102 research outputs found

    Top production at the LHC: the impact of PDF uncertainties and correlations

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    In this contribution we discuss the impact of PDF uncertainties on t\bar{t} and t-channel single-top production at the LHC. We present predictions for total cross-sections computed at NLO accuracy with different PDF sets. For single- top production, we point out that the uncertainty arising from the choice of the bottom quark mass is one of the dominant theoretical uncertainties on the total cross-section. Finally, the possibility of using PDF induced correlations between top quark and electroweak vector boson production cross-sections to improve the accuracy of LHC measurements is investigated.Comment: 8 pages, 5 figures. To appear in the Proceedings of the International Workshop on Top Quark Physics (top2010), Bruges, Belgium, May 31 - June 4, 201

    An extensive survey of the estimation of uncertainties from missing higher orders in perturbative calculations

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    We consider two approaches to estimate and characterise the theoretical uncertainties stemming from the missing higher orders in perturbative calculations in Quantum Chromodynamics: the traditional one based on renormalisation and factorisation scale variation, and the Bayesian framework proposed by Cacciari and Houdeau. We estimate uncertainties with these two methods for a comprehensive set of more than thirty different observables computed in perturbative Quantum Chromodynamics, and we discuss their performance in properly estimating the size of the higher order terms that are known. We find that scale variation with the conventional choice of varying scales within a factor of two of a central scale gives uncertainty intervals that tend to be somewhat too small to be interpretable as 68% confidence-level-heuristic ones. We propose a modified version of the Bayesian approach of Cacciari and Houdeau which performs well for non-hadronic observables and, after an appropriate choice of the relevant expansion parameter for the perturbative series, for hadronic ones too.Comment: 34 pages, 24 figure

    Next-to-leading order QCD corrections to di-photon production in association with up to three jets at the Large Hadron Collider

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    We present the computation of next-to-leading order (NLO) QCD corrections to di-photon production in association with two or three hard jets in pp collisions at a centre-of-mass energy of 8 TeV. The inclusion of NLO corrections is shown to substantially reduce the theoretical uncertainties estimated from scale variations on total cross section predictions. We study a range of differential distributions relevant for phenomenological studies of photon pair production in association with jets at the LHC. Using an efficient computational set-up we performed a detailed study of uncertainties due to parton distribution functions. The computation of the virtual corrections is performed using new features of the C++ library NJet

    Marginal evidence for cosmic acceleration from Type Ia supernovae

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    The ‘standard’ model of cosmology is founded on the basis that the expansion rate of the universe is accelerating at present — as was inferred originally from the Hubble diagram of Type Ia supernovae. There exists now a much bigger database of supernovae so we can perform rigorous statistical tests to check whether these ‘standardisable candles’ indeed indicate cosmic acceleration. Taking account of the empirical procedure by which corrections are made to their absolute magnitudes to allow for the varying shape of the light curve and extinction by dust, we find, rather surprisingly, that the data are still quite consistent with a constant rate of expansion

    Propuesta de un sistema de gestión de calidad ISO 9001: 2015 en La Molina Calidad Total Laboratorios

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    Ciclo Optativo de Especialización y Profesionalización en Gestión de Calidad Total y ProductividadEl presente trabajo profesional es una propuesta alternativa de mejora que permitirá definir con claridad las responsabilidades y actividades dentro de la organización, con una misión y visión que permitan encaminar a la organización a un mejor desenvolvimiento como empresa. Se utilizó como herramienta de comparación la norma ISO 9001:2015, que dicta los requisitos auditables que debe cumplir una organización, para lograr una certificación de sistema de gestión de la calidad. Para realizar la propuesta del Sistema de Gestión de Calidad en la organización, se revisó e interpretó cada uno de sus requisitos de los 10 capítulos que la conforman y a partir del cual se establecieron las bases para el diseño del sistema. En primer lugar, se realizó un exhaustivo análisis de la situación actual de la empresa, consiguiéndose detectar que la organización cumple en gran medida muchos de los requisitos exigidos por la norma ISO 9001:2015, alcanzando un 82% de grado de cumplimiento en relación a la norma, por lo que se propusieron acciones de mejora a implementar, de manera tal que la organización pueda tener cierta base para que la propuesta de un sistema de gestión de la calidad sea factible. Luego se revisaron los procesos que se desarrollan en la organización, y se propusieron nuevos procesos a fin de cumplir con los requisitos de la norma, estos fueron interrelacionados y ordenados, obteniéndose así un mapa de procesos integrados. Se redactaron documentos que forman parte del alcance del sistema de gestión de la calidad y otros adicionales (Manual de calidad, política de la calidad, Gestión de Riesgos y oportunidades, Procedimiento de análisis FODA), que en su conjunto permitirían encaminar a la organización a trabajar bajo los requisitos de la norma. Finalmente se elaboró una propuesta de implementación, que contiene nueve actividades a realizar para lograr la implementación del sistema de gestión de la calidad ISO 9001:2015 en el instituto La Molina Calidad Total Laboratorios.Tesi

    Polarized Parton Distributions at an Electron-Ion Collider

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    We study the potential impact of inclusive deep-inelastic scattering data from a future electron-ion collider (EIC) on longitudinally polarized parton distribution (PDFs). We perform a PDF determination using the NNPDF methodology, based on sets of deep-inelastic EIC pseudodata, for different realistic choices of the electron and proton beam energies. We compare the results to our current polarized PDF set, NNPDFpol1.0, based on a fit to fixed-target inclusive DIS data. We show that the uncertainties on the first moments of the polarized quark singlet and gluon distributions are substantially reduced in comparison to NNPDFpol1.0, but also that more measurements may be needed to ultimately pin down the size of the gluon contribution to the nucleon spin.Comment: 11 pages, 6 figures. Two plots in Fig.5 added and discussion of extrapolation uncertainties expanded. Final version, published in Phys. Lett.

    NLO Cross Sections for the LHC using GOLEM: Status and Prospects

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    In this talk we review the GOLEM approach to one-loop calculations and present an automated implementation of this technique. This method is based on Feynman diagrams and an advanced reduction of one-loop tensor integrals which avoids numerical instabilities. We have extended our one-loop integral library golem95 with an automated one-loop matrix element generator to compute the virtual corrections of the process qqˉ→bbˉbbˉq\bar{q}\to b\bar{b}b\bar{b}. The implementation of the virtual matrix element has been interfaced with tree-level Monte Carlo programs to provide the full result for the above process.Comment: 8 pages, 1 figure, contribution to the proceedings of the 9th International Symposium on Radiative Corrections (RADCOR 2009), October 25-30 2009, Ascona, Switzerlan
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