29 research outputs found
A new numerical method for obtaining gluon distribution functions , from the proton structure function
An exact expression for the leading-order (LO) gluon distribution function
from the DGLAP evolution equation for the proton structure
function for deep inelastic scattering has
recently been obtained [M. M. Block, L. Durand and D. W. McKay, Phys. Rev.
D{\bf 79}, 014031, (2009)] for massless quarks, using Laplace transformation
techniques. Here, we develop a fast and accurate numerical inverse Laplace
transformation algorithm, required to invert the Laplace transforms needed to
evaluate , and compare it to the exact solution. We obtain accuracies
of less than 1 part in 1000 over the entire and spectrum. Since no
analytic Laplace inversion is possible for next-to-leading order (NLO) and
higher orders, this numerical algorithm will enable one to obtain accurate NLO
(and NNLO) gluon distributions, using only experimental measurements of
.Comment: 9 pages, 2 figure
EPS09 - a New Generation of NLO and LO Nuclear Parton Distribution Functions
We present a next-to-leading order (NLO) global DGLAP analysis of nuclear
parton distribution functions (nPDFs) and their uncertainties. Carrying out an
NLO nPDF analysis for the first time with three different types of experimental
input -- deep inelastic +A scattering, Drell-Yan dilepton production in
p+ collisions, and inclusive pion production in d+Au and p+p collisions at
RHIC -- we find that these data can well be described in a conventional
collinear factorization framework. Although the pion production has not been
traditionally included in the global analyses, we find that the shape of the
nuclear modification factor of the pion -spectrum at
midrapidity retains sensitivity to the gluon distributions, providing evidence
for shadowing and EMC-effect in the nuclear gluons. We use the Hessian method
to quantify the nPDF uncertainties which originate from the uncertainties in
the data. In this method the sensitivity of to the variations of the
fitting parameters is mapped out to orthogonal error sets which provide a
user-friendly way to calculate how the nPDF uncertainties propagate to any
factorizable nuclear cross-section. The obtained NLO and LO nPDFs and the
corresponding error sets are collected in our new release called {\ttfamily
EPS09}. These results should find applications in precision analyses of the
signatures and properties of QCD matter at the LHC and RHIC.Comment: 34 pages, 16 figures. The version accepted for publicatio
A posteriori inclusion of parton density functions in NLO QCD final-state calculations at hadron colliders: The APPLGRID Project
A method to facilitate the consistent inclusion of cross-section measurements
based on complex final-states from HERA, TEVATRON and the LHC in proton parton
density function (PDF) fits has been developed. This can be used to increase
the sensitivity of LHC data to deviations from Standard Model predictions. The
method stores perturbative coefficients of NLO QCD calculations of final-state
observables measured in hadron colliders in look-up tables. This allows the
posteriori inclusion of parton density functions (PDFs), and of the strong
coupling, as well as the a posteriori variation of the renormalisation and
factorisation scales in cross-section calculations.
The main novelties in comparison to original work on the subject are the use
of higher-order interpolation, which substantially improves the trade-off
between accuracy and memory use, and a CPU and computer memory optimised way to
construct and store the look-up table using modern software tools.
It is demonstrated that a sufficient accuracy on the cross-section
calculation can be achieved with reasonably small look-up table size by using
the examples of jet production and electro-weak boson (Z, W) production in
proton-proton collisions at a center-of-mass energy of 14 TeV at the LHC.
The use of this technique in PDF fitting is demonstrated in a PDF-fit to HERA
data and simulated LHC jet cross-sections as well as in a study of the jet
cross-section uncertainties at various centre-of-mass energies
Inclusive Jet Production, Parton Distributions, and the Search for New Physics
Jet production at the Tevatron probes some of the smallest distance scales
currently accessible. A gluon distribution that is enhanced at large x compared
to previous determinations provides a better description of the Run 1b jet data
from both CDF and D0. However, considerable uncertainty still remains regarding
the gluon distribution at high x. In this paper, we examine the effects of this
uncertainty, and of the remaining uncertainties in the NLO QCD theory, on jet
cross section comparisons to Run 1b data. We also calculate the range of
contributions still possible from any new physics. Predictions are also made
for the expanded kinematic range expected for the ongoing Run 2 at the Tevatron
and for the LHC.Comment: 50 pages, 31 figures, RevTe
Determination of polarized parton distribution functions and their uncertainties
We investigate the polarized parton distribution functions (PDFs) and their
uncertainties by using the world data on the spin asymmetry A_1. The
uncertainties of the polarized PDFs are estimated by the Hessian method. The up
and down valence-quark distributions are determined well. However, the
antiquark distributions have large uncertainties at this stage, and it is
particularly difficult to fix the gluon distribution. The \chi^2 analysis
produces a positively polarized gluon distribution, but even \Delta g(x)=0
could be allowed according to our uncertainty estimation. In comparison with
the previous AAC (Asymmetry Analysis Collaboration) parameterization in 2000,
accurate SLAC-E155 proton data are added to the analysis. We find that the E155
data improve the determination of the polarized PDFs, especially the polarized
antiquark distributions. In addition, the gluon-distribution uncertainties are
reduced due to the correlation with the antiquark distributions. We also show
the global analysis results with the condition \Delta g(x)=0 at the initial
scale, Q^2=1 GeV^2, for clarifying the error correlation effects with the gluon
distribution.Comment: 9 pages, 15 eps figures, REVTeX, FORTRAN package is available at the
web site http://www-hs.phys.saga-u.ac.jp/aac.html. Replaced 3 eps figures in
Fig.
A systematic study of J/psi suppression in cold nuclear matter
Based on a Glauber model, a statistical analysis of all mid-rapidity J/psi
hadroproduction and leptoproduction data on nuclear targets is carried out.
This allows us to determine the J/psi-nucleon inelastic cross section, whose
knowledge is crucial to interpret the J/psi suppression observed in heavy-ion
collisions, at SPS and at RHIC. The values of sigma are extracted from each
experiment. A clear tension between the different data sets is reported. The
global fit of all data gives sigma=3.4+/-0.2 mb, which is significantly smaller
than previous estimates. A similar value, sigma=3.5+/-0.2 mb, is obtained when
the nDS nuclear parton densities are included in the analysis, although we
emphasize that the present uncertainties on gluon (anti)shadowing do not allow
for a precise determination of sigma. Finally, no significant energy dependence
of the J/psi-N interaction is observed, unless strong nuclear modifications of
the parton densities are assumed.Comment: 25 pages, 5 figure
Kaluza-Klein gravitino production with a single photon at e^+ e^- colliders
In a supersymmetric large extra dimension scenario, the production of
Kaluza-Klein gravitinos accompanied by a photino at e^+ e^- colliders is
studied. We assume that a bulk supersymmetry is softly broken on our brane such
that the low-energy theory resembles the MSSM. Low energy supersymmetry
breaking is further assumed as in GMSB, leading to sub-eV mass shift in each KK
mode of the gravitino from the corresponding graviton KK mode. Since the
photino decays within a detector due to its sufficiently large inclusive decay
rate into a photon and a gravitino, the process e^+ e^- -> photino + gravitino
yields single photon events with missing energy. Even if the total cross
section can be substantial at sqrt(s)=500 GeV, the KK graviton background of
e^+ e^- -> photon + graviton is kinematically advantageous and thus much
larger. It is shown that the observable, sigma(e^-_L)-sigma(e^-_R), can
completely eliminate the KK graviton background but retain most of the KK
gravitino signal, which provides a unique and robust method to probe the
supersymmetric bulk.Comment: Reference added and typos correcte
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
Tevatron Run-1 Z Boson Data and Collins-Soper-Sterman Resummation Formalism
We examine the effect of the Z-boson transverse momentum distribution
measured at the Run-1 of the Tevatron on the nonperturbative function of the
Collins-Soper-Sterman (CSS) formalism, which resums large logarithmic terms
from multiple soft gluon emission in hadron collisions. The inclusion of the
Tevatron Run-1 Z-boson data strongly favors a Gaussian form of the CSS
nonperturbative function, when combined with the other low energy Drell-Yan
data in a global fit.Comment: Published version; minor modifications, three references added; 19
pages, 7 figure
European Red List of Marine Fishes
The European Red List is a review of the conservation
status of European species according to IUCN regional
Red Listing guidelines. It identifies those species that are
threatened with extinction at the regional level, so that
appropriate conservation action can be taken to improve
their status. This Red List publication summarises results
for all described native European marine fishes.Postprin