The Future of Circular Colliders: FCC-ee Physics Highlights and Accelerator Design

1. FCC-ee Michael Koratzinos, ETHZ, on behalf of the FCC study Photo courtesy J. Wenninger

2. Contents • Where we are now • Physics motivation. Why circular? • The FCCs • The accelerator • Physics highlights • The collaboration Indebted to all my colleagues at FCC-ee and specifically to P. Janot, F. Zimmermann, K. Oide, A. Blondel, for the liberal use of material.

3. Physics Motivation/ Circular Colliders

4. The butterfly plot • The Standard Model is not a complete theory! • New tools are needed to unravel nature’s mysteries • olliders are discovery machines • Figure of merit for all colliders: energy vs luminosity FCC-ee circular Luminosity CEPC linear CLIC ILC CM Energy

5. An apology Q: Synchrotrons have been around for a very long time… do we really need another one, 100 kms long? A: Synchrotrons today offer still the best price/performance on the market. There are numerous examples in history where evolving an idea and making it bigger led to great things. Agood example: 1967 1926

6. The strategy behind circular colliders • Measure accurately as many parameters which are sensitive to new physics as possible • Caution: need to have a measuring power which is better than the expected signal! For example: Higgs couplings: most extensions to the standard model predict deviations from the standard model of the order of 1%. It is imperative, therefore, to build a machine that can probe these quantities to order 0.1%

7. An example: predictions of a specific model ILC The LHC cannot distinguish between models, even if it could measure a deviation Models with a new physics scale limited to 2TeV!

8. Circular colliders: luminosity • e+e- circular colliders cannot compete with linear colliders in terms of energy. But they can compensate in terms of luminosity • (they also provide a tunnel that can be later used for a hadron machine! “energy upgrade”) • To get maximum luminosity necessitates operating the machine at a new regime that was never reached before I circular machines: the beamstrahlung dominated regime. This effect comes on top of the already known beam-beam limit

9. The circular e+e- collider approach For the high luminosities aimed at, the beam lifetimes due to natural physics processes (mainly radiative Bhabha scattering) are of the order of a few minutes – the accelerator is ‘burning’ the beams up very efficiently • What kind of luminosities can be achieved? • How big a ring needs to be? • How much power will it consume? A “top-up” scheme (a la B factories) is a must Booster ring injector Main ring A. Blondel • Booster ring the same size as main ring, tops up the main ring every ~O(10s) • Main ring does not ramp up or down

10. Luminosity of a circular lepton collider The maximum luminosity is bound by the total power dissipated, the maximum achievable beam-beam parameter, the bending radius, the beam energy, the amount of vertical squeezing , and the hourglasseffect, a geometrical factor(which is a function of σzand ) Crab waist Power fixed to 100MW Proportional to ring size Steep drop with Ebeam

11. Design brief for circular accelerators • Each energy has different challenges, but key is maximizing the beam-beam parameter at all energies by reaching the beam-beam limit and beamstrahlung limits, if possible, at the same time • Opt for high momentum acceptance (2% at high energies, ~1% sufficient at 45GeV) • Opt for the smallest vertical emittance possible (around 1pm) • Run beam-beam simulations to find optimal working point – theoretical luminosities might not be attainable due to instabilities

12. FCC-ee

13. The Future Circular Colliders CDR and cost review for the next ESU (2018) • International collaboration to Study Colliders fitting in a new ~100 km infrastructure, fitting in the Genevois • Ultimate goal: 100 TeV pp-collider (FCC-hh) •  defining infrastructure requirements • Possible first steps: • e+e-collider (FCC-ee) High Lumi, ECM =90-400 GeV • HE-LHC16T  28 TeVin LEP/LHC tunnel • Possible add-on: • p-e (FCC-he) option ~16 T magnets From European Strategy in 2013: “ambitious post-LHC accelerator project” Study kicked-off in Geneva Feb 2014 Alain Blondel The FCCs

14. Alain Blondel The FCCs

15. CERN Circular Colliders & FCC 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030 2035 2040 Constr. Physics LEP Design Proto Construction Physics LHC – operation run 2 Design Construction Physics HL-LHC - ongoing project ~20 years Design Proto Construction Physics FCC – design study Must advance fast now to be ready for the period 2035 – 2040 Goal of phase 1: CDR by end 2018 for next update of European Strategy

16. tentative preliminary time line for FCC-ee construction physics start years -14 -12 -4 -2 0 -8 -10 -6 inj. complex construction injector commissioning access shafts & caverns tunnelling technical infrastruct. <12 years from construction start to first physics machine installation hardw. & beam commissioning

17. recall the construction of LEP 1989 <6 years from zero to physics 1988 1987 1986 1985 1984 E. Picasso H. Schopper

18. CDR plans Alain Blondel The FCCs

19. The FCC Home -- 2017 • Optimisation in view of accessibility surface points, tunneling rock type, shaft depth, etc. optimum: 97.5 km • NB: 97.5 km cheaper than 80 km! • Tunneling • Molasse 90% (good rock), • Limestone 5%, Moraines 5% (tough) • Shallow implementation • ~ 30 m below Léman lakebed • Reduction of shaft lengths etc... • One very deep shaft F (476m)(RF or collimation), alternatives being studied, e.g. inclined access Alain Blondel The FCCs

20. FCC: Common layouts for ee and hh IP 11.9 m 30 mrad FCC-hh/ ee Booster 9.4 m Asymmetric “moustache” IR idea by A. Blondel, implemented by K. Oide 0.6 m Lepton beams cross over (top energy: common RF) to enter the IP from inside. Common RF (tt) Common RF (tt) Key: FCC-ee 1,FCC-ee 2, FCC-ee booster (FCC-hh footprint) 2 main IPs in A, G for both machines Max. separation of 3(4) rings is about 12 m: wider tunnel or two tunnels are necessary around the IPs, for ±1.2 km. IP

21. Experimental caverns eehh Sharing the FCC experimental caverns (Preliminary layout)

22. Tunnel layout FCC-hh FCC-ee HE-LHC : constraints: No civil engineering, same beam height as LHC  Magnets OD ca. 1200 m max QRL (shorter than FCC) OD ca. 850 mm (all included) Compliant 16T magnet design ongoing (challenge) + still many items to study! If HE-LHC can work in 3.8m  ... it will feed-back to FCC tunnel design! A. Blondel

23. FCC-ee machine parameters – Aug 2017

24. SuperKEKB: an FCC-eedemostrator Ie+=3.6 A, Ie-=2.6 A PSR~ 13 MW C = 3 km beam commissioning started this year K. Oide et al. top up injection at high current by* =300 mm (FCC-ee: 1 mm) lifetime 5 min (FCC-ee: ≥20 min) ey/ex =0.25% (similar to FCC-ee) off momentum acceptance (±1.5%, similar to FCC-ee) e+ production rate (2.5x1012/s, FCC-ee: <1.5x1012/s (Zcr.waist) SuperKEKBgoes beyond FCC-ee, testing all concepts

25. RF system requirements Very large range of operation parameters “Ampere-class” machines • Voltage and beam current ranges span more than factor > 102 • No efficient single RF system solution satisfies the requirements “high gradient” machines O. Brunner, A. Butterworth, R. Calaga,…

26. RF system R&D lines 400 MHz single-cell cavities preferred for hh and ee-Z (few MeV/m) • Baseline Nb/Cu @4.5 K, development with synergies to HL-LHC, HE-LHC • R&D: power coupling 1 MW/cell, HOM power handling (damper, cryomodule) W Z hh ≈ 32 singlecell cavities per beam ≈ 120 cell per beam double cell ≈ 50 per beam single cell 400 or 800 MHz multi-cell cavities preferred for ee-H, ee-tt and ee-W • Baseline options 400 MHz Nb/Cu @4.5 K, ◄▬► 800 MHz bulk Nb system @2K • R&D: High Q0 cavities, coating, long-term: Nb3Sn material Booster ring: Same RF system (lower power) t H ≈ 800 cells per beam 4 or 5 cell ≈ common 2600 cells for both beams O. Brunner, A. Butterworth, R. Calaga

27. highly efficient RF power sources 2014 breakthrough in klystron theory: –”congregated bunch” V.A. Kochetova, 1981] - “bunch core oscillations” [A. Yu. Baikov, et al. 2014] - “BAC” method [I.A. Guzilov, O.Yu. Maslennikov, A.V. Konnov 2013] These three methods together promise a klystron efficiency ~90% An international collaboration “HEIKA” (CERN, ESS, SLAC, CEA, MFUA, Lancaster U, Thales, L3, CPI, VDBT) is now designing, building and testing prototypes. Simulations and first hardware tests extremely encouraging. A very important power consumption (and cost) driver is the klystron efficiency. For many years this has stagnated at ~65%. This translates to a power consumption by the RF system alone of ~200MW work in progress E. Jensen, I. Syratchev, C. Lingwood

28. arc magnets 2-in-1 design dipole based on twin aperture yoke and single busbars as coils A. Milanese conductor twin 2-in-1 quadrupole the novel arrangement of the magnetic circuit allows for considerable savings in Ampere-turns and power consumption, less units to manufacture, transport, install, align, remove,…

29. FCC-ee total power for comparison, total CERN complex in 1998 used up to 237 MW ** private discussions with M. Nonis *dividing total energy used by 200 days

30. CERN energy consumption [GWh] FCC-eeestimate ~300MW × 200days = 1.4TWh 3rd Energy Workshop 29-30 October 2015

31. electricity cost Courtesy: M. Seidel, EuCARD-2, V. Shiltsev, K. Oide, Q. Qin, G. Trubnikov, and others 1400 GWh / yr → ~70 MEuro / yr

32. Region around the IR is arguably the most challenging design item Final focus quads CCT final focus quads screening solenoid Compensating solenoid Luminosity counter Beam pipes X-Y view –looking towards the IP final focus quads

33. FCC-ee MDI optimization This is a very demanding , interdisciplinary problem. Good progress has been made. Beam pipe radius at IP is 15mm

34. The resonant depolarization method • The spin tune of an electron in a storage ring, , is proportional to its energy. • This energy can be measured (instantaneously) to ~100keV per beam! • Different effects change the beam energy by orders of magnitude larger than that! • This very powerful method requires a very demanding analysis, dedicated hardware, special running conditions, etc. • We have the LEP experience to assist us, but still need to do a factor 20 better than that. • Unique to FCC-ee: the resonant depolarization method can be used not only for the running around the Z, but also for the WW running Unique to circular colliders At the Z, polarization times are high (200 hours) – use dedicated wigglers Polarization of a few % sufficient for a measurement – every 5 mins / both beams Careful machine preparation + harmonic bump tuning

35. Achieving polarization Accurate energy determination is needed for: Mz, ΓZ, MW, (from the muon F-B asymmetry at the Z) • To depolarize you must first have achieved polarization; ~10% polarization sufficient • A real (imperfect) machine depolarizes fast – need careful corrections to restore polarization levels • Would this be possible? Simulation code SISTROS says yes both for the Z and for the W. Correcting an imperfect machine (quad misalignments + BPM errors) restores polarization levels. 45 GeV 80 GeV Machine with imperfections after correction Minimum polarization level required Energy spread increases Eb Eb2/ and polarization level decreases. At the W expectation similar to LEP at Z  enough for energy calibration Excellent polarization at the Z (but slow) E. Gianfelice-Wendt

36. FCC-ee detectors Two integration, performance and cost estimates ongoing: -- Linear Collider Detector group at CERN has undertaken to adapt the CLIC-SID detector for FCC-ee -- new IDEA, detector specifically designed for FCC-ee (and CEPC) A. Blondel

37. Physics highlights

38. FCC-ee operation model • Assumptions: • 200 days of physics per year (7 months minus 13 days for MDs per year) • two interaction points, • “Hübner factor”=0.75 with top up inj. (lower than value achieved at KEKB ~0.8) Total run time: 10-11 years

39. FCC-ee discovery potential Today we do not know how nature will surprise us. A few things that FCC-ee could discover : WILL EXPLORE the 10-100 TeV energy scale (and beyond) with Precision Measurements -- ~20-50 fold improved precision on many EW quantities (equiv. to factor 5-7 in mass) mZ,mW, mtop , sin2weff , Rb, QED (mz) s (mzmWm), Higgs and top quark couplings COULD DISCOVER a violation of flavour conservation or universality for example FCNC (Z -->  , e) in 5 1012 Z decays. + flavour physics (1012 bb events) (Bs  etc..) COULD DISCOVER dark matter as an «invisible decay» of H or Z or in LHC loopholes. COULD DISCOVER very weakly coupled particles in the 5-100 GeV energy scale such as: Right-Handed neutrinos, Dark Photons etc… + an enormous amount of clean, unambiguous work on QCD etc…. NB the «Z factory» plays an important role in the ‘discovery potential’ SeeM. Bicer et al., “First Look at the Physics Case of TLEP,” JHEP01 (2014) 164 A. Blondel

40. Physics goals at the Z pole • Precision EW measurements with a Z resonance scan : 2-3 years • Most measurements are systematics-limited after the first (couple) year(s) (~1012 Z) • √s precision, luminosity accuracy, higher-order theory predictions • Severe limitation comes from the knowledge of aQED(mZ) • Direct measurement possible with two more years at √s = 87.9 and 94.3 GeV • A sample of 1013 Z (two more years) opens a large variety of interesting possibilities • Discovery new physics with rare Z (visible or invisible) decays • Discovery new physics with b, c, t rare decays (Z → bb, cc, tt) • A few years at the Z make the link between the intensity and the energy frontiers • Lineshape • mZ, GZ to < 100 keV • Asymmetries • sin2W to 6×10-6 • aQED(mZ) to 3×10-5 • Branching ratios, Rl, Rb • aS(mZ) to 0.0002 (Current) (2.2 MeV) (1.6×10-4) • (1.5×10-4) _ e+e-→ Z → qq (0.002) FCC Week, Berlin

41. Physics goals at the WW threshold • Within ~1 year at the WW threshold • This mW precision is essential for the full exploitation of the Z precision measurements • With similar systematic limitations as at the Z pole • E.g., higher-order theory predictions (order of magnitude improvement) (Current) • Threshold scan • mW to < 500 keV • Branching ratios Rl, Rhad • aS(mW) to 0.0002 • Radiative returns e+e-→gZ • Nn to 0.0004 (15 MeV) e+e-→ W+W- (0.002) aQED (0.008) n • And also : • TGC / QCG • Rare W decays - n Prediction from Z measurements after the FCC-ee (~precision of direct measurement) FCC Week, Berlin

42. A note on attainable precision After FCC before FCC Prediction: Example: the W mass direct measurement: Essential to reduce theory error: necessitates calculation up to 3-4 loops. Effort has already started. 2 loop calculations finished – 3 loops started. There will be a workshop at CERN in January 2018 to kickstart this If only one ingredient is missing, the sensitivity to new physics may entirely vanish

43. Physics goals at and above the top threshold • Primary goal : precise mtop measurement at threshold • Many interesting opportunities slightly above threshold (370 GeV) • Top EW couplings, ttg and ttZ, to 1% • Sensitive to new physics • Synergetic with FCC-hh for ttH Yukawa coupling measurement • Anomalous top production and decay • Higgs decay width to 1% • … • Essential for full harnessing of Z & W precision data • 10 MeV precision (stat.) reached with 0.2 ab-1 • Benefits from aS measurement at lower √s • QCD higher orders : dominant syst. (30 MeV) • Also from threshold scan: • Top decay width, top Yukawa coupling e+e- → t t _ F. Simon FCC Week, Berlin

44. Higgs couplings Higgs couplings gHxxprecision: Important remark: for FCC-hh, we need to either assume the standard model with no deviations, or the measurements obtained at FCC-ee the combination of FCC-ee and FCC-hh is «invincible»

45. Global Fit and sensitivity to new physics • Combining all EW measurements • In the context of the SM … and beyond FCC-ee projections No theory uncertainties w/o theory uncertainties arXiv:1308:6176 with current theory uncertainties J. De Blas, Jan. 2017 Tevatron LEP + mH @ LHC SM with mH = 125 GeV Today: L> 5-10 TeV Without mZ (aQEQ)@FCC-ee, the SM line would have a 2.6 (1.8) MeV width FCC-ee sensitivity severely drops without POLARIZATION + STATISTICS (and improved theory calculations) After FCC-ee: L> 50-100 TeV ? Synergetic with FCC-hh J. Ellis and P. Janot

46. FCC-ee sensitivity to heavy RH neutrinos Simple an unambiguous signature – offset vertex

47. Sterile neutrino sensitivity

48. The link to FCC-hh The synergy between FCC-ee and FCC-hh could be another talk! (cf A. Blondel, Lepton photon, Aug 2017, Guangzhou, China http://indico.ihep.ac.cn/event/6183/ ) • Having FCC-ee followed by FCC-hh makes sense: • Smoothens out the spending profile – both machines share the same tunnel and a lot of infrastructure • For FCC-ee: it gives a chance for a discovery in case that precision measurements show deviations from the SM • For FCC-hh: it makes it affordable • This has worked perfectly in the past! e+e-1989-2000 p p2009-2039 This is 60 years later

49. Summary machine • FCC-ee is a state-of-the-art e+e- collider pushing the frontiers regarding performance • FCC-ee offers extremely high luminosities in the energy range from Z to ttbar. • FCC-ee offers precice energy calibration at the Z and W energies • FCC-ee technology is ready; ongoing R&D aims at further increasing efficiency • optics fulfils all requirements, baseline luminosity performance is predicted with confidence • FCC-ee has an excellent physics potential and can constrain the standard model by improving dramatically on EW parameters • It will measure the Higgs couplings to a precision 0.1% to 1% • It can put limits on the energy scale of new physics approaching 100TeV! • The combination of FCC-ee and FCC-hh maximizes physics reach physics

50. Backup slides