Re: Did anybody measured e/m ratio for positrons

Dear Nevzat,

No one has measured the charge to mass ratio for positron in the same
way that J.J. Thompson measured e/m for the electron.  You will understand
the reasons after you examine this website describing Thompson's
experiment: 
 http:
//www.nyu.edu/classes/tuckerman/honors.chem/lectures/lecture_2/node3.html

It is relatively easy to obtain the large numbers of electrons required
for this experiment; just supply a voltage and take as many as you need
from the cathode.  Positrons must be made to order because they are not
found naturally.  And while they are being produced a few at a time, they
must be stored in order to collect a macroscopic number of them.  The
problem is that if a positron encounters an electron, the two will
annihilate each other leaving two or three photons behind.

In the one hundred or so years since Thompson's experiment, physicists
have been able to measure the charge and independently the mass of both
electrons and positrons.  The Particle Data Group compiles the results
of the world's most precise measurements of particle properties.
 http://pdg.lbl.gov/2004/listings/s003.pdf  
(page 2)

The bottom line is that the positron charge has been measured to be
identical in magnitude (but opposite in sign) to the electron charge
to 8 parts in a billion, and the positron mass is the same as the
electron mass to 40 parts in a billion.  These are incredibly precise
measurements!  So the charge to mass ratio of the positron can be
calculated, although it has not been experimentally measured.

--Dr. Randall J. Scalise