190
5 Direct Searches for New Physics
dark matter masses the collider results complement direct detection results. In this
region, direct detection experiments have little sensitivity because of the small recoil
energy such dark matter particles would induce [1094].
Searches for mono-X signatures are complementary to resonance searches at the
LHC, where the dark matter mediator can contribute to the s-channel production of
pairs of SM particles. An analysis considering a simplified model of spin-2 mediators [1095] finds that the strongest constraints are obtained from γ γ and resonance
searches. However, if these modes are suppressed, mono-X and resonance searches
provide stringent constraints on the mass and couplings of the dark matter mediator.
Pseudo-scalar mediators can be constrained by searches for t ¯
t+χ ¯
χ and tt and dijet
resonances, as well as final states with τ lepton pairs [1096]. Only a complete search
programme at the LHC in all conceivable mono-X and di-SM-particle resonance
channels can shed light on dark matter in the future.
5.6 Light Resonances Coupling to Quarks or Gluons
Searches for resonances decaying to pairs of quarks or gluons, generically denoted by
Z
, have always been among the first analyses performed when collisions at unexplored centre-of-mass energies have become available at hadron-hadron colliders.
These searches are typically performed as a bump-hunt [706] in the dijet mass spectrum, or by analysing the scattering angle in dijet events [946]. There are many wellmotivated extensions of the SM predicting these resonances [700, 1097–1101], some
of those have been proposed already more than 30 years ago [797, 858, 945, 970,
1102]. Searches for dijet resonances have been performed already at the CERN Sp¯ pS
collider experiments UA1 [1103] and UA2 [1104, 1105], and have been extended in
mass reach by the Tevatron experiments CDF [1106–1110] and D0 [1111–1113]. At
the LHC, the reach in resonance mass could be extended considerably every time a
new record centre-of-mass energies have been reached, at 7 TeV [948, 949, 952, 953,
1114–1120], 8 TeV [950, 954, 1121–1124] and 13 TeV [801, 951, 955, 956, 971,
972, 1125–1129]. These searches focus on heavy particles with resonance masses
above 1 TeV and place stringent constraints on their allowed couplings to quarks and
gluons. With the advent of simplified models for dark matter, where a mediator coupling to quarks is responsible for the production of dark matter particles, a renewed
interest in low mass mediators has emerged. In addition to mono-X signatures, these
mediators can be probed in dijet signatures. However, at the LHC the high multijet
rates initiated by the strong force do not allow for searches below masses of about
1 TeV.
Data scouting [1130, 1131] is a way to circumvent the bandwidth limitations
of the trigger, event processing and data storage. It has been introduced by CMS to
store events with trigger-level information only, after passing the level-1 trigger and
being processed by the high-level trigger. To maintain the high rate of 1 kHz of the
high-level trigger, only the four-momenta of small-R calorimeter jets reconstructed
online are stored. The corresponding events are then processed with the standard
5 Direct Searches for New Physics
dark matter masses the collider results complement direct detection results. In this
region, direct detection experiments have little sensitivity because of the small recoil
energy such dark matter particles would induce [1094].
Searches for mono-X signatures are complementary to resonance searches at the
LHC, where the dark matter mediator can contribute to the s-channel production of
pairs of SM particles. An analysis considering a simplified model of spin-2 mediators [1095] finds that the strongest constraints are obtained from γ γ and resonance
searches. However, if these modes are suppressed, mono-X and resonance searches
provide stringent constraints on the mass and couplings of the dark matter mediator.
Pseudo-scalar mediators can be constrained by searches for t ¯
t+χ ¯
χ and tt and dijet
resonances, as well as final states with τ lepton pairs [1096]. Only a complete search
programme at the LHC in all conceivable mono-X and di-SM-particle resonance
channels can shed light on dark matter in the future.
5.6 Light Resonances Coupling to Quarks or Gluons
Searches for resonances decaying to pairs of quarks or gluons, generically denoted by
Z
, have always been among the first analyses performed when collisions at unexplored centre-of-mass energies have become available at hadron-hadron colliders.
These searches are typically performed as a bump-hunt [706] in the dijet mass spectrum, or by analysing the scattering angle in dijet events [946]. There are many wellmotivated extensions of the SM predicting these resonances [700, 1097–1101], some
of those have been proposed already more than 30 years ago [797, 858, 945, 970,
1102]. Searches for dijet resonances have been performed already at the CERN Sp¯ pS
collider experiments UA1 [1103] and UA2 [1104, 1105], and have been extended in
mass reach by the Tevatron experiments CDF [1106–1110] and D0 [1111–1113]. At
the LHC, the reach in resonance mass could be extended considerably every time a
new record centre-of-mass energies have been reached, at 7 TeV [948, 949, 952, 953,
1114–1120], 8 TeV [950, 954, 1121–1124] and 13 TeV [801, 951, 955, 956, 971,
972, 1125–1129]. These searches focus on heavy particles with resonance masses
above 1 TeV and place stringent constraints on their allowed couplings to quarks and
gluons. With the advent of simplified models for dark matter, where a mediator coupling to quarks is responsible for the production of dark matter particles, a renewed
interest in low mass mediators has emerged. In addition to mono-X signatures, these
mediators can be probed in dijet signatures. However, at the LHC the high multijet
rates initiated by the strong force do not allow for searches below masses of about
1 TeV.
Data scouting [1130, 1131] is a way to circumvent the bandwidth limitations
of the trigger, event processing and data storage. It has been introduced by CMS to
store events with trigger-level information only, after passing the level-1 trigger and
being processed by the high-level trigger. To maintain the high rate of 1 kHz of the
high-level trigger, only the four-momenta of small-R calorimeter jets reconstructed
online are stored. The corresponding events are then processed with the standard