Transcript CINDY: The Proton Asymmetry in Neutron Decay

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Quick Time™ an d a
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Quick Time™ an d a
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Magnetic field for
“PANDA*”
*Proton Asymmetry in Neutron DecAy
For the SNS-FnPB Magnet meeting
Prepared by Tim Chupp
Quick Time™ an d a
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The proton Asymmetry
p
e
p
n
N+
Asymmetry:
e
n
N-
N+ - N__________
N+ + N-
C = k(A+B) =
=
C Pn A F (1-f) + Afalse
background
spin flip efficacy
analyzing power
neutron polarization
|l|
4k ________
1+3| l
|2
l=
gA
____
gV
k=0.27484
Standard Model
dW
_____________
dEedWedWn
JTW-57
= S(Ee) [1 + a
pe.pn
______
+
m
J
p
p
pexpn
b ___e + ___.(A____e + B____n + D _______
)]
EeEn Ee J
Ee
En
EeEn
C and l
|l|
C = k(A+B) = 4k ________
2
1+3| l |
PDG 2005
sx
sl ___
___
l
x
l
-1.2695±0.0029
a
-0.103±0.004
0.2688
A
-0.1173±0.0013
0.2403
B
+0.983 ±0.004
1.385
C
+0.238 ±0.011*
1.430
D
-0.0004±0.0006
f 180.06±0.0029
* Abele, 2005
dW
_____________
dEedWedWn
JTW-57
= S(Ee) [1 + a
pe.pn
______
+
m
J
p
p
pexpn
b ___e + ___.(A____e + B____n + D _______
)]
EeEn Ee J
Ee
En
EeEn
Rudimentary Layout
By
For adiabatic neutron spin transport
Bx
M2
M1
polarizer
neutrons
Spin
Flipper
analyzer
N0(v)
P(v)
TP(v)
Neutron spins tranported
Through detector
y
X
R
Detector
A(v)
TA(v)
z
L
Detector 1
Detector 2
Neutron beam
Into page
~
+30 kV
Detailed design work needed.
Uniform field B
~
V0
Allows proton
spectroscopy
General Design Issues
Goal: sx/x ~ 10-3 or better
• Neutron spin transported adiabatically from
polarizer to analyzer (through detector)
• Uniform B in decay region: mitigates proton
reflections from magnetic traps
• Proton orbit: d= 8 mm/B(T): 1-2T Needed (2 T for
emiT proton segment
• Electrostatic proton energy resolution desired:
requirements on B in proton drift region TBA
• Vacuum requirements: TBA
Neutron Polarization and Polarimetry
M2
M1
polarizer
neutrons
Spin
Flipper
N0(v)
P(v)
TP(v)
analyzer
X
A(v)
TA(v)
R
Detector
G±=S±D RExp= S( + ) + D( - ) =N0T1T2TP [G0+DPR]
M1= N0e1+B1
P/A
PSM
3He (60%)
Pn (5Å)
99.x%
80%
Tn
10%
30%
M2= N0T1T2TPTAe3 [ 1+PAR ] +B2
P2T
0.1
0.2
features
fixed; limited l bite
flip P3; P3 varies
Flipper: Ru= 1 (unflipped); Rf=F≈-1 (flipped) (-0.999 for AFP)
u
f
(M
_________
2 - M2 )
~
(M2u + M2f)
PA(1-F) (1-f2)
BR (1% need to know to 0.1%)
Detector
L
Detector 1
Detector 2
Neutron beam
Into page
~
+30 kV
V0
~
Detailed design work needed.
Allows proton
spectroscopy
Uniform field B
Ideal: A1=A2=1, e1=e2=1, f1=f2=0
Proton detection: e.g. emiT2
• with adiabatic spin transport J||B
• with adiabatic proton orbits, A=1
(scattering: resid. gas, baffles, etc.)
1000
Counts
100
10
1
0.1
20
40
60
Channel
80
Statistics
0.6
0.5
Probability
0.4
0.3
0.2
0.1
0.0
0
1
2
3
4
5
Decay s per pulse
rn ~ 103/cm3
We expect about 0.5 decays per pulse: about 2.5 million events per day.
0.1% precision requires < a few days
NOT STATISTICS LIMITED
Focus on systematics…
Systematics
N+ - N__________
N+ + N-
=
C Pn A F (1-f) + Afalse
background
spin flip efficacy
analyzing power
neutron polarization
Need to know: neutron polarization
analyzing power
spin flip efficiency
backgrounds
spin independent
spin dependent (false asymmetry)
e.g. False asymmetry from electrons emited from n-decay (BR)
- study of proton energy dependence
Noise, gain shifts, etc.
- flip 3He
C is INDEPENDENT of Pn, xy, L, tof, 3He, B, BR, … statistical power