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Review of 10 years of LEP

12!. Review of 10 years of LEP. W. Adam Institute of High Energy Physics Austrian Academy of Sciences. Four Seas Conference Thessaloniki, Greece April 16 th , 2002. A bit of history …. 1976.

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Review of 10 years of LEP

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  1. 12! Review of 10 years of LEP W. Adam Institute of High Energy PhysicsAustrian Academy of Sciences Four Seas Conference Thessaloniki, Greece April 16th, 2002

  2. A bit of history … 1976 B.Richter: e+e- machine needed to study weak interactionsat high energy; √s~200GeV at R~6km seems feasible 1st physics study 1978 “Blue Book” Les Houches summer study: baseline140GeV (200GeV with SC cavities) at 2Rp=22.2km What to expect? E.g. possibility of an“invisible” Z for high Nn! Glashow quotes 4 scenarios; considers the assumption of a correct extra-polation of the 17 parameter model as “arrogant”. W.Adam: Review of 10 years of LEP

  3. A bit of history … 1979 “Pink Book”: 2Rp~30km 1983 Discovery of W and Z LEP Design Report: 2Rp=26.7km 1984 1986 • “Physics at LEP”: detailed study of the physics scenario • Discusses effects of radiative corrections • Treats SUSY (~neglected in first study) • Full chapter on toponium! 1989 “Z physics at LEP1” Start of LEP operations W.Adam: Review of 10 years of LEP

  4. A bit of history … • Situation at LEP startup: At LP’89 the first results from SLC were reported: • PDG’88: • W and Z masses known to few % • Limits on W and Z widths • B0 and B± masses known, lifetime at 10% level • B* still disputed • B-mixing observed • s measured to ~10% • Mt > 44GeV, Nn<5.9 Altarelli (LP’89) W.Adam: Review of 10 years of LEP

  5. Vital for LEPI: luminosity For both: b-tagging Experiments • The four LEP experiments: ALEPH, DELPHI, L3 and OPAL • Common features: • 4p general purpose detectors • Momentum measurement insolenoidal magnetic field • Detectors matched to LEPs O(100kHz) collision frequency • Specialisation on different items: • High precision muon systems • High resolution EM calorimetry • Particle identification • Large acceptance central tracking Vital for LEPII: hermeticity W.Adam: Review of 10 years of LEP

  6. LEP pilot run: start on Aug. 13th, 1989. A few hours later: first Z recorded inOPAL - the others followed. The first important LEP result was available in winter 1990: three generations of light neutrinos. Nn = 3.04 ± 0.12 But for this result LEP had arrived in second place.: MARKII at SLC in October ‘89: Nn = 2.8 ± 0.6 Start of LEP operation • The first physics run lasted for ~3 months and provided each experiment with 10-30k events. The start of several years of competition and collaboration … W.Adam: Review of 10 years of LEP

  7. Already in summer ‘90 LEP had a significant impact on the world averages in the EW sector F. Dydak summarised measurements on mass, total and partial widths of the Z, couplings, weak mixing angle … But no SM-eating Minotaur in view! Start of LEP operation W.Adam: Review of 10 years of LEP

  8. Electroweak (LEP I) Goal: extract Z-mass, widths (total and partial) and Zff couplings from measured cross-sections and asymmetries. Common procedures developed in the LEP EWWG. • Nine basic quantities fitted from data: • Mass (MZ) • Total width (GZ) • Hadronic cross-section at pole (sh0) • Hadronic to leptonic width (Rl=Gl/Gh) • Forward-backward asymmetry (AlFB) x 3 Check lepton universality, then combine the three lepton flavours. Extensible using tau polarisation, heavy flavour results, non-LEP measurements (sin2q, mW). 1990&1991: 7-point scans 1992&1994: peak 1993&1995: 3-point scans W.Adam: Review of 10 years of LEP

  9. Electroweak (LEP I) MZ W.Adam: Review of 10 years of LEP

  10. LEP beam energy • LEP beam energy Absolute energy scale and point-to-point spread  systematic error on MZ and GZ dMZ ~ 0.5 d (Epeak+2+Epeak-2)dGZ ~ 0.71 d (Epeak+2-Epeak-2) • Strategy: • resonant depolarization as reference (dEbeam~200keV) • interpolate (NMR/.., flux loop, …), correcting for systematic effects: • temperature,… • tidal & hydrogeological effects • parasitic currents E-spread / point ~ 50MeVUncertainty O(MeV) dMZLEP ~ 1.7MeV W.Adam: Review of 10 years of LEP

  11. Electroweak (LEP I)  lepton universality  Rl W.Adam: Review of 10 years of LEP

  12. Electroweak (LEP I) • Derived quantities: partial widths Nn • Use Ginv to • Determine Nv (from Ginv/Gll) • Set limits on other invisible particles by comparing with SM prediction • Alternatives: • Nn from Rl and shad • Nn from g above pole W.Adam: Review of 10 years of LEP

  13. Electroweak (LEP I) Effective couplings: Different definitions of sin2q used: and others W.Adam: Review of 10 years of LEP

  14. Top mass mt latest CDF: evidence for … An impressive demonstration of the predictive power of the SM (and of the reliability of EW precision data)!!! observation of … W.Adam: Review of 10 years of LEP

  15. EW heavy flavours (LEP I) Now adding info from heavy flavours: partial widths and asymmetry for c’s and b’s (quark mass sector: 10 of 17 SM parameters!). How? Use of (more & more sophisticated) vertex detectors! Combine information from all tracks (NN, prob. Methods, …) Efficiency vs. purity for b-events(2- & 3-layer VDs) More sophisticated tags developed for LEPII searches (see VRKs talk) Impact parameter significance = d / s(d) Tagging is more challenging for charm: reconstruct charmed hadrons decays, unfold b-contribution. W.Adam: Review of 10 years of LEP

  16. EW heavy flavours (LEP I) Measurement of Rb = Gbb/Ghad :sensitivity to new physics A seemingly small change in 1995,but … W.Adam: Review of 10 years of LEP

  17. Excitement: finally a 3.7s deviation from the standard model!! The Rb-puzzle Lots of cross checks and a new ALEPH result: Stops? Charginos?? W.Adam: Review of 10 years of LEP

  18. B physics Helpful feature of B-hadrons at LEP: they fly ! Basic (and earliest) measurements:B lifetimes Started with semi-leptonic decays, then extended to more channels. Remark:Little was known about heavy flavours (and their lifetimes) during the early discussion about LEP.  Lucky coincidence with progress in semiconductor detectors! Latest B0d - combination. Nowincluding Babar & Belle - butLEP is still competitive! W.Adam: Review of 10 years of LEP

  19. (Bs) (Bd) t±/t0 (baryon) B lifetime results All dominatedbyLEP! 1.464±0.057ps 1.542±0.016ps 1.208±0.051ps 1.083±0.017 W.Adam: Review of 10 years of LEP

  20. B physics • Based on the techniques developed for the lifetimes the whole field of B-physics was explored: about 1/3 of all LEP publications! Comparison with HQET Exclusive decays Semileptonic branching ratio and“wrong signed” charm decays B- D0D*- W.Adam: Review of 10 years of LEP

  21. Determination of |Vub| from BR(bXuln) and tb: Determination of |Vcb| from Exclusive D*ln or G(bXcl) B physics W.Adam: Review of 10 years of LEP

  22. Bd oscillations Bs oscillations B physics Dms > 14.9 ps-1(sensitivity: 19.3 ps-1!!!) Will have to wait for Tevatron RunII results … LEP results still significant, but now hunting ground for Belle & Babar! W.Adam: Review of 10 years of LEP

  23. These results can be used to constrain the unitarity triangle: • Equivalent to • sin2b = 0.696 ± 0.068 (with ek) • sin2b = 0.676 +0.078-0.096 ( Belle: 0.82±0.12±0.05Babar: 0.75±0.09±0.04) (0,0) (1,0) B-physics F2= F3= F1=b W.Adam: Review of 10 years of LEP

  24. QCD at LEP • Even if “specialised” on weak interactions - abundant results on QCD Strong coupling constant from EW fits s from EW(only exp. errors) From event shapesand jet rates W.Adam: Review of 10 years of LEP

  25. Optimised scale Q=xm MZ2 QCD at LEP • Renormalisation scale in NLO (event shapes & jet rates): Fixed scale Q=MZ2 No consistency using fixed scale  try to fit scale with as ! Consistency achieved. Conclusion? W.Adam: Review of 10 years of LEP

  26. QCD at LEP • Running of mb W.Adam: Review of 10 years of LEP

  27. Significance increased from 2s (1987) to 8s (1991). A possible solution: SUSY Unification • Early LEP data show: need new physics to achieve unification Amaldi et al., Phys.Lett.B281(1992)374 W.Adam: Review of 10 years of LEP

  28. In 1995 the LEPI era ended with the final scan of the Z-resonance. From then on the focus shifted to the extension of the search range and to precision measurements above the WW threshold. The 1995 run was ended with ~6pb-1 /expt at √s=130–140GeV (LEP1.5). In 1996 the WW threshold was passed: In the same year the production of superconducting RF cavities (the key to high energy LEP running) was stopped.  With the successive installation of all 288 SC cavities, the reuse of old copper cavities and a lot of work of the accelerator physicists the energy was increased, up to the 210GeV reached in 2000. Towards higher energies W.Adam: Review of 10 years of LEP

  29. ZWW vertex exists! Electroweak (LEP II) • MZ and sin2 measured at LEPI  need MW for better constraint. Little sensitivity for √s >> 161GeV Method 1: cross section at threshold EWWG (1996) W.Adam: Review of 10 years of LEP

  30. Electroweak (LEP II) Method 2: direct reconstruction Concern: mass bias due to final state interactions in qqqq (Bose-Einstein, colour reconnection)? • measure FSIs (need model!) Indication: M(4q-qqln) = 9±44MeV W.Adam: Review of 10 years of LEP

  31. LEP mW Moriond ‘02 Electroweak (LEP II) LEP uncertainties: stat (±26MeV)syst (±21MeV)FSI (±13MeV)LEP (±17MeV) W.Adam: Review of 10 years of LEP

  32. Also the width can be obtained from the direct W-mass reconstruction: Electroweak (LEP II) W.Adam: Review of 10 years of LEP

  33. “Single W” ZZ Electroweak (LEP II) W.Adam: Review of 10 years of LEP

  34. TGCs • Non-abelian structure of SU(2)U(1)  gauge boson self interactions • Charged triple boson couplings: WWg, WWZ • SM tree level (see above) • General: • Operators >= dim. 6 • Lorentz & EM gauge invariance • C, P, CP conservation • Low energy results •  • Dg1Z, Dkg, lg (all 0 in SM) • Inputs: • WW: stot & helicity info • Single W, g: stot & differential distributions EWWG (2000) No neutral TGCs in SM (tree level). All measurements compatible with 0. W.Adam: Review of 10 years of LEP

  35. QGCs Charged quartic gauge couplings:negligible in the SM WWg, nngg, qqgg, …: Neutral quartic gauge couplings:none in SM at tree level • Anomalous contributions to couplings: • a0V/L2, acV/L2 (VVgg) • an/L2 (WWZg) • All a = 0 at tree level EWWG (2001) W.Adam: Review of 10 years of LEP

  36. Searches • The situation after LEP1 (with a grain of salt): • whatever couples to the Z is excluded to mZ/2 (double production)or mZ (single production) … • Severe constraints for invisible states from the comparison of Ginv with SM expectations • Now every year LEP2 opened new search windows! • Change in the way collaborations analysed data: • Installation of “hot lines” • Continuous update of analyses results during a run • The unexpected could be just around the corner! • List of topics (for direct and indirect searches) would fill pages: • Higgs, technicolour, SUSY (in different breaking models), contact interactions, compositeness, extra dimensions, anomalous couplings, … W.Adam: Review of 10 years of LEP

  37. SUSY Topological search  Cross section limits for specific channel  Mass limits /limits in model parameter space  Well motivated & elegant  Low energy effective theory adds some 100 parameters to model: • Masses • Soft breaking terms  Need SUSY breaking models. Investigated at LEP: • SUGRA • GMSB • AMSB Models predict production rates, decay channels, … • Two fundamentally different scenarios (at least experimentally): • R-parity conservation: • Pair production • Emiss signature due to LSP • R-parity violation: • Single production possible • Multitude of decay chains  Use topological approach! W.Adam: Review of 10 years of LEP

  38. Sfermions L-R mixing! Lower mass states are candidates for NLSP. Lower mass reach than Tevatron, but sensitivity to amaller Evis! Search for pair production, with decay in fermion + LSP W.Adam: Review of 10 years of LEP

  39. Translated into LSP mass limits: SUSY • mSUGRA: • Parameters: tanb, sign(m), m0, m1/2, A0. Limits use also GZ and Higgs search MLSP>60.1GeV (m>0) MLSP>59.6GeV (m<0) for mt=175GeV Higgs chargino LEP1 sfermion W.Adam: Review of 10 years of LEP

  40. GMSB Light gravitino = LSP Radiative decays of neutralinos Acoplanar two-photon events Lifetime of sparticles depends on gravitino mass: dedicated searches for long lifetimes GMSB inter-pretation as neutralinopair production “standard” Direct detection Large impact parameters and kinks W.Adam: Review of 10 years of LEP

  41. Other searches Single top production via FCNC: anomalous couplings Zt(u,c), g Low scale gravity:Graviton propagates in 4+n dim. M2Planck= (MD)2+nRn Summer ‘01 • Modifies 2-boson and 2-fermion ds/d: • LEP(gg): Ms>0.97TeV (l=+1) Ms>0.94TeV (l=-1) Limits depend strongly on mt! W.Adam: Review of 10 years of LEP

  42. Summary & Conclusions It’s difficult to summarize one decade of LEP experiments. Let’s try to start with a result: LEP experiments have verified the SM with precision measurements, achieving accuracies at the level of 10-5. This often exceeded expectations by an order of magnitude. How? • Excellent performance of the accelerator:luminosity, peak energy, systematics, … • Improvements in detector technology at the beginning & during operation. • Analyses: redundancy and minimisation of the (inevitable) dependence on MC. • Close contact between collaborations and support from theory. W.Adam: Review of 10 years of LEP

  43. Summary & Conclusions • Acknowledgments: thanks a lot to • The machine people who pushed LEP beyond the 200GeV. • The technical staff who contributed to the experiments. • Theorists and phenomenologists who showed us where to look, and to interpret what we found there. • The hundreds of people who contributed to the analyses and to thosewho are still working on the finalisation and combination. • In it’s last few months LEP might have opened a door • to another decade of SM, but more likely • to the physics beyond. • Whether the excitement was justified or not: LEP has created the solid basis which is indispensable for the exploration of new physics at future colliders. W.Adam: Review of 10 years of LEP

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