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Qweak: Early Results andStatus Update

Scott MacEwanUniversity of Manitoba

Hall C Users MeetingJanuary 24-25, 2013

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A. D. Androic, D.S. Armstrong, A. Asaturyan, T. Averett, J. Balewski, J. Beaufait, R.S. Beminiwattha, J. Benesch, F. Benmokhtar, J.Birchall, R.D. Carlini1 (Principal Investigator), J.C. Cornejo, S. Covrig, M.M. Dalton, C.A. Davis, W. Deconinck, J. Diefenbach, K. Dow, J.F. Dowd, J.A. Dunne, D. Dutta, W.S. Duvall, M. Elaasar, W.R. Falk, J.M. Finn, T. Forest, D. Gaskell, M.T.W. Gericke, J.Grames, V.M. Gray, K. Grimm, F. Guo, J.R. Hoskins, K. Johnston, D. Jones, M. Jones, R. Jones, M. Kargiantoulakis, P.M. King, E. Korkmaz, S. Kowalski1, J. Leacock, J. Leckey, A.R. Lee, J.H. Lee, L. Lee, S. MacEwan, D. Mack, J.A. Magee, R. Mahurin, J.Mammei, J. Martin, M. McHugh, D. Meekins, J. Mei, R. Michaels, A. Micherdzinska, K.E. Myers, A. Mkrtchyan, H. Mkrtchyan, A.Narayan, L.Z. Ndukum, V. Nelyubin, Nuruzzaman, W.T.H van Oers, A.K. Opper, S.A. Page1, J. Pan, K. Paschke, S.K. Phillips, M.L.Pitt, M. Poelker, J.F. Rajotte, W.D. Ramsay, J. Roche, B. Sawatzky, T. Seva, M.H. Shabestari, R. Silwal, N. Simicevic, G. Smith2, P.Solvignon, D.T. Spayde, A. Subedi, R. Subedi, R. Suleiman, V. Tadevosyan, W.A. Tobias, V. Tvaskis, B. Waidyawansa, P. Wang, S.P. Wells, S.A. Wood, S. Yang, R.D. Young, S. Zhamkochyan, D. Zou 1Spokespersons 2Project Manager

23 Grad Students

~10 Post Docs

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IntroductionWhat is Qweak?●First direct measurement of the proton's weak charge

●Search for or constrain new PV physics beyond the Standard Model

● is suppressed in the SM → measurement is sensitive to new physics.

●Perform measurement of Parity-Violating Electron Scattering (PVES) elastically off of protons at very low momentum transfer

●

●Precision goals:

Nucleon structure, ~30% of asymmetry for Qweak

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Weak Mixing Angle

Beringer et al. (PDG), Phys. Rev. D86, 010001 (2012)

●Weak mixing angle determination requires calculation of E-dependent corrections

●Structure is determined by Standard Model (width=uncertainty), anchored at Z-pole by collider data

●Qweak (arbitrarily placed) provides highest precision measurement away from Z-pole → sensitive to new physics

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Accessing the Weak Sector

Tree level electric and weak charges

Electron scattering proceeds via exchange of gamma or Z bosons.

Asymmetry is proportional to interference

suppression0

0.38

0.690.07P 4

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Contact Interaction ModelsUse four-fermion contact interaction to parametrize the effective PV electron-quark couplings by mass scale and couplings

Small Large

“4% Qweak is sensitive to new physics at the TeV scale”

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Electroweak Corrections

~7% shiftUncertainty on this calculation only important at final precision.

Estimates of -Z contribution at Qweak kinematicsγ

Calculations are primarily dispersion theory type - error estimates can be firmed up with data!

Inelastic parity-violating asymmetries:PVDIS at 6 GeV (JLAB E08-011); resonance region asymmetries Qweak: inelastic asymmetry data taken at W ~ 2.3 GeV, Q2 = 0.09 GeV2

M. Dalton, Fall DNP 2012

(error constrained by DIS &PVDIS data)

Sibirtsev, Blunden, Melnitchouk, ThomasPRD 82, 013011 (2010)

Rislow & CarlsonarXiv:1011.2397 (2010)

Gorchstein, Horowitz, & Ramsey-MusolfarXiv:1102.2910 (2011)

Hall, Blunden, Melnitchouk, Thomas, & YoungPrivate communication,

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Current Status of PVESQweak will be most precise (relative and absolute) PVES result to date and will use past results to bound theoretical backgrounds

Challenges of PVES:● Statistics

● High polarization, current, high power targets, large acceptance → higher rates

● Low Noise● Electronics, target density

fluctuations, detector resolution

● Systematics● For Qweak: helicity-

correlated beam parameters, backgrounds (target windows and competing processes), polarimetry, analysis techniques, momentum transfer...

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Qweak Error Budget

Uncertainty

Statistical (2.5k hours at 150 ) 2.1% 3.2%

Systematic 2.7%

Hadronic Structure Uncertainties --- 1.5%

Beam Polarimetry 1.0% 1.5%

Absolute Q^2 Determination 0.5% 1.0%

Backgrounds 0.5% 0.7%

Helicity-Correlated Beam Properites 0.5% 0.8%

Total 2.5% 4.2%

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Experimental OverviewQuartz Cerenkov Bars

Integrating Mode

SpectrometerCollimators

E = 1.165 GeVI = 100 pA - 180 μAP ~ 87%Target = 35 cmCryopower = 2.5kW

e- beam

Tracking Mode

Horizontal Drift Chambers

Vertical Drift Chambers

Trigger Scintillator

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Target

●World's highest power cryotarget at 2.5 kW●Designed using computational fluid dynamics●Low noise contribution (<50 ppm) compared to statistical noise (~140ppm

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Detectors●8 Quartz bar Čerenkov detectors

● Spectrosil 2000:● Rad-hard● Non-scintillating● Low luminescence● 25 Angstroms RMS

polish● Azimuthal symmetry

maximizes rate and reduces systematics due to helicity-correlated beam motion and transverse asymmetries

● Yield 100 photoelectrons per incident electron after showering in 2 cm Pb preradiators.

● Showers limit resolution

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Polarimetry

●Qweak requires measurement of polarization to

●Use two different polarimeters:

● Existing Hall-C Møller polarimeter● Invasive to production● Known analyzing power from polarized Fe foil in high B-field

● New Compton polarimeter● Non-invasive● Known analyzing power from circularly-polarized laser

Commissioning period:

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Expected BountyIn addition to a ~4% measurement of the proton's weak charge, Qweak is capable of producing a number of interesting ancillary measurements:

●Elastic Transverse Asymmetry (proton) → (2γ exchange)

●Elastic Transverse Asymmetry (Aluminum)

●Measurements of PV Asymmetry in the N→Δ region● Transverse Asymmetry in N→Δ region

●PVDIS →γZ box diagrams● Transverse Asymmetry in PVDIS data

●PV Asymmetries in pion photoproduction (acquired during 3.3GeV running)● Transverse Asymmetries in pion photoproduction

Plenty of projects, plenty of results, 20+ theses (5 so far)... →plenty of work!

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PVES Asymmetry Analysis

Correction Correction (ppm)

Polarization -0.0265

Aluminum Windows -0.0592

QTOR transport channel (neutrals) 0.0000

Beamline Backgrounds (neutrals) +0.0102

N→Δ electrons +0.0006

EM radiative effects + Detector bias -0.0088

Total -0.0829

Source of Error (A) Contribution (ppm)

A_meas Statistics 0.0358

A_meas Systematic* 0.0151

Polarization 0.0049

Al Window Asym 0.0087

Al Window Dilution 0.0046

QTOR Transport Asym 0.0021

QTOR Transport Dilution 0.0017

Beamline Asym 0.0232

Beamline Dilution 0.0035

N→Δ Asym 0.0002

N→Δ Dilution 0.0006

Det. Bias correction** 0.0019

EM Rad. Corrections 0.0014

Total Systematic 0.0302

Total 0.0469 (16%)

*Includes cut dependence, regression systematics, detector non-linearities, and transverse asymmetry**Simulation-based correction for variation in light produced across the detectors & non-uniform Q^2 distributions.

16.3% relative error

For “25% Commissioning Data set”

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Aluminum :: Dilution FactorCommissioning Data:

● “Tracking” mode measurement → use of multi-hit F1TDC's for timing information

● Measure yields on full (I=100nA) and empty (I=1μA) target cells● Normalize against yields from 0.4% Carbon target at both currents● Correct for accidentals, electronic/computer dead time, and

radiative losses from interaction with Hydrogen in full target● (Radiative corrections determined by a model-dependent

simulation)

●Improvements :● Dedicated computer dead time data set● Have event mode information in all detector octants● Improved simulations for dummy targets and radiative corrections

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Aluminum :: AsymmetryCorrect for:

Polarization, backgrounds, and radiative effects

Improvements:●More data!●Improved simulations

● Quasi-elastic and inelastic generatorsundergoing upgrades

● Inclusion of “nuclear inelastic” effects

Correct for light weighting and EM radiative corrections

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Transverse Asymmetry

(Azimuthal angle)

●Took data with beam polarized in both directions transverse to motion●Plot not corrected for backgrounds or polarization

PRELIMINARY

Source Preliminary Anticipated

Polarization 2.2% ~1.0%

Statistics 1.3% ~1.3%

Q2 Acceptance 1.2% ~0.5%

Non-linearity 1.0% ~0.2%

Regression 0.9% ~0.9%

Backgrounds 0.3% ~0.3%

Relative Uncertainties (dB/B)

Even before these improvements:

The highest precisionforward angle beam normal

single spin asymmetry!

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Transverse Asymmetries

Target Relative Precision

Inelastic Measurements with Δ final state

Hydrogen ~3%

Aluminum ~5%

Carbon ~3%

Elastic Measurements

Aluminum ~4%

Carbon ~7%

●Numerous additional transverse asymmetry measurements●Still under active analysis●Capable of testing certain model predictions

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Beamline Backgrounds●Background detectors located inside the detector hut, away from elastics, but still measured significant non-zero asymmetries.

●Numerous shielding tests determined that source was the beamline.

●Hypothesis: “asymmetric beam halo” interacting with Tungsten plug inside primary collimator

●Initial studies for commissioning data lead to correction of (-10.2 ± 23.5) ppb, based on correlating background detectors

with luminosity monitors located between target and spectrometer

●Extensive study to continue in the coming months

(Artificially inflated)

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Tracking Mode/Kinematics

●Recall: require a 0.5% measurement of

●Finalizing preparations for a full replay of the tracking data.

●Improvements in simulations to increase our understanding of the octant (azimuthal) dependence of analysis.

●Implementing newest survey data into GEANT<N> simulations.

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C1q

Constraints

Combined APV

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Qweak Commissioning Data

Combined APV

C1q

Constraints

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Combined APV

Qweak Commissioning Data

Qweak + PVES

C1q

Constraints

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Combined APV

Qweak Commissioning Data

Qweak + PVES

Qweak+PVES+APV

C1q

Constraints

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Combined APV

Qweak Commissioning Data

Qweak + PVES

Qweak+PVES+APV

Arbitrarily placed band representing impact of full Qweak precision

C1q

Constraints

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Reduced Asymmetryin the forward-angle limit ( =0)θ

data rotated to the forward-angle limit

Hadronic part can be extracted from global PVES data

Standard Model

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Reduced Asymmetry

4% ofQweakdata

in the forward-angle limit ( =0)θ

data rotated to the forward-angle limit

Hadronic part can be extracted from global PVES data

Standard Model

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Analysis Timeline●Commissioning Run (Jan. 31, 2011 → Feb. 8, 2011)

● ~4% of total accumulated data● Some systems still being commissioned

● Compton, beam modulation, injector spin modulation● Fully analyzed using most up-to-date software and

analysis methodology

●Production Run 1 (February 2011 → May 2011)● ~33% of total data● Currently being analyzed ( ~100 hrs of data / day at peak)

●Production Run 2 (November 2011 → May 2012)● ~63% of total data● To be analyzed following completion of Run 1

New blinding factors for each running period.

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Future●Results already becoming available!

●Currently in the midst of a full replay of the entire Qweak data set.

●Draft of 25% publication is underway

●Intend to present more results (ancillary measurements?) at JLab in Fall 2013

●Final results expected in 2014

PRELIMINARY

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A. D. Androic, D.S. Armstrong, A. Asaturyan, T. Averett, J. Balewski, J. Beaufait, R.S. Beminiwattha, J. Benesch, F. Benmokhtar, J.Birchall, R.D. Carlini1 (Principal Investigator), J.C. Cornejo, S. Covrig, M.M. Dalton, C.A. Davis, W. Deconinck, J. Diefenbach, K. Dow, J.F. Dowd, J.A. Dunne, D. Dutta, W.S. Duvall, M. Elaasar, W.R. Falk, J.M. Finn, T. Forest, D. Gaskell, M.T.W. Gericke, J.Grames, V.M. Gray, K. Grimm, F. Guo, J.R. Hoskins, K. Johnston, D. Jones, M. Jones, R. Jones, M. Kargiantoulakis, P.M. King, E. Korkmaz, S. Kowalski1, J. Leacock, J. Leckey, A.R. Lee, J.H. Lee, L. Lee, S. MacEwan, D. Mack, J.A. Magee, R. Mahurin, J.Mammei, J. Martin, M. McHugh, D. Meekins, J. Mei, R. Michaels, A. Micherdzinska, K.E. Myers, A. Mkrtchyan, H. Mkrtchyan, A.Narayan, L.Z. Ndukum, V. Nelyubin, Nuruzzaman, W.T.H van Oers, A.K. Opper, S.A. Page1, J. Pan, K. Paschke, S.K. Phillips, M.L.Pitt, M. Poelker, J.F. Rajotte, W.D. Ramsay, J. Roche, B. Sawatzky, T. Seva, M.H. Shabestari, R. Silwal, N. Simicevic, G. Smith2, P.Solvignon, D.T. Spayde, A. Subedi, R. Subedi, R. Suleiman, V. Tadevosyan, W.A. Tobias, V. Tvaskis, B. Waidyawansa, P. Wang, S.P. Wells, S.A. Wood, S. Yang, R.D. Young, S. Zhamkochyan, D. Zou 1Spokespersons 2Project Manager

Thank You

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Supplementals

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Transverse Asymmetry

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Accessing the Weak Sector

Tree level electric and weak charges

Electron scattering proceeds via exchange of gamma or Z bosons.

Asymmetry is proportional to interference

suppression0

0.38

0.690.07

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PVES Methodology

pseudo-random quartet ordering

Asymmetry is “blinded” to avoid bias

Change helicity of beam - equivalent to parity transformation

p

p

p

p

p

p

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3.3 GeV Data●Interesting for studying non-resonant inelastic transverse asymmetries → γZ-box diagrams●PV asymmetries in pion photoproduction●Transverse asymmetries in pion photoproduction

●Need to determine how to extract inelastic data from signal

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ElectronicsLow noise electronics from PMT

base through custom 18 bit ADC,sampling at 500 kHz and summed

in FPGA.

current source

(battery) width 2.3 ppm

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Collimation

Small aperture Tungsten collimator “plug” placed in collimator 1 in order to block low angle scatterers from interacting with the downstream beam pipe.

Reduced background Without “plug”

Three layers of lead collimation and concrete shield wall to control

background.

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Radiative Corrections

Goal: make corrections such that quoted asymmetry and kinematics are concordant.

We quote the “measured” kinematics.

Average E_beam = 1155 MeV Average Q^2 = 0.0250 +- 0.0006 (GeV/c)^2Average Theta = 7.90 degrees

Vertex kinematics potentially has reduced energy

and different angle.

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Asymmetry Extraction

16.3% relative error

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PVES Asymmetry Analysis

Helicity-correlatedbeam systematics

Aluminum TargetWindows

BeamlineBackgroundsTransverse Asymmetry

(Small uncertainty, butInteresting physics!)