[en] The aSPECT retardation spectrometer measures the β-ν angular correlation coefficient a in free neutron β-decay. This measurement can be used to determine the ratio (g_A)/(g_V) of the weak coupling constants, as well as to search for physics beyond the Standard Model. In spring/summer 2013 aSPECT had a successful beam time at the Institut Laue-Langevin. The goal of this beam time is to improve the current uncertainty of a from (Δa)/(a)∝5% to about 1%. The data analysis is in its final stage and will be finished soon. In order to achieve an uncertainty of 1%, the systematics of aSPECT have to be understood accordingly. This understanding is obtained from systematic tests and measurements of a with different parameter settings for the spectrometer during the beam time. Additionally, offline measurements have been performed to determine the effect on the systematics, e.g. work-function fluctuations of the electrodes, the magnetic field ratio of the spectrometer and detailed tests of the detector electronics. These measurements are used as input for sophisticated simulations of the spectrometer to understand and reduce the systematic uncertainties further. In this talk we will present an overview of aSPECT and its measuring principle. The beam time 2013 will be presented in detail, including the current status of the data analysis and preliminary results for systematic effects and their uncertainties.

[en] The aSPECT retardation spectrometer measures the β- anti ν_e angular correlation coefficient a in the β-decay of the free neutron. This measurement can be used to determine the ratio g_A/g_V of the weak coupling constants, as well as to search for physics beyond the Standard Model. In spring/summer 2013 aSPECT had a successful beam-time at the Institut Laue-Langevin in Grenoble (France). The goal of this run is to improve the current uncertainty of a from Δ a/a ∼ 5 % to about 1 %. To achieve this goal the systematics have to be understood accordingly. This is achieved on the one hand with different configurations during the beam-time (like different beam profiles or electrode settings), which is possible, as a statistical sensitivity of 1 % was reached within a few days. On the other hand the spectrometer and its systematics are precisely characterized with work function measurements of the electrodes and the experimental determination of the magnetic field ratio of the MAC-E filter. Furthermore, simulations of the field distribution and the particle transport in the spectrometer are used to quantify and reduce the systematic uncertainties of the measurements further. In this talk we present an overview of the systematics of aSPECT and their investigations.

[en] The aSPECT retardation spectrometer measures the electron antineutrino angular correlation coefficient a in free neutron decay with high precision. This measurement can be used to determine the ratio of (gA)/(gV) of the weak coupling constants, as well as to search for physics beyond the Standard Model. Currently a is determined with a precision of (Δa)/(a)∼5 %, whereas aSPECT aims for a precision of (Δa)/(a)∼ 0.3 %. To achieve this precision a new detector electronics has been developed and implemented, which avoids a previously observed saturation effect. Also, the main electrode has been redesigned and their surface treatment/coating has been improved. Compared to the previous electrode this leads to a smaller fluctuation of the work function, hence to a more precise determination of the potential. Furthermore, the collimation system for the neutron beam has been coated with a conductive layer to avoid a potential charging of the system. These and further improvements are presented and discussed in this talk.

No abstract available

[en] The standard model of the electroweak interaction is tested with ever increasing precision by non-accelerator experiments, e.g. using beta decay. The precision of these experiments has reached a point where the variation of the work function of the materials used for electrodes starts to limit the sensitivity. We investigate these variations of the work function for the aSPECT and the KATRIN experiments using a scanning Kelvin probe and the photoelectric effect. In 2013 aSPECT had a successfull beam time at the cold neutron beam line PF1b at the Institut Laue Langevin to determine the ratio of the weak coupling constants g_A/g_V. KATRIN is being set-up at the Karlsruhe Institute for Technology to measure the absolute mass of the electron-antineutrino. In order to achieve the sensitivity goals of these experiments the variation of the work function of their electrodes in time and space have to be known at the level of 10 meV. Systematic studies of the work function of various surfaces covered with a thin gold layer are presented.

[en] For a wide range of high-precision experiments in physics, well-defined electric potentials for achieving high measurement accuracies are required. An accurate determination of the electric potential is crucial for the measurement of the neutrino mass (KATRIN) as well as the measurement of the e"- anti ν_e correlation coefficient a in free neutron decay (aSPECT). Work function fluctuations on the electrodes lead to uncertainties in the distribution of the electric potential. For aSPECT, the electric potential has to be known at an accuracy of 10 mV. However, due to the patch effect of gold, work function fluctuations of several 100 meV can occur. Therefore, the work function distributions of the gold-plated electrodes have been measured using a Kelvin probe. Furthermore, the change of work function distributions over time as well as the influence of relative humidity on the work function measurement have been investigated. For aSPECT, the work function distributions of the gold-plated electrodes have been measured using a Kelvin probe. Due to the patch effect of gold, work function fluctuations of up to 160 meV occur. This would lead to a significant uncertainty of the potential barrier, which should be known at an accuracy of 10 mV. Furthermore, the change of work function distributions over time as well as the influence of relative humidity on the work function measurement have been investigated.

[en] The detection of low energy protons is a common problem in fundamental neutron physics. Neutrons decay into an electron, an antineutrino, and a proton. The latter has a rather low energy between 0 and ∝750 eV. On the one hand, this low energy allows to use electric and magnetic fields to guide and analyse the protons with high precision. On the other hand, protons with such low energies cannot be directly detected. In experiments this is typically circumvented by putting the detectors to high voltage to post-accelerate the protons. However, this may lead to problems like penning discharges and even destruction of detectors and read-out electronics by high voltage breakdowns. Silicon drift detectors (SDDs) are a good choice for the detection of low energy protons. They have superior noise characteristics compared to a conventional semiconductor PIN diode detector and thus allow to reduce the acceleration voltage to about 10 to 15 kV. %SDDs are depleted sidewards and only a small anode is used for readout, thus the sensitive volume of the detector is decoupled from the area read out. For both aSPECT (retardation spectrometer for proton spectrum measurement) and HOPE (magnetic trap for neutron lifetime measurement) an array of 3 x 3 SDDs with an active surface of 900 mm² has been developed. In the talk the detector array, as well as possible read-out electronics are presented.

[en] High precision experiments at low energies are used in several areas of fundamental physics. Examples are, a.o., high precision beta decay experiments and experiments using Penning traps for mass measurements or for g-factor measurements. The knowledge of the potentials and potential differences inside these experiments is crucial to achieve the desired sensitivities. However, the potentials are modified by the work function of the electrodes, which can show fluctuations of of several hundred meV, both spatially and temporally. For the low energy precision experiments aSPECT and KATRIN we have commissioned and studied a scanning Kelvin probe system to investigate the work function fluctuations of gold surfaces on different substrates. Since the Kelvin probe is a relative method, also photoelectron spectroscopy was performed additionally to obtain information on the absolute work functions. The temporal stability of the work functions of the surfaces was also tested, as well as the influence of standard cleaning procedures for ultra-high vacuum applications and bake-out. This poster presents the results of these measurements.