111 research outputs found

### The Heavy Quark Parton Oxymoron -- A mini-review of Heavy Quark Production theory in PQCD

Conventional perturbative QCD calculations on the production of a heavy quark
``$H$'' consist of two contrasting approaches: the usual QCD parton formalism
uses the zero-mass approximation ($m_H=0$) once above threshold, and treats $H$
just like the other light partons; on the other hand, most recent ``NLO'' heavy
quark calculations treat $m_H$ as a % large parameter and always consider $H$
as a heavy particle, never as a parton, irrespective of the energy scale of the
physical process. By their very nature, both these approaches are limited in
their regions of applicability. This dichotomy can be resolved in a unified
general-mass variable-flavor-number scheme, which retains the $m_H$ dependence
at all energies, and which naturally reduces to the two conventional approaches
in their respective region of validity. Recent applications to lepto- and
hadro-production of heavy quarks are briefly summarized.Comment: Talk given at DIS97, Chicago; 8 pages; Latex, use aipproc.st

### Charm Production in Deep Inelastic Scattering from Threshold to High $Q^{2}

Charm final states in deep inelastic scattering constitute $\sim 25%$ of the
inclusive cross-section at small $x$ as measured at HERA. These data can reveal
important information on the charm and gluon structure of the nucleon if they
are interpreted in a consistent perturbative QCD framework which is valid over
the entire energy range from threshold to the high energy limit. We describe in
detail how this can be carried out order-by-order in PQCD in the generalized
\msbar formalism of Collins (generally known as the ACOT approach), and
demonstrate the inherent smooth transition from the 3-flavor to the 4-flavor
scheme in a complete order $\alpha_s$ calculation, using a Monte Carlo
implementation of this formalism. This calculation is accurate to the same
order as the conventional NLO $F_2$ calculation in the limit $\frac{Q}{m_c} >>
1$. It includes the resummed large logarithm contributions of the 3-flavor
scheme (generally known in this context as the fixed-flavor-number or FFN
scheme) to all orders of $\alpha_s\ln(m_c^2/Q^2)$. For the inclusive structure
function, comparison with recent HERA data and the existing FFN calculation
reveals that the relatively simple order-$\alpha_s$ (NLO) 4-flavor ($m_c \neq
0$) calculation can, in practice, be extended to rather low energy scales,
yielding good agreement with data over the full measured $Q^2$ range. The Monte
Carlo implementation also allows the calculation of differential distributions
with relevant kinematic cuts. Comparisons with available HERA data show
qualitative agreement; however, they also indicate the need to extend the
calculation to the next order to obtain better description of the differential
distributions.Comment: 22 pages (LATEX), 8 figures (EPS); A few clarifying changes made;
version published in JHE

### Collider Inclusive Jet Data and the Gluon Distribution

Inclusive jet production data are important for constraining the gluon
distribution in the global QCD analysis of parton distribution functions. With
the addition of recent CDF and D0 Run II jet data, we study a number of issues
that play a role in determining the up-to-date gluon distribution and its
uncertainty, and produce a new set of parton distributions that make use of
that data. We present in detail the general procedures used to study the
compatibility between new data sets and the previous body of data used in a
global fit. We introduce a new method in which the Hessian matrix for
uncertainties is ``rediagonalized'' to obtain eigenvector sets that
conveniently characterize the uncertainty of a particular observable.Comment: Published versio

### The Parton Structure of the Nucleon and Precision Determination of the Weinberg Angle in Neutrino Scattering

A recently completed next-to-leading-order program to calculate neutrino
cross sections, including power-suppressed mass correction terms, has been
applied to evaluate the Paschos-Wolfenstein relation, in order to
quantitatively assess the validity and significance of the NuTeV anomaly. In
particular, we study the shift of $\sin^2 \theta_{\mathrm{W}}$ obtained in
calculations with a new generation of PDF sets that allow $s(x)\neq
\bar{s}(x)$, enabled by recent neutrino dimuon data from CCFR and NuTeV, as
compared to the previous $s = \bar{s}$ parton distribution functions like
CTEQ6M. The extracted value of $\sin^2 \theta_{\mathrm{W}}$ is closely
correlated with the strangeness asymmetry momentum integral
$\int_{0}^{1}x[s(x)-\bar{s}(x)] dx$. We also consider isospin violating effects
that have recently been explored by the MRST group. The results of our study
suggest that the new dimuon data, the Weinberg angle measurement, and other
data sets used in global QCD parton structure analysis can all be consistent
within the Standard Model.Comment: 4 page

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