363 research outputs found
Multiple-Scattering Series For Color Transparency
Color transparency CT depends on the formation of a wavepacket of small
spatial extent. It is useful to interpret experimental searches for CT with a
multiple scattering scattering series based on wavepacket-nucleon scattering
instead of the standard one using nucleon-nucleon scattering. We develop
several new techniques which are valid for differing ranges of energy. These
techniques are applied to verify some early approximations; study new forms of
the wave-packet-nucleon interaction; examine effects of treating wave packets
of non-zero size; and predict the production of 's in electron scattering
experiments.Comment: 26 pages, U.Wa. preprint 40427-23-N9
The Charm Content of W+1 Jet Events as a Probe of the Strange Quark Distribution Function
We investigate the prospects for measuring the strange quark distribution
function of the proton in associated plus charm quark production at the
Tevatron. The quark signal produced by strange quark -- gluon fusion,
and , is approximately 5\%
of the inclusive jet cross section for jets with a transverse momentum
~GeV. We study the sensitivity of the plus charm quark cross
section to the parametrization of the strange quark distribution function, and
evaluate the various background processes. Strategies to identify charm quarks
in CDF and D\O \ are discussed. For a charm tagging efficiency of about 10\%
and an integrated luminosity of 30~pb or more, it should be possible to
constrain the strange quark distribution function from production at the
Tevatron.Comment: submitted to Phys. Lett. B, Latex, 12 pages + 4 postscript figures
encoded with uufile, FSU-HEP-930812, MAD/TH/93-6, MAD/PH/788. A postscript
file with text and embedded figures is available via anonymous ftp at
hepsg1.physics.fsu.edu, file is /pub/keller/fsu-hep-930812.p
Systematic Analysis Method for Color Transparency Experiments
We introduce a data analysis procedure for color transparency experiments
which is considerably less model dependent than the transparency ratio method.
The new method is based on fitting the shape of the A dependence of the nuclear
cross section at fixed momentum transfer to determine the effective attenuation
cross section for hadrons propagating through the nucleus. The procedure does
not require assumptions about the hard scattering rate inside the nuclear
medium. Instead, the hard scattering rate is deduced directly from the data.
The only theoretical input necessary is in modelling the attenuation due to the
nuclear medium, for which we use a simple exponential law. We apply this
procedure to the Brookhaven experiment of Carroll et al and find that it
clearly shows color transparency: the effective attenuation cross section in
events with momentum transfer is approximately $40\ mb\ (2.2\
GeV^2/Q^2)$. The fit to the data also supports the idea that the hard
scattering inside the nuclear medium is closer to perturbative QCD predictions
than is the scattering of isolated protons in free space. We also discuss the
application of our approach to electroproduction experiments.Comment: 11 pages, 11 figures (figures not included, available upon request),
report # KU-HEP-92-2
Diffractive vector meson electroproduction at small Bjorken within GPD approach
We study light vector meson electroproduction at small within the
generalized parton distributions (GPDs) model. The modified perturbative
approach is used, where the quark transverse degrees of freedom in the vector
meson wave function and hard subprocess are considered. Our results on the
cross section and spin observables are in good agreement with experimentComment: 6 pages, 5 figures, presented at Symmetries and Spin meeting, Prague,
8- 14 July, 200
Understanding the penguin amplitude in decays
We calculate branching ratios for pure penguin decay modes,
decays using perturbative QCD approach. Our results of branching ratios are
consistent with the experimental data and larger than those obtained from the
naive factorization assumption and the QCD-improved factorization approach.
This is due to a dynamical penguin enhancement in perturbative QCD approach.Comment: 7 pages, 2 figures, version to appear in PL
A Model for the Twist-3 Wave Function of the Pion and Its Contribution to the Pion Form Factor
A model for the twist-3 wave function of the
pion has been constructed based on the moment calculation by applying the QCD
sum rules, whose distribution amplitude has a better end-point behavior than
that of the asymptotic one. With this model wave function, the twist-3
contributions including both the usual helicity components
() and the higher helicity components
() to the pion form factor have been studied within
the modified pQCD approach. Our results show that the twist-3 contribution
drops fast and it becomes less than the twist-2 contribution at . The higher helicity components in the twist-3 wave function will give
an extra suppression to the pion form factor. The model dependence of the
twist-3 contribution to the pion form factor has been studied by comparing
three different models. When all the power contributions, which include higher
order in , higher helicities, higher twists in DA and etc., have been
taken into account, it is expected that the hard contributions will fit the
present experimental data well at the energy region where pQCD is applicable.Comment: 22pages,4 figures. Phys.Rev. D70, 093013(2004) (in press
Consistent Analysis of the Transition Form Factor in the Whole Physical Region
In the paper, we show that the transition form factor can be
calculated by using the different approach in the different regions and
they are consistent with each other in the whole physical region. For the
transition form factor in the large recoil regions, one can apply the
PQCD approach, where the transverse momentum dependence for both the hard
scattering part and the non-perturbative wavefunction, the Sudakov effects and
the threshold effects are included to regulate the endpoint singularity and to
derive a more reliable PQCD result. Pionic twist-3 contributions are carefully
studied with a better endpoint behavior wavefunction for and we find
that its contribution is less than the leading twist contribution. Both the two
wavefunctions and of the B meson can give sizable
contributions to the transition form factor and should be kept for a
better understanding of the B decays. The present obtained PQCD results can
match with both the QCD light-cone sum rule results and the extrapolated
lattice QCD results in the large recoil regions.Comment: 18pages, 6 figure
Hadron Helicity Violation in Exclusive Processes: Quantitative Calculations in Leading Order QCD
We study a new mechanism for hadronic helicity flip in high energy hard
exclusive reactions. The mechanism proceeds in the limit of perfect chiral
symmetry, namely without any need to flip a quark helicity. The fundamental
feature of the new mechanism is the breaking of rotational symmetry of the hard
collision by a scattering plane in processes involving independent quark
scattering. We show that in the impulse approximation there is no evidence for
of the helicity violating process as the energy or momentum transfer is
increased over the region 1 GeV^2 < Q^2 < 100 GeV^2. In the asymptotic region
Q^2> 1000 GeV^2, a saddle point approximation with doubly logarithmic accuracy
yields suppression by a fraction of power of Q^2. ``Chirally--odd" exclusive
wave functions which carry non--zero orbital angular momentum and yet are
leading order in the high energy limit, play an important role.Comment: uuencoded LaTeX file (21 pages) and PostScript figure
Effects of Higher-Order Threshold Corrections in High-E_T Jet Production
Results for higher-order threshold enhancements in high-E_T jet production in
hadron-hadron collisions are presented. Expressions are given for the
next-to-next-to-leading order (NNLO) threshold corrections to the single-jet
inclusive cross section at next-to-leading logarithmic (NLL) accuracy. The
corrections are found to be small for the specific choice of E_T/2 for the
factorization and renormalization scales, and the corrected cross section shows
a substantial reduction of the scale dependence. A comparison to experimental
results from the Tevatron is presented.Comment: 24 pages LaTeX, 5 figure
Leading-Log Effects in the Resonance Electroweak Form Factors
We study log corrections to inelastic scattering at high Bjorken x for Q^2
from 1 to 21 GeV^2. At issue is the presence of log corrections, which can be
absent if high x scattering has damped gluon radiation. We find logarithmic
correction of the scaling curve extrapolated to low Q^2 improves the duality
between it and the resonance plus background data in the Delta region,
indicating log corrections exist in the data. However, at W > 2 GeV and high x,
the data shows a (1-x)^3 form. Log corrections in one situation but not in
another can be reconciled by a W- or Q^2- dependent higher twist correction.Comment: 13 pages, report nos. RPI-94-N90 and WM-94-106, revtex, two figures
(available by fax or post
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