Search for Axion-Like Dark Matter and Exotic Yukawa-Like Interaction

Despite the undoubted success of the Standard Model of particle physics, it fails to answer many longstanding questions, such as the strong CP problem, the observed effects of dark matter, and the baryon asymmetry in our universe. Many theoretical models that try to answer those questions require new particles and gauge bosons which have to be verified or excluded experimentally. Here, we present the search for two such candidates. The first candidate is an ultralight pseudo-scalar particle called axion or axion-like particle (ALP). We searched for them using a Ramsey-type apparatus for cold neutrons. A hypothetical coupling of ALPs to gluons would manifest itself in a neutron electric dipole moment signal oscillating in time. Twenty-four hours of data have been analyzed in a frequency range from 23 μHz to 1 kHz, and no significant oscillating signal has been found. The usage of present dark-matter models allows for constraining the coupling of ALPs to gluons in the mass range from 10−19 to 4 × 10−12 eV. This extends the previously tested range by over three orders of magnitude. The best limit of CG / fama = 2.7 × 1013 GeV−2 (95% C.L.) is reached in the mass range from 2 × 10−17 to 2 × 10−14 eV. Together with the results of two other laboratory experiments, a large region of the ALP-gluon coupling parameter space could be excluded. The second candidate is an axial-vector gauge boson that could mediate a Yukawalike interaction in the millimeter range between Standard Model fermions like protons, neutrons, and electrons. We built a tabletop experiment that applies Ramsey’s technique to the proton spins of hydrogen in water. We performed a proof-of-principle search for this exotic interaction for the first time using protons as probe particles. Even though we could not yet detect or constrain the existence of such an interaction with statistical arguments, developments of the apparatus are underway that will allow to do this in the near future. With the apparatus we additionally investigated radio-frequency effects like the Bloch-Siegert shift and dressed spin states. This is to our knowledge the first time that the dressed spin states of protons were measured.Trotz des unbestrittenen Erfolgs des Standardmodells der Teilchenphysik scheitert es seit langem bei der Beantwortung einiger Fragen. Dazu gehören das Problem der fehlenden CP-Verletzung in der starken Wechselwirkung (engl.: strong CP problem), eine fehlende Erklärung für die beobachteten Effekte der Dunklen Materie und die Asymmetrie zwischen Materie und Antimaterie im Universum. Viele theoretische Modelle, die versuchen diese Fragen zu beantworten, erfordern neue Teilchen und Wechselwirkungen. Diese müssen experimentell nachgewiesen oder ausgeschlossen werden. In dieser Arbeit beschreiben wir die Suche nach zwei möglichen Kandidaten. Der erste Kandidat ist ein ultraleichtes, pseudoskalares Teilchen, das Axion oder axionähnliches Teilchen (engl.: axion-like particle, ALP) genannt wird. Danach suchten wir mit kalten Neutronen und einer Ramsey-Apparatur. Die hypothetische Wechselwirkung der ALPs zu den Gluonen würde in einem zeitlich oszillierenden elektrischen Dipolmoment des Neutrons resultieren. Wir analysierten Daten, die über einen Zeitraum von 24 Stunden gemessen wurden. In einem Frequenzbereich zwischen 23 μHz und 1 kHz konnten wir kein oszillierendes Signal feststellen. Mittels aktueller Modelle der Dunklen Materie konnten wir jedoch die Wechselwirkung zwischen den ALPs, mit Massen zwischen 10−19 und 4×10−12eV, und den Gluonen einschränken. Dies erweiterte den bisher untersuchten Massenbereich um über einen Faktor Tausend. Der beste Grenzwert der Wechselwirkung von CG/fama = 2.7 × 1013GeV−2 (95% KI) konnte für Massen zwischen 2 × 10−17 und 2 × 10−14eV bestimmt werden. Zusammen mit den Resultaten zweier weiterer Laborexperimente kann die Wechselwirkung der ALPs zu Gluonen somit in einem grossen Teil des Phasenraums ausgeschlossen werden. Der zweite Kandidat ist axialvektorielles Eichboson, das eine Yukawa-ähnliche Kraft zwischen Standardmodell-Fermionen wie Protonen, Neutronen und Elektronen auf der Längenskala von Millimetern vermitteln könnte. Wir entwickelten und bauten ein Kleinstexperiment, welches die Ramsey-Methode an den Spins der Wasserstoff-Protonen im Wasser anwendet. Wir untersuchten die Machbarkeit der Messung dieser exotischen Wechselwirkung. Zum ersten Mal wurden für eine solche Suche Protonen verwendet. Obwohl wir die Existenz dieser Kraft nicht nachweisen oder statistisch signifikant einschränken konnten, wird eine Erweiterung des Experiments dies in naher Zukunft ermöglichen. Wir untersuchten zudem Hochfrequenz-Effekte wie die Bloch-Siegert Frequenzverschiebung und die verkleideten Spin-Zustände (engl.: dressed spin states). Unseres Wissens wurden letztere zum ersten Mal an Protonen gemessen

Passive alignment stability and auto-alignment of multipass amplifiers based on Fourier transforms

The stability properties of Fourier-based multipass amplifier to misalignments (tilts) of its optical components has been investigated. For this purpose, a method to quantify the sensitivity to tilts based on the amplifier small signal gain has been elaborated and compared with measurements. To improve on the tilt stability by more than an order of magnitude a simple auto-alignment system has been proposed and tested. This study, combined with other investigations devoted to the stability of the output beam to variations of aperture and thermal lens effects of the active medium, qualifies the Fourier-based amplifier for the high-energy and the high-power sector.Comment: 10 pages, 11 figure

A Ramsey apparatus for proton spins in flowing water

We present an apparatus that applies Ramsey's method of separated oscillatory fields to proton spins in water molecules. The setup consists of a water circuit, a spin polarizer, a magnetically shielded interaction region with various radio frequency elements, and a nuclear magnetic resonance system to measure the spin polarization. We show that this apparatus can be used for Rabi resonance measurements and to investigate magnetic and pseudomagnetic field effects in Ramsey-type precision measurements with a sensitivity below 100 pT

New Limit on Axion-Dark-Matter using Cold Neutrons

We report on a search for axion-like dark matter using a Ramsey-type apparatus for cold neutrons. A hypothetical axion-gluon-coupling would manifest in a neutron electric dipole moment signal oscillating in time. Twenty-four hours of data have been analyzed in a frequency range from 23 $\mu$Hz to 1 kHz, and no significant oscillating signal has been found. The usage of present axion and dark-matter models allowed excluding the coupling of axions to gluons in the mass range from $1.5 \times 10^{-20}$ to $6.6 \times 10^{-13}$ eV with a best sensitivity of $C_G / f_a m_a = (3.1 \pm 0.2) \times 10^{12}$ GeV$^{-2}$ (95% C.L.)

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How Idea Creativity and Hedonic Value Influence Project Success in Crowdfunding

Crowdfunding has become a viable source of funding for a variety of projects during the last years. More and more music, creative and artistic but also entrepreneurial projects search funding through the crowd. Although first project characteristics with an impact on a project\u27s funding success have been identified, qualitative variables within crowdfunding projects have mostly remained uncovered. With that in mind, this paper empirically examines the influence of idea creativity and hedonic value on projects\u27 funding success. We assessed 108 projects from 20 platforms in order to measure the extent of these two dimensions. Our broad approach allowed us to compare results for the different types of crowdfunding. We find that idea creativity and hedonic value can have varying impacts on projects\u27 funding success depending on the type of crowdfunding

The pulsed neutron beam EDM experiment

We report on the Beam EDM experiment, which aims to employ a pulsed cold neutron beam to search for an electric dipole moment instead of the established use of storable ultracold neutrons. We present a brief overview of the basic measurement concept and the current status of our proof-of-principle Ramsey apparatus