Low Energy Tests ofthe Standard Model

Emlyn HughesSpin 2004TriesteOctober 14, 2004

* PAST

* PRESENT

* FUTURE

Electroweak Mixing Angle

e = g sinw

Characterizes the mixing between the weak and EMinteraction in the electroweak theory

sin2w = 1 - Mw Mz

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- e-

e- e-

unpolarized quarks or electrons or protons

Parity conserving Parity violating

Parity Violation in the Electroweak Theory

APV

2AW AEM

AW AEM+2 2

~ AW

AEM

~ 2

g2

mZ2 + q2

e2

q2

2

APV~

q2

mZ22

APV = - +

R L

R L

SLAC

End Station AEnd Station A

SLAC Parity Experiments

e-Target

(unpolarized)HighEnergy

Detector

APV = - +

Parity-violating asymmetryR L

R L

SLAC E80

Yale E80 Polarized Source

SLAC End Station A

SLAC E95

Results on Parity Violation

ALR < 5 x 10-3 at Q2 ~ 1.4, 2.7 GeV2

E80

E95

ALR < 3.2 x 10-3 at Q2 ~ 4 GeV2

Not sensitive to electroweak mixing in the Standard Model

First Measurementsof Electroweak Mixing

SLAC E122

SLAC E122

Detectore

16 – 22 GeVLiquid Deuterium

GaAs source

High current

30 cm target

Dedicated run

Reversed everyfew runs

120 Hz

SLAC E122 waveplate reversal

Parity-violatingasymmetry

SLAC E122 waveplate reversal

SLAC E122 Energy Scan

Parity-violating asymmetry

SLAC E122 Result

sin2w = 0.224 + 0.020

First definitive measurement of mixing between the weak and electromagnetic interaction

(1978)

Atomic Parity Violation

e- e-

ALR

~ me

2 2

mZ2 ~ 10

-14

or Z

p

q2

mZ2

~2 2

Experiment

Z3 Law Heavy Atoms

Theory

PV Signal sin2w

Bismuth Z = 83

Atomic Parity Violation

Bismuth

Atomic Parity Violation

Bismuth

Atomic Parity Violation

Bismuth

Atomic Parity Violation

BismuthE122

Gargamelle

Neutrino Physics

Bubble Chamber

HPWF Neutrino Detector

(Harvard, Pennsylvania, Wisconsin, Fermilab)

1974

1978

(1975)

(1977)

(1977)

(1977)

1978

LEP and SLC e+e- collider

sin2w = 0.00016 (PDG2004)from Z pole measurements

TODAY...

Q (GeV)

sin2w

Status in 1999

~5%

SLAC Experiment E158Detector

e

50 GeV Liquid Hydrogen

APV = -

+

Without electroweak radiative corrections,

In practice: APV ~ 1.5 x 10-7

2 (3 + cos )22

16 sin 2APV =

1

4 sin2w ( )

m E GF

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 approval1998-99: Design and Beam Tests2000: Funding and construction2001: Engineering run2002: Physics Runs 1 (Spring), 2

(Fall)2003: Physics Run 3 (Summer)

E158 Collaboration

Scattering Processese- e-

e-e-

e- e-

e-e-

Parity-conservingParity-violating

e- e-

pp

Background

Challenges

I. Statistics

II. Beam monitoring & resolution

III. Beam systematics

IV. Backgrounds

jitter vs. statistics

false asymmetries

Spectrometer magnets

Concrete shielding

target Detectorcart

Setup in End Station A

STATISTICS

# electrons per pulse 107

Rep rate (120 Hz) 109

Seconds/day 1014

100 days 1016

A ~ 10-8

II. BEAM MONITORING

Agreement (MeV)

toroid 30 ppm BPM 2 microns energy 1 MeV

BPM

24

X (

MeV

)

BPM12 X (MeV)

Resolution 1.05 MeV

Beam Monitoring Correlations

III. Beam Asymmetries

Polariz

ed

sourc

e

SLOW REVERSALS

* Halfwaveplate @ source

~few hours

* 48 vs. 45 GeV energy

~ few days

APV vs. time

ppb

Asymmetry Results

IV. BACKGROUNDS* electron-proton elastic scattering

* pion production

* radiative inelastic electron-proton scattering

W2 > 3 GeV2

* 2 photon events with transverse polarization

***

ep Detector Asymmetry

Transversely Polarized Beam

Run 1: Spring 2002Run 2: Fall 2002Run 3: Summer 2003

E158 Physics Runs

APV = 175 30 (stat) 20 (syst) ppb

sin2 = 0.2293 ± 0.0024 (stat) ±0.0016 (syst)

At Q2 = 0.027 (GeV/c)2….

w

RUN IFIN

AL RESULT

FINAL RESULT

MS

sin2 = 0.2311 ± 0.00016

wMSTheory:

Run I

APV = 128 14 (stat) 12 (syst) ppb

sin2 = 0.2330 ± 0.0011 (stat) ±0.0010 (syst)

At Q2 = 0.027 (GeV/c)2….

w

All E158 DataPRELIM

INARY

MS

sin2 = 0.2311 ± 0.00016wMSTheory:

Q (GeV)

sin2w

Status in 1999

0.240

0.238

0.236

0.234

0.232

0.2301997 1998 1999 2000

Standard Model

Cesium Atomic Parity Violation Result vs. Time

sin2w

(Colorado measurement)

Modifications in the theoretical corrections to theatomic structure

Wieman et al.

Bennett Wieman

Derevianko

DzubaFlambaum

2001 2002

KozlovPorsevTupitsyn Johnson

BednyhakovSoff

KuchievFlambaum

2003

7

Status Today

sin2w

E158 Beyond Standard Model Implications...

* Limit on LL ~ 10 TeV

* Limit on SO(10) Z’ ~ 900 GeV

* Limit on lepton flavorviolating coupling ~ 0.01GF

(95% confidence level)

FUTURE:

Low energy polarized electronscattering

* 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. Armstrong1, T. Averett1, J.D. Bowman5, R. Carlini9 (contact person), C.A. Davis11

J. Erler3, R. Ent9, M. Finn1, T.A. Forest6, K. Johnston6, R. Jones2, S. Kowalski8, L. Lee7,

A. Lung9, D. Mack9, S.A. Page7, S. Penttila5, M. Pitt10, M. Poelker9, W.D. Ramsay7,

M. Ramsey-Musolf2,4, J. Rochel9, N. Simicevic6, G. Smith9, R. Suleiman8, S. Taylor8,

W.T.H. van Oers7, S. Wells6, S. Wilburn5, S.A. Wood9

1College of William and Mary, Williamsburg, VA2University of Connecticut, Storrs, Connecticut3David Rittenhouse Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania(New address (1/1/2002): Instituto de Fisica, Universidad Nacional Autonoma de Mexico,01000 Mexico D.F., Mexico)4Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California5Los Alamos National Laboratory, Los Alamos, New Mexico6Louisiana Tech University, Ruston, Louisiana7University of Manitoba, Winnipeg, Manitoba, Canada8Massachusetts Institute of Technology, Cambridge, Massachusetts9TJNAF, Newport News, VA10Virginia Polytechnic Institute, Blacksburg, Virginia11TRIUMF, 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

ALR ~ 10-3 at Q2 ~ 20 GeV2

Measurement to 0.6% precision...

Submitted: June 2003

Projected experimental uncertainty from

DIS-parity proposal @ SLACand Qweak experiment @ 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 measurementof parity violation in e-e- scattering

* Future parity experiments active

* Complementary to collider experiments

Final result publication in ~ 1/2 year