1,709 research outputs found
Direct measurement of the pion valence quark momentum distribution, the pion light-cone wave function squared
We present the first direct measurements of the pion valence quark momentum
distribution which is related to the square of the pion light-cone wave
function. The measurements were carried out using data on diffractive
dissociation of 500 GeV/c into di-jets from a platinum target at
Fermilab experiment E791. The results show that the light-cone
asymptotic wave function, which was developed using perturbative QCD methods,
describes the data well for or more. We also
measured the transverse momentum distribution of the diffractive di-jets.Comment: 13 pages, 4 figure
Application of Jain and Munczek's bound-state approach to gamma gamma-processes of pi0, eta_c and eta_b
We point out the problems affecting most quark--antiquark bound state
approaches when they are faced with the electromagnetic processes dominated by
Abelian axial anomaly. However, these problems are resolved in the consistently
coupled Schwinger-Dyson and Bethe-Salpeter approach. Using one of the most
successful variants of this approach, we find the dynamically dressed
propagators of the light u and d quarks, as well as the heavy c and b quarks,
and find the Bethe-Salpeter amplitudes for their bound states pi0, eta_c and
\eta_b. Thanks to incorporating the dynamical chiral symmetry breaking, the
pion simultaneously appears as the (pseudo)Goldstone boson. We give the
theoretical predictions for the gamma-gamma decay widths of pi0, eta_c and
eta_b, and for the pi0 gamma* -> gamma transition form factor, and compare them
with experiment. In the chiral limit, the axial-anomaly result for
pi0->gamma-gamma is reproduced analytically in the consistently coupled
Schwinger-Dyson and Bethe-Salpeter approach, provided that the quark-photon
vertex is dressed consistently with the quark propagator, so that the vector
Ward-Takahashi identity of QED is obeyed. On the other hand, the present
approach is also capable of quantitatively describing systems of heavy quarks,
concretely eta_c and possibly eta_b, and their gamma-gamma decays. We discuss
the reasons for the broad phenomenological success of the bound-state approach
of Jain and Munczek.Comment: RevTeX, 37 pages, 7 eps figures, submitted to Int. J. Mod. Phys.
Measurement of Charged Pion Production Yields off the NuMI Target
The fixed-target MIPP experiment, Fermilab E907, was designed to measure the
production of hadrons from the collisions of hadrons of momenta ranging from 5
to 120 GeV/c on a variety of nuclei. These data will generally improve the
simulation of particle detectors and predictions of particle beam fluxes at
accelerators. The spectrometer momentum resolution is between 3 and 4%, and
particle identification is performed for particles ranging between 0.3 and 80
GeV/c using , time-of-flight and Cherenkov radiation measurements. MIPP
collected events of 120 GeV Main Injector protons striking a
target used in the NuMI facility at Fermilab. The data have been analyzed and
we present here charged pion yields per proton-on-target determined in bins of
longitudinal and transverse momentum between 0.5 and 80 GeV/c, with combined
statistical and systematic relative uncertainties between 5 and 10%.Comment: 15 pages, 13 figure
A consistent treatment for pion form factors in space-like and time-like regions
We write down some relevant matrix elements for the scattering and decay
processes of the pion by considering a quark-meson vertex function. The pion
charge and transition form factors , , and
are extracted from these matrix elements using a relativistic
quark model on the light-front. We found that, the form factors and
in the space-like region agree well with experiment.
Furthermore, the branching ratios of all observed decay modes of the neutral
pion, that are related to the form factors and
in the time-like region, are all consistent with the data as
well. Additionally, in the time-like region, which deals with the
nonvalence contribution, is also discussed.Comment: 24 pages, 6 figures, to appear in Phys. Rev.
Primakoff effect in eta-photoproduction off protons
We analyse data on forward eta-meson photoproduction off a proton target and
extract the eta to gamma gamma decay width utilizing the Primakoff effect. The
hadronic amplitude that enters into our analysis is strongly constrained
because it is fixed from a global fit to available gamma p to p eta data for
differential cross sections and polarizations. We compare our results with
present information on the two-photon eta-decay from the literature. We provide
predictions for future PrimEx experiments at Jefferson Laboratory in order to
motivate further studies.Comment: 5 pages, 6 figures, gamma-gamma*-eta form factor included, version to
appear in Eur. Phys. J. A
Transverse lattice calculation of the pion light-cone wavefunctions
We calculate the light-cone wavefunctions of the pion by solving the meson
boundstate problem in a coarse transverse lattice gauge theory using DLCQ. A
large-N_c approximation is made and the light-cone Hamiltonian expanded in
massive dynamical fields at fixed lattice spacing. In contrast to earlier
calculations, we include contributions from states containing many gluonic
link-fields between the quarks.The Hamiltonian is renormalised by a combination
of covariance conditions on boundstates and fitting the physical masses M_rho
and M_pi, decay constant f_pi, and the string tension sigma. Good covariance is
obtained for the lightest 0^{-+} state, which we identify with the pion. Many
observables can be deduced from its light-cone wavefunctions.After perturbative
evolution,the quark valence structure function is found to be consistent with
the experimental structure function deduced from Drell-Yan pi-nucleon data in
the valence region x > 0.5. In addition, the pion distribution amplitude is
consistent with the experimental distribution deduced from the pi gamma^* gamma
transition form factor and diffractive dissociation. A new observable we
calculate is the probability for quark helicity correlation. We find a 45%
probability that the valence-quark helicities are aligned in the pion.Comment: 27 pages, 9 figure
Measurement of the Inclusive Semi-electronic Branching Fraction
Using the angular correlation between the emitted in a decay and the emitted in the subsequent decay, we have measured the branching fraction for the
inclusive semi-electronic decay of the meson to be: {\cal B}(D^0
\rightarrow X e^+ \nu) = [6.64 \pm 0.18 (stat.) \pm 0.29 (syst.)] \%. The
result is based on 1.7 fb of collisions recorded by the CLEO II
detector located at the Cornell Electron Storage Ring (CESR). Combining the
analysis presented in this paper with previous CLEO results we find,
\frac{{\cal B} (D^0 \rightarrow X e^+ \nu)}
{{\cal B} (D^0 \rightarrow K^- \pi^+)}
= 1.684 \pm 0.056 (stat.) \pm 0.093(syst.) and
\frac{{\cal B}(D\rightarrow K^-e^+\nu)}
{{\cal B}(D\rightarrow Xe^+\nu)}
= 0.581 \pm 0.023 (stat.) \pm 0.028(syst.).
The difference between the inclusive rate and the sum of the measured
exclusive branching fractions (measured at CLEO and other experiments) is of the inclusive rate.Comment: Latex file, 33pages, 4 figures Submitted to PR
Further Search for the Two-Photon Production of the Glueball Candidate
The CLEOII detector at the Cornell e+ e- storage ring CESR has been used to
search for the two-photon production of the decaying into pi+ pi-.
No evidence for a signal is found in data corresponding to an integrated
luminosity of 4.77/fb and a 95% CL upper limit on of 2.5 eV is set. If this result is combined with the BES Collaboration's
measurement of in radiative decay, a 95% CL
lower limit on the stickiness of the of 73 is obtained. If the
recent CLEO result for \Gamma_{two-photon} * BR{\K_S K_S} is combined with
the present result, the stickiness of the is found to be larger
than 102 at the 95% CL. These results for the stickiness (the ratio of the
probabilities for two-gluon coupling and two-photon coupling) provide further
support for a substantial neutral parton content in the .Comment: 8 pages, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Two-loop Corrections to the B to pi Form Factor from QCD Sum Rules on the Light-Cone and |V(ub)|
We calculate the leading-twist O(alphas^2 beta0) corrections to the B to pi
transition form factor f+(0) in light-cone sum rules. We find that, as
expected, there is a cancellation between the O(alphas^2 beta0) corrections to
fB f+(0) and the large corresponding corrections to fB, calculated in QCD sum
rules. This suggests the insensitivity of the form factors calculated in the
light-cone sum rules approach to this source of radiative corrections. We
further obtain an improved determination of the CKM matrix element |V(ub)|,
using latest results from BaBar and Belle for f+(0)|V(ub)|.Comment: 18 pages, 3 figure
Determination of the Michel Parameters and the tau Neutrino Helicity in tau Decay
Using the CLEO II detector at the storage ring CESR, we have
determined the Michel parameters , , and in decay as well as the tau neutrino helicity parameter
in decay. From a data sample of
tau pairs produced at , using events of
the topology and , and the determined sign of , the combined
result of the three samples is: , , , and
. The results are in agreement with
the Standard Model V-A interaction.Comment: 18 page postscript file, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
- …