High-precision test of Einstein's energy-mass equivalence
The energy-mass equivalence expressed by the famous formula E=mc2 was the most important new finding of Einstein's special theory of relativity and is crucial for its validity. Since direct validations via precision annihilation experiments are limited to precisions of a few parts per million, less direct but more precise approaches are considered. A good candidate is the neutron capture reaction in which the newly formed isotope releases the gained binding energy as gamma rays. By comparing the precisely measured gamma-ray energy with the precisely determined mass defect of the formed isotope using Einstein's equation, the energy-mass equivalence can be tested with high accuracy.
In a recent article published in Nature Physics M. Jentschel and K. Blaum explain the verification of Einstein's simple equation by two completely independent experimental techniques. The gamma-ray wavelengths and thus the gamma ray energies can be determined by diffraction angle measurements with a double perfect-crystal spectrometer. The lattice spacing is known with eight-digit accuracy and the diffraction angle measurements can be done with seven-digit accuracy. To match this precision, the mass defect has to be determined with 11-digit accuracy by high-precision Penning-trap mass measurements.
For the combination of both experimental techniques only the three isotope pairs 1,2H, 32,33S and 28,29Si have so far been suitable. With the existing data, it has been possible to demonstrate the equality of mass and energy at the level of 1.4(4.4)·10–7. An isotope pair for an improved test of the energy-mass equivalence is proposed.
Please read more in the Nature Physics article ... >
Investigation of nucleosynthesis processes of light p-nuclei
The stellar nucleosynthesis of heavy chemical elements beyond iron is of special interest in nuclear astrophysics. Stable proton-rich nuclei, the so-called p-nuclei, can't be created by the s- or p-process. Heavy p-nuclei are usually produced by the γ-process (photo-dissociation) in supernova explosions. However, the "light p-nuclei" in the medium mass region cannot be understood in the framework of standard nucleosynthesis. For the production of such light p-nuclei, the astrophysical rp-process (rapid proton capture) and νp-process (neutrino-driven nucleosynthesis) have been suggested.
In a recent article published in Physics Letters B, Y. M. Xing et al. report on precision mass measurements of five neutron-deficient nuclei, 79Y, 81,82Zr, and 83,84Nb. The measurements were performed by isochronous mass spectrometry with the experimental storage ring CSRe at the Heavy Ion Research Facility in Lanzhou (HIRFL), China. The masses of 82Zr and 84Nb were measured for the first time with an uncertainty of ~10keV, and the masses of 79Y, 81Zr, and 83Nb were re-determined with a higher precision.
With the precise mass measurements, especially the region of low α-separation energies (Sα) predicted by
FRDM'92 (finite range droplet mass model 1992) in neutron-deficient Mo and Tc isotopes was addressed.
From the determined mass excess values the two-proton (S2p) and two-neutron (S2n) separation energies and thus
the α-separation energies could be deduced.
The new mass values do not support the existence of a pronounced low-Sα island in Mo isotopes. As a consequence, the predicted Zr–Nb cycle in the rp-process of type I X-ray bursts does not exist or at least is much weaker than previously expected.
Furthermore, the new precise mass values allowed to address the overproduction of 84Sr found in previous νp-process calculations. The new masses lead to a reduction of the 84Sr abundance. This reduces the overproduction of 84Sr relative to 92,94Mo.
Please read more in the article ... >
The high-precision comparison of basic properties of matter/antimatter counterparts provides stringent tests of charge-parity-time
(CPT) invariance of the Standard Model. The experiments of the
target comparisons of the fundamental properties
of protons and antiprotons by determining and comparing their charge-to-mass ratios and magnetic moments in Penning traps.
In 2014 the collaboration directly measured the magnetic moment of the proton with 3.3 parts per billion (p.p.b.) precision at the Johannes Gutenberg University Mainz using a challenging double Penning-trap technique (see our news of 28.05.14). In a recent experiment at Mainz the collaboration improved the precision of the proton magnetic moment by a factor of eleven using an optimized double Penning-trap technique (see our news of 24.11.17). Last year the BASE collaboration also measured the antiproton magnetic moment with an unprecedented fractional precision of 1.5 p.p.b. (see our news of 18.10.17).
The precision of these experiments is, however, largely limited by the particle mode energy in the Penning trap. A reduction of the particle preparation times using sympathetically cooled protons/antiprotons is expected to significantly further improve the measurement precision.
In a recent article published in the Journal of Modern Optics, M. Bohman et al. present an upcoming experiment
to sympathetically cool single protons and antiprotons in a Penning trap by resonantly coupling the particles to laser-cooled
beryllium ions using a common endcap technique.
The measurement of the magnetic moment of a single proton or antiproton in a Penning trap is based on the measurement of the frequency ratio of the Larmor frequency and the cyclotron frequency (νL/νc). The Larmor frequency νL is determined by detection of spin transitions, which can only be observed at very low temperatures (cyclotron energies E+/kB < 0.6 K), where the axial frequency νz is stable enough.
In the previous proton/antiproton experiments time consuming selective resistive cooling techniques have been used to prepare the
particles below a threshold E+/kB < 1 K. The successful application of sympathetic cooling of protons and antiprotons to
deterministically low temperatures by coupling the particles to laser-cooled beryllium ions drastically reduces the cycle time of
An analysis of the energy exchange in the complete system leads to cyclotron energies below 30 mK/kB. Thus, a reduction of the ion preparation time from nearly an hour or more to just a few minutes can be expected.
To apply sympathetic cooling not only to protons but also to the negatively charged antiprotons, the BASE collaboration decided to use one trap for the proton (or antiproton) and a second trap for the beryllium ion cloud and connect the two with a common endcap. Each Penning trap has an outer endcap electrode, two inner correction electrodes, a central ring electrode and one shared endcap.
To realize the new sympathetic cooling scheme a heavily modified version of the double Penning-trap setup used for the proton measurements in 2014 at Mainz has been built. The new apparatus for an improved upcoming proton g-factor measurement consists of five traps: the new source trap (ST) for particle preparation, the analysis trap (AT) for spin state analysis, the precision trap (PT) for high precision frequency measurements, the coupling trap (CT) for common endcap coupling, and the beryllium trap (BT) for storage of laser cooled beryllium ions.
The upcoming application of sympathetic cooling with the common endcap technique on protons and antiprotons using the improved five Penning trap system will provide a direct CPT test at more than an order of magnitude improved precision and allow the most precise direct CPT comparison of single baryons.
Please read more in the article ... >
The proton is one of the central building blocks of stable matter. For that reason the precise knowledge of its fundamental properties
such as its mass (see our news of 18.07.17), lifetime, charge radius and magnetic moment is of great importance and thus the subject
of many contemporary physics research programs. The mass, for example, is an input parameter for precise quantum electrodynamics
calculations and the lower bound of the proton lifetime sets constraints on possible baryon number violation.
Apart from its fundamental nature, the proton is one of the few particles, which is comparable to its antiparticle – the antiproton. This allows for a test of the Charge, Parity, and Time Reversal (CPT) symmetry of the Standard Model of particle physics and Big Bang cosmology, which postulates that the fundamental properties of a particle and its antiparticle are exactly equal. Therefore, particles and antiparticles should have been created with same amounts. The lack of antimatter in our Universe, however, is in contradiction with this assumed matter-antimatter symmetry of the Standard Model. One possible explanation of the baryon asymmetry of the Universe is a violation of CPT invariance. Therefore, the measurement of minutest differences between the properties of a proton and its corresponding antiparticle, the antiproton, provides a precise test of the particle-antiparticle equality in the baryonic sector and of the CPT symmetry of the Standard Model.
The proton magnetic moment μp was directly measured in 2014 at the University of Mainz with a unprecedented fractional precision of 3.3 parts per billion (see our news of 28.05.14) using a novel double Penning-trap technique. Since then, the researchers at Mainz have developed techniques that enabled them to improve the measurement of the proton magnetic moment by more than one order of magnitude.
In a recent article published in "Science", G. Schneider et al. report on a direct high-precision measurement of the magnetic
moment of the proton μp in units of the nuclear magneton μN. The measurement has been carried out in an improved double Penning-trap
system at the University of Mainz, Germany.
A Penning trap is formed by a superposition of an electrostatic quadrupole potential and a homogeneous magnetic field B0, which was at 1.9 T in the described proton experiment.
The measurement of the frequency ratio νL/νc of the Larmor frequency and the cyclotron frequency allows the determination of the magnetic moment of a single proton in the Penning trap independent from the magnetic field B0. The cyclotron frequency νc can be determined from the three harmonic components νz, ν+, and ν- of the proton motion in the Penning trap using the invariance theorem: νc2 = ν+2 + νz2 + ν-2. The axial frequency νz of the stored proton is directly observed by non-destructive image current detection. The modified cyclotron frequency ν+ and the magnetron frequency ν- are measured by sideband coupling.
Since the Larmor frequency νL is not accompanied by an oscillating charge it cannot be determined by image current detection but by means of spin-transition spectroscopy. The superimposition of an inhomogeneous magnetic field, called a "magnetic bottle", couples the spin-magnetic moment of the proton to its axial oscillation frequency and thus allows to apply non-destructive detection of spin transitions (spin flips) using the continuous Stern-Gerlach effect.
However, the strong magnetic bottle broadens the Larmor resonance line significantly and limits the measurement to a relative precision of order 10-6 (p.p.m.). The application of a double Penning-trap technique overcomes this problem by using two separate Penning traps which are interconnected by a transport section. A precision trap (PT) with a nearly homogenous magnetic field is used for high-precision measurements of νc and νL and an analysis trap (AT) with the magnetic bottle is deployed for spin state detection of the proton. By applying this method, the proton g-factor measurement in 2014 at Mainz reached a relative precision of 3.3 p.p.b..
With respect to the proton measurements in 2014 the recent proton experiment at Mainz used an optimized double Penning-trap technique.
The trap geometry was optimized to reach a higher magnetic homogeneity in the precision trap. Together with a superconducting
self-shielding coil this allowed to improve the cyclotron stability by one order of magnitude. The width of the g-factor resonance,
a major limitation in the previous measurement, was reduced by carefully optimizing the Larmor rf drive to probe the resonance. The
particle preparation time for each individual measurement cycle could be reduced by applying a significantly improved superconducting
detector for the modified cyclotron frequency ν+. This enabled a twice as high data acquisition rate which greatly increased statistics.
Furthermore, the simultaneous measurement of νL and ν+ instead of a sequential determination
ensured that νL and ν+ were measured at
the same energies and times which eliminated many systematic shift contributions.
The final result of the determined proton magnetic moment in units of the nuclear magneton has a fractional precision of 0.3 p.p.b. (3·10-10): μp = 2.792 847 344 62(75)(34) μN. The first value in parentheses is the statistical uncertainty and the second one the systematic uncertainty. The new value of μp is in agreement with the currently accepted CODATA (Committee on Data for Science and Technology) value, but a factor of ten more precise. It improves the 3.3 p.p.b. precision of the μp measurement in 2014 at Mainz by a factor of eleven.
The BASE collaboration
recently measured the antiproton magnetic moment with a fractional precision of 1.5 p.p.b.
(see our news of 18.10.17).
The recent results for the magnetic moments of the proton and the antiproton enable a test of the fundamental symmetry between matter and antimatter in the baryonic sector at the 10-9 - 10-10 level. The researchers expect that proton/antiproton magnetic moment measurements on the parts per trillion level (10-12) will become possible by reducing the particle preparation times by more than two orders of magnitude using sympathetically cooled protons/antiprotons by coupling them to laser cooled beryllium ions.
Please read more in the "Science" article ... >
A radio report on the most precise measurement of the proton magnetic moment (start at 2:15 min.).
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