MUON SUPERCOLLIDERS LECTURE

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MUON SUPERCOLLIDERSLECTURE 1Advanced Study
Institute on Techniques and Concepts of High
Energy PhysicsSt. Croix, US Virgin Islands
June 13-24, 2002

• Gail G. Hanson
• University of California, Riverside

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OUTLINE OF LECTURES

• Lecture 1
• Introduction and Overview
• Lecture 2
• Neutrino Factories
• Lecture 3
• Muon Colliders
• Experimental Demonstration of Muon Cooling

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WHY MUON COLLIDERS?

• Muons are fundamental particles, so same
  advantage as ee- colliders
• ? Energy of interaction is full energy of
  particle, not of constituent quarks or gluons
  (factor 10)
• Synchrotron radiation by muons is less than for
  electrons by factor of (me/mm)4 6 ?10-10
• ? Energy lost by synchrotron radiation must be
  put back
• by rf power (cost of power for operation)
• ? Muon beam can have narrow energy spread
  (10-5)
• ? High energy collider can be much smaller!

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COMPARISON OF HIGH ENERGY COLLIDERS
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WHY MUON COLLIDERS? (Continued)
S-CHANNEL HIGGS PRODUCTION

• The Higgs boson couples to mass, so cross
  section at s-channel Higgs pole is very large
  (Fig.)
• ? Small beam energy spread can allow measurement
  of mH to few hundred keV
• ? Direct measurement of Higgs width GH to 1
  MeV
• ? A Higgs Factory!

(From T. Han, talk at FNAL, May 22, 1998)
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LHC SENSITIVITY FOR DISCOVERY OF MSSM HIGGS
Muon collider?
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POSSIBLE HIGGS FACTORY SCHEMATIC

• Ring Cooler Higgs Factory
• One of the most crucial RD issues for a muon
  collider is cooling the muons - making the beam
  smaller in 6D phase space
• Ring coolers will be discussed in coming
  lectures

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WHY MUON COLLIDERS?

• Muons decay!
• A muon storage ring can produce 1019 to 1021 muon
  decays per year
• ? The stored muons can have energy 20-50 GeV
• ? The stored muons can be polarized
• ? There is no comparable source of electron
  neutrinos and antineutrinos
• ? Intense beams of neutrinos can be produced to
  study neutrino oscillations and possible CP
  violation
• ? A Neutrino Factory!

or
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NEUTRINO FACTORY FEASIBILITY STUDIES

• Two detailed feasibility studies for neutrino
  factories have been carried out
• ? Feasibility Study-I, based at Fermilab
  (1999-2000)
• ? Feasibility Study-II, based at Brookhaven
  National Lab (BNL) (2000-2001)
• Both feasibility studies were carried out in some
  detail, with simulations, and showed that either
  site was suitable for a Neutrino Factory
• Many of the components of a Neutrino Factory are
  also applicable to a Muon Collider

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POSSIBLE NEUTRINO FACTORY SCHEMATIC
Schematic of a Neutrino Factory - Study II Version
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COMPONENTS OF A NEUTRINO FACTORY

• Proton Driver
• Source of 1-4 MW of protons
• Target and Capture
• High-power proton beam interacts with a target
  (a liquid mercury jet is being tested) to produce
  pions, which then decay to muons. The target is
  immersed in a 20-T solenoidal field to capture
  the pions.
• Decay and Phase Rotation
• The energy spread of the muons from pion decay
  is reduced
• using properly phased acceleration in induction
  linacs and superconducting solenoidal focusing to
  contain the muons. A mini-cooling absorber
  section is included to reduce the emittance.

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COMPONENTS OF A NEUTRINO FACTORY (Continued)

• Bunching and Cooling
• A solenoidal focusing channel, with
  high-gradient rf cavities and liquid hydrogen
  absorbers, that bunches the 250 MeV momentum
  muons into 201.25-MHz rf buckets and reduces
  their transverse emittance from 12 mmrad to 2.7
  mmrad
• Acceleration
• A superconducting linear accelerator (linac)
  with solenoidal focusing to raise the beam energy
  to 2.48 GeV, followed by a four-pass
  superconducting recirculating linac (RLA) to
  raise the energy to 20 GeV. A second RLA could
  raise the energy further to 50 GeV.

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COMPONENTS OF A NEUTRINO FACTORY (Continued)

• Storage Ring
• A compact racetrack-shaped superconducting
  storage ring
• In which about 35 of the muons decay toward a
  detector located about 3000 km from the ring

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NEUTRINO FACTORY PERFORMANCE

• Feasibility Study 1 and Feasibility Study 2 muon
  decays in straight section per 107 s vs. muon
  energy
• With 50 kT detector and 4 MW
• Measure sin2(2q13)10-3
• Determine sign of
• Measure CP violation

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WHY MUON COLLIDERS? (Continued)

• Physics at the front end of a neutrino factory or
  muon collider

• Stopped or slow intense muon beam physics
• - N ? e - N, m ? e g, m? e e-e
• Muon anomalous magnetic moment (g - 2) and muon
  electric dipole moment
• mp scattering
• Rare K decay measurements
• Neutrino scattering experiments
• Neutrino flavor violation physics

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WHAT IS THE PROBLEM?

• So why havent we already built a muon storage
  ring or collider?
• Muons decay!
• tm 2.2 ? 10-6 s
• But high energy muons can live 1000 turns in a
  storage ring (time dilation)

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HISTORY

• Muon colliders were first proposed by G.I. Budker
  and A.N. Skrinsky in the late 1960s and early
  1970s
• The necessary concept of ionization cooling was
  developed by Skrinsky and V.V. Parkhomchuk and
  expanded by D. Neuffer in the early 1980s and
  later by R.B. Palmer
• A Muon Collider Collaboration was formed in 1995
• The idea of a muon storage ring neutrino factory
  was added in 1999, so the collaboration was
  renamed the Neutrino Factory and Muon Collider
  Collaboration

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COOLING

• A beam is described in 6-dimensional phase space
• x, y, t, px, py, E or x, y, t, x, y, E
• The area of the beam ellipse in 6-dimensional
  phase space is called the emittance. Emittance
  has several definitions. For example
• Normalized transverse emittance ex,y bgsqx,y
  sx,y
• Normalized longitudinal emittance ez bgsdp/p
  sz
• 6-dimensional emittance e6 exeyez
• Decreasing the emittance is called cooling

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COOLING (Continued)

• Types of cooling
• Stochastic cooling
• Laser cooling
• Electron cooling
• Synchrotron radiation cooling
• Ionization cooling
• The first four types of cooling take too long for
  muon beams, which have to be cooled before they
  decay

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IONIZATION COOLING
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REFERENCES

• Charles M. Ankenbrandt et al. (Muon Collider
  Collaboration), Phys. Rev. ST Accel. Beams 2,
  081001 (1999).
• Proceedings of the Fermilab Workshop on Physics
  at a Muon Collider and the Front End of a Muon
  Collider, S. Geer, R. Raja eds., November 1997,
  AIP.
• N. Holtkamp and D. Finley, eds., A Feasibility
  Study of a Neutrino Source Based on a Muon
  Storage Ring, Fermilab-Pub-00/108-E (2000)
  http//www.fnal.gov/projects/muon_collider/nu-fact
  ory/nu-factory.html
• S. Ozaki, R. Palmer, M.S. Zisman, J. Gallardo,
  eds., Feasibility Study-II of a Muon-Based
  Neutrino Source, BNL-52623, June 2001
  http//www.cap.bnl.gov/mumu/studyii/FS2-report.htm
  l
• D.B. Cline and G.G. Hanson, A Muon Collider as
  a Higgs Factory, contribution to Snowmass 2001.