Página 5 dos resultados de 15310 itens digitais encontrados em 0.006 segundos
Resultados filtrados por Publicador: Universidade Cornell

aMCfast: automation of fast NLO computations for PDF fits

Bertone, Valerio; Frederix, Rikkert; Frixione, Stefano; Rojo, Juan; Sutton, Mark
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/06/2014 Português
Relevância na Pesquisa
26.408977%
We present the interface between MadGraph5_aMC@NLO, a self-contained program that calculates cross sections up to next-to-leading order accuracy in an automated manner, and APPLgrid, a code that parametrises such cross sections in the form of look-up tables which can be used for the fast computations needed in the context of PDF fits. The main characteristic of this interface, which we dub aMCfast, is its being fully automated as well, which removes the need to extract manually the process-specific information for additional physics processes, as is the case with other matrix element calculators, and renders it straightforward to include any new process in the PDF fits. We demonstrate this by studying several cases which are easily measured at the LHC, have a good constraining power on PDFs, and some of which were previously unavailable in the form of a fast interface.; Comment: 36 pages, 10 figures

Theoretical model to deduce a PDF with a power law tail using Extreme Physical Information

Bonilla, Ricardo; Zarama, Roberto; Valdivia, Juan Alejandro
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.408977%
The theory of Extreme Physical Information (EPI) is used to deduce a probability density function (PDF) of a system that exhibits a power law tail. The computed PDF is useful to study and fit several observed distributions in complex systems. With this new approach it is possible to describe extreme and rare events in the tail, and also the frequent events in the distribution head. Using EPI, an information functional is constructed, and minimized using Euler-Lagrange equations. As a solution, a second order differential equation is derived. By solving this equation a family of functions is calculated. Using these functions it is possible to describe the system in terms of eigenstates. A dissipative term is introduced into the model, as a relevant term for the study of open systems. One of the main results is a mathematical relation between the scaling parameter of the power law observed in the tail and the shape of the head.; Comment: 11 pages, 12 figures, 1 table, 2 appendices

Nuclear PDF constraints from p+Pb collisions at the LHC

Helenius, Ilkka; Paukkunen, Hannu; Eskola, Kari J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.408977%
As the current nuclear PDF analyses are mainly constrained by fixed-target Drell-Yan and deeply inelastic scattering data only the quark nuclear modifications at fairly large $x$ values are in a good control. Inclusive pion production in d+Au collisions at RHIC provides some constraints for gluons but due to the limited kinematic reach of the data the gluon modifications remain uncertain especially at small values of $x$. In this talk, we discuss how the existing data from p+Pb collisions at the LHC can improve the nuclear PDF fits and which measurements would be sensitive to the small-$x$ gluons. In particular, we consider inclusive hadron production, compare this to direct photons, and show estimates of the effect of CMS dijet measurements to the uncertainty of nuclear gluon distributions.; Comment: Talk presented at DIS2015 conference, April 27 - May 1, 2015, Southern Methodist University, Dallas, Texas. v2: updated reference list

PDF uncertainties in the determination of the W boson mass and of the effective lepton mixing angle at the LHC

Rojo, Juan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/05/2013 Português
Relevância na Pesquisa
26.408977%
The precision measurement of the W boson mass allows to perform stringent consistency tests of the Standard Model by means of global electroweak fits. The accurate determination of the W boson mass is one of the legacy results of the Tevatron, where the experimental accuracy is such that $M_W$ is now limited by theoretical uncertainties related to the parton distributions of the proton. In this contribution, we show how to quantify the impact of PDF uncertainties in the measurement of $M_W$ at the Tevatron and the LHC by means of a template method, and study both the use of the W transverse mass and the lepton pT kinematical distributions to generate these templates. We also present preliminary results on the quantification of the PDF uncertainties in the determination of the effective lepton mixing angle at the LHC, based on the same template method as for the W mass determination; Comment: 5 pages, 4 figures, to appear in the proceedings of the XXI International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2013), Marseille, 22-26 April 2013

Charm and beauty quark masses in the MMHT2014 global PDF analysis

Harland-Lang, L. A.; Martin, A. D.; Motylinski, P.; Thorne, R. S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/10/2015 Português
Relevância na Pesquisa
26.408977%
We investigate the variation in the MMHT2014 PDFs when we allow the heavy quark masses $m_c$ and $m_b$ to vary away from their default values. We make PDF sets available in steps of $\Delta m_c =0.05~{\rm GeV}$ and $\Delta m_b =0.25~{\rm GeV}$, and present the variation in the PDFs and in the predictions. We examine the comparison to the HERA data on charm and beauty structure functions and note that in each case the heavy quark data, and the inclusive data, have a slight preference for lower masses than our default values. We provide PDF sets with 3 and 4 active quark flavours, as well as the standard value of 5 flavours. We use the pole mass definition of the quark masses, as in the default MMHT2014 analysis, but briefly comment on the $\overline{\rm MS}$ definition.; Comment: 20 pages, 12 figures

PDF uncertainties in the extraction of the W mass at LHC: a Snowmass Whitepaper

Rojo, Juan; Vicini, Alessandro
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/09/2013 Português
Relevância na Pesquisa
26.408977%
The precision measurement of the W boson mass is an important milestone for the LHC physics program in the coming years. An accurate measurement of $M_W$ allows to perform stringent consistency tests of the Standard Model by means of global electroweak fits, which in turn are sensitive to New Physics at scales potentially higher than the ones explored in direct searches. From the theoretical point of view, our limited knowledge of PDFs will be one of the dominant sources of uncertainty in ongoing and future LHC determinations of $M_W$. In this whitepaper, we have quantified the impact of PDF uncertainties in the W mass extractions from the transverse mass distribution at the LHC. The calculation has been performed using the NNPDF2.3 set, which includes direct constrains on the W boson production kinematics with data for electroweak gauge boson production from the LHC. Our results confirm previous estimates that PDF uncertainties in the determination of $M_W$ from the $m_W^T$ distribution are moderate, around 10 MeV at most. We briefly discuss also the case of the lepton $p_T$ distribution.; Comment: 6 pages, 4 figures, contribution to Snowmass 2013

PDF/A standard for long term archiving

Vasilescu, Ramona
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/06/2009 Português
Relevância na Pesquisa
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PDF/A is defined by ISO 19005-1 as a file format based on PDF format. The standard provides a mechanism for representing electronic documents in a way that preserves their visual appearance over time, independent of the tools and systems used for creating or storing the files.; Comment: 8 pages, exposed on 5th International Conference "Actualities and Perspectives on Hardware and Software" - APHS2009, Timisoara, Romania

Reengineering PDF-Based Documents Targeting Complex Software Specifications

Nojoumian, Mehrdad; Lethbridge, Timothy C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.408977%
This article aims at reengineering of PDF-based complex documents, where specifications of the Object Management Group (OMG) are our initial targets. Our motivation is that such specifications are dense and intricate to use, and tend to have complicated structures. Our objective is therefore to create an approach that allows us to reengineer PDF-based documents, and to illustrate how to make more usable versions of electronic documents (such as specifications, technical books, etc) so that end users to have a better experience with them. The first step was to extract the logical structure of the document in a meaningful XML format for subsequent processing. Our initial assumption was that, many key concepts of a document are expressed in this structure. In the next phase, we created a multilayer hypertext version of the document to facilitate browsing and navigating. Although we initially focused on OMG software specifications, we chose a general approach for different phases of our work including format conversions, logical structure extraction, text extraction, multilayer hypertext generation, and concept exploration. As a consequence, we can process other complex documents to achieve our goals.; Comment: 27 pages, 15 figures; International Journal of Knowledge and Web Intelligence (IJKWI)...

The Difference PDF of 21-cm Fluctuations: A Powerful Statistical Tool for Probing Cosmic Reionization

Barkana, Rennan; Loeb, Abraham
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/05/2007 Português
Relevância na Pesquisa
26.408977%
A new generation of radio telescopes are currently being built with the goal of tracing the cosmic distribution of atomic hydrogen at redshifts 6-15 through its 21-cm line. The observations will probe the large-scale brightness fluctuations sourced by ionization fluctuations during cosmic reionization. Since detailed maps will be difficult to extract due to noise and foreground emission, efforts have focused on a statistical detection of the 21-cm fluctuations. During cosmic reionization, these fluctuations are highly non-Gaussian and thus more information can be extracted than just the one-dimensional function that is usually considered, i.e., the correlation function. We calculate a two-dimensional function that if measured observationally would allow a more thorough investigation of the properties of the underlying ionizing sources. This function is the probability distribution function (PDF) of the difference in the 21-cm brightness temperature between two points, as a function of the separation between the points. While the standard correlation function is determined by a complicated mixture of contributions from density and ionization fluctuations, we show that the difference PDF holds the key to separately measuring the statistical properties of the ionized regions.; Comment: 11 pages...

Predictions for high energy neutrino cross-sections from the ZEUS global PDF fits

Cooper-Sarkar, Amanda; Sarkar, Subir
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.408977%
We have updated predictions for high energy neutrino and antineutrino charged current cross-sections within the conventional DGLAP formalism of NLO QCD using a modern PDF fit to HERA data, which also accounts in a systematic way for PDF uncertainties deriving from both model uncertainties and from the experimental uncertainties of the input data sets. Furthermore the PDFs are determined using an improved treatment of heavy quark thresholds. A measurement of the neutrino cross-section much below these predictions would signal the need for extension of the conventional formalism as in BFKL resummation, or even gluon recombination effects as in the colour glass condensate model.; Comment: 10 pages (RevTeX4), 6 figures; expanded discussion of additional theoretical uncertainties at low x; accepted for publication in JHEP

The photon PDF of the proton

Martin, A. D.; Ryskin, M. G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/06/2014 Português
Relevância na Pesquisa
26.408977%
We show how the photon input parton distribution function (PDF) may be calculated with good accuracy, and used in an extended DGLAP global parton analysis in which the photon is treated as an additional point-like parton. The uncertainty of the input photon PDF is relatively small, since the major part of the distribution (which is produced by the coherent emission of the photon from a proton that remains intact) is well known. We present the expected photon PDFs, and compare the predictions with ZEUS data for isolated photon electroproduction at negative rapidities.; Comment: 11 pages, 6 figures, 3 tables

PDF articles metadata harvester

Abdillah, Leon Andretti
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/01/2013 Português
Relevância na Pesquisa
26.408977%
Scientific journals are very important in recording the finding from researchers around the world. The recent media to disseminate scientific journals is PDF. On scheme to find the scientific journals over the internet is via metadata. Metadata stores information about article summary. Embedding metadata into PDF of scientific article will grant the consistency of metadata readness. Harvesting the metadata from scientific journal is very interesting field at the moment. This paper will discuss about scientific journal metadata harvesters involving XMP.; Comment: 6 Pages, 9 images, 1 table

On the initial conditions of the 1-point PDF for incompressible Navier-Stokes fluids

Tessarotto, M.; Asci, C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/03/2010 Português
Relevância na Pesquisa
26.517358%
An aspect of fluid dynamics lies in the search of possible statistical models for Navier-Stokes (NS) fluids described by classical solutions of the incompressible Navier-Stokes equations (INSE). This refers in particular to statistical models based on the so-called inverse kinetic theory (IKT) . This approach allows the description of fluid systems by means a suitable 1-point velocity probability density function (PDF) which determines, in terms of suitable "moments", the complete set of fluid fields which define the fluid state. A fundamental related issue lies in the problem of the unique construction of the initial PDF. The goal of this paper is to propose a solution holding for NS fluids. Our claim is that the initial PDF can be uniquely determined by imposing a suitable set of physical realizability constraints.

Hiding Malicious Content in PDF Documents

Popescu, Dan-Sabin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/01/2012 Português
Relevância na Pesquisa
26.517358%
This paper is a proof-of-concept demonstration for a specific digital signatures vulnerability that shows the ineffectiveness of the WYSIWYS (What You See Is What You Sign) concept. The algorithm is fairly simple: the attacker generates a polymorphic file that has two different types of content (text, as a PDF document for example, and image: TIFF - two of the most widely used file formats). When the victim signs the dual content file, he/ she only sees a PDF document and is unaware of the hidden content inside the file. After obtaining the legally signed document from the victim, the attacker simply has to change the extension to the other file format. This will not invalidate the digital signature, as no bits were altered. The destructive potential of the attack is considerable, as the Portable Document Format (PDF) is widely used in e-government and in e-business contexts.; Comment: 8 pages

A method for reconstructing the PDF of a 3D turbulent density field from 2D observations

Brunt, Christopher M.; Federrath, Christoph; Price, Daniel J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/03/2010 Português
Relevância na Pesquisa
26.517358%
We introduce a method for calculating the probability density function (PDF) of a turbulent density field in three dimensions using only information contained in the projected two-dimensional column density field. We test the method by applying it to numerical simulations of hydrodynamic and magnetohydrodynamic turbulence in molecular clouds. To a good approximation, the PDF of log(normalised column density) is a compressed, shifted version of the PDF of log(normalised density). The degree of compression can be determined observationally from the column density power spectrum, under the assumption of statistical isotropy of the turbulence.; Comment: 5 pages, 2 figures, accepted for publication in MNRAS Letters