1,720,981 research outputs found
Heavy neutral gauge bosons at the LHC in an extended MSSM
No full textSearching for heavy neutral gauge bosons Z', predicted in extensions of the Standard Model based on a U(1)' gauge symmetry, is one of the challenging objectives of the experiments carried out at the Large Hadron Collider. In this paper, we study Z' phenomenology at hadron colliders according to several U(1)'-based models and in the Sequential Standard Model. In particular, possible Z' decays into supersymmetric particles are included, in addition to the Standard Model modes so far investigated. We point out the impact of the U(1)' group on the MSSM spectrum and, for a better understanding, we consider a few benchmarks points in the parameter space. We account for the D-term contribution, due to the breaking of U(I)', to slepton and squark masses and investigate its effect on Z' decays into sfermions. Results on branching ratios and cross sections are presented, as a function of the MSSM and U(I)' parameters, which are varied within suitable ranges. We pay special attention to final states with leptons and missing energy and make predictions on the number of events with sparticle production in Z' decays, for a few values of integrated luminosity and centre-of-mass energy of the LHC. (C) 2012 Elsevier B.V. All rights reserved
Modelling non-perturbative corrections to bottom-quark fragmentation
No full textWe describe B-hadron production in e(+)e(-) annihilation at the Z(0) pole by means of a model including non-perturbative corrections to b-quark fragmentation as originating, via multiple soft emissions, from an effective QCD coupling constant, which does not exhibit the Landau pole any longer and includes absorptive effects due to parton branching. We work in the framework of perturbative fragmentation functions at NLO, with NLL DGLAP evolution and NNLL large-x resummation in both coefficient function and initial condition of the perturbative fragmentation function. We include hadronization corrections via the effective coupling constant in the NNLO approximation and do not add any further non-perturbative fragmentation function. As part of our model, we perform the Mellin transforms of our resummed expressions exactly. We present results on the energy distribution of b-flavored hadrons, which we compare with LEP and SLD data, in both x- and N-spaces. We find that, within the theoretical uncertainties on our calculation, our model is able to reasonably reproduce the data at x less than or similar to 0.92 and the first five moments of the B cross section. (C) 2007 Elsevier B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Vector boson production at hadron colliders: Results from HERWIG and resummed calculations
No full textTop-mass determination from leptonic final states
No full textThe top-quark mass is a fundamental parameter of the Standard Model, as it plays a crucial role in the electroweak precision tests, stability of the vacuum and inflation. I review the method and the main results contained in a recent ATLAS analysis which measures the top mass by using the invariant mass of the leptons coming from W and B-hadron decays. The extracted top mass turns out to be the most precise single measurement by ATLAS
Phenomenology of supersymmetric Z ′ decays at the Large Hadron Collider
Full text linkI study the phenomenology of heavy neutral bosons , predicted in GUT-inspired U(1) models, at the Large Hadron Collider. In particular, I investigate possible signatures due to decays into supersymmetric particles, such as chargino, neutralino, and sneutrino pairs, leading to final states with charged leptons and missing energy. The analysis is carried out at TeV, for a few representative points of the parameter space of the Minimal Supersymmetric Standard Model, suitably modified to accommodate the extra boson and consistent with the discovery of a Higgs-like boson with mass around 125 GeV. Results are presented for several observables and compared with those obtained for direct decays into lepton pairs, as well as direct production of supersymmetric particles. For the sake of comparison, phenomenology in an effective supersymmetric extension of the Sequential Standard Model is also discussed
The Top-Quark Mass: Challenges in Definition and Determination
Full text linkThe top-quark mass is a parameter of paramount importance in particle physics, playing a crucial role in the electroweak precision tests and in the stability of the Standard Model vacuum. I will discuss the main strategies to extract the top-quark mass at the LHC and the interpretation of the measurements in terms of well-posed top-mass definitions, taking particular care about renormalon ambiguities, progress in Monte Carlo event generators for top physics and theoretical uncertainties
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