88 research outputs found
Heavy Quark Initiated Contributions to Deep Inelastic Structure Functions
We present O(alpha_s^1) corrections to deep inelastic scattering amplitudes
on massive quarks obtained within the scheme of Aivazis, Collins, Olness and
Tung (ACOT). After identifying the correct subtraction term the convergence of
these contributions towards the analogous coefficient functions for massless
quarks, obtained within the modified minimal subtraction scheme (MSbar), is
demonstrated. Furthermore, the quantitative relevance of the contributions to
neutral current (NC) and charged current (CC) structure functions is
investigated for several choices of the factorization scale.Comment: 29 pages, 6 figures; uses epsfig.sty, amssymb.sty, axodraw.sty; minor
changes for publication in Phys. Rev.
The t W- Mode of Single Top Production
The t W- mode of single top production is proposed as an important means to
study the weak interactions of the top quark. While the rate of this mode is
most likely too small to be observed at Run II of the Fermilab Tevatron, it is
expected to be considerably larger at the CERN LHC. In this article the
inclusive t W- rate is computed, including O(1 / log (m_t^2 / m_b^2))
corrections, and when combined with detailed Monte Carlo simulations including
the top and W decay products, indicate that the t W- single top process may be
extracted from the considerable t tbar and W+ W- j backgrounds at low
luminosity runs of the LHC.Comment: 16 pages, 4 figure
Coefficient Functions and Open Charm Production in Deep Inelastic Scattering
It is shown that the problem of double counting in open charm production in
DIS can be solved by using the expression for DIS coefficient functions in
terms of 2PI diagramsComment: 11 pages, REVTeX, no figure
Treatment of Heavy Quarks in Deeply Inelastic Scattering
We investigate a simplified version of the ACOT prescription for calculating
deeply inelastic scattering from Q^2 values near the squared mass M_H^2 of a
heavy quark to Q^2 much larger than M_H^2.Comment: 14 pages, 5 figure
Heavy Quark Parton Distributions: Mass-Dependent or Mass-Independent Evolution?
In a consistently formulated pQCD framework incorporating non-zero mass heavy
quark partons, there is still the freedom to define parton distributions
obeying either mass-independent or mass-dependent evolution equations, contrary
to statements made in a recent paper by MRRS. With properly matched hard
cross-sections, different choices merely correspond to different factorization
schemes, and they yield the same physical cross-sections. We demonstrate this
principle in a concrete order \alpha_s calculation of the DIS charm structure
function. We also examine the proper matching between parton definitions and
subtractions in the hard cross-section near threshold where the calculation is
particularly sensitive to mass effects of the heavy quark. The results obtained
from the general-mass formalism are quite stable against different choices of
scale and exhibit a smooth transition in the threshold region (using either
mass-independent or mass-dependent evolution), in contrast to results of
another recently proposed scheme.Comment: 6 pages, LaTeX, 4 PostScript figures, uses epsf.sty and aipproc.sty;
Contribution to DIS97 Workshop, 14-18 April, Chicago, IL, US
Compatibility of neutrino DIS data and global analyses of parton distribution functions
Neutrino\antineutrino deep inelastic scattering (DIS) data provide useful
constrains for the flavor decomposition in global fits of parton distribution
functions (PDF). The smallness of the cross-sections requires the use of
nuclear targets in the experimental setup. Understanding the nuclear
corrections is, for this reason, of utmost importance for a precise
determination of the PDFs. Here, we explore the nuclear effects in the
neutrino\antineutrino-nucleon DIS by comparing the NuTeV, CDHSW, and CHORUS
cross-sections to the predictions derived from the latest parton distribution
functions and their nuclear modifications. We obtain a good description of
these data and find no apparent disagreement between the nuclear effects in
neutrino DIS and those in charged lepton DIS. These results also indicate that
further improvements in the knowledge of the nuclear PDFs could be obtained by
a more extensive use of these sets of neutrino data.Comment: 16 pages, 8 figure
Single-top production at future ep colliders
The production of top quarks in single mode at future ep colliders is
studied, the attention being mainly focused to the case of the proposed LEPXLHC
collider. We are motivated to reanalyse such a process following the discovery
of the top quark at Fermilab. Thanks to the measurement of its mass one is now
able to establish more accurately the relevance of single top production for
itself and for many other processes to which it may act as a background. In
addition, the recent improvement of our knowledge of the quark and gluon
dynamics inside the proton now allows one to pin down the dependence of single
top production on the partonic structure functions. Both the leptonic and
hadronic decay channels of the top quark are studied and compared to the yield
of the corresponding irreducible background in presence of b-taggingComment: 28 pages, latex, epsfig, 10 postscript figures, complete paper
available at ftp://axpa.hep.phy.cam.ac.uk/moretti/cavendish_9704 and at
http://www.hep.phy.cam.ac.uk/theory/papers
Leptoproduction of Heavy Quarks II -- A Unified QCD Formulation of Charged and Neutral Current Processes from Fixed-target to Collider Energies
A unified QCD formulation of leptoproduction of massive quarks in charged
current and neutral current processes is described. This involves adopting
consistent factorization and renormalization schemes which encompass both
vector-boson-gluon-fusion (flavor creation) and
vector-boson-massive-quark-scattering (flavor excitation) production
mechanisms. It provides a framework which is valid from the threshold for
producing the massive quark (where gluon-fusion is dominant) to the very high
energy regime when the typical energy scale \mu is much larger than the quark
mass m_Q (where the quark-scattering should be prevalent). This approach
effectively resums all large logarithms of the type (alpha_s(mu)
log(mu^2/m_Q^2)^n which limit the validity of existing fixed-order calculations
to the region mu ~ O(m_Q). We show that the (massive) quark-scattering
contribution (after subtraction of overlaps) is important in most parts of the
(x, Q) plane except near the threshold region. We demonstrate that the
factorization scale dependence of the structure functions calculated in this
approach is substantially less than those obtained in the fixed-order
calculations, as one would expect from a more consistent formulation.Comment: LaTeX format, 29 pages, 11 figures. Revised to make auto-TeX-abl
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