Soft displaced leptons at the LHC
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Springer
Received: July Revised: October Accepted: October Published: November
21, 15, 19, 20,
2020 2020 2020 2020
Freya Blekman,a Nishita Desai,b Anastasiia Filimonova,c Abanti Ranadhir Sahasransua and Susanne Westhoffc a
Inter-university Institute for High Energies, Vrije Universiteit Brussel, 1050 Brussels, Belgium b Department of Theoretical Physics, Tata Institute of Fundamental Research, 400005 Mumbai, India c Institute for Theoretical Physics, Heidelberg University, 69120 Heidelberg, Germany
E-mail: [email protected], [email protected], [email protected], [email protected], [email protected] Abstract: Soft displaced leptons are representative collider signatures of compressed dark sectors with feeble couplings to the standard model. Prime targets are dark matter scenarios where co-scattering or co-annihilation sets the relic abundance upon freeze-out. At the LHC, searches for soft displaced leptons are challenged by a large background from hadron or tau lepton decays. In this article, we present an analysis tailored for displaced leptons with a low transverse momentum threshold at 20 GeV. Using a neural network, we perform a comprehensive analysis of the event kinematics, including a study of the expected detection efficiencies and backgrounds at small momenta. Our results show that weak-scale particles decaying into soft leptons with decay lengths between 1 mm and 1 m can be probed with LHC Run 2 data. This motivates the need for dedicated triggers that maximize the sensitivity to displaced soft leptons. Keywords: Beyond Standard Model, Cosmology of Theories beyond the SM ArXiv ePrint: 2007.03708
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP11(2020)112
JHEP11(2020)112
Soft displaced leptons at the LHC
Contents 1 Introduction
1
2 Soft displaced leptons from dark sectors 2.1 Co-annihilating and co-scattering dark matter 2.2 Signal characteristics 2.3 Benchmarks
3 3 4 7 8 9 11 12 13
4 Multi-variate analysis 4.1 Kinematic distributions 4.2 Neural network structure 4.3 Performance
15 15 17 18
5 Predictions for the LHC
19
6 Conclusions and outlook
21
1
Introduction
Collider searches for long-lived particles open a new dimension in the hunt for new physics. Lifetime measurements are particularly sensitive to hidden sectors of new particles with tiny couplings to the Standard Model (SM), well below the strength of weak interactions [1, 2]. If one of the states from the hidden sector can be produced at a sizeable rate, its decay is suppressed by the tiny coupling to the hidden sector, and visible decay products appear displaced from the collision point. Such signatures are naturally predicted in dark matter scenarios beyond the thermal WIMP (for an overview see ref. [3]). The potential to discover feebly coupling dark matter through long-lived particles at colliders is unique, as potential signals in direct and indirect detection experiments are often suppressed by the tiny interaction. Tiny cou
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