200
5 Direct Searches for New Physics
large mass splitting to the ˜
χ
0
1 LSP. In addition, the mass splitting m( ˜
g, ˜
χ
0
2 ) is
small, such that pair-produced gluinos decay into a soft quark, anti-quark and ˜
χ
0
2 .
The ˜
χ
0
2 decays into a ˜
χ
0
1 and a Z or H boson. For light ˜
χ
0
1 with masses O(1 GeV),
boosted Z and H bosons are predicted to be produced in association with large
p
miss
T
and additional soft quarks. This signature arises typically in models which
preserve naturalness despite large ˜
g and ˜
t masses [1182], as suggested by LHC
searches in other decay channels. In these scenarios, jet substructure techniques are
paramount to suppress SM backgrounds. A search by CMS based on 35.9 fb
−1 of
13 TeV data [1183] targets final states with two H jets and large p
miss
T . Two largeR jets are required to have p T > 300 GeV and identified using the jet mass and the
discriminator of the double b tagger. Events are classified by the number of identified
H jets, where events with jets failing the tagging requirements are used to predict the
SM background. The p
miss
T
distribution is analysed in search for a signal in events
with one and two identified H jets. Gluino masses up to 2010 GeV are excluded
for a ˜
χ
0
1 mass of 1 GeV and m( ˜
g, ˜
χ
0
2 ) = 50 GeV, assuming B( ˜
χ
0
2 → H ˜
χ
0
1 ) = 1.
A search by CMS using 137 fb
−1 of 13 TeV data [1184] targets the same model, but
with B( ˜
χ
0
2 → Z ˜
χ
0
1 ) = 1. Large-R jets are required to have p T > 200 GeV and are
groomed with the soft drop algorithm. The use of soft drop facilitates a linear fit to
the jet mass distribution in jet mass side bands, which can be interpolated into the
signal region with 70 < m jet < 100 GeV in order to predict the background from
non-resonant SM production. The distribution of background events in bins of p
miss
T
can then be predicted under the assumption of a minimal correlation between m jet
and p
miss
T , which is verified in simulation. The p
miss
T
distribution in events with two
identified Z jets is used to interpret the results in terms of exclusion limits. The search
excludes ˜
g masses up to 1920 GeV in this model.
There are SUSY scenarios predicting multijet final states with very little p
miss
T
and non-isolated photons or leptons. The predicted final states are very difficult to
disentangle from the large SM backgrounds, such that these scenarios were named
stealth SUSY [1185, 1186]. In these models, a number of superpartners have minimal
coupling to the SUSY breaking mechanism and are therefore mass degenerate. In a
simplified model of stealth SUSY, the hidden sector can be represented by a fermionic
state ˜
S and a scalar S [1187]. The largest cross section at the LHC comes from ˜
g
pair production, followed by a long decay cascade. The first decay ˜
g → qq ˜
χ
0
1 is
followed by the neutralino decay ˜
χ
0
1 → γ ˜
S and the ˜
S decays to a massless gravitino
˜
G and the scalar S. Because of the mass degeneracy of ˜
S and S, the ˜
G is produced
nearly at rest and leads to no detectable signature. The S decays to two gluons. If
the mass difference m( ˜
g, ˜
χ
0
1 ) is large, the ˜
χ
0
1 is produced with large boost and
its decay products merge into a single jet. This results in jets containing the photon
from the ˜
χ
0
1 decay and the fragmentation products from the two gluons from the
S decay. Naturally, these signatures are indistinguishable from the large multijet
background without using jet substructure information. A dedicated analysis by CMS
using 35.9 fb
−1 of 13 TeV data [1188] targets this signature. Large-R anti-k T jets with
p T > 200 GeV are examined for the presence of a photon, i.e. a particle candidate
with an ECAL energy deposit consistent with the shower shape of a photon and no
5 Direct Searches for New Physics
large mass splitting to the ˜
χ
0
1 LSP. In addition, the mass splitting m( ˜
g, ˜
χ
0
2 ) is
small, such that pair-produced gluinos decay into a soft quark, anti-quark and ˜
χ
0
2 .
The ˜
χ
0
2 decays into a ˜
χ
0
1 and a Z or H boson. For light ˜
χ
0
1 with masses O(1 GeV),
boosted Z and H bosons are predicted to be produced in association with large
p
miss
T
and additional soft quarks. This signature arises typically in models which
preserve naturalness despite large ˜
g and ˜
t masses [1182], as suggested by LHC
searches in other decay channels. In these scenarios, jet substructure techniques are
paramount to suppress SM backgrounds. A search by CMS based on 35.9 fb
−1 of
13 TeV data [1183] targets final states with two H jets and large p
miss
T . Two largeR jets are required to have p T > 300 GeV and identified using the jet mass and the
discriminator of the double b tagger. Events are classified by the number of identified
H jets, where events with jets failing the tagging requirements are used to predict the
SM background. The p
miss
T
distribution is analysed in search for a signal in events
with one and two identified H jets. Gluino masses up to 2010 GeV are excluded
for a ˜
χ
0
1 mass of 1 GeV and m( ˜
g, ˜
χ
0
2 ) = 50 GeV, assuming B( ˜
χ
0
2 → H ˜
χ
0
1 ) = 1.
A search by CMS using 137 fb
−1 of 13 TeV data [1184] targets the same model, but
with B( ˜
χ
0
2 → Z ˜
χ
0
1 ) = 1. Large-R jets are required to have p T > 200 GeV and are
groomed with the soft drop algorithm. The use of soft drop facilitates a linear fit to
the jet mass distribution in jet mass side bands, which can be interpolated into the
signal region with 70 < m jet < 100 GeV in order to predict the background from
non-resonant SM production. The distribution of background events in bins of p
miss
T
can then be predicted under the assumption of a minimal correlation between m jet
and p
miss
T , which is verified in simulation. The p
miss
T
distribution in events with two
identified Z jets is used to interpret the results in terms of exclusion limits. The search
excludes ˜
g masses up to 1920 GeV in this model.
There are SUSY scenarios predicting multijet final states with very little p
miss
T
and non-isolated photons or leptons. The predicted final states are very difficult to
disentangle from the large SM backgrounds, such that these scenarios were named
stealth SUSY [1185, 1186]. In these models, a number of superpartners have minimal
coupling to the SUSY breaking mechanism and are therefore mass degenerate. In a
simplified model of stealth SUSY, the hidden sector can be represented by a fermionic
state ˜
S and a scalar S [1187]. The largest cross section at the LHC comes from ˜
g
pair production, followed by a long decay cascade. The first decay ˜
g → qq ˜
χ
0
1 is
followed by the neutralino decay ˜
χ
0
1 → γ ˜
S and the ˜
S decays to a massless gravitino
˜
G and the scalar S. Because of the mass degeneracy of ˜
S and S, the ˜
G is produced
nearly at rest and leads to no detectable signature. The S decays to two gluons. If
the mass difference m( ˜
g, ˜
χ
0
1 ) is large, the ˜
χ
0
1 is produced with large boost and
its decay products merge into a single jet. This results in jets containing the photon
from the ˜
χ
0
1 decay and the fragmentation products from the two gluons from the
S decay. Naturally, these signatures are indistinguishable from the large multijet
background without using jet substructure information. A dedicated analysis by CMS
using 35.9 fb
−1 of 13 TeV data [1188] targets this signature. Large-R anti-k T jets with
p T > 200 GeV are examined for the presence of a photon, i.e. a particle candidate
with an ECAL energy deposit consistent with the shower shape of a photon and no