343 research outputs found
Towards the determination of the photon parton distribution function constrained by LHC data
We provide a discussion of the impact of a subset of Drell-Yan data from LHC
on the determination of the photon parton distribution function (PDF), using
the NNPDF methodology. In previous work we have shown that the photon PDF
determined from deep-inelastic scattering (DIS) data only has large
uncertainties, suggesting the need for more data from other processes such as
Drell-Yan, which unlike DIS, includes photon-induced contributions at leading
order in QED. We describe the inclusion of ATLAS Drell-Yan W, Z data, which is
a subset of the LHC data used in a final photon PDF determination, by means of
a reweighting procedure. We show the impact of such data by comparing the
reweighted photon PDF with the photon PDF from DIS, highlighting the reduction
of uncertainties at medium/small-x. We conclude that the Drell-Yan data from
LHC allows a reasonably accurate determination of the photon PDF.Comment: 5 pages, 10 figures, to appear in the proceedings of the XXI
International Workshop on Deep-Inelastic Scattering and Related Subjects
(DIS2013), Marseille, 22-26 April 201
Machine learning challenges in theoretical HEP
In these proceedings we perform a brief review of machine learning (ML)
applications in theoretical High Energy Physics (HEP-TH). We start the
discussion by defining and then classifying machine learning tasks in
theoretical HEP. We then discuss some of the most popular and recent published
approaches with focus on a relevant case study topic: the determination of
parton distribution functions (PDFs) and related tools. Finally, we provide an
outlook about future applications and developments due to the synergy between
ML and HEP-TH.Comment: 7 pages, 3 figures, in proceedings of the 18th International Workshop
on Advanced Computing and Analysis Techniques in Physics Research (ACAT 2017
Disentangling electroweak effects in Z-boson production
Parton distributions with QED corrections open new scenarios for high
precision physics. We recall the need for accurate and improved predictions
which keeps into account higher order QCD corrections together with electroweak
effects. We study predictions obtained with the improved Born approximation and
the scheme by using two public codes: DYNNLO and HORACE. We focus our
attention on the Drell-Yan Z-boson invariant mass distribution at low- and
high-mass regions, recently measured by the ATLAS experiment and we estimate
the impact of each component of the final prediction. We show that electroweak
corrections are larger than PDF uncertainties for modern PDF sets and therefore
such corrections are necessary to improve the extraction of future PDF sets.Comment: 5 pages, 4 figures, to appear in the proceedings of the Les
Rencontres de Physique de la Vall\'ee d'Aoste, La Thuile 201
Modeling NNLO jet corrections with neural networks
We present a preliminary strategy for modeling multidimensional distributions
through neural networks. We study the efficiency of the proposed strategy by
considering as input data the two-dimensional next-to-next leading order (NNLO)
jet k-factors distribution for the ATLAS 7 TeV 2011 data. We then validate the
neural network model in terms of interpolation and prediction quality by
comparing its results to alternative models.Comment: Proceedings for the Cracow Epiphany Conference 2017, final versio
Perturbative QCD description of jet data from LHC Run-I and Tevatron Run-II
We present a systematic comparison of jet predictions at the LHC and the
Tevatron, with accuracy up to next-to-next-to-leading order (NNLO). The exact
computation at NNLO is completed for the gluons-only channel, so we compare the
exact predictions for this channel with an approximate prediction based on
threshold resummation, in order to determine the regions where this
approximation is reliable at NNLO. The kinematic regions used in this study are
identical to the experimental setup used by recently published jet data from
the ATLAS and CMS experiments at the LHC, and CDF and D0 experiments at the
Tevatron. We study the effect of choosing different renormalisation and
factorisation scales for the NNLO exact prediction and as an exercise assess
their impact on a PDF fit including these corrections. Finally we provide
numerical values of the NNLO k-factors relevant for the LHC and Tevatron
experiments.Comment: 51 pages, 13 figures, 35 tables. Final version, matches published
version in JHE
Towards the compression of parton densities through machine learning algorithms
One of the most fascinating challenges in the context of parton density
function (PDF) is the determination of the best combined PDF uncertainty from
individual PDF sets. Since 2014 multiple methodologies have been developed to
achieve this goal. In this proceedings we first summarize the strategy adopted
by the PDF4LHC15 recommendation and then, we discuss about a new approach to
Monte Carlo PDF compression based on clustering through machine learning
algorithms.Comment: 4 pages, 4 figures, to appear in the proceedings of 50th Rencontres
de Moriond, QCD and High Energy Interactions, La Thuile, Italy, March 201
Jet grooming through reinforcement learning
We introduce a novel implementation of a reinforcement learning (RL)
algorithm which is designed to find an optimal jet grooming strategy, a
critical tool for collider experiments. The RL agent is trained with a reward
function constructed to optimize the resulting jet properties, using both
signal and background samples in a simultaneous multi-level training. We show
that the grooming algorithm derived from the deep RL agent can match
state-of-the-art techniques used at the Large Hadron Collider, resulting in
improved mass resolution for boosted objects. Given a suitable reward function,
the agent learns how to train a policy which optimally removes soft wide-angle
radiation, allowing for a modular grooming technique that can be applied in a
wide range of contexts. These results are accessible through the corresponding
GroomRL framework.Comment: 11 pages, 10 figures, code available at
https://github.com/JetsGame/GroomRL, updated to match published versio
APFEL: A PDF Evolution Library with QED corrections
Quantum electrodynamics and electroweak corrections are important ingredients
for many theoretical predictions at the LHC. This paper documents APFEL, a new
PDF evolution package that allows for the first time to perform DGLAP evolution
up to NNLO in QCD and to LO in QED, in the variable-flavor-number scheme and
with either pole or MSbar heavy quark masses. APFEL consistently accounts for
the QED corrections to the evolution of quark and gluon PDFs and for the
contribution from the photon PDF in the proton. The coupled QCD+QED equations
are solved in x-space by means of higher order interpolation, followed by
Runge-Kutta solution of the resulting discretized evolution equations. APFEL is
based on an innovative and flexible methodology for the sequential solution of
the QCD and QED evolution equations and their combination. In addition to PDF
evolution, APFEL provides a module that computes Deep-Inelastic Scattering
structure functions in the FONLL general-mass variable-flavor-number scheme up
to O(). All the functionalities of APFEL can be accessed via a
Graphical User Interface, supplemented with a variety of plotting tools for
PDFs, parton luminosities and structure functions. Written in Fortran 77, APFEL
can also be used via the C/C++ and Python interfaces, and is publicly available
from the HepForge repository.Comment: 34 pages, 5 figures. Final version, to be published in CPC. Several
corrections and improvements. Program available from
http://apfel.hepforge.org
Doped Parton Distributions
Calculations of high-energy processes involving the production of b-quarks
are typically performed in two different ways, the massive four-flavour scheme
(4FS) and the massless five-flavour scheme (5FS). For processes where the
combination of the 4FS and 5FS results into a matched calculation is
technically difficult, it is possible to define a hybrid scheme known as the
doped scheme, where above the b-quark threshold the strong coupling runs with
, as in the massless calculation, while the DGLAP splitting functions
are those of the scheme. In this contribution we present NNPDF3.0 PDF
sets in this doped scheme, compare them with the corresponding 4FS and 5FS
sets, and discuss their relevance for LHC phenomenology.Comment: 5 pages, 5 figures, to appear in the proceedings of the 27th
Rencontres de Blois on Particle Physics and Cosmology, Blois, May 31 to June
05, 201
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