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+p+ n e-e- The correlation coefficient a The Neutrino Electron Correlation and the Proton Spectrum in Neutron Decay

Cabbibo-Kobayashi-Maskawa-Matrix Unitarity Condition B/D mesons Superallowed Fermi Decays Neutron Decay n → p + e - + ν e Pion Decay Kaon (Ke3) Decays K → e + π + ν e Kaon (Kμ2) Decays K → μ + ν μ Hyperons Test of the Standard Model

λ = g A /g V V u d τ n [PDG2004] A [PERKEO II] 0 + → 0 + Unitarity of the CKM Matrix Neutron Measurements needed: Neutron lifetime τ n Beta Asymmetry A(λ) Neutrino-Electron-Correlation a(λ) V us [Blucher et al., CKM 2005]  n [Serebrov05] A[PERKEOII] Situation 2004 New Ke3 and Kμ2 measurementsNew Neutron lifetime measurement [Marciano, Sirlin, 2005] Situation V ud : J. Hardy, Wed 16:30 Situation V us : P. de Simone, Wed 16:48 Situation τ n : J. Nico, Sat 9:00 ; λ = g A /g V

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

MEPHISTO Beam Line Neutrons Beam Stop aSPECT - SPECTROMETER Analyzing Plane 0 to 800 V Detector Protons Decay volume

Proton kinetic energy E [eV] decay rate w(E) Transmission function T U (E) Proton Spectrum for a = 0 Proton spectrum for a = (PDG2004) Transmission function T 375 V (E) The Transmission Function Potential Barrier eU Decay Volume Analyzing Plane Proton Trajectory Magnetic Field Transmission function T U (E) in the adiabatic limit: 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] Count rate [Hz/channel] Proton Spectra Count rate [Hz/channel]

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 field100%50%40%30%20% Δa/aΔa/a · %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] Count rate [Hz/channel] Extraction of a

Modification to measure the Proton Asymmetry Beam Line Neutrons Beam Stop aSPECT - SPECTROMETER Analyzing Plane 0 to 800 V Detector Protons Decay volume

θ Neutron SpinProbability of Proton Emission Present best (only) measurement: (integrated over all energies) N↓N↓ N↑N↑ Angular dependence of the proton emission: ,4 -0,3 -0,2 -0,1 0,0  Standard Model Proton Asymmetry α P,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