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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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