Multijet Signals Research Articles

LHC Search Strategy for Squarks in Higgsino-LSP Scenarios with Leptons and b-Jets in the Final State

The higgsino Lightest Supersymmetric Particle (LSP) scenario opens up the possibility of decays of strongly produced particles to an intermediate neutralino, due to the Yukawa-suppressed direct decays to the higgsino. Those decays produce multijet signals with a Higgs or a Z boson being produced in the decay of the intermediate neutralino to the LSP. In this paper, we study the discovery prospects of squarks that produce b-jets and leptons in the final state. Our collider analysis provides signal significances at the 3σ level for luminosities of 1 ab−1, and at the 5σ level if we project these results for 3 ab−1.

Strong signatures of right-handed compositeness

Abstract Right-handed light quarks could be significantly composite, yet compatible with experimental searches at the LHC and precision tests on Standard Model couplings. In these scenarios, that are motivated by flavor physics, one expects large cross sections for the production of new resonances coupled to light quarks. We study experimental strong signatures of right-handed compositeness at the LHC, and constrain the parameter space of these models with recent results by ATLAS and CMS. We show that the LHC sensitivity could be significantly improved if dedicated searches were performed, in particular in multijet signals.

The LHC phenomenology of vectorlike confinement

We investigate in detail the LHC phenomenology of “vectorlike confinement”, where the Standard Model is augmented by a new confining gauge interaction and new light fermions that carry vectorlike charges under both the Standard Model and the new gauge group. If the new interaction confines at the TeV scale, this framework gives rise to a wide range of exotic collider signatures such as the production of a vector resonance that decays to a pair of collider-stable charged massive particles (a “di-CHAMP” resonance), to a pair of collider-stable massive colored particles (a “di-R-hadron” resonance), to multiple photons, Ws and Zs via two intermediate scalars, and/or to multi-jet final states. To study these signals at the LHC, we set up two benchmark models: one for the di-CHAMP and multi-photon signals, and the other for the di-R-hadron and multi-jet signals. For the di-CHAMP/multi-photon model, Standard Model backgrounds are negligible, and we show that a full reconstruction of the spectrum is possible, providing powerful evidence for vectorlike confinement. For the di-R-hadron/multi-jet model, we point out that in addition to the di-R-hadron signal, the rate of the production of four R-hadrons can also be sizable at the LHC. This, together with the multi-jet signals studied in earlier work, makes it possible to single out vectorlike confinement as the underlying dynamics.

The neutrino mass and other possible signals of lepton-number violation in supersymmetric theories

We review a recently proposed framework in which the neutrino mass is a signal of supersymmetry breaking and is suppressed dynamically. In addition, we briefly comment on some possible consequences of general lepton-number violation in supersymmetric theories, e.g., dijet and multijet signals and $jj \rightarrow ll\gamma\gamma$.

Top-quark search in multijet signals.

We investigate the possibilities of finding the top quark at the Fermilab Tevatron pp\ifmmode\bar\else\textasciimacron\fi{} collider (\ensuremath{\surd}s =1.8 TeV) in the lepton plus multijet signal. The theoretical uncertainties in the normalization of the top-quark production cross section and background signals make it important to look for the top quark in a final state where the top-quark mass is reconstructible from the final state. The W+4 jet final state offers a simple and direct way to reconstruct the top-quark mass through final-state invariant masses. It is shown that from a theoretical viewpoint the top quark is easily recovered from this W+4 jet cross section. The only limitation comes from the experimental ability to correctly reconstruct the invariant masses which might contain multiple jets.

Multi-jet physics at hadron colliders

We discuss four-jet and six-jet events at the SSC, LHC and Tevatron. First, the QCD backgrounds to non-standard physics are presented. Then we investigate multi-jet signals for hadronically-decaying color-octet pseudoscalars and color-sextet or octet fermions. Finally, the discovery potential of each collider is estimated.

Top search at fermilab: Multijet signals and backgrounds

We investigate the possibilities of finding the top quark at the FNAL Tevatron p p collider (√ s = 1.8 TeV). For a top-quark mass greater than O( M W) top quark will be predominantly produced through direct QCD t t production. The decay channel into a lepton, neutrino and a number of jets together with the dominant background signal is examined. We first study the standard way of finding the top-quark mass using invariant mass distributions. We then introduce and study the quantity R 3 2 (m top ) , defined as the ratio of the number of “3 jet + lepton” events to the number of “2 jet + lepton” events. Through the strong dependence on the top-quark mass of this simple ratio it should be possible to detect the presence of a top quark for a large range of possible top-quark mass values.