Nuclear structure, elementary particles and Higgs Boson
Nucleus is, in addition to electrons, a fundamental constituent of an atom. The existence of atom lies in the capacity of the nucleus to hold several electrons. It is a matter of elementary knowledge that nuclei of same element have same number of protons but can have different numbers of neutrons. The majority of mass of atom emanates from nucleus. Number of protons of atom is also known as atomic number of the element.
Though small in size, the nucleus can have angular momentum and magnetic moment.
Entire physical processes and structures in the universe starting from atomic level to right up to galactic level can be explained by the conceptualization of four interactions of nature. These are discussed very briefly as follows:-
i. Gravitational interaction
Nothing much is required to be said about it as we all are quite familiar with it.
ii. Electromagnetic interaction
Electric field is a field which is generated by a charged particle. Any other charged particle in that field will experience an electric force. If electric field varies with respect to time, such as by motion of charged particle producing the electric field, then it produces a magnetic field too. Thus, magnetic field can be produces either by moving charges (electric current) or by intrinsic magnetic moments of magnetic materials. Now, what appears as a static charge producing constant electric field to an observer may well appear as a moving charge to another observer which is in relative motion with respect to the electric field producing charge. To that frame of reference, then, the same charge will produce a magnetic field too. Therefore, in relativity and in reality, electric field and magnetic fields are not separate rather two dimensions of singular electro-magnetic field. This interaction is called electro-magnetic interaction. Quantum Physics has established that this electromagnetic field is not continuous but quantized and electro-magnetic interactions result because of the exchange of photons.
iii. Strong nuclear interaction
It is an interaction between nucleons (a generic term for any constituent of nucleus, namely protons, neutrons etc). This interaction is essentially a short ranged one and it is this interaction which holds nucleons together to form nuclei. This interaction is so powerful at nuclear levels that it overwhelms gravitational force. However, at the scale of millimeter, the gravitational interaction overpowers this interaction.
iv. Weak nuclear interaction
It is that nuclear interaction which is responsible for radioactive decay. In structure of matter, its role in confined to radioactive decay of nuclei, whose neutron/proton ratios are not appropriate for stability.
Another question arises as to the source of these interactions. The generally accepted theory is that of basketball analogy. Its animated representation can be seen here. All interactions are thus the result of force carrier particles. What we normally think of force is actually the effect of these force carrier particles, also known as bosons, on matter particles.
A tabular summary of these interactions is as follows:-
|Type of interaction||Particles affected||Force carrier particle||Role in universe|
|Strong||Quarks||Gluons||Holds quarks together to form nucleons.|
|Hadrons||Mesons||Holds nucleons together to form nuclei.|
|Electromagnetic||Charged particles||Photons||Determines structure of atoms, molecules, solids, gases, liquids and is an important factor in astronomical universe.|
|Weak||Quarks and leptons||Intermediate bosons||Mediates transformation of quarks and leptons. Helps determine the composition of nuclei.|
|Gravitational||All||Graviton (haven’t been experimentally found)||Assembles matter into planets, stars and galaxies|
These fall basically in two classes-leptons and hadrons. This classification is done based on their responsiveness vis-à-vis strong interaction. Hadrons respond to strong interaction whereas leptons do not.
Leptons are truly elementary with no hint of internal structure or even extension in space. These are structure less and very close to be point particles. They are immune to strong interaction but do react to the other three interactions of universe. Electrons and neutrinos are the examples of leptons.
Hadrons are composed of two or three quarks. Quarks are also like leptons as these too are structure less and point like. Hadrons that consist of three quarks are called baryons (for e.g. protons and neutrons). Hadrons which consist of two quarks are called as Mesons. Hadrons are heavy and they occupy space. Hadrons respond to all four interactions of universe. Quarks are charged particles. However, their combinations have either no charge or a charge of (+/-) e.
Higgs Boson is conceptualized as a force carrier particle, like other bosons, which mediates the action of Higgs Field. This Higgs Field is a field which exists everywhere in space. The characteristic feature of Higgs Field lies in the assertion that particles acquire their characteristic mass by interacting with it. The field can be imagined to exert a kind of viscous drag on particles which move through it. This drag is nothing but the inertia, the defining property of mass.