6,165 research outputs found
Quarkonium production and decays
Quarkonium decays are studied in the charmonium model. Relativistic
corrections, higher-order perturbative QCD corrections and non- perturbative
contributions are discussed. Recent measurements of charmonium annihilation
rates are used to evaluate the strong coupling constant
simultaneously with the wave functions (and their derivatives) at the origin.
Further predictions are made for yet unobserved decay rates. The various models
for quarkonium production in hadronic collisions are critically reviewed. Based
on the charmonium model, the cross sections of different quarkonium states are
given in a well-defined QCD perturbation series, including quark--antiquark,
quark--gluon, and gluon--gluon scatterings. Numerical estimates are given for
charmonium production in \p\p, \ppbar, and \pi\p collisions. The role of
indirect \JP production via , \eta_{\c}(2S),
and \b-decays is pointed out. Relativistic effects and non-perturbative
contributions are found to be important. Existing measurements are compiled and
shown to be well explained if all contributions are included. The
cross section is calculated in complete next-to-leading order. Finally, a study
of the high-energy behaviour of quarkonium cross sections is made, based on the
asymptotical behaviour of higher-order QCD corrections.Comment: 128 pages, compressed ps file available via anonymous ftp to
darssrv1.cern.ch: cern/9402/th-7170-94.ps.Z, CERN-TH.7170/9
Model-independent QED corrections to photon structure-function measurements
We present the first calculation of QED radiative corrections to
deep-inelastic electron-photon scattering in terms of those variables that are
reconstructed in measurements of the photon structure function in
electron-positron collisions. In order to cover the low- region, we do not
invoke the QCD-improved parton model but rather express our results in terms of
the photon structure functions. Both analytical and numerical results are
given.Comment: Latex, 8 pages, 3 figures, uses epsfig.sty, 12pt.st
Central production of mesons: Exotic states versus Pomeron structure
We demonstrate that the azimuthal dependence of central meson production in
hadronic collisions, when suitably binned, provides unambiguous tests of
whether the Pomeron couples like a conserved vector-current to protons. We
discuss the possibility of discriminating between q-qbar and glueball
production in such processes. Our predictions apply also to meson production in
tagged two-photon events at electron--positron colliders and to vector-meson
production in ep collisions at HERA.Comment: 15 pages, latex, no figur
Models for Photon-photon Total Cross-sections
We present here a brief overview of recent models describing the
photon-photon cross-section into hadrons. We shall show in detail results from
the eikonal minijet model, with and without soft gluon summation.Comment: 7 pages, 5 figures, laTeX, requires espcrc2.sty. To appear in the
Proceedings of Photon-99, Freiburg, 23 -27 May 99, labels in the figures
1,3,4,5 corrected, one typo in an equation correcte
Testing factorization of charmonium production
Within the NRQCD factorization approach the production of heavy quarkonia can
be calculated in perturbative QCD in terms of a few
production-process-independent NRQCD matrix elements. We test the universality
of these long-distance matrix elements by comparing their values as determined
from charmonium production at p pbar, e p, and e+ e- colliders, and in Z^0,
Upsilon, and B decays.Comment: 19 pages, latex, 4 figure
production in annihilation
Inclusive production of in annihilation is an excellent
probe of the role of higher Fock states in the production of heavy quarkonia.
Within the non-relativistic QCD approach, contributions from the short-distance
production of colour-octet pairs are significantly larger than those
from colour-singlet production. At the same time, production rates
are significantly smaller than expected in the colour evaporation approach.
Measurements of production at CLEO and future B-factories will
thus constitute a major test of theoretical approaches to the production of
heavy quarkonia.Comment: 11 pages, Revtex, 2 figure
Photon Total Cross-sections
We discuss present predictions for the total and
cross-sections, highlighting why predictions differ. We present results from
the Eikonal Minijet Model and improved predictions based on soft gluon
resummation.Comment: 7 pages, 10 figures, LaTeX, requires espcrc2.sty, Talk presented by
G. Pancheri at PHOTON-2003, International Meeting on Structure and
Interactions of the Photon, Frascati, Italy, April 7-11, 200
Are the reactions a challenge for the factorized Pomeron at high energies?
We would like to point to the strong violation of the putative factorized
Pomeron exchange model in the reactions in the
high-energy region where this model works fairly well in all other cases.Comment: 4 pages, LaTex, 1 fig. in postscript, minor typos corrected, to be
published in Phys. Rev. D 60, 117503 (1999
Meson-photon transition form factors and resonance cross-sections in collisions
Meson--photon--photon transition form factors for S-, P-, and D-wave states are calculated, the meson being treated as a non-relativistic heavy-quark--antiquark pair. The full dependence on both photon virtualities is included. Cross-section formulas for charge-conjugation even mesons with J^P = 0^-, 0^+, 1^+, 2^+, and 2^- in electron--positron collisions are presented and numerical results for LEP energies are given. In particular, we find two-photon event rates for \chi_{\rc 1}, \eta_{\rc}(2S), and \eta_{\rb}(1S) within reach of LEP. With minor modifications to incorporate SU(3)-flavour breaking we estimate rates for 18 light mesons as well, based on the observation that their two-photon decay widths agree remarkably well with measured data. Finally we point out that e^+ e^- cross sections for 1^+ states do not vanish at low Q^2, the Landau--Yang suppression factors of the two-photon cross sections being compensated by the photon propagators
PEPSI deep spectra. III. A chemical analysis of the ancient planet-host star Kepler-444
We obtained an LBT/PEPSI spectrum with very high resolution and high
signal-to-noise ratio (S/N) of the K0V host Kepler-444, which is known to host
5 sub-Earth size rocky planets. The spectrum has a resolution of R=250,000, a
continuous wavelength coverage from 4230 to 9120A, and S/N between 150 and
550:1 (blue to red). We performed a detailed chemical analysis to determine the
photospheric abundances of 18 chemical elements, in order to use the abundances
to place constraints on the bulk composition of the five rocky planets. Our
spectral analysis employs the equivalent width method for most of our spectral
lines, but we used spectral synthesis to fit a small number of lines that
require special care. In both cases, we derived our abundances using the MOOG
spectral analysis package and Kurucz model atmospheres. We find no correlation
between elemental abundance and condensation temperature among the refractory
elements. In addition, using our spectroscopic stellar parameters and isochrone
fitting, we find an age of 10+/-1.5 Gyr, which is consistent with the
asteroseismic age of 11+/-1 Gyr. Finally, from the photospheric abundances of
Mg, Si, and Fe, we estimate that the typical Fe-core mass fraction for the
rocky planets in the Kepler-444 system is approximately 24 per cent. If our
estimate of the Fe-core mass fraction is confirmed by more detailed modeling of
the disk chemistry and simulations of planet formation and evolution in the
Kepler-444 system, then this would suggest that rocky planets in more
metal-poor and alpha-enhanced systems may tend to be less dense than their
counterparts of comparable size in more metal-rich systems.Comment: in press, 11 pages, 3 figures, data available from pepsi.aip.d
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