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Transcript
Electrons and Mirror Symmetry Krishna Kumar University of Massachusetts, Amherst Department of Physics September 11, 2006 Electrons and Mirror Symmetry 1 Outline • • • • 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 2 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 September 11, 2006 Electrons and Mirror Symmetry 3 Time and Length Scales attometers femtometers femtometers picometers September 11, 2006 Electrons and Mirror Symmetry 4 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? September 11, 2006 Electrons and Mirror Symmetry 5 Particle Accelerator September 11, 2006 Electrons and Mirror Symmetry 6 Accelerator Structure September 11, 2006 Electrons and Mirror Symmetry 7 Forces and Carriers Radioactivity Gravity and Electromagnetic Nuclear binding Strong and Weak 10-15 meter Infinite range September 11, 2006 Electrons and Mirror Symmetry 8 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 September 11, 2006 Electrons and Mirror Symmetry 9 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 40 r e mc r September 11, 2006 e [-0.45 (attometer)-1 r] (massive force carriers) Electrons and Mirror Symmetry 10 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 11 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 September 11, 2006 Electrons and Mirror Symmetry 12 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! September 11, 2006 Electrons and Mirror Symmetry 13 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 September 11, 2006 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 Electrons and Mirror Symmetry 14 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 September 11, 2006 Electrons and Mirror Symmetry 15 E158 Plan View in ESA target Concrete shielding Detector cart Spectrometer magnets September 11, 2006 Electrons and Mirror Symmetry 16 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 September 11, 2006 Electrons and Mirror Symmetry 17 Particle Magnetic Spectrometer Dipole Quadrupole September 11, 2006 Electrons and Mirror Symmetry 18 E158 Spectrometer September 11, 2006 Electrons and Mirror Symmetry 19 Particle Detector September 11, 2006 Electrons and Mirror Symmetry 20 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 September 11, 2006 Electrons and Mirror Symmetry 21 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 September 11, 2006 Electrons and Mirror Symmetry 22 Publication September 11, 2006 Electrons and Mirror Symmetry 23