Proposed measurement of the ground-state hyperfine structure of antihydrogen

The ASACUSA collaboration at CERN-AD has recently submitted a proposal to measure the hyperfine splitting of the ground state of antihydrogen in an atomic beam line. The spectrometer will consist of two sextupoles for spin selection and analysis, and a microwave cavity to flip the spin of the antihydrogen atoms. Numerical simulations show that such an experiment is feasible if ~200 antihydrogen atoms per second can be produced in the ground state, and that an accuracy of better than 10^–7 can be reached. This measurement will be a precise test of the CPT invariance. B. Juhász serves as one of the authors of this article on behalf of the ASACUSA collaboration.     

The ASACUSA CUSP: an antihydrogen experiment

In order to test CPT symmetry between antihydrogen and its counterpart hydrogen, the ASACUSA collaboration plans to perform high precision microwave spectroscopy of ground-state hyperfine splitting of antihydrogen atom in-flight. We have developed an apparatus (“cusp trap”) which consists of a superconducting anti-Helmholtz coil and multiple ring electrodes. For the preparation of slow antiprotons and positrons, Penning-Malmberg type traps were utilized. The spectrometer line was positioned downstream of the cusp trap. At the end of the beamline, an antihydrogen beam detector was located, which comprises an inorganic Bismuth Germanium Oxide (BGO) single-crystal scintillator housed in a vacuum duct and surrounding plastic scintillators. A significant fraction of antihydrogen atoms flowing out the cusp trap were detected.     

Fast antihydrogen beam spectroscopy

The motivation for production and precision spectroscopy of antihydrogen atoms is outlined. An experimental configuration is considered, concerning laser-microwave spectroscopy of a fast hydroten beam with characteristics similar to those of an antihydrogen beam emanating from an antiproton-positron overlap region in an antiproton storage ring. In particular, a possible experiment for the measurement of the ground state hyperfine structure splitting is described.     

Spectroscopy apparatus for the measurement of the hyperfine structure of antihydrogen

The ASACUSA CUSP collaboration at the Antiproton Decelerator (AD) of CERN is planning to measure the ground-state hyperfine splitting of antihydrogen (H?) using an atomic spectroscopy beamline. We describe here the latest developments on the spectroscopy apparatus developed to be coupled to the H? production setup (CUSP).     

Antihydrogen atom formation in a CUSP trap towards spin polarized beams

The ASACUSA collaboration has been making a path to realize high precision microwave spectroscopy of ground-state hyperfine transitions of antihydrogen atom in flight for stringent test of the CPT symmetry. For this purpose, an efficient extraction of a spin polarized antihydrogen beam is essential. In 2010, we have succeeded in synthesizing our first cold antihydrogen atoms employing a CUSP trap. The CUSP trap confines antiprotons and positrons simultaneously with its axially symmetric magnetic field to form antihydrogen atoms. It is expected that antihydrogen atoms in the low-field-seeking states are preferentially focused along the cusp magnetic field axis whereas those in the high-field-seeking states are defocused, resulting in the formation of a spin-polarized antihydrogen beam.     

Hyperfine interaction of d-electrons in the amorphous semiconductors MoO3-TeO2 and MoO3-P2O5

ESR spectra of the amorphous semiconducting systems MoO₃-TeO₂ and MoO₃-P₂O₅ are presented. The occurence of a hyperfine splitting is confirmed by numerical simulations of the observed spectra and by enriching with the isotope Mo⁹⁵. The isotropic hyperfine field at the molybdenum nucleus amounts to (113±10) kG at high MoO₃ concentration. This value is compared with results of measurements on crystalline MoO₃.     

Ground-state hyperfine splitting of antihydrogen

ASACUSA collaboration at CERN’s antiproton decelerator (CERN AD) plans to measure the ground-state hyperfine splitting (GS-HFS) of antihydrogen () to test the CPT symmetry to high precision. Our scheme is to produce an (anti-) atomic beam with a novel two-frequency superconducting Paul trap, and to use sextupole magnets and a 1.4-GHz cavity to analyze the HFS resonance frequency.      

Radiative and interelectronic-interaction corrections to the hyperfine splitting in highly charged B-like ions

The ground-state hyperfine splitting values of high-Z boronlike ions are calculated. Calculation of the interelectronic-interaction contribution is based on a combination of the 1/Z perturbation theory and the large-scale configuration-interaction Dirac-Fock-Sturm method. The screened QED corrections are evaluated utilizing an effective screening potential approach. Total hyperfine splitting energies are presented for several B-like ions of particular interest: ⁴⁵Sc¹⁶⁺, ⁵⁷Fe²¹⁺, ²⁰⁷Pb⁷⁷⁺, and ²⁰⁹Bi⁷⁸⁺. For lead and bismuth the experimental values of the 1s hyperfine splitting are employed to improve significantly the theoretical results by reducing the uncertainty due to the nuclear effects.     

61Ni Mössbauer spectra of fine Ni particles

We report the first measurements of fine Ni particles from⁶¹Ni Mössbauer spectroscopy. The average hyperfine field of the 10 nm particles at 4.2K is measured to be 7.7(4) T, compared to the measured value for Ni foil of 7.5(3) T. Application of an external field of 6 T to the fine particles causes a reduction of the hyperfine splitting to 1.5(6) T, a consequence of the negative hyperfine field at Ni nuclei. These results are discussed in terms of fine particle effects.     

Antihydrogen synthesis in a double-CUSP trap towards test of the CPT-symmetry

The aim of the ASACUSA-CUSP experiment at CERN is to produce a cold, polarised antihydrogen beam and perform a high precision measurement of the ground-state hyperfine transition frequency of the antihydrogen atom and compare it with that of the hydrogen atom using the same spectroscopic beam line. Towards this goal a significant step was successfully accomplished: synthesised antihydrogen atoms have been produced in a CUSP magnetic configuration and detected at the end of our spectrometer beam line in 2012 [1]. During a long shut down at CERN the ASACUSA-CUSP experiment had been renewed by introducing a new double-CUSP magnetic configuration and a new semi-cylindrical tracking detector (AMT) [2], and by improving the transport feature of low energy antiproton beams. The new tracking detector monitors the antihydrogen synthesis during the mixing cycle of antiprotons and positrons. In this work the latest results and improvements of the antihydrogen synthesis will be presented including highlights from the last beam time.     

New electron centers in neutron-irradiated natural quartz

EPR measurements on neutron-irradiated natural quartz crystals from Brazil revealed the presence of two new electron centers, each with hyperfine structure due to one proton. In one of these centers this hyperfine splitting is typical for H^? which most likely substitutes for an oxygen whereas in the other a much smaller splitting due to an OH group was observed. The properties of these centers are compared with those of the E^′_n centers with closely related structures.     

Thallium hyperfine anomaly

Measurements of the hyperfine structure in the highly charged hydrogen like systems ²⁰³Tl⁸⁰⁺ and ²⁰⁵Tl⁸⁰⁺ are underway at the Super EBIT at LLNL. This work considers the effects of the nuclear magnetization distribution on the hyperfine structure. The difference in energy splitting due to hyperfine structure for ²⁰³Tl and ²⁰⁵Tl, respectively, is found to be 0.031 04(1) eV, which corresponds to a transition wavelength difference of 3.640(1) nm. This revised version was published online in August 2006 with corrections to the Cover Date.     

Low-temperature Mössbauer studies of FeNb2O6

Fe⁵⁷ Mössbauer spectra of FeNb₂O₆ were obtained from 15.0K down to 1.9 K. The isomer shift, 1.42±0.01 mm sec^?1 relative to Cr, was found to be temperature independent, whereas the magnitude of the quadrupole splitting was observed to decrease slightly with temperature. The quadrupole splitting and the hyperfine field at 1.9 K are -2.41±0.01 mm sec^?1 and 34.6±0.3 kOe respectively. The directions of the hyperfine fields experienced by the Fe nuclei are in the a-c plane symmetrically displaced with respect to the crystallographic axes.     

Measurement of the hyperfine structure of antihydrogen in a beam

A measurement of the hyperfine structure of antihydrogen promises one of the best tests of CPT symmetry. We describe an experiment planned at the Antiproton Decelerator of CERN to measure this quantity in a beam of slow antihydrogen atoms.     

Low temperature 151Eu and 57Fe Mössbauer study of mechanically alloyed EuFeO3

Low temperature ⁵⁷Fe Mössbauer spectra of mechanically alloyed EuFeO₃ prepared by mechanical alloying depicts an interesting transformation in its hyperfine magnetic state, from a triple phase magnetic system at room temperature to a single phase ferromagnetic state at 20 K. The hyperfine magnetic field increased by 12% at 20 K from its room temperature. The isomer shift and quadrupole splitting values exhibit a peak around 200 K. Low temperature ¹⁵¹Eu Mössbauer measurements show that the line-width increased to its maximum value at 80 K which is 45% compared to its room temperature value not enough to suggest splitting.     

Rubidium and proton ENDOR on ion pairs in solution

The E.S.R. spectrum of the o-dimesitoylbenzene anion-alkali cation radical shows unusually large isotropic alkali hyperfine splitting constants. We report a solution ENDOR study of this radical in which both alkali (^85,87Rb) and proton ENDOR spectra were recorded. Both the alkali and proton intensities showed a strong dependence on the metal ion nuclear spin quantum number of the E.S.R. line being saturated. This dependence is attributed to strong flip-flop cross-relaxation induced by modulation of the isotropic alkali hyperfine splitting. The powder E.S.R. spectrum of the complex reveals a small anisotropy of the Rb hyperfine splitting tensor. This indicates a small metal non-s-contribution to the half-filled molecular orbital, which is consistent with the observed relaxation behaviour and the small g shift. The intensity variations in the alkali and proton ENDOR spectra were used to determine the relative signs of all hyperfine splitting constants, and the absolute signs of the hyperfine splitting constants are deduced from a model of the structure of the complex.     

The external magnetic field dependence of RF splitting of57Fe hyperfine lines. NMR + Mössbauer double resonance experiment

We present the results of an experimental investigation of a RF splitting of⁵⁷Fe hyperfine lines in the regime of NMR and Mössbauer double resonance. The experiments have been performed as a function of RF field intensity and static magnetic field magnitude. The intensity of the RF components and the separation between them are extremely sensitive to the frequency and amplitude of the RF magnetic field. The RF splitting of hyperfine lines is inversely proportional to the strength of the static magnetic field.     

Isotope and hyperfine splittings for two UV transitions in tungsten I by saturation and polarisation spectroscopy

Isotope shifts and hyperfine splittings in tungsten I have been measured by Doppler-free saturated absorption and polarisation spectroscopy on two UV transitions at 294.44 nm and 294.70 nm. The splittings between the even isotopes (¹⁸²W, ¹⁸⁴W, ¹⁸⁶W) and the splitting between the two strong hyperfine components of ¹⁸³W were measured in a natural isotopic mixture of tungsten introduced into a hollow cathode discharge. In addition, using single isotope ¹⁸³W, the level hyperfine splittings were measured by resolving crossover peaks between the strong and weak hyperfine components. These measured level splittings are compared with those predicted from centre of gravity considerations.     

Spectral signatures of hyperfine and isotopic effects and of Tm-Tm pairs in LiYF4:Tm

We report on the high-resolution optical Fourier-transform spectroscopy of the LiYF₄:Tm³⁺ crystals. Splitting of several lines in the optical low-temperature polarized spectra was observed. We show that these splittings are caused by (i) the hyperfine interaction, (ii) the isotopic disorder in the lithium sublattice, and (iii) the interionic interaction between neighboring Tm ions. It is the first observation of the hyperfine splitting in the spectra of the Tm³⁺ ions in crystals. From the experimentally measured hyperfine splitting we evaluate the magnetic field at the thulium nucleus and calculate the magnetic g-factors of the excited crystal-field levels.     

Microwave-plasma interactions studied via mode diagnostics in ALPHA

The goal of the ALPHA experiment is the production, trapping and spectroscopy of antihydrogen. A direct comparison of the ground state hyperfine spectra in hydrogen and antihydrogen has the potential to be a high-precision test of CPT symmetry. We present a novel method for measuring the strength of a microwave field for hyperfine spectroscopy in a Penning trap. This method incorporates a non-destructive plasma diagnostic system based on electrostatic modes within an electron plasma. We also show how this technique can be used to measure the cyclotron resonance of the electron plasma, which can potentially serve as a non-destructive measurement of plasma temperature.