Fundamental Physics With Cold and Ultra-cold Neutrons

1. FundamentalPhysicsWithColdand Ultra-cold Neutrons Albert Young North Carolina State University

2. Fundamental neutron physics [Fr. Physique Fondamental, c. 1975, first used to describe a variety of interdisciplinary research activities carried out at the high flux reactor of the Institut Laue Langevin, Grenoble] Measurements, utilizing low energy neutrons, of… Why is the universe “Left-Handed?” How much matter is in the universe? How much is “Dark Matter” Why does the universe have matter and no anti-matter? What is the origin of the Time Reversal Asymmetry? Where is the “Physics Beyond the Standard Model?” Decay of the neutron, the neutron’s static moments, fundamental physical constants, as well as tests of basic theories (such as quantum mechanics), etc…

3. A number of breakthroughs in the past five years (both CN and UCN regimes) • Opportunities for new experiments… • Very strong involvement by university groups and labs in the U.S. and abroad Some examples where new opportunities are being pursued: Hadronic Weak Interactions Neutron Beta-Decay Neutron EDM

4. Some Examples I Won’t Have the Opportunity to Discuss: • N-N Oscillations, or searches for B-L violating interactions: see Frank Plasil’s talk in the working group session • Neutron interferometry and tests of quantum mechanics • Low energy neutron studies of reactions relevant for nuclear astrophysics the list goes on…

5. The Hadronic Weak Interaction (treated in depth in David Bowman’s talk this afternoon) Example: p + n → p + n Currently parameterized in terms of a meson exchange model: Theory suggests a range of acceptible values for couplings Effects are small!

6. An Area of Vigorous Activity H12.4f H0-1.4h0 To resolve experimentally correct value for H1, new measurements required: (1) simple systems with relatively “clean” theoretical interpretation (2) excellent control of systematic errors

7. Cold Neutron Beam Experiments(neutrons with energies of a few meV) • n,p system: n + p→ d +  • n,4He system: Rotation of the transverse polarization of neutron after transmission through liquid helium (spin rotation)

8. n + p→ d +  Projected systematic errors in A 110-9 level, statistical errors  510-9 • Pulsed neutron beams will be used to identify velocity dependent systematic errors • 3He polarizers provide additional control of polarization systematic errors

9. Detector array used in recent test of npdg experiment

10. Projected Limits from Cold Neutron Beams Measurements Allowed DDH

11. Neutron Beta-Decay • Measurements provide fundamental data on the electroweak interaction, for example the CKM matrix element Vud and the weak axial form factor of the nucleon. • Lifetime measurements provide essential input data to high precision models of big bang nucleosynthesis. • Extreme simplicity of this system permits a high precisionconfrontation between the electroweak standard model and experiment (we can probe for new physics). • Semi-leptonic decay • Single nucleon system • Low Z ensures radiative corrections small • Spin ½+ ½+decay restricts the number of contributing form factors, ensures angular correlations have simple form Simplicity

12. b-decay of quarks (no strong interaction) Electroweak Standard Model Quark current Lepton current Semi-leptonic decayE. Fermi, Z. Phys 88, 161 (1934) CKM matrix

13. Breakthroughs • Most precise lifetime measurements have been performed with ultra-cold neutrons for past 10 years (neutrons with energies below about 350 neV, which can be stored in material and magnetic bottles) • Angular correlations measurements have been performed using cold neutron beams: dominant systematic errors have involved neutron polarization& backgrounds. Advent of superfluid He superthermal UCN source provides higher UCN densities and, when coupled to a magnetic trap, reduce systematic corrections to lifetime by 1 to 2 orders of magnitude 3He polarizers/analyzers can now provide absolute polarimetry at the 0.1 percent level for CN experiments Development of SD2 superthermal source provides copius extracted UCNs for angular correlations measurements

14. World record densities achieved this June A Superthermal Solid Deuterium UCN Source at LANSCE Compare to previous record of 41 UCN/cm3 (at ILL). Note: over two orders of magnitude improvement may ultimately be possible!

15. A great many extenstions to the standard model, including supersymmetry, left-right symmetric models, expanded Higgs sectors, etc…introduce unconstrained T non-invariant phases: experiments are required to determine at what level these phases actually appear. Cosmological models of the matter-antimatter asymmetry require T non-invariance to be present in the early universe at some level Time Reversal Non-invariance (see Norval Fortson’s talk later today) For neutrons T non-invariance in beta-decay Neutron static electric dipole moment (EDM) (briefly)

16. Limits from EDM have provided critical guidance for theory Limit sought in LANSCE EDM expt (roughly)

17. New opportunity to measure the neutron EDM using a superthermal He UCN source (see Martin Cooper’s talk in the working group session) Measurement performed in liquid He (similar to n lifetime), with the liquid He serving a variety of functions: • Source of UCNs • Insulator for required large electric fields • Detector for UCN spin state Measure torque that an electric field exerts on the precessing neutron spin Improvement factors Density: x  8 Electric Field: x  5 Coherence time: x  5 x 200

19. Summary • There are numerous, ongoing projects to probe fundamental physics with neutrons which show steady progress…the physics motivation is compelling • New opportunities generated for CN beam research: • New opportunities to utilize UCNs in the US: • Involves a close collaboration between many strong university groups and US national laboratories…we’re excited to seize these opportunities! 3He polarizers Pulsed neutron beams Hadronic weak interactions Neutron beta-decay Neutron beta-decay T non-invariance (EDMs) Superthermal He and SD2 sources