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1. Detector R&D needs for the next generation e+e− collider

   A. Apresyan, M. Artuso ( June 2023 , FERMILAB-PUB-23-451-CSAID-PPD Arxiv eprint = "2306.13567",)

   The 2021 Snowmass Energy Frontier panel wrote in its final report "The realization of a Higgs factory will require an immediate, vigorous and targeted detector R&D program". Both linear and circular e+e− collider efforts have developed a conceptual design for their detectors and are aggressively pursuing a path to formalize these detector concepts. The U.S. has world-class expertise in particle detectors, and is eager to play a leading role in the next generation e+e− collider, currently slated to become operational in the 2040s. It is urgent that the U.S. organize its efforts to provide leadership and make significant contributions in detector R&D. These investments are necessary to build and retain the U.S. expertise in detector R&D and future projects, enable significant contributions during the construction phase and maintain its leadership in the Energy Frontier regardless of the choice of the collider project. In this document, we discuss areas where the U.S. can and must play a leading role in the conceptual design and R&D for detectors for e+e− colliders. 

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2. Improved particle-flow event reconstruction with scalable neural networks for current and future particle detectors

   https://doi.org/10.1038/s42005-024-01599-5  

   Pata, Joosep ; Wulff, Eric ; Mokhtar, Farouk ; Southwick, David ; Zhang, Mengke ; Girone, Maria ; Duarte, Javier ( April 2024 , Communications Physics)

   Efficient and accurate algorithms are necessary to reconstruct particles in the highly granular detectors anticipated at the High-Luminosity Large Hadron Collider and the Future Circular Collider. We study scalable machine learning models for event reconstruction in electron-positron collisions based on a full detector simulation. Particle-flow reconstruction can be formulated as a supervised learning task using tracks and calorimeter clusters. We compare a graph neural network and kernel-based transformer and demonstrate that we can avoid quadratic operations while achieving realistic reconstruction. We show that hyperparameter tuning significantly improves the performance of the models. The best graph neural network model shows improvement in the jet transverse momentum resolution by up to 50% compared to the rule-based algorithm. The resulting model is portable across Nvidia, AMD and Habana hardware. Accurate and fast machine-learning based reconstruction can significantly improve future measurements at colliders.

    

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3. Precision test of the muon-Higgs coupling at a high-energy muon collider

   https://doi.org/10.1007/JHEP12(2021)162  

   Han, Tao ; Kilian, Wolfgang ; Kreher, Nils ; Ma, Yang ; Reuter, Jürgen ; Striegl, Tobias ; Xie, Keping ( December 2021 , Journal of High Energy Physics)

   A bstract We explore the sensitivity of directly testing the muon-Higgs coupling at a high-energy muon collider. This is strongly motivated if there exists new physics that is not aligned with the Standard Model Yukawa interactions which are responsible for the fermion mass generation. We illustrate a few such examples for physics beyond the Standard Model. With the accidentally small value of the muon Yukawa coupling and its subtle role in the high-energy production of multiple (vector and Higgs) bosons, we show that it is possible to measure the muon-Higgs coupling to an accuracy of ten percent for a 10 TeV muon collider and a few percent for a 30 TeV machine by utilizing the three boson production, potentially sensitive to a new physics scale about Λ ∼ 30 − 100 TeV. 

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4. Fast neutron background characterization of the future Ricochet experiment at the ILL research nuclear reactor

   https://doi.org/10.1140/epjc/s10052-022-11150-x  

   Augier, C. ; Baulieu, G. ; Belov, V. ; Berge, L. ; Billard, J. ; Bres, G. ; Bret, J-. L. ; Broniatowski, A. ; Calvo, M. ; Cazes, A. ; et al ( January 2023 , The European Physical Journal C)

   The futureRicochetexperiment aims at searching for new physics in the electroweak sector by providing a high precision measurement of the Coherent Elastic Neutrino-Nucleus Scattering (CENNS) process down to the sub-100 eV nuclear recoil energy range. The experiment will deploy a kg-scale low-energy-threshold detector array combining Ge and Zn target crystals 8.8 m away from the 58 MW research nuclear reactor core of the Institut Laue Langevin (ILL) in Grenoble, France. Currently, theRicochetCollaboration is characterizing the backgrounds at its future experimental site in order to optimize the experiment’s shielding design. The most threatening background component, which cannot be actively rejected by particle identification, consists of keV-scale neutron-induced nuclear recoils. These initial fast neutrons are generated by the reactor core and surrounding experiments (reactogenics), and by the cosmic rays producing primary neutrons and muon-induced neutrons in the surrounding materials. In this paper, we present theRicochetneutron background characterization using$$^3$$${}^3$He proportional counters which exhibit a high sensitivity to thermal, epithermal and fast neutrons. We compare these measurements to theRicochetGeant4 simulations to validate our reactogenic and cosmogenic neutron background estimations. Eventually, we present our estimated neutron background for the futureRicochetexperiment and the resulting CENNS detection significance. Our results show that depending on the effectiveness of the muon veto, we expect a total nuclear recoil background rate between 44 ± 3 and 9 ± 2 events/day/kg in the CENNS region of interest, i.e. between 50 eV and 1 keV. We therefore found that theRicochetexperiment should reach a statistical significance of 4.6 to 13.6 $$\sigma $$$\sigma$for the detection of CENNS after one reactor cycle, when only the limiting neutron background is considered.

    

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5. Search for heavy resonances decaying into a pair of Z bosons in the $$\ell ^+\ell ^-\ell '^+\ell '^-$$ and $$\ell ^+\ell ^-\nu {{\bar{\nu }}}$$ final states using 139 $$\mathrm {fb}^{-1}$$ of proton–proton collisions at $$\sqrt{s} = 13\,$$TeV with the ATLAS detector

   https://doi.org/10.1140/epjc/s10052-021-09013-y  

   Aad, G. ; Abbott, B. ; Abbott, D. C. ; Abud, A. Abed ; Abeling, K. ; Abhayasinghe, D. K. ; Abidi, S. H. ; AbouZeid, O. S. ; Abraham, N. L. ; Abramowicz, H. ; et al ( April 2021 , The European Physical Journal C)

   null (Ed.)

   Abstract A search for heavy resonances decaying into a pair of Z bosons leading to $$\ell ^+\ell ^-\ell '^+\ell '^-$$ ℓ + ℓ - ℓ ′ + ℓ ′ - and $$\ell ^+\ell ^-\nu {{\bar{\nu }}}$$ ℓ + ℓ - ν ν ¯ final states, where $$\ell $$ ℓ stands for either an electron or a muon, is presented. The search uses proton–proton collision data at a centre-of-mass energy of 13 TeV collected from 2015 to 2018 that corresponds to the integrated luminosity of 139 $$\mathrm {fb}^{-1}$$ fb - 1 recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. Different mass ranges spanning 200 GeV to 2000 GeV for the hypothetical resonances are considered, depending on the final state and model. In the absence of a significant observed excess, the results are interpreted as upper limits on the production cross section of a spin-0 or spin-2 resonance. The upper limits for the spin-0 resonance are translated to exclusion contours in the context of Type-I and Type-II two-Higgs-doublet models, and the limits for the spin-2 resonance are used to constrain the Randall–Sundrum model with an extra dimension giving rise to spin-2 graviton excitations. 

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