Re: Fwd: Kfit with timing

[Eugene Chudakov <gen@jlab.org>]

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
> ----------------------------
>