Transcript Folie 1 - uni

The Proton Spectrum in Neutron Beta Decay:
First Results with the aSPECT Spectrometer
Stefan Baeßler
University of Mainz/Germany
The aSPECT collaboration:
•Institut für Physik, Universität Mainz, Germany:
F. Ayala Guardia, M. Borg, F. Glück, W. Heil, G. Konrad, N. Luquero Llopis,
R. Muñoz Horta, M. Orlowski, Y. Sobolev, S. B.
•Institut für Kernchemie, Universität Mainz, Germany:
K. Eberhardt
•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
The Neutrino Electron Correlation
and the Proton Spectrum in Neutron Decay
The correlation coefficient a
ep+
n

e
Sensitivity of the Proton Spectrum to a:

decay rate w(E)
v


dw  1  a cos pe , pe 
c


Spectrum for a = 0
Spectrum for a = 1
0
200
400
600
Proton kinetic energy E [eV]
Test of the Standard Model
Cabbibo-Kobayashi-Maskawa-Matrix
 d '   Vud Vus Vub   d 
  
  
s
'

V
V
V
cs
cb    s 
   cd
 b '  V
 b
V
V
td
tb   
   td
Unitarity Condition
Vud  Vus  Vub  1
2
2
2
• B/D mesons
• Superallowed Fermi Decays
• Neutron Decay
n → p + e - + νe
• Pion Decay
• Kaon (Ke3) Decays
K → e + π + νe
• Kaon (Kμ2) Decays
K → μ + νμ
• Hyperons
New
New Neutron
Ke3
and lifetime
Kμ22004
measurements
measurement
Situation
0.980
Unitarity
of the2005]
CKM Matrix
Vus [Blucher et al., CKM
Vud  1  Vus  Vub
2
2
0.975
Vud
Neutron Measurements needed:
0 +→ 0 +
[Marciano, Sirlin, 2005]
0.970
• Neutron lifetime τn
n [Serebrov 05]

 n 1  GF2Vud2 1  3 
2

; λ = gA/gV
• Beta Asymmetry A(λ)
τn [PDG2004]
A [PERKEO
[PERKEO II]
II]
A
0.965
-1.25
-1.26
-1.27
Situation Vud: J. Hardy, Wed 16:30
Situation Vus: P. de Simone, Wed 16:48
Situation τn: J. Nico, Sat 9:00
2
A  2
-1.28
λ = gA/gV
  Re 
1 3 
2
• Neutrino-Electron-Correlation a(λ)
a
1 
2
1 3 
2
Determination of λ
-1,255
Yerozolimskii,
1997
Stratowa, 1978
Liaud, 1997
Unitarity,
PDG2004
λ
-1,265
PERKEO, 1986
PERKEO II, 2002
-1,275
PERKEO II, 1997
Unitarity,
CKM2005
Unitarity,
Serebrov 05
Byrne, 2002
PERKEO II, 2005
(prelim)
-1,285
•A measurement of a is independent of possible unknown errors in A, systematics
are entirely different
•An accuracy of Δa/a < 1% is needed !
Setup @ MEPHISTO
Detector
aSPECT - SPECTROMETER
Analyzing Plane
0 to 800 V
Beam Stop
Protons
Neutrons
Beam Line
Decay volume
The Transmission Function
Analyzing Plane
BAA
1.0
Potential Barrier eU
Proton Trajectory
decay rate w(E)
Magnetic Field
0.8
Proton Spectrum for a = 0
Proton spectrum for a = -0.103 (PDG2004)
0.6
Transmission function T375 V(E)
0.4
Initial proton momentum along magnetic field
B0
Decay Volume
0
200
400
600
Proton kinetic energy E [eV]
Transmission function TU(E) in the adiabatic limit:
0
;
E  eU


TU E   1  1  B0 BA 1  eU E  ;
otherwise

1
; E  eU 1- BA B0 

0.2
0.0
Transmission function TU(E)
Initial proton momentum perpendicular to the magnetic field
Count rate [Hz/channel]
Count rate [Hz/channel]
Proton Spectra
Pulseheight [ADC channels]
• Proton spectrum looks ok, Countrate ~ 500 Hz
• Signal to background ratio > 10:1
• Electron Background to other Background > 10:1
• Proton Signal not well separated from electronic noise
Systematic Uncertainties
• Magnetic field measurements
• Electric Potential measurements
• Signal to Background Ratio 10:1, Background is measured
• Test of the adiabatic approximation, not analyzed yet:
Magnetic field 100%
Δa/a
10-5
50%
40%
30% 20%
4·10-
0.5%
4%
20%
4
• Tests, not analyzed yet: Background Subtraction, Rest gas
• Future Calibration: Possible voltage offset
Count rate [Hz/channel]
Extraction of a
Simulation: a = -0.103 (PDG2004)
Simulation: a = +0.3
Experimental Data
Proton Count rate [Hz]
250
200
150
100
N U    TU  E w  E  dE
50
0
0
Pulse Height [ADC channels]
• Δa/a = 13% in nearly 1 h of data taking time
(Fulfills requirements for statistical accuracy)
• “a” according to Standard Model
100
200
300
400
500
600
Analyzing Plane Voltage U [V]
700
Modification to measure the Proton Asymmetry
Detector
aSPECT - SPECTROMETER
Analyzing Plane
0 to 800 V
Beam Stop
Protons
Neutrons
Beam Line
Decay volume
Expected Proton Asymmetry
Angular dependence of the
proton emission:
Probability of
Proton Emission
N↑ θ
N↓
Proton Asymmetry αP,exp(E)
Neutron Spin
0,0
-0,1
-0,2
-0,3
-0,4
Standard Model
0
100
200
300
400
500
600
Proton Kinetic Energy E [eV]
Present best (only) measurement:
(integrated over all energies)
N  N
P  
 0.238(11)

N N
700
Summary
• The neutron decay spectrometer aSPECT just finished its first
data taking period.
• To be done: Data Analysis, Calibration Source
• Further experiments are possible
Thank you for your attention !!