1,272 research outputs found
Next-to-next-to-leading logarithmic corrections at small transverse momentum in hadronic collisions
We study the region of small transverse momenta in qqbar- and gg-initiated
processes with no colored particle detected in the final state. We present the
universal expression of the O(alpha_s^2) logarithmically enhanced contributions
up to next-to-next-to-leading logarithmic accuracy. From there we extract the
coefficients that allow the resummation of the large logarithmic contributions.
We find that the coefficient known in the literature as B^{(2)} is process
dependent, since it receives a hard contamination from the one loop correction
to the leading order subprocess. We present the general result of B^{(2)} for
both quark and gluon channels. In particular, in the case of Higgs production,
this result will be relevant to improve the matching between resummed
predictions and fixed order calculations.Comment: LaTeX, 8 pages. Few typos corrected, particularly Eq.(25). Two
references added, to be published in PR
A next-to-next-to-leading order calculation of soft-virtual cross sections
We compute the next-to-next-to-leading order (NNLO) soft and virtual QCD
corrections for the partonic cross section of colourless-final state processes
in hadronic collisions. The results are valid to all orders in the dimensional
regularization parameter \ep. The dependence of the results on a particular
process is given through finite contributions to the one and two-loop
amplitudes. To evaluate the accuracy of the soft-virtual approximation we
compare it with the full NNLO result for Drell-Yan and Higgs boson production
via gluon fusion. We also provide a universal expression for the hard
coefficient needed to perform threshold resummation up to
next-to-next-to-leading logarithmic (NNLL) accuracy.Comment: 25 pages, 4 figure
QCD radiative corrections to prompt diphoton production in association with a jet at hadron colliders
We compute the next-to-leading order corrections in to prompt
diphoton production in association with a jet at hadron colliders. We use a
next-to-leading order general-purpose partonic Monte Carlo event generator that
allows the computation of a rate differential in the produced photons and
hadrons.Comment: 17 pages, 6 figures, JHEP3 documen
Space-like (vs. time-like) collinear limits in QCD: is factorization violated?
We consider the singular behaviour of QCD scattering amplitudes in
kinematical configurations where two or more momenta of the external partons
become collinear. At the tree level, this behaviour is known to be controlled
by factorization formulae in which the singular collinear factor is universal
(process independent). We show that this strict (process-independent)
factorization is not valid at one-loop and higher-loop orders in the case of
the collinear limit in space-like regions (e.g., collinear radiation from
initial-state partons). We introduce a generalized version of all-order
collinear factorization, in which the space-like singular factors retain some
dependence on the momentum and colour charge of the non-collinear partons. We
present explicit results on one-loop and two-loop amplitudes for both the
two-parton and multiparton collinear limits. At the level of square amplitudes
and, more generally, cross sections in hadron--hadron collisions, the violation
of strict collinear factorization has implications on the non-abelian structure
of logarithmically-enhanced terms in perturbative calculations (starting from
the next-to-next-to-leading order) and on various factorization issues of mass
singularities (starting from the next-to-next-to-next-to-leading order).Comment: 81 pages, 5 figures, typos corrected in the text, few comments added
and inclusion of NOTE ADDED on recent development
Structure and Production of Lambda Baryons
We discuss the quark parton structure of the baryon and the
fragmentation of quarks into baryons. We show that the hyperfine
interaction, responsible for the - and - mass
splittings, leads not only to sizeable SU(3) and SU(6) symmetry breaking in the
quark distributions of the , but also to significant polarized
non-strange quark distributions. The same arguments suggest flavor asymmetric
quark fragmentation functions and non-zero polarized non-strange quark
fragmentation functions. The calculated fragmentation functions give a good
description of all measured observables. We predict significant positive
polarization in semi-inclusive DIS experiments while models based on
SU(3) flavor symmetry predict zero or negative polarization. Our
approach also provides a natural explanation for the dependence of the maximum
of the spectrum on the mass of the particles produced in
annihilation.Comment: 24 pages, 9 figures, minor change
Probing Shadowed Nuclear Sea with Massive Gauge Bosons in the Future Heavy-Ion Collisions
The production of the massive bosons and could provide an
excellent tool to study cold nuclear matter effects and the modifications of
nuclear parton distribution functions (nPDFs) relative to parton distribution
functions (PDFs) of a free proton in high energy nuclear reactions at the LHC
as well as in heavy-ion collisions (HIC) with much higher center-of mass
energies available in the future colliders. In this paper we calculate the
rapidity and transverse momentum distributions of the vector boson and their
nuclear modification factors in p+Pb collisions at TeV and in
Pb+Pb collisions at TeV in the framework of perturbative QCD
by utilizing three parametrization sets of nPDFs: EPS09, DSSZ and nCTEQ. It is
found that in heavy-ion collisions at such high colliding energies, both the
rapidity distribution and the transverse momentum spectrum of vector bosons are
considerably suppressed in wide kinematic regions with respect to p+p reactions
due to large nuclear shadowing effect. We demonstrate that in the massive
vector boson productions processes with sea quarks in the initial-state may
give more contributions than those with valence quarks in the initial-state,
therefore in future heavy-ion collisions the isospin effect is less pronounced
and the charge asymmetry of W boson will be reduced significantly as compared
to that at the LHC. Large difference between results with nCTEQ and results
with EPS09 and DSSZ is observed in nuclear modifications of both rapidity and
distributions of and in the future HIC.Comment: 13 pages, 21 figures, version accepted for publication in Eur. Phys.
J.
Diffractive deeply inelastic scattering of hadronic states with small transverse size
Diffractive deeply inelastic scattering from a hadron is described in terms
of diffractive quark and gluon distributions. If the transverse size of the
hadronic state is sufficiently small, these distributions are calculable using
perturbation theory. We present such a calculation and discuss the underlying
dynamics. We comment on the relation between this dynamics and the pattern of
scaling violation observed in the hard diffraction of large-size states at
HERA.Comment: 8 pages including 3 figures, REVTE
Next-to-leading order predictions for Z gamma+jet and Z gamma gamma final states at the LHC
We present next-to-leading order predictions for final states containing
leptons produced through the decay of a Z boson in association with either a
photon and a jet, or a pair of photons. The effect of photon radiation from the
final state leptons is included and we also allow for contributions arising
from fragmentation processes. Phenomenological studies are presented for the
LHC in the case of final states containing charged leptons and in the case of
neutrinos. We also use the procedure introduced by Stewart and Tackmann to
provide a reliable estimate of the scale uncertainty inherent in our
theoretical calculations of jet-binned Z gamma cross sections. These
computations have been implemented in the public code MCFM.Comment: 30 pages, 10 figure
MINLO: Multi-scale improved NLO
In the present work we consider the assignment of the factorization and
renormalization scales in hadron collider processes with associated jet
production, at next-to-leading order (NLO) in perturbation theory. We propose a
simple, definite prescription to this end, including Sudakov form factors to
consistently account for the distinct kinematic scales occuring in such
collisions. The scheme yields results that are accurate at NLO and, for a large
class of observables, it resums to all orders the large logarithms that arise
from kinematic configurations involving disparate scales. In practical terms
the method is most simply understood as an NLO extension of the matrix element
reweighting procedure employed in tree level matrix element-parton shower
merging algorithms. By way of a proof-of-concept, we apply the method to Higgs
and Z boson production in association with up to two jets.Comment: 27 pages, 17 figure
Transverse Momentum Dependent Parton Distribution/Fragmentation Functions at an Electron-Ion Collider
We present a summary of a recent workshop held at Duke University on Partonic
Transverse Momentum in Hadrons: Quark Spin-Orbit Correlations and Quark-Gluon
Interactions. The transverse momentum dependent parton distribution functions
(TMDs), parton-to-hadron fragmentation functions, and multi-parton correlation
functions, were discussed extensively at the Duke workshop. In this paper, we
summarize first the theoretical issues concerning the study of partonic
structure of hadrons at a future electron-ion collider (EIC) with emphasis on
the TMDs. We then present simulation results on experimental studies of TMDs
through measurements of single spin asymmetries (SSA) from semi-inclusive
deep-inelastic scattering (SIDIS) processes with an EIC, and discuss the
requirement of the detector for SIDIS measurements. The dynamics of parton
correlations in the nucleon is further explored via a study of SSA in D (`D)
production at large transverse momenta with the aim of accessing the unexplored
tri-gluon correlation functions. The workshop participants identified the SSA
measurements in SIDIS as a golden program to study TMDs in both the sea and
valence quark regions and to study the role of gluons, with the Sivers
asymmetry measurements as examples. Such measurements will lead to major
advancement in our understanding of TMDs in the valence quark region, and more
importantly also allow for the investigation of TMDs in the sea quark region
along with a study of their evolution.Comment: 44 pages 23 figures, summary of Duke EIC workshop on TMDs accepted by
EPJ
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