574 research outputs found
New high order relations between physical observables in perturbative QCD
We exploit the fact that within massless perturbative QCD the same Green's
function determines the hadronic contribution to the decay width and the
moments of the cross section. This allows one to obtain relations
between physical observables in the two processes up to an unprecedented high
order of perturbative QCD. A precision measurement of the decay width
allows one then to predict the first few moments of the spectral density in
annihilations integrated up to with high accuracy.
The proposed tests are in reach of present experimental capabilities.Comment: 7 pages, Latex, no figure
The Effective Fragment Molecular Orbital Method for Fragments Connected by Covalent Bonds
We extend the effective fragment molecular orbital method (EFMO) into
treating fragments connected by covalent bonds. The accuracy of EFMO is
compared to FMO and conventional ab initio electronic structure methods for
polypeptides including proteins. Errors in energy for RHF and MP2 are within 2
kcal/mol for neutral polypeptides and 6 kcal/mol for charged polypeptides
similar to FMO but obtained two to five times faster. For proteins, the errors
are also within a few kcal/mol of the FMO results. We developed both the RHF
and MP2 gradient for EFMO. Compared to ab initio, the EFMO optimized structures
had an RMSD of 0.40 and 0.44 {\AA} for RHF and MP2, respectively.Comment: Revised manuscrip
Study of below 1 GeV using Integral Equation Approach
The scattering of is studied using the axial
anomaly, elastic unitarity, analyticity and crossing symmetry. Using the
technique to derive the Roy's equation, an integral equation for the P-wave
amplitude is obtained in terms of the strong P-wave pion pion phase shifts. Its
solution is obtained numerically by an iteration procedure using the starting
point as the solution of the integral equation of the Muskelshsvilli-Omnes
type. It is, however, ambiguous and depends sensitively on the second
derivative of the P-wave amplitude at which cannot directly be
measured.Comment: 26 pages, 10 figure
Formalism for dilepton production via virtual photon bremsstrahlung in hadronic reactions
We derive a set of new formulas for various distributions in dilepton
production via virtual photon bremsstrahlung from pseudoscalar mesons and
unpolarized spin-one-half fermions. These formulas correspond to the leading
and sub-leading terms in the Low-Burnett-Kroll expansion for real photon
bremsstrahlung. The relation of our leading-term formulas to previous works is
also shown. Existing formulas are examined in the light of Lorentz covariance
and gauge invariance. Numerical comparison is made in a simple example, where
an "exact" formula and real photon data exist. The results reveal large
discrepancies among different bremsstrahlung formulas. Of all the leading-term
bremsstrahlung formulas, the one derived in this work agrees best with the
exact formula. The issues of M_T-scaling and event generators are also
addressed.Comment: 37 pages, RevTeX, epsf.sty, 10 embedded figure
Hidden Local Symmetry for Anomalous Processes with Isospin/SU(3) Breaking Effects
We show that isospin/SU(3) breaking terms can be introduced to the anomalous
VVP coupling in the hidden local symmetry scheme without changing
Wess-Zumino-Witten term in the low-energy limit. We make the analysis for
anomalous processes of 2-body and 3-body decays; radiative vector meson
decays(V \to P\gamma), conversion decays of photon into a lepton pair(V \to P
l^+ l^-) and hadronic anomalous decays(V \to PPP). The predictions successfully
reproduce all experimental data of anomalous decays. In particular, we predict
the decay widths of \rho^0 \to \pi^0 \gamma and \phi \to \eta' \gamma as 101
\pm 9 keV and 0.508 \pm 0.035 keV, respectively, which will be tested in the
DAFNE \phi-factory. Moreover, prediction is also made for \phi \to \pi^0 e^+
e^-, \rho \to 3\pi, K^* \to K \pi \pi and so on, for which only the
experimental upper bounds are available now.Comment: 19 pages, 4 tables, no figur
Calculation of on the Z
We perform a new, detailed calculation of the hadronic contributions to the
running electromagnetic coupling, , defined on the Z particle (91
GeV). We find for the hadronic contribution, including radiative corrections,
10^5\times \deltav_{\rm had.}\alpha(M_Z^2)= 2740\pm12, or, excluding the
top quark contribution, 10^5\times \deltav_{\rm had.}\alpha^{(5)}(M_Z^2)=
2747\pm12.
Adding the pure QED corrections we get a value for the running
electromagnetic coupling of Comment: Version to appear in Phys. Rev. D. Plain TeX fil
Extracting Br(omega->pi^+ pi^-) from the Time-like Pion Form-factor
We extract the G-parity-violating branching ratio Br(omega->pi^+ pi^-) from
the effective rho-omega mixing matrix element Pi_{rho omega}(s), determined
from e^+e^- -> pi^+ pi^- data. The omega->pi^+ pi^- partial width can be
determined either from the time-like pion form factor or through the constraint
that the mixed physical propagator D_{rho omega}^{mu nu}(s) possesses no poles.
The two procedures are inequivalent in practice, and we show why the first is
preferred, to find finally Br(omega->pi^+ pi^-) = 1.9 +/- 0.3%.Comment: 12 pages (published version
Precision Determination of the Pion Form Factor and Calculation of the Muon
We perform a new calculation of the hadronic contributions, to the anomalous magnetic moment of the muon, . For the low
energy contributions of order we carry over an analysis of the pion
form factor using recent data both on and
. In this analysis we take into account
that the phase of the form factor is equal to that of scattering. This
allows us to profit fully from analyticity properties so we can use also
experimental information on at spacelike . At higher energy we
use QCD to supplement experimental data, including the recent measurements of
both around 1 GeV and near the threshold.
This yields a precise determination of the and
hadronic part of the photon vacuum polarization
pieces, As byproducts we also get the masses and
widths of the , and very accurate values for the charge radius
and second coefficient of the pion. Adding the remaining order
hadronic contributions we find The figures given are obtained
including decay data. This is to be compared with the recent
experimental value, Comment: Plain TeX file. Published version. Correct value for light-by-light
include
Resonant Structure of and Decays
The resonant structure of the four pion final state in the decay is analyzed using 4.27 million pairs
collected by the CLEO II experiment. We search for second class currents in the
decay using spin-parity analysis and establish an
upper limit on the non-vector current contribution. The mass and width of the
resonance are extracted from a fit to the
spectral function. A partial wave analysis of the resonant structure of the
decay is performed; the spectral decomposition of
the four pion system is dominated by the and final
states.Comment: 34 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
Intermediate-mass dilepton spectra and the role of secondary hadronic processes in heavy-ion collisions
We carry out a study of intermediate-mass (between 1 and 2.5 GeV) dilepton
spectra from hadronic interactions in heavy-ion collisions. The processes
considered are , , , , , and . The elementary cross sections for those are obtained
from chiral Lagrangians involving pseudoscalar, vector, and axial-vector
mesons. The respective electromagnetic form factors are determined by fitting
to experimental data for the reverse processes of . Based on
this input we calculate cross sections and thermal dilepton emission rates and
compare our results with those from other approaches. Finally we use these
elementary cross sections with a relativistic transport model and calculate
dilepton spectra in S+W collisions at SPS energies. The comparison of our
results with experimental data from the HELIOS-3 collaboration indicates the
importance of the secondary hadronic contributions to the intermediate-mass
dilepton spectra.Comment: 25 pages, including 20 postscript figure
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