# G2p Analysis Minutes

From Hall A Wiki

Minutes of the weekly analysis meetings

## Contents

## 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

F_{1}, F_{2}, g_{1}and g_{2}. He also showed two different methods for calculating the

asymmetry from the virtual photon XS; one method uses A_{1}and A_{2}, 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 P_{f}) 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 Q^{2}by fitting the data and compared them to the quantities calculated

from MAID. He also showed the results of calculating the quantities g_{1}, g_{2}, F_{1}, F_{2}, A_{L}, A_{T},

dXS_{L}, dXS_{T}, XS_{tot}andXS_{mott}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.