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Searches for top and Higgs compositeness at the LHC

• Aurelio Juste (IFAE)

A possible extension of the Standard Model that addresses the hierarchy problem in a natural way involves the existence of a new strongly-interacting sector, of which the Higgs boson would be a pseudo-Goldstone boson of a spontaneously-broken global symmetry. One particular realization of this scenario, referred to as "Composite Higgs", predicts the existence of new fermionic resonances (referred to as vector-like quarks), which can be produced in pairs or single and have multiple decay modes, giving striking experimental signatures at the LHC. Another prediction is the existence of heavy bosonic resonances from the composite sector that would predominantly couple to third-generation quarks, leading to increased 4-top and ttbb production at high energies. In this talk we will review the strategies and challenges, as well as the latest results, of this research program at the LHC. We will also discuss the prospects for Run 2 and future LHC runs.

Search strategies for pair production of heavy Higgs bosons decaying invisibly at the LHC

• Ernesto Arganda (UNLP, La Plata)

The search for heavy Higgs bosons at the LHC represents an intense experimental program, carried out by the ATLAS and CMS collaborations, as well as the hunt of invisible Higgs decays and dark matter candidates. No significant deviations from the SM backgrounds have been observed in any of these searches, imposing important constraints over the parameter space of different new physics models with an extended Higgs sector. Here we discuss an alternative search strategy for heavy Higgs bosons decaying invisibly at the LHC, focusing on the pair production of a heavy scalar $H$ together with a pseudoscalar $A$, through the production mode $q \bar q \to Z^\ast \to HA$. We identify as the most promising signal the final state made up by $4b + E_T^\text{miss}$, coming from the heavy scalar decay mode $H \to hh \to b \bar b b \bar b$, being $h$ the discovered SM-like Higgs boson of 125 GeV, together with the invisible channel of the pseudoscalar. We work within the context of simplified MSSM scenarios that contain quite heavy sfermions of most types with ${\cal O}(10)$ TeV masses, while the stops are heavy enough to reproduce the 125 GeV mass for the lightest SM-like Higgs boson. By contrast, the gauginos/higgsinos and the heavy MSSM Higgs bosons have masses near the EW scale. Our search strategies, for a LHC center-of-mass energy of $\sqrt{s} =$ 14 TeV, allow us to obtain statistical significances of the signal over the SM backgrounds with values up to $\sim$ 1.6$\sigma$ and $\sim$ 3$\sigma$, for total integrated luminosities of 300 fb$^{-1}$ and 1000 fb$^{-1}$, respectively.

pp -> hh @ LHC

• Ignacio Fabre (ICAs)
• Daniel De Florian (ICAS)

LFV Higgs decays in low-scale seesaw models within the mass insertion approximation

• Roberto Morales (UNLP)

In this talk I present a new computation of the Lepton Flavor Violating Higgs decays that are generated radiatively to one-loop from heavy right-handed neutrinos. We work within the context of the Inverse Seesaw model with three right-handed neutrinos and three extra singlets, but the results could be generalized to other Low Scale Seesaw models. The novelty of our computation is that it uses a completely different method by means of the Mass Insertion Approximation which works with the electroweak interaction states instead of the usual 9 physical neutrino mass eigenstates of the Inverse Seesaw model. This method also allows us to write the analytical results explicitly in terms of the most relevant model parameters, that are the neutrino Yukawa coupling matrix and the right-handed mass matrix, which is very convenient for a phenomenological analysis. We also study numerically the goodness of the Mass Insertion Approximation results. In the last part we present the computation of the relevant one-loop effective vertex for the Lepton Flavor Violating Higgs decay which is derived from a large right-handed neutrino mass expansion of the form factors. We believe that our simple formula found for this effective vertex can be of interest for other researchers who wish to estimate the corresponding rates in a fast way in terms of their own preferred input values for the relevant model parameters.

Measuring Vtd at the LHC

• Mariel Estevez (ICAS)

We propose a direct measurement of the CKM element Vtd at the LHC. Taking profit of the imbalance between d and d¯ quark content in the proton, we show that a non-zero Vtd induces a charge asymmetry in the tW associated production. The main backgrounds to this process, tt¯ production, and tW associated production mediated by Vtb, give charge symmetric contributions at leading order in QCD. Therefore, using specific kinematic features of the signal, we construct a charge asymmetry in the di-lepton final state which, due also to a reduction of systematic uncertainties in the asymmetry, is potentially sensitive to Vtd suppressed effects. In particular, using signal and background simulations up to detector level, we show that this new observable could improve the current direct upper bound on |Vtd| already with existing LHC data. We also project that |Vtd| values down to ∼10 times the Standard Model prediction could be probed in the high luminosity phase of the LHC.

Searching for SUSY at the LHC: promising signals for left sneutrino LSP and other possibilities

• Daniel Lopz Fogliani (UBA, Buenos Aires)

Supersymmetric extensions of the standard model provides a solution the the hierarchy problem and the possibility to give observable signals at the LHC. When R-parity is broken and the right-handed neutrinos are included in the spectrum many interesting interpretations are possible. After a brief introduction of the simplest model including many useful interpretations and desirable properties, we are going to discuss possible interesting signals in some particular cases. For instance for a left sneutrino LSP, there are two dominant channels, direct production via a Z boson, or production via a W± decaying into a left sneutrino and a left slepton next-to-LSP (NLSP), with the latter decaying into another left sneutrino plus a very soft W± subproduct. From the decay of a pair of left sneutrinos LSPs of any family, a diphoton signal plus missing transverse energy (MET) from neutrinos can be present. In addition, in the case of a pair of tau left sneutrinos LSPs, given the large value of the tau Yukawa coupling, diphoton plus leptons and/or multileptons can appear.

TBA

• Marcela Carena (FermiLab)

UBA@ATLAS

• Gustavo Otero y Garzon (UBA)

Analysis and implementations by the UBA group at ATLAS

(some) dark matter at (some) colliders

• Jose Zurita (KIT)

TBA

• Leandro Da Rold (CAB, Bariloche)

Enlarging the Regions of the MSSM Parameter Space for large tan beta via SUSY Decays of the Heavy Higgs Bosons

• Anibal Medina (UNLP, La Plata)

In the Minimal Supersymmetric Standard Model (MSSM) searches for the heaviest CP-even and CP-odd Higgs H, A to tau-lepton pairs severely constrain the parameter region for large values of tanβ and light Higgs bosons H, A. We demonstrate how the exper- imental constraint can be avoided by new decays to light third-generation sfermions, whose left-right couplings to H can be maximised in regions of large trilinear couplings Ab, Aτ for sbottoms and staus, or large supersymmetric (SUSY) Higgs mass μ for stops. Due to the tanβ-enhancement in the production cross-sections via gluon-fusion and in association with bottom-quark pairs for H and A, we find that down-type sfermions, in particular, sbottoms perform a better job in allowing more parameter space than up-type sfermions such as stops, which require much larger values of μ to compensate for tanβ. Vacuum stability as well as flavour observables constraints and direct searches for SUSY particles are imposed. We also associate the lightest CP-even Higgs with the observed 125 GeV SM-like Higgs and impose the experimental constraints from the LHC.