Positron-electron pairs emitted from metallic and oxide surfaces

Abstract

If a positron impacts onto a surface, it may lead to the emission of a positron-electron pair. We have commissioned a laboratory-based positron source and performed a systematic study on a variety of solid surfaces. In a symmetric emission geometry we can explore the fact that positrons and electrons are distinguishable particles. Following fundamental symmetry arguments we have to expect that the available energy is shared unequally among positrons and electrons. Experimentally we observe such a behavior for all materials studied. We find a universal feature for all materials in the sense that, on average, the positron carries a larger fraction of the available energy. A scattering model accounts qualitatively for the observed energy sharing in positron-electron pair emission. A comparison of the intensity levels from the different materials reveals a monotonic relation between the singles and pair coincidence count rates.

The pion quasiparticle in the low-temperature phase of QCD

“…We have investigated the pion quasiparticle and order parameters for chiral restoration in N f = 2 QCD. The results obtained from the new ensemble with a lighter quark mass are qualitatively in agreement with our previous findings [1,2], namely that the pion mass splits in a significantly lighter pion quasiparticle mass and a heavier screening mass. Furthermore, we successfully tested that the modified dispersion relation given in Eq.…”

“…At the midpoint the non-pion contributions are at the sub-percent level indicating the dominance of the pion which is an essential assumption in the definition of the estimators for the pion velocity u. The results at finite momentum are qualitatively in agreement with our previous findings [2], namely at the lowest momentum b ( p) is very small as expected from the effective theory. Table 2.…”

“…Here we present an extension of our study [1,2] concerning the pion quasiparticle in the lowtemperature phase of two-flavor QCD. In this article, we test the modified dispersion relation of the pion quasiparticle on a new ensemble with a lighter zero-temperature pion mass.…”

Reconstructing parton distribution functions from Ioffe time data: from Bayesian methods to neural networks

“…One approach to inverse problems, which has been used in a number of engineering and physics applications, is the Backus-Gilbert method [35][36][37][38]. Like many approaches to the inverse problem, the Backus-Gilbert method provides a unique solution to the ill posed problem given some condition.…”

Direct detection of metal-insulator phase transitions using the modified Backus-Gilbert method

“…Early attempts to attack this problem of analytic continuation (AC) used ansätze as well as Bayesian methods and had varied levels of success [18][19][20]. More recently, the Backus-Gilbert (BG) [21] method has been employed in lattice QCD calculations [22] as well as in calculations for strongly-correlated electrons [17,23]. In this study, we apply a newly introduced modification of the BG method that employs the so-called Tikhonov regularization to a variety of lattice models: the Hubbard model on the hexagonal lattice and the Hubbard-Coulomb model on the square lattice.…”