Probing dark matter with disappearing tracks at the LHC

Models where dark matter is a part of an electroweak multiplet feature charged particles with macroscopic lifetimes due to the charged-neutral mass split of the order of pion mass. At the Large Hadron Collider, the ATLAS and CMS experiments will identify these charged particles as disappearing tracks, since they decay into a massive invisible dark matter candidate and a very soft charged Standard-Model particle, which fails to pass the reconstruction requirements. While ATLAS and CMS have focused on the supersymmetric versions of these scenarios, we have performed here the reinterpretation of the latest ATLAS disappearing track search for a suite of dark matter multiplets with different spins and electroweak quantum numbers. More concretely, we consider the cases of the inert two Higgs doublet, minimal fermion dark matter and vector triplet dark matter models. Our procedure is validated by using the same wino and Higgsino benchmark models employed by the ATLAS Collaboration. We have found that with the disappearing track signature, one can probe a vast portion of the parameter space, well beyond the reach of prompt missing energy searches (notably monojets). We provide tables with the upper limits on the cross section and efficiencies in the lifetime—a dark matter mass plane for all the models under consideration, which can be used for an easy recast for similar classes of models. Moreover, we provide the recasting code employed here, as part of the public LLP recasting repository.

Figure 1

Feynman diagram depicting the effective $D^{+}D{\pi }^{-}$ interaction from $W-\pi$ mixing.

Figure 2

Example diagrams of the signal process used in the analysis.

Figure 3

Transverse momenta distribution $p_T$ of the chargino at the truth level (solid line) and smeared (dashed line) using a random scaling with 15% amplitude.

Figure 4

(a) Total acceptance $\times$ efficiency in the electroweak channel ($E_A\times E_E\times T_A\times T_E$) from our simulation. b) Difference of the total acceptance $\times$ efficiency in % between our simulation and ATLAS: $({\epsilon }_{\mathrm{our}}-{\epsilon }_{\mathrm{ATLAS}})/{\epsilon }_{\mathrm{our}}\times 100$

Figure 5

Exclusion limits in the chargino life-time vs mass of chargino plane from ATLAS (red line) and from our simulations. The dashed black line is the limit for which no matching or merging are used, the dotted green line is the result for MLM matching, and the continuous purple line is the limit for CKKW-L merging. The grey dashed line shows the theory curve of the chargino lifetime in the almost pure wino LSP scenario at the two-loop level [98].

Figure 6

Comparison between the official ATLAS reinterpretation of the disappearing track study in the Higgsino scenario (solid orange) and our recasting procedure. The solid blue shows our results, using NLO cross sections from PROSPINO.

Figure 7

(a) and (b) Production cross section for the charged-neutral ($D^{\pm }D$) and charged-charged ($D^{+}{D}^{-}$) pair production of dark sector particles in the models under consideration, as a function of the charged dark particle mass. (c) Transverse momentum distribution of the short-lived charged dark particle (“chargino”) at the parton level. (d) Transverse momentum distribution of the reconstructed charged track.

Figure 8

Constraints on the parameter space of the dark sector models studies in this paper. The colored lines show the 95% exclusion reach of the LHC obtained from the reinterpretation of the disappearing track ATLAS study ($36{\mathrm{fb}}^{-1}$) for different models. The solid ticks indicate the constraints from LHC monojet searches at $36{\mathrm{fb}}^{-1}$ and projections for these searches for 300 and $3000{\mathrm{fb}}^{-1}$.

Figure 9

Transverse momenta distribution $p_T$ of (a) the leading jet and (b) pair of neutralinos using CKKW-L (blue) and MLM (red) matching schemes. In this example, $M_{{\chi }^{\pm }}=400\mathrm{GeV}$, and the merging scale parameter was set to 100 GeV.