Muon Beams for Particle Physics Ajit Kurup Winter Seminar March 2010.

Muon Beams

for Particle Physics

Ajit Kurup

Winter SeminarMarch 2010

Winter Seminar March 2010

Ajit Kurup

Muon Beams for Particle Physics

Introduction• “Muon Beams for Particle Physics” means

– Accelerator challenges for muon to electron conversion experiments.

• Brief introduction to particle physics.

• Talk about proposed muon to electron conversion experiments.– Concentrate on COMET and PRISM.

• Design and technology issues.

• Some results from 6-cell PRISM test ring.

• Summary and future plans.


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The Big Picture• Standard Model of particle physics


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The Bigger Picture• We know the SM is at best incomplete.

– Does not include gravity.– Certain predictions diverge with increasing energy.

• Neutrinos in the SM are massless but observation of neutrino oscillations is direct evidence that neutrinos have mass.

– First observation from Super Kamiokande

• Possibility of Charged Lepton Flavour Violation (Lepton flavour number is not conserved). - e- - e- e+ e-

- (A,Z) e- (A,Z)

? ?


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Muon to Electron Conversion• Neutrino-less conversion of a muon into an electron in the presence

of a nucleus

• Look at muonic atoms– muon decay - e- e

– nuclear capture - (A,Z) (A,Z-1)

– muon to electron conversion - (A,Z) e- (A,Z)

• If we include neutrino mixing in the SM, the probability for muon to electron conversion is about 10-52

– Sensitive to physics beyond the SM.

SM processes


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SUSY and GUTs


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Measuring Muon to Electron Conversion• SUSY and other models give predictions >10-15

• Design an experiment that has a sensitivity of 10-16

– This means being able to identify one electron of interest from 1016 muons not of interest!

• Signal is a monoenergetic electron– E = ~ 105 MeV = m - BE

• Need to eliminate sources of

backgrounds.– Muon decay in orbit

– Muon decay in flight

– Radiative muon capture - (A,Z) (A,Z-1)* , (A,Z-1)* (A,Z-1) , e+e-

– Radiative pion capture - (A,Z) (A,Z-1)* , (A,Z-1)* (A,Z-1) , e+e-

– Cosmic rays


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Future Muon to Electron Conversion Experiments

• The COherent Muon to Electron Transition (COMET) experiment will be based at J-PARC and aims to have a sensitivity <10-16.

• The Phase Rotated Intense Slow Muon (PRISM) experiment will improve this measurement by a factor of 100 and can be the second phase of COMET.

• Mu2e aims to have a sensitivity of <10-16 and will be based at FERMILAB.

COMET

PRISM

Mu2e


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Why You Might Be Interested• Need for high intensity muon beam

Many challenges from an accelerator physics perspective.

• Intense proton beams.

• Very cleanly pulsed proton beam (extinction <109).– AC Dipole.

• Pion production.– Superconducting solenoid in high radiation environment.

• Muon beams.– Transportation and momentum selection of large emittance beams.

• Fixed-Field Alternating-Gradient (FFAG) accelerators.– Large momentum acceptance.– High gradient at low frequency cavities.– Kickers.


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COMET at J-PARC

Beam Power 56 kW

Beam Energy 8 GeV

Average Current 7A

Protons per Bunch <1011

Proton beam parameters

• Slow-extracted proton beam.

• 8 GeV to suppress anti-proton production.

• COMET requires lower power but PRISM will need 1-2MW.

Hadron Experimental Facility

Materials and Life Science Facility

3 GeV Synchrotron

Linac

50 GeV Synchrotron

Neutrino Facility

Accelerator-Driven Transmutation Experimental Facility

COMET


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COMET Overview

• Curved solenoid channel to allow pions to decay and momentum selection of muons.

• Stopping target made of 0.2mm thick Aluminium disks.

• Electron spectrometer is another curved solenoid channel for momentum selection of electrons.

• Tracker utilises straw tubes arranged in planes for precise momentum measurement.

• Calorimeter is made of scintillator crystals for energy and time measurements.

Mag

netic

Fie

ld (

T)

z (mm)


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Proton Beam for COMET

• Background rate needs to be low in order to achieve sensitivity of <10-16.

• Need proton extinction device.

Bunch Separation 1-2 s

Bunch Length 100ns

Extinction 10-9

Pulse Structure


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Proton Extinction• Extinction requirement is 10-9. Intrinsic extinction from the J-PARC main ring is expected to be

around 10-7.– Need additional extinction device to give additional factor 10-2.

• One possible solution is to use an AC dipole– Collaboration between COMET and Mu2e

B=0G - G4Beamline• TRANSPORT B=600G - G4Beamline

• TRANSPORT

B=600G

B=0G

1300ns

100nsf=385kHz

Transmission [-100:100ns] = 100%Rextinction [<-300ns, >300ns] < 1/1000Rextinction [<-200ns, >200ns] < 1/100


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Pion Production

• Keep only backward going pions.

Gold target simulations using MARS


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Solenoid Design8x1021 n/m2/1021p2x10-5 DPA/1021p

Neutron Flux

• Neutron Flux:– ~1022 n/m2 for 1021p

• Same criteria as for ITER

– ~2x10-5 DPA for 1021p• Conductor degradation

• Inner bore of solenoid increased to 1300mm.

• Copper stabilised conductors are thick.– Refrigeration load over 1kW.

• Aluminium stabilised superconducting coil R&D.

– Better radiation damage performance.

• Prototype being wound at Fermilab.


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Muon Transport Channel

• Needs to be long enough so pion survival rate is low, <10-3

• High transport efficiency for muons with momentum around 40 MeV/c

• Eliminate muons with momentum > 75 MeV/c

• Select muons with negative charge.

• Use toroid magnetic field.– Particles drift in direction perpendicular to curvature

• Need compensating dipole field to correct for this. At the end of the muon

transport channel

L

TL

p

pp

R

s

qBdrift

22121


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Muon Transport Magnet Designs

Tilted solenoid coils.Actual tilt angle is 1.43deg.

tilt angle

Double Helix from Advanced Magnet Labs.Additional dipole field windings on top of solenoid winding.Windings can be formed on a bent substrate.

Additional cosine theta coils to give dipole field.


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PRISM• Factor 100 improvement in sensitivity on COMET.• Longitudinal phase-rotation from p/p = ± 20% to ± 2%• Scaling FFAG. • Small momentum spread means stopping target can become thinner (less

degradation of electron momentum).• Many turns less pion contamination.

rf : 2MV/turn


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• Scaling FFAG has Bz(r)= B0(r/r0)k

– Constant tune over momentum range.

• Recent revival because of need for fast acceleration of muon beams.

What are FFAGs?

Synchrotrons ramp up magnetic field to keep orbit fixed Y slow acceleration

Low energy

High energy

DDF

FF

Orbit for all energies

Magnetic fields are fixed Yrapid accelerationbut orbits are more complicatedY complicated beam dynamics and larger magnets.

Fixed Field Alternating Gradient Accelerator

Synchrotron


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The PRISM Magnet

Measured Bz – TOSCA Bz


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Magnetic Alloy RF Cavity• High fields at low frequencies• Wide band operation (low Q)• Core made of magnetic alloy ribbon

Cores per cavity 4

Shunt Impedance 400

RF frequency 2.1 MHz

Field Gradient 100 kV/m

Duty Factor 0.3%

PRISM Prototype Cavity

Sawtooth Approximation

kV

nsec

1.7m

1.0m

0.35m

1.0m

1.8m

0.33m


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PRISM Test Ring

• Use 241Am alpha source (200 MeV/c degraded to 100 MeV/c with Al foil).

• Can locate position and angle of source.

• Study closed orbits, dynamic aperture and tune.

10-cell Ring 6-cell Ring

Particle muon alpha

Momentum (MeV/c) 68 100

Radius (m) 6.5 3.5

Number of cavities 8 1

Number of field clamps 20 2


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6-Cell PRISM Results


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PRISM Task Force• So why not build PRISM instead of COMET?

• Number of issues need to be solved

– Injection/extraction

– RF gradient• Technology being developed

– Matching needs to be studied.

– Can we use the same technology as the COMET muon beamline?

• A PRISM task force was set up in mid-2009 to address the issues for realising a feasible design.

• Utilise synergies with neutrino factory and other FFAG Projects.


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Summary and Future Plans• COMET and PRISM are really exciting projects to work on!

• Fundamental science, the really “big” questions, can be addressed but requires the development of accelerator technology.

– Intense, cleanly pulsed, proton beams.– Superconducting solenoid technology.– Transport channels for large emittance beams.– Radial-sector scaling FFAG magnet design.– Low frequency, high-gradient magnetic alloy rf cavities.– Kicker systems for FFAG

• Experiments– COMET has Stage-1 approval from J-PARC. Technical Design Report will be

submitted by end of 2010.– PRISM task force will report by the end of 2010 / early 2011.– Mu2e has CD-0 from US Department Of Energy. Expects to get CD-1 approval

in 2010.


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References• COMET

– “Conceptual design report for experimental search for lepton flavor violating mu- - e- conversion at sensitivity of 10**(-16) with a slow-extracted bunched proton beam (COMET).” By COMET Collaboration (Y.G. Cui et al.). KEK-2009-10, Jun 2009. 208pp.

• http://ccdb4fs.kek.jp/tiff/2009/0924/0924011.pdf

– “J-PARC Accelerator Scheme for Muon to Electron Conversion Search”, EPAC08• http://accelconf.web.cern.ch/AccelConf/e08/papers/mopc128.pdf

• PRISM – “FFAG as Phase Rotator for the PRISM Project”, EPAC04

• http://cern.ch/AccelConf/e04/PAPERS/MOPLT070.PDF

– “Six-sector FFAG Ring to Demonstrate Bunch Rotation for PRISM”, EPAC08• http://accelconf.web.cern.ch/AccelConf/e08/papers/thpp007.pdf

• Mu2e – Proposal

• http://mu2e-docdb.fnal.gov/cgi-bin/ShowDocument?docid=388

– http://mu2e.fnal.gov/

Muon Beams for Particle Physics Ajit Kurup Winter Seminar March 2010.

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