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e+e - Colliders II At the Z 0 resonance and beyond

e+e - Colliders II At the Z 0 resonance and beyond. Overview SLC at the Z 0 LEP II above the Z 0 Physics at the ILC. Dave Jackson Oxford University 21 st February 2006. Stanford Linear Accelerator Centre, California. Forward-Backward Asymmetries at LEP. eff W.

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e+e - Colliders II At the Z 0 resonance and beyond

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  1. e+e- Colliders IIAt the Z0 resonance and beyond Overview • SLC at the Z0 • LEP II above the Z0 • Physics at the ILC Dave Jackson Oxford University 21st February 2006

  2. Stanford Linear Accelerator Centre, California

  3. Forward-Backward Asymmetries at LEP eff W • LEP measures AeAe,AeAm ,AeAt → Ae, Am , At (All rely on determination ofAe)

  4. Left-Right Asymmetry, ALR at SLD SLC e- beam polarization measured with Compton polarimeter Pe ds/dcosqα (1 – PeAe)(1 + cos2q) + 2cosq(Ae – Pe)Af integrate over cosq and take left-right asymmetry: sL – sR NL – NR sL + sR NL + NR ALR0 = ALR/< Pe> =Ae → ve /ae → sin2qW ALR = = = PeAe eff eff A ‘counting experiment’, the single most precise measure ofsin2qW

  5. Comparison of Z-pole asymmetries sensitive to sin2qWeff

  6. sF – sB3sL – sR sF + sB4sL + sR f AFB = = AeAf ALR = = PeAe The Left-Right Forward-Backward asymmetry at SLD With e- beam polarization can also form the double asymmetry: ~ (sF – sB)L –(sF – sB)R 3 (sF + sB)L + (sF + sB)R 4 f AFB = = PeAf Since Pe~ 75% (at SLD) compared withAe ~ 15% the new asymmetry is much larger, hence greater statistical power. Also have benefit of measuring Ae, Am , At directly. With identification of B and D decays in hadronic jets can also measure quark asymmetriesAband Ac

  7. Z0 → bb event at SLD Precise tracking allows reconstruction of secondary vertices from B and D hadron decays and tagging of b and c-quark flavoured jets

  8. The left-right forward-backward asymmetry in b-tagged events Vertex charge is used here to identify B+ or B- decays and hence the b or b-quark jet direction SLD

  9. Quark and Lepton Asymmetries

  10. Above the Z0 resonance • Around √s ~ 91 GeV e+e- → g/Z0→ qq or l+l- Measure cross-sections and asymmetries • Above √s ~ 161 GeV e+e- → g/Z0→ W+W- cross-sections, W mass and couplings • Above √s ~ 182 GeV e+e- → g/Z0→ Z0Z0 cross-sections and anomalous couplings • Above √s ~ 200 GeV e+e- → g/Z0→ Z0H0 ? New physics, Higgs, SUSY, extra dimensions ?

  11. ‘Return-to-the-Z’ g e- f Z0 f e+ LEPII For two-jet events, plot shows: qq c.o.m. energy 2 x beam energy The Z0 peak is due to initial state radiation: Suppress with cut√s’ > 0.85√s

  12. Two-fermion production cross-section Lepton forward-backward asymmetries

  13. WW Production at LEP • Rates and angular distributions as predicted for triple gauge coupling ZWW (self-coupling of non-Abelian gauge theory). • No evidence for anomalous triple boson couplings

  14. W mass at LEP II qqqq and qqlu events are used; with care taken to unravel systematic theoretical bias in the former MW

  15. Production of Z0 pairs at LEPII The OPAL event display shows two Z0 decays: Z0 → m+m- Z0 → qq

  16. The Standard Model has 18 free parameters: • 3 couplings • 2 Higgs parameters • 9 fermion masses • 4 quark mixing parameters Strategy of the global fit Measuring > 18 observables overconstrains the SM

  17. Masses of the W and top Indirect measurements constrain MW and Mtop through Standard Model electroweak radiative corrections Direct measurements from LEPII and the TEVATRON Successful test of SM Light Higgs preferred

  18. Direct search for Standard Model Higgs at LEP II LEP2 limit Mhiggs > 114.1 GeV. LEP Higgs search – Maximum Likelihood for Higgs signal at mH = 115.6 GeV with overall significance (4 experiments) ~ 2s

  19. e+e- c.o.m. energy

  20. World’s Physicists Endorse Linear Collider Paris, April 23 2004 (Linear Collider Workshop) Over 2600 physicists from around the world have signed a document supporting a high-energy electron-positron linear collider as the next major experimental facility for frontier particle physics research, members of the World Wide Study of Physics and Detectors for a Linear Collider announced today: Understanding Matter, Space and Time http://sbhep1.physics.sunysb.edu/~grannis/lc_consensus.html The press release contains quotes from Masatoshi Koshiba, Jim Brau, Francois Le Diberder, Maury Tigner For the full text see www.interactions.org

  21. International Linear Collider c.o.m energy 500 GeV – 1 TeV ‘ILC’ • In August 2004 ITRP recommended that the linear collider be based on super-conducting rf technology • This recommendation is made with the understanding that we are recommending a technology, not a design. We expect the final design to be developed by a team drawn from the combined warm and cold linear collider communities, taking full advantage of the experience and expertise of both(from the Executive Summary). • We submitted the Executive Summary to ILCSC & ICFA at the Beijing Conference • http://www.interactions.org/pdf/ITRPexec.pdf SLC

  22. Detector designed for the Main LC physics themes: • Study the `Higgs boson’ (or its surrogate) and understand what it really is.The SM Higgs mechanism is unstable; find and explore the required new physics sector… • Supersymmetry • New gauge bosons • Extra Dimensions • (Also a rich program of study of the top quark, QCD, precision EW measurements, etc.) TESLA In general LC and LHC both needed to explore new high energy phenomena (compare history of proton/e+e- colliders)

  23. Higgs mass & gauge couplings Dominant Higgs production for lower mass Higgs at LC is ‘ZH bremsstrahlung’. At higher energy, WW (or ZZ) fusion becomes dominant yielding Hnn (Hee) final state. In ZH bremsstrahlung, observing the Z decay products (ee, mm, qq modes) allows Higgs mass meas. (to 0.1%) and study without bias; even invisible decays of Higgs are possible using the recoil Z. • Tag Zl+ l • Select Mrecoil = MHiggs 500 fb-1 @ 500 GeV, TESLA TDR, Fig 2.1.4 HWW coupling and the Higgs width Measuring WW fusion gives the HWW coupling (exactly predicted in SM). With BR(H→WW), use to determine GTOT to few%, testing for unexpected Higgs decays. Can distinguish WW from ZH using jet tags and missing mass.

  24. BR MH Higgs fermion couplings Need to determine experimentally that Higgs couplings to fermions are indeed proportional to mass. SM couplings differ from Susy couplings. With vertex reconstruction can distinguish b, c, light quark jets: and measure BRs into various particles. Higgs self couplings Measures Higgs potential shape l, independent of Higgs mass measurement. Determination of l and MH gives new constraint on SM. ZHH Study ZHH production and decay to 6 jets (4 b’s). Cross section is small; premium on very good jet energy resolution and b-jet tagging Can enhance production with positron polarization.

  25. Physics beyond the Standard Model There are serious defects of the SM: Gauge interactionunification not indicated Higgs mass is unstable to loop corrections Can’t explain baryon asymmetry in universe … Many possible new theories are proposed to cure these ills and embed the SM in a larger framework: Supersymmetry Susy models come in many variants, with different scales of Susy breaking (supergravity, gauge mediation, anomaly mediation … ) Each has a different spectrum of particles, underlying parameters. A new gauge interaction like QCD with `mesons’ at larger masses. (Technicolor/topcolor) These interactions avoid introducing a fundamental scalar. `technipions’ play the role of Higgs; new particles to be observed, and modifications to WW scattering. String-inspired models with some extra dimensions compactified at millimeter to femtometer scales. Something different? LC must be able to sort out which is at work. (Cases where LHC sees new phenomena, but misunderstands the source.)

  26. Extra Dimensions The only known path to a theory of quantum gravity and unification of all forces is string theory, in which extra curled-up spatial dimensions exist. The chief defect of the SM is the hierarchy problem – our failure to understand why the EW scale at O(TeV) is so different from the scale of gravity at O(1015 TeV). Supersymmetry and Strong Coupling seek to solve this through new physics at the TeV scale that shields the EW interaction scale from instability. Another possibility is to modify gravity by postulating extra dimensions in which gravity (or other fields) propagate.There are many possible phenomenologies to distinguish, depending on size of extra dimensions and which fields (gravity, gauge bosons, quarks … ) propagate in the bulk. Kinetic motion in small extra dimension gives ‘particle in a box’ set of modes called Kaluza Klein states as seen in 3+1 dimensions. Mass spacing depends on size of extra dimensions. Gravity propagating in usual 3+1 dim. brane PLUS d extra (small) bulk dimensions. The KK states modify the amplitudes for observable processes, or can be directly observed at high mass. Our 4-d world (brane)

  27. ‘Large’ Extra Dimensions (mm scale):gravity propagates in 4+ddimensions with true Fundamental Planck scale = M* << MPlanck. Towers of KK states modify ee → g/Z + unseen GKK rate or angular distributions in e+e- → ff . TheECM dependence at LC gives d. s(ee gGn) d=6 5 4 3 d=2 If supersymmetry in the bulk, KK tower of gravitinos modifies ee → ee , sensitive to M* = 12 TeV for d= 6 at LC500,using polarized e-. 400 800 600 ECM Warped ED/localized gravity: Sensitivity to KK resonances at LC500 is comparable to LHC; LC1000 exceeds LHC. Mini Black Hole production mini Black Hole evaporation event at a 5 TeV e+e- collider e+e- → m+m-

  28. Overview of Oxford ILC activities • The John Adams Institute for Accelerator Science (joint with RHUL in London) • Beam Profile Measurements at Linear Colliders • Transverse profiles = Laser Wire • Longitudinal profile = Smith Purcell Radiation • Linear Collider Survey and Alignment • StaFF • LiCAS • Linear Collider Vertex Detectors • LCFI

  29. A 500-800GeV com • Collider 33km in length • Beams start at O(0.1mm) • Beams end up O(1nm) at interaction point • No recirculation, one shot to collide a given bunch

  30. Tolerances: 200mm vertical, 500 mm horizontal over 600m (betatron wavelength) Many beam lines Tight space (1m wide) Space is emergency escape route Need automation (radiation) Not all sections geometrically straight Electronically noisy environment Temperature and pressure gradients in tunnel No long-term stable reference monuments… LC Survey Problem LiCAS(Linear Collider Alignment and Survey) aims to develop a survey system that can be used to align accelerator components during construction and initial operation • It uses FSI (Frequency Scanning Interferometry) and LSM (Laser Straightness Monitors) to measure absolute co-ordinates. • The group closely collaborates with the DESY metrology group. • A 3-car prototype will be studied in a test tunnel at DESY.

  31. Linear Collider Flavour Identification (LCFI) Collaboration of five UK institutes (Bristol U, Glasgow U, Liverpool U, Oxford U and RAL) studying Vertex Detector Design for the ILC • Three research areas: • Electronics • Thin Ladders • Physics Studies To reconstruct secondary vertices for excellent b and c-jet flavour tagging 5 layers of CCDs at radii 15, 26, 37, 48 and 60 mm; 120 CCDs, ~8x108 pixels in total Thin detector, target thickness < 0.1% X0 / layer; Close to the interaction point

  32. ILC requires parallel register clocking at 50 MHz • stimulated concept of ‘column parallel’ operation • Max possible readout speed, for given noise performance Column Parallel CCD Readout time = N/Fout M N N “Classic CCD” Readout time  NM/Fout CPC1 motherboard • Alternative sensor architecture also under investigation

  33. LCFI Physics Studies • Much of the ILC physics will depend on b-tag and c-tag performance in multi-jet event environment. • Simulated events with a 120 GeV Higgs at a c.o.m. energy of 500 GeV are shown. e+e ZH 100% b-tag efficiency 0 0 180 GeV e+e ZHH jet momentum

  34. Time scale ILCSC (International Linear Collider Steering Committee): 2004 technology recommendation(confirmed by ITRP) Establish Global Design Initiative / Effort (GDI/E) 2006 RDR (Reference DR, incl. first cost estimate) 2008 TDR (Technical Design Report) 2008 site selection 2009 construction could start (need approval of funding but not yet major spending !) 2015 LC and Detector ready for Physics

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