Post on 18-Jan-2016
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
Stefan Baeßler University of Mainz/Germany
The Proton Spectrum in Neutron Beta Decay: First Results with the aSPECT Spectrometer
Sensitivity of the Proton Spectrum to a:p+
n
e-
e
The correlation coefficient a
epp
c
vadw e ,cos1
The Neutrino Electron Correlation and the Proton Spectrum in Neutron Decay
0 200 400 600
Spectrum for a = 0
Spectrum for a = 1
deca
y ra
te w
(E)
Proton kinetic energy E [eV]
cd cs cb
td
ud
td tb
us ubd ' d
s ' s
b ' b
V V V
V V V
V V V
Cabbibo-Kobayashi-Maskawa-Matrix
Unitarity Condition
12
ub
2
us
2
ud VVV
• 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
Test of the Standard Model
-1.28-1.27-1.26-1.25
λ = gA/gV
0.965
0.970
0.975
0.980
Vud
τn [PDG2004]A [PERKEO II]
0+→ 0+
ud u
2
u
2
s b1V V V Unitarityof the CKM Matrix
Neutron Measurements needed:
• Neutron lifetime τn
• Beta Asymmetry A(λ)
• Neutrino-Electron-Correlation a(λ)
21 2n ud
2 1 3FVG
2
2
Re2
1 3A
2
2
1
1 3a
Vus [Blucher et al., CKM 2005]
n [Serebrov 05]
A [PERKEO II]
Situation 2004New Ke3 and Kμ2 measurementsNew Neutron lifetime measurement
[Marciano, Sirlin, 2005]
Situation Vud: J. Hardy, Wed 16:30
Situation Vus: P. de Simone, Wed 16:48
Situation τn: J. Nico, Sat 9:00
; λ = gA/gV
•A measurement of a is independent of possible unknown errors in A, systematics are entirely different
•An accuracy of Δa/a < 1% is needed !
Determination of λ
PERKEO II, 1997
PERKEO II, 2002
Yerozolimskii, 1997
PERKEO, 1986
Liaud, 1997
Unitarity,CKM2005
Unitarity,Serebrov 05
Unitarity,PDG2004
Stratowa, 1978
Byrne, 2002
PERKEO II, 2005 (prelim)
-1,285
-1,275
-1,265
-1,255
λ
Setup @ MEPHISTO
Beam Line
Neutrons
Beam Stop
aSPECT - SPECTROMETER
Analyzing Plane0 to 800 V
Detector
Protons
Decay volume
0 200 400 600Proton kinetic energy E [eV]
deca
y ra
te w
(E)
0.0
0.2
0.4
0.6
0.8
1.0
Tra
nsm
issi
on f
unct
ion
TU(E
)
Proton Spectrum for a = 0Proton spectrum for a = -0.103 (PDG2004)
Transmission function T375 V(E)
The Transmission Function
ABPotential Barrier eU
Decay Volume
Analyzing Plane
Proton Trajectory
Magnetic Field
0A
0
1;1
otherwise;111
;0
BB-eU E
EeUBB
eUE
ET AU
Transmission function TU(E) in the adiabatic limit:
0B
AB
Initial proton momentum perpendicular to the magnetic field
Initial proton momentum along magnetic field
• 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
Pulseheight [ADC channels]C
oun
t ra
te [
Hz/
chan
nel
]
Proton SpectraC
oun
t ra
te [
Hz/
chan
nel
]
• Magnetic field measurements
• Electric Potential measurements
• Signal to Background Ratio 10:1, Background is measured
• Test of the adiabatic approximation, not analyzed yet:
• Tests, not analyzed yet: Background Subtraction, Rest gas
• Future Calibration: Possible voltage offset
Magnetic field 100% 50% 40% 30% 20%
Δa/a 10-5 4·10-4 0.5% 4% 20%
Systematic Uncertainties
• Δa/a = 13% in nearly 1 h of data taking time
(Fulfills requirements for statistical accuracy)
• “a” according to Standard Model
Pulse Height [ADC channels]
Cou
nt
rate
[H
z/ch
ann
el]
Extraction of a
0 100 200 300 400 500 600 7000
50
100
150
200
250
Experimental Data
Simulation: a = -0.103 (PDG2004) Simulation: a = +0.3
Pro
ton
Co
un
t ra
te [
Hz]
Analyzing Plane Voltage U [V]
UN U T E w E dE
Modification to measure the Proton Asymmetry
Beam Line
Neutrons
Beam Stop
aSPECT - SPECTROMETER
Analyzing Plane0 to 800 V
Detector
Protons
Decay volume
θ
Neutron Spin Probability of Proton Emission
)11(238.0P
NN
NNPresent best (only) measurement:
(integrated over all energies)
N↓
N↑
Angular dependence of the proton emission:
0 100 200 300 400 500 600 700
-0,4
-0,3
-0,2
-0,1
0,0
Standard Model
Pro
ton
Asy
mm
etry
αP
,exp
(E)
Proton Kinetic Energy E [eV]
Expected Proton Asymmetry
• 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 !!
Summary