Muon g2 Experiment at BNL Presented by Masahiko
Muon g-2 Experiment at BNL Presented by Masahiko Iwasaki (Tokyo Institute of Technology) Akira Yamamoto (KEK) for E 821 g-2 Collaboration: Boston, BNL, Cornell, Fairfield, Heidelberg, Illinois-UIUC, Minnesota, Budker Institute, KEK, Tokyo I. T. , Yale 1
Contents – Objectives – Features of Experiment at BNL – Superconducting Magnet System – Detector System – Experimental Results – Status and Future Plan 2
Muon Anomalous Magnetic Moment • The gyromagnetic ratio, g, g magnetic moment (eh/mc) = –––––––––––––––– 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 g >> 2 • electron • muon g almost equal to 2 coupling to virtual fields e 3
Anomalous Magnetic Moment • The muon anomalous magnetic moment is: 4
Experimental Approach • Polarized Muons n • Precession gives (g-2) p+ m+ µ • Pm The Magic Momentum • E field doesn’t affect muon spin when g = 29. 3 • Parity Violation in the decay 5
Getting the Answer (1) Precession Frequency (2) Muon distribution (3) Magnetic Field Map B 6
Experimental Setup at E-821 Superconducting Beam Inflector Superconducting Muon Storage Ring ~ 14 m Muon Beam Injection Electron Detectors 7
Muon Beam to E 821 Protons from AGS p production m injection p m decay m storage ring 8
Comparisons with a Previous Experiment • CERN BNL-E 821 • Beam Injection • Inflector pion Resistive > Pulsive muon Superconducting > DC Yes Superconducting > Single Ring • Kicker • Storage ring Resistive > Multi-sector 9
Storage Ring Dipole CRERN BNL Sector complex Continous Ring 10
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 11
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 12
Superconducting Storage Ring Radius 7112 mm Storage Aperture 90 mm Magnetic Field 1. 45 T Momentum 3. 094 Ge. V/c 13
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 14
Al-stabilized Superconductor • Advantage of Al stabilizer – Low resistivity – High thermal conductivity • >> Excellent stability in superconductivity • Technology advanced in Japan Applied for G-2 Dipole CDF >> Tristan >> LEP >> SSC >> LHC 15
Superconducting Coil Winding Largest SC coil ever built by 1990. 16
Dipole Magnetic Field with Superconducting Ring COil LHe Cooling Pole Shimming vertical (cm) Continuously monitored with 378 fixed probes mounted above and below the storage region Superconductor radial (cm)17
Muon Storage Ring Installed Superconducting Ring Coil Continuous Iron Yoke m beam 18
Superconducting Beam Inflector for Muon Beam Injection Superconducting Beam Inflector Muon Beam Injection Inflector Coil Inner Coil Muon Storage Ring Provide Field Free (B=0) Beam Channel 19
Concept of Beam Inflector Coil >> Modified Toroid Ordinal Toroid Modified Toroid >> Both have closed field. 20
Artistic Inflector Fabrication Superconducting Shield Superconducting coil 21
Superconducting Beam Inflector Dipole Yoke Dipole Field Uniforminty: 1 ppm B = 1. 5 T Muon Beam Storage Region Muon Injection Aperture Toroidal Flux Line B=0 B =3 T B = 1. 5 T Superconducting Coil Al Coil Case Surrounded by SC Shiled Plate ~ 50 mm 22
Principle of Beam Inflector only Combination of Inflector with Dipole Ext. Field is Cancelled 23
Magnetic Field Uniformity Integrated through Ring CERN • Sector yokes • Cu coil, • Pulse Inflector a little asymmetry BNL-E 821 • Continous yoke • Sophisticated shimming • Superconducting Ring coil • DC superconducting Inflector with SC shield • Further Improvement for Leads 24
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. 25
Field Disturbance by Current Leads ~ 1999 Run With Inflector #1 DB = m 0 I / 2 p • (1/R+-1/R-) = ~ 500 gauss (locally) 2000 Run W/ Inf-#2 ~ 50 mm Field distortion produced by Current Leads 26 (in the first Inflector) >>>Improved to be zero in 2 nd Inflector
Integral Magnetic Field. Uniformity @ BNL 99 , 2000 Run 1999 Separate Leads Run 2000 Closely tightened Field much improved 27
Summary of Superconducting Magnets in BNL g-2 Experiment • Al-stabilized Superconducting Ring Magnet – Largest Superconducting coil by 1999. – 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. 28
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