https://doi.org/10.1140/epjc/s10052-023-11536-5
Regular Article - Experimental Physics
Constraining light thermal inelastic dark matter with NA64
1
Institute for Particle Physics and Astrophysics, ETH Zürich, 8093, Zurich, Switzerland
2
Theoretical Physics Department, Fermi National Accelerator Laboratory, 60510, Batavia, IL, USA
3
Department of Physics, Institute for Particle Physics Phenomenology, Durham University, South Road, DH1 3LE, Durham, UK
4
Perimeter Institute for Theoretical Physics, ON, N2J 2W9, Waterloo, Canada
5
School of Physics and Astronomy, University of Minnesota, 55455, Minneapolis, MN, USA
6
William I. Fine Theoretical Physics Institute, School of Physics and Astronomy, University of Minnesota, MN, 55455, Minneapolis, USA
7
Dipartimento di Fisica e Astronomia, Università di Bologna, Via Irnerio 46, 40126, Bologna, Italy
8
INFN, Sezione di Bologna, viale Berti Pichat 6/2, 40127, Bologna, Italy
9
Theoretical Physics Department, CERN, Geneva, Switzerland
10
Centre for Cosmology, Particle Physics and Phenomenology (CP3), Université Catholique de Louvain, 1348, Louvain-la-Neuve, Belgium
11
Instituto de Fisica Corpuscular (CSIC/UV), Carrer del Catedrátic José Beltrán Martinez 2, 46980, Paterna, Valencia, Spain
Received:
9
March
2023
Accepted:
18
April
2023
Published online:
10
May
2023
A vector portal between the Standard Model and the dark sector is a predictive and compelling framework for thermal dark matter. Through co-annihilations, models of inelastic dark matter (iDM) and inelastic Dirac dark matter (i2DM) can reproduce the observed relic density in the MeV to GeV mass range without violating cosmological limits. In these scenarios, the vector mediator behaves like a semi-visible particle, evading traditional bounds on visible or invisible resonances, and uncovering new parameter space to explain the muon 
anomaly. By means of a more inclusive signal definition at the NA64 experiment, we place new constraints on iDM and i2DM using a missing energy technique. With a recast-based analysis, we contextualize the NA64 exclusion limits in parameter space and estimate the reach of the newly collected and expected future NA64 data. Our results motivate the development of an optimized search program for semi-visible particles, in which fixed-target experiments like NA64 provide a powerful probe in the sub-GeV mass range.
© The Author(s) 2023
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