G2p Analysis Minutes
From Hall A Wiki
Minutes of the weekly analysis meetings
Contents
8/12/2015
Present: Jie, Chao, Kalyan, Min, Jixie, Melissa
By Phone: Pengjia, Ryan, Toby, Karl, Ellie, Alex
Feature Presentations:
- Chao
- Gave an update on optics studies. Previously, Min has shown comparisons of data/simulation
where she looked at different columns of sieve holes. Chao continued this study by cutting on
individual sieve holes. Looking at the center sieve hole, the φ distribution looks reasonable, but
the θ distribution has some issues. Specifically, the data is wider on the left side (negative θ)
than the simulation. He showed results for several sieve holes, including one that was in the
row as the center hole, but in the farthest column on the left side of the sieve slit. In this case
the θ distribution had similar width for both data and simulation, but the height of the simulation
distribution was larger. This may suggest that something is wrong with the acceptance in the
simulation. The problem with θ seems to be systematic; for most of the sieve holes there are
more events on the left side of the data than in the simulation. Kalyan asked whether the
thickness of the sieve slit was taken into account, Chao says it was included in the simulation
and optimizer. Jixie suggested comparing the dp distributions for each sieve hole. More details
can be seen in Chao's slides here.
- Gave an update on optics studies. Previously, Min has shown comparisons of data/simulation
7/29/2015
Present: Chao, Min, JP, Melissa
By Phone: Alex, Pengjia
Feature Presentations:
- Min
- Gave an update on acceptance studies. Previously, Chao showed a correction for the beam
position in g2psim. Min checked this correction by looking at optics runs. On the data she
applied a cut on dp (to select elastic events) and on the focal plane (to get rid of junk
events). On the simulation, only an aperture cut was applied. She compared the data and
simulation results for θ and φ both before and after drifting from the sieve slit to the target.
The effect of the target field on θ is not very large, though there is a shift down in angle.
However, the shape of the θ distribution is different between data and simulation. The
effect of the target field on φ is significant; it's not clear why this is the case. To try to
determine the reason for the discrepancies, she applied a cut along each column of sieve
slit holes in φ and compared the data and simulation results for θ,φ and dp. Column 2
seems to have the best agreement (for dp), columns 1 and 2 have a shift while columns
3-6 have a difference in width. Chao suggested also cutting along each row of sieve slit
holes to better study the effect of the drift on φ. Min will work on identifying the differences
between data and simulation, specifically whether the boundaries are different between
the two. More details can be seen in her slides here.
- Gave an update on acceptance studies. Previously, Chao showed a correction for the beam
7/22/2015
Present: JP, Min, Jixie, Melissa
By Phone: Alex, Ryan, Toby, Ellie, Karl, Pengjia
Feature Presentations:
- Melissa
- Showed various checks for packing fraction runs that have large discrepancies, including
beam position, beam energy, spectrometer central momentum setting, septum current, and
the location of anneals. For both the 2.2 and 1.1 GeV settings, there are significant shifts in
the x and y beam position (2mm or more). She showed the average and standard deviation
of epics readings for the LHRS septum current for each run. For several runs, there are small
number of epics readings that drift from the average current. It's not clear if this is the
current is actually changing or if it is a readout problem. She will look into the yield vs time
to try to determine this. JP suggested making a raster cut on the center of the beam to get
rid of any potential scraping. Pengjia says there is a way to cut on raster size, but there will
be an additional BPM uncertainty. Melissa will discuss this more offline with Pengjia. More
details can be seen in her slides here.
- Showed various checks for packing fraction runs that have large discrepancies, including
- Pengjia
- Gave an update on calculating asymmetries/cross sections using the MAID model. This time,
he used the Bosted model to get the unpolarized cross sections for the proton. Using unradiated
cross section models, he still saw a factor of 6 difference when compared with data. Ryan also
calculated asymmetries using unradiated models, and the results were consistent with Pengjia's,
so it seems the radiative effects contribute significantly to the factor of 6 difference. More
details can be seen in his slides here.
- Gave an update on calculating asymmetries/cross sections using the MAID model. This time,
7/15/2015
Present: JP, Min, Chao, Jixie, Melissa
By Phone: Ryan, Toby, Ellie, Karl, Vince, Pengjia
Feature Presentations:
- Chao
- Doing a check of simulation/data results for the 2.2 GeV, longitudinal setting in order
to check that the optics calibration matrix will work for all momentum settings (not
just elastic). He showed a comparison for several different momentum settings.
Vince suggested simulating more events, since the statistics start to drop off for
lower momentum settings. In general, the data is broader then the result from
simulation. In the θ distribution, the "tails" seen in the data are not symmetric. JP
suggested carefully selecting cuts to remove any background from the data to
ensure a good comparison with simulation. More details can be seen in his
slides here.
- Doing a check of simulation/data results for the 2.2 GeV, longitudinal setting in order
- Pengjia
- More discussion on Pengjia's slides from last week. Pengjia has seen a factor of
six difference between his asymmetry calculated from data compared to the
asymmetry determined using the MAID model. Ryan did not see this factor of six
in his study, but in addition to using radiated XS models, he is using a combination
of the Bosted and MAID models (Pengjia is using just the MAID model). Karl
commented that the XS from MAID is not very good for our kinematics. Pengjia
also showed an estimated NH3 XS. JP commented that it was surprising that the
delta peak wasn't visible. Pengjia will look into this for next time.
- More discussion on Pengjia's slides from last week. Pengjia has seen a factor of
7/8/2015
Present: JP, Min, Chao, Melissa
By Phone: Toby, Vince
Feature Presentations:
- Pengjia
- Working on comparing asymmetries determined from MAID to those calculated from
data; last time he showed a factor of 6 difference between the two results. This
time, he showed two different methods for calculating the differential XS from the
virtual photon XS. The first method calculates the differential XS directly from
the virtual photon XS, and the second method calculates the differential XS using
F1, F2, g1 and g2. He also showed two different methods for calculating the
asymmetry from the virtual photon XS; one method uses A1 and A2, while the other
is calculated from the virtual photon XS. There was a discrepancy between the two
methods, but he found that there was actually a mistake in one of the equations.
While the results from the two methods agree with each other, they are still a factor
of 6 larger than the results from data. More details can be seen in his slides here.
- Working on comparing asymmetries determined from MAID to those calculated from
- Toby
- Showed an update of his scattering angle study for model reconstruction. He is
using BPM and optics data to determine the scattering angle. He showed an example
of the calculated scattering angle; JP questioned whether the range was really from
0-16 deg. Toby pointed out that there really aren't many events at the boundaries,
the distribution is peaked between 4.5-9 deg. He then uses this scattering angle as
input for the Bosted model. At low ν the simulation results match reasonably well
with the data, but the discrepancy starts to become larger as ν increases. He took
a closer look at the reconstructed scattering angle for each central momentum, and
found that a second peak is visible for smaller values of p0. If this second peak was
real, the simulation should recreate the data, so this could suggest a problem with
the reconstruction. However, Chao pointed out that, for this energy setting, the optics
calibration is not complete (currently using the longitudinal optics matrix), so the
reconstructed θ and φ may not be correct yet. For next time, Toby will test this
analysis using the 1.7 GeV setting, which has calibrated optics. More details can
be seen in his slides here.
- Showed an update of his scattering angle study for model reconstruction. He is
- Melissa
- Gave a summary of packing fraction analysis. For some settings, the variation in the
yields (and Pf) is due to a fluctuation in the beam position. This will hopefully be
resolved by Jie's beam position/acceptance study. For the 2.2 GeV, 2.5T transverse setting
there is also an issue of a shift in ν between runs. For the 1.1 GeV, 2.5T transverse
setting, the yields vary depending on the beam current used for each run. JP suggested
a few things to check as the possible cause for these discrepancies including drift in the
BCM calibration, anneals of the target material, drift in field (HRS or septum), etc. She
has posted a technote draft here, feedback would be appreciated. More details can be seen in her slides here.
- Gave a summary of packing fraction analysis. For some settings, the variation in the
- Min
- Gave an update on her acceptance study. Last time, she showed that the simulation results
are more narrow than the data. For this time, she tried cutting on just the center hole,
and found that the dp distribution from data better matched the simulation. JP suggested
cutting on each of the different holes individually to determine which hole causes the dp
distribution to be wider. More details can be seen in her slides here.
- Gave an update on her acceptance study. Last time, she showed that the simulation results
- Chao
- Gave an update on optics analysis, currently checking whether simulation results match
with data, starting with optics data. First he checked whether the geometry was correct,
some deviation was found in the recent optics meeting. The position of the BPMs is hard-
coded into the simulation, and the drifting algorithm is used to drift the electrons
backward to the BPMs to simulate the readout of BPM A and B. He compared the θ
distribution before drifting in the target field using a fixed and non-fixed BPM location.
The results using a fixed BPM match well with the data. He is currently working on
checking this for all momentum settings, and will follow up with Pengjia about the BPM
problem. More details can be seen in his slides here.
- Gave an update on optics analysis, currently checking whether simulation results match
7/1/2015
Present: Chao, Vince, Jie, JP, Min, Melissa
By Phone: Pengjia
Feature Presentations:
- Min
- Gave an update on acceptance studies. She showed a summary table of each energy
setting and septum configuration. There hasn't been any problems in the 2.2 GeV, 5T
longitudinal and 1.7 GeV, 2.5T transverse settings, but some settings (2.2 GeV, 2.5T
transverse, 1.2 GeV, 2.5T transverse and 2.2 GeV, 5T transverse) have a discrepancy
in the focal plane between data and simulation. She compared the data divided by the
Mott XS to the simulation results without XS, and found that the simulation results
of θ and φ are narrower then the data. JP commented that, while including the Mott
XS might change the shape of the distribution, it shouldn't change the boundary. She
work on figuring out the cause for this discrepancy before calculating the acceptance.
More details can be seen in her slides here.
- Gave an update on acceptance studies. She showed a summary table of each energy
- Pengjia
- Comparing asymmetries determined from the MAID model to those calculated from data.
Last time he showed a factor of 6 difference between the two results. He determined the
scattering angle and Q2 by fitting the data and compared them to the quantities calculated
from MAID. He also showed the results of calculating the quantities g1, g2, F1, F2, AL, AT,
dXSL, dXST, XStot andXSmott using MAID. He hasn't included radiative corrections in his
calculations, but this probably won't account for the factor of 6. More details can be seen
in his slides here.
- Comparing asymmetries determined from the MAID model to those calculated from data.