Strong SUSY at ATLAS and CMS
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Strong SUSY at ATLAS and CMS
Alison Elliot – Queen Mary University of London
On behalf of the ATLAS and CMS Collaborations
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021
Strong Supersymmetry
LHC Cross Section Working Group
● Physics beyond the standard model is strongly motivated
● Models are used as tools to guide searches for new physics
● Supersymmetry is a very appealing theory that provides a
rich set of models with a variety of final states to explore
● Solves hierarchy problem, dark matter, etc...
● Symmetry between bosons and fermions, R-parity,
when conserved gives new resonances, DM candidate
● Four main strong production mechanisms at the LHC
● Squark-gluino (˜q˜g)
● Gluino-pair (˜g˜g)
● Squark-pair (˜q˜q)
● Stop/sbottom pair (˜t˜t/˜b˜b)
● Strong production of squarks and gluinos give high cross section, high masses, and lots of jets
● Third generations squarks, while having lower cross sections, have b-jets in the final states, so
provide an interesting and challenging area of exploration 2
Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021
CMS stop production, all hadronic
arXiv:2103.01290 [hep-ex]
● Targeting a vast range of SUSY
models with top-quark final states
● Direct top squark production
● Gluino mediated production
● Highlights of new 137 fb-1 analysis:
● multiple jets, no leptons, and
large transverse
momentum imbalance
● Novel algorithms based on
deep neural networks to
identify hadronically
decaying top quarks and W
bosons
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021
All hadronic stop techniques
arXiv:2103.01290 [hep-ex]
● Top quark utilises a deep neural network, and tagging done in two ranges:
● Resolved – algorithm optimised for pT range of ~100 to 500 GeV
● Merged – algorithm optimised with jet shapes, heavy-flavour discrimination, and trained on
simulated ttbar events and QCD multijet events, and collision data dominated by QCD
● W-jets candidates that were identified in the NN are tagged after not passing the top quark tagger
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021
All hadronic stop analysis results
arXiv:2103.01290 [hep-ex]
Background top-quark pair
contributions can arise when
a lepton is 'lost' from the
analysis acceptance.
This is estimated from a 'lost
lepton', or LL control region
Background model
validated in
kinematically
similar but non-
overlapping regions
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021
All hadronic stop interpretations
arXiv:2103.01290 [hep-ex]
● Results significantly extended by 100-300 GeV.
● Direct stop search results are most stringent to date
● Benefits from both
● extended dataset
● improved analysis methods 6
Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021
Other CMS top squark searches
● Recent CMS top squark results:
Shown!
● All hadronic final state: arXiv:2103.01290 [hep-ex]
● Top quark + light quarks: arXiv:2102.06976 [hep-ex]
→ As seen in talk by Jordan Damgov !
● Same sign 2-lepton final state: Eur. Phys. J. C 81 (2021) 3
● Three lepton final state Eur. Phys. J. C 80 (2020) 752
● One-lepton final state: JHEP 05 (2020) 032
● Soft leptons and missing momentum:
SUS-18-004
● Combination and dedicated corridor
search: SUS-20-002
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021
New ATLAS result: stop to stau
ATLAS-CONF-2021-008
mT2, the 'stransverse mass', is useful for finding masses of pair-
produced particles that have invisibly decaying components, and
efficiently separating signal from background in the di-tau channel
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021
New ATLAS result: RPV multijet, 1 ℓ
ATLAS-CONF-2021-007
Search done for final states with
one or two SS leptons (e or μ), at
least 8 - 15 jets, and either zero or
many jets containing b-jets
The analysis uses a data driven
method to predict the background
to a very high number of jets.
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021
Other ATLAS top squark searches
● Recent ATLAS top squark results:
● Two-lepton final state: arXiv:2102.01444 [hep-ex]
● One-lepton final state: arXiv:2012.03799 [hep-ex]
● With higgs or Z bosons: Eur. Phys. J. C 80 (2020) 1080
● All hadronic final state: Eur. Phys. J. C 80 (2020) 737
● High-mult b-jets final state: Eur. Phys. J. C 81 (2021) 11
Shown!
● Stop to stau: ATLAS-CONF-2021-008
● RPV multijet, 1 lepton: ATLAS-CONF-2021-007
● Displaced vertex plus muon: Phys. Rev. D 102 (2020) 032006
● Combinations (include top squarks): ATL-PHYS-PUB-2021-007
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021Top squark summary plots
SUS-20-002 ATL-PHYS-PUB-2021-007
A statistical combination of three analyses in the main final Three main decay modes of the stop shown alongside
state with a dedicated search for the corridor where stop limits set by the monojet analysis in the case where stop 11
signal
Alison and top
A Elliot background are very similar. Moriond QCD 2021
(QMUL) and neutralino are nearly mass degenerate March 31st, 2021Top squark summary plots
SUS-20-002 ATL-PHYS-PUB-2021-007
A statistical combination of three analyses in the main final Three main decay modes of the stop shown alongside
state with a dedicated search for the corridor where stop limits set by the monojet analysis in the case where stop 12
signal
Alison and top
A Elliot background are very similar. Moriond QCD 2021
(QMUL) and neutralino are nearly mass degenerate March 31st, 2021ATLAS sbottom search, fully hadronic
arXiv:2101.12527
● Highlights of new 139 fb-1 search:
● Using final states of b-tagged quarks, no
leptons, and missing energy
● Dedicated signal regions to target very
small mass splittings of 10 GeV
– Enhancing low momentum b-jets with a
dedicated secondary-vertex algorithm
● BDTs to target specific model attributes
● Targeting different aspects of
● single SUSY model with sbottom
quarks.
● Final state also interpreted with respect to
● Simplified dark matter scenario
● Third generation down-type leptoquarks
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021Hadronic sbottom analysis techniques
arXiv:2101.12527 ATLAS-CONF-2019-027
● Tricky corners of phase space are targeted with tailored analysis techniques:
● A BDT is trained to target bulk low mass-splitting scenarios (Δm between 50 and 200 GeV)
● A track cluster based low-pT vertex tagger, TC-LVT, targets highly compressed scenarios (Δm < 50 GeV)
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021Hadronic sbottom analysis results
arXiv:2101.12527
Control the backgrounds Validate the analysis
Measure the results
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Alison A Elliot (QMUL)
Estimate the Uncertainties Moriond QCD 2021 March 31st, 2021Hadronic sbottom interpretation
arXiv:2101.12527
● Results showed a marked
improvement over and
above the luminosity
increases
● Compressed regions were
particularly benefitted by
the new analysis techniques
● Other scenarios beyond
SUSY were interpreted
● See also ATLAS sbottom
searches:
● JHEP 06 (2020) 46
● JHEP 12 (2019) 060
● https://arxiv.org/abs/2103.08189
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021CMS: gluino searches with Z bosons
JHEP 09 (2020) 149
● Search highlights for this new 137 fb-1 result:
● Large-radius jet substructure to
identify Z boson decays, soft
quarks, and missing transverse
momentum
● First search for this final state with
highly boosted Z boson pairs and
missing transverse momentum
● Parameter models used are: ● Model is a gluino decay cascade
● χ~2 → Zχ~0 branching fraction of 100% ● motivated by the desire to preserve
● m(χ~2)Gluino searches with Z bosons results
JHEP 09 (2020) 149
● Addition of Z boson candidate reduces backgrounds
significantly
● Search is sensitive to the unique SUSY model at high pTmiss
● The results exclude gluino masses below 1.9 TeV at 95%
confidence level, slightly less than expected, from the
fluctuation above standard model expectations
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021Summary
● Highlighted a few of the most interesting recent results from strong SUSY searches. SUSY
searches are now focused on probing more difficult and interesting phase spaces:
● All-hadronic stop search in CMS
● Stop to stau search in ATLAS
CMS SUSY publications
(and preliminary results)
● R-parity violating search with 1 lepton in ATLAS
ATLAS SUSY publications
● All-hadronic sbottom search in ATLAS
● Gluino searches with boosted Z bosons in the final state in CMS
● No time to cover many other excellent SUSY analyses
● See talk just before this by Jordan Damgov for new CMS top quark + light quark results
● Also see search highlights by Stefania Xella for SUSY highlights and beyond
● See talk by Cristiano Sebastiani after the coffee break to see brand new results of the
ATLAS stopped particle search, setting limits on R-hadrons
● See talk on Sunday by Vinay Hegde for CMS + ATLAS Electroweak SUSY results
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021backup
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021New ATLAS sbottom analysis paper
arXiv:2103.08189
A key discriminant used is Θ:
● The smallest three-dimensional
angle of the four combinations
between
● Either two leading τ-leptons
● Either of the two leading b-jets
● Probes the lowest mass regions of squark and neutralinos
● Exploits a low-background final state of b-quarks and tau
leptons in a higgs mass range
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021ATLAS: all-hadronic squark and gluinos
JHEP 02 (2021) 143
● Search highlights of new 139 fb-1 analysis:
● Jets and missing momentum, with no
electrons or muons
● Multi-pronged search strategies of:
– Multi-bin
– Boosted decision tree
– Model independent
● Designed to be sensitive to
generic SUSY models
● Final states separated by jet
multiplicities
● Targeted models include:
● Squark-squark
● Gluino-gluino
● Squark-gluino
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021ATLAS All-hadronic squark and gluinos
JHEP 02 (2021) 143
● Gluino pair prediction limits
extend the results from
previous search
● Limit on a gluino mass up to
2.4 TeV, for lightest SUSY
neutral particle (LSP) of ~300
GeV or less
● Squark-gluino production providing
● Model independent limit sensitivity up to 4 TeV in compressed
results show agreement with regions
Standard Model predictions ● Combined production limits of squark
● Range from 2 jets at 1.6 TeV pairs, gluino pairs, and squark-gluino
pairs for neutralino mass of 995 GeV
to 6 jets at 3.4 TeV ● Limits extended dramatically from
previous search
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Alison A Elliot (QMUL) Moriond QCD 2021 March 31st, 2021ATLAS: squark and gluino summaries
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