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Polarized positrons at the ILC: physics goal and source requirements

Polarized positrons at the ILC: physics goal and source requirements. EuCARD Workshop “Spin optimization at lepton accelerators” 13 February 2014 Sabine Riemann, DESY Zeuthen. Physics goal of future colliders. Precision measurements Higgs measurements ee  tt

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Polarized positrons at the ILC: physics goal and source requirements

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  1. Polarized positrons at the ILC: physics goal and source requirements EuCARD Workshop “Spin optimization at lepton accelerators” 13 February 2014 Sabine Riemann, DESY Zeuthen

  2. Physics goal of future colliders Precision measurements Higgs measurements ee  tt Top quark mass and coupling ee  WW Gauge couplings Fermion pair production,  Sensitivity to deviations from SM disentangle new phenomena beyond SM discovered at LHC new physics SUSY (?) new gauge bosons, extra dim, Dark matter … Precision and physics potential improves with polarization (e- and e+)  Status of ILC polarized e+ source S. Riemann

  3. Outline EuCARD Workshop, Mainz 2014 3 • ILC positron source • e+ production • Undulator based source • Helical undulator • Target • Optical matching device (flux concentrator) • Source parameters for Ecm≥ 240GeV e+ polarization • Spin flipper • GigaZ • Summary

  4. ILC layout (TDR) 2013 Ready for construction… Positron source not to scale • Requirements: • Long bunch trains: ~1ms • 1312 (2625) bunches per train, rep rate 5Hz • 2×1010 particles/bunch • Small emittance • Beam polarizationP(e-) > 80% • P(e+) ≥ 30% 31 km EuCARD Workshop, Mainz 2014 S. Riemann

  5. Production of Positrons Problems g: Large heat load in target e-: Huge heat load in target Courtesy: K. Floettmann • Generation of (polarized) photons • - Compton backscattering of circ. pol. laser light off an e- beam • - Undulator passed by e- beam • helical vs. planar undulator: • -- helical undulator gives ~1.5…2 higher g yield for the parameters • of interest (See also Mikhailichenko, CLNS 04/1894) • -- circular polarized photons  long. Polarized e+ • -- sign of polarization sign is determined by undulator, i.e. direction of the • helical field 5 S. Riemann EuCARD Workshop, Mainz 2014

  6. ILC Undulator based e+ source EuCARD Workshop, Mainz 2014 S. Riemann

  7. ILC Positron Source Positron source is located at the end of the electron linac required positron yield Y = 1.5 e+/e- Superconducting helical undulator – 231m maximum active length  positron beam is polarized Photon-Collimator to increase e+ pol Removes part of photon beam with lower polarization e+ Production Target, 400m downstream the undulator Positron Capture: OMD (Optical Matching Device) Pulsed flux concentrator 400m EuCARD Workshop, Mainz 2014 7 S. Riemann

  8. Undulator Parameters • Photon energy (cut-off first harmonic) and undulator K value • Number of photons • Increase intensity of g beam by longer undulator  Y = 1.5 e+/e- ILC requirement • Upper half of energy spectrum is emitted in cone • Smaller beam spot for higher Ee • Photon spectrum • Higher polarization with g collimation lu = undulator period EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  9. ILC Undulator Parameters Undulator windings: NbTi Positron yield and polarization vs. drive e- beam energy (und. Length Lu=147m, w/o photon collimation)  P ≈ 30% EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  10. ILC Undulator Prototype • sc undulator  high peak field • 4m long prototype built at Daresbury Lab (UK): • Two 1.75m long undulators (11.5mm period) • RAL team has shown that both undulators have very high field quality • Field on axis 0.86 T (K=0.92) measured at 214 A • ILC specification  now show stopper identified More details see J. Clarke, BAW-2 Meeting, SLAC Jan 2011, Ivanyushenko, POSIPOL2013 Workshop EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  11. e+ source is located at end of the linac  polarization and yield are strongly coupled to the electron beam energy • Optimum undulator parameters (K, undulator length) depend on Ee • With higher energies smaller beam photon beam spot size on target  high polarization is difficult to achieve for high energies (heat load on target and photon collimator) ILC TDR EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  12. Positron Target • Material: Titanium alloy Ti-6%Al-4%V Thickness: 0.4 X0 (1.4 cm) • Incident photon spot size on target: s ~ 2 mm (rms) (Ee- = 150GeV) ~ 1.2 mm (Ee- = 250GeV) • Power deposition in target: TDR 5-7% (~4kW) small beam size  high peak energy density • spinning wheel to avoid damage due to high energy deposition density • 2000 r.p.m. (100m/s) • Diameter: 1m • Wheel is in vacuum • water-cooled • Potential problems • Stress waves due to cyclic heat load  target lifetime • High peak energy deposition • Eddy currents • rotating vacuum seals to be confirmed suitable (design and prototyping is ~ongoing) EuCARD Workshop, Mainz 2014 S. Riemann

  13. Target ‘risk’ issues and improvements ‘risk’ issues • Limited lifetime of vacuum seal (2000rpm) • LLNL prototype: • few weeks with vacuum spikes • No further experiments due to lack of funding • No tests yet with water cooling • No radiation damage tests Potential improvements: • spinning target with lower speed (1000rpm instead 2000rpm) • New type of sealing • Differential pumping • better cooling • Alternative target design considerations EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  14. Optical matching device • Pulsed flux concentrator EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann S. Riemann

  15. Pulsed Flux Concentrator Pulsed flux concentrator: capture efficiency to ~25% (quarter wave transformer: e ~ 15%) - low field on target (low eddy current) - high peak field (≥3T), 1ms flat top Design: LLNL J. Gronberg prototype test: 3.2 T peak field possible EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  16. Flux concentrator • Full field with 1ms flat top has been demonstrated • Still to be done: • full average power operation over extended period including cooling J. Gronberg, LLNL EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  17. ILC e+ source parameters (TDR) EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  18. Ecm = 240 GeV Higgs-Boson measurements EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  19. ILC as Higgs Factory Ecm = 240 GeV: mH = 126 GeV Higgs Strahlung (HZ) (dominating) WW Fusion HZ EuCARD Workshop, Mainz 2014 S. Riemann

  20. Higgs Mass and Higgs Coupling to the Z Select events: e+e-  ZH and Z mm,ee Fit to the spectrum of recoil mass of both leptons  Higgs mass and coupling ILC RDR Peak position Higgs mass Peak height Model independent measurement!! Higher lumi improves precision Dm < 100 MeV sZH ~ gZH2 EuCARD Workshop, Mainz 2014 S. Riemann

  21. L (R) Higgs Strahlung dominates e+R e-L e+L e-R e+L e-L e+R e-R With e+ and e- polarization ‘ineffective’ processes are suppressed R (L) •  ZH • ZH •  ZH • ZH EuCARD Workshop, Mainz 2014 S. Riemann

  22. Higgs Strahlung eff. luminosity e+R e-L ZH e+L e-R ZH e+L e-L ZH e+R e-R ZH P(e-,e+) = (±80%; ∓30%)  24% lumi gain  DsZH reduced by 11% WW Fusion e+R e-L nnH e+L e-R nnH e+L e-L nnH e+R e-R nnH L (R) s = 0 for 100% polarized beams With e+ and e- pol. suppression of ‘ineffective’ processes R (L) for P(e+)=+1 s(e+R e-L nnH) enhanced by factor 2 L R EuCARD Workshop, Mainz 2014 S. Riemann

  23. ILC as Higgs factory Ecm = 240 GeV • For Ee < 150 GeV e+ yield decreases below 1.5e+/e- (low g energy  only ‘small’ shower0  TDR: “10 Hz scheme” • Alternating with e- beam for physics (Ee~120GeV) an e- beam with Ee=150GeV passes undulator generate g for e+ production • use almost full length of undulator and optimize system see: next talk, and A. Ushakov, LC-REP-2013-019 10Hz scheme: e- beam (150GeV) to dump EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  24. ILC undulator @ low electron beam energies (120GeV) use almost full length of undulator and optimize system(Ushakov, LC-REP-2013-019)  see next talk by Andriy Ushakov EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  25. Ecm = 350 GeV Top-quark measurements  High positron polarization desired EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  26. Top quark physics @ LC heaviest quark (as heavy as gold atom), pointlike Extremely unstable (t ~ 4×10-25s) Decay of top-quark before hadronization Top-polarization gets preserved to decay (similar to t-lepton)  The ‘pure’ top quark can be studied Top mass and coupling are important for quantum effects affecting many observables Top quark coupling as test of SM and physics beyond  top quark coupling, spin, spin correlations are observable by measuring polarization and LR asymmetries with high precision Need high degree of polarization e+ polarization highly desired (see i.e., Grote, Koerner, arXiv:1112.0908) Need precise measurement of polarization EuCARD Workshop, Mainz 2014 S. Riemann

  27. Photon collimator parameters for polarization upgrade 60% e+ polarization at 350GeV  ~60% of photon beam power absorbed in collimator  high load on the collimator materials ILC TDR 350 59 60.4 EuCARD Workshop, Mainz 2014 S. Riemann

  28. Photon beam collimation • Increase of e+ polarization using photon collimator • Details see talk of Friedrich Staufenbiel • Collimator parameters depend on energy • Multistage collimator (3 stages with each pyr. C, Ti, Fe)  flexible design for energies 120 GeV ≤ Ee- ≤ 250GeV Ee-≤150 GeV Pe+ = 50% Ee- = 175 GeV, Ecm = 350 GeV Pe+≈ 60% EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  29. Ecm≥ 500 GeVFull spectrum of physics processesBest flexibility with polarized e+ and polarized e- beam -- Polarization as high as possible and reasonable e+ polarization improves substantially identification of models in case of deviations from SM -- Physics with transversely polarized beams; only possible if both beams are polarized EuCARD Workshop, Mainz 2014 S. Riemann

  30. Photon collimator parameters for polarization upgrade 60% e+ polarization at 500GeV  collimator absorbs ~70% of photon beam power  50% e+ polarization should be ‘sufficient’ ILC TDR 500 50 59 52.3 70.1 EuCARD Workshop, Mainz 2014 S. Riemann

  31. Photon beam collimation • Increase of e+ polarization using photon collimator • Details see talk of Friedrich Staufenbiel • Collimator parameters depend on energy • Multistage collimator (3 stages with each pyr. C, Ti, Fe) Ee- = 250 GeV Pe+≈ 50% EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  32. TeV upgrade scenarios Goal • A reasonable scheme for the 1 TeV option without major impact on the ILC configuration. Assumptions • Drive beam energy: 500 GeV • Target: 0.4 X0 Ti • Drift from end of undulator to target: 400m • OMD: FC 1st approach (Gai, Liu) • Longer undulator period, lu = 4.3cm • K = 1 (B = 0.25T) P = 20% • Polarization upgrade requires small collimator iris (≤0.85mm) 2nd approach (see next talk by Andriy) • lu = 4.3cm • K ≈2, P ≈ 50% W. Gai, W. Liu OMD = QWT lu(cm) EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  33. Helicity reversal – rapid or slow? EuCARD Workshop, Mainz 2014 S. Riemann

  34. Precision Measurements with Pe+> 0 One precision key observable: Left-right polarization asymmetry for measurements with equal luminosities for (- +) and (+ -) helicity • Effective polarization • Peff is larger than e- polarization • error propagation  D Peff is substantially smaller than the uncertainty of e- beam polarization, dP • Higher effective luminosity  Smaller statistical error =1/Peff EuCARD Workshop, Mainz 2014 S. Riemann

  35. Helicity reversal • Net polarization depends on direction of undulator windings  Need facility to reverse e+ helicity • It has to be synchronous with reversal of e- polarization to achieve: • enhanced luminosity • Cancellation of time-dependent effects  small systematic errors EuCARD Workshop, Mainz 2014 S. Riemann

  36. Left-Right Asymmetry ALR for equal luminosities LLR = LRL • Essential for ALR measurement: • luminosity and polarization have to be helicity-symmetric: LLR = LRL PL = -PR • Achieved by rapid helicity reversal (SLC: bunch-to-bunch) • small differences have to be known and corrected AL = asymmetry in luminosity for LR and RL APeff = asymmetry in LR and RL polarization ALR< 1  AL is more important than APeff Remember SLC: AL, dAL ~ 10-4 AP ,dAP ~ few 10-3  Small AL, dAL , APeff ,dAPeff required also for ILC • Slow helicity reversal: Despite of very precise monitoring of relative intensities and polarizations for LR and RL states, systematic uncertainties will be larger for most observables (could be even larger than without e+ polarization) EuCARD Workshop, Mainz 2014 S. Riemann

  37. Spin flipper • Net polarization depends on direction of undulator windings • Reversal of e+ helicity necessary • It has to be synchronous with reversal of e- polarization to achieve • enhanced luminosity • Cancellation of time-dependent effects  small systematic errors • Helicity reversal requires spin flipper (5Hz)  Spin rotation + flipper (2 parallel lines) EuCARD Workshop, Mainz 2014 S. Riemann

  38. Spin flipper (see Gudi’s talk, and L. Malysheva, …..) • beam is kicked into one of two identical parallel transport lines to rotate the spin • Horizontal bends rotate the spin by 3 × 90° from the longitudinal to the transverse horizontal direction. • In each of the two symmetric branches a 5m long solenoid with an integrated field of 26.2Tm aligns the spins parallel or anti-parallel to the B field in the damping ring. • Both lines are merged using horizontal bends and matched to the PLTR lattice. • The length of the splitter/flipper section section ~26m; horizontal offset of 0.54m for each branch EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  39. GigaZ • Running again at the Z resonance (LEP, SLC) • High statistics: 109 Z decays/few months • With polarized e+ and e- beamsthe left-right asymmetry ALR and the effective polarization Peff can be determined simultaneously with highest precision  relative precision of less than 5x10-5 can be achieved for the effective weak mixing angle, sin2qWeff, 10x better than LEP/SLD  Together with other LC precision measurements at higher energies (i.e. top-quark mass) theoretical predictions can be tested and physics models beyond the Standard Model distinguished EuCARD Workshop, Mainz 2014 S. Riemann

  40. Blondel scheme • Can perform 4 independent measurements (s-channel) • determination of Pe+ and Pe-, su and ALR simultaneously (ALR≠0); for Pe(+) = Pe(-): • need polarimeters at IP for measuring polarization differences between + and – helicity states • Have to understand correlation between Pe(+) = Pe(-) =0 (SM) if both beams 100% polarized EuCARD Workshop, Mainz 2014 S. Riemann

  41. Summary • Weak interaction is parity violating  Polarized beam(s) are mandatory for future precision physics at high energy e+e- colliders • ILC: helical undulator  P(e+) ≥ 30%; useful for physics at all energies • Higher effective luminosity, enhancement of interesting processes • new physics signals can be fixed and interpreted with substantially higher precision • No problem to achieve P(e+) ~60% at Ecm≈350GeV. But e+ source parameters and P(e+) depend on energy • High e+ polarization allows polarization measurement using annihilation data • no design show stoppers identified for a polarized e+ source; however, R&D and prototyping still necessary EuCARD Workshop, Mainz 2014 S. Riemann

  42. Backup EuCARD Workshop, Mainz 2014 S. Riemann

  43. Target design improvements • Lower rotation speed 2000rpm  1000rpm? • Friedrich Staufenbiel (POSIPOL13, LCWS13): • Simulation of dynamic response to cyclic heat load on target (ANSYS)  no shock waves • Inertia and torque calculation and simulation • Torque |t| = m r2w2 • Lower w increases energy deposition density in target  Heat load with lower w? Beam induced deformation reaction Reaction force EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  44. Dynamical stress of the Ti-wheel Ti-alloy fatigue stress limit (to be checked and verified) F. Staufenbiel, LCWS2013  Reduction to ~1000rpm seems possible EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  45. W. Gai (ANL) Target system alternative Bullet target system EuCARD Workshop, Mainz 2014

  46. Rail gun target • Braking • Eddy current braking • Magnetic braking with or without external power source • Cooling • Conduction cooling in the recycling line • Turnarounds of bullets  ~60s cooling time • Details require simulation taking into account non-uniform energy deposition • Estimate: using a 10oC cooling agent outside on bottom of recycling line, 200oC can be cooled to 25oC within 46s Further studies needed but it seems feasible W. Gai EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

  47. EuCARD Workshop, Mainz 2014 12/19/2019S. Riemann

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