2,940 research outputs found
Tetramixing of vector and pseudoscalar mesons: A source of intrinsic quarks
The tetramixing of pseudoscalar mesons --- and
vector mesons --- are studied in the light-cone
constituent quark model, and such mixing of four mesons provides a natural
source for the intrinsic charm components of light mesons. By mixing
with the light mesons, the charmonium states and could decay
into light mesons more naturally, without introducing gluons or a virtual
photon as intermediate states. Thus, the introduction of light quark components
into is helpful to reproduce the new experimental data of
decays. The mixing matrices and the behaviors of the transition form
factors are also calculated and compared with experimental data.Comment: 20 pages, 10 figures. Version for publication in PR
Probing Intrinsic Charm with Semileptonic B Decays
We discuss semileptonic B decays of the form B -> J/Psi e nu X as possible
probes of intrinsic charm. We calculate the leading order perturbative
contribution to the process B- -> J/Psi e- nu_e X and find it to be
unobservably small, with a branching ratio ~ 10^-10. We propose a modified
spectator model to estimate the intrinsic charm contribution and find that it
can be significantly larger, with a branching ratio for B -> (c cbar) e- nu_e X
as large as 5 X 10^-7. We show that the process could be observed at these
levels by CDF assuming a Run II integrated luminosity of 15 fb^-1, making this
a useful reaction to probe the idea of intrinsic charm.Comment: 25 pages, LaTeX, 7 figures, uses epsf.sty. Version substantially
revise
Gluon Virtuality and Heavy Sea Quark Contributions to the Spin-Dependent g_1 Structure Function
We analyze the quark mass dependence of photon gluon fusion in polarized deep
inelastic scattering for both the intrinsic and extrinsic gluon distributions
of the nucleon. We calculate the effective number of flavors for each of the
heavy and light quark photon gluon fusion contributions to the first moment of
the spin-dependent structure function .Comment: LaTex, 19 page
Systematics of Heavy Quark Production at HERA
We discuss heavy quark and quarkonium production in various kinematic regions
at the HERA ep collider. In contrast to fixed target experiments, collider
kinematics allows the possibility of detailed measurements of particle
production in the proton fragmentation region. One thus can study parton
correlations in the proton Fock states materialized by the virtual photon
probe. We discuss various configurations of inelastic electron-proton
scattering, including peripheral, diffractive, and deep inelastic processes. In
particular, we show that intrinsic heavy quark Fock states can be identified by
the observation of quarkonium production at large and a low mean
transverse momentum which is insensitive to the virtuality of the photon.Comment: 17 pages, postscript. To obtain a copy of this paper send e-mail to
[email protected]
Experimental determination of the effective strong coupling constant
We present a first attempt to experimentally extract an effective strong
coupling constant that we define to be a low Q2 extension of a previous
definition by S. Brodsky et al. following an initial work of G. Grunberg. Using
Jefferson Lab data and sum rules, we establish its Q2-behavior over the
complete Q2-range. The result is compared to effective coupling constants
inferred from different processes and to calculations based on Schwinger-Dyson
equations, hadron spectroscopy or lattice QCD. Although the connection between
the experimentally extracted effective coupling constants and the calculations
is not established it is interesting to note that their behaviors are similar.Comment: Published in Physics Letters B 650 4 24
Rapidity gaps in perturbative QCD
We analyze diffractive deep inelastic scattering within perturbative QCD by
studying lepton scattering on a heavy quark target. Simple explicit expressions
are derived in impact parameter space for the photon wave function and the
scattering cross sections corresponding to single and double Coulomb gluon
exchange. At limited momentum transfers to the target, the results agree with
the general features of the ``aligned jet model''. The color--singlet exchange
cross section receives a leading twist contribution only from the aligned jet
region, where the transverse size of the photon wave function remains finite in
the Bjorken scaling limit. In contrast to inclusive DIS, in diffractive events
there is no leading twist contribution to from the lowest
order photon Fock state, and the cross section for heavy quarks is
power suppressed in the quark mass. There are also important contributions with
large momentum transfer to the target, which corresponds to events having high
transverse momentum production in both the projectile and target rapidity
regions, separated by a rapidity gap.Comment: 27 pages, LaTeX, 6 figures. Duplicate figure removed, paper unchange
ON THE INTRINSIC CHARM COMPONENT OF THE NUCLEON
Using a meson cloud model we calculate the squared charm radius
of the nucleon . The ratio between this squared radius and the ordinary baryon
squared radius is identified with the probability of ``seeing'' the intrinsic
charm component of the nucleon. Our estimate is compatible with those used to
successfully describe the charm production phenomenology.Comment: 9 pages, 2 figures not included, avaiable from the author
Testing QCD with Hypothetical Tau Leptons
We construct new tests of perturbative QCD by considering a hypothetical tau
lepton of arbitrary mass, which decays hadronically through the electromagnetic
current. We can explicitly compute its hadronic width ratio directly as an
integral over the e^+ e^- annihilation cross section ratio, R_{e^+e^-}.
Furthermore, we can design a set of commensurate scale relations and
perturbative QCD tests by varying the weight function away from the form
associated with the V-A decay of the physical tau. This method allows the wide
range of the R_{e^+e^-} data to be used as a probe of perturbative QCD.Comment: 4 pages, 4 figure
The Two-Loop Scale Dependence of the Static QCD Potential including Quark Masses
The interaction potential V(Q^2) between static test charges can be used to
define an effective charge and a physically-based
renormalization scheme for quantum chromodynamics and other gauge theories. In
this paper we use recent results for the finite-mass fermionic corrections to
the heavy-quark potential at two-loops to derive the next-to-leading order term
for the Gell Mann-Low function of the V-scheme. The resulting effective number
of flavors in the scheme is determined as a
gauge-independent and analytic function of the ratio of the momentum transfer
to the quark pole mass. The results give automatic decoupling of heavy quarks
and are independent of the renormalization procedure. Commensurate scale
relations then provide the next-to-leading order connection between all
perturbatively calculable observables to the analytic and gauge-invariant
scheme without any scale ambiguity and a well defined number of
active flavors. The inclusion of the finite quark mass effects in the running
of the coupling is compared with the standard treatment of finite quark mass
effects in the scheme.Comment: 27 pages, 13 figure
Accuracy of the pion elastic form factor extracted from a local-duality sum rule
We analyze the accuracy of the pion elastic form factor predicted by a
local-duality (LD) version of dispersive sum rules. To probe the precision of
this theoretical approach, we adopt potential models with interactions that
involve both Coulomb and confining terms. In this case, the exact form factor
may be obtained from the solution of the Schroedinger equation and confronted
with the LD sum rule results. We use parameter values appropriate for hadron
physics and observe that, independently of the details of the confining
interaction, the deviation of the LD form factor from the exact form factor
culminates in the region Q^2~4-6 GeV^2. For larger Q^2, the accuracy of the LD
description increases rather fast with Q^2. A similar picture is expected for
QCD. For the pion form factor, existing data suggest that the LD limit may be
reached already at the relatively low values Q^2=4-10 GeV^2. Thus, large
deviations of the pion form factor from the behaviour predicted by LD QCD sum
rules for higher values of Q^2, as found by some recent analyses, appear to us
quite improbable. New accurate data on the pion form factor at Q^2=4-10 GeV^2
expected soon from JLab will have important implications for the behaviour of
the pion form factor in a broad Q^2 range up to asymptotically large values of
Q^2.Comment: 12 pages, extended version, conclusions remain unchange
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