Selected results from ATLAS SUSY searches Focus on

Selected results from ATLAS SUSY searches: Focus on compressed spectra Vasiliki A. Mitsou HEP 2018 Recent Developments in High Energy Physics and Cosmology 28 March – 1 April 2018, NTUA, Athens, Greece

2 HEP 2018 V. A. Mitsou Supersymmetry (SUSY) • What it is? ▫ global symmetry between fermions & bosons • Why is it attractive? ▫ Higgs: predicts a below-135 -Ge. V Higgs scalar �may be SM-like �completely solves hierarchy problem ▫ unification of gauge couplings at single scale ▫ dark matter candidate

3 HEP 2018 V. A. Mitsou SUSY searches strategy Strong-production channels • Copious production at hadron colliders • MET-based generic channels Third-generation sparticles • Naturalness ➜ mass of O(<Te. V) • Lighter than other squarks Leptons/photons Coloured spartners too heavy ➞ direct gaugino/slepton production ➞ relevant for Dark Matter searches ATL-PHYS-PUB-2013 -011 (Meta)stable sparticles • Suppressed (effective) coupling • Lack of phase space, e. g. mass degeneracies • May induce non-trivial signals in detectors RPC or RPV • RPV implies more leptons and/or jets and less MET • RPV prompt or delayed LSP decay

4 HEP 2018 V. A. Mitsou SUSY searches strategy Strong-production channels • Copious production at hadron colliders • MET-based generic channels Third-generation sparticles • Naturalness ➜ mass of O(<Te. V) • Lighter than other squarks Leptons/photons Coloured spartners too heavy ➞ direct gaugino/slepton production ATL-PHYS-PUB-2013 -011 (Meta)stable sparticles • Suppressed (effective) coupling • Lack of phase space, e. g. mass degeneracies • May induce non-trivial signals in detectors ➞ relevant for Dark Matter searches RPC or RPV • RPV implies more leptons and/or jets and less MET • RPV prompt or delayed LSP decay

5 HEP 2018 V. A. Mitsou Typical SUSY search • Signal region (SR) ▫ optimised for best discovery in targeted production/decay mode (see next slide) ▫ to cover different mass hierarchies ➜ few SRs for each final state • Data-driven background estimate ▫ irreducible backgrounds estimated using control region (CR) data as a constraint and Monte Carlo to extrapolate from CR to SR ▫ reducible background (fake/non-isolated leptons, MET from jet mis-measurement) from data ▫ validation regions (VR) to check background estimate method and CR ➔ SR variable modelling • Likelihood fit of data in SRs and CRs using the CLs technique ▫ hypothesis testing of signal models ➜ 95% CL cross-section upper limits ▫ background versus data ➜ model-independent upper limits at 95% CL in visible cross-section

6 HEP 2018 V. A. Mitsou Interpretation • Sparticle masses from SUSY breaking not fixed by theory ⇒ huge parameter space to explore ▫ MSSM: > 100 parameters ▫ p. MSSM: 19 parameters ▫ CMSSM: 5 parameters • How to test that at LHC? 1. Top-down approach ▫ SUSY breaking mechanism ➞ different models ▫ GUT scale unification ➞ few free parameters 2. Bottom-up approach ▫ Phenomenological models � fix mass hierarchy and mass scales � scan remaining parameters ▫ Simplified topologies � specific decay chain � easy to interpret results in terms of other models T. Rizzo

7 HEP 2018 V. A. Mitsou (From simplified models to interpretations) Simplified-model exclusions can be re-casted to SUSY models SModel. S

8 V. A. Mitsou (From simplified models to interpretations) • LHC experiments provide detailed info on analysis (code, efficiency, x-section upper limits, . . . ) ➜ HEPDATA • Recasting tools ▫ Check. MATE, SModel. S, Mad. Analysis 5 PAD, Gambit, Rivet, Contur, . . . ▫ models (spectrum or simulated events LHE, . hep. . . ) ➜ detector simulation (Delphes) ➜ confrontation with simplified-topology exclusions (➜ find best-fit scenario) • More info: Forum on the Interpretation of the LHC Results for BSM studies https: //twiki. cern. ch/twiki/bin/view/LHCPhysics/Interpreti ng. LHCresults Eur. Phys. J C 77 (2017) 144 HEP 2018

9 HEP 2018 V. A. Mitsou LHC and ATLAS performance Results presen ted here • up to ~36 fb -1 at 13 Te • for Mo V riond 20 18 LHC REMARKABLE Luminosity Peak instantaneous luminosity > 2 × 1034 cm-2 s-1 Great performance from ATLAS In total 80 fb-1 good for physics in 2015 -2017

10 HEP 2018 V. A. Mitsou ☞ talk by Lisa Paspalaki on γ+MET CMS search Strong production • Production of 1 st and 2 nd generation squarks and gluinos with subsequent cascade decay to lighter sparticles • Signatures include (+MET): • • 0/1/2 leptons hadronic taus b-jets photons

11 HEP 2018 V. A. Mitsou Strong production results squarks gluinos Exclusion curves not necessarily directly comparable; different: • sparticle mass hierarchies • simplified decay scenarios

12 HEP 2018 rd 3 V. A. Mitsou generation quarks • Inspired by naturalness arguments (see next slide) • Focuses on stop and sbottom production • + higgsinos (compressed spectra) • Signatures include (+MET): • 0/1/2 leptons • hadronic taus • (di-)bosons ➔ b-jets, photons

13 HEP 2018 V. A. Mitsou “Natural” SUSY To cancel large top corrections to Z mass (fine-tuning) … … only need light higgsinos, stops, gluinos Examples of production and decay diagrams at LHC L. Hall, Berkeley 2011 (and light messenger scale Λ)

14 HEP 2018 V. A. Mitsou Stop production Stop 0 lepton Charm tagging m(stop) ≲ m(top) + m(χ 10) Stop 2 lepton Stop 1 lepton Overlaid contours belong to different Limits depend on chargino-neutralino mass splitting • • chargino masses stop decay channels sparticle mass hierarchies simplified decay scenarios

15 HEP 2018 V. A. Mitsou Electroweak production • Involves neutralino, chargino, slepton direct production • Final states (+MET): • multileptons • hadronic taus • (di-)bosons ➔ b-jets, photons • Results also interpreted in the context of dark matter, e. g. p. MSSM [JHEP 1609 (2016) 175] • NEW: Compressed-spectra scenarios [PRD 97 (2018) 052010]

16 HEP 2018 V. A. Mitsou Electroweak production (no compressed spectra) Sensitive to details of scenario considered, e. g. nature of gaugino (bino, wino, higgsino)

17 HEP 2018 V. A. Mitsou Electroweak production (no compressed spectra) Sensitive to details of scenario considered, e. g. nature of gaugino (bino, wino, higgsino) Compressed spectra region, i. e. m(χ 20) ≈ m(χ 10), still to be covered��� ⇓ analysis presented here

18 HEP 2018 V. A. Mitsou Higgsino signatures Δm(χ 20, χ 1±, χ 10) ~ a few Ge. V Δm(χ 20, χ 1±, χ 10) ~ 300 Me. V • Decays via off-shell W/Z • Soft-leptons + jets • Extremely compressed • Disappearing tracks PRD 97 (2018) 052010 arxiv: 1712. 02118 Δm(χ 20, χ 1±, χ 10) ~ a few Ge. V • Decays via on-shell h/Z • ≥ 3 b-jets ATLAS-CONF-2017 -081 Depending on model details, wide variety of signatures possible

19 HEP 2018 V. A. Mitsou Soft leptons and jets Initial-state radiation to boost final-state objects large MET from neutralino LSPs two low-p. T opposite-sign leptons • Sensitivity driven by low-p. T leptons • Binned m���� starting from 1 Ge. V (higgsino scenario) • High-p. T jet(s) and MET (well separated) • Binned m. T 2 starting from 100 Ge. V (slepton scenario) Signal regions

20 HEP 2018 V. A. Mitsou Kinematic features • Critical to identify soft leptons from off-shell Z decays • Different kinematic edge in m���� distribution between higgsinos and winobino * m 1 and m 2 are the signed mass eigenvalues of the daughter and parent neutralino respectively [EPJC 52, 743 (2007)] PRD 97 (2018) 052010

21 HEP 2018 V. A. Mitsou Signal vs. background • m���� distribution in the Higgsino signal region ▫ ∈ [1, 60] Ge. V excluding [3. 0, 3. 2] Ge. V to suppress J/ψ • ETmiss/HTlep higher in signal than background for both higgsino and slepton selections PRD 97 (2018) 052010

22 HEP 2018 Background V. A. Mitsou Tau Top • Estimated via backgroundenriched control regions • Tested in validation regions Fake leptons • Estimated via “fake factor” method • Validated in regions with same-sign leptons PRD 97 (2018) 052010

23 HEP 2018 V. A. Mitsou Results & interpretation PRD 97 (2018) 052010 Higgsinos Sleptons SRs optimised for higgsinos SRs optimised for sleptons Sensitivity beyond LEP limits in fairly compressed scenarios

24 HEP 2018 V. A. Mitsou Wino-bino interpretation • SRs optimised for higgsinos also interpreted in wino-χ 20 / bino-χ 10 scenario • m(χ 20) ≈ m(χ 1±), Δm(χ 20, χ 10) ~ few tens Ge. V • Focus region: motivated by dark matter relic density arguments • Enhanced χ χ annihilation cross section focus region EPJC 52, 743 (2007) PRD 97 (2018) 052010

25 HEP 2018 V. A. Mitsou R-parity violation

26 HEP 2018 V. A. Mitsou R-parity Lightest Supersymmetric Particle (LSP) and R-parity conservation/violation largely define final states of SUSY events L-number violation • R = (-1)3(B-L)+2 s → R = +1 for SM particles – 1 for superpartners bilinear terms • R-parity conservation hinted but not required by proton stability • If R-parity conserved ▫ stable LSP neutral and colourless ▫ in colliders could be detected as “missing energy”(MET) ▫ dark matter candidate • In broken R-parity ▫ LSP may be charged and/or carry colour ▫ LSP is not stable B-number violation

27 HEP 2018 V. A. Mitsou R-parity violation – summary • Future searches can be optimised to further increase the sensitivity throughout the RPV phasespace • RPV through bilinear terms offers a well-motivated (neutrino masses) scenario and compact way (no additional parameters) to search for RPV SUSY JHEP 10 (2015) 054

28 HEP 2018 V. A. Mitsou Long-lived particles

29 HEP 2018 V. A. Mitsou Stable or metastable particles • Long-lived decays of spartners possible in several frameworks, including ▫ nearly conserved symmetry �e. g. long lived gluinos or squarks that hadronise before decaying → R-hadrons in Split SUSY ▫ low coupling between the particle and the final state �e. g. weak RPV couplings ▫ Mass degeneracy between the particle and the final state • Depending on the lifetime, different detection techniques involving various objects: tracks, photons, leptons, …

30 HEP 2018 V. A. Mitsou Long-lived particles – summary 8 -Te. V results on R-hadrons Summary 8 -Te. V & 13 Te. V on disappearing track Split SUSY with metastable g → g/qq χ 10 Long lived chargino, χ 1± → π± χ 10 ⊕ long-lived sleptons ⊕ displaced vertices ⊕ non-pointing photons

31 HEP 2018 V. A. Mitsou Summary & outlook • LHC experiments have developed a vast program to search for supersymmetry ▫ strategy and techniques continue involving • No SUSY signal seen up to now • Still, various theoretically well-motivated & experimentally challenging scenarios remain to be further explored ▫ e. g. electroweak production of SUSY and compressed spectra ▫ also R-parity breaking scenarios and long-lived sparticles • Challenging years for SUSY lie ahead of us at LHC and future accelerators!

32 HEP 2018 V. A. Mitsou Project supported by a 2017 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation

33 HEP 2018 Spares V. A. Mitsou

34 HEP 2018 V. A. Mitsou Strong production results Gtt model Exclusion curves not necessarily directly comparable; different: • stop decay channels • sparticle mass hierarchies • simplified decay scenarios

35 HEP 2018 V. A. Mitsou

36 HEP 2018 V. A. Mitsou