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BSM searches at HERA

This article discusses the running conditions and latest results from the HERA experiment at the University of Toronto. It focuses on the search for new physics phenomena, including isolated lepton events, multi-lepton events, resonances, and contact interactions. The results from H1 and ZEUS experiments are compared, and prospects for future discoveries are discussed.

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BSM searches at HERA

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  1. BSM searches at HERA John Martin University of Toronto / ZEUS for H1 and ZEUS

  2. Running conditions • HERA-II running very well • Lumi high and still increasing for both e+p and e-p (1.5 pb-1/day achieved) • Polarization at ~ 40% • Expect >600 pb-1/expt. from HERA-II by June 2007 • (HERA-I was ~120 pb-1/expt., almost all e+p) 2005 e-p 215 pb-1 LISHEP 2006 J. Martin

  3. Outline e,n e Q2 xP p General BSM searches • Intriguing excess in isolated lepton events? • Multi-lepton events • Search for eq type resonances • HERA good for single particle production with Yukawa coupling to eq • LQ, Rp violating SUSY, LFV • Gaugino and gravitino searches • Contact interactions • Magnetic monopoles NB: HERA generally has little SM background for BSM searches LISHEP 2006 J. Martin

  4. General search • H1: model independent search for new phenomena by topology (as D0) • isolated, high PT particles: e, , , jet,  • PTpart > 20 GeV, 10 < part < 140, D(- )part > 1.0 • use probability estimator sensitive to narrow resonances, unusual events, broad signals • similar sensitivity to dedicated searches • basic agreement with SM, except … -j- : 4 data / 0.8 ± 0.2 Data from HERA-I LISHEP 2006 J. Martin

  5. Intriguing excess at H1… n X e,m H1 • Isolated leptons and missing PT • SM W production ~ 1 pb-1 • Background from mis-measured DIS and di-lepton events e+p e-p LISHEP 2006 J. Martin

  6. The latest H1 numbers • Choose cut at PTX >25 GeV, ~ best discrimination between background and decay of a heavy particle, like top. 3.4 s excess LISHEP 2006 J. Martin % of SM expectation from W production

  7. But ZEUS… • ZEUS e+p data with similar cuts, purity: • H1 continues to see an excess in e+p (recall HERA I was almost all e+p), but not in e-p • ZEUS doesn’t confirm • Still a puzzle, more data needed LISHEP 2006 J. Martin

  8. What about the t channel? • Isolatedt events with PT,miss t hadrons use 6 jet-shape variables to suppress QCD background • ForPTX> 25 GeV • ZEUS observes 2 events • expect0.12 0.02 • Anomalous top, stop, another heavy particle?? • But, H1 sees no events • Both Hera-I data, await HERA-II results… LISHEP 2006 J. Martin

  9. Iso-lepton events: single top? • Anomalous FCNC couplings • Search for single top production via W decay to en, mn, or jets high PTX ( > 40 GeV, ZEUS) H1 cuts Mt > 140 GeV • SM background negligible: • No evidence found, set limits • H1 excess needs ktug ~ 0.2, still just about compatible with FCNC top production LISHEP 2006 J. Martin

  10. Or bosonic stop decay? • Consider model with : • For bosonic decay, slight excess only in jmPTmiss channel • No excess in ej channel • Iso-lepton events therefore unlikely to arise from bosonic decay of stop LISHEP 2006 J. Martin

  11. Multi-lepton events (H1) e+p • Search for  2 leptons (PT1 , PT2 > 10, 5 GeV) in sample of 209 pb-1 (45 pb-1e-p, 164 pb-1 e+p) • - interactions ~ 1pb-1 • Overall agreement with SM: • But, for PT > 100 GeV : Nobs = 4 (3 ee, 1 emm) Nexp = 0.81  0.14 • 3 ee, 3 eee, 2 emm events withM12 > 100 GeV H1 excess, not in ZEUS LISHEP 2006 J. Martin

  12. Multi-lepton events (update) (275 pb-1) • H1 analysis extended to include 05 data • no new 2e/3e event at high M12 • one new eμμ event at Mμμ > 100 GeV • one new eμμ event at Meμ > 100 GeV • for ΣPT > 100 GeV: Nobs = 4 Nexp = 1.1 0.2 • highest ΣPT events appear in e+p collisions LISHEP 2006 J. Martin

  13. Doubly charged Higgs? • H++(--) occurs in BSM models extending the Higgs sector, such as L-R symmetric models • Search for high massdi-leptons with same charge as beam • Only 1 ee event found, no mm, em, tt, et events • anomalous multi-lepton events unlikely to be doubly charged Higgs, so set limits • LEP, Tevatron better except for off-diagonal couplings LISHEP 2006 J. Martin

  14. Generic Leptoquarks q q + e e LQ LQ e e,n LQ q e,n depend on Yukawa coupling, l q e q q LQ q LQ + e q e LQ LQ • Search for resonance in e-jets, e-n • Likelihood analysis in Mej, cosq* • Coupling limits for BRW LQs • 7 scalars, 7 vectors LISHEP 2006 J. Martin

  15. Comparison to Tevatron • HERA complementary to Tevatron: • Tevatron good for high BR to eq. Background is severe for nq decay of LQ • HERA can reach to low BR to eq for reasonable coupling LISHEP 2006 J. Martin

  16. LQ mediated LFV • Search for high PTm, t • After optimizing cuts: • ZEUS: 0 candidates (SM: 0.43±0.08 m, 2.3±0.5 t ) • H1: 1 t candidate (SM: 0.56±0.16) • Low mass: set limits with ,eg,eq = q , q • High mass: set bounds on eq lq / M2LQ(TeV-2) • em: low energy limits generally better • et: ZEUS results generally better eb  ts Similar results from H1 eb  tb best non-ZEUS limit ZEUS limit LISHEP 2006 J. Martin

  17. R-parity violating SUSY ~ e+ d  u Lj via ’1j1 e- u  d Rk via ’11k ~ • At HERA probe: • Search in both l-jet and gauge decays (multi-jets and leptons) • No evidence found at ZEUS or H1 LISHEP 2006 J. Martin

  18. Coupling limits in MSSM • ZEUS: stop search with 1st and 2nd generation squark masses set to 1 TeV • H1: unconstrained model with sfermion masses free parameters, gluino mass ~ M3 at EW scale (common gaugino mass m1/2 at GUT scale) • Limits largely independent of MSSM parameters • Improved limits from HERA up to 255 GeV for LISHEP 2006 J. Martin

  19. Limits in mSUGRA model L3 (tan = 2) D0 Run I j=1,2 • in mSUGRA assume also a common scalar mass m0 at GUT scale (gives a 5 parameter SUSY model) • H1 HERA-I data: LEP limits better except for stop • Tevatron limits weaker due to large branching ratio to jets + missing ET • HERA-II will improve sensitivity to RPV stop LISHEP 2006 J. Martin

  20. Gaugino production • Production by RPV t-channel slepton exchange • Search in ejj channel with multi-variate discriminant against NC DIS background • No deviation from SM ZEUS Prelim., LP05 HERA extends LEP limits in part of parameter space LISHEP 2006 J. Martin

  21. If gravitino is the LSP • Gauge mediated symmetry breaking (GMSB) has N extra “messenger” fields of mass M to transmit the SB • NLSP is neutralino or slepton • Search for high PTg + missing ET (bkgrd: radiative CC) D0 bound D0 bound • For small m: neutralino masses up ~ 120 GeV are excluded for ’ = 1.0 • Complementary to Tevatron, where production is by pairs or LISHEP 2006 J. Martin

  22. Excited fermions • Fermion substructure excited fermions • For f/L=1/MF* , 95% upper limits: • e* 250 GeV (H1) • q* 205 GeV (ZEUS) • n* 135 (f=f’), 158 (f=-f’) GeV (ZEUS) • for n*, e-p 100x more sensitive than e+p • await HERA-II e-p analysis LISHEP 2006 J. Martin

  23. Contact interaction e- • HERA-I form factor fit gives Rq < 0.85 . 10-18 m • Can also set limits on eqeq contact interactions e+ • Similar limits from LEP, Tevatron • n extra dimensions? • Graviton exchange effective coupling Parity conserving u quark only APV limits Limits close to 1 TeV LISHEP 2006 J. Martin

  24. Magnetic monopoles? • Dirac monopoles: large magnetic charge, highly ionizing • Some BSM models predict light monopoles • Could stop in beampipe and stay trapped • Cut 1994-7 beampipe into strips • passed through superconducting coil • system sensitive to 0.1gD LISHEP 2006 J. Martin

  25. Summary • Many BSM scenarios have been studied at HERA • Most results still from HERA-I (~120 pb-1/expt, almost all e+p) • Competitive and/or complementary to LEP, Tevatron • Only possible sign of BSM physics are the anomalous W-like events from H1: need more data • HERA-II will provide a data set of > 600 pb-1/expt with lepton polarization, both e+p and e-p • new sensitivity to BSM physics with higher cross section in e-p • Still some chance of a discovery before the LHC LISHEP 2006 J. Martin

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