27,183 research outputs found
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 symmetric quantum square well on an
interval of (with an dependent
non-Hermiticity given by Robin boundary conditions) and generalize it. In
essence, we just replace the support interval (reinterpreted
as an equilateral two-pointed star graph with the Kirchhoff matching at the
vertex ) by a pointed equilateral star graph
endowed with the simplest complex-rotation-symmetric external
dependent Robin boundary conditions. The remarkably compact form of
the secular determinant is then deduced. Its analysis reveals that (1) at any
integer , there exists the same, independent and infinite
subfamily of the real energies, and (2) at any special , there
exists another, additional and 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
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