2024 Articles

A search for top-squark pair production, in final states containing a top quark, a charm quark and missing transverse momentum, using the 139 fb⁻¹ of 𝑝𝑝 collision data collected by the ATLAS detector

Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Acharya, B. S.; Adam Bourdarios, C.; Adamczyk, L.; Addepalli, S. V.; Addison, M. J.; Adelman, J.; Adiguzel, A.; Adye, T.; Affolder, A. A.; Afik, Y.; Agaras, M. N.; Agarwala, J.; Aggarwal, A.; Agheorghiesei, C.; Ahmad, A.; Ahmadov, F.; Ahmed, W. S.; Ahuja, S.; Ai, X.; Aielli, G.; Aikot, A.; Ait Tamlihat, M.; Aitbenchikh, B.; Aizenberg, I.; Akbiyik, M.; Åkesson, T. P. A.; Akimov, A. V.; Akiyama, D.; Akolkar, N. N.; Aktas, S.; Al Khoury, Konie

This paper presents a search for top-squark pair production in final states with a top quark, a charm quark and missing transverse momentum. The data were collected with the ATLAS detector during LHC Run 2 and correspond to an integrated luminosity of 139 fb⁻¹ search for top-squark pair production, in final states containing a top quark of proton-proton collisions at a centre-of-mass energy of √s = 13 TeV. The analysis is motivated by an extended Minimal Supersymmetric Standard Model featuring a non-minimal flavour violation in the second- and third-generation squark sector.

The top squark in this model has two possible decay modes, either 𝑡̃₁ → 𝑐χ̃₁⁰ or 𝑡̃₁ → 𝑡χ̃₁⁰, where the χ̃₁⁰ is undetected. The analysis is optimised assuming that both of the decay modes are equally probable, leading to the most likely final state of 𝑡𝑐 + 𝐸_𝑇 ^miss. Good agreement is found between the Standard Model expectation and the data in the search regions. Exclusion limits at 95% CL are obtained in the 𝑚(𝑡̃₁ ) vs. 𝑚(χ̃₁⁰) plane and, in addition, limits on the branching ratio of the 𝑡̃₁ → 𝑡χ̃₁⁰ decay as a function of 𝑚(𝑡̃₁ ) are also produced. Top-squark masses of up to 800 GeV are excluded for scenarios with light neutralinos, and top-squark masses up to 600 GeV are excluded in scenarios where the neutralino and the top squark are almost mass degenerate.