Ed Hartouni Study Commentary
Date: Fri, 21 Mar 2003 09:53:27 -0800
From: "Edward P. Hartouni" <hartouni1@LLNL.GOV>
Subject: TOF MCS
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To: E907@fnal.gov
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Hi all,
here are some thoughts I've written up on track fitting, momentum
resolution, and the TOF multiple scattering. I appologize for the
inclusion of the MSExcel file, but I thought it would be good to
include for those interested in the details. While I have attempted
to be careful in these calculations, I believe it is important to
provide the details in a way that the collaboration can check.
Summary:
Using the fact that the Rosie magnet can be approximated as a "thin
magnetic lens" element, the change in x-z slope of a particle before
and after the magnet is a measure of the z-component of momentum. A
straight line fit of the track upstream and downstream, and the
momentum "kick" of the magnet suffice to measure the track momentum.
The fit proceeds by using 3 chambers, 1,2,3 upstream and 4,5,6
downstream with the trajectory parameters being the slope and the
position of the trajectory at the "bend point" in Rosie. The fit
includes realistic mesurement resolution in the chambers and the
current MIPP geometry. The TOF can be introduced as a scatterer and
the effect on the momentum reconstruction studied.
First finding is that, with the resolution of the E690 and the Iowa
chambers,the momentum resolution of the "Rosie spectrometer" is
dpz/pz = 0.0034 pz [GeV/c]. Note that his gives 34% resolution at 100
GeV/c. At this high momentum the scattering angle variation
introduced by a 5 cm thick scintillator plane is comperable to the
error in the determination of the downstream slope. At 10 GeV/c, the
error would be dominated by the multiple scattering, but the
fractional error is small, and would probably tolerable for the MIPP
measurement program (Rosie probably does not have to be good at
measuring these particles, the "Jolly Green Giant spectrometer" does
a good job up to 15 - 20 GeV/c).
The conclusion: if this momentum resolution is tolerable, the 5 cm
thick scintillator is not a big effect.
However, if a high resolution chamber (for example, 50 microns) is
added at the chamber 6 location, the momentum resolution at 100 GeV/c
is lowered to rougly 2.5% with no TOF. Adding the 5cm thick TOF then
dominates the slope determination. A hole of roughly +- 15 cm, +-11
cm (x,y) in the scintillator would allow 50 GeV/c particles with as
much as +-1 GeV/c of transverse momentum to pass unscattered.
Attachment converted: Charged_Particle_Tracking.pdf (PDF /CARO) (0014C4F0)
Attachment converted: TOF_MCS.pdf (PDF /CARO) (0014C4F1)
Attachment converted: E907_trajectories.xls (XLS8/XCEL) (0014C4F4)
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Ed Hartouni N-Division Leader
hartouni1@llnl.gov
L-056
University of California
(925)422-3801 (office)
Lawrence Livermore National Laboratory (925)423-3371 (FAX)
7000 East Ave., P.O.Box 808
(800)759-8888 1750246
Livermore, CA 94551
1750246@skytel.com (short emails)
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