Hi,
we had a long meeting last Wednesday which was not always delightful.
Here's my recollection, I apologize for its length. Read it nevertheless.
Minutes:
-Find these minutes along with all plots shown in
http://blast.lns.mit.edu/PRIVATE_RESULTS/USEFUL/ANALYSIS_MEETINGS/meeting_060329/
-New spin angle measurements
+Genya's plots (see excel file),
+Chi's spin angle from ed elastic tensor asymmetry measurement was
31.7 and 47.7 degrees for 2004 and 2005.
+Chris' spin angle from ep elastic vector asymmetry measurement was
47.5 degrees
+ed-elastic yield-weighted average for January2005 map was 31.3 and
46.8 degrees. ep-elastic yield weighted average was 47.1 degrees.
+ed-elastic yield-weighted average for June2005 map according to CZ
was 30.7 and 46.2 degrees, i.e. up to 1.5 degrees smaller than the
angle determined from the asymmetry analysis.
+Spin angle map with 3d hall probe has been repeated in March 2006.
Comparison of June2005 map (Blast field on) with March2006 map
(Blast field off): Profile is reproduced but shifted by ~1 degree in
average, hence increasing the discrepancy with CZ to 2.5 degrees.
Constancy of the difference along z could point to an alignment
issue with the hall probe (would be good to check the constancy of
the shift between two measured maps!!).
+Effect of the Blast field on the March2005 map would decrease the
angle by another ~0.4 degrees (still needs to be confirmed),
increasing the discrepancy with Chi to as much as 3 degrees.
+Results of the compass method are mostly (but not entirely) in
agreement with the March2006 map.
+Spin angle results with the long probe are ~0.5 degrees smaller than
with the short probe.
+Two sources of systematics for the compass method:
1) The extension of the probe implies an averaging effect over the
angle profile along the length. If the profile is an even
distribution, a systematic shift would result.
2) There could be a misalignment of the magnetic and geometrical
axis of the probe.
+Current strategy is to consider building a shorter probe whose
magnetic axis can be adjusted to the geometrical axis at the same
time.
+To summarize, right now the problem is worse than before. We will
discuss about the issue at the collaboration meeting next week.
+My suggestion: The fact that the spin angle z-profiles are shifted by
more or less constant amounts relative to each other raises doubts in
the absolute alignment while relative measurements on the same jig are
consistent. Hence, Chi's determination of the average spin angle from
the tensor asymmetry analysis should be based on a comparison with
the Montecarlo that uses a measured profile. (So far the used
Montecarlo has assumed a flat distribution). Chi's subsequent
analysis result for the average spin angle can then be compared with
the ed-elastic yield weighted average of the initially used
profile and will then reveal by how much the measured profile needs
to be shifted in order to become realistic (=in agreement with the
physics). The method needs to be cross-checked with the ep-elastic
analysis (so far both ed and ep analyses have given consistent
results). Result should be a corrected spin angle map that can be
equally used by every analysis. Please let me know what you think.
-Mascarad+Epel issue
+Mascarad only produces the radiative tail starting at a cutoff
energy for the radiated photon (ad hoc set to 10 MeV).
+Electron momentum generated with Mascarad is thus shifted relative
to the unradiated momentum by at least 10 MeV.
+Average momentum shift of electrons due to internal radiation
convoluted with resolution can only be correctly estimated by
Montecarlo if Mascarad is properly combined with the unradiated
yield.
+The proper combination of Mascarad with Epel needs to be established.
-Energy loss correction, kinematic corrections for v3_4_17
+Eugene's plots (ppt).
+Proton vs. electron angle shifts of 0.2 degrees within resolution of
0.5 degrees
+Introducing multiplicative offsets for momenta instead of shifts
+Reconstructed beam energy from electron and proton variables. Energy
loss effect for protons visible at large angles=low momenta. Beam
energy from electron variables 10-20 MeV lower. Shift almost
independent of the angle. Possible effect due to radiative-tail
convoluted with resolution??
-Recipe for v3_4_17
+For v3_4_17, kinematic corrections need to be produced and be made
available (EG).
+Electron radiative effect (convoluted with resolution) will be
effectively absorbed in the residual kinematic correction for the
electron.
+Momentum loss for the proton should be parametrized and applied
before residual kinematic corrections are determined.
+Resulting kinematic corrections should be independent of energy
loss, i.e. applicable to both proton and piplus data.
+Usage of kinematic corrections by people also requires separately
applying momentum loss correction.
+Reconstructed Montecarlo for analysis should presently not be
radiated, and should use energy loss correction for the proton.
-Geometry transformations
+Chris' plots (gif)
+Chris established and tested code that calculates derivatives of
reconstructed variables with respect to shifts and rotations of the
entire wire chamber in each sector.
+Minimization procedure of p_e-p_e(th_e), p_p-p_p(th_p),
th_e-the(th_p), phi_e-phi_e(phi_p) and z_e-z_e(z_p) for both sectors
with a most likely position and orientation of the chambers.
+Results so far in disagreement with range of variations allowed by
the surveys.
+Method needs some fine-tuning, some partameters may be more
constrained than others, and the importance of the momentum, angle
and vertex measurements has to be weighted with the respective
resolutions.
+Aki noted that the holding field was apparently not superponed with
the Blast field for reconstruction (turned off in blastrc), which
could be potentially responsible for the nonzero coplanarity.
Will be addressed with the next recrunch.
-Timing calibration issue in 2005 runs in v3_4_17
Chi's plots:
+td-te shifted for runs 14336-14435; multiple peaks for all runs
+copl: multiple peak + continuum, should be one peak
+before: with static calibration no problem
+diagnosis: T0's are wrong for left-14-top for 14228-~15200
Investigation by MK (ppt)
+Strategy of time calib was to use cosmics for time calib at a
certain time and to use this also to calibrate the timing of the
flasher signal such that the offsets found with the flasher
run-by-run would be identical with the required offsets for physics
run-by-run.
+Flasher monitoring was problematic in 2005 because of periods with
no flasher signals, laser replacement, and subsequent weak flasher
amplitudes. Periods with missing flasher interpolated with constant.
+Database monitor: Black is T0. Red is MeanTDC.
Obviously wrong T0's for LT14T between 14336 and 15200. Why? T0's in
database are differences between positions of flasher in TDC and
flasher calib from cosmics. Flasher position in TDC = MeanTDC
+Flasher calibration by cosmics done for 14134 before, and 16278 after
-> huge difference for left-14-top, but also for l15t/b and r7t/b
-little difference before and after laser replacement
+Concluding, time calib with cosmics run 14134 wrong, to be fixed.
+Calibration with cosmics has weakness that coplanarity is not well
defined. Could be improved by comparing phi from tracking with phi
from top-bottom timing.
+Sidebands in flasher difference (with left-Tof-0-top subtracted).
Mark had reported last September that in 6% of the runs timing is
shifted. Problem due to peak finding failure!
-> Will have to fix this run by run. Demonstrated that it can be
fixed for the example of runs 16252-16254.
+Any changes to the TOFs will possibly impact the calib for the
neutrons, too.
+Flasher resolution: Difference between two TOF channels is within
2ns over months. Even static calib for T0's may work.
+Motivation to use run-by-run calib was originally due to strongly
varying ADC pedestals. Neutron timing relies on walk correction that
requires proper ADC evaluation. It may be sufficient to assume
constant T0's also for the neutron counters and only use run-by-run
pedestals. However, simplest solution right now seems to me to fix
the database for the wrong entries and stick with the same method.
-Conferences and contributions
List will be generated at collaboration meeting
Regards,
Michael
+-------------------------------------+--------------------------+
| Office: | Home: |
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