Exploring new possibilities to discover a light pseudo-scalar at LHCb

We study the possibility of observing a light pseudo-scalar a at LHCb. We target the mass region $$2.5\,\mathrm{GeV}\lesssim m_a\lesssim 60\,\mathrm{GeV}$$ 2.5 GeV ≲ m a ≲ 60 GeV and various decay channels, some of which have never been considered before: muon pairs, tau pairs, D meson pairs, and di-photon. We interpret the results in the context of models of 4D Composite Higgs and Partial Compositeness in particular.

Vector-like quarks decaying into singly and doubly charged bosons at LHC

We investigate the production of vector-like quarks with charge 5/3 at the LHC and their subsequent decays into new singly or doubly charged bosons plus a heavy quark (top or bottom). In particular, we explore final states with same-sign di-leptons (electron or muon pairs), with the leptons coming from the decay of the new bosons and, in the case of production of singly charged bosons, from top quarks as well. These processes are predicted by classes of models based on extensions of the gauge group of the Standard Model, such as the 331 Model, where the electroweak symmetry is described by SU(3)L × U(1)X, X being a new abelian charge. For this purpose, a CMS search for vector-like partners with charge 5/3 decaying into Wt is recast to obtain model-independent bounds and projected reaches at future luminosity stages of the LHC. The results are then interpreted as mass bounds for the new particles predicted in the 331 Model and as a constraint on the scale of its spontaneous symmetry breaking. The complete set of model-independent results are provided as recast efficiencies, to allow for reinterpretation in different scenarios.

Probing Dense QCD Matter: Muon Measurements with the CBM Experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt is designed to investigate the properties of high-density QCD matter with multi-differential measurements of hadrons and leptons, including rare probes such as multi-strange anti-hyperons and charmed particles. The research program covers the study of the high-density equation-of-state of nuclear matter and the exploration of the QCD phase diagram at large baryon chemical potentials, including the search for quark matter and the critical endpoint of a hypothetical 1st order phase transition. The CBM setup comprises detector systems for the identification of charged hadrons, electrons, and muons; for the determination of collision centrality and the orientation of the reaction plane; and a free-streaming data read-out and acquisition system, which allows online reconstruction and selection of events up to reaction rates of 10 MHz. In this article, emphasis is placed on the measurement of muon pairs in Au-Au collisions at FAIR beam energies, which are unique probes used to determine the temperature of the fireball, and hence to search for a caloric curve of QCD matter. Simultaneously, the subthreshold production of charmonium can be studied via its dimuon decay in order to shed light on the microscopic structure of QCD matter at high baryon densities. The CBM setup with focus on dimuon measurements and the results of the corresponding physics performance studies will be presented.

Discovery potential of FASERν with contained vertex and through-going events

FASERν is a newly proposed detector whose main mission is to detect the neutrino flux from the collision of the proton beams at the ATLAS Interaction Point (IP) during the run III of the LHC in 2022–2024. We show that this detector can also test certain beyond standard model scenarios, especially the ones in which the neutrino interaction with matter fields can produce new unstable particles decaying back into charged leptons. Models of this kind are motivated by the MiniBooNE anomaly. We show that, if the new physics involves multi-muon production by neutrinos scattering off matter fields, including the neutrino flux interactions in the rock before the detector in the analysis (i.e., accounting for the through-going muon pairs) can significantly increase the effective detector mass and its sensitivity to new physics. We propose a concrete model that can give rise to such a multi-muon signal.

Prospects of measuring the branching fraction of the Higgs boson decaying into muon pairs at the International Linear Collider

The prospects for measuring the branching fraction of $$H \rightarrow \mu ^{+} \mu ^{-}$$ H → μ + μ - at the International Linear Collider (ILC) have been evaluated based on a full detector simulation of the International Large Detector (ILD) concept, considering centre-of-mass energies ($$\sqrt{s}$$ s ) of 250 GeV and 500 GeV with two different beam polarisation configurations of $${\mathcal {P}} (e^{-}, e^{+}) = (-\,80{\%}, +\,30{\%})$$ P ( e - , e + ) = ( - 80 % , + 30 % ) and $$(+\,80{\%}, -\,30{\%})$$ ( + 80 % , - 30 % ) . For both $$\sqrt{s}$$ s cases, the two final states $$e^{+} e^{-} \rightarrow q\overline{q}H$$ e + e - → q q ¯ H and $$e^{+} e^{-} \rightarrow \nu \overline{\nu }H$$ e + e - → ν ν ¯ H have been analyzed. For integrated luminosities of 2 $$\hbox {ab}^{-1}$$ ab - 1 at $$\sqrt{s} =250$$ s = 250 GeV and 4 $$\hbox {ab}^{-1}$$ ab - 1 at $$\sqrt{s} =500$$ s = 500 GeV, the combined precision on the branching fraction of $$H \rightarrow \mu ^{+} \mu ^{-}$$ H → μ + μ - is estimated to be 17%. The impact of the transverse momentum resolution for this analysis is also studied.

Electron-Positron Annihilation

This chapter works out the theory of electron-positron annihilation to muon pairs as a model for electron-positron annihilation to quarks. It explains that this naive model provides a good description of observed properties of the process of electron-positron annihilation to hadrons.

Recent results of quarkonium and heavy flavour physics at ATLAS

Heavy quark spectroscopy and exotic states are studied with the ATLAS detector, mainly through final states containing muon pairs from J/ψ decays. This proceedings will summarise recent results from ATLAS on these topics, including production of quarkonium and heavy flavour, searches for exotic states and measurements of decay properties in open beauty production.