1 Muon g-2 Experiment at BNL Presented by Masahiko Iwasaki (Tokyo Institute of Technology) Akira Yamamoto (KEK) for E821 g-2 Collaboration: Boston, BNL, Cornell, Fairfield, Heidelberg, Illinois-UIUC, Minnesota, Budker Institute, KEK, Tokyo I.T., Yale

2 Contents –Objectives –Features of Experiment at BNL –Superconducting Magnet System –Detector System –Experimental Results –Status and Future Plan

3 Muon Anomalous Magnetic Moment The gyromagnetic ratio, g, magnetic moment (eh/mc) g = –––––––––––––––––––––––––––––––– angular momentum (h) Spin-1/2 particles have g = 2, but... –g is a fundamental property of a particle, and –not exactly = 2 proton hyperons electron muon e   coupling to virtual fields g >> 2 g almost equal to 2

4 Anomalous Magnetic Moment The muon anomalous magnetic moment is:

5 Experimental Approach P olarized Muons P recession gives (g-2) P  The Magic Momentum E field doesn’t affect muon spin when  = 29.3 P arity Violation in the decay     µ

6 Getting the Answer (1) Precession Frequency (2) Muon distribution (3) Magnetic Field Map B

7 Experimental Setup at E-821 Superconducting Muon Storage Ring Superconducting Beam Inflector Muon Beam Injection Electron Detectors ~ 14 m

8 Muon Beam to E821 Protons from AGS  decay  injection  production  storage ring

9 Comparisons with a Previous Experiment CERNBNL-E821 Beam Injectionpionmuon InflectorResistiveSuperconducting > Pulsive > DC KickerYes Storage ringResistive Superconducting > Multi-sector > Single Ring

10 Storage Ring Dipole CRERNBNL Sector complexContinous Ring

11 Keys in the Experiments Very uniform and large aperture magnetic field –Superconducting Single-Ring Dipole Magnets Muon injection –Superconducting Inflectors –Modified Toroid coil and Superconducting Shield –No leakage field and no disturbance to muon storage field Muon Orbit Matching in the Ring –Pulsed Kicker Magnet Muon focusing in the Dipole Ring –Electrostatic Quadrupole Lense Electron meausrement after muon decaying

12 Japanese Contribution (in Experimental Preparation) Institutes –KEK (Hirabayashi, Mizumachi, Endo, Nagamine, Kurokawa, Sato, Ishino, Makida, Tanaka, Yamamoto et al.) –Tokyo Institute of Technology (Iwasaki et al.) Subjects –Superconducting Storage Ring, Coil design and development with Al-stabilized superconductor Iron yoke and pole piece –Superconducting Beam Inflector –Beam Monitor –Data Analysis

13 Superconducting Storage Ring Radius7112 mm Storage Aperture90 mm Magnetic Field 1.45 T Momentum3.094 GeV/c

14 Superconducting Ring-Dipole Single Ring Coil realized by: –using Al-stabilized superconductor, Technology transfer from TRISTAN/TOPAZ solenoid Becoming standard technology based on development in Japan –Indirect cooling by using force flow Lhe in cooling channel (not pool-boiling) Compact coil design realized

15 Al-stabilized Superconductor Advantage of Al stabilizer –Low resistivity –High thermal conductivity >> Excellent stability in superconductivity Technology advanced in Japan CDF >> Tristan >> LEP >> SSC >> LHC Applied for G-2 Dipole

16 Superconducting Coil Winding Largest SC coil ever built by 1990.

17 Dipole Magnetic Field with Superconducting Ring COil Continuously monitored with 378 fixed probes mounted above and below the storage region radial (cm) vertical (cm)  Cooling Superconductor Pole Shimming

18 Muon Storage Ring Installed Superconducting Ring Coil Continuous Iron Yoke  beam

19 Superconducting Beam Inflector for Muon Beam Injection Superconducting Beam Inflector Muon Beam Injection Provide Field Free (B=0) Beam Channel Inflector Coil Inner Coil Muon Storage Ring

20 Concept of Beam Inflector Coil >> Modified Toroid Ordinal ToroidModified Toroid >> Both have closed field.

21 Artistic Inflector Fabrication Superconducting Shield Superconducting coil

22 Superconducting Beam Inflector Toroidal Flux Line Dipole Field Uniforminty: 1ppm Muon Beam Storage Region Muon Injection Aperture Superconducting Coil Al Coil Case Surrounded by SC Shiled Plate Dipole Yoke B = ３ T B = 0 ~ 50 mm B = 1.5 T

23 Principle of Beam Inflector Inflector only Combination of Inflector with Dipole Ext. Field Field is Cancelled

24 Magnetic Field Uniformity Integrated through Ring CERN Sector yokes Cu coil, Pulse Inflector BNL-E821 Continous yoke Sophisticated shimming Superconducting Ring coil DC superconducting Inflector with SC shield Further Improvement for Leads a little asymmetry

25 Further Improvement Current Leads Layout in Inflector Run ~1999 Leads in Inflector No. 1 –~ 5 cm in parallel –Differential field of 10 gauss in sotrage region. Run 2000, Leads in Inflector No.2 –Tightly in parallel, –Field well cancelled out.

26 Field Disturbance by Current Leads ~ 50 mm Field distortion produced by Current Leads (in the first Inflector) >>>Improved to be zero in 2nd Inflector  B =  0 I / 2   R + -1/R - ) = ~ 500 gauss (locally) ~ 1999 Run With Inflector # Run W/ Inf-#2

27 Integral Magnetic BNL 99, 2000 Run 1999 Run 2000 Separate LeadsClosely tightened Field much improved

28 Summary of Superconducting Magnets in BNL g-2 Experiment Al-stabilized Superconducting Ring Magnet –Largest Superconducting coil by –Very uniform and stable field Superconducting Beam Inflector –Muon Injection ideally at B = 0 without leakage field, –DC operation and no disturbance to muon ring, –Perfect magnetic field shielding.