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