High-precision studies in fundamental physics with …...High-precision studies in fundamental...
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High-precision studies in fundamental physics with
slow neutrons
Oliver Zimmer
Institut Laue Langevin
ILL, 20 September 2016
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Topics
• The impossible particle and its properties
• Search for an electric dipole moment of the neutron
• Short-range gravity
• Test of Einstein’s E = mc2
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The neutron before Chadwick
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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)
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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)
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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
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Trapping potential #2:
neutron gravity mgz
as good for trapping (if bottle is tall enough):
for z = 1 m: E = 100 neV
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Trapping potential #2:
neutron gravity mgz for z = 1 m: E = 100 neV
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Trapping potential #3:
magnetic interaction ±µB
for B = 1 T: E = ±60 neV
Adiabatic spin transport if
Magnetic gradient fields suppress losses due to wall collisions
mT fields sufficient in typical situations
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Neutron properties:
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nEDM
neutronlifetime
???
nuclear few-bodyinteractions
Heavy elements
n-gravity
nn oscillations
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+
-
magnetic
momentE
DM
Search for an electric dipole moment of the neutron
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+
-
Violation of fundamental symmetries
+
-
+
-
+
-
T
P
• A non-zero particle EDM violates T (time reversal symmetry) and parity P
• If we assume CPTconservation, also CP is violated, which is needed to explain the matter/antimatter asymmetry in the Universe
Purcell and Ramsey, PR 78 (1950) 807
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• 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
• nEDM sensitive probe to search new fundamental forcesPendlebury and Hinds, NIM A 440 (2000) 471
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RAL/SUSSEX/ILL experiment:
B0
Ultra-cold neutrons (UCN)
trapped at 300 K in vacuum
~ 0.5 m
How is it measured?
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po
lari
zati
on
1 - L („detuning“)
n 2d
ET N
EdBL nn~
EDM changes frequency:
Particle beam or trapped particles(...spin echo)
E
Ramsey’s method
Experimental sensitivity:
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0 5 10 15 20
29.9260
29.9265
29.9270
29.9275
29.9280
29.9285
29.9290
29.9295
10-10
T
Ne
utr
on
re
so
na
nt
fre
qu
en
cy (
Hz)
Run duration (hours)
7.7882
7.7884
7.7886
7.7888
7.7890
rati
o o
f p
rece
ssio
n f
req
ue
nci
es
199Hg co-magnetometer for correction of magnetic field drifts
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|dn| < 2.9 10-26 e cm (90% CL)
Best result so far (RAL / Sussex / ILL)
• 10-22 eV spin-dependent interaction
• one spin precession per half year
C.A. Baker et al., PRL 63 (2006) 131801
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Next steps?
• World-wide effort: projects at PSI, SNS, TRIUMF, TUM, PNPI, ILL
• Accuracy goal: below 10-27 ecm
• needs new UCN sources, excellent magnetic shielding…
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n
n
r
L
r
mmg
r
mmGF
2
21
2
21
Modification of gravity with n additional dimensions at distances r < R:
Short-range gravitySmall extra-dimensions:Explanation why gravity is such a weak force?
New spectroscopic tool:
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First observations (2002)
V. Nesvizhevsky et al., Nature 415 (2002) 299
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Rabi-type spectroscopy of gravityqBounce collaboration (H. Abele, T. Jenke…)
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Most recent results on Gravity Resonance Spectroscopy
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Ramsey spectrometer for gravity statesH. Abele et al., Phys. Rev. D 81 (2010) 065019
Advantages:
• Long flight path smaller uncertainty E
• static central mirror for free state evolution
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Snapshots of II2 with 1.5 m resolution
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E = mc2
• need process, where mass is converted in energy
• thermal-neutron capture reaction:
i
i
LL γ X n X 11
thermal energies
~10-2 eV
excess energy:
several 106 eV
total energy uncertainty: < 10-8
How can we test it?
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i
L
i
LL
c
hNAAA
X)(
110 X)(X)(n)(
1
A31
X)( 1 LA
i jK
j
L
i
KL
c
hNAA
Y)(
1
X)(
110 Y)(X)(
11
A311
Penning trap measurements (4 masses)
Gamma-ray wavelength measurements
(2 nuclides after neutron capture)
molar Planck constant
? )γ( X)](X)(n)([ 21
i
i
LL Ecmmm
In terms of mass units A relative to an atomic mass scale u = 10-3/NA kg :
hchE )γ(
m
qB Double crystal monochromator
GAMS
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Which isotopes?
Pe
Penning Trap: A(L,L+1X) can be measured with 10-11 relative uncertainty!
Need mass values for two pairs of stable isotopes
= 0.3 barn
= 0.17 barn = 0.55 barn = 43.7 barn
Atomic Mass data
available
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What is needed to determine gamma energies (or wavelengths) with high accuracy?
A 10-11 relative uncertainty on A requires measurements with accuracy 10-8
is necessary but insufficient
High accuracy use gamma spectroscopy based on Laue diffraction
Bragg’s law for photons
sin2dE
hcn
222
~
d
d
E
E
d/d < 10-8
Need absolute measurements of:
• lattice constant d
• scattering angle
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Flat double-crystal monochromator spectrometer
for gamma rays: GAMS
measures instrument response
contains additional broadening
dispersive non-dispersive
sin2dE
hcn
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Implantation of spectrometer
Neutron Flux: 5×1014
Targets: 0.1 – 10g
Target change during reactor cycle
Flat Crystals:
• Resolution: 10-6
• Eff. Solid Angle: 10-11
• absolute Energy: 10-7
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Silicon crystal for GAMS6 from WASO4 reference material• Fabricated by PTB, Braunschweig, Germany• Characterized by INRIM, Torino, Italy
d/d < 10-8, extremely perfect silicon crystals, d known in SI units
d/d: How perfect are GAMS crystals?
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L
L
k
sin4kL
Linear displacement interferometer
Angle interferometer
Angle interferometer with self-calibration
N
i
i
k
L
4arcsin2
• N Li are measured• Equation is solved for k
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Result of E = mc2 test using GAMS4
Wavelength measurements are limiting
E – mc2 = -(1.2 4.3) × 10-7
S. Rainville et al., Nature 438 (2005) 1096
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Accuracy reach of GAMS4
41
Stability of calibration: 2.1x10-7
Angle measurement and calibration under
atmosphere possible not better than on 10-7 level
J. Krempel, PhD LMU, 2011
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spectrometer table
interferometer blockspectrometer axis
polygon + autocollimators
New instrument GAMS6
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Challenge:redefinition of the
kilogram
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uNm A
3
kg 10
E = mc2
kg mol
Hz
Avogadro project
Number of atoms in 1 kg
9090
2
90 )(
v4
UIRR
gmh
KJ
kg
2
A uchN
Routes to a new mass unit definition
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Acknowledgements
Neutron EDM
Maurits van der GrintenRutherford Appleton Laboratory
Peter FierlingerTechnische Universität München
Short-range gravity
Hartmut AbeleAtominstitut Wien
E = mc2
Michael JentschelInstitut Laue Langevin
Material for this talk courtesy of: