Muon Radiative Capture - 12/2007

Muons: Radiative Muon Capture (RMC)

Presented to PHSX 741,Fall ‘07, David File

Introduction to Nuclear Physics

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Muon Radiative Capture - 12/2007

Introduction• Focus on muonic radiative capture (RMC)

– General muonic interactions: How are they used?– Nuclear focus and model concepts– Determine core papers to begin review

• References:– Paper published in 2007

• Gamma rays from muon capture in I, Au, and Bi, Measday, D., Stocki, T., Tam H.

– Books• Introductory Muon Science, Nagamine, K., 2003• Introductory Nuclear Physics, Krane, K.

!

µ" # e" + $ e + $ µ

RMC, p + µ" # n + $ + %

OMC, p + µ" # n + $

Weak, uud +W " # udd ,(p# n)

Muon Radiative Capture - 12/2007

RMC Basics• The role of the muon: Muonic Atoms

– Center of mass: mz+nmµ/(mz+n+ mµ)– Rµ = 1/207th Re results in more time spent in the nucleus– Decays at the location of the capturing proton - 136 MeV

(6MeV per nucleon)– Krane: Figure 3.9, Isotope shifts and nuclear radius

• Ordinary electron x rays (10+ keV) verses muonic x rays (1+ MeV)

• Muon Capture– Zero angular momentum transferred to nucleus– Ordinary (OMC): Thermalized nucleons-> Neutrons emitted– Radiative (RMC): +Excited states -> Gamma radiation emitted

• Muon Experiments– TRIUMP– MuLAN and MuCAP

– COMPASS experiment at CERN w/ polarized muon beam 6 MeV

136 MeV“Bomb”

!, n, 2n…"1 , "2 , "3…

RMC Reaction Products

Muon cascades downto capture from 12s

Rs1,e= 52,900 fm, Bohr

Rs1,µ= 256 fm

Muon Radiative Capture - 12/2007

Muon History• Muons are Leptons

– What are they?– Development of models using available and

lower energy nuclear interactions– Table III - Properties vary with atomic

number

• Nuclear structure– Historical perspective towards

development of both experiments andmodels

• Standard model - particle type• MIT Bag model - alpha particles• EMC effect - overlapping wave functions

– Current significance: coupling constants

TABLE III. Values of the experimental parameters for muon capture in iodine, gold, and bismuth [1].

Muon Radiative Capture - 12/2007

RMC - TRIUMP• TRIUMP

– Canada's National Laboratory for Particle andNuclear Physics located on the campus of theUniversity of British Columbia.

– TRI-University Meson Facility• World's biggest cyclotron• Magnet diameter: 18m• Magnetic field: Up to 5600 gauss• 1000-trillion particles each second

• Extensive data– 58,60,62Ni (1998); O,Al,Si,Ti,Zr,Ag (1999); 27Al,28Si

(2007); Ca,Fe,Ni (2006)… 40Ca (1979)• Experiment and Instrumentation

– Figure 1, schematic representation of the RMC atTRIUMF. Muon beam: 100% duty cycle on the M9Bbeam line (6 m 1.2 T superconducting solenoid)(90MeV/c #-) which decays into muons. Final beam hasa 2x105 s-1 muon count of which 20% are electrons.

– Two primary " ray detectors at right angles to thebeam axis, Ge1 and Ge2. Only one used in theanalysis.

– Three sheets of scintillating plastic detectors (S1,S2, S3) used to monitor the passage and capture ofmuons. Detection relies on the first and secondsensors to agree and the third to anti-correlate(diameter of S2 is 51mm).

Muon Radiative Capture - 12/2007

New Data for I, Au and Bi

FIG. 2. Histogram, Au example [1].

FIG. 3. Nucleus excitation response

TABLE V. Observed " ray yields, per muon capture127I(µ-, !2n")125Te

TABLE VI – Comparison of Elements – Total Yields (%)

Reaction

+ !, implied127I " xTe 197Au " xPt 209Bi " xPb

(µ-, #) 8 8 5

(µ-, #n) 52 48 47

(µ-, #2n) 18 20 29

(µ-, #3n) 14 14 9

(µ-, #4n) 5 6 5

(µ-, #5n) 2.5 3 3

(µ-, #6n) 0.4 0.8 1.5

(µ-, #7n) 0.1 0.2 0.2

0

10

20

30

40

50

60

0 2 4 6 8

Neutron Count

Excit

ati

on E

vents

Reviewer’s PlotThermal DistributionkT => tbd

Muon Radiative Capture - 12/2007

TRIUMP - Experiment• X ray data from muon cascading given in the paper are not presented

– Paper contained and contributed a total of 4 x ray series for each element and 8,3 and 7 tables (I, Au, Bi respectively) presenting reaction-correlated " ray yields.

• Run times: 2 hrs

• Spectra divided among 2048 channels.– Histograms (Figure 2) include both types of radiation events and are used in

conjunction with existing x ray calibration data– Normalization accomplished using pre-existing and well establish baselines of atomic

x ray muonic emissions

• Improvement described in the paper– Substitution of the standard “off the shelf” HPGe " ray detectors with the

facility’s own “Toronto Detector”.– Allows greater characterization of the dedicated detector and calibration with

previous data measured by the Toronto detector.

Muon Radiative Capture - 12/2007

General Muon Parameters• Muon parameters are key to many areas of research

– “The Fermi coupling constant GF is one of the fundamentalconstants of the standard model. GF is obtained from themuon lifetime via a calculation in the Fermi Model, inwhich weak interactions are represented by a contactinteraction…” Bernhard Lauss, MuCap

• MuLan and MuCAP– The MuLan experiment at the Paul Scherrer Institute

(PSI) measures the lifetime of the positive muon with aprecision of 1 ppm, giving a value for the Fermi couplingconstant GF at the level of 0.5 ppm. (online)

– The MuCap experiment determines the rate of muoncapture, giving the proton’s pseudoscalar coupling, gp to7%. This coupling is calculated precisely from heavybaryon chiral perturbation theory and therefore permitsa test of QCD’s chiral symmetry. (online)

MuLan

MuCAP

Muon Radiative Capture - 12/2007

RMC - Summary

• Review of TRIUMP efforts and supporting referencesintroduced muon physics, nuclear instrumentation andgeneral experimental framework.

• TRIUMP Team– Extensive data though continued experiments over the

past decades.– Real, working-world examples

• Muon as a nuclear physics workhorse– Able to can get past electrons and into the nucleus– Continued work and precision development of its properties

and interactions is vital.

• Reviewer-related: Continued interest in muon physics.

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