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A New Search on the Neutron Electric Dipole Moment (nEDM)

A New Search on the Neutron Electric Dipole Moment (nEDM)

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A New Search on the Neutron Electric Dipole Moment (nEDM)

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  1. A New Search on the Neutron Electric Dipole Moment (nEDM) 2008 Fall Chinese Physical Society Meeting September 20, 2008 Jinan, China Haiyan Gao (高海燕) Duke University

  2. Outline • Introduction • Existing measurements • A new search for neutron EDM • Summary

  3. Introduction [1] T. D. Lee and C. N. Yang. Physical Review, 104:254, 1956. [2] C. S. Wu et al. Physical Review, 105:1413, 1957. [3] R. L. Garwin et al. Physical Review, 105:1415, 1957. [4] J. I. Friedman and V. L. Telegdi. Physical Review, 105:1681, 1957. • P – Parity (Space Inversion) • T – Time Reversal • C – Charge Conjugation Particle Anti-particle • Parity violation • Theory - 1956, Lee & Yang[1] • Experiments in 1957 • Wu et al. 60Co β-decay[2] • Garwin et al. πμe[3] • Friedman & Telegdi et al.[4]

  4. CP Violation in weak interactions In 1964, Christenson, Cronin, Fitch and Turlay discovered at BNL that the long-lived neutral K meson with CP=-1 could decay occasionally to with CP=+1 about once every 500 decays CP=-1 0.2% CP=+1 • CP violations in nuclear systems • More CP violations in experiments: • B meson decays, SLAC and KEK • Future experiments studying CP in neutrino sector

  5. CP violation in Standard Model • The CKM matrix: the complex phase of CKM matrix leads to CP violation   Mass eigenstates Weak eigenstates For n generations: n(n-1)/2 angles 3 (n-1)(n-2)/2 phases 1 • To lowest order, CP violation occurs only in flavor-changing processes.

  6. Strong CP problem [1] Maxim Pospelov and Adam Ritz. Phys. Rev. Lett., 83, 2526 (1999) [2] V. Baluni. Phys. Rev. D 19, 2227 (1979) [3] R. J. Crewther et al. Phys. Lett. B 88, 123 (1979) [4] C.A. Baker et al. Phys. Rev. Lett. 97, 131801 ( 2006) One proposed remedy, Peccei-Quinn symmetry, predicts axions. However, axions have not been observed. • The θ term in QCD lagrangian • If θ≠0, violates P & T • Neutron EDM ~ O(10-16 θ) e.cm[1,2,3] • Current nEDM upper limit 2.9×10-26 e.cm[4]

  7. CPT Invariance CPT is a good symmetry in a local field theory which is Lorentz invariant and has a hermitian Lagrangian • CP violation thus implies time-reversal symmetry T violation • Direct search for T violation is important! • CPLEAR: semi-leptonic decay of neutral kaons • KTev experiment • Neutron electric dipole moment (nEDM)

  8. Neutron Electric Dipole Moment (EDM) - + • If neutron possesses EDM, in an electric field, Hamiltonian • changes sign under T (P) symmetry operation • is more sensitive to than it is to d•E s = 1/2 Quark EDM appears only at the three-loop level

  9. Predictions for Neutron EDM • SM: • Renormalization of QCD vacuum parameter arising from CP violation in weak interaction (CKM) • Strong CP:  (m)2ln (m)2 ,…… • Left-right symmetric gauge models: • Non-minimal Higgs models: • CP odd gluonic operators inducing: • Supersymmetry (SUSY) models

  10. gBB B-B ASYMMETRY IN THE UNIVERSE After Phase Transition Today Before Phase Transition 1010 N 0 gBB gBB

  11. CP Violation and Cosmology • Baryon asymmetry of the universe (BAU) • To explain BAU, substantial New Physics in the CP violating sector is required • Neutron EDM may play an important role in quantifying New Physics • New source of CP beyond SM may have significant impact on our understanding of baryongenesis Seminar paper by A. Sakharov (1967) on calculating BAU

  12. Existing Measurements of Experimental techniques: • Neutron scattering • Interference between neutron-nucleus and neutron-electron • Magnetic resonance technique • thermal or cold neutron beams • bottled ultra-cold neutrons (UCN) Ref: R. Golub and S. K. Lamoreaux, Phys. Report 237, 1-62 (1994)

  13. Magnetic Resonance Technique Look for a precession frequency wd B E s = 1/2 dipole moment dn - + • A strong static electric field applied parallel • (anti-parallel) to the magnetic field causes a shift in • the Larmor freq.

  14. Frequency Measurement • Neutron spin aligned perpendicular to a static magnetic field • The frequency shifts as the direction of E is reversed is from parallel to B to antiparallel to B: (*It takes two months to make a 2p rotation.)

  15. First nEDM experiment at ORNL J.H.Smith, E.M.Purcell, and N.F.Ramsey, Phys. Rev. 108, 120 (1957) Magnetic field Electric field Permanent magnet Neutron spin f Electrodes w Polarizer Analyzer Neutron beam Detector

  16. Neutron electric dipole moment 1950, Smith, Purcelland Ramsey[2] (n beam) Current upperlimit (ILL)[3] New Physics!!!New sources of CP violation? [4] [1] Jiang Liu, C. Q. Geng, and John N. Ngl. Phys. Rev. Lett., 63:589, 1989. [2] E. M. Purcell and N. F. Ramsey. Phys. Rev., 78:807, 1950. [3] C.A. Baker et al. Phys. Rev. Lett., 97:131801, 2006. [4] B. McKellar et al., Phys. Lett. B, 197:556, 1987. Projected result in 2014 nEDM more sensitive to θQCD than to δCKM[1]

  17. Experimental limits on the particle EDM Current best limit on neutron EDM is from ILL reactor at Grenoble Phys. Rev. Lett. 97, 131801 (2006) nEDM < ecm [90 % C.L.]

  18. A new nEDM Experiment(Spokespersons: S. K. Lamoreaux, M. Cooper) Figure of Merit for EDM Experiments ~ E ® 5E t® 5t N ® 250 N ® 175 Compared to ILL experiment

  19. Overview of the Experiment • A three-component fluid of ultra cold neutrons,3He atoms in a bath of superfluid 4He at ~400 mK • Neutron and 3He magnetic dipoles precess in a plane perpendicular to the external magnetic field • Precision measurement of the freq.difference in the 3He and neutron precession frequency modified when strong E field is turned on (or reversed) --> neutron EDM

  20. Production of Ultracold Polarized Neutrons • Closed neutron trap filled with ultra-pure superfluid 4He cooled to ~ 350 mK • Placed in a beam of cold neutron (E=1 meV), polarized (~100%) using two total reflecting magnetic supermirror surfaces • Neutrons interacting with the superfluid are downscattered to with a recoil phonon in the superfluid carrying away the missing energy and momentum (Golub, Pendelbury, 1975) • Technique has been demonstrated at a number of laboratories (France, Japan, US)

  21. Superthermal process to produce UCNs • Superfluid 4He elementary excitation dispersion curve Upscattering process suppressed by a factor • Cold neutron polarized by “supermirror”[1] • “Superthermal” process • Neutrons with energy ~0.001eV (λ=8.9Å, v=446m/s) can scatter into UCNs (v<7 m/s) by emitting a phonon[2]. [1] The nEDM Collaboration. Conceptual Design Report for the nEDM Project, 2007. [2] R. Golub, D. J. Richardson, and S. K. Lamoreaux. Ultra-Cold Neutrons. Adam Hilger, Bristol, 1991.

  22. Measurement Principle - UCN with Polarized 3He in superfluid 4He • Experimental cellRectangular, made of acrylic coated with d-TPB (Deuterated tetraphenyl butadiene) • Three-component fluid y Polarized cold neutron beam(E = 1 meV, v = 440 m/s, l = 8.9 Å) B E x UCN, 3He, 4He z B~10mGE~50kV/cm Superfluid 4He at~300-500 mK Superthermal process to produce UCN. E<0.13µeV, v<7 m/s Polarized 3He

  23. How to measure the UCN Precession Frequency? In the trap volume: atoms per liter of cell volume  ? • Expect a production of ~ 0.3 UCN/cc/s • With a 500 second lifetime, UCN~150/cc and NUCN~1.2x106 for an 8 liter volume

  24. Measurement of the UCN Precession Frequency • UCN precession frequency beat against the 3He precession frequency • Spin dependence of the nuclear interaction cross-section: • Scintillation light from nuclear reaction products (and beta decay products) (80 nm) can be wave-length shifted (440 nm) and detected

  25. B E B E - + 3He MAGNETOMETRY 3He n s = 1/2 dn dipole moment d3 =0 Look for a difference in precession frequency wn - w3±wd dependent on E and corrected for temporal changes in w3 L.I. Schiff, Phys. Rev. 132, 2194 (1963)

  26. UCN Precession Frequency The time dependent, velocity independent loss rate SQUID will be used for monitoring the 3He spin precession Frequency, 3He also a co-magnetometer

  27. Error analysis Systematic Error • effect (UCN) • B field fluctuation (Comagnetometer) • Accuracy of flipping the E field • Gravitational offset[1] • Geometric phase effect[2] • …… E0=50 kV/cmTm=500 sN=106 n/cyclem=6000 cycles Statistical Error • nEDM uncertainty • Uncertainty principle • Higher UCN density  higher sensitivity • Measure nEDM or lower the current upper limit by ~2 orders of magnitude [1] I. B. Khriplovich and S. K. Lamoreaux. CP Violation Without Strangeness. Springer, page 93, 1997. [2] J. M. Pendlebury et al. Phys. Rev. A, 70(3):032102, Sep 2004.

  28. EDM Experiment SchematicVertical Section View 3He Polarized Source Dilution Refrigerator (DR: 1 of 2) Upper Cryostat Services Port Central LHe Volume (300mK, ~1000 Liters) Upper Cryostat DR LHe Volume 450 Liters Re-entrant Insert for Neutron Guide 5.6m 3He Injection Volume Lower Cryostat 4 Layer μ-metal Shield

  29. Spallation Neutron Source (SNS) at ORNL 1 GeV, 1.4 mA Proton Linac January 25, 2005 • SNS completed: 2006 • FNPB Beam line completed: 2007 • Full design flux: 2008 • SNS Total Project Cost: 1.411B$

  30. SNS Target Hall 7 - Engineering Diffractometer IDT CFI Funded Commission 2008 11A - Powder Diffractometer Commission 2007 9 – VISION 6 - SANS Commission 2007 12 - Single Crystal Diffractometer Commission 2009 5 - Cold Neutron Chopper Spectrometer Commission 2007 13 - Fundamental Physics Beamline Commission 2007 4B - Liquids Reflectometer Commission 2006 14B - Hybrid Spectrometer Commission 2011 4A - Magnetism Reflectometer Commission 2006 15 – Spin Echo 3 - High Pressure Diffractometer Commission 2008 17 - High Resolution Chopper Spectrometer Commission 2008 18 - Wide Angle Chopper Spectrometer Commission 2007 1B - Disordered Mat’ls Commission 2010 2 - Backscattering Spectrometer Commission 2006 SNS IDT

  31. Summary CD-2 review 08 PRL 97, 131801 Projected result ~ 2014 CD-1 Feb 2007 This work is supported by the US Department of Energy DE-FG02-03ER41231 and School of Arts and Science at Duke Thanks to Qiang Ye for the preparation of a few nice slides

  32. OCPA6 Conference August 3-7, 2009 in Lanzhou, China. Hosts: IMP and Lanzhou Univ. Conference web page: http://snst.lzu.edu.cn/web1/index.html Please visit OCPA web page: www.ocpaweb.org We invite you to become a member! Achievement in Asia Award (Robert T. Poe Prize) http://www.ocpaweb.org/new/aaaaward/aaaaward.html