Physics at a Future Muon Collider

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Physics at a FutureMuon Collider

• Amit Klier
• University of California, Riverside
• WIN05 Delphi, Greece June 2005

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OUTLINE

• Why muon colliders?
• Advantages
• Problems
• Some physics
• Light Higgs Factory
• Heavy Higgs
• Toward a muon collider
• Recent advances in 6-D Cooling RD

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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

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Muon Colliders, Other Machines
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The Problem with Muons

• They DECAY muon lifetime 2.2 ms
• Everything has to be fast, specifically
• Cooling (ionization)
• Acceleration (RLA, FFAG)
• Muon Collider detectors need shielding against
  gs from decay electrons
• Decay neutrinos can be harmful at Emm?4 TeV
• (they can be useful for a Neutrino Factory, but
  thats for another talk)

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Some Physics
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Light Higgs Boson

• Precision EW data seem to favor light SM Higgs
  Boson
• So does SUSY
• (from theory)

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SM (or SM-like) Higgs Factory

• Higgs Boson width few MeV for mhSMlt160 GeV
• Fine scan for DE ? G hSM
• Use spin precession for in situ energy
  determination to 1 ppm
• Luminosity is compromised by resolution, e.g.
• R0.003 Lyear 0.1 fb-1
• R0.01 Lyear 0.22 fb-1
• R0.1 Lyear 1.0 fb-1
• ( R2DE/E )

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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 L0.2 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 Gh can be measured directly
  (otherwise need accurate WW rate measurement,
  difficult at mhlt120 GeV)
• Precise measurement of the cross section of
  mm-?h0?bb independent of mb

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Heavy Higgs Bosons

• SUSY H0 and A0 may be observed at the LHC
• Light h0 indicate high tanb, which implies
  greater H0-A0 mass degeneracy
• Muon g-2 results also favor high tanb 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

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Separating the Heavy Higgses
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Another Scenario

• For some values of tanb (8-10) and mA (?250 GeV)
  LHC/LC may not be able to observe H0 or A0
• A muon collider may be needed to discover the
  heavy Higgs in this region

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CP Violation in the Higgs Sector

• Polarized muon beams can be used to measure CP
  violation in the Higgs sector

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RD Advances
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Toward a Muon Collider

• The physics part of this talk is mostly based on
  Snowmass 2001 (and earlier) results. Thats old
  news
• Muon Collaboration attention has shifted to the
  (seemingly more feasible, and probably as
  important) neutrino factory
• This shouldnt have affected the Muon Collider
  RD effort
• Indeed, impressive advances were made, especially
  in simulating 6-D cooling

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How To Build a Muon Collider
?
p
? ? ?
?-
target
proton driver (a few MW)
proton linac
pion decay
muon cooling
muon acceleration (up to 0.1 - 3 TeV)
storage ring
detector
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How Much Cooling is Needed
Light Higgs Factory
Beam reduction of about ?100 needed in each
transverse and in the longitudinal direction
(106 6-D cooling) compared with muons from pion
decay
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6-D Cooling
absorber
absorber

• Ionization cooling
• Fast, but cools only in
• transverse directions
• (sufficient for n factory)
• 6-D cooling via emittance exchange
• Repeated cooling/
• emittance exchange
• cools m beam in all six
• phase-space dimensions

RF
RF
?
large angular spread
small angular spread
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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

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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)

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Gas-Filled Cooling Ring

• The idea use the dipole volume itself as a
  wedge absorber by filling it with high-pressure
  H2 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
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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)

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Helical Cooling Channel

• Suggested by Y.Derbenev/Muons Inc.
• High-pressure-H2-filled helical dipole RF
  cavities in a solenoid
• Simulated cooling ?300
• Advantage no need for injection/kicker
• Challenges high dipole fields, rather complicated

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Parametric Resonance Cooling

• Suggested by Y.Derbenev Muons Inc.
• Potential cooling ?10 after the HCC/ Ring Cooler

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Reversed Emittance Exchange

• For TeV-scale muon colliders, longitudinal
  cooling is sufficient, but more transverse
  cooling is needed
• Reverse the emittance exchange process

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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