2010 PREx Run – Dithering & Compton Polarimetry

Chun-Min Jen on behalf of the Hall-A collaboration @ JLab.Institution: Syracuse University, NY, 13244,

USAE-mail: cjen@physics.syr.edu

supervised by P. A. Souder, R. S. Holmes

Dithering for high-current (70uA) runswhere are we?

What’sWhat’s NewNew in PREx beam modulation in PREx beam modulation system?system?

OFF_STATEallow beam modulation to be

controlled?

CONFIG_STATEdriving a sine wave with a specific

set of frequency (10 - 250Hz) and amplitude (0 - 300mAmps)

TRIGGER_STATE a sine wave was triggered

loading to VMI4145 function generator, enter the number of periods (1 - 511)

connected to the trim card

ON

relay is open set function generator to configure

relay is closed trigger requested set function generator to trigger

start a super-cycleFFB (Fast Feed-Back) was paused

start looping over the coil sequence

What do weWhat do we LearnLearn from PREx from PREx Dithering?Dithering?

• We make use of FFT (fast Fourier Transformation) to see the frequency spectrum in PREx dithering data as well as MC, which is generated with signals plus random noises. The random noise's frequency spectrum is rather flat (red graph), and it suggests us the probability of finding all of the possible noise's frequencies, except for the signal's, be "equal." In contrast, PREx dithering data are composed of not only the driving frequency but low-frequency noises which are resulted from "slow drift".

run 4755, cycle 61

run 4755, cycle 61curvature at

lower frequency

obviously, flat at lower frequency

MC

Monitor against Coil Dithering Monitor against Coil Dithering SlopeSlope

• Here, we showed you monitor against coil dithering slope history plot. According to this, the dithering slope is very stable with time, and there exists very tiny fluctuations which are negligible.

• Certainly, we applied a list of standard cuts to our dithering data.

•

Detector against Coil Dithering Detector against Coil Dithering SlopeSlope

• Here, we looked at detector (normalized to beam current) against coil dithering slope history plot.

Sinusoidal FitSinusoidal Fit

Sinusoidal Fit – Phase Shift Sinusoidal Fit – Phase Shift UnderstandingUnderstanding

Rich’s work Some dithering outliers are found to be associated with apparent problems with dithering. In each dither cycle a large BPM transient marks the restoration of feedback, which is turned off before the cycle begins. In a few cycles the feedback restoration occurs too early, before dithering is over. This early restoration results in energy vernier dithering slopes close to zero and large phase differences in the position BPMs with respect to the coils. A cut on small energy slope eliminates these bad cycles.

regress-corrected (regress-corrected (blackblack-line) v.s. -line) v.s. dither-corrected ( dither-corrected (redred-line)-line)

UMassregression

SUdithering

Compton Polarimetrywhere are we?

Compton Polarimeter for PREx – convention dictionary

• T : sumON, where ON means “laser-on”

• S (or called sig in plots) : T – B, where B is either Bkg1 (background type 1) or Bkg2 (background type 2)

• diff : diffON, where ON means “laser-on”

• Araw : raw asymmetry is defined as

• Acor (from data points) : corrected asymmetry is defined as

• 1st-kind Acor (based on the raw asymmetry) : defined as

• 2nd-kind Acor (based on the raw asymmetry) : defined as

• Δdiff : RMS of diff distribution• Δ(T-B) : RMS of (S = T – B) distribution

• dilution factor f is defined as

0

0

sumON

diffON

))(1(0

0

ctordilutionfafsumON

diffON

meanraw BT

T

meanraw BT

T

11

T

Bf

weighted average

Compton Polarimeter for PREx – background level study in each laser

cycle (1)

sym

beforecountoff

sumoffBbeforecountoffbkg offlaser __

0__1

aftercountoffbeforecountoff

sumoffAaftercountoffsumoffBbeforecountoffbkg offlaser ____

0__0__2

laser on right laser on left

each laser cycle

laser on right

laser off before

laser off after in each laser cycle, there are a bunch of MPS pulsars.

for each pair of MPS pulsars with the opposite sign of helicity state (+/-), the “corrected” asymmetry can be obtained based on the following formula:

meanofflaserofflaser

corpairwise bkgONsum

ONdiff

bkgONsum

ONdiff

21 0_

0_

0_

0_

accumulator type

take the mean of the sum of both of the histograms

Compton Polarimeter for PREx – Raw/Corrected Asymmetry / background level

study in each laser cycle (2)1

.11

T

B

sumbkg

sum

diff

bkgsum

diff measrawpairwise

corpairwise

true

truetruemeastruemeas

BT

B

T

BT

T

BBBT

T

BT1.

systematic error from the beam condition and the accelerator ???

11

1

truetrue

meas

BT

B

BT

T

T

BT

.exp

1

.exp.exp

. 1

truetrue

rawpairwise

corpairwise BT

B

BT

T

how to estimate ???

go to the next slide…

the statistical weighted average

Since we cannot measure Btrue, the way that we can estimate how large ΔB is can be based on the fluctuation of T-Bmeas. distribution.

Furthermore, we found

In other words,

Compton Polarimeter for PREx – background level study in each laser

cycle (3)2221

2

11

2

11

2

111

truetruetruetruetruetrue BT

B

BT

B

BT

B

BT

B

BT

B

BT

B

X

X11

true

true

rawpairwise

corpairwise

BTB

BT

T

1

1

1

1

1

1

truetrue BTB

BTB

1

1

1

1

0

corpairwise

corpairwise

1

1

before 2010 Fall donedone_ _ investigate the discrepancy in “everything” between

two adjacent laser states, i.e. laser-left and laser-right state. donedone__ investigate the error’s error (or called more accurately,

residual) in σB1, σB2, σT and σ(T-B), while applying the linear fitting to the B1, B2, T and (T-B) functions.

donedone_ investigate the discrepancy between pair-wise asymmetry as well as laser (-cycle) wise asymmetry

donedone_ study the selection criteria further donedone_ give the average of laser cycle wise asymmetry

measurement in accumulator 0 for PREx donedone_ yield the best fit 2 value donedone_“suppress” the statistic error (background suppression)

in the average of beam polarization measurement donedone_yield the average of beam polarization measurement in

accumulator 0 for PREx

Compton Analyzing Power• without adding PMT non-linearity.

• without adding smearing of resolution

• adding pile-up and pile-down events

• there’s no obvious difference between with and without pile-down effect

Future Plan – where we are going Future Plan – where we are going to beto be

• Dithering –– asked to finish low-current slugs; keep looking at the

stability of dithering data quality

• Compton –– need to complete the estimation of systematic

uncertainties