Folie 1

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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

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The Neutrino Electron Correlation and the Proton
Spectrum in Neutron Decay
The correlation coefficient a
Sensitivity of the Proton Spectrum to a
3
Cabbibo-Kobayashi-Maskawa-Matrix
Unitarity Condition

• B/D mesons

4
New Ke3 and Kµ2 measurements
New Neutron lifetime measurement
0
.
9
8
0
0
.
9
7
5

• Neutron Measurements needed
• Neutron lifetime tn
• Beta Asymmetry A(?)
• Neutrino-Electron-Correlation a(?)

d
u
0? 0
V
Marciano, Sirlin, 2005
0
.
9
7
0
? gA/gV
0
.
9
6
5
-
1
.
2
8
-
1
.
2
7
-
1
.
2
6
-
1
.
2
5
? gA/gV
Situation Vud J. Hardy, Wed 1630 Situation Vus
P. de Simone, Wed 1648
Situation tn J. Nico, Sat 900
5

• A measurement of a is independent of possible
  unknown errors in A, systematics are entirely
  different
• An accuracy of ?a/a lt 1 is needed !

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aSPECT - SPECTROMETER
Analyzing Plane 0 to 800 V
Beam Stop
Beam Line
7
1
.
0
0
.
8
Proton Spectrum for a 0
0
.
6
Transmission function TU(E)
Proton spectrum for a -0.103 (PDG2004)
decay rate w(E)
Transmission function T375 V(E)
0
.
4
0
.
2
0
.
0
0
2
0
0
4
0
0
6
0
0
Proton kinetic energy E eV
8

• Proton spectrum looks ok, Countrate 500 Hz
• Signal to background ratio gt 101
• Electron Background to other Background gt 101
• Proton Signal not well separated from electronic
  noise

9

• Magnetic field measurements
• Electric Potential measurements
• Signal to Background Ratio 101, Background is
  measured
• Test of the adiabatic approximation, not
  analyzed yet
• Tests, not analyzed yet Background Subtraction,
  Rest gas
• Future Calibration Possible voltage offset

10

• ?a/a 13 in nearly 1 h of data taking time
• (Fulfills requirements for statistical accuracy)
• a according to Standard Model

11
aSPECT - SPECTROMETER
Analyzing Plane 0 to 800 V
Beam Stop
Neutrons
Beam Line
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Angular dependence of the proton emission

0,0
-0,1
Neutron Spin
Probability of Proton Emission
N?
-0,2
?
Proton Asymmetry aP,exp(E)

-0,3
N?
-0,4

Standard Model
0
100
200
300
400
500
600
700
Proton Kinetic Energy E eV
Present best (only) measurement (integrated over
all energies)
13

• 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 !!