Strong Nuclear Force

                                       Strong Nuclear Force

           
            This is the strongest force of all four kinds of forces. It is carried by spin 1 particles, called gluons, which interacts only with itself and quarks. Spin 1 particles are like an arrow which looks same if one rotate it 360 degrees [fig(1)].

         

            You must have heard about the nucleus of atom which contains some protons with positive charge and some neutrons with neutral charge. You should think that the nucleus contains many positive charges but how it is stable because among the same charges, there should be repulsive force. Actually strong nuclear force works to hold them together. According to the new scientific theories, The protons are also make of quarks [fig(3)]. There are at least six types of quarks- up, down, strange, charmed, bottom and top. Each flavour comes in three colours- red, green and blue. Protons and neutron contains three colours, one of each colour. A proton contains two up quarks and one down quark and a neutron contains two down quarks with one up quark.

                 The strong nuclear force has a curious property called confinement: it always binds particles together. And these combinations have no colour. It means a single quark cannot exist. A red quark has to be joined to a green and a blue quark with the help of strings of gluons. Such a triplet constitutes a proton or a neutron. There is another possibility that quark and antiquark can make (red+antired=white, green+antigreen=white, blue+antiblue=white). This combination produces meson particles which are not stable because quarks and antiquarks can annihilate each other. Similarly, confinement prevents one having a single gluon on its own because gluons also have colour. You have to collect such gluons whose colour add up to white. This collection makes an unstable particle called a glueball.

              

            The fact that confinement prevents one from observing an isolated quark or gluon might seem to make the whole notion of quark and gluons as particles somewhat metaphysical. There is a different property of the strong nuclear force, called asymptotic freedom that makes the concept of quarks and gluons well defined. At normal energies, this force is much strong but in high energies, it becomes weaker. So the quarks and gluons feel themselves free and behave like free particles. In this picture, proton and antiproton are annihilating each other at high energy and quarks are getting free.

           

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