p The Q weak Experiment: A Search for New TeV Scale Physics via a Measurement of the Proton’s Weak Charge Measure: Parity-violating asymmetry in e + p elastic scattering at Q2 ~ 0.03 GeV2 to ~4% relative accuracy at JLab p 2 Extract: Proton’s weak charge Q weak ~ 1 – 4 sin θW 2 2 2 to get ~0.3% on sin θW at Q ~ 0.03 GeV 2 2 2 tests “running of sin θW”from M Z to low Q sensitive to new TeV scale physics W.T.H. van Oers The Standard Model • Building blocks are quarks and leptons point-like, spin ½ particles • Forces mediated by exchange of spin 1 particles: • Mostly neutral currents (gamma,Z,gluon) • One charged current (W+-) • One colored current (gluon) • The different strengths and characters of these forces yield a rich phenomenology: most of the nucleon mass, the elements and their isotopes, fusion in stars, chemistry and life. Courtesy of D.J. Mack The Standard Model: Issues • Lots of free parameters (masses, mixing angles, and couplings) How fundamental is that? • Why 3 generations of leptons and quarks? Begs for an explanation (smells like a periodic table) • Insufficient CP violation to explain all the matter left over from Big Bang Or we wouldn’t be here. • Doesn’t include gravity Big omission … gravity determines the structure of our solar system and galaxy Belief in a rational universe (that something “ordered the muon”) suggests that our SM is only a low order approximation of reality, as Newtonian gravity is a low order approximation of General Relativity. Courtesy of D.J. Mack Running coupling constants in QED and QCD QED (running of α) QCD(running of αs) 137 → αs Q2, GeV2 2 What about the running of sin θW? 2 “Running of sin θW” in the Electroweak Standard Model • Electroweak radiative corrections 2 → sin θW varies with Q + + ••• 2 • All “extracted” values of sin θW must agree with the Standard Model prediction or new physics is indicated. LE Experiments: Good News/Bad News A 1% measurement of a weak-scale quantity, suppressed by an order of magnitude, is sensitive to physics at the scale 3 TeV. This is well above present colliders and complementary to LHC. Fine print: • Low energy experiments can’t measure Λ or g separately, only Λ /g. • With no bump to display, enormous burden of proof on experiment and theory. • If limited by systematic errors, a factor of 2 increase in mass scale requires 22 = 4 reduction in the systematic error. (eg, atomic experiments) • If limited by statistical errors, a factor of 2 increase in mass scale requires (22 )2 = 16 improvement in statistical figure of merit. (eg, scattering experiments) A factor of 2 increase in Λ /g in the scattering sector may happen only once per generation! Nevertheless, JLab can do that and a bit more. Courtesy of D.J. Mack Low Energy Weak Neutral Current Standard Model Tests Low energy Z weak charge “triad” (M. Ramsey-Musolf) probed in weak neutral current experiments e N SLAC E158: parity-violating Moller scattering e 2 e + e → e + e Q(≈W 1 − 4 − sinθW ) Cesium Atomic Parity Violation: JLAB Qp : parity-violating primarily sensitive to neutron weak e-p elastic scattering weak charge A 2 e + p → e + p p 2 QNZ≈W −( 1 + 4 − sinθW ≈ −N ) Q1≈ 4 − sinθ W W These three types o experiments are a complementafry set for exploring new physics possibilities well below the Z pole. Weak Charge Phenomenology Note how the roles of the proton and neutron are become almost reversed (ie, neutron weak charge is dominant, proton weak charge is almost zero!) This accidental suppression of the proton weak charge in the SM makes it more sensitive to new physics (all other things being equal). Courtesy of D.J. Mack p Q weak: Extract from Parity-Violating Electron Scattering As Q2 → 0 MEM MNC p p measures Q – proton’s electric charge measures Q weak – weak chargesproton’ 2M ⎡ − G ⎤ NC F 2 p p 2 A = = ⎢ QQ⎥[]weak+F ()Q, θ M EM ⎣4πα 2⎦ Q2 → 0 θ →0 ⎡ − G F ⎤ 2 p 4 2 ⎯⎯→⎯ ⎢ QQQ⎥[]weak + BQ() ⎣4πα 2⎦ γ Z containsGEM , GEM, and p 2 Q 1weak= 4 − sinW θ ~ 0(at . tree 072 level) p •Qweak is a well-defined experimental observable p • Q weak has a definite prediction in the electroweak Standard Model Energy Scale of an “Indirect” Search for New Physics • Parameterize New Physics contributions in electron-quark Lagrangian 2 PV PV PV GF μ g q μ Le-q = LSM + LNEW =− e γ μ γ 5eC∑ 1qq γ q + 2 e γ μγ 5eh∑ V q γ q q q 2 4Λ p g: coupling constant, Λ: mass scale • A 4% Q Weak measurement probes with 95% confidence level for new physics p p Mass Sensit ivit y vs ΔQ /Q at energy scales to: Weak Weak 4 68% CL Λ 1 ∼ ≈ 2.3 TeV 3 95% CL g p 2 2GF ΔQW p Q Weak projected 4% (2200 hours production) 2 p • The TeV discovery potential of weak Q Weak projected 8% (14 days production) charge measurements will be unmatched SLAC E158, Cs APV until LHC turns on. 1 FermiLab Run II projected • If LHC uncovers new physics, then precision FermiLab Run I low Q2 measurements will be needed to 0 determine charges, coupling constants, etc. 024681012 p p ΔQ Weak/Q Weak (%) p e Q weak & Q weak – Complementary Diagnostics for New Physics JLabJLab QweakQweak SLACSLAC E158E158 - (proposed) Run I + II + III (preliminary) ±0.006 Erler, Kurylov, Ramsey-Musolf, PRD 68, 016006 (2003) • Qweak measurement will provide a stringent stand alone constraint on Lepto-quark based extensions to the SM. p • Q weak (semi-leptonic) and E158 (pure leptonic) together make a powerful program to search for and identify new physics. Model-Independent Constraints Forget about the predictions of any specific new physics model! Do the up- and down-quarks have their expected SM weak charges? today -Qw(down)/2 now -Qw(down)/2 future Dot is SM value -Qw(up)/2 -Qw(up)/2 Constraints by 12C and APV are nearly parallel (N ~ Z). Proton measurement is needed so weak charges can be separated with interesting errors. Qw(He) where N = Z could provide an important cross-check on Cs APV. Figures courtesy of Paul Reimer (ANL) New Physics Sensitivity of Qw(p) Qw(p) is sensitive to new electron-quark interactions such as • Leptoquarks • A new heavy vector (Z’) • R-parity violating SUSY • Compositeness but not the usual R parity- conserving SUSY (she’s very shy and hides in loops). Courtesy of D.J. Mack p Overview of the Q Weak Experiment Elastically Scattered Electron Elastically Scattered Electrons LuninosityLuminosity MonitorMonitors 5inchPMTinLowGain Integrating Mode on Each End of Quartz Bar Region III 325 cm Experiment Parameters Drift Chambers (integration mode) Region 3 Drift Chambers Toroidal Magnet 580 cm Toroidal Magnet Incident beam energy: 1.165 GeV Beam Current: 180 μA Region II Beam Polarization: 85% Drift Chambers Region 2 LH2 target power: 2.5 KW Region I Drift Chambers Eight Fused Silica (quartz) Eight CerenkovFused Silica Detectors (quartz) GEM DetectorsRegion 1 Čerenkov Detectors GEM Detectors Collimator With Eight Openings Collimator with 8 openings θ =9±2° θ= 8° ± 2° Central scattering angle: 8.4° ± 3° 35 cm Liquid Hydrogen Target Phi Acceptance: 53% of 2π Polarized35cm Electron Liquid Beam Hydrogen Target 2 Average Q²: 0.030 GeV Polarized Electron Beam Acceptance averaged asymmetry: –0.29 ppm Integrated Rate (all sectors): 6.4 GHz Integrated Rate (per detector): 800 MHz How it Works: Qweak Apparatus in GEANT4 Courtesy of Klaus Grimm (W&M) Courtesy of D.J. Mack p Anticipated Q Weak Uncertainties Δ Δ pp pp ΔAAphysphys /A/Aphysphys ΔQQ weakweak/Q/Q weakweak StatisticalStatistical (2200(2200 hourshours productiproduction)on) 1.8%1.8% 2.9%2.9% Systematic:Systematic: HadronicHadronic structurestructure uncertaintiesuncertainties ---- 1.9%1.9% BeamBeam polarimetrypolarimetry 1.0%1.0% 1.6%1.6% AbsoluteAbsolute QQ22 determinationdetermination 0.5%0.5% 1.1%1.1% BackgroundsBackgrounds 0.5%0.5% 0.8%0.8% Helicity-correlatedHelicity-correlated BeamBeam PropertiesProperties 0.5%0.5% 0.8%0.8% ________________________________________________________________________________ __________________________________ TotalTotal 2.2%2.2% 4.1%4.1% p 2 2 2 4% error on Q W corresponds to ~0.3% precision on sin θW at Q ~ 0.03 GeV (Erler,(Erler, Kurylov,Kurylov, Ramsey-Musolf,Ramsey-Musolf, PRDPRD 6868,, 016006016006 (2003))(2003)) pp ± QQ WW == 0.07160.0716 ± 0.00060.0006 theoreticallytheoretically 0.8%0.8% errorerror comescomes fromfrom QCDQCD unceuncertaintiesrtainties inin boxbox graphs,graphs, etc.etc. Nucleon Structure Contributions to the Asymmetry A = A p + A + A Q hadronic axial W Constraints on Ahadronic from other Measurements 4 2 =−.19 ppm − .09 ppm − .01 ppm AQBQhadronic = () hadronic:hadronic: (31%(31% ofof asymmetry)asymmetry) γγ ZZ -contains-contains GGE,ME,M GG E,ME,M ConstrainedConstrained byby 00 HAPPEX,HAPPEX, GG ,, MAMIMAMI PVA4PVA4 axial:axial: (4%(4% ofof asymmetry)asymmetry) -- ee containscontains GG AA,, hashas largelarge electroweakelectroweak radiativeradiative corrections.corrections. ConstrainedConstrained byby GG00 andand SAMPLESAMPLE Quadrature sum of expected ΔAhadronic = 1.5% and ΔAaxial = 1.2% errors p contribute ~1.9% to error on Q W The Qweak Apparatus (Calibration Mode Only - Production & Calibration Modes) Quartz Cherenkov Bars (insensitive to Region 2: Horizontal non-relativistic particles) Region 1: GEM drift chamber location Gas Electron Multiplier Mini-torus e- beam Ebeam = 1.165 GeV Ibeam = 180 μA Polarization ~85% Target = 2.5 KW Lumi Monitors QTOR Magnet Collimator System Region 3: Vertical Drift chambers Trigger Scintillator p Q Weak Toroidal Magnet - QTOR •8 toroidal coils, 4.5m long along beam •Resistive, similar to BLAST magnet • Pb shielding between coils • Coil holders & frame all Al • ∫B⋅dl ~ 0.7 T-m • bends elastic electrons