Low Energy Tests of the Standard Model Emlyn Hughes Spin 2004 Trieste October 14, 2004 *PAST *PRESENT *FUTURE

Electroweak Mixing Angle e = g sin  w Characterizes the mixing between the weak and EM interaction in the electroweak theory sin 2  w = 1 - MwMw MzMz 2 2

3 Types of Measurements *Electron scattering (parity violation) *Atomic parity violation *Neutrino physics (NC/CC cross section)

Parity Violation in Polarized Electron Scattering e-   unpolarized quarks or electrons or protons Parity conserving Parity violating

Parity Violation in the Electroweak Theory A PV  2A W A EM AWAW A EM + 22 ~ A W A EM ~ 2 g2g2 mZmZ 2 + q 2 e2e2 q2q2 2 A PV ~ q2q2 mZmZ 2 2 A PV =  -   +  RL RL

SLAC

End Station A

SLAC Parity Experiments e- Target (unpolarized) High Energy Detector A PV =  -   +  Parity-violating asymmetry RL RL

SLAC E80

Yale E80 Polarized Source

SLAC End Station A

SLAC E95

Results on Parity Violation A LR < 5 x at Q 2 ~ 1.4, 2.7 GeV 2 E80 E95 A LR < 3.2 x at Q 2 ~ 4 GeV 2 Not sensitive to electroweak mixing in the Standard Model

First Measurements of Electroweak Mixing

SLAC E122

Detector e 16 – 22 GeV Liquid Deuterium GaAs source High current 30 cm target Dedicated run

Reversed every few runs 120 Hz

SLAC E122 waveplate reversal

Parity-violating asymmetry SLAC E122 waveplate reversal

SLAC E122 Energy Scan Parity-violating asymmetry

SLAC E122 Result sin 2  w = First definitive measurement of mixing between the weak and electromagnetic interaction (1978)

Atomic Parity Violation e- A LR ~ m e  22 mZmZ 2 ~  or Z p q2q2 mZmZ 2 ~22

Experiment Z 3 Law Heavy Atoms Theory PV Signal sin 2  w Bismuth Z = 83

Atomic Parity Violation Bismuth

Atomic Parity Violation Bismuth

Atomic Parity Violation Bismuth

Atomic Parity Violation Bismuth E122

Gargamelle Neutrino Physics Bubble Chamber

HPWF Neutrino Detector (Harvard, Pennsylvania, Wisconsin, Fermilab)

1974

1978

(1975) (1977) 1978

LEP and SLC e + e - collider  sin 2  w = (PDG2004)from Z pole measurements TODAY...

Q (GeV) sin 2  w Status in 1999 ~5%

SLAC Experiment E158 Detector e 50 GeV Liquid Hydrogen A PV =  -   +  Without electroweak radiative corrections, In practice: A PV ~1.5 x  (3 + cos  ) sin  2 A PV = 1 4  sin 2  w () m E G F e-e- scattering

UC Berkeley Caltech Jefferson Lab Princeton Saclay SLAC Smith College Syracuse UMass Virginia 7 Ph.D. Students 60 physicists Sept 97: EPAC approval : Design and Beam Tests 2000: Funding and construction 2001: Engineering run 2002: Physics Runs 1 (Spring), 2 (Fall) 2003: Physics Run 3 (Summer) E158 Collaboration

Scattering Processes e-   Parity-conserving Parity-violating e-  p p  Background

Challenges I. Statistics II. Beam monitoring & resolution III.Beam systematics IV.Backgrounds  jitter vs. statistics  false asymmetries

Spectrometer magnets Concrete shielding target Detector cart Setup in End Station A

STATISTICS # electrons per pulse10 7 Rep rate (120 Hz)10 9 Seconds/day days10 16  A ~ 10 -8

II. BEAM MONITORING

Agreement (MeV)  toroid  30 ppm  BPM  2 microns  energy  1 MeV BPM24 X (MeV) BPM12 X (MeV) Resolution 1.05 MeV Beam Monitoring Correlations

III. Beam Asymmetries Polarized source

SLOW REVERSALS source ~few hours *48 vs. 45 GeV energy ~ few days

A PV vs. time ppb

Asymmetry Results

IV. BACKGROUNDS *electron-proton elastic scattering *pion production *radiative inelastic electron-proton scattering W 2 > 3 GeV 2 *2 photon events with transverse polarization ******

ep Detector Asymmetry

Transversely Polarized Beam

Run 1: Spring 2002 Run 2: Fall 2002 Run 3: Summer 2003 E158 Physics Runs

A PV =  175  30 (stat)  20 (syst) ppb sin 2  = ± (stat) ± (syst) At Q 2 = (GeV/c) 2 …. w RUN I FINAL RESULT MS sin 2  = ± w MS Theory:

Run I

A PV =  128  14 (stat)  12 (syst) ppb sin 2  = ± (stat) ± (syst) At Q 2 = (GeV/c) 2 …. w All E158 Data PRELIMINARY MS sin 2  = ± w MS Theory:

Q (GeV) sin 2  w Status in 1999

Standard Model Cesium Atomic Parity Violation Result vs. Time sin 2  w (Colorado measurement) Modifications in the theoretical corrections to the atomic structure Wieman et al. Bennett Wieman Derevianko Dzuba Flambaum Kozlov Porsev Tupitsyn Johnson Bednyhakov Soff Kuchiev Flambaum 2003

77 Status Today sin 2  w

E158 Beyond Standard Model Implications... *Limit on  LL ~ 10 TeV *Limit on SO(10) Z’ ~ 900 GeV *Limit on lepton flavor violating coupling ~ 0.01G F (95% confidence level)

FUTURE: Low energy polarized electron scattering *Jefferson Lab *SLAC (could do it, but won’t)

The Qweak Experiment: A Search for New Physics at the TeV Scale Via a Measurement of the Proton’s Weak Charge December 3, 2001 D. Armstrong 1, T. Averett 1, J.D. Bowman 5, R. Carlini 9 (contact person), C.A. Davis 11 J. Erler 3, R. Ent 9, M. Finn 1, T.A. Forest 6, K. Johnston 6, R. Jones 2, S. Kowalski 8, L. Lee 7, A. Lung 9, D. Mack 9, S.A. Page 7, S. Penttila 5, M. Pitt 10, M. Poelker 9, W.D. Ramsay 7, M. Ramsey-Musolf 2,4, J. Rochel 9, N. Simicevic 6, G. Smith 9, R. Suleiman 8, S. Taylor 8, W.T.H. van Oers 7, S. Wells 6, S. Wilburn 5, S.A. Wood 9 1College of William and Mary, Williamsburg, VA 2University of Connecticut, Storrs, Connecticut 3David Rittenhouse Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania (New address (1/1/2002): Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Mexico D.F., Mexico) 4Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 5Los Alamos National Laboratory, Los Alamos, New Mexico 6Louisiana Tech University, Ruston, Louisiana 7University of Manitoba, Winnipeg, Manitoba, Canada 8Massachusetts Institute of Technology, Cambridge, Massachusetts 9TJNAF, Newport News, VA 10Virginia Polytechnic Institute, Blacksburg, Virginia 11TRIUMF, Vancouver, Canada Approved January 2002

Jefferson Lab Qweak Experiment * 180  Amp current * 1 GeV beam * 2200 hours of data Elastic electron-proton scattering experiment

SLAC DIS-Parity Letter of Intent ~39 GeV polarized electrons scattering off deuterium target A LR ~ at Q 2 ~ 20 GeV 2 Measurement to 0.6% precision... Submitted: June 2003

Projected experimental uncertainty from DIS-parity SLAC and Qweak Jefferson Lab

LHC Not a parity experiment …  Has major impact on precision low energy tests for discovery potential Z’, supersymmetry, compositeness, leptoquarks, etc… in the TeV range

SUMMARY *Performed a first measurement of parity violation in e - e - scattering *Future parity experiments active *Complementary to collider experiments Final result publication in ~ 1/2 year