From: Glen Warren (gwarren_at_anti-spam)
Date: 30-Apr-2003 16:16:23
GEn01 analysis meeting Apr. 30, 2003
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attended by: Donal, Paul, Oscar, Jechiel at UVa
Hongguo, Frank, Nikolai and Glen at JLab
REPORTS
*) field on- field off studies: Nikolai showed a plot of dry Carbon
using standard proton definitions for two runs, one with field on and
one with field off. The shapes and peaks were similar but had some
differences. Nikolai attributed the differences to a difference in
acceptance in the two situations. The rates for the two runs are
similar, but Nikolai could not be me quantitative.
*) 98 Data: Hongguo and Nikolai compared run 22325 (NH3) from 98.
Hongguo used his old engine and Nikolai the '01 engine. The 98 engine
had fewer counts, the peak looked slightly lower and slightly wider than
the 01 engine. The 01 engine had troubles analyzing the run, so it is
not clear how to do an absolute normalization of the two. Nikolai and
Hongguo will attempt to replay the same number of events.
The 98 data with the 01 engine gave a peak location of 945 +- 5 MeV.
*) Energy loss in 01 engine on 98 data: Nikolai had earlier expressed
some concern about the energy loss for the 98 data with the 01 engine.
He checked the values, and they are reasonable.
*) 98 NH3 W peak: Nikolai recalled that he observed a shift in the W
peak when he bypassed the target field code in the reconstruction. This
is in contradiction to some earlier observations of Frank.
*) x musings: Frank had looked at x instead of W and found it to be
about 0.05 below 1.0 for 3rd pass. Hongguo pointed out that a 22 MeV
shift in E' would shift x by about 4%.
*) histogram normalization: We agreed that histograms that are for
data/MC comparison are to be in units of 1/nA/h = 1/3.6 mC. It is
possible that we will need an overall scale for MC to agree with data,
but we will determine that when we need it.
*) theta_np^cm: There was a discussion about the need for charge
normalization of the theta_np^cm histogram. Hongguo argued that shifted
W or ndet angle only reallocates events from one side of 180 degrees to
the other. Frank argued that the two sides are affected different.
Frank will sum the histograms for different ndet angles and W cuts to
check this.
*) Chi**2: Some concern was raised that the chi**2 in 3rd pass got
dramatically worse compared to 2nd. Glen argued that the chi**2 for 2nd
pass were unreasonably low, i.e. 0.1-0.2 / DOF, and that the increase in
chi**2 is entirely acceptable.
*) Shift W cuts: To avoid a long discussion, Frank will shift the W cut
by +15 MeV on the 2nd pass data to see what the impact may be.
*) Data-MC comparison: Neutron data looks reasonable within statistics.
Proton doesn't look as pretty, but is probably equally acceptable in
terms of statistics. Hongguo needs to make a plot of 2nd and 3rd pass
proton data compared to MC.
*) theta_nq: Frank reiterated his concern about the disagreement in
theta_nq. Nikolai pointed out that a proper normalization would make
much if not all of the difference go away.
*) ypos: there was much vigorous discussion about ypos and what the ndet
angle should be. Hongguo, Frank and Glen will complete the discussion
later.
*) 4k shield energy loss: It is not corrected for in the engine, and it
is not included in the MC. The impact will be small, probably sub-MeV,
so it is should not be much of a problem.
*) Radiation: Donal presented a plot of radiated and born inclusive
cross sections from a 3He measurement at similar kinematics to Q2=1.
The radiated cross sections were peaked at much higher W than one would
naively expect. However, this is what we see our single arm MC, i.e. W
peaks much higher than 940, and our data peak is above the MC.
TO DO
Hongguo:
*) Replay same number of events as Nikolai for run 22325
*) Replay over NH3 runs to see if they are okay.
*) compare carbon with and without target field at Q2=1 to MC
*) Compared 2nd and 3rd pass proton data to MC.
*) Make data-MC comparison weighted by Charge (in particular theta_nq)
*) reach some agreement about ypos
Frank:
*) Check counts in theta_np^cm for different ndet angles and E'
offsets.
*) Shift W cut by +15 MeV on 2nd pass data.
*) reach some agreement about ypos
Glen
*) reach some agreement about ypos
*) review data and MC slopes in W vs theta. Make recommendation
for slope in W cut.
Nikolai
*) Replay same number of events as Hongguo for run 22325
*) Continue to attempt replay of Q2=1 data from 1998
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