Ruprecht Karls Universität Heidelberg

Welcome to

FP13

Measurement of Muon Properties in the Advanced Students Laboratory

of the
Universität Heidelberg
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Feynman diagram of muon decay
Feynman diagram of muon decay.
The muon decays into an electron,an electron antineutrino and a muon neutrino.		 Qustion raised by I.I. Rabi after learning about the lepton muon
When I.I. Rabi learned about the lepton muon
  he asked this still puzzling question.
 		 poster of the STANDARD MODEL from the particle data group
Summary of the STANDARD MODEL in particle physics (particle data group)
The setup of the experiment FP13 was prepared by the high energy physics group.
 

Introductory Remarks



The muon is an elementary particle which differs according to our present knowledge from the electron only in its mass and its mass dependent properties. The muon and the electron are leptons of two different particle generations. In this experiment we are studying the behaviour of the muon as a heavy leptonic particle and its fundamental interactions.

Even though not mandatory for this experiment it is of help to have
  • basic knowledge in elementary particle physics (Ex-Phys V)
  • some (little) experience in programming
Data aquisition is done using a Labview program, but no experience in Labview is required. Data analysis is performed in a Linux environment.
 This page is supposed to give you additional information in the context of the experiment. Details about the available instrumentation and the necessary background can be found in the script to the  experiment FP13
The muons for this experiment are born in the earth atmosphere when pions are created in the interaction of primary cosmic rays (e.g. protons) with the nuclei of the air up there. Those pions decay into muons and their antineutrinos.

In this FP13 you will become acquainted with 

     
    • particle physics and its relations to other parts of physics, 
    • interaction of particles with matter,
    • scintillation particle detectors, 
    • photomultipliers, 
    • nuclear electronics
    • fast coincidence circuits
    • elementary data acquisition concepts
    • data analysis(particularly statistics).
    		A cosmic muon is stopped in a sandwich of metal plates and plastic scintillators

    Principle of the experiment:Cosmic muons are stopped in metal plates, which are sandwiched  between plastic scintillation detectors. The positive muon decays into a positron which can also be detected by the plastic counters.The scintillation light is read by photomultipliers.
    Their electrical signals are transformed into norm pulses and fed into a multihit Time to Digital Converter. The time dependent hit pattern  is recorded by a computer and analyzed. Cosmic muons are polarized; therefore one can observe muon spin precession in an external magnetic field. 
Particularly you will use cosmic muons to
  • determine the lifetime of muons
  • observe the muon spin precession in a magnetic field
  • extract the weak interaction Fermi coupling constant  from your measurements
  • measure the Larmor frequency of the muon. This measurement is used to determine the magnetic moment of the muon
  • and you will interpret your results in the context of parity violation in the decay of the muon.
The experiments will extend over a week and in the end you yourself will have set up a system which takes data over a weekend all by its own. This will allow you to collect sufficient events for good result.


Some pictures from the experimental set-up:

Different views of the experimental set-up
The 'black box' surrounding the scitillators is a 
magnet providing the fiel;d for spin rotation.
NIM electronics used for data aquisition
Front panel of the DAQ software realized in Labview


The study of muon properties is a field of intense modern research. In particular of interest are
  • a measurement of the lifetime of muons to extract Fermis constant, one of the fundamental constants in the standard model of particle physics. The precision aimed for is 1ppm. See for example the MuLan experiment at the Paul-Scherrer Institut (PSI).
  • a measurement of lepton-flavor violating muon decays, like the decay &mu &rarr e &gamma. Nowadays experiments have a sensitivity for that decay of 10,sup> -14 See for example the MEG experiment , also at the Paul-Scherrer Institut (PSI).
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