## General context

Approximately 85% of the mass contents of the universe is in the form of dark matter, which could be composed of new particles. The search for such particles, which could eventually be produced in the proton-proton collisions at the LHC, is underway with the ATLAS detector. These searches have so far mostly focused on supersymmetric particles, whose decay chains contain dark matter candidates (for ex. the neutralinos), and on the direct production of dark matter particles in so-called "simplified" models by looking for mono-X final states (where X=jet, photon, W/Z/H boson – see Figure 1).

The LPSC group has mainly participated in supersymmetry searches in Run-1 [1,3] and in simplified model searches [a,b,c,d,e] afterwards, especially by contributing to the mono-photon channel searches [2,4,5] and to the combination of the various search channels [6] (see Figure 1).

With the start of Run-3 in 2021, it will be possible to strenghten the limits provided by these types of searches [f], but the discovery space beyond the already existing limits will be reduced. It is therefore important to cover less explored scenarios which require a very good understanding of the objects in the detector, understanding which can now benefit from many years of data taking. One of these scenarios is the existence of a 'hidden' or 'dark' sector (including a dark matter candidate) which can be evinced by the presence of jets with unusual characteristics of their associated inner detector tracks and/or of their calorimeter energy deposition pattern, as these jets come from the decay of dark-sector particles which can have long lifetimes. The focus of the group is now on these types of searches.

## Prospectives for the next few years

In the next few years, the group will hence focus on the search for jets from the dark sector with the ATLAS detector, in the context of dark matter searches. The work will first focus on the searches with the full Run-2 dataset.

If these do not reveal any sign of new physics, the work will then focus on identifying possible weaknesses in the parameter space coverage in order to prepare the Run-3 searches. This will necessarily include work on the peculiar jet performances (displaced vertices associated to atypical calorimeter energy deposition, possibility of new triggers,...), which will necessitate validation in the first Run-3 data.

## Team

Current team :

• Convener of the ATLAS exotics group (October 2017-October 2019)
• Nathan Lalloué (PhD since October 2019)
• Topic : Searching for dark jets with the ATLAS detector

Previous members : see here

## Bibliography

Publications within the ATLAS collaboration (searches in the context of simpified models or supersymmetry):

• [1] ATLAS Collaboration, Further search for supersymmetry at sqrt(s) = 7 TeV in final states with jets, missing transverse momentum and isolated leptons with the ATLAS detector, PRD 86 (2012) 092002, arXiv:1208.4688
• [2] ATLAS Collaboration, Search for new phenomena in events with a photon and missing transverse momentum in pp collisions at sqrt(s)=8TeV with the ATLAS detector,  Phys. Rev. D 91, 012008 (2015), arXiv:1411.1559
• [3] ATLAS Collaboration, Search for squarks and gluinos in events with isolated leptons, jets and missing transverse momentum at sqrt(s)=8 TeV with the ATLAS detector, JHEP04(2015)116, arXiv:1501.03555.
• [4] ATLAS Collaboration, Search for new phenomena in events with a photon and missing transverse momentum in pp collisions at sqrt(s)=13 TeV with the ATLAS detector, JHEP 1606 (2016) 059, arXiv:1604.01306.
• [5] ATLAS Collaboration, Search for dark matter at √s=13 TeV in final states containing an energetic photon and large missing transverse momentum with the ATLAS detector, Eur. Phys. J. C 77 (2017) 393,  arXiv:1704.03848.
• [6] ATLAS Collaboration, Constraints on mediator-based dark matter and scalar dark energy models using $\sqrt{s} = 13$ TeV $pp$ collision data collected by the ATLAS detector, arXiv:1903.01400, submitted to JHEP.

Other publications linked to dark matter searches at the LHC:

• [a] J. Abdallah et el. (incl. M-H. Genest), Simplified Models for Dark Matter Searches at the LHC, Phys. Dark Univ. 9-10 (2015) 8-23, arXiv:1506.03116.
• [b] D. Abercrombie et al. (incl. M-H. Genest & M. Wu), Dark Matter Benchmark Models for Early LHC Run-2 Searches: Report of the ATLAS/CMS Dark Matter Forum, arXiv:1507.00966.
• [c] A. Boveia et al. (incl. M-H. Genest), Recommendations on presenting LHC searches for missing transverse energy signals using simplified s-channel models of dark matter, arXiv:1603.04156.
• [d] A. Albert et al. (incl. M-H. Genest), Recommendations of the LHC Dark Matter Working Group: Comparing LHC searches for heavy mediators of dark matter production in visible and invisible decay channels, arXiv:1703.05703.
• [e] T. Abe et al (incl. M-H. Genest), LHC Dark Matter Working Group: Next-generation spin-0 dark matter models, arXiv:1810.09420
• [f] X. Cid Vidal et al., Beyond the Standard Model Physics at the HL-LHC and HE-LHC, https://arxiv.org/abs/1812.07831.