Post on 14-Mar-2021
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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
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●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!)