Magnetic field for PANDA* * P roton A symmetry in N eutron D ec A y - - PowerPoint PPT Presentation

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Magnetic field for “PANDA*”

*Proton Asymmetry in Neutron DecAy

For the SNS-FnPB Magnet meeting Prepared by Tim Chupp

The proton Asymmetry

p ν e p ν e N- N+ Asymmetry: __________ = C Pn A F (1-f) + Afalse N+ - N- N+ + N-

background spin flip efficacy analyzing power neutron polarization

C = k(A+B) = 4k ________

|λ| 1+3| λ |2

Standard Model λ = ____ gA gV

k=0.27484

_____________ = S(Ee) [1 + a ______ + b ___ + ___.(A____ + B____ + D _______ )]

dEedΩedΩν EeEn Ee J Ee Eν EeEν dW pe.pn me J pe pν pexpν

JTW-57

C and λ

C = k(A+B) = 4k ________

|λ| 1+3| λ |2

PDG 2005

σλ λ

___ ___

λ -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 φ 180.06±0.0029 σx x

* Abele, 2005 _____________ = S(Ee) [1 + a ______ + b ___ + ___.(A____ + B____ + D _______ )]

dEedΩedΩν EeEn Ee J Ee Eν EeEν dW pe.pn me J pe pν pexpν

JTW-57

Rudimentary Layout

neutrons P(v) TP(v)

Spin Flipper

M2 N0(v) R A(v) TA(v) M1 X Detector z y polarizer analyzer Bx By For adiabatic neutron spin transport

Neutron spins tranported Through detector

V0

~ ~ ~ ~

+30 kV

Neutron beam Into page

L Detector 2 Detector 1

Detailed design work needed.

Allows proton spectroscopy

Uniform field B

General Design Issues

Goal: σx/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

neutrons P(v) TP(v)

Spin Flipper

M2 N0(v) R A(v) TA(v) M1 X polarizer analyzer Detector

RExp= Σ( + ) + ∆( - ) =N0T1T2TP [Γ0+∆PR] Γ±=Σ±∆ M1= N0ε1+B1 M2= N0T1T2TPTAε3 [ 1+PAR ] +B2 P/A Pn (5Å) Tn P2T features PSM 99.x% 10% 0.1 fixed; limited λ bite

3He (60%)

80% 30% 0.2 flip P3; P3 varies Flipper: Ru= 1 (unflipped); Rf=F≈-1 (flipped) (-0.999 for AFP)

_________ ~ PA(1-F) (1-f2)

(M2

u - M2 f)

(M2

u + M2 f)

BR (1% need to know to 0.1%)

Detector

V0

~ ~ ~ ~

+30 kV

Neutron beam Into page

Detector 2 L

Detailed design work needed.

Allows proton spectroscopy

Detector 1

Uniform field B Ideal: A1=A2=1, ε1=ε2=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.)

0.1 1 10 100 1000 Counts 80 60 40 20 Channel

Statistics

0.6 0.5 0.4 0.3 0.2 0.1 0.0 Probability 5 4 3 2 1 Decays per pulse

ρn ~ 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

__________ = C Pn A F (1-f) + Afalse

N+ - N- N+ + N-

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