High-precision studies in fundamental physics with slow neutrons. Oliver Zimmer Institut Laue Langevin

Transcription

1 High-precision studies in fundamental physics with slow neutrons Oliver Zimmer Institut Laue Langevin ILL, 20 September 2016

2 Topics The impossible particle and its properties Search for an electric dipole moment of the neutron Short-range gravity Test of Einstein s E = mc 2

3 The neutron before Chadwick

4 The neutron before Chadwick Such an atom would posses striking properties. Its outer field would vanish [...] and therefore it should easily penetrate matter. The existence of such an atom is presumably difficult to observe with a spectrograph, and... ( Nuclear Constitution of Atoms, Proc. Royal Soc. 1920)

5 The neutron before Chadwick Such an atom would posses striking properties. Its outer field would vanish [...] and therefore it should easily penetrate matter. The existence of such an atom is presumably difficult to observe with a spectrograph, and it could not be stored in a closed vessel. ( Nuclear Constitution of Atoms, Proc. Royal Soc. 1920)

6 How to store it nevertheless? Mirror reflection under any angle of incidence UCN can be trapped in neutron bottles Trapping potential #1: neutron optical potential V + iw Physical origin: neutron scattering by nuclei interference of incident and scattered waves refractive index: Typical values for V: Be: 252 nev, Al: 54 nev, Ti: -49 nev

7 Trapping potential #2: neutron gravity mgz for z = 1 m: E = 100 nev as good for trapping (if bottle is tall enough):

8 Trapping potential #2: neutron gravity mgz for z = 1 m: E = 100 nev

9 Trapping potential #3: magnetic interaction ±µb for B = 1 T: E = ±60 nev Adiabatic spin transport if mt fields sufficient in typical situations Magnetic gradient fields suppress losses due to wall collisions

10 Neutron properties:

11 nn oscillations neutron lifetime nedm??? n-gravity Heavy elements nuclear few-body interactions

12 Search for an electric dipole moment of the neutron magnetic moment - EDM +

13 Violation of fundamental symmetries Purcell and Ramsey, PR 78 (1950) T A non-zero particle EDM violates T (time reversal symmetry) and parity P - + P + - If we assume CPT conservation, also CP is violated, which is needed to explain the matter/antimatter asymmetry in the Universe

14 CP violation within the Standard Model (SM) is too weak to explain the matter/antimatter asymmetry in the Universe nedm tiny in the SM (10-31 ecm), but large in many beyond-sm theories Pendlebury and Hinds, NIM A 440 (2000) 471 nedm sensitive probe to search new fundamental forces

15 How is it measured? Ultra-cold neutrons (UCN) trapped at 300 K in vacuum RAL/SUSSEX/ILL experiment: B 0 ~ 0.5 m

16 polarization Ramsey s method Particle beam or trapped particles (...spin echo) E 1 - L ( detuning ) Experimental sensitivity: EDM changes frequency: L ~ B n d n E d n 2 ET N

17 199 Hg co-magnetometer for correction of magnetic field drifts ratio of precession frequencies Neutron resonant frequency (Hz) T Run duration (hours)

18 Best result so far (RAL / Sussex / ILL) d n < e cm (90% CL) C.A. Baker et al., PRL 63 (2006) ev spin-dependent interaction one spin precession per half year

19 Next steps? World-wide effort: projects at PSI, SNS, TRIUMF, TUM, PNPI, ILL Accuracy goal: below ecm needs new UCN sources, excellent magnetic shielding

20 Short-range gravity Small extra-dimensions: Explanation why gravity is such a weak force? Modification of gravity with n additional dimensions at distances r < R: New spectroscopic tool: m1 m2 m1m F G g 2 2 r r 2 L r n n

21 First observations (2002) V. Nesvizhevsky et al., Nature 415 (2002) 299

22 Rabi-type spectroscopy of gravity qbounce collaboration (H. Abele, T. Jenke )

23 Most recent results on Gravity Resonance Spectroscopy

24 Ramsey spectrometer for gravity states H. Abele et al., Phys. Rev. D 81 (2010) Advantages: Long flight path smaller uncertainty E static central mirror for free state evolution

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26 Snapshots of II 2 with 1.5 m resolution

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32 E = mc 2 How can we test it? need process, where mass is converted in energy thermal-neutron capture reaction: L X 1 n L1 X i γ i thermal energies ~10-2 ev excess energy: several 10 6 ev total energy uncertainty: < 10-8

33 [ m(n) m( L X) m( L1 X)] c 2 i E(γ i )? E(γ) In terms of mass units A relative to an atomic mass scale u = 10-3 /N A kg : h hc A L L1 3 A ( n) A( X) A( X) 10 L c 1 i i ( A( L1 X) N h 1 X) molar Planck constant L1 K 1 3 NAh 1 1 A X) A( Y) 10 L 1 K c i i ( X) j j ( ( 1 Penning trap measurements (4 masses) Y) qb m Gamma-ray wavelength measurements (2 nuclides after neutron capture) Double crystal monochromator GAMS

34 Which isotopes? Penning Trap: A( L,L+1 X) can be measured with relative uncertainty! Need mass values for two pairs of stable isotopes = 0.17 barn = 0.55 barn = 43.7 barn = 0.3 barn Pe Atomic Mass data available

35 A relative uncertainty on A requires measurements with accuracy 10-8 What is needed to determine gamma energies (or wavelengths) with high accuracy? is necessary but insufficient High accuracy use gamma spectroscopy based on Laue diffraction n hc E 2d sin Need absolute measurements of: lattice constant d scattering angle Bragg s law for photons E E 2 2 d/d < 10-8 d ~ d 2

36 Flat double-crystal monochromator spectrometer for gamma rays: GAMS non-dispersive n hc E 2d sin dispersive measures instrument response contains additional broadening

37 Implantation of spectrometer Flat Crystals: Resolution: 10-6 Eff. Solid Angle: absolute Energy: 10-7 Neutron Flux: Targets: g Target change during reactor cycle

38 d/d: How perfect are GAMS crystals? d/d < 10-8, extremely perfect silicon crystals, d known in SI units Silicon crystal for GAMS6 from WASO4 reference material Fabricated by PTB, Braunschweig, Germany Characterized by INRIM, Torino, Italy

39 Angle interferometer with self-calibration L Linear displacement interferometer k L L 4k sin Angle interferometer 2 N i L arcsin 4k N L i are measured Equation is solved for k i

40 Result of E = mc 2 test using GAMS4 E mc 2 = -( ) 10-7 S. Rainville et al., Nature 438 (2005) 1096 Wavelength measurements are limiting

41 Accuracy reach of GAMS4 Stability of calibration: 2.1x10-7 Angle measurement and calibration under atmosphere possible not better than on 10-7 level J. Krempel, PhD LMU,

42 New instrument GAMS6 spectrometer table spectrometer axis interferometer block polygon + autocollimators

43 Challenge: redefinition of the kilogram

44 Routes to a new mass unit definition Hz h R 4m gv kg 2 J 90 RK 90( UI) 90 E = mc 2 NA h uc 2 kg Avogadro project Number of atoms in 1 kg mol m kg 3 10 N A u

45 Acknowledgements Material for this talk courtesy of: Neutron EDM Maurits van der Grinten Rutherford Appleton Laboratory Peter Fierlinger Technische Universität München Short-range gravity Hartmut Abele Atominstitut Wien E = mc 2 Michael Jentschel Institut Laue Langevin