> >------------------------------------------------------
> >Eugene Chudakov
> >http://www.jlab.org/~gen
> >phone (757) 269 6959 fax (757) 269 5703
> >
> >On Sat, 22 Mar 2008, Matt wrote:
> >
> >> Hi Eugene,
> >>
> >> I've uploaded a summary talk to the portal, GlueX-1009. This talk
> >> summarizes what I've done on these PID studies involving pi/K separation.
> >> I've also uploaded the source file with all the figures in case you want to
> >> include any of them.
> >>
> >> There's a lot of information there, so I leave it to your discretion what
> >> you want to use. But I wanted to make sure there is enough background for
> >> you to be able to answer any questions you may or may not get at the review.
> >>
> >>
> >> Some of this may answer a question Alex raised in an earlier email this
> >> morning regarding using the kinematic fitter for PID.
> >>
> >> Matt
> >>
> >>
> >> On Fri, Mar 21, 2008 at 10:47 AM, Eugene Chudakov <gen@jlab.org> wrote:
> >>
> >> > Matt,
> >> >
> >> > I am going to include a slide on the kinem. fitting with the something
> > > > like:
> >> > - 3-C fit improves the track resolutions
> >> > - kin. fitting allows a considerable improvement in identification of
> >> > events with kaons over simple kin. constraints.
> >> > - the results depend on prominance of backrounds which are flat
> >> > or non-Gaussian in the residual space.
> >> > - in the ideal case a strong possible suppression can been obtained
> >> > - the work is in progress
> >> >
> >> > You may send me a few statements (items) you would like to make.
> >> > Also, you may include a plot. Will you do it?
> >> >
> >> > Yesterday, I tried the 3-C fit, using the event 3-momentum. It gave me
> >> > some additional
> >> > BG reduction, a factor of 2 perhaps, with simple cuts and without
> >> > a signal suppression. I will look further into it.
> >> >
> >> > BTW, what improvement in track momentum resolution did you obtain with the
> >> > 3-momentum fit? For p2K3pi events I get on average 2.4%-->2.0% - not that
> >> > much.
> >> > I assumed the diagonal covariance matrix for p,theta,phi.
> >> > The energy residual becomes very narrow for "true" events,
> >> > so adding the 4-th fit should not change the track resolution.
> >> >
> >> >
> >> > ------------------------------------------------------
> >> > Eugene Chudakov
> >> > http://www.jlab.org/~gen <http://www.jlab.org/%7Egen>
> >> > phone (757) 269 6959 fax (757) 269 5703
> >> > Thomas Jefferson National Accelerator Facility
> >> > 12000 Jefferson Ave, Newport News, VA 23606 USA
> >> >
> >> >
> >> >
> >>
> >>
> >> --
> >> --
> >> ----------------------------
> >> Matt Bellis
> >> Carnegie Mellon University
> >> (office) 412-268-6949
> >> (cell) 412-310-4586
> >> ----------------------------
> >>
>
>
> --
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Alex R. Dzierba
> Chancellor's Professor of Physics (Emeritus)
> Department of Physics / Indiana U / Bloomington IN 47405 / 812-855-9421
> JLab Visiting Fellow
> Jefferson Lab / 12000 Jefferson Ave / Newport News, VA 23606 / 757-269-7577
> Home Phone: 812-825-4063 Cell: 812-327-1881 Fax: 866-541-1263
> http://www.dzre.com/alex
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
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