Search for resonanttt¯production in proton-proton collisions ats=8 <

Abstract

A search is performed for the production of heavy resonances decaying into topantitop quark pairs in proton-proton collisions at √ s = 8 TeV. Data used for the analyses were collected with the CMS detector and correspond to an integrated luminosity of 19.7 fb −1 . The search is performed using events with three different final states, defined by the number of leptons (electrons and muons) from the tt → WbWb decay. The analyses are optimized for reconstruction of top quarks with high Lorentz boosts, where jet substructure techniques are used to enhance the sensitivity. Results are presented for all channels and a combination is performed. No significant excess of events relative to the expected yield from standard model processes is observed. Upper limits on the production cross section of heavy resonances decaying to tt are calculated. A narrow leptophobic topcolor Z resonance with a mass below 2.4 TeV is excluded at 95% confidence level. Limits are also derived for a broad Z resonance with a 10% width relative to the resonance mass, and a Kaluza-Klein excitation of the gluon in the Randall-Sundrum model. These are the most stringent limits to date on heavy resonances decaying into top-antitop quark pairs. Published in Physical Review D asThe CMS experiment uses a particle-flow (PF) based event reconstruction [37,38], which aggregates input from all subdetectors. This information includes charged-particle tracks from the tracking system and deposited energy from the electromagnetic and hadronic calorimeters, taking advantage of excellent granularity of the sub-systems. Particles are classified as electrons, muons, photons, charged hadrons, and neutral hadrons. Primary vertices are reconstructed using a deterministic annealing filter algorithm [39]. The vertex with the largest squared sum of the associated track p T values is taken to be the primary event vertex.Electrons are reconstructed in the pseudorapidity range |η| < 2.5, by combining tracking information with energy deposits in the electromagnetic calorimeter [40,41]. Electron candidates are required to originate from the primary event vertex. Electrons are identified using infor-6 5 Reconstruction of tt events B The CMS Collaboration

Constraining new resonant physics with top spin polarisation information

“…Resonance searches at the LHC tt final states are a well motivated strategy for discovering new physics beyond the SM [1,2]. While peaks in the mass spectrum are very powerful indicators of the presence of such new physics, we also often expect to see large modifications to other distributions and combining this information through multi-dimensional distributions often offers a good way to improve sensitivity.…”

“…For the graviton, branching fractions to hh and V L V † L are also sizeable as the Higgs and therefore also the longitudinal modes of the weak bosons are located on the TeV brane, but strong constraints on the masses of both particles m(g K K ) and m(G K K ) are typically derived from top resonance searches [1,2].…”

“…Our model setup follows these strategies of ATLAS and CMS [1,2] but varies slightly between the gluon and graviton signals. In general the gluon will always be easier to detect due to much larger cross sections as it can be produced efficiently through uū and dd annihilation, whereas graviton production is dominated by gluon fusion.…”

“…2 Following [54], we top-tag the leading fat jet with HEPTopTagger [55,56] mostly using the default setup of [56]. Note our choice of R = 1.2 is well motivated compared to the choice of R = 1.5 in the benchmark study in [56] since we consider much heavier resonances.…”

Heavy Higgs boson resonances and their decay into top quarks at the LHC

“…We are interested in heavy Higgs bosons with masses m φ > 2m t and unsuppressed Yukawa couplings to the top quark that can appear as resonances in the tt decay channel. Experimental searches for such resonances have been performed by ATLAS [5] and CMS [6,7] but so far no signals above the SM continuum were detected. However, due to experimental (and theoretical) uncertainties these measurements are limited in constraining heavy Higgs models.…”