The radiative return at small angles: virtual corrections

Virtual corrections for electron--positron annihilation into one real and one off-shell photon of invariant mass Q^2 are evaluated. Special attention is paid to those configurations where the real photon is collinear with the beam direction. This calculation is an important ingredient of a Monte Carlo program, which simulates events with tagged photons from initial-state radiation, including NLO corrections.Comment: 8 pages, 2 figure

Reply to the Comment on `Deterministic Single-Photon Source for Distributed Quantum Networking'

Reply to the comment of H. J. Kimble [quant-ph/0210032] on the experiment realizing a "deterministic single-photon source for distributed quantum networking" by Kuhn, Hennrich, and Rempe [Phys. Rev. Lett. 89, 067901 (2002), quant-ph/0204147].Comment: 1 page 1 figur

tau Decays to Five Mesons in TAUOLA

The tau-decay library TAUOLA has gained popularity over the last decade. However, with the continuously increasing precision of the data, some of its functionality has become insufficient. One of the requirements is the implementation of decays into five mesons plus a neutrino with a realistic decay amplitude. This note describes a step into this direction. For the 2pi- pi+ 2pi0 mode the three decay chains tau- --> a_1- nu --> rho- (--> pi- pi0) omega (--> pi- pi+ pi0) nu, tau- --> a_1- nu --> a_1- (--> 2pi- pi+) f_0 (--> 2pi0) nu, and tau- --> a_1- nu --> a_1- (--> pi- 2pi0) f_0 (--> pi + pi-) nu are introduced with simple assumptions about the couplings and propagators of the various resonances. Similar amplitudes (without the rho omega contributions) are adopted for the pi- 4pi0 and 3pi- 2pi+ modes. The five-pion amplitude is thus based on a simple model, which, however, can be considered as a first realistic example. Phase-space generation includes the possibility of presampling the omega and a_1 resonances, in one channel only, however. This is probably sufficient for the time being, both for physics applications and for tests. The technical test of the new part of the generator is performed by comparing Monte Carlo and analytical results. To this end a non-realistic, but easy to calculate, purely scalar amplitude for the decay into five massless pions was used.Comment: 10 page

Axial Contributions at the Top Threshold

We calculate the contributions of the axial current to top quark pair production in e+ e- annihilation at threshold. The QCD dynamics is taken into account by solving the Lippmann-Schwinger equation for the P wave production using the QCD potential up to two loops. We demonstrate that the dependence of the total and differential cross section on the polarization of the e+ and e- beams allows for an independent extraction of the axial current induced cross section.Comment: LaTeX, 12 pages, including 5 Postscript figures using eps

Quantum star-graph analogues of PT-symmetric square wells

We pick up a solvable ${\cal PT}-$symmetric quantum square well on an interval of $x \in := (-L,L)\mathbb{G}^{(2)}$ (with an $\alpha-$dependent non-Hermiticity given by Robin boundary conditions) and generalize it. In essence, we just replace the support interval $\mathbb{G}^{(2)}$ (reinterpreted as an equilateral two-pointed star graph with the Kirchhoff matching at the vertex $x=0$) by a $q-$pointed equilateral star graph $\mathbb{G}^{(q)}$ endowed with the simplest complex-rotation-symmetric external $\alpha-$dependent Robin boundary conditions. The remarkably compact form of the secular determinant is then deduced. Its analysis reveals that (1) at any integer $q=2,3,...$, there exists the same, $q-$independent and infinite subfamily of the real energies, and (2) at any special $q=2,6,10,...$, there exists another, additional and $q-$dependent infinite subfamily of the real energies. In the spirit of the recently proposed dynamical construction of the Hilbert space of a quantum system, the physical bound-state interpretation of these eigenvalues is finally proposed.Comment: 20 pp, 1 figur

Assimilation via prices or quantities? Sources of immigrant earnings growth in Australia, Canada and the United States

Using 1980/81 and 1990/91 census data from Australia, Canada, and the United States, we estimate the effects of time in the destination country on male immigrants’ wages, employment, and earnings. We find that total earnings assimilation is greatest in the United States and least in Australia. Employment assimilation explains all of the earnings progress experienced by Australian immigrants, whereas wage assimilation plays the dominant role in the United States, and Canada falls in-between. We argue that relatively inflexible wages and generous unemployment insurance in countries like Australia may cause assimilation to occur along the “quantity” rather than the price dimension

Radiative return at NLO and the measurement of the hadronic cross-section in electron-positron annihilation

Electron-positron annihilation into hadrons plus an energetic photon from initial state radiation allows the hadronic cross-section to be measured over a wide range of energies. The full next-to-leading order QED corrections for the cross-section for e^+ e^- annihilation into a real tagged photon and a virtual photon converting into hadrons are calculated where the tagged photon is radiated off the initial electron or positron. This includes virtual and soft photon corrections to the process e^+ e^- \to \gamma +\gamma^* and the emission of two real hard photons: e^+ e^- \to \gamma + \gamma + \gamma^*. A Monte Carlo generator has been constructed, which incorporates these corrections and simulates the production of two charged pions or muons plus one or two photons. Predictions are presented for centre-of-mass energies between 1 and 10 GeV, corresponding to the energies of DAPHNE, CLEO-C and B-meson factories.Comment: 13 pages, 15 figure

Perspectives for the radiative return at meson factories

The measurement of the pion form factor and, more generally, of the cross section for electron-positron annihilation into hadrons through the radiative return has become an important task for high luminosity colliders such as the Phi- or B-meson factories. This quantity is crucial for predictions of the hadronic contributions to the anomalous magnetic moment of the muon, and to the running of the electromagnetic coupling. But the radiative return opens the possibility of many other physical applications. The physics potential of this method at high luminosity meson factories is discussed, the last upgraded version of the event generator PHOKHARA is presented, and future developments are highlighted.Comment: Presented at SIGHAD03: Worskhop on Hadronic Cross Section at Low Energy, Pisa,Italy, October 8th-10th, 200

Measurement of sigma_Total in e+e- Annihilations Below 10.56 GeV

Using the CLEO III detector, we measure absolute cross sections for e+e- -> hadrons at seven center-of-mass energies between 6.964 and 10.538 GeV. R, the ratio of hadronic and muon pair production cross sections, is measured at these energies with a r.m.s. error <2% allowing determinations of the strong coupling alpha_s. Using the expected evolution of alpha_s with energy we find alpha_s(M_Z^2)=0.126 +/- 0.005 ^{+0.015}_{-0.011}, and Lambda=0.31^{+0.09+0.29}_{-0.08-0.21}.Comment: Comments: Presented at "The 2007 Europhysics Conference on High Energy Physics," Manchester, England, 19-25 July 2007, to appear in the proceedings. Three pages, 1 figur