# G2p Analysis Minutes

Minutes of the weekly analysis meetings

## Contents

## 3/12/2014

Present: JP, Jixie, Kalyan, Jie, Min, Chao

By Phone: Melissa, Pengjia

**Feature Presentations:**

- Pengjia:
- Gave an update about the status of BPM calibrations. He is studying the BPM pedestal value for the run 3600~3900. The typical fluctuation of the

pedestal value is about 1000 channels. However, Pengjia pointed out that the pedestal value of BPM B changed during some runs (like 3714 and 3732),

especially for the channel 7 of BPM B. JP suggests that multiple pedestal values can be used in the same run to correct those big jump of pedestal values

and treat the rest small fluctuations as uncertainty. More details can be seen in his slides here.

- Gave an update about the status of BPM calibrations. He is studying the BPM pedestal value for the run 3600~3900. The typical fluctuation of the

**General Discussion:**

- Jie is working on radiative corrections in the simulation.

- Chao is working on optics calibration of 1.1GeV and will compare the result with longitudinal optics.

## 3/5/2014

Present: JP, Kalyan, Vince, Jie, Min, Chao, Jixie, Melissa

By Phone: Pengjia

**Feature Presentations:**

- Jie:
- Gave an update on including radiative corrections in simulation. Included a list of definitions for all the terminology and different processes used

in the calculations. He showed a comparison of using the peak approximation versus the exact calculation for the NH3 target using two different

radiation lengths. For small values of nu, there isn't a large difference between the methods. He also showed a comparison of using the exact

calculation method for two different radiation lengths (0.1/0.03), both with and without the multi-photon correction. Without the correction, the ratio

is pretty flat, but including the correction causes the ratio to drop for smaller values of nu. He included a plot of the total radiative corrections for the

carbon target (internal and external), and a plot showing the the carbon cross section with and without corrections. It's unclear why the uncorrected

cross section is not symmetric; it appears to already have some energy loss. Jie will check this and will also include detector resolution and acceptance,

which aren't included in these plots. More details can be seen in his slides here.

- Gave an update on including radiative corrections in simulation. Included a list of definitions for all the terminology and different processes used

- Chao:
- Gave an update on longitudinal optics. He took a closer look at the BPM x fluctuation during the course of a run; it seems the beam position is

slowly fluctuating over the course of the run. He described the method for matrix calibration; the matrix elements are calibrated by the open angle of

2 different sieve holes with respect to the scattering point. The fluctuation in the beam position will slightly influence the calibration. The matrix

calibration can be calculated using geometry relations, so he simulated several different beam positions and calculated the open angle; the results

showed that the change in angle due to the beam position is small. JP suggested that he should look at the absolute value of the sieve holes, instead

of the difference between them. He also showed a comparison of the first order matrix for the cases with and without the target field. The theta offset is

large, which is due to the bend from the target field. JP asked about the effect on the left septum after the right septum broke; according to simulation

there is ~10% effect. More details can be seen in his slides here.

- Gave an update on longitudinal optics. He took a closer look at the BPM x fluctuation during the course of a run; it seems the beam position is

**General Discussion:**

- Pengjia is working on checking the pedestals for all periods for BPM calibrations. The change in pedestals seems to be random. There also seems

to be an effect where changes in current affect the BPMS. Pengjia says this effect seems to be random, but he will show more details on this next time.

## 2/26/2014

Present: JP, Jixie, Jie, Min, Chao, Kalyan, Melissa

By Phone: Karl, Ellie, Toby, Ryan, Pengjia, Moshe

**Feature Presentations:**

- Melissa:
- Gave a short update on the inconsistency in the yields. There seems to be a correlation between beam position and yield; for p0 = 2.072 GeV/c

(2.5GeV beam, 2.5T magnetic field) setting, an ~8% drop in yields can be seen when the beam position changes ~3mm in X and ~2mm in Y. She

also tested the effect of applying different raster cuts, in case the shift in beam caused scraping. The raster cuts did not help to make the yields

agree. JP suggested that, due to our small scattering angle, a change in beam position can have a significant change in the kinematics. She will

look more into this, and look at the corresponding effect on the RHRS. Her slides can be seen here.

- Gave a short update on the inconsistency in the yields. There seems to be a correlation between beam position and yield; for p0 = 2.072 GeV/c

- Min:
- Gave an update on the pointing uncertainty. Previously, she used the carbon ground state and first excited state to determine the uncertainty.

A landau-gaussian convolution fit was used to fit the two peaks and determine the uncertainty. JP cautioned against using fits in Root, as they

can be unreliable. Min will take a closer look at this and the determination of the uncertainty. Using this method gives a d-theta of ~0.2mr, which

is within the requirement. She also showed another method to calculate the uncertainty, using the difference in energy between two nuclei (carbon

and helium), this time using a Monte Carlo simulation to determine the beam offset. The beam position at the target looks identical for both carbon

and helium, though JP suggested only using one "blob" (the "blobs" arise from drift in the beam position during the run) in order to get better

resolution. If only survey results are used, the value for d-theta is ~0.7mr. More details can be seen in Min's slides here.

- Gave an update on the pointing uncertainty. Previously, she used the carbon ground state and first excited state to determine the uncertainty.

- Pengjia:
- Gave an overview of status of BPM calibrations. The beampackage tools have been updated, he has dumped all the raw BPM data from volatile

rootfiles to a data pool and have saved all calculated positions to disk. Students can now insert this information into their own rootfiles. He is

calculating the uncertainty for each run and checking for any weird changes in beam position. His results will be published on the ELOG when he

is done. A database containing the average position for each run is built along with a script to access the information. He showed global plots

of the beam position for every run at BPMA, BPMB and the target. He also showed a global plot of pedestal values for the entire run period. Some

pedestal runs were taken with out any current (real pedestal runs), while some were taken during long beam trips. Currently, he uses the pedestal

closest in time to each production run as the pedestal value, but JP suggested breaking them up by setting instead. Pengjia is still working on how to

estimate the uncertainty for the pedestal value. More details can be seen in his slides here.

- Gave an overview of status of BPM calibrations. The beampackage tools have been updated, he has dumped all the raw BPM data from volatile

**General Discussion:**

- Moshe has his simulation ready, but needs optics calibrations! JP suggested using straight thru optics results for now.

## 2/19/2014

Present: Jixie, Kalyan, JP, Min, Chao, Jie, Melissa

By Phone: Toby, Ryan, Ellie, Karl, Pengjia

**Feature Presentations:**

- Jie:
- Gave an update on his work to determine the packing fraction using simulation. He is working on updating his simulation to include radiative

corrections. He is including a correction for the straggling effect, which arises due to "real" bremsstrahlung and ionization. He showed a comparison

between the peak-approximation method and the exact calculation, for a carbon foil. They agree within 1%, but the difference would probably be

larger for a (thicker) ammonia target. He also showed the simulated result for the radiative tail in the carbon target, which suggests that the "internal"

contribution is larger than the "external contribution, except at small values of nu. Finally, he showed the effect of the multi-photon radiation correction,

which is fairly large at small values of nu. He is still working on optimizing the code. More details can be seen in his slides here.

- Gave an update on his work to determine the packing fraction using simulation. He is working on updating his simulation to include radiative

- Ryan:
- Gave an update on the work he's been doing on the radiative corrections for small angle GDH data. At our kinematics (2.1GeV, 6deg), the cross section

has a strong dependence on the scattering angle, which means the cross section could vary greatly over the entire angular acceptance. The code used to

produce the elastic radiative tail uses one central scattering angle, so angular acceptance needs to be corrected for. He broke up the acceptance into a grid

in theta and phi bins, calculated the elastic tail at different angles across the acceptance, and averaged the results. The difference in the cross section using

the central scattering angle vs. using the average of the reconstructed scattering angles is about 20-25%. He will do a comparison of carbon/nitrogen data

for 3.7 GeV once he gets the nitrogen data from Vince. He is also writing up a technote documenting this work. More details can be found in his slides here.

- Gave an update on the work he's been doing on the radiative corrections for small angle GDH data. At our kinematics (2.1GeV, 6deg), the cross section

- Chao:
- Gave an update on the status of optics calibration. A program (g2prec) is written to read in L.gold.* (effective angles) and Lrb.tgt_0_* (bpm) type

variables as input for projection and drifting functions in the simulation package to calculate the final reconstructed variables. It will be configured by the

database to deal with different kinematic settings, and will write L.rec.* type variables into the final rootfiles as the final reconstructed scattering angle and

and momentum. He also showed a diagram depicting the structure of the "do_replay" script, which will be automated to insert all necessary information

into the final rootfiles. He is currently working on determining the calibration matrix for the 9 different optics settings, which can probably be completed in

~1 month, though the uncertainties will take longer. His slides can be found here.

- Gave an update on the status of optics calibration. A program (g2prec) is written to read in L.gold.* (effective angles) and Lrb.tgt_0_* (bpm) type

## 2/12/2014

Present: Chao, Jixie, Jie, JP, Min, Melissa

By Phone: Toby, Ryan, Ellie, Karl, Pengjia

**Feature Presentations:**

- Melissa:
- Showed a summary of checks she's done to try to understand the discrepancy in yields for packing fraction runs. Many different tests were

done testing the cuts (acceptance, PID and raster) as well as checking the multitrack efficiency and comparing the first and second half of each run.

JP pointed out a few odd things that should be resolved (such as the "spikes" in the reconstructed phi variable, events above the good electrons in

leadglass 2D plot, etc.) The difference in yields is still not clear, but it's possible that a Moller measurement that was taken between runs 3503 and

3574 could have altered the beam conditions. She will discuss with Pengjia to see if the Moller measurement had a large effect on beam position.

More details can be seen in her slides here.

- Showed a summary of checks she's done to try to understand the discrepancy in yields for packing fraction runs. Many different tests were

- Min:
- Showed an update on her pointing study to determine the central scattering angle. She showed the details of calculating the uncertainty in the

scattering angle using survey results. She used the assumption that z and x are the same for both theta1 and theta2, which JP warned could in be

incorrect. Looking at the results for the left and right HRS, the results from pointing and survey agree for the LHRS, but not for the RHRS. The pointing

uncertainty is different for left and right HRS; this is determined using the difference in the carbon ground state and first excited state, compared to

the nominal value. Min is currently writing up the details of the pointing study so far. More details can be seen in her slides here.

- Showed an update on her pointing study to determine the central scattering angle. She showed the details of calculating the uncertainty in the

- Pengjia:
- Gave an update on the status of BPM calibrations. He is working on the calibration for the optics run near 3185, but unfortunately there are no straight

through calibrations with div=2. The closest calibration is from 3/6 with div=3. Looking at the results for run 3185 using this calibration gives a beam

position of -0.84mm(X) and 2.39mm(Y) at the target. Chao's fitting result for this run was -3.5mm(X). JP asked how much a change in beam position of

3mm would affect the central angle calibration. Pengjia will try to get the calibration as good as possible, then summarize his work and determine the

uncertainty for the beam position. Also, he will compile a table of all beam condition changed throughout the run. His slides can be seen here.

- Gave an update on the status of BPM calibrations. He is working on the calibration for the optics run near 3185, but unfortunately there are no straight

## 2/05/2014

Present: Kalyan, JP, Chao, Jie, Min, Jixie, Melissa

By Phone: Toby, Ryan, Ellie

**Feature Presentations:**

- Toby:
- Working on dilution analysis. Gave an explanation of his method to determine the background yield in terms of the dilution runs (carbon,

empty, dummy). He also needed to create a scaling factor to relate the carbon runs to the nitrogen background. Using Moshe's nitrogen

simulation he was able to scale the carbon production data (with the "empty" run yield subtracted out) to match the nitrogen yield. He made

a graphical cut on the carbon and empty dilution to isolate the elastic/quasi-elastic channels so that each channel could be scaled separately.

He can then use these scaling factors to determine the overall background yield. The current scaling factors result in a background contribution

that is much too large; the yield is greater than the yield for a production run. This is most likely due to the fact that Toby currently doesn't

include any radiative corrections, which he will include in his method for next time. The details of his method can be seen in his slides here.

- Working on dilution analysis. Gave an explanation of his method to determine the background yield in terms of the dilution runs (carbon,

- Chao:
- Gave an update on the status of optics calibrations. He is currently working on longitudinal optics for the 2.2 GeV, 5T setting, since Min will

need this for her pointing study. He first used a simulation to show the effect of the longitudinal field, setting the beam position to the average

value of the BPM readout. The beam positions actually vary slightly between different optics runs, so he had to approximate the beam position for

"bunches" of 5000 events. An event by event simulation was used to calculate the effective theta and phi angle. The calibration looks pretty good

for this setting. The calibration tool kit, which combines the optimizer and the simulation, is almost finalized. He is currently working on updating

the reconstruction script to calculate the kinematic variables. More details can be seen in Chao's slides here.

- Gave an update on the status of optics calibrations. He is currently working on longitudinal optics for the 2.2 GeV, 5T setting, since Min will

- Jie:
- Working on updating the simulation package to include radiative corrections. There are two pieces to the correction; the radiation effect and the

straggling effect. The radiation effect includes the contribution from the dynamical effect (Bremstrahlung), which Jie has approximated as two

external radiator lengths. Ryan suggested just doing the full internal calculation, as it doesn't require much extra computing power. Since our target

thickness is ~0.03, the straggling effect is significant. He showed the simulated yields for the elastic nitrogen peak with and without the radiative

corrections, but neglected to include the radiative tail, which he will include this for next time. He also looked at the simulated yields using the actual

beam positions for the packing fraction runs 3503, 3574 and 3864. The yields agree within 4.5%, meaning that the differences in beam position is not

what is causing the discrepancy in the yields of the packing fraction runs. Jie's slides can be seen here.

- Working on updating the simulation package to include radiative corrections. There are two pieces to the correction; the radiation effect and the

## 1/24/2014

Present: Kalyan, JP, Chao, Jie, Min, Melissa

By Phone: Toby, Ryan, Karl, Pengjia

**Feature Presentations:**

- Melissa:
- Gave an update on packing fraction analysis. Compared the x/y beam positions for the four packing fraction runs for material 7; one

run (3727) has unreliable beam position information, but the other 3 runs seem fairly consistent. There is still a large discrepancy in the

yield for one run (3503). This is the earliest run taken; she will go through the logbook to look for any condition changes that could cause

this discrepancy. The results for the packing fraction for the other 3 runs seem fairly consistent, but lower than expected. More details can

be seen here.

- Gave an update on packing fraction analysis. Compared the x/y beam positions for the four packing fraction runs for material 7; one

- Pengjia:
- Gave an overview of his calibration method; the raw signal received in the antenna is compared to the recorded ADC value, and the

linear region is fit. This can then be rewritten using a diff/sum value and the nonlinearity corrected for. The position is then calibrated

using data from harp scans. Some of the calibrations were used for runs with different currents, assuming that the beam position

didn't change for these runs, which JP suggested was a dangerous assumption to make. There were several periods where the pedestal

was different between the calibration and production runs. This fluctuating pedestal could change the resulting beam position by ~2mm.

For next time, Pengjia will summarize the assumptions made for these calibrations so the uncertainty can be assessed for each one. More

details of his calibration method can be seen in his slides here.

- Gave an overview of his calibration method; the raw signal received in the antenna is compared to the recorded ADC value, and the

- Min:
- Gave an update on the pointing study to determine the central scattering angle. She showed the equation for elastic scattering

(which includes energy loss); she will look at the difference in the scattered energy for two different nuclei. She included two different

methods for calculating the pointing uncertainty. The first method uses the carbon-12 ground state and first excited state, and gave

a result for d-theta/theta <1%. JP suggested Min will probably need to combine left and right data to get the precision we need. The

second method combines various uncertainties (from survey, beam_x, etc.) and uses 2 different scattering angles; one including the

z-offset and one without. Using just one scattering angle to compute d-theta gives an uncertainty of ~2mr, using the quotient of the

two scattering angles gives an uncertainty of ~0.2mr, and using the difference of the two angles gives an uncertainty of ~0.04mr. She

still needs to include input for the incoming beam angle, and include the uncertainty from energy loss. More details can be seen in her

slides here.

- Gave an update on the pointing study to determine the central scattering angle. She showed the equation for elastic scattering

**General Discussion:**

- Ryan:
- Working through Rosetail to understand radiative correction calculations/code.

- Toby:
- Looking at scaling carbon data to nitrogen for dilution analysis.

- Chao:
- Working on longitudinal optics calibration.

## 1/15/2014

Present: Kalyan, Chao, Jie, Min, JP, Jixie, Melissa

By Phone: Ellie, Toby, Ryan, Karl, Alexandre, Pengjia

**Feature Presentations:**

- Jie:
- Gave an update on using the simulation package to determine the packing fraction. He showed multiple methods for extracting

the packing fraction, which account for different contributions to the overall yield. He used the g2psim package to get relative cross

sections for each contributing material. Next he will work on including the radiative corrections to the elastic peak and include the

calibrated beam position information (once it is ready). Details for the methods used can be seen is his slides here.

- Gave an update on using the simulation package to determine the packing fraction. He showed multiple methods for extracting

## 1/8/2014

Present: Kalyan, Chao, Jie, Min, Melissa

By Phone: Ellie, Toby, Ryan, Karl, Alexandre, Pengjia

**Feature Presentations:**

- Melissa:
- Gave a short update on yields for packing fraction runs. For one run (3864), the ungated livetime is significantly different then

the helicity-gated livetime. Using the average of the helicity gated LT values for the normalization makes this run agree better with

other packing fraction runs (3574 and 3727). She will check the beam position for these runs to see if this could have a large effect

on the yields. Her slides can be seen here.

- Gave a short update on yields for packing fraction runs. For one run (3864), the ungated livetime is significantly different then

- Chao
- Gave an update on the simulation package. Previously, the real theta and phi were not determined event by event, but for an entire

run. Since we know the position of the reaction point and the sieve hole, and the momentum of the electron, it is possible to use a

bisection method to determine the real theta and phi for each event. With this update it will be easier to determine the calibration for

different dp settings. Next he will work on finishing the optics calibration for the first setting with the target field. His slides can be

seen here.

- Gave an update on the simulation package. Previously, the real theta and phi were not determined event by event, but for an entire

- Min
- Gave an update on pointing analysis. The calculation was done using the March 14th calibration, using a carbon foil in liquid helium.

Using the carbon-12 ground state and first excited state to do the calibration of d(delta-E'), the results for the LHRS (4.40MeV) and

RHRS (4.42 MeV) agreed within the uncertainty with the nominal value (4.44MeV). However, including other uncertainties (survey and

beam x), add up to ~0.11 deg uncertainty in the scattering angle. She concluded that using the carbon foil in LHe is not ideal for a

pointing study. Next she will try CH2 run in longitudinal target field setting, once the optics calibration is complete for this setting. Her

slides can be seen here.

- Gave an update on pointing analysis. The calculation was done using the March 14th calibration, using a carbon foil in liquid helium.

- Pengjia
- Gave an update on the status of the BPM calibrations. He has finalized the calibrations for data taken from April 11th to May 18th,

which includes three different BPM gain settings. For settings before April 11th, the process is more complicated (larger pedestals,

auto-gain), but he will try to finalize the calibrations soon. He will provide a technote of his procedures and results. More details can

be seen here.

- Gave an update on the status of the BPM calibrations. He has finalized the calibrations for data taken from April 11th to May 18th,

**General Discussion:**

- If any students are interested in giving a talk at the APS April Meeting, please circulate an abstract to the group. The deadline for abstract submission is this Friday, January 10th.