From: Glen Warren (gwarren_at_jlab.org)
Date: 16-Apr-2003 16:30:47
GEn01 analysis meeting Apr. 16, 2003
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attended by: Paul, Oscar at UVa
Hongguo, Frank, Nikolai, Donal and Glen at JLab
REPORTS
*) new archiver: there was a lot of good comments about the new
archiver. Glen will provide Paul with his list of emails so that Paul
can make a complete copy of the jlab archive.
*) carbon runs, with and without field: no progress because of lack of
run identification. Paul will help identify periods in which the field
was off. It should be fairly easy as we only change once from straight
through to field on for each Q2.
*) theta_nq cut study of background: there was some discussion as to
exactly what can be interpreted from this plot. Nikolai's original
comment that the W peak does not significantly shift with a tighter cut
on theta_nq is true, and it is also true that a wider cut does shift the
W peak. Glen noted that he was uncomfortable with the significant
reduction of events on the high W side for the tight cut compared to the
nominal cut. It is possible that a minor shift in the tight cut
distribution to make the peaks align better would make the impact of the
cut more symmetric. Nikolai then argued that we have solid evidence for
a lack of dilution from background because the proton asymmetries are
very close to being correct, so that further investigation was not a
good use of time.
*) Q2=0.5 Data and MC comparison: there is an approximately 5 MeV shift
between data and MC in W for Q2=0.5. After we complete the third pass
of Q2=1, will will look at the correcting this for Q2=0.5. Glen
expressed some concern that theta_np^cm agreed, but ypos did not. ypos
in MC is only used for cuts, not for construction of neutron angles.
Hongguo shifts the cuts to account for the shift between data and MC, so
everything is okay, although in the future Hongguo should shift the MC
ypos by the the shift in the cut to get good visual agreement in ypos
between data and MC.
*) Radiative correction check: they appear to work well. Glen
questioned why the full MC and data agree for Q=0.5, but the cross
section model and the NE3 data do not, which suggested that we get a
different cross section from NE3. The thought was that it was mostly a
matter of acceptance averaging.
*) inclusive MC-data comparison with and without momentum shifts: From
the previous week, Nikolai had generated this comparison which shows at
face value better agreement between data and MC for shifted data than
for unshifted data. However, his normalizations are arbitrary, so one
cannot really reach that conclusion.
*) Mock extraction of proton asymmetry: Nikolai looked at the proton
asymmetry by comparing measured proton asymmetry times the dilution
factor from MC to proton asymmetries from the data for nominal W and for
shifted W . He sees that the asymmetry changes by 1.3%, which is quite
small. This gives us some hope that the the neutron sensitivity to a
shift in W is small.
*) W for different targets: Hongguo has looked compared data and MC for
non-ND3 targets for Q2=1 and sees a shift in W in all of them.
*) W shift versus momentum shift: Nikolai passionately argued that there
is a certain degree of arbitrariness to our shifting the HMS momentum
because we have no physical evidence to suggest it was not what it was
set to. He argued instead that we should just shift the W spectrum.
Perhaps the problem is a code bug of some short that only affects W. The
problem with this argument is one of consistency with all the other facts.
*) Uncertainties due to momentum shift: The plan is to make a third pass
through Q2=1 data with all the shifts that we believe. We will then
compare the extracted Gen with the shifted and unshifted data
asymmetries using the same MC results. If that difference is small, we
will call that an uncertainty due to this momentum shift.
*) Other avenues to investigate:
-) Carbon with and without field is getting more important
-) look at ND3 and NH3 data from 1998
-) does RSS get the correct W for ND3
-) analyze run without target field reconstruction
TO DO
Hongguo:
*) compare carbon with and without target field at Q2=1 to MC
Frank:
*) target polarization uncertainties for Q2=1 (low)
*) look at W peak variation with run number. (low)
*) determine the ndet position offset to make theta_np^cm agree.
(highest)
*) begin Q2=1 third pass. (high)
*) analyze run without target field reconstruction (low)
Glen
*) review data and MC slopes in W vs theta. Make recommendation
for slope in W cut.
Nikolai
*) Analyze carbon runs without target field to be compared to MC
(both coincidence and inclusive)
*) Investigate Q2=1 data from 1998 (start with Chris Harris' work).
Paul
*) Locate when field was turned on so that we can find Carbon runs
without the field on.
This archive was generated by hypermail 2.1.7 : 16-Apr-2003 16:31:08 EDT