6 Summary
211
of b flavour tagging on subjets and identification of the three-prong structure of jets
has extended the reach of measurements in the lepton+jets channel and enabled measurements in the all-hadronic channel. These measurements allow for comparisons
with precision calculations in regions where electroweak and higher-order QCD
corrections are important. Additionally, these measurements have sensitivity to the
gluon PDF at high longitudinal momentum fraction, making unbiased simultaneous
extractions of the top quark mass, the strong coupling constant and proton PDFs
possible in the future.
Data analyses in search for new physical phenomena have relied on jet substructure techniques since the first pp collisions have been recorded at the LHC.
Algorithms for electroweak boson tagging have been crucial in searches for resonant
diboson production. Similarly, Higgs boson taggers made searches for HH and VH
resonances feasible. Top quark tagging has been central in searches for resonant tt
production. Heavy partners of third-generation quarks have been searched for using
the full suite of V , H and t taggers, in some cases combined in multiclass taggers.
Jet substructure techniques have also been instrumental in searches for dark matter,
probing parameter regions of large mediator and small dark matter masses. In addition, searches for very light mediators have been made possible with jet substructure
methods, by analysing the jet mass distribution in events where a light mediator is
expected to recoil against a highly energetic jet from initial state radiation. In searches
for supersymmetry, t tagging has been employed in searches for top squarks, probing
the region of high squark and gluino masses. In supersymmetry models with R-parity
violation, dedicated substructure taggers have allowed to probe a parameter space
inaccessible before. Last but not least, t taggers have been employed in searches
for leptoquarks with large couplings to top quarks, improving the sensitivity at high
masses. In all of these searches, dedicated methods have been employed to estimate
the backgrounds from SM processes, in some cases ameliorated by jet substructure methods. A very important ingredient is the knowledge of the signal efficiency,
directly related to the efficiency of jet substructure taggers, and consequently affecting the analysis sensitivity. Measurements in control regions are performed to assess
the efficiencies, and estimate the corresponding uncertainties. The background estimation and the measurement of signal efficiencies are the most crucial aspects in
searches for new physics, and often represent the most arduous parts. Despite the
numerous results from ATLAS and CMS in search for new phenomena, there are still
a number of final states uncovered. An example are cascade decays of beyond-theSM resonances, which can be classified by the SM particles produced [1283, 1284].
In some cases, these decays can be theoretically motivated [1285], in other cases,
the final states are signal agnostic, but could lead to an unexpected discovery.
Besides analyses where jet substructure methods have been used explicitly, there
are many analyses profiting from the developments in this field. Improvements of
particle flow algorithms, progress in novel reconstruction methods such as TCCs and
UFOs, together with dedicated calibrations, have led to performance improvements
for jet measurements. The development and commissioning of pileup mitigation
methods such as PUPPI, SoftKiller and Constituent Subtraction have led to a stable
jet reconstruction performance up to very high instantaneous luminosities. Lepton
211
of b flavour tagging on subjets and identification of the three-prong structure of jets
has extended the reach of measurements in the lepton+jets channel and enabled measurements in the all-hadronic channel. These measurements allow for comparisons
with precision calculations in regions where electroweak and higher-order QCD
corrections are important. Additionally, these measurements have sensitivity to the
gluon PDF at high longitudinal momentum fraction, making unbiased simultaneous
extractions of the top quark mass, the strong coupling constant and proton PDFs
possible in the future.
Data analyses in search for new physical phenomena have relied on jet substructure techniques since the first pp collisions have been recorded at the LHC.
Algorithms for electroweak boson tagging have been crucial in searches for resonant
diboson production. Similarly, Higgs boson taggers made searches for HH and VH
resonances feasible. Top quark tagging has been central in searches for resonant tt
production. Heavy partners of third-generation quarks have been searched for using
the full suite of V , H and t taggers, in some cases combined in multiclass taggers.
Jet substructure techniques have also been instrumental in searches for dark matter,
probing parameter regions of large mediator and small dark matter masses. In addition, searches for very light mediators have been made possible with jet substructure
methods, by analysing the jet mass distribution in events where a light mediator is
expected to recoil against a highly energetic jet from initial state radiation. In searches
for supersymmetry, t tagging has been employed in searches for top squarks, probing
the region of high squark and gluino masses. In supersymmetry models with R-parity
violation, dedicated substructure taggers have allowed to probe a parameter space
inaccessible before. Last but not least, t taggers have been employed in searches
for leptoquarks with large couplings to top quarks, improving the sensitivity at high
masses. In all of these searches, dedicated methods have been employed to estimate
the backgrounds from SM processes, in some cases ameliorated by jet substructure methods. A very important ingredient is the knowledge of the signal efficiency,
directly related to the efficiency of jet substructure taggers, and consequently affecting the analysis sensitivity. Measurements in control regions are performed to assess
the efficiencies, and estimate the corresponding uncertainties. The background estimation and the measurement of signal efficiencies are the most crucial aspects in
searches for new physics, and often represent the most arduous parts. Despite the
numerous results from ATLAS and CMS in search for new phenomena, there are still
a number of final states uncovered. An example are cascade decays of beyond-theSM resonances, which can be classified by the SM particles produced [1283, 1284].
In some cases, these decays can be theoretically motivated [1285], in other cases,
the final states are signal agnostic, but could lead to an unexpected discovery.
Besides analyses where jet substructure methods have been used explicitly, there
are many analyses profiting from the developments in this field. Improvements of
particle flow algorithms, progress in novel reconstruction methods such as TCCs and
UFOs, together with dedicated calibrations, have led to performance improvements
for jet measurements. The development and commissioning of pileup mitigation
methods such as PUPPI, SoftKiller and Constituent Subtraction have led to a stable
jet reconstruction performance up to very high instantaneous luminosities. Lepton