19 research outputs found
Testing nuclear parton distributions with pA collisions at the LHC
Global perturbative QCD analyses, based on large data sets from
electron-proton and hadron collider experiments, provide tight constraints on
the parton distribution function (PDF) in the proton. The extension of these
analyses to nuclear parton distributions (nPDF) has attracted much interest in
recent years. nPDFs are needed as benchmarks for the characterization of hot
QCD matter in nucleus-nucleus collisions, and attract further interest since
they may show novel signatures of non-linear density-dependent QCD evolution.
However, it is not known from first principles whether the factorization of
long-range phenomena into process-independent parton distribution, which
underlies global PDF extractions for the proton, extends to nuclear effects. As
a consequence, assessing the reliability of nPDFs for benchmark calculations
goes beyond testing the numerical accuracy of their extraction and requires
phenomenological tests of the factorization assumption. Here we argue that a
proton-nucleus collision program at the LHC would provide a set of measurements
allowing for unprecedented tests of the factorization assumption underlying
global nPDF fits.Comment: 4 pages, 3 figure
Jet Fragmentation Function Moments in Heavy Ion Collisions
The nature of a jet's fragmentation in heavy-ion collisions has the potential
to cast light on the mechanism of jet quenching. However the presence of the
huge underlying event complicates the reconstruction of the jet fragmentation
function as a function of the momentum fraction z of hadrons in the jet. Here
we propose the use of moments of the fragmentation function. These quantities
appear to be as sensitive to quenching modifications as the fragmentation
function directly in z. We show that they are amenable to background
subtraction using the same jet-area based techniques proposed in the past for
jet p_t's. Furthermore, complications due to correlations between
background-fluctuation contributions to the jet's p_t and to its particle
content are easily corrected for.Comment: 15 pages, 5 figure
AAMQS: a non-linear QCD description of new HERA data at small-x
We present a global analysis of available data on inclusive structure
functions measured in electron-proton scattering at small values of Bjorken-x,
including the latest data from the combined HERA analysis on reduced cross
sections. Our approach relies on the dipole formulation of DIS together with
the use of the non-linear running coupling BK equation for the description of
the small-x dynamics. With the resulting parametrization we are able to
describe the latest FL data measured by the H1 collaboration. Further, we
discuss the kinematical domain where significant deviations from NLO-DGLAP
should be expected and the ability of non-linnear physics to account for such
deviations.Comment: 4 pages, 2 figures, Proceedings of Quark Matter 2011, Annecy, Franc
A predictive phenomenological tool at small Bjorken-x
We present the results from global fits of inclusive DIS experimental data
using the Balitsky-Kovchegov equation with running coupling.Comment: 5 pages, 2 figures, prepared for the Proceedings of 'Hot Quarks 2010
Testing collinear factorization and nuclear parton distributions with pA collisions at the LHC
Global perturbative QCD analyses, based on large data sets from
electron-proton and hadron collider experiments, provide tight constraints on
the parton distribution function (PDF) in the proton. The extension of these
analyses to nuclear parton distributions (nPDF) has attracted much interest in
recent years. nPDFs are needed as benchmarks for the characterization of hot
QCD matter in nucleus-nucleus collisions, and attract further interest since
they may show novel signatures of non- linear density-dependent QCD evolution.
However, it is not known from first principles whether the factorization of
long-range phenomena into process-independent parton distribution, which
underlies global PDF extractions for the proton, extends to nuclear effects. As
a consequence, assessing the reliability of nPDFs for benchmark calculations
goes beyond testing the numerical accuracy of their extraction and requires
phenomenological tests of the factorization assumption. Here we argue that a
proton-nucleus collision program at the LHC would provide a set of measurements
allowing for unprecedented tests of the factorization assumption underlying
global nPDF fits.Comment: 4 pages, 5 figure
Reaction-diffusion processes in zero transverse dimensions as toy models for high-energy QCD
We examine numerically different zero-dimensional reaction-diffusion
processes as candidate toy models for high-energy QCD evolution. Of the models
examined -- Reggeon Field Theory, Directed Percolation and Reversible Processes
-- only the latter shows the behaviour commonly expected, namely an increase of
the scattering amplitude with increasing rapidity. Further, we find that
increasing recombination terms, quantum loops and the heuristic inclusion of a
running of the couplings, generically slow down the evolution.Comment: 17 pages, 7 figure
Medium dependence of multiplicity distributions in MLLA
We study the modification of the multiplicity distributions in MLLA due to
the presence of a QCD medium. The medium is introduced though a multiplicative
constant () in the soft infrared parts of the kernels of QCD evolution
equations. Using the asymptotic ansatz for quark and gluons mean multiplicities
and respectively, we study two
cases: fixed as previously considered in the literature, and fixed
. We find opposite behaviors of the dispersion of the multiplicity
distributions with increasing in both cases. For fixed the
dispersion decreases, while for fixed it increases.Comment: LaTeX, 9 pages, 4 eps figures; proceedings of the 3rd International
Conference on Hard and Electromagnetic Probes in High-Energy Nuclear
Collisions - Hard Probes 2008 (Illa de A Toxa, Spain, June 8th-14th 2008
Out of Medium Fragmentation from Long-Lived Jet Showers
We study the time structure of vacuum jet evolution via a simple uncertainty
principle estimate in the kinematic range explored by current heavy ion
collisions at the LHC. We observe that a large fraction of the partonic
splittings occur at large times, of the order of several fm. We compare the
time distribution of vacuum splittings with the distribution of path lengths
traversed by jets in a heavy ion collision. We find that if no medium induced
modification of the jet dynamics were present, a very large fraction (larger
than 80% for inclusive jets) of the jet splittings would occur outside of the
medium. We confront this observation with current available data on jet
properties in heavy ion collisions and discuss its implications for the
dynamics of jet-medium interactions.Comment: 10 pages, 6 figure
Análisis de las actitudes de los estudiantes hacia el aprendizaje colaborativo y en línea
El presente proyecto aborda dos aspectos muy importantes y estrechamente ligados a la adquisición de competencias básicas de cualquier titulación de grado actual y altamente demandadas por los empleadores: la adquisición de habilidades para desarrollar trabajo colaborativo y la capacidad de desarrollar actividades de aprendizaje en línea. Estas últimas tienen una doble función. Por una parte, deben preparar a los estudiantes para ser capaces de gestionar su trabajo, de manera autónoma, con vistas al posible desarrollo de trabajo no presencial, cada vez más importante en muchos entornos laborales. Por otra parte, deber permitirles adquirir las habilidades necesarias para continuar se formación a lo largo de su vida (LLL, Long Life Learning) a través de entornos más informales, pero no por ello menos efectivos, como puede ser el caso de los Massive Online Open Courses (MOOC), ofertados cada vez por más instituciones, con cursos de calidad, impartidos por grandes expertos y con posibilidades de certificación del trabajo realizado
Testing factorization in pA collisions at the LHC
Global perturbative QCD analyses, based on large data sets from e-p and hadron collider experiments, provide tight constraints on the parton distribution function (PDF) in the proton. The extension of these analyses to nuclear parton distributions (nPDF) has attracted much interest in recent years. nPDFs are needed as benchmarks for the characterization of hot QCD matter in nucleus-nucleus collisions, and attract further interest since they may show novel signatures of non-linear density-dependent QCD evolution. However, it is not known from first principles whether the factorization of long-range phenomena into process-independent parton distribution, which underlies global PDF extractions for the proton, extends to nuclear effects. As a consequence, assessing the reliability of nPDFs for benchmark calculations goes beyond testing the numerical accuracy of their extraction and requires phenomenological tests of the factorization assumption. Here we argue that a proton-nucleus collision programme at the LHC, including a rapidity scan, would provide a set of measurements allowing for unprecedented tests of the factorization assumption underlying global nPDF fits