arXiv subjects

Sascha Liechti

Publications and source records attributed to Sascha Liechti.

3 recordsLinked to original sources

arXiv2023

Optimal transport for a novel event description at hadron colliders

We propose a novel strategy for disentangling proton collisions at hadron colliders such as the LHC that considerably improves over the current state of the art. Employing a metric inspired by optimal transport problems as the cost function of a graph neural network, our algorithm is able to compare two particle collections with different noise levels and learns to flag particles originating from the main interaction amidst products from up to 200 simultaneous pileup collisions. We thereby sidestep the critical task of obtaining a ground truth by labeling particles and avoid arduous human annotation in favor of labels derived in situ through a self-supervised process. We demonstrate how our approach - which, unlike competing algorithms, is trivial to implement - improves the resolution in key objects used in precision measurements and searches alike and present large sensitivity gains in searching for exotic Higgs boson decays at the High-Luminosity LHC.

hep-ph↗

arXiv2023

The CMS inner Tracker Endcap PiXel upgrade

The High Luminosity Large Hadron Collider (HL-LHC) at CERN is expected to collide protons at a center-of-mass energy of 14 TeV and to reach the unprecedented peak instantaneous luminosity of $7.5 \times 10^{34} \text{cm}^{-2} \text{s}^{-1}$ with an average number of pileup vertices of 200. This will allow the ATLAS and CMS experiments to collect a data sample with an integrated luminosity up to $4000\,\mathrm{fb}^{-1}$ during the project's lifetime. To adapt to these harsh conditions, the CMS detector will be substantially upgraded before starting the HL-LHC, a plan known as CMS Phase-2 upgrade. The entire CMS silicon pixel detector (IT) will be replaced and the new detector will feature increased radiation hardness, higher granularity and capability to handle higher data rate and longer trigger latency. The upgraded IT will be composed of a barrel part, TBPX, as well as small and large forward disks, TFPX and TEPX. The TEPX detector has four large disks on each end, extending the coverage up to $\lvert η\rvert \approx 4.0$. In TEPX, the modules are arranged in five concentric rings. In this contribution the new TEPX detector will be presented, with particular focus on the mechanics design and thermal performance, using finite element methods. Effects of the material choice for the cooling pipes and disk support structures connecting the modules with the CO$_2$ coolant are presented as well.

physics.ins-det↗

arXiv2020

Hunting for $B^+\to K^+ τ^+τ^-$ imprints on the $B^+ \to K^+ μ^+μ^-$ dimuon spectrum

We investigate the possibility of indirectly constraining the $B^{+}\to K^{+}τ^+τ^-$ decay rate using precise data on the $B^{+}\to K^{+}μ^+μ^-$ dimuon spectrum. To this end, we estimate the distortion of the spectrum induced by the $B^{+}\to K^{+}τ^+τ^-\to K^{+} μ^+μ^-$ re-scattering process, and propose a method to simultaneously constrain this (non-standard) contribution and the long-distance effects associated to hadronic intermediate states. The latter are constrained using the analytic properties of the amplitude combined with data and perturbative calculations. Finally, we estimate the sensitivity expected at the LHCb experiment with present and future datasets. We find that constraints on the branching fraction of $O(10^{-3})$, competitive with current direct bounds, can be achieved with the current dataset, while bounds of $O(10^{-4})$ could be obtained with the LHCb upgrade-II luminosity.

hep-ph↗