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Low Energy Tests of the Standard Model. * PAST. * PRESENT. * FUTURE. Emlyn Hughes Spin 2004 Trieste October 14, 2004. Electroweak Mixing Angle. e = g sin q w. Characterizes the mixing between the weak and EM interaction in the electroweak theory. 2. M w. 2. sin 2 q w = 1 -. M z.

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slide1

Low Energy Tests of

the Standard Model

* PAST

* PRESENT

* FUTURE

Emlyn Hughes

Spin 2004

Trieste

October 14, 2004

slide2

Electroweak Mixing Angle

e = g sinqw

Characterizes the mixing between the weak and EM

interaction in the electroweak theory

2

Mw

2

sin2qw = 1 -

Mz

slide3

3 Types of Measurements

* Electron scattering (parity violation)

* Atomic parity violation

* Neutrino physics (NC/CC cross section)

slide4

Parity Violation in

Polarized Electron Scattering

e-

e-

e-

e-

g

Z

unpolarized quarks or electrons or protons

Parity conserving

Parity violating

slide5

Parity Violation in the Electroweak Theory

R

L

s - s

APV =

R

L

s + s

g2

2

+ q2

AW

mZ

2AW AEM

PV

2

~

2

~

~

A

AEM

2

2

+

e2

AW

AEM

q2

PV

q2

A

~

2

2

mZ

slide7

End Station A

End Station A

slide8

SLAC Parity Experiments

Detector

e-

Target

High

Energy

(unpolarized)

R

L

s - s

APV =

Parity-violating asymmetry

R

L

s + s

slide13

Results on Parity Violation

E80

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

E95

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

Not sensitive to electroweak mixing

in the Standard Model

slide14

First Measurements

of Electroweak Mixing

slide16

SLAC E122

Detector

e

16 – 22 GeV

Liquid

Deuterium

GaAs source

High current

30 cm target

Dedicated run

slide17

120 Hz

Reversed every

few runs

slide19

SLAC E122 waveplate reversal

Parity-violating

asymmetry

slide20

SLAC E122 Energy Scan

Parity-violating

asymmetry

slide21

SLAC E122 Result

(1978)

sin2qw = 0.224 + 0.020

First definitive measurement of mixing between

the weak and electromagnetic interaction

slide22

Atomic Parity Violation

e-

e-

g or Z

p

2

2

mea

LR

q2

-14

A

~

2

~

2

10

~

2

2

mZ

mZ

slide23

Experiment

Z3 Law

Heavy Atoms

Theory

PV Signal

sin2qw

Bismuth Z = 83

slide28

Neutrino Physics

Bubble

Chamber

Gargamelle

slide29

HPWF Neutrino Detector

(Harvard, Pennsylvania, Wisconsin, Fermilab)

slide33

(1977)

(1977)

(1975)

(1977)

1978

slide34

TODAY...

LEP and SLC e+e- collider

Dsin2qw = 0.00016 (PDG2004)

from Z pole measurements

slide35

Status in 1999

sin2qw

~5%

Q (GeV)

slide36

SLAC Experiment E158

Detector

e

50 GeV

Liquid

Hydrogen

e-e-

scattering

s - s

APV =

s + s

Without electroweak radiative corrections,

2

m E GF

16 sin q

1

(

)

-

sin2qw

APV

=

2

4

2p 

(3 + cos q)2

In practice:

APV

~

1.5 x 10-7

slide37

E158 Collaboration

  • SLAC
  • Smith College
  • Syracuse
  • UMass
  • Virginia
  • UC Berkeley
  • Caltech
  • Jefferson Lab
  • Princeton
  • Saclay

7 Ph.D. Students

60 physicists

Sept 97: EPAC approval

1998-99: Design and Beam Tests

2000: Funding and construction

2001: Engineering run

2002: Physics Runs 1 (Spring), 2 (Fall)

2003: Physics Run 3 (Summer)

slide38

Scattering Processes

e-

e-

e-

e-

g

Z

e-

e-

e-

e-

Parity-conserving

Parity-violating

e-

e-

g

g

Background

p

p

slide39

Challenges

I. Statistics

II. Beam monitoring & resolution

 jitter vs. statistics

III. Beam systematics

 false asymmetries

IV. Backgrounds

slide40

target

Detector

cart

Concrete shielding

Spectrometer magnets

Setup in End Station A

slide43

STATISTICS

# electrons per pulse 107

Rep rate (120 Hz) 109

Seconds/day 1014

100 days 1016

DA ~ 10-8

slide45

toroid 30 ppm

energy 1 MeV

BPM 2 microns

Agreement (MeV)

BPM24 X (MeV)

Resolution 1.05 MeV

BPM12 X (MeV)

Beam Monitoring Correlations

slide47

III. Beam Asymmetries

Polarized

source

slide48

SLOW REVERSALS

* Halfwaveplate @ source

~few hours

* 48 vs. 45 GeV energy

~ few days

slide51

IV. BACKGROUNDS

* electron-proton elastic scattering

* pion production

* radiative inelastic electron-proton scattering

W2 > 3 GeV2

* 2 photon events with transverse polarization

*

*

*

slide54

E158 Physics Runs

Run 1: Spring 2002

Run 2: Fall 2002

Run 3: Summer 2003

slide55

RUNI

FINAL RESULT

At Q2 = 0.027 (GeV/c)2….

APV= -175  30 (stat)  20 (syst) ppb

MS

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

w

MS

Theory:

sin2  = 0.2311 ± 0.00016

w

slide57

All E158 Data

PRELIMINARY

At Q2 = 0.027 (GeV/c)2….

APV= -128  14 (stat)  12 (syst) ppb

MS

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

w

MS

Theory:

sin2  = 0.2311 ± 0.00016

w

slide58

Status in 1999

sin2qw

Q (GeV)

slide60

Cesium Atomic Parity Violation Result vs. Time

(Colorado measurement)

sin2qw

0.240

Standard Model

0.238

Kuchiev

Flambaum

0.236

Kozlov

Porsev

Tupitsyn

Johnson

Bednyhakov

Soff

0.234

Derevianko

Bennett

Wieman

Dzuba

Flambaum

0.232

Wieman et al.

0.230

2000

1999

1998

2001

2002

2003

1997

Modifications in the theoretical corrections to the

atomic structure

slide61

7s

Status Today

sin2qw

slide62

E158 Beyond Standard Model Implications...

(95% confidence level)

* Limit on LLL ~ 10 TeV

* Limit on SO(10) Z’ ~ 900 GeV

  • * Limit on lepton flavor

violating coupling ~ 0.01GF

slide63

FUTURE:

Low energy polarized electron

scattering

* Jefferson Lab

* SLAC (could do it, but won’t)

slide64

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, 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,

01000 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

slide65

Jefferson Lab Qweak Experiment

Elastic electron-proton scattering experiment

* 180 mAmp current

* 1 GeV beam

* 2200 hours of data

slide66

Submitted: June 2003

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...

slide67

Projected experimental uncertainty from

DIS-parity proposal @ SLAC

and Qweak experiment @ Jefferson Lab

slide68

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

slide69

SUMMARY

* Performed a first measurement

of parity violation in e-e- scattering

Final result publication in ~ 1/2 year

* Future parity experiments active

* Complementary to collider experiments

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