Search results for "Físicas"
showing 10 items of 251 documents
Measurement of the production cross section of jets in association with a Z boson in pp collisions at $\sqrt{s}$ = 7 TeV with the ATLAS detector
2013
Measurements of the production of jets of particles in association with a Z boson in pp collisions at s√ = 7 TeV are presented, using data corresponding to an integrated luminosity of 4.6 fb[superscript −1] collected by the ATLAS experiment at the Large Hadron Collider. Inclusive and differential jet cross sections in Z events, with Z decaying into electron or muon pairs, are measured for jets with transverse momentum p [subscript T] > 30 GeV and rapidity |y| < 4.4. The results are compared to next-to-leading-order perturbative QCD calculations, and to predictions from different Monte Carlo generators based on leading-order and next-to-leading-order matrix elements supplemented by parton sh…
Measurement of upsilon production in 7 TeV pp collisions at ATLAS
2013
Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAM
Search for new particles in two-jet final states in 7 TeV proton-proton collisions with the ATLAS detector at the LHC
2010
19 páginas, 2 figuras, 1 tabla.-- et al.(ATLAS Collaboration).
Measurement of multi-jet cross sections in proton-proton collisions at a 7 TeV center-of-mass energy
2011
Inclusive multi-jet production is studied in proton–proton collisions at a center-of-mass energy of 7 TeV, using the ATLAS detector. The data sample corresponds to an integrated luminosity of 2.4 pb−1. Results on multi-jet cross sections are presented and compared to both leading-order plus parton-shower Monte Carlo predictions and to next-to-leading-order QCD calculations.
Medium effects in DIS from polarized nuclear targets
2014
The behavior of the nucleon structure functions in lepton nuclei deep inelastic scattering, both polarized and unpolarized, due to nuclear structure effects is reanalyzed. The study is performed in two schemes: an x-rescaling approach, and one in which there is an increase of sea quark components in the in medium nucleon, related to the low energy N-N interaction. In view of a recent interesting experimental proposal to study the behavior of the proton spin structure functions in nuclei we proceed to compare these approaches in an effort to enlighten the possible phenomenological interest of such difficult experiment.
The triple collinear limit of one-loop QCD amplitudes
2003
We consider the singular behaviour of one-loop QCD matrix elements when several external partons become simultaneously parallel. We present a new factorization formula that describes the singular collinear behaviour directly in colour space. The collinear singularities are embodied in process-independent splitting matrices that depend on the momenta, flavours, spins and colours of the collinear partons. We give the general structure of the infrared and ultraviolet divergences of the one-loop splitting matrices. We also present explicit one-loop results for the triple collinear splitting, $q \to q {\bar Q} Q$, of a quark and a quark--antiquark pair of different flavours. The one-loop triple …
The pion distribution amplitude and the pion-photon transition form factor in a nonlocal chiral quark model
2014
We study the pion Distribution Amplitude (\pi DA) in the context of a nonlocal chiral quark model. The corresponding Lagrangian reproduces the phenomenological values of the pion mass and decay constant, as well as the momentum dependence of the quark propagator obtained in lattice calculations. It is found that the obtained \pi DA has two symmetric maxima, which arise from the new contributions generated by the nonlocal character of the interactions. This \pi DA is applied to leading order and next-to-leading order calculations of the pion-photon transition form factor. Implications of the results are discussed.
Collinear splitting, parton evolution and the strange-quark asymmetry of the nucleon in NNLO QCD
2004
We consider the collinear limit of QCD amplitudes at one-loop order, and their factorization properties directly in colour space. These results apply to the multiple collinear limit of an arbitrary number of QCD partons, and are a basic ingredient in many higher-order computations. In particular, we discuss the triple collinear limit and its relation to flavour asymmetries in the QCD evolution of parton densities at three loops. As a phenomenological consequence of this new effect, and of the fact that the nucleon has non-vanishing quark valence densities, we study the perturbative generation of a strange--antistrange asymmetry $s(x)-\bar{s}(x)$ in the nucleon's sea.
Form factors of radiative pion decays in nonlocal chiral quark models
2012
We study the radiative pion decay π +→e +ν eγ within nonlocal chiral quark models that include wave function renormalization. In this framework we analyze the momentum dependence of the vector form factor F V(q2) and the slope of the axial-vector form factor F A(q2) at threshold. Our results are compared with available experimental information and with the predictions given by the Nambu-Jona-Lasinio model. In addition we calculate the low energy constants δ 5 and δ 6, comparing our results with the values obtained in chiral perturbation theory.
A search for new physics in dijet mass and angular distributions in pp collisions at [subscript √s=7] TeV measured with the ATLAS detector
2011
A search for new interactions and resonances produced in LHC proton–proton (pp) collisions at a centre-of-mass energy ps = 7 TeV was performed with the ATLAS detector. Using a dataset with an integrated luminosity of 36 pb−1, dijet mass and angular distributions were measured up to dijet masses of 3.5 TeV and were found to be in good agreement with Standard Model predictions. This analysis sets limits at 95% CL on various models for new physics: an excited quark is excluded for mass between 0.60 and 2.64 TeV, an axigluon hypothesis is excluded for axigluon masses between 0.60 and 2.10 TeV and quantum black holes are excluded in models with six extra space–time dimensions for quantum gravity…