5.5 Dark Matter and Mono-X
183
If dark matter production proceeds through the exchange of a scalar mediator,
couplings to light quarks are suppressed and the sensitivity of mono-jet searches
is limited. For this class of models, dark matter produced in association with third
generation quarks is a promising search channel, including mono-b, bb+ p
miss
T
and
tt+ p
miss
T
signatures [1048]. In addition, models with baryon number violating or
flavour changing neutral current interactions predict the existence of mono-t signatures [1049], which can be probed at the LHC [1050, 1051]. ATLAS has reported
a search with 8 TeV data in final states with large p
miss
T
and one or two b-tagged
small-R jets, optimised for b +χ ¯
χ and bb+χ ¯
χ production [1052]. The same analysis considers final states with large p
miss
T
and more than five jets, two of which have
to be b tagged, or one lepton and more than four jets, where one has to be b tagged, to
achieve sensitivity to tt+χ ¯
χ production. Mono-t signatures are studied using 8 TeV
data by ATLAS in the p
miss
T +νb channel [1053] and by CMS in the p
miss
T +qq
b
channel, where the t decay is reconstructed with three small-R jets [1054]. These
analyses are most sensitive for low values of m χ , for which lower mass limits are
derived of 1 TeV for a scalar coupling to b quarks and between 330 and 650 GeV on
a scalar or vector mediator coupling to t quarks, respectively.
The use of jet substructure has proliferated in analyses of 13 TeV data and helped
to improve the sensitivity of dark matter searches. Searches without jet substructure
could also extend the coverage of the parameter space thanks to improved analysis and
reconstruction methods compared to 8 TeV analyses, as well as the larger data set and
increased
√
s. Mono-γ searches by ATLAS [779, 1055, 1056] and CMS [1057] using
up to 139 fb
−1 of 13 TeV data, report lower limits on the EFT scale of 790 GeV
at 95% CL. Dark matter particles with m χ below 255–520 GeV and m φ below 810–
1310 GeV are excluded at 95% CL, where the ranges refer to different couplings.
Mono-jet analyses by ATLAS, also using the full 13 TeV data recorded until 2018,
exclude m φ below 2.1 TeV for m χ = 1 GeV [1058–1060]. Mono-Z analysis in the
p
miss
T
+ final state have also been carried out by ATLAS [1061] and CMS [1062–
1064] using up to 137 fb
−1 of data. The results are interpreted in a number of models,
including different dark matter mediators, two-Higgs-doublet models and models
with large extra dimensions. These are complemented by mono-V searches in
the all-hadronic final state, enabled by jet substructure methods. Two CMS analyses
based on data taken in the year 2016 use pruned large-R jets with p T > 250 GeV,
65 < m jet < 105 GeV and τ 21 < 0.6 to define the V -tag signal region [1065, 1066].
Events not passing this selection, but with a small-R jet with p T > 100 GeV and
p
miss
T
> 250 GeV, are sorted into a mono-jet category. This has the advantage of a
straight-forward combination of the mono-V and mono-jet channels. In ATLAS,
resolved and fully merged V categories are considered [1067, 1068]. In the merged
category, large-R jets have to fulfil p T -dependent requirements on the trimmed jet
mass and D 2 . In addition, b-tagged track-jets are used for a further categorisation in
order to gain sensitivity to Z → bb decays. This analysis also considers a Z
produced
in association with χ ¯
χ instead of the SM V , where Z
→ qq decays are assumed
with a branching fraction of unity. To account for this possibility in the analysis, the
jet mass window is shifted according to the mass of the Z
probed in the range from
0.85m Z (0.75m Z ) to m Z + 10 GeV, for jets without (with) matched b-tagged small-
183
If dark matter production proceeds through the exchange of a scalar mediator,
couplings to light quarks are suppressed and the sensitivity of mono-jet searches
is limited. For this class of models, dark matter produced in association with third
generation quarks is a promising search channel, including mono-b, bb+ p
miss
T
and
tt+ p
miss
T
signatures [1048]. In addition, models with baryon number violating or
flavour changing neutral current interactions predict the existence of mono-t signatures [1049], which can be probed at the LHC [1050, 1051]. ATLAS has reported
a search with 8 TeV data in final states with large p
miss
T
and one or two b-tagged
small-R jets, optimised for b +χ ¯
χ and bb+χ ¯
χ production [1052]. The same analysis considers final states with large p
miss
T
and more than five jets, two of which have
to be b tagged, or one lepton and more than four jets, where one has to be b tagged, to
achieve sensitivity to tt+χ ¯
χ production. Mono-t signatures are studied using 8 TeV
data by ATLAS in the p
miss
T +νb channel [1053] and by CMS in the p
miss
T +qq
b
channel, where the t decay is reconstructed with three small-R jets [1054]. These
analyses are most sensitive for low values of m χ , for which lower mass limits are
derived of 1 TeV for a scalar coupling to b quarks and between 330 and 650 GeV on
a scalar or vector mediator coupling to t quarks, respectively.
The use of jet substructure has proliferated in analyses of 13 TeV data and helped
to improve the sensitivity of dark matter searches. Searches without jet substructure
could also extend the coverage of the parameter space thanks to improved analysis and
reconstruction methods compared to 8 TeV analyses, as well as the larger data set and
increased
√
s. Mono-γ searches by ATLAS [779, 1055, 1056] and CMS [1057] using
up to 139 fb
−1 of 13 TeV data, report lower limits on the EFT scale of 790 GeV
at 95% CL. Dark matter particles with m χ below 255–520 GeV and m φ below 810–
1310 GeV are excluded at 95% CL, where the ranges refer to different couplings.
Mono-jet analyses by ATLAS, also using the full 13 TeV data recorded until 2018,
exclude m φ below 2.1 TeV for m χ = 1 GeV [1058–1060]. Mono-Z analysis in the
p
miss
T
+ final state have also been carried out by ATLAS [1061] and CMS [1062–
1064] using up to 137 fb
−1 of data. The results are interpreted in a number of models,
including different dark matter mediators, two-Higgs-doublet models and models
with large extra dimensions. These are complemented by mono-V searches in
the all-hadronic final state, enabled by jet substructure methods. Two CMS analyses
based on data taken in the year 2016 use pruned large-R jets with p T > 250 GeV,
65 < m jet < 105 GeV and τ 21 < 0.6 to define the V -tag signal region [1065, 1066].
Events not passing this selection, but with a small-R jet with p T > 100 GeV and
p
miss
T
> 250 GeV, are sorted into a mono-jet category. This has the advantage of a
straight-forward combination of the mono-V and mono-jet channels. In ATLAS,
resolved and fully merged V categories are considered [1067, 1068]. In the merged
category, large-R jets have to fulfil p T -dependent requirements on the trimmed jet
mass and D 2 . In addition, b-tagged track-jets are used for a further categorisation in
order to gain sensitivity to Z → bb decays. This analysis also considers a Z
produced
in association with χ ¯
χ instead of the SM V , where Z
→ qq decays are assumed
with a branching fraction of unity. To account for this possibility in the analysis, the
jet mass window is shifted according to the mass of the Z
probed in the range from
0.85m Z (0.75m Z ) to m Z + 10 GeV, for jets without (with) matched b-tagged small-