<IMG SRC="logo2.gif"> Quark physics

Production of a Bs meson in a Z decay

Three dimensional view of a collision.

Two white arrows show the incoming electron and positron. The interaction produces two clear jets which are recognized as generated by b quarks:

On the right side the jet is made of:

Two red tracks piercing through the hadron calorimeter, they are muons and the mass of their system is 3.69 GeV. This is a psi', a c-cbar quark system.

Two light blue tracks penetrating the hadron calorimeter, they are kaons, ubar-s and u-sbar systems, and the mass of their system is 1.02 GeV. This is a phi, a s-sbar quark system.

Two orange tracks which make a K0 (s-dbar quark system).

The red and blue tracks together have a mass of 5.38. This is a Bs made of a b and a sbar quark.

These are the 3-momenta of the observed particles (the units are GeV/c). You can then reconstruct the masses of the particles which decayed into these.

 particle  px         py          pz   
   mu+   9.409      1.500      9.485
   mu-  13.044      4.368      8.817
   K+    5.095      2.350      4.459 
   K-    3.577      1.523      3.229

Starting from a decay of the Z into a b bbar quark pair the upper diagram shows the intermediate particles in this event. The Bs is created together with a K0. The latter decays eventually via the weak interaction into a pair of pions. The Bs also decays via the weak interaction into a phi meson and a psi' meson. The phi decays via the strong interaction into a pair of kaons and the psi' decays electromagnetically into a pair of muons.

The lower part of the diagram shows the quark composition of the mesons that appear in the event and shows how the quark flavors are transmuted by the charged current weak interaction. The outgoing quark anti-quark pairs are observed as pions or kaons depending on the quark composition.
The diagonal dotted line separates the interesting jet containing the Bs on the upper right from the opposite jet (which is not fully specified) on the lower left side of the diagram.

Henri Videau, videauh@polhp4.in2p3.fr , March 26 1996