Electroweak Physics: Lecture V

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1 Electroweak Physics Lecture V: Survey of Low Energy Electroweak Physics (other than neutral current interactions) Acknowledgements: Slides from D. DeMille, G. Gratta, D. Hertzog, B. Kayser, D. Kawall, M.J. Ramsey-Musolf

2 Review 1. Introduction to Electroweak Physics Electroweak force properties; electronpositron collisions 2. Status of Electroweak Physics Precision electroweak data from colliders 3. Electroweak Physics at low Q 2 Weak Neutral Current interactions E158 experiment 4. Weak Neutral Current Interactions (cont d) Future Weak Neutral Current experiments Strange Quarks in the Nucleon Neutron Skin of a Lead Nucleus

Muon g-2 The gyromagnetic ratio, g, relates spin angular momentum to the particle s magnetic moment r µ r g( )S Dirac theory: point-like, spin-1/2 particles have g = 2, but.

3 Muon g-2 The gyromagnetic ratio, g, relates spin angular momentum to the particle s magnetic moment r µ r g( )S Dirac theory: point-like, spin-1/2 particles have g = 2, but...» proton g >> 2» hyperons S = e 2 m» electron» muon g almost equal to 2 The muon anomalous magnetic moment is coupling to virtual fields e γ γ a µ = ( g 2) 2 µ α 2π D. Hertzog / Illinois

4 g 2 because of virtual loops, many of which can be calculated very precisely µ γ µ Z π π B QED Weak Had VP Had LbL (29) 15.4(3) 696.3(7) (2003: +1.8 shift) or 711.0(6) +13.0(25) New: +50% shift! Not agreed on yet Units: x10-10 Others cannot D. Hertzog / Illinois

5 Precession proportional to (g-2) at rest B in flight µ g eb ω = s = ω g 2 eb L ω 2 s = mc 1 + γ 2 mc γ µ ω c eb = mc γ MOVIE θ ω = ω a = g 2 2 eb mc INDEPENDENT of γ! D. Hertzog / Illinois

6 4 key miracles make it happen Polarized muons ν π + µ + Precession proportional to (g-2) ω = ω a spin ω cyclotron µ P µ The magic momentum E field doesn t affect muon spin when γ = 29.3 v e v 1 v v = aµ B a β E mc 2 γ 1 ω a µ Parity violation in the decay D. Hertzog / Illinois

7 a µ is proportional to the difference between the spin precession and the rotation rate e Momentum Spin ω = ω a = g 2 2 eb mc D. Hertzog / Illinois

8 Fit to Simple 5-Par Function Few billion events Getting a good χ 2 is a challenge Counts per 150 ns N(t) = N 0 e -t/τ [1+Acos(ω a t + φ)] Counts per 150 ns x time (µs) Counts per 150 ns time (µs) D. Hertzog / Illinois

9 Results and Implications Non-zero a µ appeals to a catalog of SM Extensions New physics SUSY Leptoquarks Muon substructure Anomalous W couplings ν µ µ µ W B W Theory is being improved New design to reduce error by factor of 2 D. Hertzog / Illinois

10 CC Weak Interaction within the SM

11 PV in Charged Current Processes M CC g2 Fermi Constants 8M W 2 (V A) (V A) µ decay G F µ 2 = g2 8M W 2 ( ) 1+ r µ β decay g 2 8M W 2 G F β 2 = g2 8M W 2 V ud is universal Universality obscured by G F β ( ) 1+ r β G F µ =V ud New physics ( 1 + r β r ) µ

12 Weak decays d ue ν e s ue ν e u c t b ue ν e ( ) V ud V us V ub d V cd V cs V cb s V td V ts V tb b V ud 2 + V us 2 + V ub 2 = 1 SM ±0.001 Expt ± ± ±0.0000

13 Weak decays d ue ν e s ue ν e b ue ν e u c t ( ) V ud V us V ub d V cd V cs V cb s V td V ts V tb b ν µ µ ν µ µ χ 0 β-decay ν µ W n pe µ ν e ν e A(Z,N) A(Z 1,N+1) χ 0 ν e + e ν e π + ν µ π 0 e + ν e ν +L e χ e e δo SUSY +L~0.00 SM O SUSY G F β G F µ = V ud 1+ r β r µ ( ) New physics

14 Weak decays G F β G F µ = V ud 1+ r β r µ ( ) β-decay n pe ν e A(Z,N) A(Z 1,N+1) e + ν e π + π 0 e + ν e Ultra cold neutrons LANSCE: UCN A 58 Ni coated stainless guide Liquid N 2 Be reflector LHe Flapper valve dw 1+ a r p e p r ν E e E ν + A r σ n r p e E e +L Solid D 2 77 K poly Tungsten Target UCN Detector Future SNS: Pulsed Cold Neutrons: abba

15 Weak decays G F β G F µ = V ud 1+ r β r µ ( ) β-decay n pe ν e A(Z,N) A(Z 1,N+1) e + ν e π + π 0 e + ν e 0 +! 0 + Superallowed Ft= ft1+ ( δ R +δ ( NS )1 δ ) C =K 2(G F β ) 2 Nuclear structuredependent corrections

16 Weak decays G F β G F µ = V ud 1+ r β r µ ( ) β-decay n pe ν e A(Z,N) A(Z 1,N+1) e + ν e π + π 0 e + ν e 0 +! 0 + Superallowed New tests Ft= ft1+ ( δ R +δ ( NS )1 δ ) C =K 2(G F β ) 2 Nuclear structuredependent corrections

17 Weak decays G F β G F µ = V ud 1+ r β r µ ( ) β-decay n pe ν e A(Z,N) A(Z 1,N+1) e + ν e π + π 0 e + ν e PSI: Pi-Beta Γπ ( + π 0 e + ν e )Γπ ( + µ + ν µ )~1 10 8

18 Weak Decays (Ongoing) Muon lifetime (MuLan at PSI) Neutron lifetime (UCNA at LANSCE, NIST) Pion Decays (PiBeta at PSI) Kaon Decays (KLOE at INFN Frascati) Muon Michel Parameters (TWIST at TRIUMF) Search for right-handed charged currents

19 TWIST physics motivation -- test the Standard Model for µ-decay Most general interaction does not presuppose the W e ± ν µ ± ν 2 rate ~ γ =S,V,T i, j=r,l γ g ij ψ ei Γ γ ψ ν e ψ ν µ Γ γ ψ µ j S,V,T = scalar, vector or tensor interactions R, L = right and left handed leptons (e, µ, or τ )

20 Couplings in the present Standard Model 2 rate ~ γ =S,V,T i, j=r,l γ g ij ψ ei Γ γ ψ ν e ψ ν µ Γ γ ψ µ j S g RR = 0 V g RR = 0 T g RR 0 S g LR = 0 V g LR = 0 T g LR = 0 S g RL = 0 V g RL = 0 T g RL = 0 S g LL = 0 V g LL =1 T g LL 0

21 e + spectrum in x, cosθ e rate ~ x 2 3 3x ρ ( 4 x 3 1 x )+ 3ηx o + P x µ ξ cosθ e 1 x δ ( 4x 3 ) Spectral shape in x, cosθ e is characterized in terms of four parameters -- ρ, η, ξ, δ P µ is the muon polarization x E e E e max θ e r p e r s µ x o m e E e max (L. Michel, A. Sirlin) E e max m µ 2 + me 2 2m µ

22 TWIST at TRIUMF TWIST at TRIUMF ρ δ ξ η P µ ξδ ρ SM 3/4 3/ Highly polarized µ + TWIST will measure ρ, ρ, ξ, ξ, δ in in two steps in in 2004; ~3x in in 2005/6

23 Discrete Symmetries P, C and CP violated CPT likely conserved (being tested) Therefore, T violation expected Baryon number violation Proton decay? Lepton Number Violation Neutrino mass and mixing Charge lepton number violation?

24 D S P T 3

25 x γ P and CP-violating processes e e

26 Electric dipole moment (EDM) searches may test new CP-violation CKM f d SM d exp d future e < < n < < Hg < < µ < < If new CP violation is responsible for abundance of matter, will these experiments see an EDM?

27 Proton Decay & Neutrino Mass Small amount of baryon number violation expected Does the proton decay? Is the solar neutrino flux as expected? Birth of Underground Science! We now know neutrinos have mass We now understand the dynamics of hydrogen burning in the sun to ~1%

30 Dirac or Majorana neutrinos?

33 Double Beta Decay

35 Future Underground Science Precision solar neutrino spectra Neutrino MNS matrix parameters CP Violation? Proton Decay Double Beta Decay

36 Lepton Flavor Violation When a muon stops in matter, the principal interactions are: Capture on Nucleus: µ - N(Z,A) ν µ N(Z-1,A) Decay in Orbit: µ - ν µ e - ν e (DIO) Coherent conversion is µ - N(Z,A) e - N(Z,A), and the signal is a monoenergetic electron beyond the DIO endpoint. The MECO experiment at BNL will measure: R µe = Γ[µ - N(Z,A) e - N(Z,A)]/ Γ[µ - N(Z,A) ν µ N(Z-1,A)] A single event implies R µe > 2 X

New Physics at High Energy Scales Supersymmetry ~ ~ l µ - j l j e - q ~ χ 0 i q µ - q e - q Compositeness Predictions at 10-15 Λ = 3000 TeV C N Heavy Neutrinos µ - e

37 New Physics at High Energy Scales Supersymmetry ~ ~ l µ - j l j e - q ~ χ 0 i q µ - q e - q Compositeness Predictions at Λ = 3000 TeV C N Heavy Neutrinos µ - e - µ - W e - q q q q H t e - t t Higgs Leptoquarks µ - d L µ - e - γ,z,z Heavy Z, Anomalous Z coupling d e - q After W. Marciano q M Z = 3000 TeV/c B(Z µ e) <

38 Features of the MECO Experiment 1000 fold increase in µ beam intensity over existing facilities High Z target for improved pion production Axially-graded 5 T solenoidal field to maximize pion capture Superconducting Solenoids 1 T Muon Beam Calorimeter Straw Tracker 1 T Stopping Target Foils 2 T Proton Beam Curved transport selects low momentum µ Muon stopping target in a 2 T axially-graded field to improve conversion e - acceptance 2.5 T High rate capability electron detectors in a constant 1 T field 5 T Pion Production Target

39 MECO Detector Elements Magnetic spectrometer measures electron momentum with precision of 0.3% (rms) essential to eliminate decay in orbit background. Consists of ~2800 axial straw tube detectors 2.6 m x 5 mm. 25 µm wall thickness. ~1200 element PbWO 4 (3.5 x 3.5 x 12 cm) calorimeter measures electron energy to ~5%, providing trigger and confirming trajectory. Electron starts here. Position resolution: 0.2 mm transversely, 1.5 mm axially

40 Summary An extraordinary amount has been learnt about electroweak physics in the past fifty years Further progress requires a coherent effort across High Energy Physics, Nuclear Physics and Particle Astrophysics Accelerator- and non-accelerator experiments will play equally important roles Together, we will finally address some of the outstanding questions unanswered by the current version of the electroweak theory Your generation can help towards generating the required unity and coherence

Low Energy Precision Tests of Supersymmetry

Low Energy Precision Tests of Supersymmetry M.J. Ramsey-Musolf Caltech Wisconsin-Madison M.R-M & S. Su, hep-ph/0612057 J. Erler & M.R-M, PPNP 54, 351 (2005) Outline I. Motivation: Why New Symmetries? Why