Ultra-Cold Neutrons: From neV to TeV

1. Ultra-Cold Neutrons: From neV to TeV • What are UCN? (how cold?) • How to produce UCN? • Conventional reactor sources • New “superthermal” sources • Experiments with UCN • Neutron beta-decay (tn, n decay asymmetry) • Neutron Electric Dipole Moment Fermilab 7/13/06

3. The Caltech UCN group Nick Hutzler Gary Cheng Jenny Hsiao Riccardo Schmid Kevin Hickerson Junhua Yuan Brad Plaster Bob Carr BF

4. Ultra-Cold Neutrons (UCN) (Fermi/Zeldovich) • What are UCN ? • Very slow neutrons (v < 8 m/s ’l > 500 Å ) that cannot penetrate into certain materials Neutrons can be trapped in bottles or by magnetic field

5. Material Bottles Neutron “repulsion” comes from coherent scattering from nuclei in solids. Recall (for short-range potential): At low energies (kr0<<1; eg s-wave) elastic scattering determined solely by scattering length a For k’0 selas = 4pa2

6. Fermi Pseudo-potential EUCN The coherent nuclear potential can lead to repulsive pseudopotential (Fermi potential) for a > 0 For EUCN < VF, UCN are trapped Attractive potential can also lead to neutron absorption but often Lmfp >> ln (~10-5 probability per bounce)

7. Typical Fermi Potentials neutron velocity vn ~ 8 m/s

8. Magnetic Bottles also possible • B-field and neutron magnet moment • produces a potential • Thus can produce a 3D potential well • at a field minimum (traps one spin state) Ioffe Trap For vn<8 m/s need B<6T

9. UCN Properties g 3m UCN

10. How to make UCN? • Conventional Approach: • Start with neutrons from nuclear • reactor core • Use collisions with nuclei to slow down neutrons Some of neutron’s energy lost to nuclear recoil in each collision • Gives a Maxwell-Boltzmann Distribution

11. But… • Only small fraction of neutron distribution is UCN

12. Can improve some via gravity and moving turbines • Record density at • Institut Laue-Langevin • (ILL) reactor in • Grenoble (1971) Best vacuum on earth ~104 atoms/cm3 Can we make more?

13. Higher Density UCN Sources • Use non-equilibrium system • (aka Superthermal) • Superfluid 4He • (T<1K) (neutron) 11K (9Å) incident n produces phonon & becomes UCN NIST tn Experiment Very few 11K phonons if T<1K \ minimal upscattering

14. Solid deuterium (SD2)Gollub & Boning(83) • Small absorption probability • Faster UCN production • Small Upscattering if T < 6K Cold Neutron UCN Phonon

15. Proton Linac (½ mile long) UCN Source (Los Alamos Neutron Science CEnter) LANSCE

16. Schematic of prototype SD2 source Flapper valve 58Ni coated stainless guide Liquid N2 Be reflector LHe Solid D2 77 K polyethylene UCN Detector Tungsten Target Caltech, LANL, NCState, VaTech, Princeton, Russia, France, Japan Collaboration

17. First UCN detection Total flight path ~ 2 m 50 ml SD2 0 ml SD2 Proton pulse at t = 0

18. New World Record UCN Density Previous record for bottled UCN = 41 UCN/cm3 (at ILL) Measurements of Ultra Cold Neutron Lifetimes in Solid Deuterium [PRL 89,272501 (2002)] Demonstration of a solid deuterium source of ultra-cold neutrons [Phys. Lett. B 593, 55 (2004)]

19. Physics with higher density UCN Sources • Macroscopic Quantum States • Neutron decay (lifetime & correlations) • Solid Deuterium Source • Neutron Electric Dipole Moment (EDM) • Superfluid He Source Also possible: Characterize structure of large (~ 500Å) systems (Polymers, Biological molecules)

20. mgz V z Macroscopic Quantum States in a Gravity Field 1-d Schrödinger potential problem neutron in ground state “bounces” ~ 15 mm high

21. Neutron Energy Levels in Gravity Height Selects Vertical Velocity UCN @ ILL

22. Classical expectation Nesvizhevsky, et al, Nature 2002 May allow improved tests of Gravity at short distances (need more UCN!)

23. or in quark picture… u p d u u d e- d W- ne n Neutron Beta Decay

24. Precision neutron decay measurements • Neutron lifetime essential in Big-Bang • Nucleosynthesis Calculations • Can provide most precise measurement of Vud • < 0.3% measurements can be sensitive to new physics (from loops in electroweak field theory) Mass eigenstates Weak eigenstates æ ö æ ö æ ö d V V V d ç ÷ ç ÷ ç ÷ w ud us ub Single complex phase is possible (gives “CP” Violation -more later) = s V V V s ç ÷ ç ÷ ç ÷ w cd cs cb ç ÷ ç ÷ ç ÷ b V V V b è ø è ø è ø w td ts tb a.k.a. Radiative Corrections

25. Particle Data Group Primordial He Abundance

26. Neutron Lifetime versus Year Data points used by Particle Data Group (PDG) 2004 for averaging Serebrov et al., Phys. Lett. B 605, 72 (2005) (878.5 ± 0.7 ± 0.3) seconds

27. WMAP Big-Bang Nucleosynthesis Constraints New neutron lifetime New Lifetime Experiment using our Solid Deuterium Source is under development

28. Neutron Decay in the Standard Model GF = Fermi Constant (known from m decay) Vud = up-down quark weak coupling (more later) GA = Axial vector weak coupling constant GV = Vector weak coupling constant f = phase space integral DR = Electroweak radiative correction Note: Z0 Boson (M=91 GeV) gives 2% correction! GA/GV from parity violating decay asymmetry in n decay

29. Sensitivity to New Physics? m- nm u GFVud d GF e- e- W- W- m- d ~ u ne ne ne ne ~ nm c0 c0 ~ ~ ~ ~ m u n d e- e- W- W- Kurylov&Ramsey-Musolf Phys. Rev. Lett. 88, 071804 (2002) • Vud in Standard Model • (from m vs. b-decay) • Supersymmetric particles produce loop corrections

30. Asymmetry Measurement with UCN e- q n UCNA

31. Asymmetry measurement with UCN • All previous measurements of GA/GV used cold neutrons from a reactor • Gives continuous, large, background from reactor and polarizer (magnetized solid) • Gives > 1% systematic error due to neutron polarization (95-98%) • New experiment uses pulsed UCN source • Neutron decays counted with the source “off” • Can produce high neutron polarization (~99.9%) using 6T magnetic field

32. Experiment Layout Neutron Polarizing Magnets UCN Guides UCN Source Superconducting Spectrometer Electron Detectors

33. UCNA experiment Experiment commissioning underway Initial goal is 0.2% measurement of A-correlation (present measurement ~ 1%) UCNA Liquid N2 Be reflector LHe Solid D2 77 K poly Tungsten Target

34. Most Recent Collaborator

35. + - Neutron Electric Dipole Moment (EDM) • Why Look for EDMs? • Existence of EDM implies violation of Time Reversal Invariance Cartoon + - • Time Reversal Violation seen in K0–K0 system • May also be seen in early Universe • - Matter-Antimatter asymmetry • but the Standard Model effect is too small !

36. C P T m - + - d - + - E - - + B - + - J + + - Quantum Picture – Discrete Symmetries Non-Relativistic Hamiltonian 123 123 C-even P-even T-even C-even P-odd T-odd

37. Possible Mechanisms for Matter/Antimatter Asymmetry in the Universe • Sakharov Criteria • Baryon Number Violation • Departure from Thermal Equilibrium • CP & C violation • Standard Model CP violation is insufficient • Must search for new sources of CP • B-factories, Neutrinos, EDMs

38. Origin of EDMs • Standard Model EDMs are due to observed CP violation in the K0/B0-system but… • e- and quark EDM’s are zero at first order • Need at least two “loops” to get EDM’s • Thus EDM’s are VERY small in standard model Neutron EDM in Standard model is ~ 10-32 e-cm (=10-19 e-fm) Electron EDM in Standard Model is < 10-40 e-cm

39. Physics Beyond the Standard Model • New physics (e.g. SuperSymmety = SUSY) has additional CP violating phases in added couplings • New phases: (fCP) should be ~ 1 (why not?) • Contributions to EDMs depends on masses of new particles • In Minimal Supersymmetric Standard Model dn ~ 10-25 (e-cm)x (200 GeV)2/M2SUSY Note: exp. limit: dn < 0.3 x 10-25 e-cm

40. Chang, et al, hep-ph/0503055 MSUSY=750GeV n e- 199Hg fA/p fm/p Pospelov, et al, 2004 Possible impacts of non-zero EDMs • Must be new Physics • Sharply constrains models beyond the Standard Model (especially with LHC data) • May account for matter- antimatter asymmetry of the universe

41. Experimental EDMs • Present best limits come from atomic systems and the free neutron • Electron EDM - 205Tl • Quark ColorEDM - 199Hg • Quark EDM - free neutron • Future best limits (x10 – 1000) may come from • Molecules(PbO, YbF = e-) • Liquids(129Xe = nuclear) • Solid State systems(Gadolinium-Gallium-Garnet = e-) • Storage Rings(Muons, Deuteron) • Radioactive Atoms(225Ra, 223Rn) • New Technologies for Free Neutrons • Switzerland = PSI • France = ILL • US = Spallation Neutron Source = SNS

42. n-EDM vs Time

43. Simplified Measurement of EDM E-field 1. Inject polarized particle 2. Rotate spin by p/2 3. Flip E-field direction 4. Measure frequency shift B-field Must know B very well

44. ILL-Grenoble neutron EDM Experiment Trapped Ultra-Cold Neutrons (UCN) with NUCN = 0.5 UCN/cc |E| = 5 kV/cm 100 sec storage time sd = 3 x 10-26 e-cm Harris et al. Phys. Rev. Lett. 82, 904 (1999)

45. Careful magnetometry is essential ! 199Hg Magnetometer

46. New EDM Experiment (ASU/Berkeley/Caltech/Duke/Harvard/Indiana/Kentucky/LANL/ MIT/NIST/NCSU/ORNL/HMI/SFU/Tennessee/UIUC/Yale) (AMO/HEP/NP/Low Temp expertise) Superfluid He UCN converter with high E-field >2 orders-of-magnitude improvement possible

47. New Technique for n-EDM E-field • Inject polarized neutron • & polarized 3He 2. Rotate both spins by 90o 3. Measure n+3He capture vs. time (note: sih>>shh) 4. Flip E-field direction B-field 3He functions as “co-magnetometer”

48. EDM Sensitivity

49. Spallation Neutron Source (SNS) @ Oak Ridge National Lab 1 GeV proton beam 1.4 MW on spallation target Fundamental Physics Beamline

50. EDM Experiment at SNS He Liquifier Isolated floor