The Antineutrino Electron Angular Correlation Coefficient a in the Decay of the Free Neutron

Transcription

1 The Antineutrino Electron Angular Correlation Coefficient a in the Decay of the Free Neutron Gertrud Konrad University of Mainz / Germany 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 e - n p + e EURONS Laser and Trap collaboration meeting April 11-15, 2007, Saariselkä, Finland

2 Outline Motivation Setup of the Neutron Decay Spectrometer aspect Status Report Outlook Summary

3 The Neutrino Electron Correlation and the Proton Spectrum in Neutron Decay The correlation coefficient a Differential decay probability: p + n ν e e - v ( dw 1 + a cos pe, pυ ) e c ν e e - e - Sensitivity of the Proton Spectrum to a: n p Proton kinetic energy is big n ν e p Proton kinetic energy is small Decay rate w(e) Proton spectrum for a = (PDG 2006) Proton spectrum for a = Proton kinetic energy E [ev]

4 Motivation to measure a Determination of the Coupling Constants g A, g V of the Weak Interaction Possible Tests of the Standard Model: Test of the Unitarity of the Cabbibo Kobayashi Maskawa-Matrix Search for Scalar and Tensor Interactions Search for Right-handed Currents Present experiments: Our aim: Δa / a Δa / a ~ 5% ~ 0.3%

5 Outline Motivation Setup of the Neutron Decay Spectrometer aspect Status Report Outlook Summary

6 MEPHISTO / FRM-II aspect - SPECTROMETER Detector Beam Stop Analyzing Plane 0 to 800 V Protons Neutrons Beam Line Decay volume Cold n-source of reactor

7 The Transmission Function Analyzing Plane p Adiabatic conversion p p p B A B A = 0.6 T Potential Barrier eu Magnetic Field Proton Trajectory B 0 = 3.0 T Decay Volume Decay rate w(e) Proton spectrum for a = (PDG 2006) Proton spectrum for a = Transmission U = 375V Proton kinetic energy E [ev] 1,0 0,8 0,6 0,4 0,2 0,0 Transmission function T U (E) Transmission function T U (E) in the adiabatic limit: 0 ; E < eu TU ( E) = 1 1 B0 BA ( 1 eu E) ; otherwise 1 ; E > eu 1 ( - B B ) A 0

8 Outline Motivation Setup of the Neutron Decay Spectrometer aspect Status Report: Latest Results of the beam FRM-II Outlook Summary

9 Proton Spectra Pulse height spectrum: After background subtraction: Electronic noise Proton peak Due to bad separation Proton spectrum looks ok; Count rate: ~ 500 Hz Signal to background ratio: > 10:1 Proton Signal not well separated from electronic noise

10 Background Spectra Pulse height spectrum: Proton-like peak: not stable with time leads to non-statistical fluctuation in the proton count rate additional systematic uncertainty limits our present accuracy

11 Extraction of a After background subtraction: Total Proton Count rate [s -1 ] N Integral Proton Spectrum: Simulation: a = (PDG2006) Simulation: a = +0.3 Experimental Data Preliminary! ( U ) T ( E) w( E)dE U Analyzing Plane Voltage U [V] Function of aspect is demonstrated Data Analysis still in progress

12 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

13 Outline Motivation Setup of the Neutron Decay Spectrometer aspect Status Report Outlook: Improvements for the next beam time Summary

14 Anti-Magnetic Screen: Design and First Results Magnetic Flux Density B [Gauss] Influence on the External Magnetic Field: ,1 Simulation w/o Anti-Magnetic Screen (F.Glück) Simulation w/o Anti-Magnetic Screen (FEMLAB) 0,01 Simulation with Anti-Magnetic Screen (FEMLAB) Experimental Data 1E-3 0, Radial Distance from Decay Volume r [m] Influence on the Internal Magnetic Field: influence quite small only the value of B 0 /B A changes Planned: Online-monitoring of B 0 /B A with 2 static NMR probes

15 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!!!