Neutron Polarization and polarimetry for precision neutron decay measurments Tim Chupp University of Michigan For the Nab/abBA/PANDA collaboration Outline: The goal: control <J> and measure to <0.1% Polarization techniques (PSM, 3 He) Spin flipping Polarimetry Outlook
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Neutron Polarization and polarimetry for precision neutron decay
measurments Tim Chupp
University of Michigan For the Nab/abBA/PANDA collaboration
Outline: The goal: control <J> and measure to <0.1%
Also a slow (100s) increase Not fully understood Requires increased laser power (e.g. few times) Double cell – T Gentile
T1>100 h; P3~46% (in progress)
SRb = 10.8 SK = 6
[ion] or [e]
Neutron Beam
3He (60%)
XSM
Neutron density Fluence
Figure of Merit (P2dρn/dλ)
Polarization Summary • Both approaches can be perfected for abBA/PANDA • 3He provides Pα(tof) (Bowman and Pentilla) • Supermirror design for m=3+ guides required • Magnetic field accomodations for spin transport • Rate estimates based on 0.1 of Nab flux (XSM): 75 live days for 0.1% measurement of A
asymmetry
The fast adiabatic spin flipper
€
i dψdt
= − µ ⋅ B ( )ψ = −
µ+B− + µ−B+
2+ µzBz
⎛
⎝ ⎜
⎞
⎠ ⎟ ψ
€
ψ =ψ+
ψ−
⎡
⎣ ⎢
⎤
⎦ ⎥
€
B± =B12e±iω 0t
€
Bz = β0t = β0zt
€
i ddt
ψ+
ψ−
⎡
⎣ ⎢
⎤
⎦ ⎥ =
µzβ0tB12eiω 0t
B12e− iω0t µzβ0t
⎡
⎣
⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥
ψ+
ψ−
⎡
⎣ ⎢
⎤
⎦ ⎥
1.0
0.8
0.6
0.4
0.2
0.0
ψ±
10008006004002000time
z=z’
x’
z=z’
x’
z=z’
x’
z=z’
x’
z=z’
x’
99.9x% “efficient” AND we can measure it!
RF ON
Spatial gradient RF
AFP of 3He Neutron Polarimetry – thick 3He
1.0
0.8
0.6
0.4
0.2
Anal
yzin
g Po
wer
8642n3tσa
1.00
0.98
0.96
0.94
0.92
0.90
Anal
yzin
g Po
wer
8.07.57.06.56.05.55.0n3tσa
λ=5 Å
Opaque Analyzer: For n3tσa large enough (1-A) small enough (Zimmer) Characterize Polarizer AND Flipper
40%
60%
neutrons P(v) TP(v)
Spin Flipper
N0(v)
R A(v) TA(v)
X
Detector
polarizer analyzer Detector
3He Spin Filter Spin Flipper
n+p ___> d + γ (@LANSCE) 3He and Pn test:
Booboo is the Cell
GE-180 Glass (boron free)
12 cm
Flipper
FP-12 P(v) TP(v)
M3
N0(v) R A(v) TA(v)
M2 M1
Experiment
M1= N0ε1+B1 M2= N0T1TP ε2+B2
M2(0)/M2(out) = T0 M2(P)/M2(0) = cosh αPPP
(Coulter et al. NIMA 288, 463 (1989)
TA/P=T0cosh αA/PPA/P T0=exp(-αA/P- αgl-…)
P/A=tanh αA/PPA/P
2.0
1.5
1.0
0.5
0.0
Sig
nal (
arb
units
)
642Wavelength (Å)
M2 Cell Out M2 Polarized M2 Unpolarized
normalized to M1 Bragg edges (Al)
Pulsed Beam Neutron Polarimetry
npdgamma FP12
Flipper
FP-12 P(v) TP(v)
M3
N0(v) R A(v) TA(v)
M2 M1
Experiment
M1= N0ε1+B1 M2= N0T1TP ε2+B2
TA/P=T0cosh αA/PPA/P T0=exp(-αA/P- αgl-…)
P/A=tanh αA/PPA/P
Pulsed Beam Neutron Polarimetry
npdgamma FP12
Offsets/Backgrounds
0.6
0.4
0.2
M2(
0)/M
2(ou
t)
642wavelength(Å)
-4-2024
x10-3
2.5
2.0
1.5
1.0
M2(
P)/M
2(0)
642wavelength (Å)
-4-2024
x10-3
Residual (10-3)
Residual (10-3)
coshαPPP _> Pn=tanhαPPP
expαP
Demonstrates understanding at 10-3 level; also LANSCE FP12 available