First Result from Qweak

David S. ArmstrongCollege of William & Mary

MENU 2013 Rome, ItalyOct 1 2013

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Search for physics Beyond the Standard Model

10/1/2013

• Neutrino mass and their role in the early universe 0νββ decay, θ13 , β decay,…• Matter-antimatter asymmetry in the present universe EDM, DM, LFV, 0νββ, θ13

• Unseen Forces of the Early Universe Weak decays, PVES, gμ-2,…

LHC new physics signals likely will need additional indirect evidence to pin down their nature

• Neutrons: Lifetime, P- & T-Violating Asymmetries (LANSCE, NIST, SNS...)• Muons: Lifetime, Michel parameters, g-2, Mu2e (PSI, TRIUMF, FNAL, J-PARC...)• PVES: Low-energy weak neutral current couplings, precision weak mixing angle

(SLAC, Jefferson Lab, Mainz) Atoms: atomic parity violation

Ideal: select observables that are zero, or significantly suppressed, in Standard Model

- Received Wisdom: Standard Model is incomplete, and is low-energy effective theory of more fundamental physics

- Low energy (Q2 <<M2) precision tests: complementary to high energy measurements

Qweak: Proton’s weak charge

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The Standard Model makes a firm prediction of

EM Charge Weak Charge

u 2/3

d -1/3

P (uud) +1N (udd) 0 -1

“Accidental suppression”sensitivity to new physics

Note:

Q-weak is particularly sensitive to the quark vector couplings ( and ) .

𝑄𝑊𝑛 =−2(𝐶1𝑢+2𝐶1𝑑)

- Neutral current analog of electric charge

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Parity-violating electron scattering

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PVA

APV ∝

G FQ2

4πα 2gAe gV

T βgVe gA

T( )~10−4Q2 GeV 2⎡⎣ ⎤⎦

2gM

M Z

Electroweak interference

Qweak: Proton’s weak charge

Use four-fermion contact interaction to parameterize the effective PV electron-quark couplings (mass scale and coupling)

Large θSmall θ

Erler, Kurylov, and Ramsey-Musolf, PRD 68, 016006 2003

A 4% measurement of the proton’s weak charge would probe TeV scale new physics

New physics:

new Z', leptoquarks, SUSY ...

For electron-quark scattering:

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SM

Qweakkinematics Hadronic term extracted from fit

Extracting the weak charge

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𝐴𝑃𝑉=−𝐺𝐹𝑄2

4𝜋𝛼 √2[𝑄𝑤

𝑝 +𝐵 (𝜃 ,𝑄2 )𝑄2 ]Hadron structure enters here: electromagnetic and

electroweak form factors…

Previous experiments (strange form factor program: SAMPLE, HAPPEX, G0, PVA4 experiments at MIT/Bates, JLab and MAMI) explored hadron structure more directly; allow us to subtract our hadronic contribution

𝐴0=−𝐺𝐹𝑄2

4𝜋𝛼 √ 2

One must extrapolate to .We measure

at .

Reduced asymmetry more convenient: Data rotated to

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PVES challenges:• Statistics

– High rates required• High polarization, current• High powered targets with large

acceptance• Low noise

– Electronics, target density fluctuations– Detector resolution

• Systematics– Helicity-correlated beam parameters– Backgrounds (target windows)– Polarimetry– Parity-conserving processes

PVES Challenges

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Qweak’s goal: most precise (relative and absolute) PVES result to date.

Parity violating asymmetry

Unc

erta

inty

Difficulty

𝛿 𝐴𝑃𝑉 ≈±2.1 %𝛿𝑄𝑊

𝑝 ≈± 4 %𝛿 (sin2𝜃𝑊 )≈±0.3 %

Small absolute and relative uncertainty (5ppb on )

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Meeting PVES Challenges

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- Rapid helicity reversal (960 Hz)- 180 μA beam current (JLab record) - Small scattering angle: toroidal magnet, large acceptance- GHz detected rates: data taking in integrating mode- High power cryogenic target- Exquisite control of helicity-correlated beam parameters- Two independent high-precision polarimeters- Radiation hard detectors- Low noise 18-bit ADCs- High resolution Beam Current monitors

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The Qweak ApparatusMain detectors

8-fold symmetry

Vertical drift chambers (VDC)

(rotate)

Trigger scintillator

Shield wall

Lintels

QTOR

Lead collar

Cleanup collimators

Target

Tungsten plug Horizontal drift

chambers (HDC)(rotate)

e- beam

e- beam

Acceptance defining

collimator

QTOR

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35 cm, 2.5 kW liquid hydrogen targetWorld’s highest powered cryotarget

• Temperature ~20 K• Pressure: 30-35 psia• Beam at 150 – 180uA

Qweak Target

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Target boiling might have been problematic!

MD LH2 Asymmetry

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35 cm, 2.5 kW liquid hydrogen targetWorld’s highest powered cryotarget

• Temperature ~20 K• Pressure: 30-35 psia• Beam at 150 – 180uA

Qweak Target

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LH2 statistical width (per quartet):• Counting statistics: 200 ppm• Main detector width: 92 ppm• BCM width: 50 ppm• Target noise/boiling: 37 ppm

228 ppm

Target boiling might have been problematic!

MD LH2 Asymmetry

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• Main detectorsToroidal magnet focuses elastically scattered electrons onto each bar– 8 Quartz Cerenkov bars – Azimuthal symmetry maximizes rates and reduces systematic uncertainties– 2 cm lead pre-radiators reduce background

Main Detectors

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Simulation of scattering rate MD face

Close up of one detector in situ

Measured

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To determine , we go to “tracking” mode:• Currents ~ 50 pA• Use Vertical + Horizontal Drift Chambers• Re-construct individual scattering events

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Correct for radiative effects in target with Geant 4 simulations, benchmarked with gas-target & solid target studies

𝐴𝑃𝑉=−𝐺𝐹𝑄2

4𝜋𝛼 √2{𝑄𝑤

𝑝 +𝐵 (𝜃 ,𝑄2 )𝑄2}

Simulation blueData red

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Kinematics (Q2) determination

Beam Polarimetry

Polarization is our largest systematic uncertainty (goal: 1%)This is a challenging goal; so we built a second, independent measurement device.

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Møller polarimeter– Precise, but invasive– Thin, pure iron target– Brute force polarization– Limited to low current

Compton polarimeter– Installed for Q-weak– Runs continuously at high currents– Statistical precision: 1% per hour

We detect both recoil electron and photon.

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Beam Polarimetry

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Note the good agreement between both polarimeters

Preliminary Run 2 Polarization – For Illustrative Purposes Only

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A of Auxiliary Measurements

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Qweak has data (under analysis) on a variety of observables of potential interest for Hadron physics:

• Beam normal single-spin asymmetry* for elastic scattering on proton• Beam normal single-spin asymmetry for elastic scattering on 27Al• PV asymmetry in the region.• Beam normal single-spin asymmetry in the region.• Beam normal single-spin asymmetry near W= 2.5 GeV • Beam normal single-spin asymmetry in pion photoproduction• PV asymmetry in inelastic region near W=2.5 GeV (related to box diagrams) • PV asymmetry for elastic/quasielastic from 27Al• PV asymmetry in pion photoproduction

*: aka vector analyzing power aka transverse asymmetry; generated by imaginary part of two-photon exchange amplitude (pace Wim van Oers)

N → Δ

N → Δ

gZ

Q-weak ran from Fall 2010 – May 2012 : four distinct running periods• Hardware checkout (Fall 2010-January 2011)• Run 0 (Jan-Feb 2011)• Run 1 (Feb – May 2011)• Run 2 (Nov 2011 – May 2012)

First result

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We have completed and unblinded the analysis of “Run 0” (about 1/25th of our total dataset).

ppb ⟨𝑄2 ⟩=0.0250±0.0006𝐺𝑒𝑉 2

⟨𝐸𝑏𝑒𝑎𝑚 ⟩=1155𝑀𝑒𝑉 𝜃𝑒𝑓𝑓=7.90°

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arXiv:1307:5275 accepted in PRL, to appear online Oct. 13

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Reduced Asymmetry

Hadronic part extracted through global fit of PVES data.

in the forward-angle limit (θ=0)4% of total data

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Reduced Asymmetry

Hadronic part extracted through global fit of PVES data.

in the forward-angle limit (θ=0)4% of total data

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The C1q & the neutron’s weak charge

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The C1q & the neutron’s weak charge

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Combining this result with the most precise atomic parity violation experimentwe can also extract, for the first time, the neutron’s weak charge:

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Weak mixing angle result4% of total data

* Uses electroweak radiative corrections from Erler, Kurylov, Ramsey-Musolf, PRD 68, 016006 (2003)

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Recall: in Standard Model, at tree-level, = = (1 - 4sin2θW)

“Teaser”

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“Teaser”

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Anticipated precision of full data set

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Summary

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ppb ⟨𝑄2 ⟩=0.0250±0.0006𝐺𝑒𝑉 2

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First result (4% of data set):

Lots of work to push down systematic errors, but no show-stoppers found….

Expect final result in 12-18 months time.

Grazie to MENU-2013 organizers for the chance to give this talk!

Thanks to my Qweak collaborators, from whom many slides borrowed…

Qweak Collaboration

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D.S. Armstrong, A. Asaturyan, T. Averett, J. Balewski, J. Beaufait, R.S. Beminiwattha, J. Benesch, F. Benmokhtar, J. Birchall, R.D. Carlini1, 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. Finn1, 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.J. 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.R. 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

1Spokespersons 2Project Manager Grad Students

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Extra slides

10/2/2013

Electroweak Radiative Corrections

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Electroweak Radiative Corrections

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Normal production running: 89% longitudinal beam polarizationSmall amount of transverse polarization

• Large parity conserving asymmetry (~5ppm)• Leaks into the experimental asymmetry through broken azimuthal symmetry

Measurements of the Beam Normal Single Spin Asymmetry (BNSSA) provide:• Direct access to imaginary part of two-photon exchange

We need to correct for this…

Transverse Asymmetry Measurement

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Horizontal and vertical components measured separately

𝐴𝐵𝑁𝑆𝑆 (𝜙𝑑𝑒𝑡 )=𝐵𝑛|𝑃𝑇|sin (𝜙𝑑𝑒𝑡−𝜙𝑠)

Detector number

Normal production running: 89% longitudinal beam polarizationSmall amount of transverse polarization

• Large parity conserving asymmetry (~5ppm)• Leaks into the experimental asymmetry through broken azimuthal symmetry

Transverse Asymmetry Measurement

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This is the most precise measurement of Beam Normal Single Spin Asymmetry to date.

ppm

Source Preliminary Anticipated

Polarization 2.2% ~1.0%

Statistics 1.3% ~1.3%

1.2% ~0.5%

Non-linearity 1.0% ~0.2%

Regression 0.9% ~0.9%

Backgrounds 0.3% ~0.3%

PhD thesis of Buddhini Waidyawansa; being prepared for publication

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Global PVES Fit Details• 5 free parameters ala Young, et al. PRL 99, 122003 (2007):

• Employs all PVES data up to Q2=0.63 (GeV/c)2 • On p, d, & 4He targets, forward and back-angle data

• SAMPLE, HAPPEX, G0, PVA4

• Uses constraints on isoscalar axial FF • Zhu, et al., PRD 62, 033008 (2000)

• All data corrected for E & Q2 dependence of• Hall et al., arXiv:1304.7877 (2013) & Gorchtein et al., PRC84, 015502 (2011)

• Effects of varying Q2, θ, & λ studied, found to be small

GAZ

□γZ RC

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𝐴𝑒𝑝=𝑅𝑅𝐶𝑅𝐷𝑒𝑡 𝑅𝐵𝑖𝑛𝑅𝑄2❑

𝐴𝑚𝑠𝑟𝑃 −∑

𝑖=1

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𝑓 𝑖 𝐴𝑖

1−∑𝑖𝑓 𝑖

Qweak “Run 0” corrections and their corresponding sizes

Target aluminum windows are our largest (~30%) correction

Beam line background is currently our largest uncertainty