Search results for "Positronium"
showing 10 items of 33 documents
Accumulation of positrons from a LINAC based source
2020
International audience; The GBAR experiment aims to measure the gravitational acceleration of antihydrogen H̅. It will use H̅+ ions formed by the interaction of antiprotons with a dense positronium cloud, which will require about 1010 positrons to produce one H̅+. We present the first results on the positron accumulation, reaching 3.8±0.4×108 e+ collected in 560 s.
Positron Annihilation Lifetime Spectroscopy Insight on Free Volume Conversion of Nanostructured MgAl2O4 Ceramics
2021
H.K. and A.I.P. are grateful for the support from the COST Action CA17126. H.K. was also supported by the Ministry of Education and Science of Ukraine (project for young researchers No. 0119U100435). In addition, I.K. and H.K. were also supported by the National Research Foundation of Ukraine via project 2020.02/0217, while the research of A.I.P. was funded by the Latvian research council via the Latvian National Research Program under the topic ?High-Energy Physics and Accelerator Technologies?, Agreement No: VPP-IZM-CERN-2020/1-0002. In addition, the research of A.I.P. has been supported by the Latvian-Ukrainian Grant LV-UA/2021/5. The Institute of Solid State Physics, University of Latvi…
Large numbers of cold positronium atoms created in laser-selected Rydberg states using resonant charge exchange
2016
Lasers are used to control the production of highly excited positronium atoms (Ps*). The laser light excites Cs atoms to Rydberg states that have a large cross section for resonant charge-exchange collisions with cold trapped positrons. For each trial with 30 million trapped positrons, more than 700 000 of the created Ps* have trajectories near the axis of the apparatus, and are detected using Stark ionization. This number of Ps* is 500 times higher than realized in an earlier proof-of-principle demonstration (2004 Phys. Lett. B 597 257). A second charge exchange of these near-axis Ps* with trapped antiprotons could be used to produce cold antihydrogen, and this antihydrogen production is e…
Evidence for eta(c) -> gamma gamma and measurement of J/psi -> 3 gamma
2013
The decay of J/psi to three photons is studied using psi (3686) -> pi(+) pi(-) J/psi in a sample of 1.0641 X 10(8) psi (3686) events collected with the BESIII detector. Evidence of the direct decay of eta(c) to two photons, eta(c) -> gamma gamma, is reported, and the product branching fraction is determined to be B(J/psi -> gamma eta(c,) eta(c) -> gamma gamma = (4.5 +/- 1.2 +/- 0.6) X 10(-6), where the first error is statistical and the second is systematic. The branching fraction for J/psi -> 3 gamma is measured to be (11.3 +/- 1.8 +/- 2.0) X 10(-6) with improved precision.
Positronium as a probe in natural polymers: decomposition in starch
2009
Ortho-positronium (o-Ps) is used as a probe in positron annihilation lifetime spectroscopy (PALS) experiments, to characterise the behaviour of free volumes in natural starch samples, as a function of temperature (T). Up to about 540 K, the o-Ps intensity, I(3), remains constant at 26.2% while its lifetime, tau(3), is found to increase linearly. Both parameters undergo a decrease above this T, due to the onset of decomposition, which results in a shrinking of the sample pellets. The results indicate that the glass transition temperature should be above 501 K. Data from thermal gravimetry analysis (TGA) measurements are well described by supposing a first order process for the survival proba…
Temperature dependence of slow-positron production and of positronium formation on untreated surfaces
1987
Low-energy positron emission from tungsten moderators, placed at a electron accelerator beam stop slows down with increasing moderator temperature. Efficient positronium formation is reported on untreated and unoriented metal surfaces at higher target temperatures.
New Schemes for the Production and Spectroscopy of Positronium
1989
The rate of positronium formation has been increased by 2–3 orders of magnitude using recently developed accelerator based slow positron sources. This opens the possibility of improvements of precision experiments on the Ps atom as well as new experiments on excited states. First evidence for enhanced metastable Ps formation is presented and future possibilities are discussed.
Physics at CERN's Antiproton Decelerator
2013
The Antiproton Decelerator of CERN began operation in 1999 to serve experiments for studies of CPT invariance by precision laser and microwave spectroscopy of antihydrogen ($\bar{\rm H}$) and antiprotonic helium ($\bar{p}{\rm He}^+$). The first 12 years of operation saw cold $\bar{\rm H}$ synthesized by overlapping clouds of positrons ($e^+$) and antiprotons ($\bar{p}$) confined in magnetic Penning traps. Cold $\bar{\rm H}$ was also produced in collisions between Rydberg positronium atoms and $\bar{p}$. Ground-state $\bar{\rm H}$ was later trapped for up to $\sim 1000$ s in a magnetic bottle trap, and microwave transitions excited between its hyperfine levels. In the $\bar{p}{\rm He}^+$ ato…
Multiphoton annihilation of monopolium
2017
We show that due to the large coupling constant of the monopole-photon interaction the annihilation of monopole-antimonopole and monopolium into many photons must be considered experimentally. For monopole-antimonopole annihilation and lightly bound monopolium, even in the less favorable scenario, multi-photon events (four and more photons in the final state) are dominant, while for strongly bound monopolium, although two photon events are important, four and six photon events are also sizable.
The general expression for the transition amplitude of two-photon ionization of atomic hydrogen
2003
Two-photon ionization of atomic hydrogen with an excess photon is revisited. The non-relativistic dipole approximation and Coulomb Green function (CGF) formalism are applied. Using the CGF Sturmian expansion straightforwardly, one gets the radial transition amplitude in the form of an infinite sum over Gauss hypergeometric functions which are polynomials. It is convergent if all intermediate states are in the discrete spectrum. In the case of two-photon ionization with an excess photon, when photoionization is also possible, intermediate states are in the continuum. We performed the explicit summation over intermediate states and got a simple general expression for the radial transition amp…