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Interactions of muons with atoms & nuclei

Interactions of muons with atoms & nuclei. BNL Muon Storage Ring. Introduction of muons m + , m - (Leptons, electro-weak interactions)  a major component of natural radioactive background produced by “cosmic rays” in upper atmosphere.

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Interactions of muons with atoms & nuclei

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  1. Interactions of muons with atoms & nuclei Weak Beta/Muon Interactions BNL Muon Storage Ring

  2. Introduction of muons m+, m- (Leptons, electro-weak interactions) a major component of natural radioactive background produced by “cosmic rays” in upper atmosphere. Application: Demonstration of relativistic time dilatation; Nuclear structure,…., radiography (?). Energy loss by Coulomb interactions with matter. (biomed/radio-imaging application). Kinematics of muon decay. Nuclear capture of negative muons. The ANSEL cosmic muon experiment, counters & electronics. Today’s Agenda Weak Beta/Muon Interactions

  3. Muons from Cosmic Ray Showers Muons produced in energetic p-induced reactions.Cosmic ray shower in the upper atmosphere generated by primary protons from solar system (Sun etc.) Weak Beta/Muon Interactions Muon momentum spectrum at sea level. Solid line: parameterization of high momentum spectrum. 30% m-, 70% m+

  4. Direct measurement of the muon lifetime. Images from the 1962 documentary “Time Dilation”. Measure survival of energetic muons, compare to stopped muon decay. Stopper Decay products. Weak Beta/Muon Interactions Decay Product Muon Stop Frisch and Smith, AJP 31, 342 (1963).

  5. Demonstration of Time Dilatation Weak Beta/Muon Interactions Frisch & Smith, AJP 31, 342 (1963) t = (2.2 ± 0.2) µs.

  6. Properties of Electrons and Muons Weak Beta/Muon Interactions Electromagnetic interactions via charge and magnetic moment. Weak muonic interactions: m± decay and m- capture (EC)

  7. Electronic Interactions of Muons with Matter Stronger electric + weaker magnetic interactions of muon Bethe-Bloch Formula Energetic muons are minimum ionizing particles (“mips”). Lose most of their energy near the end of trajectory. mips Weak Beta/Muon Interactions

  8. Electronic Interactions of Muons with Matter Plastic Target: Monitored in experiment Expect a line E/DE spectrum for traversing muons. Stop, Decay following Transmitted Plexiglas Plastic: CnHmpolymer ([H]/[C]≈1.11), rT=1.03 g/cm3IE=64.7 eV. Cosmic ray muons = mostly minimum ionizing particles (mips) For plastic: DE=2MeV/cm Weak Beta/Muon Interactions

  9. Weak Interactions: Muon Decay Configuration of maximum pe Rest mass Maximum

  10. Muon Decay: Electron Energy Spectrum Less than maximum momentum transfer to electron Electron Momentum x

  11. Cosmic-Muon Disappearance Rates Partial muon life times and disappearance rates (branching decay) m+ , m- decay m-Capture Light nuclei (Li, Be, …C, O,..): long partial capture muon life times (tc~ 100 ms » td) Random Background Heavy nuclei (Cu,..W,..Pb,..): short partial capture muon life times (tc ~ 50 ns « td)

  12. Exotic (Muonic) m- Atoms Negative muonm- captured by (electronic) atom, ejects 1 e-, cascades down to 1sm Muonic X rays  muonic atom formed with m- in 1s 1sm (Z, N) decay capture Heavy m atom: Muon mostly inside nucleus shielding of Z  effective Zeff < Z Isomeric shift, magnetic HF splitting nuclear levels

  13. Negative Muon K-Capture Negative muonm- in K shell (1sm) is captured by proton (analog to EC process) 1sm (Z, N) Isotopic effect in capture rates due to differences in n, n phase space n Strength factor K=272 s-1 (A-1,Z-1)+n p n

  14. Neutrino momentum transfer depends on Nucleonic momentum distribution influencedby correlations (m*)  Spectrum I(E*) of Nuclear excitations can be broad, emission of neutrons, charged particles, g-rays m-Capture Nuclear Excitation Function Q = excitation energy E* Theoretical n Multiplicity Distribution (Singer Model) Evaporation Non-Equilibrium Curves to guide the eye and to illustrate evaporative and pre-equilibrium n components

  15. The ANSEL Cosmic Muon Telescope ExtendedActual version Weak Beta/Muon Interactions

  16. Electronics for ANSEL Muon Experiment Active target AT= plastic scintillator Placed between telescope counters #3 and #4 Muon transmission Muon stop in AT Measure energy deposit in both modes Active target AT= plastic scintillator between #3 and #4 stops muon  decay Measure decay lifetime in plastic AT (negligible capture) Weak Beta/Muon Interactions

  17. The END (For Now) Weak Beta/Muon Interactions

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