[BLAST_ANAWARE] new calibration in use

From: Chi Zhang (zhangchi@MIT.EDU)
Date: Fri Sep 17 2004 - 16:03:15 EDT


Hi, all

since run 11143, we have been using a new set of calibratoins. Wire
Chamber time to distances are calibrated to 9th-order polynomials per
side per wire. when such a calbibration is not available, Garfield is
used as fall back(with theta correction and k-factor correction).

this set of calibration is tested on unpol H2 data since April and showed
improved resolution in all aspect. In particular left sector electron
momentum resolutions are as low as 18MeV for half of those unpol H2 runs.
left sector electron resolutions are at 22-25MeV level. theta/phi
resolutions are at 0.5-0.6degree level. beam energy is resolved with sigma
of ~25MeV. chi square of fits are reduced by factor of at least 2 compare
to ealier.

the last two days running did not show any problem with this setup. In
addition, the data showed improved resolution in ed-elastic samples. In
particular, mass peak of deuteron samples are resolved now at 1.77+-0.17
GeV, this puts 3-sigma cut at 1.25 which is very promising at further
reducing proton contamination in ed-elastic samples.

It would be interesting to see how this affects(improves or destroys)
critical kinematic variables in other channels such as missing momentum,
missing energy, invariant mass.

In addition to that, the plateau region in phi is expanded from +-10
to beyond +-12 degrees, see from ed-elastic event sample. So we gain some
extra statisctics on top of the improvement of ABS intensity. I am seeing
close to 0.9/C event rate within +-12 degree region.

the idea of this calibration comes from thesis of Aki's and Bin
Zhang's(former student of Bill's worked at CLAS) and a lot help was
received in the implementations of it especially from Chris and Eugine.

I hope dst generated from this calibration could serve as a better
starting point for other calibration methods (Doug's, Chris/Eugine's and
Taylan's) so we converge to a final version of calibrations quicker.

Chi



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