Phenomenology of photons-enriched semi-visible jets

This Letter proposes a new signature for confining dark sectors at the LHC. Under the assumption of a QCD-like hidden sector, hadronic jets containing stable dark bound states originating from hidden strong dynamics, known as semi-visible jets, could manifest in proton-proton collisions. In the proposed simplified model, a heavy Z ' mediator coupling to SM quarks allows the resonant production of dark quarks, subsequently hadronizing in stable and unstable dark bound states. The unstable dark bound states can then decay back to SM quarks via the same Z ' portal or photons via a lighter pseudo-scalar portal (such as an axion-like particle). This mechanism creates a new signature where semi-visible jets are enriched in non-isolated photons. We show that these exotic jets evade the phase space probed by current LHC searches exploiting jets or photons due to the expected high jet neutral electromagnetic fraction and photons candidates non-isolation, respectively. In the proposed analysis strategy to tackle such signature, we exploit jets as final state objects to represent the underlying QCD-like hidden sector. We show that, by removing any selection on the neutral electromagnetic fraction from the jet identification criteria, higher signal efficiency can be reached. To enhance the signal-to-background discrimination, we train a deep neural network as a jet tagger that exploits differences in the substructure of signal and background jets. We estimate that with the available triggers for Run 2 and this new strategy, a high mass search can claim a 5 σ discovery (exclusion) of the Z ' boson with a mass up to 5 TeV (5 TeV) with the full Run 2 data of the LHC when the fraction of unstable dark hadrons decaying to photons pairs is around 30 % , and with a coupling of the Z ' to SM quarks of 0.25.

Highly Enhanced Contributions of Heavy Higgs Bosons and New Leptons to Muon g-2 and Prospects at Future Colliders

We show that, in a two Higgs doublet model type II extended by vectorlike leptons, the contributions from heavy neutral and charged Higgs bosons to the anomalous magnetic moment of the muon simultaneously feature chiral enhancement from masses of new leptons and tan^{2}β enhancement from couplings of Higgs bosons. Assuming moderate values of new Yukawa couplings, not exceeding one, that can remain perturbative to very high energy scales, the measured value of muon g-2 can be explained within one standard deviation even with 6.5 TeV leptons or 20 TeV Higgs bosons. Allowing new couplings near the perturbativity limit, these mass ranges extend to 45 TeV for leptons and 185 TeV for Higgs bosons. In spite of the high scale of new physics, this scenario can be completely probed at planned future colliders.