Minutes:
Chris was showing some studies of the effect that the bugfix of the
fieldmap has on the reconstruction.
The change of the field is at most on the order of 100G, however most
of the changes are outside or at the edges of the wire chamber
tracking regions. Chris evaluated the "kinematic" corrections for
electrons and protons in both sectors based on ep elastic scattering,
assuming that the angles are correct, for both field maps. The
comparison of those momentum corrections between the two fieldmaps
shows that the changes are in fact small, except for a localized
region in the right sector near th=35 degree and phi=0. What matters
most for the momentum determination is the curvature of the track at
the wire chamber, and here the field changes are small. In swimming
the track back to the target, a change in the field would rather affect
the angle and z more than momentum. The question is how much theta, z and
p are shifted when using either one of the two fieldmaps.
Chris then argued that the observed corrections of momenta as
functions of angles are asymmetric both with respect to the particle
species (electron vs. proton) as well as with respect to the sector
and argued that this cannot be explained by a change of the field
(would cause symmetric offsets). Chris generated code that translates
momentum offsets into corrections to the field map. In tuning the
field to correctly track electrons, proton reconstruction gets worse,
and vice versa. So the discussion points back to the geometry which
could in principle cause asymmetric momentum shifts. Apart from the
survey it is also questioned if e.g. the wire chambers have some
internal degrees of freedom that are not apparent when surveyed from
outside. We agreed on the following near-term to-do-list:
-switch sectors in blast.geom
-hand integration of tracking
-vary middle wire chamber vs inner and outer chamber (this is a
potential candidate as it would affect protons and electrons in
opposite ways, and it would be sector-dependent)
-test geometry with global geometry fit with straight tracks or
comsics.
Chris is leaving us after next week. It would be great if a dedicated
analyst can be found to further investigate these things
(Chi?, Eugene?, Taylan?).
We talked about agendas of upcoming meetings:
07/27 - MK at APFB5, no meeting unless someone runs it
08/03 - MK on way back to Boston, suggest to hold meeting on Thursday
08/04 at 10am
08/04 - Review of N-Delta analysis, inclusive p(e,e'), and exclusive
p(e,e'pi+), p(e,e'p)pi0, p(e,e'n)pi+. Runlist, event
selection, particle ID, yields vs W,Q2,thcms;normalized yield vs
time, experimental asymmetries. Status of MC: MAID + ep elastic,
radiative effects (YX,AS,TF)
08/10 - MK unavailable, someone else needs to run it. Perhaps on MC,
radiative effects, eloss (VZ,NM,AM)
08/17 - Review of d(e,e'p) vector and tensor polarized breakup (AM,RF).
Pzz from T20 vs Pzz from A_d^T incl. statistics and systematics
08/24 - Review GEn analysis 2005, compare with 2004 (VZ,EG)
likely:
08/31 - Big analysis prior to collaboration meeting on 09/02. Review
of all results to be shown at DNP/Hawaii.
Possibly attended by H. Arenhoevel
09/07 - Rehearsals for Hawaii
09/14 - MK at workshop in Mainz
09/21 - DNP/Hawaii, no meeting
It is envisioned to recrunch (lrd) 2005 data in the week from 08/08,
then with proper timing, refined blast.geom.2005, and fixed fieldmap
Regards,
Michael
--+-------------------------------------+--------------------------+ | Office: | Home: | |-------------------------------------|--------------------------| | Dr. Michael Kohl | Michael Kohl | | Laboratory for Nuclear Science | 5 Ibbetson Street | | MIT-Bates Linear Accelerator Center | Somerville, MA 02143 | | Middleton, MA 01949 | U.S.A. | | U.S.A. | | | - - - - - - - - - - - - | - - - - - - - - -| | Email: kohlm@mit.edu | K.Michael.Kohl@gmx.de | | Work: +1-617-253-9207 | Home: +1-617-629-3147 | | Fax: +1-617-253-9599 | Mobile: +1-978-580-4190 | | http://blast.lns.mit.edu | | +-------------------------------------+--------------------------+
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