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EURONS Laser and Trap collaboration meeting April 11 - 15, 2007, Saariselkä, Finland
n
p+
e-e
The Antineutrino Electron Angular Correlation Coefficient ain the Decay of the Free Neutron
The aSPECT collaboration:Institut für Physik, Universität Mainz, Germany:
F. Ayala Guardia, S. Baeßler, M. Borg, L. Cabrera Brito, W. Heil, N. Luquero Llopis, R. Muñoz Horta, M. Orlowski, Ch. Palmer, Y. Sobolev, G. K.
Institut für Kernchemie, Universität Mainz, Germany:K. Eberhardt
Research Institute for Nuclear and Particle Physics, Budapest, Hungary: F. Glück
Physik-Department E18, TU München, Germany: H. Angerer, I. Konorov, G. Petzoldt, M. Simson, H.-F. Wirth, O. Zimmer
Forschungsneutronenquelle Heinz-Maier-Leibnitz, Garching, Germany: D. Rich
Gertrud KonradUniversity of Mainz / Germany
The Neutrino Electron Correlation and the Proton Spectrum in Neutron Decay
Sensitivity of the Proton Spectrum to a:
p+
n
e-
The correlation coefficient a
( )⎟⎠⎞
⎜⎝⎛ +∝
epp
cvadw e υ,cos1
Differential decay probability:
0 200 400 600
Proton spectrum for a = - 0.103 (PDG 2006)Proton spectrum for a = + 0.3
Proton kinetic energy E [eV]
Dec
ay ra
te w
(E)
n
e-
p
Proton kinetic energy is big
n
e-
p
Proton kinetic energy is small
eν
eν
eν
Determination of the Coupling Constants gA, gV of the Weak Interaction
Possible Tests of the Standard Model:Test of the Unitarity of the Cabbibo Kobayashi Maskawa-MatrixSearch for Scalar and Tensor InteractionsSearch for Right-handed Currents
Present experiments:Our aim:
Motivation to measure a
%5~/ aaΔ0.3%~/ aaΔ
Setup @ MEPHISTO / FRM-II
Beam LineNeutrons
Beam Stop
aSPECT - SPECTROMETER
Detector
Cold n-source of reactor
Analyzing Plane0 to 800 V
Decay volume
Protons
0 200 400 600
Proton spectrum for a = - 0.103 (PDG 2006)Proton spectrum for a = + 0.3
Proton kinetic energy E [eV]D
ecay
rate
w(E
)
The Transmission Function
( ) ( )( )
0
A 0
0 ;
1 1 1 ; otherwise
1 ; 1U A
E e
T E e E
E
B B
B B e
U
-
U
U
<⎧⎪
= − − −⎨⎪ >⎩
Transmission function TU(E) in the adiabatic limit:
Transmission function @ U = 375V0,0
0,2
0,4
0,6
0,8
1,0
Tran
smis
sion
func
tion
T U(E
)
ABPotential Barrier eU
Decay Volume
Analyzing Plane
Proton Trajectory
Magnetic Field
B0 = 3.0 T
BA = 0.6 T
Adi
abat
ic
conv
ersi
on
p⊥
||p
p⊥
||p
Outline
Motivation
Setup of the Neutron Decay Spectrometer
aSPECT
Status Report: Latest Results of the beam time
@ FRM-II
Outlook
Summary
Proton SpectraPulse height spectrum:
Proton peak
Electronic noise
Due to bad separation
After background subtraction:
Proton spectrum looks ok; Count rate: ~ 500 Hz Signal to background ratio: > 10:1Proton Signal not well separated from electronic noise
Background Spectra
Proton-like peak:not stable with timeleads to non-statisticalfluctuation in the proton count rate
⇒ additional systematic uncertainty limits our present accuracy
Pulse height spectrum:
Extraction of a
Function of aSPECT is demonstratedData Analysis still in progress …
After background subtraction:
0 100 200 300 400 500 600 7000
100
200
300
400
500 Simulation: a = −0.103 (PDG2006) Simulation: a = +0.3 Experimental Data
Analyzing Plane Voltage U [V]T
otal
Pro
ton
Cou
nt r
ate
[s-1]
Integral Proton Spectrum:
Preliminary !
( ) ( ) ( )dEEwETUN U∫∝
Systematic Uncertainties
Magnetic field measurements: Accurate Field Mapping in Decay Volume and Analyzing Plane
Electric Potential measurements: Accurate Voltage Measurement with Multimeter,
but: Surface Charges
Signal to Background Ratio: 10:1,
Background is measured, but: Instabilities
Residual Gas Influence calculations
Outline
Motivation
Setup of the Neutron Decay Spectrometer
aSPECT
Status Report
Outlook: Improvements for the next beam time
Summary
Anti-Magnetic Screen:Design and First Results
Influence on the Internal Magnetic Field:• influence quite small• only the value of B0/BA changes⇒ Planned: Online-monitoring of B0/BA
with 2 static NMR probes
0,1 1 101E-3
0,01
0,1
1
10
100
1000
10000
Mag
netic
Flu
x D
ensi
ty B
[Gau
ss]
Simulation w/o Anti-Magnetic Screen (F.Glück)Simulation w/o Anti-Magnetic Screen (FEMLAB)Simulation with Anti-Magnetic Screen (FEMLAB)Experimental Data
Radial Distance from Decay Volume r [m]
Influence on the External Magnetic Field: