Some comments:
--Chris
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TA-53/MPF-1/D111 P-23 MS H803
LANL, Los Alamos, NM 87545
505-665-9804(o) 665-4121(f) 662-0639(h)
_______________________________________
On Mar 30, 2006, at 21:52:23, Michael Kohl wrote:
> 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.
The shift seemed about the same at even and odd points along the
profile.
> 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.
Last year I investigated an promising alternative approach to
alignment of the Hall probe (internal sensitivity better than .1
deg), which involved measuring a fairly dense 3-d map of the field
both on-axis and also at locations with large gradients. Using
Maxwell's equations, the alignment of the probe is traced back to the
geometrical alignment of the XYZ table. This could be done without
the BLAST field.
> +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).
Chi and Vitaliy, is Mascarad implemented in MC this way? I'm just
checking that both the hard and soft parts have been integrated out
to the cutoff energy, and that both both parts are included in the
radiative cross section past that. The original Mascarad did not
generate cross sections in this manner.
Adrian and Eugene, please send me (and everyone) the locations of
your Eloss and R.C. MC runs, along with descriptions of the runs.
I'll test them against the original Mascarad code.
> +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.
We can get this straight from the original Mascarad code, by
calculating the radiated cross section as a function of cutoff energy
and then taking the derivative to get the W-spectrum (and then
convoluting with the BLAST W-resolution). Note that the momentum
shift depends on the cutoff energy used in the analysis (not the 10
MeV), and you must be consistent. I'm calculating it this way for
the geometrical offsets code.
> +The proper combination of Mascarad with Epel needs to be
> established.
This is just a matter of running the original Mascarad to calculate
the radiated elastic cross section with the cutoff set to 10 MeV. It
is probably best to add an elastic channel with the <10MeV radiation-
corrected cross section. Chi, don't we already have this channel?
>
> -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
Why multiplicave?
> +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.
The dZ/dZ ~ 1.17 (kin. offset / geom. offset) for electrons was
indeed due to dBfield/dZ. It went back to 1 after testing with
TBLFieldRho (constant azimuthal field). That brings up the point
that another significant geometrical shift to be considered is a
translation of the B-field (left and right sectors independently,
since they were surveyed separately).
I've verified azimuthal rotations in the geometry (i.e.
GeomWC.LeftOffset=(1-cos(phi)),sin(phi),0,0,phi[deg],0 ), but am
still trying to verify that dPhi/dPhi=1.
> +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.
Most important thing to be added is eloss and rad. corrections.
> +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.
This was already done.
> +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.
I will turn on the holding field while fitting for geometrical
offsets to have results before 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!
>
Take a look at robust peak-finding methods in 'exp/analysis/utils/
hist.C' There are different functions for finding the median and
mode, and corresponding widths. Once locating the peak, you can fit
it to a gaussian with a tight cut on the tails.
Another option might be correct for the offsets averaged over an
entire time period using cosmics in the data, as I investigated at
the last collaboration meeting.
> -> 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: |
> |-------------------------------------|--------------------------|
> | Dr. Michael Kohl | Michael Kohl |
> | Laboratory for Nuclear Science | 5 Ibbetson Street |
> | MIT-Bates Linear Accelerator Center | Somerville, MA 02143 |
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> | U.S.A. | |
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