The Other B

For tracks E, F, G, and H, we can find the net momentum just as we did before: 
pnet = pE  + pF  + pG  + pH

      = (0.9,0.5,0.0)  +  (0.1,-0.5,0.0)  +  (-0.2,-0.3,-0.1)  +  (0.1,-1.1,0.6)

      = (0.9,-1.4,0.5) GeV/c.

The sum of the energies for these four tracks is 

Etotal = 1.2 + 0.5 + 0.4 + 1.3 =  3.4 GeV.
The net momentum is nowhere near (0,0,0) GeV/c, and there is 
5.3 GeV - 3.4 GeV = 1.9 GeV
of energy "missing."

Because we trust energy and momentum conservation, we can infer that there must be something else happening that we cannot see. In fact, one of the decay products of the other B particle is a particle called a neutrino that is virtually impossible to detect. It carries the "missing" energy and momentum.

Now, we said that
  • 2 B particles were produced in the event,
  • one of them decayed to particles that we can detect, and
  • from the missing energy and momentum in the decay of the other B we determined that its decay contained an undetected neutrino.
    So let's think about this: Did you really have to know that 2 B particles were produced in the event in order to determine that the event contained a neutrino? What is the minimum information needed for making this determination? Share your thoughts on the HiPPP discussion forum.
    Last modified: Tue Nov 2 16:37:44 PST 2004