Dithering Corrections and Correlations of Corrected Detectorspeople.virginia.edu/~kdp2c/downloads/Qweak-Nov2013/Dithering... · Dithering corrections very important for Beamline Background

Dithering Corrections and Correlations of Corrected Detectors

Manolis Kargiantoulakis

Qweak Collaboration Meeting 07/30/13

Nov 14, 2013 Beamline Background Correlations 2

Importance and connection to Beamline Backgrounds

Dithering corrections very important for Beamline Background correction.

Backgrounds are generated through interactions with the plug and the beamline and are tied to beam jitter.

Effects folded into regression of natural beam motion: Regression tries to correct for the effect of beamline backgrounds, clouding interpretation of the regressed detectors.

We don't want the background detectors to be (partially) corrected for backgrounds, this is what we want them to measure.

With the dithering correction we hope to correct the true geometric/monitor effect of helicity-correlated differences in our detectors.


Range examined here: Slugs 213-225, last part of Wien8.The only period for which we have accepted averages of correction slopes so far.

Big tune change in the middle of this range, the “M56 retune” (hclog 252851,253443)

USLumi asymmetry


The period immediately after the retune was called ““Golden””: background asymmetries became tiny, USLAW was smallest-ever,

Compton photon S/N was best-ever.

Probably the best period Qweak ever had, and very interesting to examine in its own

right.

Mark Pitt noted that (IN+OUT)/2 was large immediately after the retune, 147+-47 ppb

(hclog 253428). Has not been investigated yet.

Range examined here: Slugs 213-225, last part of Wien8.The only period for which we have accepted averages of correction slopes.

Big tune change in the middle of this range, the “M56 retune” (hclog 252851,253443)

USLumi asymmetry


In this talk I am examining the results of the dithering correction, while also comparing our golden period with the one preceding it. The large background asymmetries of that period were unfortunately perfectly typical.

Example:After the retune the dithering correction slope of the USLumis wrt targetX is suppressed by a factor of 30: the Lumis are a lot less sensitive to the beam (specifically targetX) which explains their width reduction.

Dithering correction slopes only available in last month. We are seeing a lot of interesting things for the first time, but no conclusions yet.

USLumi dithering correction slope wrt targetX

Gap corresponds to Al running right

before the retune


Effect of dithering correction on asymmetry widths


Effect on asymmetry widths: Background detectors



USLumi_sum:The dithering correction reduces the width by a factor of 2

before the retune, but has little effect after. Makes sense.

Same behaviour for background detectors, correction has smaller effect on their width after the retune. But note that

their width is actually increased after the retune.



“Noise removed” by the dithering correction:

Sometimes the correction actually increases the asymmetry width, then it “injects noise” to the asymmetry measurement.

Red points correspond to that case.Monitor noise too small to account for that. Possibly a sign

that our correction slopes are not perfect yet.Note similarity between Lumis and PMTonl.

[Noise ] = √ [Raw width ]2− [Corrected width ]

2


Effect on asymmetry widths: MD





Dithering correction removes noise reliably from all MD bars

except the vertical onesexcept the vertical ones, especially MD7 where it

seems to consistently add noise.

Important note: X-like differences and noise are

larger than Y for all this period, and for most of Qweak. Needs

to be investigated and included in our story.

And/or, it could be an indication that our Y-like

correction slopes are problematic. Need to

understand how much can be attributed to monitor noise.



Raw width

Corrected with dithering

In fact this was first seen 2 years ago, with Run1 data

and with an amateur dithering correction scheme!

(elog 434)

The width reduction is minimal on the vertical bars.

Seems out of phase with the “Dalton-dipole”, but may still be related to something like

Q2 variation on bars(David's elog 921).

Interesting to see if it holds in different periods.

From run 12162From run 12162


Size of dithering corrections


Dithering correction slopes tables (elog 1015) Just for reference, important Just for reference, important points to be shown in plots.points to be shown in plots.


Corrections on MDall from individual monitors


Corrections on MDall from individual monitors

X-like corrections are much larger than Y-like. Partly because dX was

much larger than dY (60nm – 20nm).

But also the large XP-corrections cancelcancel

the large X-corrections!

Overall correction remains small.


Overall dithering corrections on MD bars

Smallest correction on vertical bars Small overall correction Corrections cancel on opposite

bars


Overall dithering corrections on background detectors


Difference between dithering and regression corrections

Difference between dithering and regression corrections: not much smaller point-to-point variation than corrections themselves (except for Lumis before retune).

Difference not always consistent with zero on the Lumis – not necessarily surprising.

If regression is not to be dropped out completely, then these could serve as estimates of the error in our correction (similarly to differences between regression schemes).


Quartet-level correlations of corrected detectors


Quartet-level Correlations of background detectors to dX


Difference not always consistent with zero on the Lumis – not very surprising.


USLumi_sum USLumi1+5 USLumi3+7USLumi1+5

MD9PMTonlPMTltg


Quartet-level Correlations of background detectors to dX


Difference not always consistent with zero on the Lumis – not very surprising.



MD9PMTonlPMTltg

Looks quite good!“Residual” correlations very close to zero, not affected very much by the retune, unlike raw correlations.


Quartet-level Correlations of background detectors to dY


MD9PMTonlPMTltg

Similar picture, but residual correlations not zero

anymore.

Again, not necessarily bad: dithering is not supposed to take these correlations to zero like regression, and stability is encouraging.


Quartet-level Correlations of background detectors to Aq


MD9PMTonlPMTltg

Here the residual correlation is not consistent with zero

and not stable, even drifting with time.

Interestingly the correction has no effect on this

correlation after the retune for any detector.


Quartet-level Correlations of MD to dX

Residual correlations to all parameters exist also in the MD.

Larger on individual bars for Y-like correlations, averaging to the same values for MDall (~0.3 ppb/nm for positions) due to cancellation on

opposite bars.


Quartet-level Correlations of MD to dY


Quartet-level Correlations of MD to dY

Residual correlations to beam parameters at quartet-level do not necessarily mean that our correction slopes are wrong. But it is unclear what these residual correlations mean.

Halo, backgrounds?

We would hope to see some consistency with zero at least

in some periods.It would be reasonable to expect to see this in our “Golden” period, but...


Quartet-level Correlations of MD to USLumi_sum

Correlations to background detectors are very important for

the Beamline Background correction. Perhaps a little early to

look at these without characterizing the dithering

correction.

We also need to understand better the effects going into the

quartet-level correlations, especially to the Lumis.

5 ppb/ppm expected contribution (for USLAW 600 ppm) from target

boiling (elog 963).


Quartet-level Correlations of MD to PMTltg

To finish with a little optimism:

The corrected correlations to PMTltg are about what we

hope to see: Stable over runs, reduced after the retune,

consistent magnitude with our naive expectations.

Qualitatively similar picture for PMTonl and MD9.


Summary and future work

● Come up with models to explain the effects of dithering corrections; why is noise consistently injected to MD7 from the correction?● Clean the correction slopes dataset (identify/remove outliers) and form averages over appropriate ranges; apply corrections over longer periods● Is comparison with regression useful?

..

Dithering correctionsDithering correctionsStarted testing very recently, first results still being produced and parsed.Lots of leads to follow.

Residual correlationsResidual correlationsNot clear what is the meaning of these at quartet-level.● Quantify possible contributions, such as common noise from target boiling: ~5 ppb/ppm in the MDall-to-USLumi correlation for USLAW~600 ppm (elog 963). What about residual correlations to beam parameters?● Extract and compare to runlet-level correlations. Enough statistics in these two periods? Compare to our expectations from dilutions.

..


Extra slides





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Dithering Corrections and Correlations of Corrected Detectorspeople.virginia.edu/~kdp2c/downloads/Qweak-Nov2013/Dithering... · Dithering corrections very important for Beamline Background