Prof. Dr. Markus Oberthaler
Phone: +49 6221 54 5170
markus.oberthaler@kip.uni-heidelberg.de
You can find the lastest results of the project in:
Antihydrogen atoms with K or sub-K temperature are a powerful tool to precisely probe the validity of fundamental physics laws and the design of highly sensitive experiments needs antihydrogen with controllable and well defined conditions. We present here experimental results on the production of antihydrogen in a pulsed mode in which the time when 90% of the atoms are produced is known with an uncertainty of ~250 ns. The pulsed source is generated by the charge-exchange reaction between Rydberg positronium atoms—produced via the injection of a pulsed positron beam into a nanochanneled Si target, and excited by laser pulses—and antiprotons, trapped, cooled and manipulated in electromagnetic traps. The pulsed production enables the control of the antihydrogen temperature, the tunability of the Rydberg states, their de-excitation by pulsed lasers and the manipulation through electric field gradients. The production of pulsed antihydrogen is a major landmark in the AE $$\bar{g}$$ ? IS experiment to perform direct measurements of the validity of the Weak Equivalence Principle for antimatter.
A setup with three equally spaced transmission gratings can be described as a moiré deflectometer in the classical regime and as a Talbot–Lau interferometer in the quantum regime. We successfully operate such a three-grating device with a de Broglie wavelength span of more than two orders of magnitude (20 fm to 2.2 pm), employing different particles such as xenon, krypton, argon, helium, and hydrogen. With that we directly observe the transition from the classical description with fast xenon atoms, to the characteristic quantum behaviour of the Talbot–Lau interferometer using hydrogen atoms with correspondingly long de Broglie wavelength. The systematic study of the interference pattern gives important insights in the feasibility of a proton or antiproton interferometer with this setup.
Producing positronium (Ps) in the metastable 2(3)S state is of interest for various applications in fundamental physics. We report here on an experiment in which Ps atoms are produced in this long-lived state by spontaneous radiative decay of Ps excited to the 3(3)P level manifold. The Ps cloud excitation is obtained with a UV laser pulse in an experimental vacuum chamber in presence of guiding magnetic field of 25 mT and an average electric field of 300 V cm(-1). The evidence of the 2(3)S state production is obtained to the 3.6 sigma level of statistical significance using a novel analysis technique of the single-shot positronium annihilation lifetime spectra. The dynamic of the Ps population on the involved levels has been studied with a rate equation model.
The Talbot-Lau interferometer is a proven tool to perform measurements in the near-field regime. It has been extensively used for investigating the wave nature of electrons, atoms, and complex organic molecules. However, when designing devices with high geometrical acceptances, which would be desirable when dealing with low-intensity sources of particles, the alignment requirements become much more stringent. Furthermore, if the particles are charged, the influence of external fields becomes quickly non-negligible when increasing the length of the device. This paper focuses on both the geometric and physical constraints of an ion Talbot-Lau interferometer, with emphasis on the scaling of such constraints with the size of the device. Mathematical formulas which set limits on the critical parameters are derived and applied to a test setup for protons.
A new contact-free approach for measuring simultaneously electric and magnetic field is reported, which considers the use of a low energy ion source, a set of three transmission gratings and a position sensitive detector. Recently tested with antiprotons (Aghion et al., 2014) [1] at the CERN Antiproton Decelerator facility, this paper extends the proof of principle of a moiré deflectometer (Oberthaler et al., 1996) [2] for distinguishing electric from magnetic fields and opens the route to precision measurements when one is not limited by the ion source intensity. The apparatus presented, whose resolution is mainly limited by the shot noise is able to measure fields as low as 9 mVm−1 Hz−1/2 for electric component and 100 μG Hz−1/2 for the magnetic component. Scaled to 100 nm pitch for the gratings, accessible with current state-of-the-art technology [3], the moiré fieldmeter would be able to measure fields as low as 22 μVm−1 Hz−1/2 and 0.2 μG Hz−1/2.
We demonstrate the laser excitation of the n=3 state of positronium (Ps) in vacuum. A combination of a specially designed pulsed slow positron beam and a high-efficiency converter target was used to produce Ps. Its annihilation was recorded by single-shot positronium annihilation lifetime spectroscopy. Pulsed laser excitation of the n=3 level at a wavelength λ≈205 nm was monitored via Ps photoionization induced by a second intense laser pulse at λ=1064 nm. About 15% of the overall positronium emitted into vacuum was excited to n=3 and photoionized. Saturation of both the n=3 excitation and the following photoionization was observed and explained by a simple rate equation model. The positronium's transverse temperature was extracted by measuring the width of the Doppler-broadened absorption line. Moreover, excitation to Rydberg states n=15 and 16 using n=3 as the intermediate level was observed, giving an independent confirmation of excitation to the 3P3 state.
The main goal of the \{AEgIS\} experiment at \{CERN\} is to test the weak equivalence principle for antimatter. We will measure the Earth's gravitational acceleration g ¯ with antihydrogen atoms being launched in a horizontal vacuum tube and traversing a moiré deflectometer. We intend to use a position sensitive device made of nuclear emulsions (combined with a time-of-flight detector such as silicon μ - strips ) to measure precisely their annihilation points at the end of the tube. The goal is to determine g ¯ with a 1% relative accuracy. In 2012 we tested emulsion films in vacuum and at room temperature with low energy antiprotons from the \{CERN\} antiproton decelerator. First results on the expected performance for \{AEgIS\} are presented
"Abstract The \{AEgIS\} experiment is an international collaboration with the main goal of performing the first direct measurement of the Earth's gravitational acceleration on antimatter. Critical to the success of \{AEgIS\} is the production of cold antihydrogen ( H ¯ ) atoms. The \{FACT\} detector is used to measure the production and temperature of the H ¯ atoms and for establishing the formation of a H ¯ beam. The operating requirements for this detector are very challenging: it must be able to identify each of the thousand or so annihilations in the 1 ms period of pulsed H ¯ production, operate at 4 K inside a 1 T solenoidal field and not produce more than 10 W of heat. The \{FACT\} detector consists of two concentric cylindrical layers of 400 scintillator fibres with a 1 mm diameter and a 0.6 mm pitch. The scintillating fibres are coupled to clear fibres which transport the scintillation light to 800 silicon photomultipliers. Each silicon photomultiplier signal is connected to a linear amplifier and a fast discriminator, the outputs of which are sampled continuously by Field Programmable Gate Arrays (FPGAs). In the course of the developments for the \{FACT\} detector we have established the performance of scintillating fibres at 4 K by means of a cosmic-ray tracker operating in a liquid helium cryostat. The \{FACT\} detector was installed in the \{AEgIS\} apparatus in December 2012 and will be used to study the H ¯ formation when the low energy antiproton physics programs resume at \{CERN\} in the Summer of 2014. This paper presents the design requirements and construction methods of the \{FACT\} detector and provides the first results of the detector commissioning. "
The main goal of the AEgIS experiment at CERN is to test the weak equivalence principle for antimatter. AEgIS will measure the free-fall of an antihydrogen beam traversing a moir'e deflectometer. The goal is to determine the gravitational acceleration ##IMG## [http://ej.iop.org/icons/Entities/barg.gif] {bar g} with an initial relative accuracy of 1% by using an emulsion detector combined with a silicon μ-strip detector to measure the time of flight. Nuclear emulsions can measure the annihilation vertex of antihydrogen atoms with a precision of ~ 1–2 μm r.m.s. We present here results for emulsion detectors operated in vacuum using low energy antiprotons from the CERN antiproton decelerator. We compare with Monte Carlo simulations, and discuss the impact on the AEgIS project.
The AEGIS experiment, currently being set up at the Antiproton Decelerator at CERN, has the objective of studying the free fall of antimatter in the Earth’s gravitational field by means of a pulsed cold atomic beam of antihydrogen atoms. Both duration of free fall and vertical displacement of the horizontally emitted atoms will be measured, allowing a first test of the WEP with antimatter.
