34 research outputs found
Determination of the asymptotic behaviour of the heavy flavour coefficient functions in deep inelastic scattering
Determination of the asymptotic behaviour of the heavy flavour coefficient functions in deep inelastic scattering
Deep-inelastic production of heavy quarks
Deep-inelastic production of heavy quarks at HERA, especially charm, is an
excellent signal to measure the gluon distribution in the proton at small
values. By measuring various differential distributions of the heavy quarks
this reaction permits additional more incisive QCD analyses due to the many
scales present. Furthermore, the relatively small mass of the charm quark,
compared to the typical momentum transfer , allows one to study whether and
when to treat this quark as a parton. This reaction therefore sheds light on
some of the most fundamental aspects of perturbative QCD. We discuss the above
issues and review the feasibility of their experimental investigation in the
light of a large integrated luminosity.Comment: 10 pages, uses epsfig.sty, five ps figures included. To appear in the
proceedings of the workshop Future Physics at HERA, eds. G. Ingelman, A. De
Roeck and R. Klanner, DESY, Hamburg, 199
Determination of the asymptotic behaviour of the heavy flavour coefficient functions in deep inelastic scattering
Using renormalization group techniques we have derived analytic formulae for
the next-to-leading order heavy-quark coefficient functions in deep inelastic
lepton hadron scattering. These formulae are only valid in the kinematic regime
Q^2 >> m^2, where Q^2 and m^2 stand for the masses squared of the virtual
photon and heavy quark respectively. Some of the applications of these
asymptotic formulae will be discussed.Comment: Latex with two PostScript figures and style file. Presentation at the
Rheinsberg Meeting on Higher Order QCD and QE
Recombination Models
We review the current status of recombination and coalescence models that
have been successfully applied to describe hadronization in heavy ion
collisions at RHIC energies. Basic concepts as well as actual implementations
of the idea are discussed. We try to evaluate where we stand in our
understanding at the moment and what remains to be done in the future.Comment: Plenary Talk at Quark Matter 2004, submitted to J. Phys. G, 8 pages,
3 figure
Deep-inelastic production of heavy quarks
Deep-inelastic production of heavy quarks at HERA, especially charm, is an excellent signal to measure the gluon distribution in the proton at small values. By measuring various differential distributions of the heavy quarks this reaction permits additional more incisive QCD analyses due to the many scales present. Furthermore, the relatively small mass of the charm quark, compared to the typical momentum transfer , allows one to study whether and when to treat this quark as a parton. This reaction therefore sheds light on some of the most fundamental aspects of perturbative QCD. We discuss the above issues and review the feasibility of their experimental investigation in the light of a large integrated luminosity
Pade-Improvement of QCD Running Coupling Constants, Running Masses, Higgs Decay Rates, and Scalar Channel Sum Rules
We discuss Pad\'e-improvement of known four-loop order results based upon an
asymptotic three-parameter error formula for Pad\'e-approximants. We derive an
explicit formula estimating the next-order coefficient from the previous
coefficients in a series . We show that such an
estimate is within 0.18% of the known five-loop order term in the O(1)
-function, and within 10% of the known five-loop term in the O(1)
anomalous mass-dimension function . We apply the same formula to
generate a [22] Pad\'e-summation of the QCD -function and anomalous
mass dimension in order to demonstrate both the relative insensitivity of the
evolution of and the running quark masses to higher order
corrections, as well as a somewhat increased compatibility of the present
empirical range for with the range anticipated via evolution
from the present empirical range for . For
we demonstrate that positive zeros of any [22] Pad\'e-summation estimate of
the all-orders -function which incorporates known two-, three-, and
four-loop contributions necessarily correspond to ultraviolet fixed points,
regardless of the unknown five-loop term. Pad\'e-improvement of higher-order
perturbative expressions is presented for the decay rates of the Higgs into two
gluons and into a pair, and is used to show the relative
insensitivity of these rates to higher order effects. However,
Pad\'e-improvement of the purely-perturbative component of scalar/pseudoscalar
current correlation functions is indicative of large theoretical uncertainties
in QCD sum rules for these channels, particularly if the continuum-threshold
parameter is near 1 GeV.Comment: latex, 22 pages, 8 figures, references correcte
Status and Prospects of Top-Quark Physics
The top quark is the heaviest elementary particle observed to date. Its large
mass of about 173 GeV/c^2 makes the top quark act differently than other
elementary fermions, as it decays before it hadronises, passing its spin
information on to its decay products. In addition, the top quark plays an
important role in higher-order loop corrections to standard model processes,
which makes the top quark mass a crucial parameter for precision tests of the
electroweak theory. The top quark is also a powerful probe for new phenomena
beyond the standard model. During the time of discovery at the Tevatron in 1995
only a few properties of the top quark could be measured. In recent years,
since the start of Tevatron Run II, the field of top-quark physics has changed
and entered a precision era. This report summarises the latest measurements and
studies of top-quark properties and gives prospects for future measurements at
the Large Hadron Collider (LHC).Comment: 76 pages, 35 figures, submitted to Progress in Particle and Nuclear
Physic
CHARMED QUARK FRAGMENTATION INTO CHARMED HADRONS
We show that in a model where fragmentation functions are created from jet calculus followed by recombination, the fragmentation function of charmed quarks into D mesons will fail to peak at low x at currently accessible values of Q2. Likewise, the fragmentation of a c quark into a Λc is much less peaked toward small x than the production of protons by u quarks. The model predicts a magnitude for the fragmentation function much smaller than is experimentally observed