10/2/2012
1
Stefan Baeβler
Fundamental Physics with Neutrons
The physicist’s view of a neutron
For most experiments, it is a point(with some properties: mass and spin).
dd
u
For neutron beta decay, it has (at least) the structure given by its valence quarks.
d
d
u
With more resolution, more structure appears
Different physicist’s have different views:
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What is our interest?
How? Fermilab’s view to this is:
David MacFarlane, Director of Particle Physics and Astrophysics division, SLAC
“The Intensity Frontier involves many diverse lower-energy precision experiments; and its discovery potential, being less direct, is therefore harder to understand.”
Answer: We want to find the fundamental laws of physics .
3
p+
n
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e
Table of contents
4
1. Production of Low Energy Neutrons
2. Experiments with Low Energy Neutrons:
• Neutron Beta Decay
• Spectroscopy of gravitationally bound quantum states
• Weak Hadronic Interaction in neutron capture on hydrogen
3. Future plans
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3
The Spallation Neutron Source SNS in Oak Ridge, TN
Linear H- accelerator Accumulator ring (buncher)
Target
Target
Guide Hall
1B - Disordered Mat’lsCommission 2010
2 - Backscattering Spectrometer Commission 2006
3 - High Pressure Diffractometer Commission 2008
4A - Magnetism Reflectometer Commission 2006
4B - Liquids ReflectometerCommission 2006
5 - Cold Neutron Chopper Spectrometer Commission 2007
18 - Wide Angle Chopper Spectrometer Commission 2007
17 - High Resolution Chopper SpectrometerCommission 2008
13 - Fundamental Physics Beamline Commission 2008
11A - Powder Diffractometer Commission 2007
12 - Single Crystal Diffractometer Commission 2009
7 - Engineering Diffractometer IDT CFI Funded Commission 2008
6 - SANS Commission 2007
14B - Hybrid Spectrometer Commission 2011
15 – Spin Echo
9 –VISION
Usage of neutrons @ SNS
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Transport (cold neutrons)
V
~ 100 neV
2
Fermin
2 big: V nb
m
Storage (ultracold neutrons)
Interactions of low energy neutrons with matter
2
Fermin
2( )i i
i
V b x xm
UCN
Typical properties:
Energy: EUCN ~ 100 neV
Velocity: vUCN ~ 5 m/s
Height: hUCN ~ 1 m 7
p+
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Table of contents
8
1. Production of Low Energy Neutrons
2. Experiments with Low Energy Neutrons:
• Neutron Beta Decay
• Spectroscopy of gravitationally bound quantum states
• Weak Hadronic Interaction in neutron capture on hydrogen
3. Future plans
10/2/2012
5
Beta Decay in the Standard Model
Parity Violation found by Wu et al, 1956
ud 5Fweak 5 h.c.
21 μ μ e
GH p γ γ γ n e γ γ γ ν
V
3. Helicity
… of elementary fermions: –p/E,
… of elementary anti-fermions: +p/E
60Co
I
e-
60Co
I
e-
≠
e-e
ep
μ- νμ
d u
b t
s c
1. Quark mixing
2
ud 95%V
2. Nucleon structure effects
gV = GF·Vud·1
gA = GF·Vud·λ
(No nuclear structure effects)
Fermi’s golden rule:
2
weak
2 decay probability i f f H i
9
d
2
eu2
e
221 3F V
dwG E
dE
Observables in Neutron Beta Decay
u1 2 2
e2
n d
21 3FG V E
pn
e-
e
n
e
Neutron lifetime
Jackson et al., PR 106, 517 (1957):
Observables in Neutron beta decay, as a function of generally possible coupling constants (assuming only Lorentz-Invariance)
2 ee
e
e en
e
ee
e
1 3 1
+
a b
A B
p p
E E
p p p
md E
E
Dp
E E E E
Beta-Asymmetry
Neutrino-Electron-Correlation
2
2
Re2
1 3A
2
2
1
1 3a
Fierz interference term 0b
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Search for Standard Model Parameters
-1.290 -1.280 -1.270 -1.260
λ = gA/gV
0.960
0.965
0.970
0.975
0.980
Vud
ft(0+→0+) [Hardy09]
ft(0+→0+) [Liang09 – PKO1]
ft(0+→0+) [Liang09 – DD-ME2]
PIBETA [Pocanic04]
λ[P
DG
201
2]
A[P
ER
KE
O I
I, 2
012]
Kaons+Unitarity [PDG 2012]
-1.667
(if neutron was aelementary particle)
-1.000
(if neutron was (udd))
Nab, goal
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13
~ GeV: quarks combine to form nucleons: → , → , ′ → , , …Problem: If nucleons were formed as many as anti-nucleons (CP-symmetry), nucleons and anti-nucleons would have annihilated and disappeared.Solution: Need (more) CP violation in theory
Experiments: Measure electric dipole moments, e.g. of neutron
14
. MeV: nucleons on thermal equilibrium: ~ ⁄ →
. MeV: heavier nuclei form:→ , → , → , …
(This is primordial nucleosynthesis, it stops at mass 5 and 8)We find element abundances from nuclear and particle physics!
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Neutron beta decay data in Primordial Nucleosynthesis
Experimental input from fundamental physics with neutrons:Stronger coupling constants in n ↔ p reactions (as determined by neutron lifetime)⇒ Phase transition later ⇒ nucleon density lower after phase transition ⇒ less 4He, more d
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W±
e-
νen
p
n + νe ↔ p + e-
W±
e+
νe
n
p
n + e+ ↔ p + νe
Reactions in equilibrium
n ↔ p + e-+ νe
W±
e-
νen
p
Ee [MeV]
p p2
[MeV
2 /c2 ]
cos θeν = 1
Proton phase space (Dalitz plot) Probability (arb. units)
0
0.25
0.5
0.75
1
1.25
1.5
0 0.2 0.4 0.6 0.8
cos θeν = 0cos θeν = -1
1 cosee
e
pd a
E
n
e-
e
epKinematics in Infinite Nuclear Mass Approximation:
• Energy Conservation:
• Momentum Conservation2 2 2
e ep 2 cos ep p p p p
e,max eEE E
Idea of the cos θeν spectrometer Nab @ SNS
Ee =
75 keV
236 keV
450 keV
700 keV
22p emin, max
2ep
e
Edges:
Slope:
1 cos e
p p p
pa p
E
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SegmentedSi detector
decay volume (field rB,DV·B0)
0 kV
0 kV
30 kV
magnetic filterregion (field B0)
Neutronbeam
TOF region(field rB·B0)
Nab spectrometer principle: measurement of Ee and tp
• Measurement of Ee and tp for each event; protons only in upper detector
• Background suppression through coincidences of electron and proton.
• Long flight path improves spectrometer
Proton Trajectory
Magnetic Field
Adi
abat
ic
conv
ersi
on
p
||p
p
||p
18
Sim
ulat
ed c
ount
s [A
.U.]
0.002 0.004 0.0060
Ee = 300 keVEe = 500 keV
Ee = 700 keV
1/tp2 [µs-2]
Extraction of a in Nab
Data analysis: Use edge to determine or verify the shape of the detection function.
Then, use central part to determine slope and the correlation coefficient a.
pp2 [MeV2/c2]
p p2
dist
ribu
tion
0.0 0.5 1.0 1.5
2ep
e
1 cos e
pa p
E
Ee = 550 keV
2pcos 1e p
2pcos 1e p
pp
p pcos ( )
m dzt
p zq= ò
2p
2p,0 0
sin ( ) ( )
sin
z B z
B
q
q=
Nab spectrometer simulations:• J. Brown (2nd prize at Undergraduate Research Symposium
2011), T. Niu, D. van Petten (Mitchell Fellowship), S.B.• E. Frlez, L. P. Alonzi, D. McLaughlin, D. Pocanic(all UVa)• J. D. Bowman (ORNL) 19
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Nab: Spectrometer Magnet System
20
z [cm]
Mag
neti
cfi
eld
[T]
B
0
1
2
3
4
-1 0 1 2 3 4 5
neutrondecay volume
lowerdetector
upperdetector
z [cm]
Mag
neti
cfi
e ld
[T]
B
0
1
2
3
4
neutrondecay volume
Bz (on axis)Bz (off axis)
Filter
-30 -20 -10 0 10 20 30
Nab setup at Spallation Neutron Source (SNS)
FNPB beamline @ SNS
Spectrometer magnet
Si detectors
Neutron beam
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Uncertainty budget
PLANNED systematic uncertainty budget:PLANNED statistical uncertainty budget:
About 2×109 events can be detected in 6 weeks (Decay volume V = 246 cm3, decay density nd = 20 cm-3, 12.7 % of decay protons go to upper detector, 80% duty factor)
→ (Δa/a)stat < 1×10-3 can be reached
Compare to Δa/a = 5 % of existing experimental results
lower Ee cutoff none100 keV
100 keV
300 keV
upper tp cutoff none none 40 μs 40 μs
Δa 2.4/√N 2.5/√N 2.5/√N 2.6/√N
Δa (Ecal, lvariable)
2.5/√N 2.6/√N 2.7/√N 2.7/√N
Δa (Ecal, lvariable, inner 70% of data)
4.1/√N 4.1/√N 4.1/√N 4.1/√N
Experimental parameterSystematic
uncertainty Δa/a
Magnetic field... curvature at pinch 5·10-4
… ratio rB = BTOF/B0 2.5·10-4
… ratio rB,DV = BDV/B0 3·10-4
Length of the TOF region (*)Electrical potential inhomogeneity:… in decay volume / filter region 5·10-4
… in TOF region 1·10-4
Neutron Beam:… position 4·10-4
… profile (including edge effect) 2.5·10-4
… Doppler effect smallUnwanted beam polarization can be made smallAdiabaticity of proton motion 1·10-4
Detector effects:… Electron energy calibration (*)… Electron energy resolution 5·10-4
… Proton trigger efficiency 2.5·10-4
Residual gas smallBackground smallAccidental coincidences smallSum 1·10-3
0 50 100 150 200 250 300 3500
5
10
15
20
25
30
35
40
Angle [°]
Hei
ght [
mm
]
4900
4950
5000
5050
5100
Work Function [meV]
Kelvin Probe: First results from early work on aSPECT
In collaboration with Prof. I. Baikie, KP Technologies 25
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0 4 8 120
4
8
12
16
Hei
ght [
mm
]
Work Function [meV]
Width [mm]
0 50 100 150 200 250 300 3500
5
10
15
20
25
30
35
40
Azimuth angle [°]
Hei
ght [
mm
]
4900
4950
5000
5050
5100
In collaboration with Prof. I. Baikie, KP Technologies
Now: Better coating
Thanks to:Rachel Hodges (undergraduate research prize)Sean McGovern (M. Sc., 2010)Henry Bonner,Xuying Tong(all UVa)Gertrud Konrad(University of Mainz)
(arbitrary offset added)
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Silicon detector for Nab / abBA / PANDA
Segmented ion-implanted silicon detector with fast readout electronics:
• Thickness 2 mm (less for testing)
• Thin dead layer of < 100 nm silicon (measured!):
Energy loss for 30 keV protons: < 11 keV (measured!)
• 127 channels
Sufficiently small count rate/pixel,
Allows to find electron and correlated proton.
Front side Back side
Ø 81 mm
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Si detector properties: proton detection
A. Salas-Bacci, P. McGaughey, Dinko Pocanic, S.B. et al @ NCSU proton source (A. Young et al.)
Threshold lost protons efficiency slope
8 keV 0.19% 110(30) ppm/keV
10 keV 0.20% 131(31) ppm/keV
12 keV 0.21% 165(32) ppm/keV
14 keV 0.28% 304(76) ppm/keV
For uncertainty in a, we assume a threshold of 10 keV and direct measurement of efficiency slope to 50%.
20 30 40 50 60 70 80 90energy [keV]
dead layer: 70-100 nm Si(corrected for nuclear defect,
charge recombination)
Cen
troi
dpu
lse
heig
ht [
chan
nels
]
0
50
100
150
200
250
10 20 30 40 50 60 70 80pulse height [channels]
Yie
ld [
A.U
.]
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Ionization chamberin Faraday Cage
Bending magnet
Proton detector(in vacuum chamber)
Proton path
29
Proton source for detector tests (and advanced lab)
100
0.4 0.5 0.6 0.7
1000
10000
ion
coun
tra t
e[1
/s]
magnetic current [A]
mass 1(protons)
mass 2 (H)2+
Commissioning results:
Proton source is planned to be used for intermediate or advanced lab.
Support:Jeffress Memorial TrustJefferson TrustHEETFProton source team:Aaron Ross (Mitchell fellowship), Ryan Slater, Zia Tompkins, Americo Salas Bacci, Panaiot Zotev, S.B., Dinko Pocanic(all UVa)Martin Schlegel (DAAD fellowship), Y. Kahvaz
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Goal: Δb ~ 3×10-3
2 ee
e
1 3 1m
dw E bE
The determination of the Fierz Interference term
Electron spectrum:
Systematic uncertainties:1. Electron energy determination
2. Background
0 200 400 600 800Ee,kin (keV)
Yie
ld(a
rb.u
nits
)
b = +0.1SM
2% of events in tail(deadlayer,external bremsstrahlung)
Yie
ld
1
101
102
103
104
105
detected Ee [keV]
0 50 100 150 200 250 300
Detector response to decayelectron with Ee = 300 keV
30
Sensitivity to left-handed S-T couplings
Present limits (n decay data)SM is in the origin of this plot
Future limits,assuming a = -0.1059(1), A = -0.1186(1) ,B = 0.9807(30), C = -0.23785(24), τn = 882.2(13) s, b = 0±0.003
Model-dependent predictions: Supersymmetry, leptoquarks, …
Analysis similar to G. Konrad, S.B. et al., ArXiv:1007.3027
neutron and nuclear decays(survey, 68% C.L.)
superallowed0+→0+ decays(68% C.L.)
“present limits”(68% C.L.)
muon decay“90% C.L.”
nuclear decays
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Sensitivity to right-handed S-T couplings
Present limits (n decay data)SM is in the origin of this plot
Future limits,assuming a = -0.1059(1), A = -0.1186(1) ,B = 0.9807(30), C = -0.23785(24), τn = 882.2(13) s
Analysis similar to G. Konrad, S.B. et al., ArXiv:1007.3027
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35
Relevance in the LHC aera
1
b0+=-0.0022≤0.0043
p Ø e n g
bn<0.001
-0.004 -0.002 0.000 0.002 0.004-0.02
-0.01
0.00
0.01
0.02
eT
e S
LHC7, 1 fb-1
LHC7, 5 fb-1
LHC8, 15 fb-1
LHC14, 50 fb-1
-0.004 -0.002 0.000 0.002 0.004-0.02
-0.01
0.00
0.01
0.02
eT
e S
1 ∙ CMS-Search for → after pp collisions
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The Nab collaboration
R. Alarcona, L.P. Alonzib , S.B.b,c (Project Manager), S. Balascutaa, L. Barrón-Palos n, J.D. Bowmanc (Co-Spokesmen), M.A. Bychkovb, J. Byrned, J.R. Calarcoe, T. Chupp, T.V. Ciancioloc, C. Crawfordf, E. Frležb, M.T. Gerickeg, F. Glückh, G.L. Greenec,i, R.K. Grzywaczi, V. Gudkovj, D. Harrisong, F.W. Hersmane, T. Itok, M. Makelak, J. Martinl, P.L. McGaugheyk, S. McGovernb, S. Pageg, S.I. Penttiläc (On-site Manager), D. Počanićc (Co-Spokesmen), K.P. Rykaczewskic, A. Salas-Baccib, Z. Tompkinsb, D. Wagnerf, W.S. Wilburnk, A.R. Youngm
a Department of Physics, Arizona State University, Tempe, AZ 85287-1504b Department of Physics, University of Virginia, Charlottesville, VA 22904-4714c Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831d Department of Physics and Astronomy, University of Sussex, Brighton BN19RH, UKe Department of Physics, University of New Hampshire, Durham, NH 03824f Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506g Department of Physics, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canadah IEKP, Universität Karlsruhe (TH), Kaiserstraße 12, 76131 Karlsruhe, Germanyi Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996j Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208k Los Alamos National Laboratory, Los Alamos, NM 87545l Department of Physics, University of Winnipeg, Winnipeg, Manitoba R3B2E9, Canadam Department of Physics, North Carolina State University, Raleigh, NC 27695-8202n Universidad Nacional Autónoma de México, México, D.F. 04510, Méxicoi University of Michigan, Ann Arbor, MI 48109
Tasks of UVa group: Spectrometer design, Superconducting magnet, Electrodes, Magnetometry, Proton Source36
37
From the 2011 NSAC report about priorities in “Fundamental Physics with Neutrons”
Scientific Priorities
Dec 1, 2011NSAC Neutron Physics Subcommittee
Report6
(Constant effort is discussed in more detail on a later slide…)
The only experiment that requires new funding
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p+
n
e-
e
Table of contents
38
1. Production of Low Energy Neutrons
2. Experiments with Low Energy Neutrons:
• Neutron Beta Decay
• Spectroscopy of gravitationally bound quantum states
• Weak Hadronic Interaction in neutron capture on hydrogen
3. Future plans
Bound States in Physics
proton
Sun
Mercury
Venus
Earth
Moon
Mars
neutron
electron
d
d
u
Responsible for binding:Electromagnetic interaction Strong interaction Gravitational interaction
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18
Gravitationally Bound states – The idea
n ; 0
; otherwise
m gz zV
Height [µm]
Ene
rgy
[peV
]
0 10 20 30 400
1
2
3
4
Ψ1
Ψ2
Ψ3
Ψ4
E1 = 1.41 peV
E2 = 2.46 peV
E3 = 3.32 peV
E4 = 4.08 peV
2 nΨ Ψ Ψ
Ψ ∝ Ai ; ∙ ; , n ∙
with 2.34, 4.09, 5.52, 6.79, … ~⁄
40
V.I. Lushikov,Physics Today, June 1977
Detection of the size of the quantum states
Collimator
Absorber/Scatterer
Neutron detector
L ~10-12 cm
Inclinometers
UCN
Slit Height Measurement
Bottom mirrors (Glass)
41
25Absorber height Δh [μm]
Cou
nt r
ate
N [
Hz]
5 10
background
15 200.00
0.01
0.02
0.03
0.04
0.05
Tunneling model fit
z1z2
Results (corrected for non-parallelism):
z1 = 12.2 ± 0.7(stat) ± 1.8(syst) μm
z2 = 21.6 ± 0.7(stat) ± 2.2(syst) μm
Comparison to theory, undisturbed wave functions:
z1 = 13.7 μm, z2 = 24.0 μm
V.V. Nesvizhevsky, H. Abele, S. B. et al., EPJC 40, 479 (2005)
10/2/2012
19
Development of gravity resonance spectroscopy
Accuracy of position-type observables: ~ 10%
Improvement: do spectroscopy
; 0
; otherwise
mgz zV
E1 = 1.41 peV
E2 = 2.46 peV
E3 = 3.32 peV
Ene
rgy
[peV
]
0 10 20 30 400
1
2
3
4
Ψ1
Ψ2
Ψ3
Ψ4 E4 = 4.08 peV
Absorber Height Δh [μm]
Induce state transitions through:
• Oscillating magnetic field gradients
• Vibrations (→ QuBounce, H. Abele et al.)
• Oscillating Masses
ΔE ~ h·kHz
42
Resonance transitions = Rabi oscillations
2 2
n2n
0
( ) cos2
, defines , N N
H m gz V z tm z
H N E
01
( ) e wit( h ) Ni tN
NNt Na t H N N
Schroedingerequation:
Ansatz:
Insert in Schroedingerequation, restrict to 2 states “1” and “3”:
13
13
13 33
1 33
3 111
3 11
( )( ) ( )
(
e cos cos
e cos co)
) ( ) s(
i t
i t
i t t
i
da ta t a t
dtda t
a t a tdt
t t
13 3 1 13 1 ( ) 3V z 11 1 ( ) 1V z
33 3 ( ) 3V z
2 passage2 213 13
23 1 passage 13 2 2
13 13
sin2
P
Rabi formula:
Neglect fast self coupling and fast oscillating terms:
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Resonance transitions = Rabi oscillations
2 passage2 213 13
23 1 passage 13 2 2
13 13
sin2
P
Rabi formula:
0.05 0.10 0.200.15t [s]
0.0
0.2
0.4
0.6
0.8
1.0
tran
sitio
n pr
obab
ility
ω = 0.95ω13
ω = ω13
“Rabi oscillations”
passagefor 0.05 s
Resonance behavior
0.2
0.4
0.6
0.8
1.0
max
. tra
nsit
ion
prob
abil
ity
0 200 400 600ω/2π [Hz]
t passage = 0.5 st passage = 0.05 s
3 → 1
4 → 12 → 1
Transition probability at maximum for and 13 passage 13
44
Oscillating potential: Fluctuating magnetic field
0I 0
1
2I 0 0
1
2I 0I 0
1
2I 0
• • •
0I0
1
2I
Bottom mirror
0
1
2I 0 0
1
2I 0I
1 mm
1 cm
Magneticholdingfield B0
100 µm above mirror surfaceat mirror surface
-130 -120 -110 -100 -90 -80
x [mm]
-1.0
-0.5
0.0
0.5
1.0
mag
. fie
ld g
radi
ent ∂
Bz/∂z
[T
/m]
-130 -120 -110 -100 -90 -80
x [mm]
-1.0
-0.5
0.0
0.5
1.0
mag
neti
c fi
eld
[mT
]
Bz
Bx
47
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21
First setup to detect magnetically induced resonance transitions in flow-through mode
New UCNSource
1. Prepare initial state,ground state suppressed
3. Filter ground state2. Induce transitions in periodic magnetic field gradient
Position-sensitive
Detector
4. Measure horizontal velocity in position-sensitive detector
Bottom mirror
1. Prepare initial state (mostly the 3rd), ground state suppressed
2. Induce Transitions 3→1 in time-dependent magnetic field gradient
3. Filter ground state
4. Detect neutrons in dependence of free fall height
(corresponding to horizontal velocity, corresponding to oscillation frequency)
1 mm
1 cm
Magnetic holding field B0
Hor
izon
tal U
CN
vel
ocit
yv h
or
Mag
. Fie
ld o
scil
latio
n fr
eq. ω
48
Velocity-selective detection
Filter ground state
Position-sensitive
Detector
Measure horizontal velocity
30 cm
3 → 1
4 → 1
Monte-Carlo-Simulation, takes into account:
• 10000 incoming neutrons per incoming state
• Background: 10% in ground state
• Filter: 80 mm long, slit height: 25 μm
• Wave function evolves in free fall
• Detector resolution: 0.2 mm
Not simulated: Interference effects, Stern-Gerlach shift
Main systematic effect: Geometry G. Pignol et al., Thesis UJF Grenoble, 2009
Filter height chosen
49
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22
50
Systematic effects
• 3D descriptionThe previous discussion assumes time-dependent fields (so: reference frame of the incoming neutron). In reality, loss of energy in the vertical component is transferred into gain of energy in the horizontal component. We have proven that at estimated precision of Δ ⁄ ~10 , both descriptions are equivalent.
• Depolarization:Need magnetic holding field of 13 Gauss in order to stabilize spin.
• Stern-Gerlach shift:At moderate magnetic field, interplay between magnetic holding field and rotating field with amplitude
and associated field gradient with amplitude
leads to spin-dependent frequency shift, that to the first non-vanishing order is given as
The sign of this term depends on the spin state, and our system can act as a UCN polarizer.In addition, the there is a slowing down of the transition frequency.
2600 2700 2800 2900 3000 3100 3200
resonance frequency [rad/s]
0
20
40
60
80
100
max
imum
tran
siti
onpr
obab
ilit
y[%
]
numerical simulation
Rabi formula
S.B. et al., CRP 12, 707 (2011)
Δ ⁄ ~6
∙ ⋯
S.B. et al., to be published
UCNproductionvolume(est: 1000 UCN/cm3)
coldshutter
Intermediate volume(est: 320 UCN/cm3)
Collimator channel optimization:A. Mietke, V. Nesvizhevsky, S.B., et al., CRP 12, 729 (2012)
GRANITexperiment
Installation of GRANIT: New UCN Source
O. Zimmer et al, arXiV:0708.1373v2
O. Zimmer et al, PRL 107, 134801 (2011)
warmshutter
cleanroom
51
10/2/2012
23
Installation of GRANIT: In the clean room
probably dual use, interest for a UCN reflectometer
52
UVa contributors:J. Prince, A. Mietke (DAAD fellowship), D. Morton, S.B. (vice spokesperson)
Search for Chameleon fields
Quintessence: Hypothetical scalar field φ that explains the accelerated expansionof the universe.
E.g., Potential density const +… with Λ 2.4 meV,
Chameleon field: Scalar field of the type above, position dependent, with a hypothetical coupling to matter (density ρ) of the type:
const with ,
Relevant properties:• Non-linear interaction, no superposition principle• Self-shielding of macroscopic bodies: only outer shell of macroscopic bodies contributes to the
force between macroscopic bodies (this evades constraints from torsion balance experiments) 54
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Search for Chameleon fields
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(assumed to be ΔE/E ~ 10-3)
(assumed to be ΔE/E ~ 10-7)
Excluded, high β would cause extra quantum state of UCN
Chameleon field above mirror, for high β:
ΛΛ
⁄
Consequence:
Pl
P. Brax, G. Pignol, PRL 107, 111301 (2011)
V(z
)
1. Production of Low Energy Neutrons
2. Experiments with Low Energy Neutrons:
• Neutron Beta Decay
• Spectroscopy of gravitationally bound quantum states
• Weak Hadronic Interaction in neutron capture on hydrogen
3. Future plans
p+
n
e-
e
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npdgamma
Weak Hadronic Interaction in neutron capture on hydrogen:
UVa contribution:• A. Mietke, J. Schaedler, S. Schroeder (DAAD fellowships), J. Prince, S.B. (EC member
and magnetic field subsystem manager)• E. Askanazi, J. Hall, E. Frlez, D. Pocanic
18.00"
spin flipper
LH2 targetbeam monitor
supermirror polarizercompensation magnet
heavy concreteshielding
segmentedCsI(Tl) detector
segmentedCsI(Tl) detector
np
γ
Bea
mst
op
main magnet coils
1. Production of Low Energy Neutrons
2. Experiments with Low Energy Neutrons:
• Neutron Beta Decay
• Spectroscopy of gravitationally bound quantum states
• Weak Hadronic Interaction in neutron capture on hydrogen
3. Future research plans:
• G-2: Responsibility for trolley magnetic field measurement in g-2 at Fermilab
• nEDM: Purification of Helium, PULSTAR
• Nab: can be used with polarized neutron beam (abBA, PANDA), ~2020
• GRANIT: Use trapping mode to achieve ultimate accuracy
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Summary
• Fundamental physics with neutrons has many ways to make important discoveries
• Precision measurements take time
• Nab experiment promises to determine the coupling constants of weak interaction with high precision, allowing for Standard Model Tests and Searches for “Beyond the Standard Model”-physics
• GRANIT looks for new short-range interactions.