76 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

### Heavy flavour mass corrections to the longitudinal and transverse cross sections in e^+e^- - collisions

The sentence, 7th line below Eq. (28), starting with "Further we exclude all
interference terms ...." is wrong and has been corrected. Eq. (33) :
f_k^{l,(i)} -> h_k^{l,(i)} i=0,1 Second line below Eq. (33) m_bar(m)=m is
replaced by m_bar(\mu_0)=\mu_0 with \mu_0=4.10 GeV and \mu_0=166.1 GeV for
bottom and top respectively. The numbers in the third column of tables 1 and 2
are a little bit changed.Comment: 8 pages Latex, all compressed by uufile

### 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 $\alpha_s^2$ the
two sets are discontinuous at $\mu=m_b$ which follows from mass factorization
of the heavy quark coefficient functions when it is carried out in the ${\bar
{\rm MS}}$-scheme. Both variable flavor number schemes give almost identical
predictions for the bottom structure functions $F_{2,b}$ and $F_{L,b}$. Also
they both agree well with the corresponding results based on fixed order
four-flavor perturbation theory over a wide range in $x$ and $Q^2$.Comment: Latex with seventeen PostScript figure

### Theoretical Uncertainties in the QCD Evolution of Structure Functions and their Impact on $\alpha_s(M_Z^2)$

The differences are discussed between various next-to-leading order
prescriptions for the QCD evolution of parton densities and structure
functions. Their quantitative impact is understood to an accuracy of 0.02\%.
The uncertainties due to the freedom to choose the renormalization and
factorization scales are studied. The quantitative consequences of the
different uncertainties on the extraction of the strong coupling constant
$\alpha_s$ from scaling violations in deep--inelastic scattering are estimated
for the kinematic regime accessible at HERA.Comment: 10 pages Latex, including 3 eps-figures, and a style file. To appear
in: Proc. of the International Workshop: QCD and QED in Higher Orders,
Rheinsberg, April, 1996, Nucl. Phys. {\bf B} (Proc. Suppl); The lay-out of
the paper has been changed, one figure sent separately before has been bound
i

### 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 $d \Delta\sigma/d Q$ of
the Drell-Yan process. We study the effect of these corrections on the process
$p+p\to l^+l^-+`X'$ at an C.M. energy $\sqrt{S}=200 GeV$. 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
$Q<50 GeV$. For this reaction the dominant subprocess is given by $q+\bar q\to
\gamma^*+`X'$ 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

### Second order QCD corrections to the forward-backward asymmetry in e^+e^- - collisions

The sentence, 11th line below Eq. (30), starting with "Further in [14] one
has included all interference terms ...." is wrong and has been corrected.
Second line below Eq. (40) m_bar(m)=m is replaced by m_bar(\mu_0)=\mu_0 with
\mu_0=4.10 GeV, \mu_0=1.30 GeV and \mu_0=166.1 GeV for bottom, charm and top
respectively. The numbers in the second and third column of table 3 are a
little bit changed. In the acknowledgement the funding agency is mentioned and
one reference i.e. [20] is added.Comment: 11 pages Late

### NLO corrections to the polarized Drell-Yan cross section in proton-proton collisions

We present the full next-to-leading order (NLO) corrected inclusive cross
section for massive lepton pair production in longitudinally polarized
proton-proton collisions. All QCD partonic subprocesses have been included
provided the lepton pair is created by a virtual photon, which is a valid
approximation for $Q<50 {\rm GeV}$. Like in unpolarized proton-proton
scattering the dominant subprocess is given by the $q(\bar q)g$-channel so that
massive lepton pair production provides us with an excellent method to measure
the spin density of the gluon. Using our calculations we give predictions for
the longitudinal spin asymmetry measurements at the RHIC.Comment: 4 pages, LaTeX, 2 Postscript figures. Talk presented at the 6th
International Symposium on Radiative Corrections "RADCOR 2002" and 6th
Zeuthen Workshop on Elementary Particle Theory. Kloster Banz, Germany,
September 8-13, 200

### Non-singlet structure functions beyond the next-to-next-to leading order

We study the evolution of the flavour non-singlet deep-inelastic structure
functions F_{2,NS} and F_3 at the next-to-next-to-next-to-leading order (N^3LO)
of massless perturbative QCD. The present information on the corresponding
three-loop coefficient functions is used to derive approximate expressions of
these quantities which prove completely sufficient for values x > 10^{-2} of
the Bjorken variable. The inclusion of the N^3LO corrections reduces the
theoretical uncertainty of alpha_s determinations from non-singlet scaling
violations arising from the truncation of the perturbation series to less than
1%. We also study the predictions of the soft-gluon resummation, of
renormalization-scheme optimizations by the principle of minimal sensitivity
(PMS) and the effective charge (ECH) method, and of the Pade' summation for the
structure-function evolution kernels. The PMS, ECH and Pade' approaches are
found to facilitate a reliable estimate of the corrections beyond N^3LO.Comment: 29 pages, LaTeX, 12 eps-figure

### 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

### Top Quark Production Cross Section

The production rate for top quarks at the Fermilab Tevatron is presented
using the exact order $\alpha_s^3$ 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

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