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

Outline Introduction Existing measurements A new search for neutron EDM Summary

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

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 violations in nuclear systems More CP violations in experiments: B meson decays, SLAC and KEK Future experiments studying CP in neutrino sector CP=-1 CP=+1 0.2%

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

Strong CP problem The θ term in QCD lagrangian If θ≠0, violates P & T Neutron EDM ~ O( θ) e.cm [1,2,3] –Current nEDM upper limit 2.9× e.cm [4] [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, ( 2006) One proposed remedy, Peccei-Quinn symmetry, predicts axions. However, axions have not been observed.

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)

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 +- s = 1/2dE Quark EDM appears only at the three-loop level

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

B-B ASYMMETRY IN THE UNIVERSE Before Phase Transition After Phase Transition Today N 0 10  BB

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

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)

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

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 2  rotation.)

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

Neutron electric dipole moment nEDM more sensitive to θ QCD than to δ CKM [1] [1] Jiang Liu, C. Q. Geng, and John N. Ngl. Phys. Rev. Lett., 63:589, [2] E. M. Purcell and N. F. Ramsey. Phys. Rev., 78:807, [3] C.A. Baker et al. Phys. Rev. Lett., 97:131801, [4] B. McKellar et al., Phys. Lett. B, 197:556, Current upper limit (ILL) [3] New Physics!!! New sources of CP violation? [4] Projected result in 2014 (n beam) NameVelocity thermal~2200 m/s Cold m/s Very cold m/s Ultra cold<7.6 m/s 1950, Smith, Purcell and Ramsey [2]

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

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

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

Production of Ultracold Polarized Neutrons Closed neutron trap filled with ultra-pure superfluid 4 He 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)

Superthermal process to produce UCNs 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, [2] R. Golub, D. J. Richardson, and S. K. Lamoreaux. Ultra-Cold Neutrons. Adam Hilger, Bristol, Upscattering process suppressed by a factor Superfluid 4 He elementary excitation dispersion curve

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

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 N UCN ~1.2x10 6 for an 8 liter volume

Measurement of the UCN Precession Frequency UCN precession frequency beat against the 3 He 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

Spin StateCross Section (barns) (v=2200 m/sec) Cross Section (barns) (v=5 m/sec) J=0 J=1

d n dipole moment d 3 =0 Look for a difference in precession frequency  n -  3   d dependent on E and corrected for temporal changes in  EBEB s = 1/2 n 3 He 3 He MAGNETOMETRY L.I. Schiff, Phys. Rev. 132, 2194 (1963)

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

Systematic Error effect (UCN) B field fluctuation (Comagnetometer) Accuracy of flipping the E field Gravitational offset [1] Geometric phase effect [2] …… Error analysis 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, [2] J. M. Pendlebury et al. Phys. Rev. A, 70(3):032102, Sep E 0 =50 kV/cm T m =500 s N=10 6 n/cycle m=6000 cycles

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

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

SNS Target Hall SNS IDT 1B - Disordered Mat’ls Commission Backscattering Spectrometer Commission High Pressure Diffractometer Commission A - Magnetism Reflectometer Commission B - Liquids Reflectometer Commission Cold Neutron Chopper Spectrometer Commission Wide Angle Chopper Spectrometer Commission High Resolution Chopper Spectrometer Commission Fundamental Physics Beamline Commission A - Powder Diffractometer Commission Single Crystal Diffractometer Commission Engineering Diffractometer IDT CFI Funded Commission SANS Commission B - Hybrid Spectrometer Commission – Spin Echo 9 – VISION

Summary CD-2 review 08 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 CD-1 Feb 2007 PRL 97, Projected result ~ 2014

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