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, 3He) Spin flipping Polarimetry

Outlook

e

p

ν

e

p

ν N+ N-

Asymmetry: __________ = k(E)A Pn A F (1-f) + Afalse N+ - N- N+ + N-

background spin flip efficacy analyzing power neutron polarization–Averaged appropriately

Polarization���

€

d5ΓdEedΩedΩν

= G(Ee ) 1+ a p e ⋅ p ν

Ee Eν

+ b me

Ee

+ A σ n ⋅

p eEe

+ B σ n ⋅

p νEν

+ D σ n ⋅

p e × p ν( )

Ee Eν

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

A 0.1% measurement of A requires a 0.1% measurment of Pn

Polarization

P/A Pn (5Å) Tn P2ρ features PSM(XSM) 99.x% 10% 0.1 Pn~ 1; static He (60%) 80% 30% 0.2 flip P3; P3 varies

neutrons

Spin Flipper

M2

N0(v)

R A(v) TA(v)

M1 polarizer analyzer

€

P(v, r )T(v, r )

A 0.1% measurement of A requires a 0.1% measurment of <Pn>

Crossed Supermirror (XSM)���Kreuz et al.

Thick 3He analyser Pn=0.997±0.001 Schuman PRL 99, 191803 (2007)

0

0.2

0.4

0.6

0.8

1

Reflectivity

θ

No θc !

Si substrate B

θ

R

3He spin filter: n +3He _> 1H + 3H

σ0=5333 b

1.0

0.8

0.6

0.4

0.2

0.0

Tran

smiss

ion

1086420Distance (cm)

0.2 0.4 0.6 0.8 0.9Polarization

€

T± = e−n3σ 0t

v0v(1P3 )

neutrons

Spin Flipper

M2

N0(v)

R

M1 polarizer analyzer

€

P(v, r )T(v, r )

€

A(v, r )TA (v,

r )

3He: continuous polarization by Spin Exchange

• Glass/cell technology (GE180) • Hybrid Spin Exchange • Metastability exchange/compressors • Lasers • Magnetic boxes …

Huge Progress with 3He (NIST-Wisc/ILL/UVa/Jlab…)

Earl Babcock – FRMII (Juelich)

3He Polarizer Neutron-flux Limitations? 0.54

0.53

0.52

0.51

0.50

Pola

rizat

ion

120100806040200Time (in hrs)

Beam

off

4.5

hrs

Beam

off

1.5

hrs

Beam

off

for 0

.5 h

rs

Beam

off

2.5

hrs

Beam

off

5 hr

s

Beam

off

7 hr

s

Rb re

laxa

tion

rate

incr

ease

Lansce data shows effect on PRb

€

PRb =γ opt

γ opt + SΓA

€

ΔΓA ∝ φnSNS/NIST

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

Thick 3He analyser Pn=0.997±0.001 (0.0005 reasonable)

Polarimetry Summary •  Use opaque 3He and pulsed/chopped beam: measure , •  Pulsed beam (SNS): measure continuously

•  Chopped beam (NIST): monitor continuously – calibrate monitor

•  Neutron flux-3He issues not limiting •  Statistics not limiting •  Systematics: backgrounds (beta delayed neutrons), 3He AFP losses

•  LANSCE FP12 test beam available

€

P(v, r )

€

R(v, r )

~10-4 at LANSCE Should be ~constant vs tof at SNS

T. Soldner

Community 3He resources •  NIST/Wisconsin/MunichORNL/SNS/LANL/Mich/

Indiana/Hamilton: Gentile, Walker, Babcock, Tong… •  PLUS neutron scattering AND electron scattering communities

Cell production, lasers, optical pumping research, 3He in beam

SNS FP13: Apr 1, 2011 (M. Musgrave, N. Fomin et al.)

Flipper off

Flipper on

Summary���• Polarizer: 99.xx % polarization; 10% transmission • Flipper: 99.xx % effiecient • 0.1% measurement of <Pn>, spin flipper: CONSERVATIVE • Community has expertise and resources

Segmented Si detector

decay volume (field rB,DV·B0)

0 kV

0 kV

-30 kV

TOF region (field rB·B0)

Supermirror (3He)

AFP Spin

Flipper

3He Polarimeter

AFP