2010 PREx Run – Dithering & Compton Polarimetry
Chun-Min Jen on behalf of the Hall-A collaboration @ JLab.Institution: Syracuse University, NY, 13244,
USAE-mail: [email protected]
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