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Search for Gravitinos in R-Parity violating Supersymmetry at HERA

Search for Gravitinos in R-Parity violating Supersymmetry at HERA. SLAC experimental seminar Claus Horn (DESY / Univ. Hamburg). Introduction HERA & ZEUS SUSY processes at HERA Analysis Summary & Outlook. SUSY Motivation. Coleman-Mandula theorem / Haag-Lopuszanski-Sohnius theorem

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Search for Gravitinos in R-Parity violating Supersymmetry at HERA

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  1. Search for Gravitinos in R-Parity violating Supersymmetry at HERA SLAC experimental seminar Claus Horn (DESY / Univ. Hamburg) Introduction HERA & ZEUS SUSY processes at HERA Analysis Summary & Outlook

  2. SUSY Motivation • Coleman-Mandula theorem / • Haag-Lopuszanski-Sohnius theorem • Unification of the forces • Solution of the hierarchy problem • Candidates for dark matter • Necessary for quantum-gravity SUSY is our last chance to discover a fundamental space-time symmetry!

  3. 27.5 GeV e± HERA accelerator e± p collider, in Hamburg Protons: 920 GeV Leptons: 27.5 GeV CMS-Energy: 320 GeV Length: 6.3km HERA I (1992-2000) L=1.6 1031 cm-2s-1 HERA II (2002-2007) L=7.0 1031 cm-2s-1 p 920 GeV HERA II: polarised lepton beam also at H1 & ZEUS.

  4. P e± ZEUS detector Calorimeter: Uranium Scintillator • 3° < q< 178° • EMC DE/E = 18%/(E/GeV) 1% • HAC DE/E = 35%/(E/GeV)1% Central Tracking Detector:Drift Chamber • 15° < q< 164° • 1.4 T magnetic field Weight: 3500T, Size: 12m ×10m ×19m

  5. In MSSM SUSY breaking is introduced “by hand“ via soft terms. over 100 free parameters! Supersymmetry Postulate superpartner for each SM particle with same QNs but spin different by ½. Q|boson> = |fermion> Q+|fermion> = |boson> [H,Q]=0 No superpartners with same masses are observed. SUSY is a broken symmetry. MSSM: Minimal number of sparticles and couplings.

  6. LSP is always gravitino. Typically very light: Candidate for dark matter (even in RPV models). Possible NLSPs: neutralino, stau, (right-handed slepton) Distinct event signature: photon/tau + missing energy. Gauge Mediated SUSY Breaking Model Super trace theorem: SUSY breaking not possible in visible sector. ->Hidden Sector Models Example for generation of sfermion masses: GMSB parameters: sqrt(F), Mmess, N, L, tan(b), sign(m)

  7. R-Parity +1 for SM particles -1 for sparticles Multiplicative discrete symmetry: RP=(-1)3B+L+2S RPC: sparticles pair-produced, LSP stable Most general Lagrangian contains additional trilinear terms in superpotential which violate RP: Unique initial state HERA ideal place to look for l‘ couplings. Former analyses looked for resonant squark production. squarks are heavy.

  8. SUSY Classification Scheme Motivation: Check all possible SUSY channels at HERA before start of LHC. Systematic approach: • List all possible diagrams with potentially high cross section. • Include also R-parity violating vertices. Particles are producedon-shell (same for all SUSY models). Decay depends on sparticle spectra of SUSY model. Sparticle creation at HERA: } HERA topologies Abstract notation SUSY-flow graphs Fundamental vertices Abstract diagrams

  9. HERA Topologies • All topologically distinct graphs • with up to three outgoing (s)particle lines • Initial state is fixed to electron+quark • (g and g from proton are only considered with 2 outgoing lines)

  10. SUSY-flow Graphs Choose RPV vertices Mark sparticle lines with a „~“. In the case of RPC: C-like loops result. Example F, RPC: Number of SUSY propagators Number of SUSY particles discarded

  11. Abstract Notation & Fundamental Vertices Physics description on an abstract level to reduce complexity. All vertices of the MSSM ! (neglecting pure bosonic SM vertices and Higgs)

  12. Single slepton production. Only SM propagators. All l‘ couplings can be investigated. Signature e.g. in GMSB: l+G ~ ~ s=0.2pb for m(l)=100 GeV. Results After all cuts: 55 abstract diagrams of sparticle production. Additionally consider dominant sparticle decays: Complete list of SUSY signatures at HERA. Characteristic signatures for different SUSY models / scenarios. Example of new found diagram: (now investigated by new PhD student)

  13. Analysis • Signal processes & Topologies • Event selection • Discriminant method • GMSB phenomenology • Limits Investigated data set (1996-2005) e- p : L=155 pb-1 e+ p : L=145 pb-1 Total: L=300 pb-1 (HERA I and HERA II) First ZEUS thesis with complete data set!

  14. Signal Processes Gaugino production via slepton exchange: Gravitino channel R-parity violating decay channels Electron channel e±+ multiple jets Neutrino channel Signature: n + multiple jets jet + g + missing energy

  15. Signal Topologies Simulated events (SUSYGEN+Geant detector simulation) RPV decay GMSB decay p • 3 hard forward jets • low pT electron or • neutrino (missing PT) • jets nearly isotropic in r-f plane • 1 hard forward jet • isolated, high pT photon • missing energy

  16. 1.step Event Selection – Gravitino Channel Loos selection to maximize signal efficiency! • n trigger selection • Q²JB > 700 GeV •  1 jet with pT>6 GeV • and –1.5 < h < 2.5 • PT miss > 22 GeV • Df(jet,g) < 3.0 • Background rejection Data/MC : 4751/4787 e70%-77% -> good agreement.

  17. 2.step Gravitino Channel – Final Selection Additional cuts: • photon candidate, with • E > 4 GeV, –2.8 < h < 2.8 • DCA > 30 cm (track cut) Data/MC : 1254/1275 e61%-68% -> good agreement.

  18. Signal to Background Optimization One dimensional cuts do not maximize S/B (for a given signal efficiency) if correlations between variables exist. Discriminant: Only select events in signal dominated areas! Disadvantage: A lot of MC needed. Advantages compared to: Likelihood ratios • Take into account all correlations. Neural Networks • No training needed. • No interpolation into empty phase space.

  19. Dynamic Discriminant Method Box size needs to be fixed before counting starts, however counting several too small boxes is faster than counting one too big box. 1-dim factor for which N Nmin. # events /box ~ (box_size)dim 464000 Advantages of variable bin size method: Less parameters have to be set by hand. More events get classified. Faster calculation. More accurate results.

  20. Gravitino Channel – Discriminant Vars Selection of best set of discriminant variables: • Chose characteristic • variables. • Calculate discriminants for • all possible combinations. Purity and efficiency after different discriminant cuts.

  21. Gravitino Channel Discriminant ZEUS data 1996-2005 No excess observed in signal region!

  22. RPV Electron Channel • e±trigger selection • ET > 60 GeV •  2 jet with –0.5 < h < 2.7 • pT>25 GeV (first jet) • pT>12 GeV (second jet) • electron candidate with • E>10 GeV, • –1.2 < h < 2.8, • pT>15 GeV (3°<q<17°) • pT>6 GeV (17°<q<115°)

  23. RPV Neutrino Channel • n trigger selection • ET > 50 GeV • PT>20 GeV •  1 jet with –0.5 < h < 2.7 • pT>10 GeV • reject electron with • pT>6 GeV, • q < 180

  24. RPV Discriminants Electron channel Neutrino channel No excess observed in signal region!

  25. Observables SUSY Parameters Process Parameters Parameter Dependence Problem factorizes: Effects of model parameters sometimes interchangeable, or have only small effect. Set limits on process parameters. Slepton mass treated as free parameter.

  26. Results ~ ~ Limit set in mass plane of process particles m(e)-m(c). For l‘111=1 sparticle masses of up to m(e) < 360 GeV and m(c) < 190 GeV can be excluded at 95%CL. ~ ~ Best existing limits in RPV GMSB! Limits calculated for different strengths of l‘ coupling.

  27. GMSB Phenomenology Dominating decay channels: ~ ~ ~ ~ BR(c->gG)+BR(c->eqq)+BR(c->nqq)  100%. RPV decays get important: • Toward high sqrt(F); • for stronger RPV couplings. Contribution from different gauginos: Low sqrt(F): Lightest neutralino dominates. High sqrt(F): Partly contribution from lightest chargino. NLSP: Neutralino is NLSP for low N and high tanb.

  28. ~ ~ ~ ~ ~ ~ ~ c = (W, H) c0 = ( H0, Z0, g ) Gaugino Composition Gauginos are superposition: High cross section requires: 1. Small higgsino component (for large eec coupling) 2. Large photino component (for GMSB decay into photon) ~ ~ MSSM GMSB

  29. Limit Variations Variation of M and sign(m): Different RPV couplings: Variation of N: Dependence on sqrt(F): mSUGRA-like scenario Typical GMSB scenario Similar limits are valid in large part of GMSB parameter space!

  30. Outlook

  31. SUSY Discovery at LHC SUSY gauge couplings are the same as in SM. Cross sections only surpressed by mass terms. At high energies SUSY production rates are similar to SM! Measure SUSY spectrum: • Masses • QNs • Lifetimes • Decay modes

  32. Summary • SUSY is a promising candidate for physics BSM. • New methods: • Classification scheme for SUSY processes • There are still open SUSY discovery channels at HERA • Dynamic discriminant method • Best existing limits in RPV GMSB: • LHC will give the final answer: • Be prepared to discover a new world !

  33. Backup slides

  34. Solution of the Hierarchy Problem Corrections to the Higgs mass: SM: Cancelation requires fine tuning to 17 orders of magnitude! MSSM: Contributions of SM particles and their superpartners compensate each other.

  35. SM MSSM Unification of the Forces Renormalisation Group Equations describe running of the coupling constants due to screening / antiscreening. Example: Slope depends on number and masses of particles in the model. Miracle!

  36. Status of SUSY Searches Examples of best current limits: Neutralinos/Charginos: LEP: m(c0) > 45GeV (RPV) m(c±) > 103GeV Sleptons: selectronR > 100 GeV smuonR > 95 GeV stauR > 86 GeV LEP: D0: sneutrinoR > 460 GeV (l132=0.05 & l‘311=0.16) Squarks: D0: squark > 320 GeV gluino > 232 GeV HERA: squark > 275 GeV (l‘1j1=0.3)

  37. MSSM Parameters • mA : pseudoscalar Higgs boson mass • tan(b) : ratio of VEV of two Higgs doublets • m: Higgsino mixing parameter • M1, M2, M3 : gaugino mass terms • All sfermion masses • Ai: all mixing parameters of squark and slepton sector

  38. Broken Supersymmetry Explain origin of SUSY breaking! Spontaneous SUSY breaking in SM sector not possible supertrace theorem-> sum rules between particle and sparticle masses, e.g.: excluded! Hidden sector models mSUGRA, GMSB AMSB, gMSB, ... ~

  39. Data Set

  40. Investigated Production Processes

  41. Radiative EW Symmetry Breaking

  42. Slepton mass splitting where the al are positively correlated with tanb.

  43. Example: Application to type C Diagrams RPC: RPV: SUSY-flow graphs:

  44. Possible abstract diagrams: C3: disfavoured due to high limits on squark masses C7: - “ – C6: lepto-quark search / contact interaction C5: -> gaugino production analysis !

  45. Sparticle Decays Neutralino: RPC MSSMRPV MSSMGMSB stable LSP missing energy Chargino: RPCRPV

  46. Sparticle Decays Sleptons: RPV: RPC: RPC MSSM: missing E, e / m / t RPV MSSM: 2 jets / 2 l / 2jets+2l GMSB: l + g + G~ Squarks decay in the same way.

  47. Results 55 abstract diagrams. Diagrams with squarks are neglected. Characteristic signatures for different models!

  48. Results With two outgoing lines: C5 With three outgoing lines and one sparticle: F4-2 With three outgoing lines and two sparticles: D1

  49. Restrictions • diagrams with > 3 on-shell produced (s)particles are neglected • diagrams with outgoing g, g, Z0 are not discussed • diagrams with initial g/g and 3 outgoing particles are discarded • u-channel diagrams are not stated explicitly • diagrams with > 1 sparticle propagator are discarded • interactions of Higgs bosons are not considered • vertices with only SM bosons are neglected • diagrams with three RPV vertices are discarded

  50. GMSB Parameter Space

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