1. WIN'05, June 7 2005A. Klier - Muon Collider Physics1 Physics at a Future Muon Collider Amit Klier University of California, Riverside WIN’05 – Delphi, Greece – June 2005

2. WIN'05, June 7 2005 A. Klier - Muon Collider Physics2 OUTLINE Why muon colliders? –Advantages –Problems Some physics –Light Higgs Factory –Heavy Higgs Toward a muon collider –Recent advances in 6-D Cooling R&D

3. WIN'05, June 7 2005 A. Klier - Muon Collider Physics3 Why Muons? As fundamental as electrons … –Unlike p, p, all the collision energy is useful … and 200 times as heavy Sync. radiation energy loss is 2 billion times less: –Compact storage rings up to a few TeV –Very good energy resolution Coupling to the Higgs boson is 40,000 times greater: –Produce Higgs Bosons via the s-channel

4. WIN'05, June 7 2005 A. Klier - Muon Collider Physics4 Muon Colliders, Other Machines

5. WIN'05, June 7 2005 A. Klier - Muon Collider Physics5 The Problem with Muons They DECAY: muon lifetime = 2.2  s Everything has to be fast, specifically: –Cooling ( ionization ) –Acceleration( RLA, FFAG ) Muon Collider detectors need shielding against  ’ s from decay electrons Decay neutrinos can be harmful at E  ≳ 4 TeV (they can be useful for a Neutrino Factory, but that ’ s for another talk)

6. WIN'05, June 7 2005 A. Klier - Muon Collider Physics6 Some Physics

7. WIN'05, June 7 2005 A. Klier - Muon Collider Physics7 Light Higgs Boson Precision EW data seem to favor light SM Higgs Boson So does SUSY (from theory)

8. WIN'05, June 7 2005 A. Klier - Muon Collider Physics8 SM (or SM-like) Higgs Factory Higgs Boson width – few MeV for m h SM <160 GeV Fine scan for  E ≲  h SM Use spin precession for in situ energy determination to ~ 1 ppm Luminosity is compromised by resolution, e.g. R=0.003%L year ~ 0.1 fb -1 R=0.01%L year ~ 0.22 fb -1 R=0.1%L year ~ 1.0 fb -1 ( R ≡ 2  E/E )

9. WIN'05, June 7 2005 A. Klier - Muon Collider Physics9 Precision Measurements For a SM-like ~110-GeV Higgs Boson, a muon collider Higgs Factory can measure the mass to an uncertainty of ~10 -6 with L=0.2 fb -1 (compared to ~10 -4 at a 500 GeV, 500 fb -1 LC and ~10 -3 at the LHC) Only in the s-channel  h can be measured directly (otherwise need accurate WW * rate measurement, difficult at m h <120 GeV ) Precise measurement of the cross section of  +  -  h 0  bb – independent of m b

10. WIN'05, June 7 2005 A. Klier - Muon Collider Physics10 Heavy Higgs Bosons SUSY H 0 and A 0 may be observed at the LHC Light h 0 indicate high tan , which implies greater H 0 - A 0 mass degeneracy Muon g-2 results also favor high tan  values ( ≳ 8 ), with similar consequences An “intermediate energy” (few hundred GeV) muon collider can be used to scan the the heavy Higgs mass range & separate the two

11. WIN'05, June 7 2005 A. Klier - Muon Collider Physics11 Separating the Heavy Higgses

12. WIN'05, June 7 2005 A. Klier - Muon Collider Physics12 Another Scenario For some values of tan  ( ~8-10 ) and m A ( ≳ 250 GeV ) LHC/LC may not be able to observe H 0 or A 0 A muon collider may be needed to discover the heavy Higgs in this region

13. WIN'05, June 7 2005 A. Klier - Muon Collider Physics13 CP Violation in the Higgs Sector Polarized muon beams can be used to measure CP violation in the Higgs sector

14. WIN'05, June 7 2005 A. Klier - Muon Collider Physics14 R&D Advances

15. WIN'05, June 7 2005 A. Klier - Muon Collider Physics15 Toward a Muon Collider The physics part of this talk is mostly based on Snowmass 2001 (and earlier) results. That ’ s “ old news ” Muon Collaboration attention has shifted to the (seemingly more feasible, and probably as important) neutrino factory This shouldn ’ t have affected the Muon Collider R&D effort … Indeed, impressive advances were made, especially in simulating 6-D cooling

16. WIN'05, June 7 2005 A. Klier - Muon Collider Physics16 How To Build a Muon Collider p ±  ±±  ± targetproton driver (a few MW) proton linac pion decay muon cooling muon acceleration (up to 0.1 - 3 TeV) detector storage ring ++ --

17. WIN'05, June 7 2005 A. Klier - Muon Collider Physics17 How Much Cooling is Needed Beam reduction of about  100 needed in each transverse and in the longitudinal direction ( ~10 6 6-D cooling) compared with muons from pion decay Light Higgs Factory

18. WIN'05, June 7 2005 A. Klier - Muon Collider Physics18 Ionization cooling: Fast, but cools only in transverse directions (sufficient for factory) 6-D cooling via emittance exchange: Repeated cooling/ emittance exchange cools  beam in all six phase-space dimensions 6-D Cooling absorber RF absorber  large angular spread small angular spread

19. WIN'05, June 7 2005 A. Klier - Muon Collider Physics19 Ring Coolers First suggested by V.Balbekov in 2001 6-D cooling – about  50 However: Problems trying to introduce realistic magnetic fields Injection/extraction very difficult and affects performance badly

20. WIN'05, June 7 2005 A. Klier - Muon Collider Physics20 The RFOFO Ring Suggested by R.Palmer in 2002 6-D cooling ~  300 Simulations work with realistic magnetic field Injection/extraction still a problem, but performance is less affected (still cools by about  200 )

21. WIN'05, June 7 2005 A. Klier - Muon Collider Physics21 Gas-Filled Cooling Ring The idea: use the dipole volume itself as a “ wedge absorber ” by filling it with high-pressure H 2 gas Small Dipole Ring – suggested by A.Garren, H.Kirk in 2004 Can be used to demonstrate 6D cooling experimentally: moderate performance, but low cost (no SC … ) 1.6 m

22. WIN'05, June 7 2005 A. Klier - Muon Collider Physics22 Further Cooling – Lithium Lens Recently simulated transverse cooling down to ~0.3 mm But longitudinal emittance blows up Latest development use bent Lithium Lenses ( “ Li ring ” )

23. WIN'05, June 7 2005 A. Klier - Muon Collider Physics23 Helical Cooling Channel Suggested by Y.Derbenev/Muons Inc. High-pressure- H 2 -filled helical dipole & RF cavities in a solenoid Simulated cooling:  300 Advantage: no need for injection/kicker Challenges: high dipole fields, rather complicated

24. WIN'05, June 7 2005 A. Klier - Muon Collider Physics24 Parametric Resonance Cooling Suggested by Y.Derbenev & Muons Inc. Potential cooling  10 after the HCC/ Ring Cooler

25. WIN'05, June 7 2005 A. Klier - Muon Collider Physics25 Reversed Emittance Exchange For TeV-scale muon colliders, longitudinal cooling is sufficient, but more transverse cooling is needed Reverse the emittance exchange process

26. WIN'05, June 7 2005 A. Klier - Muon Collider Physics26 Conclusions Muon colliders can contribute to Higgs physics in unique ways, complement LHC/LC Being compact, muon colliders may eventually cost less than the “ conventional ” ones (LHC/LC), but are extremely challenging A lot of progress in 6-D cooling simulations Greater effort is needed to put everything together, demonstrate 6-D cooling in real life