Search for R-parity violating supersymmetry with ATLAS

1. Search for R-parity violating supersymmetry with ATLAS E. Torró, V. A. Mitsou, C García IFIC Valencia II PCI 2009 Workshop Valencia, 18-19 November 2010

2. Vasia Mitsou Outline • Introduction to Supersymmetry • R-parity violation (RPV) • bilinear RPV • LSP decay – displaced vertex • Prospects for RPV discovery with ATLAS at 10 TeV • documented in Torró, VAM, García, ATL-PHYS-INT-2010-042 • Data analysis with 7 TeV; periods A-H • very preliminary; work in progress • Summary • References

3. Supersymmetry = fermion-boson symmetry: all particles have SUSY-partners with spin ±1/2 SUSY-partners of quarks and leptons are squarks and sleptons, with spin=0 SUSY-partners of gauge particles (g, W, Z, gluon, graviton) and Higgs are “photinos, winos, zinos, gluinos, gravitinos,higgsinos’’ with spin=1/2 (3/2) Lightest SUSY-particle (LSP) stable when R-parity conserved dark matter candidate LHC: very good chances to observe squarks, gluinos, supersymmetric Higgs, ... Vasia Mitsou Supersymmetry...

4. Vasia Mitsou R-parity +1, for SM particles –1, for superpartners • Defined as: R = (-1)3B+L+2S→ R = • R-parity violating part of the superpotential (48 parameters) • Proton stability → either lepton or baryon number may be violated (not both!) • R-parity violation → • Single sparticle production is allowed • LSP is not stable! • No missing energy (if LSP decays in the detector)! • LSP may be charged (e.g. stau, sleptons) L-number violating terms bilinear terms B-number violating term

5. Vasia Mitsou Bilinear RPV & neutrinos • RPV through bilinear terms (εi≠0): • Bilinear terms → mixing between neutrinos-neutralinos • tree level → atmospheric scale • 1-loop → solar scale • Model parameters • three parameters εi in bilinear terms • three soft SUSY breaking parameters Bi expressed through sneutrino vev’s vi or “alignment” parameters Λi = εivd+μvi • BRs of LSP sensitive to neutrino mixing parameters, e.g.: • RPV parameters chosen to be consistent with constraints from neutrino experiments: Δmatm2, Δmsol2, tan2θatm • After naturalness constraint imposed, no free RPV parameters remain

6. Secondary Vertex LSP Lxy PT(LSP)  5 GeV Primary Vertex Lxy  0.5 mm d = impact parameter Vasia Mitsou Displaced vertex from LSP decay • LSP lifetime: cτ ≃ 0.5 mm in minimal Supergravity (mSUGRA) point studied → secondary-vertex tagging possible • Studies for longer decay lengths under way in ATLAS • For these decay lengths considerable background from B-mesons (“b-tagging region”) de Campos et al, arXiv:1006.5075 [hep-ph]

7. Vasia Mitsou Channel under study χ10→μW→μqq’ • mSUGRA point SU3: m0=100 GeV, m1/2=300 GeV, tanβ=6, A0=-300 GeV, μ>0 • RPV parameters: ε1= 102 MeV, ε2 = -102 MeV, ε3 = 102 MeV, Λ1 = -3.71·103 MeV2, Λ2 = 82.9·103 MeV2, Λ3 = 82.9·103 MeV2 • Total SUSY cross-section:4.9 pb @ 10 TeV, 1.41 pb @ 7 TeV • Neutralino LSP produced at the end of SUSY cascade • Neutralino mass reconstruction possible • One high-pT muon or tau required plus two jets • Other decays also interesting (e.g. μτν,ττν, eτν) SPheno used for mass spectrum and decay rates calculations

8. Vasia Mitsou Background and trigger • Cascade decay identical with Rp conserving (RPC) SUSY; only difference: neutralino LSP decays • Background same as in RPC SUSY:QCD, ttbar, W/Z+jets, di-bosons, single top • Data-driven methods for background estimation, e.g. HT2 method for ttbar • Single muon triggers used so far • Isolated muons may be used in the future

9. Vasia Mitsou Analysis E. Torró, VAM, C. Garca, ATL-PHYS-INT-2010-042 • Cuts applied to suppress Standard Model processes • similar to those for RPC • no MT cut (assumes MET due to escaping LSP) • softer MET cut; MET due to • neutrinos produced “upstream” • LSP decays to neutrinos + X • Additional selection criteria to disentangle signal decay from “SUSY bkg” • separation angles between jets (and muons) • finally the neutralino mass should be visible in μjj invariant mass

10. Vasia Mitsou Cut flow for 10-TeV study (I) 2 fb-1 soft MET cut

11. Vasia Mitsou Meff and MET • After preselection and SM cuts (previous slide) • “Signal” events lower MET than “SUSY bkg” • Yet MET high enough when compared to SM processes to worth applying the cut

12. Vasia Mitsou Muon pT and W candidates • Target muon has higher pT than “bkg muons” • W candidate: |mjj-MW|< 5 GeV

13. Vasia Mitsou pT – separation angles correlation

14. Vasia Mitsou Separation angles,  DR=√Δφ2+Δη2 • ΔRjj : between any two jets • ΔRμW : between a muon and a W candidate Final cuts (upper limits)

15. Vasia Mitsou Cut flow (II) 2 fb-1

16. Vasia Mitsou LSP mass peak • With 2 fb-1 @ 10 TeV (not all systematics taken into account) • Significance Zn = 7.6 in mass window (90,140) GeV • 50% (20%) uncertainty on QCD (ttbar, W/Zjets, dibosons) bkg estimation • MLSPexp = (115.3±0.8) GeV MLSPtheo = 118 GeV • Systematic uncertainties • Jet absolute energy scale • SUSY combinatorics • SM background • Fit range

17. 7 TeV Vasia Mitsou MC vs data #muons muon pT muonη • SUSY D3PDs • A-H period • Only shown statistical errors! • Red line: total bkg • Black dots: data • Cuts applied in plots: • Object definitions and cleaning cuts as defined in SUSY WG • >= 1 isolated μ pT>10 GeV, |η|<2.4 • >= 2 jets, pT>20 GeV, |η|<2.5 # jets jet pT jet η • Additional cuts • >= 2 jets, pT>30, 60 GeV, |η|<2.5 • MET > max{80 GeV, 0.3 Meff} • Sphericity ST > 0.2 • Δφ(MET,2jets)min > 0.2

18. Vasia Mitsou Meff, ST and MET L1_2j15 • No errors on luminosity, background estimation, etc. shown here • Period A-H • Good agreement between MC and data

19. Vasia Mitsou Conclusions & outlook • R-parity violating Supersymmetry, if it exists at low mass scale, will be discovered with ATLAS with ~100 pb-1 • The Valencia group is very active on the μ+2jets channel • collaborating with groups in Santiago, Würzburz and Bonn • activities within the informal “prompt RPV” sub-sub-group • Hoping to have first results approved for winter 2011 conferences • Possibility to improve the analysis by looking for displaced vertex from the LSP decay

20. Vasia Mitsou Some references… • E. Torró, V.A. Mitsou, C. García, “Prospects for detecting R-parity violating supersymmetry with ATLAS in the muon plus jets channel,” CERN-ATL-PHYS-INT-2010-042, 2010, 20 p • Prompt RPV activities in ATLAStwiki: http://indico.cern.ch/materialDisplay.py?materialId=slides&confId=110488Informal meetings in Indico: http://indico.cern.ch/categoryDisplay.py?categId=2931e-group: atlas-phys-susy-prompt-RPV@cern.ch • F. de Campos, O.J.P. Eboli, M. Hirsch, M.B. Magro, W. Porod, D. Restrepo, J.W.F. Valle, ``Probing Neutrino Oscillations in Supersymmetric Models at the Large Hadron Collider,’’ Phys. Rev. D 82 (2010) 075002 [arXiv:1006.5075 [hep-ph]];``Probing bilinear R-parity violating supergravity at the LHC,'' JHEP 0805 (2008) 048 [arXiv:0712.2156 [hep-ph]] • M. Hirsch, M.A. Diaz, W. Porod, J.C. Romao and J.W.F. Valle, ``Neutrino masses and mixings from supersymmetry with bilinear R-parity violation: A theory for solar and atmospheric neutrino oscillations,'' Phys. Rev. D 62 (2000) 113008 [Erratum-ibid. D 65 (2002) 119901] [arXiv:hep-ph/0004115] • W. Porod, ``SPheno, a program for calculating supersymmetric spectra, SUSY particle decays and SUSY particle production at e+ e- colliders,'' Comput. Phys. Commun. 153 (2003) 275 [arXiv:hep-ph/0301101]