1,354 research outputs found
Pseudoscalar Higgs boson production at hadron colliders in NNLO QCD
We compute the total cross-section for direct production of the pseudoscalar
Higgs boson in hadron collisions at next-to-next-to-leading order (NNLO) in
perturbative QCD. The O(alpha_s^2) QCD corrections increase the NLO production
cross-section by approximately 20-30 per cent.Comment: 5 pages, revtex
NNLO Corrections to the Polarized Drell-Yan Coefficient Function
We present the full next-to-next-to-leading order (NNLO) corrections to the
coefficient function for the polarized cross section of
the Drell-Yan process. We study the effect of these corrections on the process
at an C.M. energy . All QCD partonic
subprocesses have been included provided the lepton pair is created by a
virtual photon, which is a valid approximation for a lepton pair invariant mass
. For this reaction the dominant subprocess is given by and its higher order corrections so that it provides us with an
excellent tool to measure the polarized sea-quark densities.Comment: 5 pages, 5 figures, 7th DESY Workshop on Elementary Particle Theory,
Loops and Legs in Quantum Field Theory, Zinnowitz, Germany, April 25-30, 200
Bottom quark electroproduction in variable flavor number schemes
Two variable flavor number schemes are used to describe bottom quark
production in deep inelastic electron-proton scattering. In these schemes the
coefficient functions are derived from mass factorization of the heavy quark
coefficient functions presented in a fixed flavor number scheme. Also one has
to construct a parton density set with five light flavors (u,d,s,c,b) out of a
set which only contains four light flavors (u,d,s,c). In order the
two sets are discontinuous at which follows from mass factorization
of the heavy quark coefficient functions when it is carried out in the -scheme. Both variable flavor number schemes give almost identical
predictions for the bottom structure functions and . Also
they both agree well with the corresponding results based on fixed order
four-flavor perturbation theory over a wide range in and .Comment: Latex with seventeen PostScript figure
Molecular beam epitaxy of highly mismatched N-rich GaNSb and InNAs alloys
GaN materials alloyed with group V anions form the so-called highly mismatched alloys (HMAs). Recently, the authors succeeded in growing N-rich GaNAs and GaNBi alloys over a large composition range by plasma-assisted molecular beam epitaxy (PA-MBE). Here, they present first results on PA-MBE growth and properties of N-rich GaNSb and InNAs alloys and compare these with GaNAs and GaNBi alloys. The enhanced incorporation of As and Sb was achieved by growing the layers at extremely low growth temperatures. Although layers become amorphous for high As, Sb, and Bi content, optical absorption measurements show a progressive shift of the optical absorption edge to lower energy. The large band gap range and controllable conduction and valence band positions of these HMAs make them promising materials for efficient solar energy conversion devices
Top Quark Production Cross Section
The production rate for top quarks at the Fermilab Tevatron is presented
using the exact order corrected cross section and the resummation
of the leading soft gluon corrections in all orders of perturbation theory.Comment: preprint FERMILAB-Pub-93/270-T, ITP-SB-93-55, THU-93/23, Latex 9
pages, 8 postscript figures, uuencoded and appended at end of fil
NLO corrections to differential cross sections for pseudo-scalar Higgs boson production
We have computed the full next-to-leading (NLO) QCD corrections to the
differential distributions for pseudo-scalar Higgs (A)
production at large hadron colliders. This calculation has been carried out
using the effective Lagrangian approach which is valid as long as the mass of
the pseudo-scalar Higgs boson and its transverse momentum do
not exceed the top-quark mass . The shape of the distributions hardly
differ from those obtained for scalar Higgs (H) production because, apart from
the overall coupling constant and mass, there are only small differences
between the partonic differential distributions for scalar and pseudo-scalar
production. Therefore there are only differences in the magnitudes of the
hadronic differential distributions which can be mainly attributed to the
unknown mixing angle describing the pseudo-scalar Higgs coupling to the
top quarks.Comment: 9 pages, LaTeX, 3 Postscript figures In the previous version we have
forgotten to include contributions which arrise from interferences between
graphs containing vertices corresponding to the operator in Eq. (3)
with graphs originating from the operator . These interferences occur
because of the prescription for the Levi-Civita tensor given in our paper.
These extra contributions are added to Eqs. (19) and (20). Numerically they
are completely negligible so that the figures are not altere
The curvature of as a probe of the range of validity of perturbative QCD evolutions in the small- region
Perturbative NLO and NNLO QCD evolutions of parton distributions are studied,
in particular in the (very) small- region, where they are in very good
agreement with all recent precision measurements of . These
predictions turn out to be also rather insensitive to the specific choice of
the factorization scheme ( or DIS). A characteristic feature of
perturbative QCD evolutions is a {\em{positive}} curvature of which
increases as decreases. This perturbatively stable prediction provides a
sensitive test of the range of validity of perturbative QCD.Comment: 17 pages, 6 figures, 2 tables; minor corrections, to appear in EPJ
NNLO corrections to massive lepton-pair production in longitudinally polarized proton-proton collisions
We present the full next-to-next-to-leading order (NNLO) coefficient
functions for the polarized cross section for the Drell-Yan
process . Here denotes any inclusive hadronic
state and represents the invariant mass of the lepton pair. All QCD
partonic subprocesses have been included provided the lepton pair is created by
a virtual photon, which is a valid approximation for GeV. Unlike the
differential distribution w.r.t. transverse momentum the dominant subprocess
for the integrated cross section is given by and
its higher order corrections so that massive lepton pair production provides us
with an excellent tool to measure the polarized anti-quark densities. Our
calculations are carried out using the method of -dimensional regularization
by making a special choice for the matrix. We give predictions for
double longitudinal spin asymmetry measurements at the RHIC.Comment: 45 pages, 22 figures. Due to a bug in our program the mass
factorization plots in fig. 8-11 are changed. All parton density sets, in
particular the set BB1 (J. Blumlein, H. Bottcher), lead to an improvement in
the scale dependence while going from LO to NLO and then to NNL
Comparison between variable flavor number schemes for charm quark electroproduction
Where appropriate, the abbreviation 'VFNS' is replaced by 'CSN' to indicate
the scheme using massive heavy quark coefficient functions proposed in this
paper. The text below Eq. (2.13) and between Eqs. (2.33) and (2.36) has been
considerably changed.Comment: 64 pages, LaTeX, 16 Postscript figure
Reconstructing the primordial power spectrum from the CMB
We propose a straightforward and model independent methodology for
characterizing the sensitivity of CMB and other experiments to wiggles,
irregularities, and features in the primordial power spectrum. Assuming that
the primordial cosmological perturbations are adiabatic, we present a function
space generalization of the usual Fisher matrix formalism, applied to a CMB
experiment resembling Planck with and without ancillary data. This work is
closely related to other work on recovering the inflationary potential and
exploring specific models of non-minimal, or perhaps baroque, primordial power
spectra. The approach adopted here, however, most directly expresses what the
data is really telling us. We explore in detail the structure of the available
information and quantify exactly what features can be reconstructed and at what
statistical significance.Comment: 43 pages Revtex, 23 figure
- âŠ