Jay Martone, age 17, of Nashua, N.H., for his question:

WHAT IS A MESON?

A meson is an elementary nuclear particle. Mesons are responsible for most forces acting between the protons and neutrons in the nuclei of atoms. Mesons are unstable and spontaneously decay or break down into other particles.

Mesons exist in several forms, classed by their weight.

K mesons may have a positive or negative electrical charge, or they may be neutral. A charged K meson will have a weight 966 times that of an electron while a neutral K meson will have a weight 974 times that of an electron. They were discovered in 1947.

Also discovered in 1947 is the Pi meson, also called pious. They exist in positive, negative and neutral forms. Charged pi mesons have a weight 273 times that of an electron while neutral pi mesons have a weight 264 times that of an electron.

Mu mesons, also called muons, exist in positive and negative form. They do not contribute to nuclear forces like other mesons. They resemble electrons and neutrons and should logically be grouped with these particles. They were discovered in 1936.