1,464 research outputs found
Momentum space saturation model for deep inelastic scattering and single inclusive hadron production
No full textWe show how the Santana Amaral-Gay Ducati-Betemps-Soyez (AGBS) model, originally developed for deep inelastic scattering applied to HERA data on the proton structure function, can also describe the RHIC data on single inclusive hadron yield for d þ Au and p þ p collisions through a new simultaneous fit. The single inclusive hadron production is modeled through the color glass condensate, which uses the quark (and gluon) condensate amplitudes in momentum space. The AGBS model is also a momentum space model based on the asymptotic solutions of the Balitsky-Kovchegov equation, although a different definition of the Fourier transform is used. This aspect is overcome, and a description entirely in transverse momentum of both processes arises for the first time. The small difference between the simultaneous fit and the one for HERA data alone suggests that the AGBS model describes very well both kinds of processes and thus emerges as a good tool to investigate the inclusive hadron production data.We use this model for predictions at LHC energies, which agrees very well with available experimental data
Publisher’s Note: Estimations for the Higgs boson production with QCD and electroweak corrections in exclusive events at the LHC [Phys. Rev. DPRVDAQ1550-7998<b>84</b>, 034042 (2011)]
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Fotoprodução de mésons vetoriais pesados em colisões ultraperiferais e periferais
No full textNeste trabalho, investigamos a fotoprodu c~ao exclusiva dos m esons vetoriais pesados V (J= ; (2S); Y (1S); Y (2S); Y (3S)) em colisões periféricas e ultraperiféricas para as energias do Large Hadron Collider (LHC). Utilizando o método de Weizsacker-Williams, a seção de choque hadrônica e descrita em função de duas componentes: o uxo de fotons e a seção de choque de fotoprodução. O primeiro descreve a radiação eletromagnética emitida por um dos hadrons em colisão, enquanto o segundo caracteriza a interação da radiação (fótons) com o alvo hadrônico. Em nossos calculos, descrevemos a seção de choque de fotoprodução a partir do formalismo de dipolos de cor, no qual j a estão includos efeitos de supressão como o fenômeno de saturação partônica. No formalismo em questão, o fotonutua em um par quark-antiquark que, por sua vez, interage com o alvo e, por m, se recombina para formar o meson. Para descrever a interação do dipolo com o alvo, modelos de dipolo baseados na equação BK, a qual governa a dinâmica de evolução do dipolo, são utilizados. No regime UPC, calculamos a distribuição em rapidez e a seção de choque total dos m esons citados em colisões pp, p-Pb e Pb-Pb. Para pp e p-Pb, os modelos de dipolo CGC e BCGC apresentam melhor concordância com os dados de LHC. Por outro lado, os resultados para colis~oes Pb-Pb superestimam os dados (somente para J= at e o momento), nos levando a concluir que o formalismo de dipolos não est a considerando todo o efeito de supressão. No regime periferal, as colaborações ALICE e STAR observaram um grande excesso na produção de J= para pequeno pT . Visto que a fotoprodução exclusiva atua nesta região cinematica, n os estendemos o formalismo de dipolos usado em UPC atrav es da construção de três cenarios baseados na geometria da colisão: (cenario 1) aplicação direta do uxo de fotons usual, com dependencia no parametro de impacto, e da seção de choque fotonuclear UPC sem qualquer outra modicação relevante; (cenario 2) aplicação de um uxo de fotons efetivo, construdo em função do uxo de fotons usual, e da seção de choque fotonuclear UPC; (cenario 3) alem do uxo de fotons efetivo, tambem foi considerada uma seção de choque fotonuclear efetiva. Os resultados obtidos com os três diferentes cenarios foram comparados com as medidas de ALICE, mostrando melhor acordo com os dados no cenario 3, principalmente nas regiões mais centrais (30%-50% and 50%-70%). Embora não seja possível armar que a fotoprodução exclusiva e a unica responsável pelo excesso de J= observado nos experimentos, existem indicações de que este mecanismo de produção e respons avel por uma significativa parte deste efeito.In this work, the exclusive photoproduction for the heavy vector mesons V (J= ; (2S); Y (1S); Y (2S); Y (3S)) is investigated in peripheral and ultrapheriferal collisons at LHC energies. Using the Weizsacker-Williams method, the hadronic cross section was written in function of two components: the photon ux and the photoproduction cross section. The photon ux describes the eletromagnetic radiation emitted for one of the incomming hadrons, while the photoproduction cross section characterizes the scattering of radiation (photons) on the hadronic target. In our calculations, the photoproduction cross section is described by colour dipole formalism, in which are already present suppression e ects like the partonic saturation phenomenon. In this formalism, the incoming virtual photon uctuates into a quark-antiquark pair, then the q q pair scatters elastically into the proton, and nally the q q pair recombines to form the meson. To describe the dipole-target interaction, dipole models based in the BK equation, which governs the dynamics of dipole evolution, was used. In the UPC regime, the rapidity distribution and the total cross section was calculated for the V mesons in pp, p-Pb and Pb-Pb collisions. For pp and p-Pb, the dipole models CGC and bCGC presented better aggrement with the LHC data. Therefore, the results for Pb-Pb collisions overestimate the data (only for J= so far) in the large rapidity range, possibly meaning that the dipole formalism is not considering all the suppresion e ects. In the peripheral regime, the ALICE and STAR collaborations observed an excess for J= production at very small pT . Since exclusive photoproduction operates in this kinematic region, the dipole formalism used in UPC was extended to peripheral regime considering three scenarios based in the geometry of the collision: (scenario 1) the direct application of the usual photon ux with b dependence and of the photonuclear cross section with no relevant change in relation to the UPC, (scenario 2) the application of an e ective photon ux keeping the photonuclear cross section unchanged, and (scenario 3) also considering an e ective photonuclear cross section. The results obtained with the three di erent scenarios were compared with the ALICE measurements, showing a better agreement with the data in the more complete approach (scenario 3), mainly in the more central regions (30%-50% and 50%-70%). Although it is not yet possible to con rm that the exclusive photoproduction is fully responsible for the J= excess observed in ALICE, however there are good indications that it produces a considerable part of the e ect
High Density QCD Through Eletromagnetic Probes
No full textIn this work we investigate the high density QCD system through the dilepton production. First, the dilepton production in the color dipole approach is investigated, studing perturbative unitarity corrections to the dipole cross section and its consequence in the transverse momentum distribution of the dileptons at RHIC and LHC energies. Second, the dilepton production in the context of the Color Glass Condensate is investigated. The transverse momentum distribution and the rapidity distribution are investigated to dilepton production at RHIC and LHC energies in this framework
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Unitarity corrections to the structure functions through the dipole picture
No full textWe study the dipole picture for the description of deep inelastic scattering, focusing on the structure functions which are driven directly by the gluon distribution. One performs estimates using the effective dipole cross section given by the Glauber-Mueller approach in QCD, which encodes the corrections due to the unitarity effects associated with the saturation phenomenon. We also address issues about frame invariance of the calculations when analyzing the observables
Diffractive higgs boson photoproduction in peripheral collisions
No full textAn alternative process is proposed for the diffractive Higgs boson production inspired in the Durham model, exploring it through the photon-proton interaction. In this sense, we estimate the production cross section of the Higgs boson, comparing some sets of parton distributions in the proton and confronting this results with those from other processes
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