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Een precieze spectrumvorm meting van de toegelaten Gamow-Teller overgang 114In → 114Sn door middel van een plastic scintillator en een tracker voor elektronen / A precise spectrum shape measurement of the allowed Gamow-Teller transition 114In → 114Sn using a plastic scintillator and an electron tracker

  • De Keukeleere, Lennert; 111340;
Publication Date
Feb 20, 2024
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For decades long, the Standard Model has shown to be the best theory explaining many phenomena in particle, nuclear and astro- physics. Nevertheless, there are still a great number of observations, mainly in astrophysics, which deviate from SM predictions. This has lead many physicists to devise Beyond Standard Model (BSM) theories, in an attempt to account for these observations. Many of these BSM's include the existence of bosons with a mass at the TeV scale. As a result, two approaches exist to test these theories. First, in collider experiments, such as those carried out at LHC, these bosons are directly produced in high energy proton - proton collisions. Another way to test these BSM's, is by studying β-decay. This is facilitated by the small effects/currents of these exotic bosons on the decay observables, including correlations between momenta, energy and spin, of the contributing particles. Each observable is sensitive to specific currents. The shape of the beta spectrum, which is the topic of this research, is sensitive to two exotic currents, scalar and tensor, that are prohibited in the SM weak interaction. For allowed transitions, these currents introduce a correction term which is inversely proportional to the energy and the magnitude of the correction is known as the Fierz term. Depending on whether the decay is of the Fermi or Gamow-Teller type, the Fierz term is sensitive to the scalar or tensor current, respectively. In addition to BSM, the beta spectrum shape is a useful tool to probe SM effects. Since beta decay occurs between leptons and quarks, which are confined within a nucleon (protons or neutrons), it will be strongly affected by QCD interactions between the participating and spectator quarks. Among these effects is Weak Magnetism (WM), which introduces a correction term in the spectrum shape which is approximately linear in energy. For some particular transitions, a measurement of WM can provide a good test for the Conserved Vector Current hypothesis (CVC). Furthermore, the knowledge of WM for high mass neutron rich nuclei is crucial in the analysis of reactor anti-neutrino experiments. At the level of future experimental precision (1e-3), several higher order effects, such as radiative corrections and nuclear and atomic effects, come into play. Hence, the theoretical description of these higher order terms should be known with a better precision, preferably at least one order of magnitude (1e-4). This was recently carried out and published by colleagues, and naturally serves as a reference for the spectrum shape analysis. To study effects in the beta spectrum shape at a precision level that is needed to be competitive, a new spectrometer was designed and built. It consists of a 3D low-pressure gas electron tracker and a plastic scintillator used for triggering the data acquisition and recording the beta particle energy. The tracker is employed to reconstruct the path of the β electrons towards the scintillator, to infer the position of entry, and to catalogue the different event types. This eventually leads to a cleaner spectrum shape, which in turn results in a higher precision. In this work the newly designed spectrometer will be characterized, supported by Monte Carlo simulations. In addition, a spectrum shape measurement of the allowed Gamow-Teller transition In-114 → Sn-114 will be carried out, aiming to obtain a first extraction of the weak magnetism form factor in the high nuclear mass range and to obtain a first estimate of a confidence interval for the Fierz term from a spectrum shape. / status: published

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