Constraining portals with displaced Higgs decay searches at the LHC

It is very easy to write down models in which long-lived particles decaying to standard model states are pair-produced via Higgs decays, resulting in the signature of approximately back-to-back pairs of displaced narrow hadronic jets and/or lepton jets at the LHC. The LHC collaborations have already searched for such signatures with no observed excess. This paper describes a Monte Carlo method to reinterpret the searches. The method relies on (ideally multidimensional) efficiency tables, thus we implore collaborations to include them in any future work. Exclusion regions in mixing-mass parameter space are presented which constrain portal models.Comment: 19 pages, 4 figures. [v2] This version accepted for publication in JHEP: some important clarifications made, plot schemes updated for ease of reading, new experimental results included, and a handful of minor additions and alteration

Quark-lepton symmetric model at the LHC

We investigate the quark-lepton symmetric model of Foot and Lew in the context of the Large Hadron Collider (LHC). In this `bottom-up' extension to the Standard Model, quark-lepton symmetry is achieved by introducing a gauged `leptonic colour' symmetry which is spontaneously broken above the electroweak scale. If this breaking occurs at the TeV scale, then we expect new physics to be discovered at the LHC. We examine three areas of interest: the Z$'$ heavy neutral gauge boson, charge $\pm1/2$ exotic leptons, and a colour triplet scalar diquark. We find that the LHC has already explored and/or will explore new parameter space for these particles over the course of its lifetime.Comment: 24 pages, 6 figure

Phenomenology of a very light scalar (100 MeV <mh<<m_h< 10 GeV) mixing with the SM Higgs

In this paper we investigate the phenomenology of a very light scalar, $h$, with mass 100 MeV $<m_h<$ 10 GeV, mixing with the SM Higgs. As a benchmark model we take the real singlet scalar extension of the SM. We point out apparently unresolved uncertainties in the branching ratios and lifetime of $h$ in a crucial region of parameter space for LHC phenomenology. Bounds from LEP, meson decays and fixed target experiments are reviewed. We also examine prospects at the LHC. For $m_h \lesssim m_B$ the dominant production mechanism is via meson decay; our main result is the calculation of the differential $p_T$ spectrum of $h$ scalars originating from B mesons and the subsequent prediction of up to thousands of moderate (triggerable) $p_T$ displaced dimuons possibly hiding in the existing dataset at ATLAS/CMS or at LHCb. We also demonstrate that the subdominant $Vh$ production channel has the best sensitivity for $m_h \gtrsim m_B$ and that future bounds in this region could conceivably compete with those of LEP.Comment: 13 pages, 9 figure