Phys. Rev. A 99, 033405 (2019) Positronium in the $2^3S$ metastable state exhibits a low electrical
polarizability and a long lifetime (1140 ns) making it a promising candidate
for interferometry ...experiments with a neutral matter-antimatter system. In the
present work, $2^3S$ positronium is produced - in absence of electric field -
via spontaneous radiative decay from the $3^3P$ level populated with a 205nm UV
laser pulse. Thanks to the short temporal length of the pulse, 1.5 ns
full-width at half maximum, different velocity populations of a positronium
cloud emitted from a nanochannelled positron/positronium converter were
selected by delaying the excitation pulse with respect to the production
instant. $ 2^3S $ positronium atoms with velocity tuned between $ 7 \cdot 10^4
$ m/s and $ 10 \cdot 10^4 $ m/s were thus produced. Depending on the selected
velocity, a $2^3S$ production effciency ranging from $\sim 0.8 \%$ to $\sim
1.7%$, with respect to the total amount of emitted positronium, was obtained.
The observed results give a branching ratio for the $3^3P$-$2^3S$ spontaneous
decay of $(9.7 \pm 2.7) \% $. The present velocity selection technique could
allow to produce an almost monochromatic beam of $\sim 1 \cdot 10^3 $ $2^3S$
atoms with a velocity spread $ < 10^4 $ m/s and an angular divergence of $\sim$
50 mrad.
Phys. Rev. A 98, 013402 (2018) Producing positronium (Ps) in the metastable $2^3\text{S}$ state is of
interest for various applications in fundamental physics. We report here about
an experiment in ...which Ps atoms are produced in this long-lived state by
spontaneous radiative decay of Ps excited to the $3^3\text{P}$ 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. The indication of the $2^3\text{S}$ state
production is obtained from a novel analysis technique of single-shot
positronium annihilation lifetime spectra. Its production efficiency relative
to the total amount of formed Ps is evaluated by fitting a simple rate
equations model to the experimental data and found to be $ (2.1 \pm 1.3) \, \%
$.
The characteristics of low energy antiproton annihilations on nuclei (e.g. hadronization and product multiplicities) are not well known, and Monte Carlo simulation packages that use different models ...provide different descriptions of the annihilation events. In this study, we measured the particle multiplicities resulting from antiproton annihilations on nuclei. The results were compared with predictions obtained using different models in the simulation tools GEANT4 and FLUKA. For this study, we exposed thin targets (Cu, Ag and Au) to a very low energy antiproton beam from CERN's Antiproton Decelerator, exploiting the secondary beamline available in the AEgIS experimental zone. The antiproton annihilation products were detected using emulsion films developed at the Laboratory of High Energy Physics in Bern, where they were analysed at the automatic microscope facility. The fragment multiplicity measured in this study is in good agreement with results obtained with FLUKA simulations for both minimally and heavily ionizing particles.
We investigate experimentally the possibility of enhancing the production of \(2^3S\) positronium atoms by driving the \(1^3S\)-\(3^3P\) and \(3^3P\)-\(2^3S\) transitions, overcoming the natural ...branching ratio limitation of spontaneous decay from \(3^3P\) to \(2^3S\). The decay of \(3^3P\) positronium atoms towards the \(2^3S\) level has been effciently stimulated by a 1312.2nm broadband IR laser pulse. The dependence of the stimulating transition efficiency on the intensity of the IR pulse has been measured to find the optimal enhancement conditions. A maximum relative increase of \( \times (3.1 \pm 1.0) \) in the \(2^3S\) production efficiency, with respect to the case where only spontaneous decay is present, was obtained.
Positronium in the \(2^3S\) metastable state exhibits a low electrical polarizability and a long lifetime (1140 ns) making it a promising candidate for interferometry experiments with a neutral ...matter-antimatter system. In the present work, \(2^3S\) positronium is produced - in absence of electric field - via spontaneous radiative decay from the \(3^3P\) level populated with a 205nm UV laser pulse. Thanks to the short temporal length of the pulse, 1.5 ns full-width at half maximum, different velocity populations of a positronium cloud emitted from a nanochannelled positron/positronium converter were selected by delaying the excitation pulse with respect to the production instant. \( 2^3S \) positronium atoms with velocity tuned between \( 7 \cdot 10^4 \) m/s and \( 10 \cdot 10^4 \) m/s were thus produced. Depending on the selected velocity, a \(2^3S\) production effciency ranging from \(\sim 0.8 \%\) to \(\sim 1.7%\), with respect to the total amount of emitted positronium, was obtained. The observed results give a branching ratio for the \(3^3P\)-\(2^3S\) spontaneous decay of \((9.7 \pm 2.7) \% \). The present velocity selection technique could allow to produce an almost monochromatic beam of \(\sim 1 \cdot 10^3 \) \(2^3S\) atoms with a velocity spread \( < 10^4 \) m/s and an angular divergence of \(\sim\) 50 mrad.
Producing positronium (Ps) in the metastable \(2^3\text{S}\) state is of interest for various applications in fundamental physics. We report here about an experiment in which Ps atoms are produced in ...this long-lived state by spontaneous radiative decay of Ps excited to the \(3^3\text{P}\) 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. The indication of the \(2^3\text{S}\) state production is obtained from a novel analysis technique of single-shot positronium annihilation lifetime spectra. Its production efficiency relative to the total amount of formed Ps is evaluated by fitting a simple rate equations model to the experimental data and found to be \( (2.1 \pm 1.3) \, \% \).
We present arguments that additional effects besides laterally homogenous tunnelling might occur in carrier-selective poly-Si/c-Si junctions: (i) the symmetrical electrical behaviour of n+ and p+ ...poly-Si/c-Si junctions, (ii) direct observation of structural modifications of the interfacial oxide upon thermal treatment by transmission electron microscopy, even for poly-Si/c-Si junctions with good passivation quality, and (iii) the achievement of low junction resistances even for interfacial oxide thicknesses >2nm after thermal treatment. We present an alternative picture, essentially based on a localized current flow through the interfacial oxide, mediated either by local reduction of the oxide layer thickness or by pinholes. In consequence, the local current flow implies transport limitations for both minority and majority carriers in the c-Si absorber, and thus a correlation between recombination current and series resistance. Thus, a poly-Si/c-Si junction can also be explained within the framework of a classical pn junction picture for a passivated, locally contacted emitter, e.g. by the model of Fischer. Both electron selective contacts (n+ poly-Si) and hole selective contacts (p+ poly-Si) can be described consistently when using reasonable input parameters. Especially for p+ poly-Si/c-Si junctions, our model could guideline further improvement.
•Plausible arguments for additional current transport mechanisms in POLO junctions besides tunneling.•Presentation of an alternative picture based on local current flow.•Excellent agreement between model and experimental data for reasonable input parameters.•Deduction of an optimization strategy for p+ poly-Si/c-Si junctions.•Record J0 values for n+ POLO junctions with wet chemically (thermally) grown interfacial oxide – 1.5 (0.7) fA/cm2.•Record J0 values for p+ POLO junctions with wet chemically grown interfacial oxides – 8 fA/cm2.
Carrier selective junctions using a poly-silicon/ silicon oxide stack on crystalline silicon feature low recombination currents J0 whilst allowing for low contact resistivity ρC. We describe the ...limiting current transport mechanism as a combination of homogeneous tunneling through the interfacial silicon oxide layer and transport through pinholes where the interfacial silicon oxide layer is locally disrupted. We present an experimental method and its theoretical basis to discriminate between homogenous tunneling and local pinhole transport mechanisms on n + /n or p + /p junctions by measuring the temperature-dependent contact resistance. Theory predicts opposing trends for the temperature dependencies of tunneling and pinhole transport. This allows identifying the dominant transport path. For the contact resistance of two differently prepared poly-Si/ silicon oxide/ c-Si junctions we either find clear pinhole-type or clear tunneling-type temperature dependence. Pinhole transport contributes more than 94% to the total current for the sample with a 2.1 nm-thick interfacial silicon oxide that we anneal at a temperature of 1050 °C to achieve highest selectivity. In contrast pinhole transport contributes less than 35 % to the total current for the sample with a 1.7 nm-thick silicon oxide that we annealed at only 700 °C in order to avoid pinholes.
•Contact resistance measurements of a pinhole dominated sample can be modelled with drift currents.•Contact resistance measurements of a tunneling dominated sample can be modelled like a metal-insulator semiconductor.•The maximum contribution of the non-dominant current is deduced from temperature-dependent contact resistance measurements
The design of the n2EDM experiment Ayres, N. J.; Ban, G.; Bienstman, L. ...
The European physical journal. C, Particles and fields,
2021/6, Letnik:
81, Številka:
6
Journal Article
Recenzirano
Odprti dostop
We present the design of a next-generation experiment, n2EDM, currently under construction at the ultracold neutron source at the Paul Scherrer Institute (PSI) with the aim of carrying out a ...high-precision search for an electric dipole moment of the neutron. The project builds on experience gained with the previous apparatus operated at PSI until 2017, and is expected to deliver an order of magnitude better sensitivity with provision for further substantial improvements. An overview is of the experimental method and setup is given, the sensitivity requirements for the apparatus are derived, and its technical design is described.
PDF
