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

Outline

Motivation

Setup of the Neutron Decay Spectrometer

aSPECT

Status Report

Outlook

Summary

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

Outline

Motivation

Setup of the Neutron Decay Spectrometer

aSPECT

Status Report

Outlook

Summary

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:

Summary

The neutron decay spectrometer aSPECT finished its first data taking period in 2006

In progress: Data Analysis

Improvements: Calibration Source, Proton Detector, Online-Monitoring, Kelvin Probe, Anti-Magnetic Screen

Thank you for your attention !!!