Searches for SUSY & Exotics with ATLAS Evelyn Thomson University of Pennsylvania
May 17 2017 BLV 2017 Cleveland, Ohio
1 Outline
Introduction ATLAS speakers in parallel sessions Supersymmetry searches Exotics at the LHC Gluinos Search for New Phenomena in Dijet Events Scalar top Lydia Beresford (May 15 14:20) Electroweakinos Searches for new phenomena in leptonic final states Exotic searches Chikuma Kato (May 15 14:40) Dilepton Search for vector-like quarks Dijet Takuya Tashiro (May 15 15:00) Diboson Lepton number violation searches Vector-like quarks Antonio Salvucci (May 16 14:50) Dark matter Dark Matter Summary Dark Matter searches with the ATLAS Detector Stanislav Suchek (May 15 14:40)
2 The Large Hadron Collider
Run 2 proton collisions at √s=13 TeV Delivered 42 fb-1 in 2015+2016 Goal 90 fb-1 more in 2017+2018 Run 3 2021-2023 Goal 300 fb-1 Phase II upgrades -> High Luminosity 2026-2035 Goal 3000 fb-1
3 Searching for Supersymmetry
SUSY pair production R-Parity R=(-1)3B-3L+2s
1 pb 1 pb
Status and implications of BSM searches 1 fb E. Halkiadakis, G. Redlinger, D. Shih arXiv:1105.1110, arXiv:hep-ph/9611232 Ann.Rev.Nucl.Part.Sci. 64 (2014) 319-342 4 Searching for Supersymmetry
SUSY pair production R-Parity R=(-1)3B-3L+2s LHC signature depends on LSP and R-Parity
1 pb
Figure from S. Spinner
1 fb ATLAS-CONF-2015-018 Run 1 Constraints on promptly decaying SUSY arXiv:1105.1110, arXiv:hep-ph/9611232 particles with lepton-number-violation and RPV 5 Solving rapid proton decay in SUSY
R-Parity Conservation R=(-1)3B-3L+2s R-Parity Violation R=(-1)3B-3L+2s Forbids violation of baryon and lepton number Allows violation of baryon OR lepton number Proton stable Proton stable Lightest Supersymmetric Particle (LSP) stable LSP decays through small RPV couplings Significant consequences for LHC signatures Significant consequences for LHC signatures Pair production of superpartners Pair production of superpartners High MET from stable LSPs No MET since collider LSP decays LSP is a dark matter candidate (must be neutralino) Decaying dark matter ad hoc introduction of new quantum number Add an extra local gauge symmetry to MSSM 6 Gluino pair production
Simplified model with squarks decoupled Direct decay to LSP
Four high pT jets High effective mass (meff) from High MET scalar sum of jet pT and MET Exclude gluino up to 2000 GeV for low LSP mass Similar limits for more complicated decay chains and pMSSM
ATLAS-CONF-2017-022 7 Background estimation
Showing control regions for major backgrounds 푡푡 → 휏휐푞푞 ′푏푏 and hadronic tau decay Z+jets with 푍 → 휐휐 W+jets with 푊 → 휏휐 and hadronic tau decay Normalize backgrounds using control regions Check in validation regions (not shown here)
ATLAS-CONF-2017-022 8 Scalar top search Direct production of stop pairs
4 high pT jets, 1 b-tag MET > 250 GeV
Exclude stop up to 950 GeV for low LSP Improved reach in region where stop mass close to sum of top and LSP New search region with ISR Exclude stop between 235-590 GeV
ATLAS-CONF-2017-020 see also 2017-037 for 1 lepton and 2017-034 for 2 lepton 9 Exploring LSP type
One step decay Two step decay significant and W bosons may be off-shell
For results, please see Keisuke Yoshihara’s talk at LHCP this morning and ATLAS-CONF-2017-037
10 Gluino with RPV
LSP has baryon-number violating decay One lepton 5 to 12 or more jets, b-tags No MET Data-driven backgrounds Exclude gluino up to 2100 GeV for Bino LSP
arXiv:1704.08493 11 Stop with RPV (Bino LSP or Higgsino LSP)
LSP has baryon-number violating decay One lepton 5 to 12 or more jets, b-tags No MET Data-driven backgrounds Interpretation for scalar top production BinoBinoLSPLSP Wino LSP (no leptons) Higgsino LSP
arXiv:1704.08493 12 Stop RPV 2x2
Baryon-number violating decay 2 resonances decay to 2 jets No MET, background from QCD multijets Data-driven estimate
Average mass of di-jet pairs
For each mavg bin Preselection data Preselection data ND=NAxNF/NC
Mass Asymmetry Production angle ATLAS-CONF-2017-025 13 Stop RPV 2x2
Baryon-number violating decay 2 resonances decay to 2 jets Decay to two light quarks Exclude stop from 100 to 410 GeV
ATLAS-CONF-2017-025 14 Stop RPV 2x2
Baryon-number violating decay 2 resonances decay to 2 jets Decay to two light quarks Exclude stop from 100 to 410 GeV Decay to a b quark and light quark Exclude stop from 100 to 470 and 480 to 610 GeV
ATLAS-CONF-2017-025 15 휏푏휏푏 PLB 732 (2014) 325 Stop RPV with U(1)B-L Minimal model with extra U(1) B-L gauge group, spontaneously broken by RH sneutrino Stop LSP with lepton number violating decay 2 resonances decay to lepton and b-quark 2 leptons ee, eμ, μμ, 2 jets, 1 b-tag Backgrounds normalized in control regions 휇푏휇푏 푒푏푒푏 푡푡, Wt, Z/γ*+jets
Mass Asymmetry ATLAS-CONF-2017-036 Highest Mass Lepton b-jet pair 16 Electroweakinos Decay via W, Z, h bosons Smaller leptonic branching fractions
Decay via scalar leptons Run 1 results, Run 2 results soon
→ Decreasing ∆M Decreasing
Increasing ∆M → Assumptions: LSP is pure bino; NLSP is pure wino; large ∆M between NLSP and LSP ATLAS SUSY summary plots 17 Electroweakinos 4 lepton (RPV)
LSP has lepton-number violating decay 4 isolated leptons from massive LSP decays Backgrounds ttZ, ZZ with 4 leptons Reducible with 1 or 2 fake leptons
Exclude wino NLSP below 1000 GeV assuming LSP decay 50% eµν 25% eeν 25% µµν
ATLAS-CONF-2016-075 18 Disappearing track IBL Run 2 33 mm New pixel layer at 33 mm for Run 2 (IBL) 120 mm Run 1 New tracklet reconstruction (4 hits) 300 mm completely in pixel detector Sensitive to charged particles with shorter lifetimes than Run 1 Long-lived Chargino small ∆M for Wino LSP
ATLAS-CONF-2017-017 19 Long-lived particles summary
Long-lived chargino Long-lived gluino R-hadron Only 2015 data
See new ATLAS-CONF-2017-026 displaced vertices SUSY-Summary-Plots 20 Outline
Introduction Highest dijet invariant mass 8.12 TeV, both jets have pT 3.79 TeV Supersymmetry searches Gluinos Scalar top Electroweakinos Exotic searches Dilepton Dijet Diboson Vector-like quarks Dark matter Summary
21 Dijet resonances
Data-driven background Dijet invariant mass Angular distribution
arXiv:1703.09127 22 Searches with same flavor leptons
20 GeV for ee Experimental mass resolution at 3 TeV 420 GeV for μμ
ATLAS-CONF-2017-027 23 Searches with same flavor leptons Exclude Z’ with mass below 4 TeV at 95% CL Exclude llqq contact interactions with energy scale Λ below 23 to 40 TeV
ATLAS-CONF-2017-027 24 Searches with Lepton Flavor Violation Only 2015 data Updates for summer
Eur. Phys. J. C76 (2016) 541 25 Diboson resonances
Search for 푉퐻 → 푞푞 ′푏푏 with high Lorentz boost
Two high pT large R=1.2 jets (450, 250 GeV) Jet mass > 50 GeV Higher mass jet with 1 or 2 b-tagged track jets Lower mass jet has two-prong substructure Background 90% from QCD multijets Data-driven background from sidebands Above 2.5 TeV, Higgs Lorentz boost high enough for overlap of decay of two b hadrons 1 tag has better sensitivity above 2.5 TeV ATLAS-CONF-2017-018 26 Diboson resonances
Search for 푉퐻 → 푞푞 ′푏푏 with high Lorentz boost
Two high pT large R=1.2 jets (450, 250 GeV) Jet mass > 50 GeV Higher mass jet with 1 or 2 b-tagged track jets Lower mass jet has two-prong substructure Data are in agreement with Standard Model expectations Largest excess observed at 3.0 TeV Local significance of 3.3σ Global significance of this excess is 2.2σ ATLAS-CONF-2017-018 27 Vector-like Quarks: ZtZt final state
Spin-1/2 but not chiral like standard model quarks Vector: same left and right-handed couplings Bare mass terms allowed in Lagrangian Solves hierarchy problem for Higgs boson mass TT pair production One T → Zt decay with 푍 → 휐휐 HtHt Signature One lepton
4 high pT jets MET Exclude T mass below 1.16 TeV with 100% T→ Zt Here T->Zt ATLAS-CONF-2017-015 See also for T->Wb EXOT-2016-14 See also for T->Ht ATLAS-CONF-2016-104 ZtZt WbWb 28 Vector-like Quarks: WbWb final state
Optimized for TT, also sensitive to BB, XX, YY One T → Wb decay with W→ 푙휐 Signature One lepton, MET
3 high pT jets 1 b-tag HtHt Large R jet for boosted W Exclude T mass below 1.35 TeV with 100% T→ Wb Exclude B mass below 1.25 TeV with 100% B→ Wt
EXOT-2016-14 ZtZt WbWb 29 Dark matter search
Mono-photon+MET Backgrounds 푍 → 휐휐 + QED ISR Cleaner background than in mono-jet+MET with QCD ISR
ATLAS-EXOT-2016-32 30 Dark matter search
Mono-photon+MET Set limits in 2D plane (mediator mass, DM mass)
Proton collisions so larger gq gives better limits
ATLAS-EXOT-2016-32 31 Dark matter and dijets
Dark matter mediator produced in proton- proton collisions, so must also decay to dijets
Dijet searches give strong limits for gq=0.25, weaker limits for smaller gq=0.1
Exotics summary plots 32 Summary
Searches for strongly produced SUSY not showing any deviations from SM…yet Searches for rarer electroweak produced SUSY starting to explore new territory in Run 2 Searches for exotics not showing any deviations from SM…yet
New Supersymmetry results New Exotics results 33 Backup
34 rd Gluino pair production: 3 gen ATLAS-CONF-2017-021
All final states have 4 b-jets Require 3 b-tags Combine multiple search regions 4-9 jets Low-Int-High effective mass 0 or 1 lepton Exclude gluino below 1900 GeV for low LSP mass, expected limits slightly higher
0 tops 4 tops
35 Pileup
Reconstruction of charged particle tracks important to remove effects of pileup Select anti-kt jets with tracks from primary vertex (hard scatter) Calculate MET with calibrated objects and other tracks from primary vertex
36