Parity-Violating Electron Scattering at JLab David S. Armstrong College of William & Mary MENU 2013 Rome, Italy Oct (replacing Juliette Mammei, who kindly provided most of the slides)

Parity-Violating Electron Scattering at JLab Electroweak interaction (neutral current) - not one of the canonical probes for Hadron Physics (i.e. strong or electromagnetic) - nevertheless, much of the program should be of interest to this community -Focus today: - new results since MENU plans for 12 GeV era at Jefferson Lab

Outline 1)Intro to Parity-Violating Electron Scattering (PVES) 2)The Vector Strange Form Factors a ≈ completed program 3)Qweak: first results on the proton’s weak charge 4)Neutron radius in Heavy Nuclei 5) Standard Model Tests with PVES: plans at JLab-12 GeV

1) Search for physics Beyond the Standard Model – Low energy (Q 2 <<M 2 ) precision tests complementary to high energy measurements 10/2/2013MENU Neutrino mass and their role in the early universe 0νββ decay, θ 13, β decay,… Matter-antimatter asymmetry in the present universe EDM, DM, LFV, 0νββ, θ 13 Unseen Forces of the Early Universe Weak decays, PVES, g μ -2,… LHC new physics signals likely will need additional indirect evidence to pin down its 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) new since MENU2010: first result from QWeak 2) Study nucleon and nuclear properties – Strange quark content of nucleon new since MENU2010: HAPPEX-III – Neutron radius of heavy nuclei new since MENU2010 – first PREx results

A brief history of parity violation R R L L 1930s – weak interaction needed to explain nuclear β decay 1950s – parity violation in weak interaction; V-A theory to describe 60 Co decay 1970s – neutral weak current events at Gargamelle late 1970s – parity violation observed in electron scattering - SLAC E122 10/2/2013MENU 20135

Parity-violating electron scattering 10/2/2013MENU Electroweak interference

SLAC Experiments 10/2/2013MENU SLAC E122 – crucial confirmation of WSG electroweak model Electron-deuteron deep inelastic scattering High luminosity: photoemission from NEA GaAs cathode Rapid helicity-flip (sign of e- polarization) Polarimetry to determine beam polarization Magnetic spectrometer: backgrounds and kinematic separation A PV ~ 100 ± 10 ppm SLAC E158 – 1999 electron-electron scattering - purely leptonic interaction electron-electron weak attractive force had never been measured! A PV ~ -131 ± 14 ± 10 ppb sin 2 θ W =0.20±0.03 sin 2 θ W =0.2403±0.0013

Genesis of a Strange Idea Puzzle: Initial DIS measurements of spin-structure of nucleon (EMC): valence quarks contribute unexpectedly low fraction to total spin - “Spin Crisis” Possible reconciliation: large fraction of spin from ? eg. D. B. Kaplan and A. Manohar, Nucl. Phys. B310, 527 (1988). Theoretical realization: not only did many available nucleon model calculations allow this, but they also allowed (and in some cases favored) large strange quark contributions to other properties of nucleon. Consternation and excitement: at the time, data gave no constraint on strange contributions to charge distribution and magnetic moment! Challenge: how to isolate strange vector form factors? Answer: exploit the weak neutral current as a probe

strange quark contribution Assume isospin symmetry, and we have this and this are well known what about this? (Assume neutral weak charges are known) MENU /2/2013

Nucleon Form Factors NC and EM probe same hadronic flavor structure, with different couplings: Assume Charge Symmetry:

Strange Form Factors 10/2/2013MENU

Qweak: Proton’s weak charge 12 EM ChargeWeak Charge u2/3 d-1/3 P (uud)+1 N (udd)0 “Accidental suppression”  sensitivity to new physics -Neutral current analog of electric charge: 10/1/2013MENU 2013

Qweak: Proton’s weak charge Use four-fermion contact interaction to parameterize the effective PV electron- quark couplings (mass scale and coupling) Large θ Small θ Erler, Kurylov, and Ramsey-Musolf, PRD 68, Planned 4% measurement of proton’s weak charge - probes TeV scale new physics New physics: new Z', leptoquarks, SUSY... For electron-quark scattering: MENU /1/2013

SM Qweak kinematics Hadronic term extracted from fit Extracting the weak charge 14 Hadron structure enters here: electromagnetic and electroweak form factors… The previous strange form factor program (experiments at MIT/Bates, JLab and MAMI) allow us to subtract our hadronic contribution Reduced asymmetry more convenient: 10/1/2013MENU 2013

The Qweak Apparatus 15 Main 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 Acceptance defining collimator QTOR MENU /2/2013

Reduced Asymmetry Hadronic part extracted through global fit of PVES data. 16 in the forward-angle limit (θ=0) 4% of total data MENU /1/2013MENU 2013

The C 1q & the neutron’s weak charge 17MENU /1/2013

The C 1q & the neutron’s weak charge 18MENU /1/2013 Combining this result with the most precise atomic parity violation experiment we can also extract, for the first time, the neutron’s weak charge:

Qweak – first result 1910/1/2013MENU 2013 First result (4% of data set): Lots of work to push down systematic errors, but no show-stoppers found…. Expect final result in months time. More details: Fundamental Symmetries 3, this afternoon

A of Auxiliary Measurements 2010/1/2013MENU 2013 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 27 Al 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 27 Al 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)

208 Pb 2 Neutron skin – PREx MENU /2/2013 Exploit the large weak charge of neutron to extract radius of neutron distribution in heavy nucleus; theoretically clean probe. First result of PREx experiment at JLab: PRL 108(2012) A PV = ± (stat) ± (syst) ppm

PREX-II (proposed ) PREX, PREX II and CREX Theory from P. Ring et al. Nucl. Phys. A 624 (1997) Pb more closely approximates infinite nuclear matter The 48 Ca nucleus is smaller, so A PV can be measured at a Q 2 where the figure of merit is higher and are expected to be correlated, but the correlation depends on the correctness of the models The structure of 48 Ca can be addressed in detailed microscopic models Measure both and - test nuclear structure models over a large range of A MENU 2013 More info: yesterday’s talks by G. Urcioli and M. Thiel in Fundamental Symmetries 2

Future: PVES at JLab in 12 GeV era 10/2/2013MENU MOLLER - precision Standard Model test by measuring weak charge of electron in PV electron-electron scattering (revisit SLAC E158) SOLID - precision Standard Model test by measuring PV DIS on deuteron: access the quark weak axial couplings C 2q (also – a similar measurement was made at 6 GeV in Hall A at Jefferson Lab, X. Zheng et al., being readied for publication, but I’m not authorized to show the results; stay tuned…) Large kinematic coverage: disentangle CSV and higher-twist effects

2.3% MOLLER uncertainty Coupling constants Mass scale Lepton compositeness – strong coupling – 47 TeV LEP2 (g LR and sum) mass scale sensitivity ~5.2 and 4.4 TeV e- MOLLER at 12 GeV MENU /2/2013 Doubly-charged scalar, heavy Z’, SUSY, dark Z…

MOLLER and weak mixing angle 10/2/2013MENU Reminder: at tree-level Q W e = (1 – 4 sin 2 θ W ) Higgs discovery at LHC allows firm prediction of MOLLER asymmetry in Standard Model

MOLLER and weak mixing angle 10/2/2013MENU

Detector Array Scattering Chamber Target Hybrid Torus Upstream Torus Incoming Beam Collimators 28 m The MOLLER Experiment MENU /2/2013

SOLID – accessing the C 2q ’s 10/2/2013MENU XN e- Z* γ* e- Cahn and Gilman, PRD (1978) polarized electrons on deuterium

10/2/2013MENU Large θ Small θ Red ellipses are PDG fits Blue bands represent expected data: Qweak (left) and PVDIS-­6GeV (right) Green bands are proposed SOLID PVDIS

SOLID – Large Acceptance Device 10/2/2013MENU

SOLID – Parity-Conserving Physics 10/2/2013MENU SIDIS with Transversely Polarized 3He approved 90 days - SIDIS with Longitudinally Polarized 3He approved 35 days - SIDIS with Transversely Polarized Proton approved 120 days - Near Threshold Electroproduction of J/Psi approved 60 days PVDIS approved for 169 days (half of full request)

PVES Experiment Summary 10/2/2013MENU

Summary 10/2/2013MENU Grazie to the MENU 2013 organizers for inviting Juliette Mammei to give this talk, and for accepting me as a poor substitute…. Strange vector form factors of proton – small, consistent with zero. Qweak: First measurement of proton’s weak charge, consistent with Standard Model, 25x more data on tape PREx: two-sigma evidence for neutron “skin” of 208 Pb; will improve after JLab comes online after 12 GeV upgrade, and will extend to 48 Ca MOLLER and SOLID: major programs after JLab upgrade two complementary Standard Model tests.

Extra slides 10/2/2013MENU

Qweak and weak mixing angle 10/2/2013MENU

Magnetic spectrometer Background and kinematic separation SLAC Experiment E122 10/2/2013MENU Polarimetry Integrating detectors High luminosity from photoemission from NEA GaAs cathode Rapid helicity-flip (sign of e- polarization) Huge achievement! Highest P 2 I ever, by far. Developed for this experiment at SLAC and used ever since

SLAC Experiment E122 10/2/2013MENU sin 2 θ W =0.20±0.03 GWS --‐ Nobel Prize 1979 Parity Non-Conservation in Inelastic Electron Scattering, C.Y. Prescott et. al, 1978 Deep inelastic scattering: Y dependence reflects quark axial/electron vector coupling strength At high x LeftRight γ Charge0, ±1, ±1/3, ±2/3 W ChargeT= ±1/2 0 Z ChargeT-qsin 2 θ W -qsin 2 θ W A PV ~ 100 ± 10 ppm

C OMPLEMENTARY TO THE LHC - Z ΄ Assume LHC discovers a new spin 1 gauge boson with M =1.2 TeV MOLLER can distinguish between models Erler and Rojas If the SM value is measured Half-way between SM and E158 central value MENU /2/2013

Isolating strange form factors ~ few parts per million For a proton: For 4 He: G E s alone Forward angle Backward angle For deuteron: enhanced G A e sensitivity 39MENU /2/2013

Electroweak Radiative Corrections 40

Electroweak Radiative Corrections 41

Normal production running: 89% longitudinal beam polarization Small 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 42 Horizontal and vertical components measured separately Detector number

Normal production running: 89% longitudinal beam polarization Small amount of transverse polarization Large parity conserving asymmetry (~5ppm) Leaks into the experimental asymmetry through broken azimuthal symmetry Transverse Asymmetry Measurement 43 This is the most precise measurement of Beam Normal Single Spin Asymmetry to date. SourcePreliminaryAnticipated Polarization2.2%~1.0% Statistics1.3%~1.3% 1.2%~0.5% Non-linearity1.0%~0.2% Regression0.9%~0.9% Backgrounds0.3%~0.3% PhD thesis of Buddhini Waidyawansa; being prepared for publication

Global PVES Fit Details 5 free parameters ala Young, et al. PRL 99, (2007) : Employs all PVES data up to Q 2 =0.63 (GeV/c) 2 On p, d, & 4 He targets, forward and back-angle data SAMPLE, HAPPEX, G0, PVA4 Uses constraints on isoscalar axial FF Zhu, et al., PRD 62, (2000) All data corrected for E & Q 2 dependence of Hall et al., arXiv: (2013) & Gorchtein et al., PRC84, (2011) Effects of varying Q 2, θ, & λ studied, found to be small 44 □ γ Z RC

10/2/2013MENU

46 Qweak “Run 0” corrections and their corresponding sizes Target aluminum windows are our largest (~30%) correction Beam line background is currently our largest uncertainty

MOLLER: if Z ‘ seen at LHC... Virtually all GUT models predict new Z’s (E6, SO(10)…): LHC reach ~ 5 TeV With high luminosity at LHC, 1-2 TeV Z’ properties can be extracted Suppose a 1 to 2 TeV heavy Z’ is discovered at the LHC… LHC data can extract the mass, width and A FB (s) MOLLER: resolve signs on e R, e L MOLLER F. Petriello et al, PRD 80 (2009) SLHC, 1 ab -1

MOLLER: if SUSY seen at LHC... MSSM sensitivity if light super- partners and large tan β RPV SUSY MSSM MOLLER Ramsey-Musolf and Su, Phys. Rep. 456 (2008)