Diego Becciolini

Z' at the LHC: interference and finite width effects in Drell-Yan

A bstractThe interference effects between an extra neutral spin-1 Z′-boson and the Standard Model background in the Drell-Yan channel at the LHC are studied in detail. The final state with two oppositely charged leptons is considered. The interference contribution to the new physics signal, currently not fully taken into account by experimental collaborations in Z′-searches and in the interpretation of the results, can be substantial. It may affect limits or discovery prospects of Z′ at the LHC. As the Z′-boson interference is model-dependent, a proper treatment would a priori require a dedicated experimental analysis for each particular model. Doing so could potentially improve the sensitivity to new physics, but would require significantly more experimental effort.At the same time, it is shown that one can define an invariant mass window, valid for a wide range of models, for which the contribution of the model-dependent interference to the Beyond the Standard Model signal is reduced to

Interference effects in heavy W'-boson searches at the LHC

\mathcal{O}

Constraining new colored matter from the ratio of 3 to 2 jets cross sections at the LHC

(10%), comparable to the level of the combined uncertainty from parton densities and higher order corrections. This quasi-model-independent “magic cut” does not scale with the mass of the Z′-boson and is approximately constant over a large range of masses. Such control of the interference effects relies on not-too-small branching ratios of Z′ to leptons (typically of at least a few percent) which can be suppressed, however, by additional new decay channels of the Z′; a small width-to-mass ratio alone does not guarantee the interference to be small over an arbitrary kinematic range. Under the general assumption that these new decay channels of Z′ are not dominant, one can perform quasi-model-independent analyses, preserving the current scheme used by the experimental collaborations for the Z′-boson search using the suggested invariant mass window cut.

UV-complete composite Higgs models

Interference effects are widely neglected in searches for new physics. This is the case in recent publications on searches for W?-bosons using leptonic final states. We examine the effects of interference on distributions frequently used to determine mass limits for possible W?-bosons and show that there are important qualitative effects on the behaviour of the new physics signal. There are two main consequences. The first is that current exclusion limits, where interferences effects have not been considered, are likely to have been overestimated. The second is that the way observed limits on the cross-section are presented, in terms of the contribution of new physics to the total cross-section, is not meaningful.

W' production at the LHC in the 4-site Higgsless model

The Large Hadron Collider experiments are probing the evolution of the strong coupling

Custodial vector model

\alpha_s

Improved analysis of the bounds from the electroweak precision tests on the 4-site model

up to the TeV scale. We show how the ratio of 3- to 2-jets cross sections is affected by the presence of new physics and argue that it can be used to place a model-independent bound on new particles carrying QCD color charge. The current data potentially constrains such states to be heavier than a few hundred GeVs.

Publisher’s Note: Constraining new colored matter from the ratio of 3 to 2 jets cross sections at the LHC [Phys. Rev. D91, 015010 (2015)]

We study confining gauge theories with fermions vectorial under the Standard Model (SM) that produce a Higgs doublet as a Nambu-Goldstone boson. The vacuum misalignment required to break the electroweak symmetry is induced by an elementary Higgs doublet with Yukawa couplings to the new fermions. The physical Higgs is a linear combination of elementary and composite Higgses while the SM fermions remain elementary. The full theory is renormalizable and the SM Yukawa couplings are generated from the ones of the elementary Higgs allowing to eliminate all flavor problems but with interesting effects for electric dipole moments of SM particles. We also discuss how ideas on the relaxation of the electroweak scale could be realized within this framework.

Publisher’s Note: Custodial vector model [Phys. Rev. D92, 015013 (2015)]

We study the phenomenology of the 4-site Higgsless model, based on the SU(2)_L × SU(2)_1 × SU(2)_2 × U(1)_Y gauge symmetry, at present colliders. The model predicts the existence of two neutral and four charged extra gauge bosons, Z_(1,2) and W±. In this paper, we focus on the charged gauge sector. We first derive limits on W1,2-boson masses and couplings to SM fermions from direct searches at the Tevatron. We then estimate at the 7 TeV LHC the exclusion limits with the actual L=1 fb?1 and the discovery potential with the expected L=10 fb?1. In contrast to the minimal (or 3-site) Higgsless model which predicts almost fermiophobic extra gauge bosons, the next-to-minimal (or 4-site) Higgsless model recovers sizeable W_(1,2)-boson couplings to ordinary matter, expressing the non-fermiophobic multiresonance inner nature of extra-dimensional theories. Owing to this feature, we find that in one year from now the new heavy gauge bosons, W± , could be discovered in the final state with an electron and large missing transverse energy at the 7 TeV LHC for W1,2-boson masses in the TeV region, depending on model parameters

W' and Z' searches at the LHC

We analyze the Large Hadron Collider (LHC) phenomenology of heavy vector resonances with a