Detector aspects important for Physics Beyond the SM

New particles with near-degenerate mass spectra produce very soft decay products. Their reconstruction is challenging even in the clean environment at future Higgs factories, e.g. due to material effects and beam background.

Reconstruction of long-lived particle signatures

Future lepton collider detectors with continuous tracking offer ideal conditions to search for all kinds of long-lived exotic particles. For instance a Time Projection Chamber is ideally suited to detect and precisely measure in-flight decays, based on typical signatures including V0s, kinks, or "disappearing" tracks. Based on appropriate reconstruction algorithms, the reach in various BSM models should be evaluated, with the goal to derive requirements and R&D goals for the detectors.

PhD thesis, single aspects can be covered in Master theses

Reconstruction of sub-GeV photons in a particle-flow detector

Eg. in case of light Higgsinos (s.a.), the reconstruction of sub- to few-GeV photons is crucial. The efficiency and purity achievable with the current design of the ILD detector concept should be evaluated. This includes the development of dedicated reconstruction algorithms. Based on these, potential critical aspects of the detector design should be identified and realistic options to optimise the design should be evaluated.

Master thesis, single aspects can be covered in Bachelor theses.

Reconstruction of sub-GeV charged particles

The reconstruction of sub-GeV tracks suffers beam background, which creates a lot of additional hits in the inner detectors. In particular for particles which do not reach the TPC, the stand-alone pattern recognition in the inner silicon detectors in the presence of beam background is a not yet fully solved problem, depending on the assumed time-stamping capabilities of the silicon detectors. In this project, the stand-alone silicon pattern recognition should be advanced, using as a test case eg. light Higgsinos (s.a.) or other new particles with small mass differences. The physics impact of the number of bunch-crossings integrated by the different layers of the inner tracking system should be evaluated and the overall design of the silicon tracking system optimized for stand-alone tracking in the presence of background.

PhD thesis, single aspects can be covered in Master or Bachelor theses.

Non-pointing photons from New Physics

Another special signature of new physics could be meta-stable particles decaying into a photon and an invisible particle. In such events, it is crucial to b able to reconstruct the angle of the photon from the cluster shape in the calorimeter. Currently, two different technologies are being discussed for the electromagnetic calorimeter of ILD, or even a hybrid of the two. The performance of all options w.r.t. cluster angle reconstruction should be investigated and the physics impact evaluated.

Master thesis or part of an PhD thesis

 

Supersymmetry and Other BSM Models

Although a Higgs factory is mainly targeting precision studies of the Higgs boson, it has very interesting discovery potential for exotic particles, often highly complementary to signatures which can be looked for at the LHC. Here are a few examples:

Dark Photons

New vector bosons as BSM sisters of the photon or the Z appear in various extensions of the SM, motivated for instance by explaining the existence of dark matter.  They can be rather light and are thus an excellent target for searches at a Higgs factory. In this study, the discovery prospects at a Higgs factory should be evaluated for various final states, and considering the role of top-level parameters of the accelerator, like luminosity, energy and polarisation.

Master thesis or part of an PhD thesis, single aspects can be covered in Bachelor theses.

Light Higgsinos

A key prediction of natural SUSY models are light, nearly mass-degenerate Higgsinos. Due to their small mass differences, their soft decay products provide a very interesting test case for many aspects of detector performance. While an initial feasibility study based on fast detector simulation and very few decay modes has been published recently, many aspects remain to studied. This includes the reconstruction of exclusive hadronic decay modes using particle identification information, measurement of the lifetimes of the charged and neutral Higgsinos, the impact of beam background, reconstruction algorithms for very low energetic particles and so on.

Master thesis or part of an PhD thesis, single aspects can be covered in Bachelor theses.

SUSY with extra Gauge Groups

The extension of the MSSM with an extra U(1) gauge group is well motivated (eg by explaining neutrino masses) and can change the collider signatures significantlty. We would like to investigate strategies how to distinguish such scenarios from plain MSSM, in both the Higgs and SUSY sectors, and test them in realistic detector simulations.

PhD thesis, single aspects can be covered in a Master thesis.