Download First Result from the SLAC E158

Electrons and Mirror
Symmetry
Krishna Kumar
University of Massachusetts, Amherst
Department of Physics
September 11, 2006
Electrons and Mirror Symmetry
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Outline
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What is the science?
Why do we do it?
Where do we do the work?
Some details
I have stolen numerous cartoons from the
following website at
Lawrence Berkeley Laboratory:
www.particleadventure.org
September 11, 2006
Electrons and Mirror Symmetry
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Fundamental Questions
What are we made of? What
holds us together?
Are there other forces?
Do quarks and leptons have structure?
Visible matter
Is there a single superforce? made up of
How does one build nucleons and nuclei
firstfrom
quarks and gluons?
generation
…
quarks and
…
leptons
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Electrons and Mirror Symmetry
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Time and Length Scales
attometers
femtometers
femtometers
picometers
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Electrons and Mirror Symmetry
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Femtoscience
Resolving objects at 10-15 m
(femtometer) requires special
instrumentation
At nuclear scales, particles
behave mostly like waves
Wave mechanics or
quantum mechanics
How to produce femtometer
wavelengths in the laboratory?
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Electrons and Mirror Symmetry
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Particle Accelerator
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Electrons and Mirror Symmetry
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Accelerator Structure
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Electrons and Mirror Symmetry
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Forces and Carriers
Radioactivity
Gravity and Electromagnetic
Nuclear
binding
Strong and Weak
10-15 meter
Infinite range
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Picture of an Interaction
e-
Electromagnetic
interaction
characterized by
electric charge
Photon is the force carrier
e-
60Ni
60Co
Weak
interaction
characterized by
weak charge
60Co
60Ni
L
W boson is the force carrier
R
Radioactive decay of
60Co Nucleus
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Electrons and Mirror Symmetry
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The Short Range Weak Force
W+, W-, Z0
Massive Gauge Bosons

Massless Gauge Boson
The Unified Electroweak Force
How can a short range and long range force be unified?
1 q
V
40 r
e
 mc r
September 11, 2006
e
[-0.45 (attometer)-1  r]
(massive force carriers)
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Mirror (A)symmetry
parity transformation
x,y,z x,y,z
p  p, L  L, s  s
matter particles
possess spin:

h  s  p  1
handedness or
helicity
h  h
60Ni
60Co

right-handed
Weak decay of
60Co Nucleus
September 11, 2006
left-handed
anti-neutrino
Parity
Nonconservation
anti-neutrino
Electrons and Mirror Symmetry
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Neutral Weak Force
between Electrons
e-
e-
weak
interaction
characterized by
weak charge
Z0
Z boson is the force carrier
1. Scatter two electrons at very high energy
2. Measure probability of scattering
3. Look for a difference in the mirror process
Problem: Only one Z exchange for every 10 million photon exchanges
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Electrons and Mirror Symmetry
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Weak Force Asymmetry
in Electron-Electron Scattering
•One of the incident beams longitudinally polarized
•Change sign of longitudinal polarization
•Measure fractional rate difference
Parity Violating Asymmetry:
Imagine The
measuring
length
of Central
Park in NYC with 2
effect isthe
about
150 parts
per billion!
different meter scales: answer is expected to differ by 1 mm!
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Electrons and Mirror Symmetry
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E158 at SLAC
Parity-Violating Left-Right Asymmetry In Fixed Target Møller Scattering
At the Stanford Linear Accelerator Center
Goal: error small enough to test fundamental theory
E158 Collaboration
•Berkeley
•Caltech
•Jefferson Lab
•Princeton
•Saclay
•SLAC
•Smith
•Syracuse
•UMass
•Virginia
8 Ph.D. Students
60 physicists
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E158 Chronology
Sep 97: EPAC approval
Mar 98: First Laboratory Review
1999: Design and Beam tests
2000: Funding and construction
2001: Engineering run
2002-2003: Physics
2004: First PRL
2005-2006: Final publications
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Experimental Setup
•Beam power is 0.5 MegaWatts
•Left- and Right-handed beams matched to 10-8 m
•1.5 m long liquid hydrogen target
•Massive magnetic spectrometer
•Sensitive, radiation hard particle detectors
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E158 Plan View in ESA
target
Concrete shielding
Detector
cart
Spectrometer magnets
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Liquid Hydrogen Target
Simplest source of target
electrons is liquid hydrogen
Z/A = 1
No nuclei or
neutrons
Refrigeration Capacity 1 kW
Operating Temperature 20 K
Length
1.5 m
Flow Rate
5 m/s
Vertical Motion
6 inches
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Particle Magnetic
Spectrometer
Dipole
Quadrupole
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E158 Spectrometer
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Particle Detector
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Final Analysis of All 3 Runs
APV = (-131 ± 14 ± 10) x 10-9
APV Sign Flips
g-2 spin precession
45 GeV: 14.0 revs
48 GeV: 14.5 revs
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Implications
Parity Violation observed in Møller scattering:
First measurement of the weak force between 2 electrons
Input to theories on physics of the early universe
Part per billion systematic control:
Several new experiments spawned studying a variety of physics topics
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Publication
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