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Searches for new physics at HERA

Johannes Haller CERN, PH-ATR. EP seminar 6. December 2004 CERN. Searches for new physics at HERA. Not covered: Observation of events with multiple electrons at high p T Excited leptons and quarks GMSB SUSY with sleptons and gravitinos General search for new physics

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Searches for new physics at HERA

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  1. Johannes Haller CERN, PH-ATR EP seminar6. December 2004 CERN Searches for new physics at HERA

  2. Not covered: Observation of events with multiple electrons at high pT Excited leptons and quarks GMSB SUSY with sleptons and gravitinos General search for new physics Contact Interactions Large Extra Dimensions RP-conserving SUSY Doubly charged Higgs LFV Leptoquarks Magnetic monopols (beam pipe!) Pentaquarks . . . Content of the Talk • HERA: machine, luminosities and data sets • example detector: H1 • SM background at high pT (Q2) • Searches for new Physics: - Deviations in DIS at high Q2 ? - Quark Radius - Resonances in eq scattering - Leptoquarks - Squarks in RPV SUSY - Observation of isolated Leptons in events with pT,miss - Bosonic Decays of Stops - Single Top Production • HERA II, upgrade and first results Searches for new physics at HERA

  3. HERA - the only ep collider • HERA in numbers: • pre-accelerator: PETRA, … • circumference: 6.3 km • 1 tunnel, 2 storage rings • operational since 1992 • up to 220 bunches • bunch crossing: 96 ns 2 fixed target exp.: • HERMES (since 1995, uses e-beam) study of nucleon spin structure • HERA-B (2000-2003, used p-beam) production of heavy quark flavors in pp interactions 2 ep collider exp.: H1 + ZEUS e± 27.6 GeV p 920(820) GeV √s = 320 (300) GeV Searches for new physics at HERA

  4. Example Detector : H1 HERA detectors are asymmetric Liquid Argon Calorimeter (em and had.) super conducting solenoid (1.4 T, large coil) p warm backward spaghetti-calorimeter muon chambers silicon trackers toroid magnet Central Jet Chambers e+/- forward tracking devices forward muon chambers Searches for new physics at HERA

  5. HERA, Luminosities and Data Sets • HERA I (1993 - 2000): • - 110 pb-1 e+p per experiment • - 15 pb-1 e-p per experiment • excellent performance during HERA I (1993-2000) • peak luminosity: 1.5 · 1031 cm-2s-1 • electron beam not long. polarized HERA II : 2001 : major upgrade of the machine aim: higher luminosities and polarized electron beams I will first discuss the results from HERA I, recent results form HERA II are given at the end of my talk Searches for new physics at HERA

  6. Main SM Background at high pT Deep Inelastic Scattering (DIS) at high Q2: Neutral Current (NC) e p • e± at high pT • had. jet at high pT • pT -balance e+/- Charged Current (CC) ν • had. jet at high pT • missing pT from ν W± Photoproduction: • 2 had. jet at high pT • pT –balance • e± escapes through • beam pipe Searches for new physics at HERA

  7. NC and CC DIS at high Q2 final DIS cross-sections from HERA I photon NC W boson CC NC: e+p / e-p differences due to interference between γ and Z0 CC: e+p (e-p) cross section dominated by d (u) quarks. Measurements of the NC DIS cross section at high Q2 are sensitive to many models of new physics. Searches for new physics at HERA

  8. Limit on Quark Radius models with quark substructure: form factors for e and q Re,q: RMS radii of the electroweak charge of electron and quark expect deviations from SM at high Q2 with assume point-like electron : Rq < 0.85 · 10-16cm [H1, Phys. Lett. B568 (2003) 35.] [ZEUS, Phys. Lett. B591 (2004) 23.] similar methods allow to set constraints on: eeqq Contact Interactions, LED, heavy Leptoquarks no significant deviation at high Q2 statistical error dominant Searches for new physics at HERA

  9. Resonances in eq Scattering (Leptoquarks) Search for eq resonances is possible up to m = √s = 320 GeV. • LQ carry both L and B • LQs appear in many extensions of SM: GUT-like theories, Superstring-’inspired’ E6-models, Technicolor-like theories, Compositeness models, … HERA: single LQ production via lepton-quark-LQ coupling λ e + jet λ λ both channels: no resonance observed in full HERA I data set Searches for new physics at HERA

  10. Leptoquarks: Exclusion Limits • general effective LQ theory: • BRW model • assume: • LQ interaction invariant under SM • gauge group and renormalisable • LQs conserve L and B separately Tevatron: LQ pair production, independent of λ. LEP: t-channel LQ contribution to hadr. cross-section, strongly dependent on λ. [Buchmüller, Rückl, Wyler, Phys. Lett. B191 (1987) 442.] e.g. S0,Lβ(eq) =β(νq) = 0.5 14 LQ states with fixed β(eq) = 0, ½ or 1. • HERA limits: • dependent on λ • particular stringent for m < √s [H1, prelim., EPS03] [ZEUS, Phys. Rev. D68 (2003) 052004] Searches for new physics at HERA

  11. Resonant Production of Squarks • Rp conservation: • LSP is stable • sparticles are produced in pairs SM particles : Rp=1 SUSY particles : Rp=-1 But : no theoretical reason to exclude RP-violating terms! terms violate L and B For proton stability: λ’∙λ’’= 0 sufficient • consequences: • fundamental instability of SUSY matter (LSP decay)  no golden SUSY signature of ET, miss • single production of sparticles at colliders. HERA: single squark production via λ’1jk e.g. stop production via λ’131 in e+p collisions Searches for new physics at HERA

  12. Squarks: Decay Modes λ’ ≠ 0 opens a large variety of squark decay modes. LSP decay: examples: considermany final states to reduce dependence on SUSY parameters  BRtot ~1 all channels in agreement with SM expectation [H1, Eur. Phys. J. C36 (2004) 425.] Searches for new physics at HERA

  13. Squarks: Exclusion Limits constraints on λ’(Msquark): e.g. third generation (j=3, k=3) stop sbottom • For λ’=0.3 (e.m. strength) squarks up to 280 GeV are ruled out • small couplings: improvement of indirect low-energy limits Searches for new physics at HERA

  14. Squarks: mSUGRA Interpretation particular SUSY model with just 5 new parameters: m0: common sfermion mass at GUT scale m1/2: common gaugino mass at GUT scale direct HERA limits follow squark isomass curve for λ’ = 0.3 : squark masses up to 275 GeV ruled out HERA sensitivity comparable with LEP and Tevatron bounds L3 (tanβ=2) D0 (j=1,2) Searches for new physics at HERA

  15. Isolated Leptons in Events with pT,miss H1 observes spectacular events: • isolated leptons (e or μ) with pT > 10 GeV • pT,miss > 12 GeV • hadronic jet main SM contribution from Wproduction known in NLO QCD H1: e & μ excess at high pThad p e+/- pThad (GeV) not confirmed by ZEUS Searches for new physics at HERA

  16. Isolated Leptons in Events with pT,miss • ZEUS: search for isolated taus • in events with pT,miss> 20 GeV • select isolated tracks coming from hadronic tau decays • pencil-like jets ZEUS: τhad. 3 events found, 0.40 ± 0.13 exp. not confirmed by a preliminary H1 analysis Searches for new physics at HERA

  17. Events with Isolated Leptons Situation after HERA I: observed /expected • interpretation unclear • need more data from HERA II [H1, Phys. Lett. B561 (2003) 241.] [ZEUS, Phys. Lett. B559 (2003) 153.] [H1, prelim., DIS04] [ZEUS, Phys. Lett. B583 (2004) 1.] e/m : tau: pTX ≙ pThad Searches for new physics at HERA

  18. Bosonic Stop Decay possible SUSY explanation of isolated leptons: [T. Kon et al, Mod. Phys. Lett. A12 (1997) 3143.] • sbottom is significantly lighter than stop • stop decay to gauginos kinematically forbidden signature: 3 jets + pT,missjet + l +pT,miss excess injμpT,miss not confirmed by other channels [H1, Phys. Lett. B 599 (2004) 159., hep-ex/0405070] Searches for new physics at HERA

  19. Bosonic Stop Decay: Interpretation allowed signal cross sections (σ±Δσ) excluded (Mstop,Msbottom) area all channels (exceptjμpT,miss) consistent with non-observation stops up to 275 GeV excluded for λ’131=0.3  Isolated lepton events can hardly be interpreted as scalar tops. Searches for new physics at HERA

  20. Production of single Top Quarks another possible explanation of isolated leptons • SM top cross section tiny: < 1fb • possible via FCNC (κtuγ,νtuZ) [H1, Eur. Phys. J. C33 (2004) 9.] [ZEUS, Phys. Lett. B559 (2003) 153. and add. DESY-03-188] Sensitive to new physics: e.g. SUSY excluded area • isolated lepton topology • - H1 excess at high ET • high ET 3 jet events: • - no deviation from SM • - large QCD background exp. reach of HERA II Searches for new physics at HERA

  21. HERA II, luminosity upgrade 3 times higher luminosity new focussing magnets close to IP so far: e+p only integrated luminosity compare: LHERAI=130 pb-1 time [d] background problems after restart are solved ! exp. ~ 700 pb-1 by mid 2007 Searches for new physics at HERA

  22. HERA II, polarisation of e-beam new spin rotators before and after the IPs longitudinal polarisation of e-beam • measurement via compton back scattering of laser light in TPOL and LPOL • Pe up to 50 % achieved polarisation of e+ beam polarisation opens new windows to search for new physics time [h] Searches for new physics at HERA

  23. First Results from HERA II First measurements of polarised DIS cross sections have been presented at ICHEP04 SM: total CC cross section has linear dependence on polarisation: no hint for right-handed charged currents result from linear fit: σ(P=-1) = (-0.2 ± 1.8 (stat.) ± 1.6 (sys.)) pb Searches for new physics at HERA

  24. New results on Isolated Leptons selection repeated in new data excess in electron channel, no new candidate in muon channel H1: HERA I+II combined pTX > 25 GeV pTX > 25 GeV more data from HERA II needed Searches for new physics at HERA

  25. For more than a decade the HERA collaborations have contributed to the quest for new physics in a significant manner. A large variety of searches for SUSY and exotics has been performed with HERA I data The HERA I data are generally in good agreement with SMexpectation.However outstanding events have been observed(isolated leptons, multi-electrons). The background problems after the HERA II upgrade are solved. HERA II runs with high luminosity and polarised lepton beams. ~ 700 pb-1 are expected by mid 2007. First results from HERA II are available now, more to come ! currently preparation for first e-p HERA II run. 2007: stop of HERA operation due to conversion of PETRA to high brilliance synchrotron light source. Conclusion Searches for new physics at HERA

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