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2010 PREx Run – Dithering & Compton Polarimetry Chun-Min Jen on behalf of the Hall-A JLab. Institution: Syracuse University, NY, 13244,

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Presentation on theme: "2010 PREx Run – Dithering & Compton Polarimetry Chun-Min Jen on behalf of the Hall-A JLab. Institution: Syracuse University, NY, 13244,"— Presentation transcript:

1 2010 PREx Run – Dithering & Compton Polarimetry Chun-Min Jen on behalf of the Hall-A JLab. Institution: Syracuse University, NY, 13244, USA supervised by P. A. Souder, R. S. Holmes

2 Dithering for high-current (70uA) runs where are we?

3 WhatsNewin PREx beam modulation system? Whats New in PREx beam modulation system? 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-cycle FFB (Fast Feed-Back) was paused start looping over the coil sequence

4 What do weLearnfrom PREx Dithering? What do we Learn from PREx 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 curvature at lower frequency obviously, flat at lower frequency MC

5 Monitor against Coil Dithering Slope 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.

6 Detector against Coil Dithering Slope Here, we looked at detector (normalized to beam current) against coil dithering slope history plot.

7 Sinusoidal Fit

8 Sinusoidal Fit – Phase Shift Understanding

9 Richs 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.

10 regress-corrected (black-line) v.s. dither-corrected (red-line) UMass regression SU dithering

11 Compton Polarimetry where are we?

12 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 Bkg 1 (background type 1) or Bkg 2 (background type 2) diff : diffON, where ON means laser-on A raw : raw asymmetry is defined as A cor (from data points) : corrected asymmetry is defined as 1 st -kind A cor (based on the raw asymmetry) : defined as 2 nd -kind A cor (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 weighted average

13 Compton Polarimeter for PREx – background level study in each laser cycle (1) laser on rightlaser 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 (+/-), thecorrected asymmetry can be obtained based on the following formula: accumulator type take the mean of the sum of both of the histograms

14 Compton Polarimeter for PREx – Raw/Corrected Asymmetry / background level study in each laser cycle (2) systematic error from the beam condition and the accelerator ??? how to estimate ??? go to the next slide… the statistical weighted average

15 Since we cannot measure B true, the way that we can estimate how large ΔB is can be based on the fluctuation of T-B meas. distribution. Furthermore, we found In other words, Compton Polarimeter for PREx – background level study in each laser cycle (3) 0

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18 before 2010 Fall done_ done_ investigate the discrepancy in everything between two adjacent laser states, i.e. laser-left and laser-right state. done_ done_ investigate the errors 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. done done_ investigate the discrepancy between pair-wise asymmetry as well as laser (-cycle) wise asymmetry done done_ study the selection criteria further done done_ give the average of laser cycle wise asymmetry measurement in accumulator 0 for PREx done done_ yield the best fit 2 value done done_suppress the statistic error (background suppression) in the average of beam polarization measurement done done_yield the average of beam polarization measurement in accumulator 0 for PREx

19 Compton Analyzing Power without adding PMT non-linearity. without adding smearing of resolution adding pile-up and pile-down events theres no obvious difference between with and without pile-down effect

20 Future Plan – where we are going to 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


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