Hi,
below are the minutes of the analysis meeting of last Wednesday.
The next meeting on Wednesday 02/15/2006 at 13:30 will be run by Doug.
Regards,
Michael
-Status of wire chamber geometry (DH)
Within each chamber the location of the wires seem to be correct.
A global 13mm shift in both sectors along z was observed in addition
to a 1.2mm shift of one chamber relative to the other two in the right
sector. The latter shift may explain a 50MeV offset. Progress is made
toward a re-determination of the geometry calibration. Once the proper
positions are known, a recrunch from DST will be carried out (doable
within ~2 weeks.). The hope is that with an appropriate geometry
calibration the "kinematic offsets" are cured consistently and
simultaneously in all reaction channels. Overdetermined elastic and
quasielastic kinematics will be used to determine the residual
corrections.
The 13 mm longitudinal shift likely affects the reconstructed target-z
distribution by this amount. It was noted that the average spin angle
for a given spin angle map may therefore be affected.
-Plan for new mapping of target spin angle (ET)
ET will check with the Jlab group if their setup can be borrowed to
re-map the spin angle for BLAST. The method aims for a direct spin
angle measurement similar to a compass. It is suggested to address
the method and expected accuracy in an upcoming (analysis?) meeting.
-FF from super ratio and hPz from vector d(e,e'p) (RF)
The sqrt(3/2) factor explained the previous discrepancy of the hPz
extraction comparing the super ratio method with the Arenhoevel-MC based
method (within a few %)). Still, the extracted hPz values show a Q2
dependence. The earlier suspicion that this Q2-dependence of the
extracted hPz product may be due to different nucleon form factors in
deuterium than the dipole form factors used in HA's model seems not to
hold. Next step is to use a spin angle map instead of a fixed value
for the hPz and super ratio determination.
-Status of radiated MC (ASUNH)
Shown was the normalized yield as measured compared with the
MASCARAD-MC result (with Hoehler form factors). Very good
agreement. Suggested to plot
1) Unradiated and radiated MC result vs. Q2 after all cuts in one plot
2) Measured and MC yield as a function of W (without W-cut!)
3) The ratio of measured/MC yields (with errors) to spot details of the
agreement
-How to extract inclusive yields and asymmetries for N-Delta (OF)
Relevant trigger types for this consideration 1 (charged-charged),
2 (charged-neutral) and 7 (residual singles with Cerenkov). Trigger 7
was prescaled with a factor 9 for the Dec2004 hydrogen experiment.
The inclusive normalized yield for a given phase space element is
Y=(N1 + N2 + 9*N7)/Q, where Ni are the measured counts for the
trigger type i and Q is the total charge.
The yield in each trigger type Yi selects different physics processes
with individual cross sections Si and with different efficiencies
ei. It is important that trigger 7 is the "residual" trigger type
whose efficiency is related to the ones of trigger types 1 and 2:
Y1=e1*S1, e1=ee*echarged (ee=electron efficiency, echarged=charged
hadron efficiency)
Y2=e2*S1, e2=ee_eneutral (eneutral=neutral particle efficiency)
Y7=e7*S7=ee*[(1-echarged)*S1 + (1-eneutral)*S2)
-> Y=Y1+Y2+Y7= ... =ee*(S1+S2)=ee*S
The so-constructed inclusive yield Y is proportional to the inclusive
cross section. As such, the inclusive asymmetry does not depend on the
electron efficiency. The above consideration requires the identical
treatment of electron-related cuts for all three trigger types.
A Montecarlo of elastic scattering with MASCARAD needs to be carried
out to determine the fraction of elastic events in the radiative tail
ranging into the inelastic region. The elastic-tail events correspond
to a dramatically different asymmetry than the N-Delta events, and
MASCARAD with realistic form factors will exactly tell the fraction of
elastic events in each spin state separately.
The extracted inelastic yields can be compared to a MAID-based MC that
also incorporates spin-dependent radiative processes as calculated
from POLRAD.
+-------------------------------------+--------------------------+
| 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. | |
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| 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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