1. W. M. Snow Physics Department Indiana University Center for the Exploration of Energy and Matter wsnow@indiana.edu Nuclear/Particle/Astrophysics with Slow Neutrons 1. Neutron technology and slow neutrons 2. Neutron lifetime 3. NN weak interaction: parity violation 4. Search for neutron electric dipole moment: time reversal violation 5. Neutron gravitational bound states and search for extra dimensions For more: J. Nico and W. M. Snow, Annual Reviews of Nuclear and Particle Science 55, 27-69 (2005) Thanks for slides to: Geoff Greene, Chen-Yu Liu, Jen-chieh Peng, Philip Harris, Hartmut Abele, Hiro Shimizu, T. Soldner,…

2. Nuclear/Particle/Astrophysics with Slow Neutrons... is Particle Physics: but at an energy of 10 -20 TeV, using a low energy decelerator employs a particle which, according to Big Bang Cosmology, is lucky to be alive is “Nuclear” physics, but with an “isotope of nothing” relies on experimental techniques and ideas from nuclear, particle, atomic, and condensed matter physics is pursued at facilities built mainly for chemistry, materials science, and biology

3. Neutron Properties Mass: m n =939.56536(8) MeV [m n > m p + m e, neutrons can decay] Size: r n ~10 -5 Angstrom=1 Fermi [area~ 10 -25 cm 2 =0.1 “barn”] Internal Structure: quarks [ddu, m d ~ m u ~few MeV ] + gluons Electric charge: q n =0, electrically neutral [q n <10 -21 e] Spin: s n = 1/2 [Fermi statistics] Magnetic Dipole Moment:  n /  p = -0.68497935(17) Electric Dipole Moment: zero[d n < 3x10 -26 e-cm] Lifetime:  n =885.7 +/- 0.8 seconds

4. Why is it such hard work to get slow neutrons? E E=0 pn V NN Neutrons are bound in nuclei, need several MeV for liberation. We want E~kT~25 meV (room temperature) or less How to slow down a heavy neutral particle with M n = M p ? Lots of collisions… E0 E/2 [1/2] N =(1 MeV)/(25 meV) for N collisions Neutrons are unstable when free->they can’t be accumulated easily

5. The ILL reactor Cold Source

6. Inside the ILL Reactor 1 mILL7 H9H8 H6 IH4 H5 ILL22 H4 H2 IH3 H3 H1 H12 H13IH1H10 H11 H7 VCSHCSHS IH2thermalcoldhot D2OD2OH2OH2O IHinclined tube

7. The Spallation Neutron Source  $1.4B--1GeV protons at 2MW, started in 2007.  Short (~1 usec) pulse– mainly for high TOF resolution

8. Target Moderators

9. “Slow” Neutrons: MeV to neV 235 U n 2MeV ν β γ γ β ν 235 U n 0.1eV 235 U n n 30K 300K Nuclear reactor/ Spallation source Neutron Moderator (LH2, LD2) meVneV

10. Neutron Energy, Momentum, and Wavelength

11. Neutrons in Condensed Matter |k> |p> for a “thermal” neutron (E K =mv 2 /2=3/2 k B T, T=300K-> E K =25 meV) the de Broglie wavelength of the neutron is ≈ 2 Angstroms Thermal neutrons have the right energies and momenta to match excitations (phonons, spin waves, molecular rotations…) and static structures (crystals, molecular shapes,…) in condensed media phonon |k> |p> diffraction

12. Many Condensed Matter Phenomena lie within the Ranges of Length & Time Seen by Neutron Scattering

13. Potential step -> neutron index of refraction Neutron kinetic energy If a > 0, total external reflection =2  h 2  b s /m, ~+/- 100 neV =  B, ~+/- 60 neV/Tesla =mgz~100 neV/m =[2  h 2  b w /m]s·k/|k|~10- 7 All forces contribute to the neutron optical potential:

14. Neutron optical guides at ILL/Grenoble (top view)

15. Cold Neutron Guide Hall at NIST n

16. What methods are used to polarize neutrons? B B gradients (Stern-Gerlach, sextupole magnets) electromagnetic F=(  )B Reflection from magnetic mirror: electromagnetic+ strong f  =a(strong) +/- a(EM) with | a(strong)|=| a(EM)|  f+=2a, f-=0 B  Transmission through polarized nuclei: strong  ≠  -  T  ≠ T  Spin Filter:T  =exp[-   L] L

17. Ultra-Cold Neutrons (UCN) (Fermi/Zeldovich)  What are UCN ? –Very slow neutrons (v 500 Å, E<V optical ) that cannot penetrate into certain materials Neutrons can be trapped in material bottles or by magnetic fields

18. The weak interaction: just like EM, but not really: 3 “weak photons” [W +, W -, Z 0 ], can change quark type e-e- e-e- e-e- e-e-  one EM photon e-e- e-e- e-e- Z0Z0 e-e- ud u W +- d V(r)=e 2 /r, m   ‘V’(r)≈[e 2 /r]exp(-Mr), M Z,W ≈ 80-90 GeV “Empty” space (vacuum) is a weak interaction superconductor |B| vacuumsuperconductor penetration depth r weak field our “vacuum” 1/ M Z,W r uu u Z0Z0 u

19. The weak interaction violates mirror symmetry and changes quark type ue W +- d Only the weak interaction breaks mirror symmetry: not understood weak interaction = eigenstates [CKM]  quark mass eigenstates V ud in n decay Matrix must be unitary r->-r in mirror, but s->+s Discovered by C.S.Wu

20. Neutron  -decay Input for theory of Big Bang element creation Clean extraction of fundamental parameters of the electroweak theory.

21. Neutron Lifetime Effect on Primordial 4He Abundance in Universe Influence of  : Shift  by 9  (1%)  = 885.7(8)s  Y p = 0.2479(6)  = 878.5(8)s  Y p = 0.2463(6) Astrophysical observations: large systematic uncertainties, Y p = 0.238(2)(5), Y p = 0.232 … 0.258, … 878.5(8)s 885.7(8)s

22. Neutron Lifetime Measurement with a Proton Trap and Flux Monitor (Dewey et al) dN(t)/dt=-N(t)/ , measure decay rate and total # of neutrons in a known beam volume Protons from neutron decay trapped in a Penning trap and counted Neutron # in trap inferred from flux monitor

23. In-Beam Lifetime Apparatus @ NIST

24. Neutron Lifetime Using UCN Bottle Measure storage time, vary S/V Lifetime extrapolated to S/V->0 limit

25. “History” of Neutron Lifetime Measurements World average [PDG] Last (single) measurement

26. N-N Weak Interaction: Size and Mechanism Relative strength of weak / strong amplitudes: NN weak amplitudes first-order sensitive to qq correlations Weak interaction violates parity. Use parity violation to isolate the weak contribution to the NN interaction. NN repulsive core → 1 fm range for NN strong force ~1 fm = valence + sea quarks + gluons + … NN strong force at low energy mediated by mesons QCD possesses only vector quark-gluon couplings → conserves parity Both W and Z exchange possess much smaller range [~1/100 fm] weak

27. PV Gamma Asymmetry in Polarized Neutron Capture  Asymmetry A  of gamma angular distribution upon polarized neutron capture due to weak NN interaction [from s n  p  ]  Goal: 1x10 -8 at SNS/7000 MW-hours  Asymmetry depends mainly on the weak pion coupling f  for n-p  PV gamma asymmetry in n+D->3H+  also possible (SNS letter of intent)

28. NPDGamma Experimental Setup at Los Alamos (LANSCE) B 0 =10 gauss

29. Parity Violating Asymmetry in n+p->D+gamma at LANSCE

30.  Analogous to optical rotation in an “ handed ” medium.  Transversely-polarized neutrons corkscrew due to the NN weak interaction  PV Spin Angle is independent of incident neutron energy in cold neutron regime,  In combination with n-p experiment, determine weak interactions between nucleons and use it to calculate parity violation in atoms Another Parity-Violating Observable: Neutron Spin Rotation f Refractive index dependent on neutron helicity

31. Cross section of Spin Rotation Apparatus n Side View

32. Liquid Helium Motion Control System Nonmagnetic cryostat: target feedthroughs and liquid motion control system

33. Distribution of Raw Asymmetries Data under analysis Result consistent with zero at 1E-6 rad/m level Future experiments in H,D, and 4He possible

34. Where’s the antimatter in the universe? Diffuse  -ray flux expected from annihilation Cohen, De Rujula, Glashow; astro-ph/9707087 In the lab we make equal amounts of matter and antimatter So why is the universe lopsided? Is it just an accident?

35. Sakharov Criteria to generate matter/antimatter asymmetry from the laws of physics –Baryon Number Violation (not yet seen) –C and CP Violation (seen but too small by ~10 10 ) –Departure from Thermal Equilibrium (no problem?) A.D. Sakharov, JETP Lett. 5, 24-27, 1967 Matter/Antimatter Asymmetry in the Universe in Big Bang, starting from zero Relevant neutron experimental efforts Neutron-antineutron oscillations (B) Electric Dipole Moment searches (T=CP)

36. Neutron Electric Dipole Moment Non-zero d n violates both P and T Under a parity operation:Under a time-reversal operation:

37. Factor ~10 per 8 years EDM limits: the first 50 years Barr: Int. J. Mod Phys. A8 208 (1993)

38. Reality check I f neutron were the size of the Earth... xx -e +e... current EDM limit on neutron would correspond to charge separation of  x  10 

39. EDM Measurement Principle (  ) – (  ) = – 4 E d/ h assuming B unchanged when E is reversed. B0B0 E = + h/2 = - h/2 h (0) h (  ) h (  ) B0B0 B0B0 E Present EDM limit corresponds to energy difference of 1E-22 eV!

40. nEDM apparatus at ILL using UCN N S Four-layer mu-metal shield High voltage lead Quartz insulating cylinder Coil for 10 mG magnetic field Upper electrode Main storage cell Hg u.v. lamp PMT to detect Hg u.v. light Vacuum wall Mercury prepolarising cell Hg u.v. lamp RF coil to flip spins Magnet UCN polarising foil UCN guide changeover Ultracold neutrons (UCN) UCN detector Use 199 Hg co- magnetometer to sample the variation of B-field in the UCN storage cell Limited by low UCN flux of ~ 5 UCN/cm 3 Figure–of-merit ~ E(NΤ) 1/2

41. UCN production in liquid helium  1.03 meV (11 K) neutrons downscatter by emission of phonon in liquid helium at 0.5 K  Upscattering suppressed: Boltzmann factor e -E/kT is small if T<<11K n = 8.9 Å; E = 1.03 meV Landau-Feynman dispersion curve for 4 He excitations Dispersion curve for free neutrons R. Golub and J.M. Pendlebury Phys. Lett. 53A (1975), Phys. Lett. 62A (1977)

42. nEDM experiment at SNS, ~2014 GOAL: ~1E-28 e-cm Figure–of-merit ~ E(NΤ) 1/2 New approach aims at N  100 N, T  5 T, E  5 E

43. Classical/QM Bouncing Neutrons

44. Neutron Probability Distributions Above the Mirror

45. V horizont ~4-15 m/s V vertic ~2 cm/s Selection of vertical and horizontal velocity components General scheme of the experiment (flow-through integral mode)

46. Experimental Apparatus

47. the Experiment

48. Observation/Comparison to Theory

49. Large Extra Dimensions of Spacetime? New Forces of nature? Why not? Infinite dimension compact dimension R Maybe gravity is so weak because some of its flux flows into extra “compact” dimensions of size If so, V is not 1/r if r~

50. Limits for alpha and lambda Green: Neutron Limits

51. V.V.Nesvizhevsky - Search for extra fundamental forces at short distances of 1 nm - 10  m -Verification of electrical neutrality of neutrons Perturbation frequency, Hz Transition probability induced by vibrating mass Quantum trap Resonance transitions Potential Applications in fundamental physics

52. Nuclear/Particle/Astrophysics with Slow Neutrons Uses techniques and concepts from atomic physics, condensed matter physics,low temperature physics, optics Neutron physics measurements test fundamental laws of weak interaction and can be used to search for new phenomena New facilities are on the way (NIST, SNS, JSNS, UCN facilities). for more: http://www.bnl.gov/NPSShttp://www.bnl.gov/NPSS Nico/Snow, Annual Reviews Nuclear Particle Science 55, 27-69 (2005)

53. Neutron EDM Experiment with Ultra Cold Neutrons Use 199 Hg co-magnetometer to sample the variation of B-field in the UCN storage cell Limited by low UCN flux of ~ 5 UCN/cm 3 Figure–of-merit ~ E(NΤ) 1/2 A new approach aims at N  100 N, T  5 T, E  5 E Most Recent ILL Measurement

54. P, CP, T, and CPT  Parity violation (1956) –only in weak interaction  CP violation (1964) –parametrised but not understood –only seen so far in K 0 & B 0 systems –Doesn’t seem to be responsible for baryon asymmetry of universe  T violation (1999) –CPT is good symmetry: T  CP      KSKS KLKL e-e- 60 Co Detector

55. Big Bang Nucleosynthesis (BBN) kT [MeV] t [s] d destroyed by  (kT < 2.2MeV, but N  / N B  10 9 )   decay rate 1 200   reaction rate 1 0.1 Freeze-out if Hubble expansion rate greater than reaction rate   T f All rates depend on baryon density N B /N  =  10  10 10 4 He formation

56. V ud from neutron  decay needs the neutron lifetime

57. Classical Theory of Weak Decay Standard Model for neutron decay: Unitarity of CKM matrix Expression for neutron lifetime in Standard Model