International Linear Collider Physics Prospects and Detector Designs

1. International Linear Collider Physics Prospects and Detector Designs Sonja Hillert Stockholm University 30th April 2009

2. Why a Linear Collider is needed • To understand galaxies, it helps to observe them at different wavelengths: Hitoshi Murayama, TILC08 • To understand physics at a new energy scale, it helps to use complementary colliders

3. Complementarity of colliders • LEP, SLC & Tevatron: led to understanding of SM at the quantum level prediction of masses of top quark and Higgs boson Higgs mass limit, 95%CL 1996 year 2006 • HERA observations of high Q2 events  dedicated leptoquark searches at the Tevatron, which in turn fed back into HERA analyses • Belle discovery of X(3872)  dedicated search at CDF & D0: independently confirmed

4. Physics at the TeraScale • LHC will give access to TeV energy scale: expect ground-breaking discoveries: • How is electroweak symmetry broken? Higgs? Which one? SM and light SUSY-Higgs accessible • Does the top-quark play a special role in this? mass ~ scale at which ew symm. is broken • Why is mW/MPl ~ 10-17? many possible explanations involving New Physics at TeV-scale • Dark Matter ~ 22% of the Universe: what is it? could be explained by New Physics at TeV-scale • BUT: at LHC, very different New Physics can look alike experimentally:  A complementary accelerator is needed to understand what the SM can’t explain 4th generation SUSY technicolor

5. The International Linear Collider (ILC) • Work towards a high-precision e+e- collider begun 20 years ago • advantages: use full beam energy, tuneable and precisely known; polarised beams • synchrotron radiation prohibitive at > LEP energies  Linear Collider challenges: • can’t build up energy by circulating beams many times • to reach required luminosity, need extremely focused bunches, know their position • Stanford Linear Collider (SLC) proof of principle for linear collider concept • until 2004: three independent strands of R&D in the US, Asia and Europe: • Next Linear Collider (NLC, SLAC) design with X-band acceleration • Global Linear Collider (GLC, KEK) design with X- or C-band • TESLA (DESY) design with superconducting RF • August 2004: following consultation ICFA decided for Superconducting RF • Global Design Effort (GDE) to develop common design: International Linear Collider “warm technology” “cold technology”

6. Towards nanometer sized beams • ILC lumi requires beam size 640 nm x 6 nm • for collisions, stability of beam position also a critical issue • Final Focus Test Beam (FFTB) facility extension of SLC accelerator (1993) • established beams of 1000 nm x 50 nm

7. 2004: Decision for Superconducting RF Superconducting RF cavity International Technology Recommendation Panel: • following 6 meetings (RAL, DESY, SLAC, KEK, Caltech, Korea) in report to ICFA emphasised that both warm and cold technology had considerable strengths; to proceed further, recommended to ICFA the Superconducting RF technology – reasons: • less sensitive to ground motion, possibility of inter-bunch feedback (higher beam current?) • main linac and RF systems of comparatively lower risk • superconducting XFEL Free Electron Laser will provide prototypes and test many aspects • industrialization of many components underway • use of superconducting RF significantly reduces power consumption

8. Brian Foster

9. ILC baseline machine (2007) • beam energy: initial maximum centre of mass energy 500 GeV, upgradable to 1 TeV • tuneable: physics runs possible between 200 GeV and 500 GeV • low beam energy spread,low beamstrahlung  CM-energy of hard process well known • high luminosity: L ~ 2x1034 cm-2s-1(at least 500 fb-1 over 4 years) • beam polarisation: baseline: e- beam: 80%; possible upgrade: e+ beam polarisation > 50% • beam energy and polarisation must be measurable to 10-3 or better

10. The ILC Physics scope • Precision top physics • Understanding electroweak symmetry breaking • The precision Higgs programme: SM Higgs and beyond SM Higgs • New Physics • Dark Matter and new particle spectra • Distinguishing between possible New Physics interpretations • Determining model parameters • Beyond the TeraScale • Indirect sensitivity to higher energies through virtual effects • Extrapolation to the unification scale

11. e+e-  tt at threshold: top mass measurement • precise measurement of top mass and couplings needed for • prediction of electroweak parameters • indirect determination of Higgs mass • prediction of dark matter density • extrapolation of masses, couplings to GUT scale • understanding of flavour physics • From energy scan of tt-production threshold: determine top mass with Dmtop ~ 100 MeV, dominated by theoretical uncertainty

12. e+e-  tt at threshold: further observables • additional observables • help disentangle correlations between parameters (mt, as, Gt) • increase New Physics sensitivity • observables are for example • top momentum distribution • forward-backward asymmetry • top polarization • W decay lepton spectra • peak of top momentum distribution depends strongly on mt, not very sensitive to as disentangle correlations between mt, as in cross section

13. Precision Higgs physics • To fully establish the Higgs mechanism need to measure: • Higgs mass • absolute couplings of Higgs to Z, W, t, b, c, t , 1 – 5 % precision • total width • spin, CP • top Yukawa coupling (precision at ILC: ~ 5 %) • self-coupling (~20% precision, for 120 GeV < mH <140 GeV) • Higgs recoil mass measurement (decay-mode independent): • select di-lepton events consistent with Z  ee, mm • calculate recoil mass as • find Higgs mass from recoil mass spectrum, • precision ~ 70 MeV Z mm ILD LoI

14. Higgs couplings and spin • Higgs spin can be measured from rise of cross section near threshold • in some models same rise for spin 0 and spin 2, but different angular distributions • Precision measurement of Higgs coupling sensitive to number, shape and size of possible extra spatial dimensions mH = 120 GeV 20 fb-1 / point KEK-REPORT-2003-7 V. Barger et al., Phys Rev D49, 79 (1994)

15. Higgs branching ratios • At ILC absolute measurement of branching ratios possible • most challenging: disentangling hadronic Higgs decays • analysis performed for all ZH events • classify according to number of leptons and vis. energy • for each Z decay channel, fit b-likeness, c-likeness • simultaneous fit of Z  qq, ll, nn distributions • resulting branching ratio precision 1.6 % (bb) to 8.3% (cc) Kuhl, Desch LC-PHSM-2007-002

16. MSSM Higgs sector • Two Higgs doublets needed for electroweak symmetry breaking in MSSM • corresponds to 8 degrees of freedom, 3 of which needed for Higgs mechanism  5 physical Higgs states remaining: h, H: neutral, CP-even; A: neutral, CP-odd; H± • h detectable in entire MSSM parameter space (e+e-  hZ, e+e-  hA) • heavy Higgses visible up to √s/2  1 TeV ILC covers large part of interesting region Kiyoura et al., hep-ph/0301172

17. Higgs parameters at LHC and ILC Barger, Logan, Shaughnessy, arXiv:0902.0170

18. Connections to cosmology: dark matter • Standard Model: no Dark Matter (DM) candidate  clear indication of New Physics • examples of models with candidates: SUSY, extra dimensions, Littlest Higgs • typically dark matter candidates are: • neutral • relatively massive • absolutely stable • LHC should produce DM particles • signature: long decay chains, missing ET • Once observed need to: • precisely measure the mass of seen candidate • determine physics of the new model that leads to the WIMP • from model parameters determine what should be seen in astrophysical experiments • compare with astrophysical observations Reference Design Report, part II

19. Models with DM candidates: two examples Eur. Phys. J. C46, 43 (2006) • MSSM: • for each SM particle have DJ = ± ½ SUSY particle with same gauge quantum number & couplings • Higgs sector: h, H, A, H± • for conservation of R parity ( R = (-1)3(B-L)+2S ): • sparticles pair-produced • lightest SUSY-particle (LSP) stable • 15-20 free model parameters in constrained MSSM • Models with extra dimensions, e.g. • “Large” flat extra dimensions: SM fields localised on one brane, gravitons propagate into extra dim’s • Randall Sundrum (RS): only 1, curved extra dim. • both cases: compactified dimensions give rise to Kaluza-Klein tower of excited states for the gravitons Phys Rev Lett 84, 2080 (2000), Phys Rev D63, 075004 (2001)

20. Precision measurements of new particle spectra • To understand possible new particle spectra will measure • masses • branching ratios • cross sections • angular distributions • Advantages at ILC: tunable energy permits threshold scans; polarised initial beams important for determining spin S. Y. Choi et al., hep-ph/0612301

21. Large extra dimensions • Energy dependence of cross section sensitive to number of extra dimensions  can be determined from measurement at two centre of mass energies • spin-two nature of exchanged particle tested by azimuthal asymmetry requires both beams to be polarized (assumed: e-: 80%, e+: 60%) √s = 500 GeV 500 fb-1 G. W. Wilson, LC-PHSM-2001-010 T. G. Rizzo, JHEP 02, 008 (2003)

22. Constrained MSSM • Common SUSY reference points studied at ILC and LHC • chosen to be compatible with DM-favoured regions in constrained MSSM with all experimental and phenomenological constraints imposed • ILC can distinguish between SUSY reference points much better than LHC Phys. Lett. B565, 176 (2003) Phys. Rev. D74, 103521 (2006)

23. Possible SUSY spectrum at LHC Bechtle, Wienemann, Uhlenbrock, Desch (2009)

24. The same spectrum as seen with LHC + ILC Bechtle, Wienemann, Uhlenbrock, Desch (2009)

25. Couplings of gauge bosons to fermions • Fermion pair production sensitive to virtual effects • O(106) e+e-  ff events allow couplings to be measured with permille accuracy • virtual effects of New Physics parameterised in a model independent way in terms of contact interactions: • ILC sensitive up to scales Lij = 100 TeV • for a new Z’ boson couplings cLl and cRl can be determined from asymmetries in Z’  mm • permits distinguishing different models √s = 500 GeV 1 ab-1 S. Godfrey et al., hep-ph/0511335

26. Extrapolation to unification scale • direct measurement of as vs energy would improve extrapolation to unification scale • discrepancy between as, weak and em couplings at 1016 GeV constrains particle content at that energy hep-ph/0403133 Nucl. Phys. Proc. Suppl. 135, 107 (2004) hep-ph/0106315 hep-ex/9912051

27. Detector requirements • ILC physics and machine conditions challenging for detector systems: • Physics requires excellent jet energy resolution well beyond current state of the art requires new detector technologies and reconstruction algorithms • Higgs studies need charge-track momentum resolution better than at LEP, SLC, LHC high field magnets and low mass trackers under development • flavour and quark charge tagging (e.g. Higgs branching ratios, quark asymmetries) require new generation of vertex detectors • March 2009: three Detector Concept Groups submitted Letters of Intent • Characteristics shared by all detector concepts: • pixellated vertex detector for high-precision vertex reconstruction and tracking • sophisticated tracking systems for high tracking efficiency & excellent momentum resolution • calorimeters inside the magnet coil • high field solenoids (3.5 – 5 T), building on successful CMS solenoid • trigger-less readout to maximise physics sensitivity

28. Particle Flow • For many physics processes need to distinguish di-jets from W- and from Z-decays • To obtain a di-jet mass resolution of order corresponding to ~ 2.75 s separation between W and Z peaks need • Simulations show excellent performance to cos q ~ 0.975 √s = 1 TeV

29. Dual Readout Calorimetry • Hadron calorimeters generally suffer from signal non-linearity, non-Gaussian response • main reason: fluctuation in fraction of hadron energy that is deposited in electromagnetic shower • idea of dual readout calorimetry: • separately measure scintillation and Cerenkov signal • from these separate measurements determine the electromagnetic shower fraction on an event-by-event basis •  permits correction for fluctuations • technology developed by DREAM collaboration • extensively studied in beam tests and simulation • for ILC a combination of BGO crystals in front of a fibre calorimeter is proposed

30. Precision Tracking • Momentum resolution important for full reconstruction of events • Excellent impact parameter resolution needed for vertexing and flavour tag, goal: • High efficiency over full polar angle coverage (forward region important at ILC) TPC + silicon tracking (ILD LoI) All-silicon tracker (SiD LoI)

31. Central idea: describe tracks by probability density functions and combine them to form a vertex function encoding the topological information for a jet • Track probability functions: Gaussian profile in the plane normal to trajectory at point of closest approach p to 3D-space point r at which function is evaluated: • Vertex function: simplest form: • used to identify vertices and to determine if two vertices are resolved from each other • original ZVTOP algorithm developed by D. Jackson (SLD), NIM A 388 (1997) 247 • new C++ implementation with improvements for ILC (LCFIVertex, paper submitted to NIM A) Topological vertexing

32. Flavour Tagging • Neural networks used to distinguish • b from u, d, s and c jets • c from u, d, s and b jets • c from b jets (in some processes only b jet background) • Secondary vertex information best indication of jet-flavour LCFIVertex

33. The ILD concept • Vertex Detector: long-barrel geometry 3 double-layers OR 5 single-layers, technology tbd • SIT: 2 Si-strip-layers in barrel, FTD: pixel+strip detectors in forward region • TPC: large volume, up to 224 3D space points per track, provides dE/dx-based particle ID • SET, ETD: Si-strip detectors between TPC & ECAL and behind TPC endplate & ECAL • Particle flow calorimetry • ECAL: highly segmented, up to 30 • samples in depth, small cell size • HCAL: up to 48 samples in depth, • small cell size; two options • LumiCal, BeamCAL, LHCal: • measure luminosity, monitor beam • Superconducting Coil: 3.5 T • Iron yoke:m filter, detector, tail catcher • 676 signatories, 152 institutes, 32 countries

34. Main ILD subdetector options Mark Thomson {NB: for detailed simulation in LoI, similar to what is usual for a TDR, a “software baseline” was chosen}

35. The SiD concept • Vertex Detector: 5 cylinders, 4 endcaps on each side, technology to be decided • Main tracker: silicon strip detector, 5 barrel layers + 4 endcaps per side, sensors 15x15 cm2, • single sided, 50 mm pitch, endcaps: 2 sensors bonded for stereo angle measurement • Particle flow calorimetry: EM calorimeter: dense, highly segmented Si-W • 20 layers of 2.5 mm W + 10 layers of 5 mm W (Si: 1.25mm/layer) • HCAL: 4.5 l of stainless steel, 40 layers of steel + detector • LumCal, BeamCal: Si-W (LumCal) and • low resistivity Si or diamond (BeamCal) • Superconducting Coil: 5 T; baseline: CMS conductor, • developing advanced conductor (easier to wind) • Flux return: 11 layers of 20 cm iron • absorber for m identifier, important for shielding • Polarimeters and energy spectrometers • 246 signatories, 77 institutes, 18 countries

36. The SiD concept • All concepts were asked to provide a cost estimate as part of their LoI • SiD example shows how cost is typically distributed over the different subsystems

37. The 4th concept • Vertex Detector: SiD-design, relying on developments of R&D groups, technology tbd • Cluster timing drift chamber: ultra-low mass, He-based gas, • over 100 three-dimensional 55 mm space point per track  TPC-like pattern recognition • high-precision dual readout fibre calorimeter plus EM dual readout crystal • calorimeter: for energy measurement of hadrons, jets, electrons, photons, • missing momentum, tagging of m, t • extensively tested (e, m, p, 20 – 300 GeV) • described in 15 papers • dual solenoid: return the flux without • iron, improves m identification, • final focus and MDI advantages • 140 signatories, 33 institutes, 15 countries

38. Towards an approved project

39. Summary • The ILC is needed to understand the open questions posed by the SM and • by astrophysical observations. • It will go far beyond the LHC in the high precision with which it allows exploration • of new phenomena at energies up to 1 TeV (directly) and up to 100 TeV (indirectly). • ILC R&D both for the accelerator and for the detectors is far advanced • and strongly backed by the Particle Physics community. • It is regularly reviewed internally and externally and an important part of the • Particle Physics roadmap. • Further information: • ILC Reference Design Report (RDR, 2007): http://www.linearcollider.org/cms/?pid=1000437 • ILC Detector Concept LoIs (2009): http://www.linearcollider.org/cms/?pid=1000472

40. Additional Material

41. ILC baseline design parameters (at √s = 500 GeV)

42. Thomas Teubner

43. Constrained MSSM

44. The case for polarisation of BOTH beams

46. ILC Reference Design Report, Vol. 4: Detectors

47. Beam bunch structure at ILC 337 ns 0.2 s 2820x 0.95 ms Multiple collisions Data Acquisition • ILC precision likely to require ~ 10 times as many readout channels than at LHC • ILC: pulsed operation • Bursts of collisions at 3 MHz for ~1 ms, • followed by 200 ms quiet period • Integrated collision rate 15 kHz moderate • and comparable to LHC event building rate • DAQ system: • Dead time free pipeline of 1 ms • No hardware trigger • Front-end pipeline readout within 200 ms • Event selection by software • Front end needs to perform zero suppression and data suppression

48. Cluster-timing drift chamber • record drift times of all individual ionization electrons collected on sense wires • due to passage of ionizing particle through active gaseous medium • particular attention to materials used, especially gas mixture •  momentum resolution uncertainty from multiple Coulomb scattering minimized • mechanical design based on KLOE • digitized pulse shape from cosmic • 2 cm radius, 30 cm length drift tube • gas: 90% He, 10% isobutane • trigger: plastic scintillator telescope • 8-bit, 4GHz sampling oscilloscope Data: CluCou;“4th” LoI