1. TLEP: a first step on a long vision for HEP M. Koratzinos Univ. of Geneva On behalf of the TLEP study group Beijing, 16 August 2013 1

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3. A preamble “…we chose these things not because they are easy, but because they are hard, because that goal will serve to measure and organize the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win”: J.F. Kennedy, president of the US, 1962 3

4. On challenges… The ILC community has taken a formidable challenge and have managed to come with a solid design and TDR on what is a very tricky machine but The Higgs is light and there is not yet any hint of new physics! So, the circular collider approach should be given a chance. It already promises better performance than an equivalent linear machine. We need to allow the circular approach to reach CDR level and compare. 4

5. Contents The physics case Circular collider challenges TLEP implementation TLEP physics reach TLEP design study Acknowledgements: I am indebted to the whole TLEP community and especially R. Aleksan, A. Blondel, P. Janot, F. Zimmermann for liberal use of material This talk would not have been complete without the comparison data with the ILC. I hope I have represented them accurately 5

6. The physics case The energy scale of any new physics is already pushed to beyond a few hundreds of GeV and will probably be pushed to 1TeV or more with the next LHC run. In this scenario, Physics beyond the standard model is only accessible via loop corrections rather than direct observation of a (heavy) state. The sensitivity of precision measurements can be to energy scales far above what is directly accessible in current or next generation machines (LHC, ILC, CLIC) A clearer picture on this will emerge after the next LHC run. Meaningful over-constraining of the standard model can only start now that the Higgs sector is known and might lead to revealing weaknesses of the standard model 6

7. Precision needed 7

8. Circular colliders In the next few slides I would like to overview the parameters that affect circular collider performance. I will then show what can reasonably be achieved in terms of luminosity. The following is not TLEP specific; it can apply to any circular machine (CEPC?) 8

9. Major limitations The major limitations of circular colliders are: – Power consumption limitations that affect the luminosity – Tunnel size limitations that affect the luminosity and the energy reach – Beam-beam effect limitations that affect the luminosity – Beamstrahlung limitations that affect beam lifetimes (and ultimately luminosity) 9

10. Energy reach In a circular collider the energy reach is a very steep function of the bending radius. To make a more quantitative plot, I have used the following assumptions: – RF gradient: 20MV/m – Dipole fill factor: 90% (LEP was 87%) I then plot the energy reach for a specific ratio of RF system length to the total length of the arcs 10

11. Energy reach Assumptions: 20mV/m, 90% dipole fill factor. What is plotted is the ratio of RF length to total arc length LEP2 had a ratio of RF to total arc length of 2.2% TLEP175 sits comfortably below the 1% line 11

12. Luminosity of a circular collider 12

13. Luminosity of a circular collider 13

14. Total power Luminosity is directly proportional to the total power loss of the machine due to synchrotron radiation. In our approach, it is the first parameter we fix in the design (the highest reasonable value) Power loss is fixed at 100MW for both beams (50MW per beam) 14

15. Machine radius The bending radius of the collider also enters linearly in the luminosity formula The higher the dipole filling factor, the higher the performance [there is a small dependance on the maximum beam-beam parameter since smaller machines for the same beam energy can achieve higher beam-beam parameters] 15

16. Beam-beam parameter 16

17. Maximum beam-beam 17

18. Beta* and hourglass We are opting for a realistic β* y value of 1mm. σ z beam sizes vary from 1mm to 3mm. In this range the hourglass effect is between 0.9 to 0.6 Self-consistent σ z at different energies for TLEP 18

19. Luminosity of a circular collider 19

20. Beamstrahlung Beamstrahlung is the interaction of an incoming electron with the collective electomagnetic field of the opposite bunch at an interaction point. Main effect at circular colliders is a single hard photon exchange taking the electron out of the momentum acceptance of the machine. If too many electrons are lost, beam lifetime is affected [the beamstrahlung effect at linear colliders is much larger and it increases the beam energy spread] 20

21. Beamstrahlung (2) *: arXiv:1203.6563 21

22. Comparison with simulation The Telnov formula was checked against a realistic simulation (Guineapig – courtesy the ILC) at different energies [work of M. Zanetti] and found to be pessimistic The ‘tuned’ model corresponds to an ad hoc tuning of the Telnov formula to fit the data better: instead of 10% of the electrons seeing a 100% field, 100% of electrons see a 70% field 22

23. Beamstrahlung limitation Plot on left is if we run with a value of the beam-beam parameter of 0.1 Above ~180 GeV is difficult to run without opting for a more modest beam-beam parameter value (which would reduce the luminosity) TLEP Latest parameter set, mom. acceptance 2.2% Can even run at 250GeV with a beam-beam parameter of 0.05 23

24. A specific implementation: TLEP A study has been commissioned for an 80-km tunnel in the Geneva area. For TLEP we fix the radius (conservatively 9000m) the power (100MW) and try to have beams as flat at possible to reduce beamstrahlung. Our arc optics design (work in progress) conservatively uses a cell length of 50m, which still gives a horizontal emittance of 2nm at 120GeV We assume that we can achieve a horizontal to vertical emittance ratio of 500-1000 (LEP was 200) LHC Possible TLEP location 24

25. Other tunnel diameters …but of course other tunnel diameters and locations are equally good Many other proposals floating, but I would like to mention the Circular Electron-Positron Collider in China (CEPC) – certainly the tunnel can be built more cheaply in China Performance scales with tunnel size, but in case no funds are available for a new tunnel, the LHC tunnel can be used after the end of the LHC physics programme (a project we call LEP3) 25

26. Patrick Janot TLEP implementation  At 350 GeV, beams lose 9 GeV / turn by synchrotron radiation u Need 600 5-cell SC cavities @ 20 MV/m in CW mode l Much less than ILC (8000 9-cell cavities@ 31 MV/m) l Length ~900 m, similar to LEP (7 MV/m) u 200 kW/ cavity in CW : RF couplers are challenging l Heat extraction, shielding against radiation, …  Luminosity is achieved with small vertical beam size :  y ~ 100 nm u A factor 30 smaller than at LEP2, but much more relaxed than ILC (6-8 nm) l TLEP can deliver 1.3 × 10 34 cm -2 s -1 per collision point at √s = 350 GeV  Small beam lifetime due to Bhabha scattering ~ 15 minutes u Need efficient top-up injection 26 BNL 5-cell 700 MHz cavity RF Coupler (ESS/SPL) A. Blondel F. Zimmermann

27. SuperKEKB: a TLEP demonstrator SuperKEKB will be a TLEP demonstrator Beam commissioning starts early 2015 Some SuperKEKB parameters : – Lifetime : 5 minutes TLEP : 15 minutes –  * y : 300  m TLEP : 1 mm –  y : 50 nm TLEP : ~100 nm –  y /  x : 0.25% TLEP : 0.20%-0.10% – Positron production rate : 2.5 × 10 12 / s TLEP : < 1 × 10 11 / s – Off-momentum acceptance at IP : ±1.5% TLEP : ±2.0 to ±2.5% 27

28. Patrick Janot TLEP Cost (Very Preliminary) Estimate  Cost in billion CHF As a self-standing project : Same order of magnitude as LHC As an add-on to the VHE-LHC project : Very cost-effective : about 2-3 billion CHF Cost per Higgs boson : 1 - 3 kCHF / Higgs (ILC cost : 150 k$ / Higgs) [ NB : 1CHF ~ 1$ ] 28 80-100 km tunnel LEP/LHC Bare tunnel3.1 (1) Services & Additional infrastructure (electricity, cooling, service cavern, RP, ventilation, access roads …) 1.0 (2) RF system0.9 (3) Cryo system0.2 (4) Vacuum system & RP0.5 (5) Magnet system for collider & injector ring0.8 (6) Pre-injector complex SPS reinforcements0.5 Total7.0 Note: detector costs not included – count 0.5 per detector (LHC) (1): J. Osborne, Amrup study, June 2012 (2): Extrapolation from LEP (3): O. Brunner, detailed estimate, 7 May 2013 (4): F. Haug, 4 th TLEP Days, 5 April 2013 (5): K. Oide : factor 2.5 higher than KEK, estimated for 80 km ring (6): 24,000 magnets for collider & injector; cost per magnet 30 kCHF (LHeC); Cost for the 80 km version : the 100 km version might be cheaper.) Absolutely Preliminary Not endorsed by anybody

29. Power consumption TLEP 120TLEP 175 RF systems173-185 MW cryogenics10 MW34 MW top-up ring3 MW5 MW Total RF186-198 MW212-224 MW Power consumptionTLEP 175 RF including cryogenics224MW cooling5MW ventilation21MW magnet systems14MW general services20MW Total~280MW Highest consumer is RF: Total power consumption for 350GeV running: IPAC13 TUPME040, arXiv:1305.6498 [physics.acc-ph]arXiv:1305.6498 Limited by Klystron CW efficiency of 65%. This is NOT aggressive and we hope to be able to do better after dedicated R&D CERN 2010 power demand: Full operation 220MW Winter shutdown 50MW 29

30. A note on power consumption TLEP is using ~280MW while in operation and probably ~80MW between physics fills. So for 1×10 7 sec of operation and 1×10 7 sec of stand-by mode, total electricity consumption is ~1TWh CERN is currently paying ~50CHF/MWh TLEP yearly operation corresponds to ~50MHF/year This should be seen in the context of the total project cost (less than 1% of the total cost of the project goes per year to electricity consumption) 30

31. TLEP parameter set TLEP ZTLEP WTLEP HTLEP t E beam [GeV]4580120175 circumf. [km]80 beam current [mA]118012424.35.4 #bunches/beam44006008012 #e − /beam [10 12 ]196020040.89.0 horiz. emit. [nm]30.89.4 10 vert. emit. [nm]0.070.02 0.01 bending rad. [km]9.0 κεκε 440470 1000 mom. c. α c [10 −5 ]9.02.01.0 P loss,SR /beam [MW]50 β ∗ x [m]0.5 1 β ∗ y [cm]0.1 σ ∗ x [μm]1247868100 σ ∗ y [μm]0.270.14 0.10 hourglass F hg 0.710.75 0.65 E SR loss /turn [GeV]0.040.42.09.2 V RF,tot [GV]22612 d max,RF [%]4.05.59.44.9 ξ x /IP0.070.10 ξ y /IP0.070.10 f s [kHz]1.290.450.440.43 E acc [MV/m]331020 eff. RF length [m]600 f RF [MHz]700 δ SR rms [%]0.060.100.150.22 σ SR z,rms [cm]0.190.220.170.25 56001600480130 number of IPs4444 beam lifet. [min]67251620 By definition, in a project like TLEP, from the moment a set of parameters is published it becomes obsolete and we now already have an improved set of parameters. The new parameter set contains improvements to our understanding, but does not change the big picture. IPAC13 TUPME040, arXiv:1305.6498 [physics.acc-ph]arXiv:1305.6498 Too pessimistic! 2nm @120GeV or lower should he easy Revised (taking into account BS) but similar 31

32. Luminosity of TLEP TLEP : Instantaneous lumi at each IP (for 4 IP’s) Instantaneous lumi summed over 4 IP’s Z, 2.10 36 WW, 6.10 35 HZ, 2.10 35 tt, 5.10 34 Why do we always quote 4 interaction points? It is easier to extrapolate luminosity from the LEP experience. Lumi of 2IPs is larger than half the lumi of 4IPs According to a particle physicist: “give me an experimental cavern and I guarantee you that it will be filled” 32

33. Upgrade path TLEP offers the unique possibility to be followed by a 100TeV pp collider (VHE-LHC) Luminosity upgrade: a study will be launched to investigate if luminosity can be increased by a significant factor at high energies (240 and 250GeV E CM ) by using a charge-compensated scheme of four colliding beams. We will aim to gain a factor of 10 (to be studied and verified) 33

34. Patrick Janot TLEP : Possible Physics Programme  Higgs Factory mode at √s = 240 GeV: 5+ years u Higgs boson properties, WW and ZZ production. l Periodic returns at the Z peak for detector and beam energy calibration  Top Threshold scan at √s ~ 350 GeV: 5+ years u Top quark mass, width, Yukawa coupling; top quark physics; more Higgs boson studies. l Periodic returns at the Z peak for detector and beam energy calibration  Z resonance scan at √s ~ 91 GeV: 1-2 years u Get 10 12 Z decays @ 15 kHz/IP. Repeat the LEP1 Physics Programme every 15 minutes. l Continuous transverse polarization of some bunches for precise E beam calibration  WW threshold scan at √s ~ 161 GeV: 1-2 years u Get 10 8 W decays; Measure the W mass; Precise W studies. l Continuous transverse polarization of some bunches and returns to the Z peak.  Longitudinally polarized beams at √s = m Z : 1 year u Get 10 11 Z decays, and measure A LR, A FB pol, etc. l Polarization wigglers, spin rotators  Luminosity, Energy, Polarization upgrades u If justified by scientific arguments (with respect to the upgrade to VHE-LHC) 34

35. Patrick Janot TLEP as a Mega-Higgs Factory (1) 35 ILC-250TLEP-240ILC-350TLEP-350 Lumi / 5 yrs 250 fb  10 ab  350 fb  2.6 ab  Beam Polarization80%, 30%– – # of HZ events 70,0002,000,00065,000325,000 # of WW → H events 3,00050,00020,00065,000 Z → Z → All Unpolarized cross sections PJ and G. Ganis

36. Patrick Janot TLEP as a Mega-Higgs Factory (2)  Example : e  e  → ZH → l  l  + anything  Measure  HZ Summary of the possible measurements : (TLEP : CMS Full Simulation + some extrapolations for cc, gg) 36 ILC-250TLEP-240  HZ 2.5%0.4%  HZ * BR(H → bb) 1.1%0.2%  HZ * BR(H → cc) 7.4%1.2%  HZ * BR(H → gg) 9.1%1.4%  HZ * BR(H → WW) 6.4%0.9%  HZ * BR(H →  ) 4.2%0.8%  HZ * BR(H → ZZ) 19%3.1%  HZ * BR(H →  ) 35%3.0%  HZ * BR(H →  ) 100%13%  INV /  H < 1%< 0.2% mHmH 40 MeV8 MeV e+e+ e-e- Z* Z H e    e    g HZZ TLEP-240 1 year 1 detector ILC TDR From P. Azzi et al. arXiV:1208.1662

37. Patrick Janot Global fit of the Higgs couplings  Model-independent fit u NB : Theory uncertainties must be worked out. 37 M. Bachtis CouplinggZgZ gWgW gbgb gcgcg gg gg gg BR exo LEP-2400.16%0.85%0.88%1.0%1.1%0.94%6.4%1.7%0.48% LEP-3500.15%0.19%0.42%0.71%0.80%0.54%6.2%1.5%0.45% ILC-3500.9%0.5%2.4%3.8%4.4%2.9%45%14.5%2.9% 1.0% Snowmass 2013

38. Patrick Janot TLEP as a Mega-Top Factory 38 TLEP ILC TLEP, Lumi / 5 years# top pairs  m top  top  top / top TLEP4 × 650 fb -1 1,000,000 10 MeV12 MeV13% ILC350 fb -1 100,00030 MeV35 MeV40% - Stat. only M. Zanetti Expected sensitivity for TLEP (full study to be done) and ILC

39. Patrick Janot TLEP as a Tera-Z and Oku-W Factory (1)  TLEP repeats the LEP1 physics programme every 15 minutes u Added value: Transverse polarization up to the WW threshold (LEP: up to 60GeV) l Exquisite beam energy determination with resonant depolarization  Up to 5 keV precision – unique at circular e  e  colliders  Measure m Z, m W,  Z, … with unbeatable accuracy u Measure the number of neutrinos l From the peak cross section at the Z pole – Luminosity measurement is a challenge From radiative returns to the Z from the WW threshold – e+e- →  39 Z lineshape, asymetries WW threshold scan New Physics in loops ? - No beamstrahlung is a clear advantage

40.  This is a unique part of the TLEP programme (that was not covered by the snowmass reports yesterday). It is also very challenging for the accelerator (intensity, longitudinal polarization), experiments (rate) and Theory  Measurements with Tera-Z u Caution : TLEP will have 5×10 4 more Zs than LEP - Predicting achievable accuracies with 250 times smaller statistical precision is difficult u The study is just beginning : errors might get better with increasing understanding  Much more to do at the Z peak e.g., asymmetries, flavour physics (>10 11 b, > 10 11 c, > 10 10 t), rare Z decays, …  Measurements with Oku-W u Caution : TLEP will have 5×10 6 more W than LEP at the WW threshold -Predicting achievable accuracies with 1000 times smaller statistical precision is difficult u Much more W physics to do at the WW threshold and above e.g., G W, l W, rare W decays, diboson couplings, …  Measurement with longitudinal polarization u One year data taking with luminosity reduced to 20% of nominal (requires spin rotators) l 40% beam longitudinal polarization assumed – NB: LEP kept polarization in collisions - hardware needed is challenging TLEP as a Tera-Z and Oku-W Factory (2) NB: ILC limited to a factor > 30 larger errors 40

41. Patrick Janot EWSB Precision tests at TLEP: Teaser  lkjfs 41 TLEP ILC m H =126 GeV Warning : indicative only. Complete study being done Very stringent SM closure test. Sensitivity to weakly-interacting BSM Physics at a scale > 10 TeV

42. TLEP Design Study: Structure 42 26 Working Groups: Accelerator / Experiment / Phenomenology

43. TLEP Design Study: People 43 295 subscribers from 23 countries (+CERN) – Distribution reflects the level of awareness in the different countries 4 physicists from China: subscribe at http://tlep.web.cern.ch !http://tlep.web.cern.ch 296

44. Watch this space http://tlep.web.cern.ch Next event : Sixth TLEP workshop 16-18 October 2013 http://indico.cern.ch/conferenceDisplay.py?ovw=True&confId=25771 http://indico.cern.ch/conferenceDisplay.py?ovw=True&confId=25771 Joint VHE-LHC + TLEP kick-off meeting in February 2014 44

45. Conclusions TLEP is a 3-in-1 package: – It is a powerful Higgs factory – It is a high-intensity EW parameter buster – It offers the path to a 100TeV pp collider TLEP is based on solid technology and offers little risk, has a price tag which is expensive but not out of reach, has reasonable consumption, offers multiple interaction points and might even have an upgrade potential. 45

46. Concluding remarks GeV OR The debate has started and we are looking forward to upgrades and performance improvements from both sides ? 46

47. THANK YOU end 47

48. Extra slides 48

49. Beamstrahlung I am using the approach of Telnov throughout* The energy spectrum of emitted photons during a collision of two intense bunches (usual bremstrahlung formula) is characterized by a critical energy Where ρ is the radius of curvature of the affected electron which depends on the field he sees And the maximum field can be approximated by *: arXiv:1203.6563 49

50. Beamstrahlung So, the critical energy turns out to be for the maximum field (it would be smaller for a smaller field) Telnov’s approximation: 10% of electrons see maximum field 90% of electrons see zero field constants 50

51. Beamstrahlung 51

52. Beamstrahlung energy dependence For a specific ring, power consumption, emittances and ξ: Number of particles per bunch scales with gamma: And u scales with γ 2. This produces a steep drop in lifetime with increased energy 52

53. European Strategy recommendations High-priority large-scale scientific activities – Second-highest priority, recommendation #2 Excerpt from the CERN Council deliberation document (22-Mar-2013) 53 d) To stay at the forefront of particle physics, Europe needs to be in a position to propose an ambitious post-LHC accelerator project at CERN by the time of the next Strategy update, when physics results from the LHC running at 14 TeV will be available. CERN should undertake design studies for accelerator projects in a global context, with emphasis on proton-proton and electron-positron high-energy frontier machines.These design studies should be coupled to a vigorous accelerator R&D programme, including high-field magnets and high-gradient accelerating structures, in collaboration with national institutes, laboratories and universities worldwide. CERN should undertake design studies for accelerator projects in a global context, with emphasis on proton-proton and electron-positron high-energy frontier machines. These design studies should be coupled to a vigorous accelerator R&D programme, including high-field magnets and high-gradient accelerating structures, in collaboration with national institutes, laboratories and universities worldwide. The two most promising lines of development towards the new high energy frontier after the LHC are proton-proton and electron-positron colliders. Focused design studies are required in both fields, together with vigorous accelerator R&D supported by adequate resources and driven by collaborations involving CERN and national institutes, universities and laboratories worldwide. The Compact Linear Collider (CLIC) is an electron-positron machine based on a novel two-beam acceleration technique, which could, in stages, reach a centre-of-mass energy up to 3 TeV. A Conceptual Design Report for CLIC has already been prepared. Possible proton-proton machines of higher energy than the LHC include HE-LHC, roughly doubling the centre-of-mass energy in the present tunnel, and VHE-LHC, aimed at reaching up to 100 TeV in a new circular 80km tunnel. A large tunnel such as this could also host a circular e  e  machine (TLEP) reaching energies up to 350 GeV with high luminosity.

54. CERN medium term plan 54

55. The TLEP tunnel Standard size tunnel boring machines dictate a larger tunnel size of 5.6m diameter (LHC: 3.8m) Maximize boring in ‘molasse’ (soft stone) 80km design necessitates a bypass tunnel to avoid very deep shafts at points 4 and 5 A larger tunnel might actually be cheaper This is only the beginning of the geological study 55

56. Patrick Janot Global fit of the Higgs couplings (2)  Model-dependent (seven-parameter) fit a-la-LHC  Assume no exotic Higgs decays, and  c =  t u Quantitative added value from ILC – wrt HL-LHC – does not stick out clearly. l In contrast, sub-per-cent TLEP potential is striking for all couplings è Only TLEP is sensitive to (multi-)TeV new physics with Higgs measurements u Much theoretical progress is needed to reduce accordingly theory uncertainties 56 HL-LHC : One experiment only … CMS Scenario 1 CMS Scenario 2 In bold, theory uncertainty are assumed to be divided by a factor 2, experimental uncertainties are assumed to scale with 1/√L, and analysis performance are assumed to be identical as today (HL-LHC : One experiment only) CMS, July 13

57. Patrick Janot TLEP as a Mega-Higgs Factory (3)  Determination of the total width u From the number of HZ events and of ZZZ events at √s = 240 GeV  From the bb final state at √s = 350 GeV (and 240 GeV) 57 -  H from: ILCTLEP  → ZZZ @ 240 20%3.2% WW → H @240 12%2.4% WW → H @350 7%1.2% Combined 5.8%1.0% Note :  collider  H /  H ~ 5%

58. Patrick Janot Higgs Physics with √s > 350 GeV ? (1)  Signal cross sections in e  e  collisions  Measurements at higher energy  √s > 350 GeV does not do much for couplings to c, b, g, Z, W, ,  and  tot. (slide 15) l Invisible width best done at √s = 240 GeV u The ttH coupling benefits from higher energy l TLEP 350 : 13% l ILC 500 : 14% ; ILC 1 TeV : ~4% ; CLIC : ~4% u The HL-LHC will already do the measurement with 5% precision (and improving) l Sub-per-cent precision will need the ultimate pp machine at 100 TeV : VHE-LHC 58 H H +

59. Patrick Janot Higgs Physics with √s > 350 GeV ? (2)  Measurements at higher energy (cont’d)  Higgs tri-linear self coupling very difficult for all machines Particularly difficult for √s < 2-3 TeV Few per-cent precision will need VHE-LHC  Summary  For the study of H(126), the case for e  e  collisions above 350 GeV is not compelling. l A stronger motivation will exist if a new particle found (or inferrred) at LHC  IF e  e  collisions can bring substantial new information about it 59 ILC500, HL-LHC ILC1TeV, HE-LHC CLIC3TeV, VHE-LHC 0.5 ab -1 3 ab -1 1 ab -1 3 ab -1 2 ab -1 3 ab -1 J. Wells et al. arXiV:1305.6397 Snowmass, Aug 13

60. EW parameter summary QuantityPhysics Present precision TLEP Stat errors Possible TLEP Syst. Errors TLEP key Challenge Alain Blondel, Snowmass on Minnesota, 2 August 2013 M Z ( keV) Input 91187500  2100 Z Line shape scan 5 keV<100 keVE_calQED corrections  Z (keV)  (T) (no  !) 2495200  2300 Z Line shape scan 8 keV<100 keVE_calQED corrections RlRl  s,  b 20.767  0.025 Z Peak0.0001<0.001StatisticsQED corrections N PMNS Unitarity sterile ’s 2.984  0.008 Z Peak0.00008<0.004Bhabha scat. N PMNS Unitarity sterile ’s 2.92  0.05 (  +Z_inv) (  +Z  ll ) 0.001 (161 GeV) <0.001Statistics RbRb bb 0.21629  0.00066 Z Peak0.000003<0.000060 Statistics, small IP Hemisphere correlations A LR ,  3,  (T, S ) 0.1514  0.0022 Z peak, polarized 0.000015<0.000015 4 bunch scheme, > 2exp Design experiment M W MeV/c2 ,  3,  2,  (T, S, U) 80385 ± 15 Threshold (161 GeV) 0.3 MeV <0.5 MeV E_cal & Statistics QED corections m top MeV/c2 Input 173200 ± 900 Threshold scan 10 MeV <10MeV E_cal & Statistics Theory interpretation 40MeV? 60