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Particle Physics


Particle physics is the branch of science concerned with the ultimate constituents of matter and the fundamental interactions that occur among them. The subject is also known as high energy physics or elementary particle physics.

Experiments over the last 40 years have revealed whole families of short lived particles that can be created from the energy released in the high energy collisions of ordinary particles, such as electrons or protons. The classification of these particles and the detailed understanding of the manner in which their interactions lead to the observable world has been one of the major scientific achievements of the twentieth century.

What is Particle Physics?

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Particle physics is a branch of physics which deals with the study of elementary particle, which are the basic constituents of every matter. Elementary particles are very small in size like quark, which are not visible in our eyes. The interaction between these elementary particles are also considered in this field.

History of Particle Physics

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The history of particle physics is described as a time line in very brief manner.To understand the progress in this field lets go through this time line.

1932: Positron and neutron were discovered by Carl Anderson and James Chadwick

1933: Fermi theory of beta decay

Leptons were discovered by Carl Anderson

Cecil Powel was discovered the charged pi meson which is known as pion

Quantum electrodynamics was formulated by Richard Feynman

Anti matter concept was put forward by Owen Chamberlin and Emilio Segre

Discovery of quarks and anti quarks

The interaction between quarks and gluons were studied

Charm type quark were discovered by Stanford and Brookhaven

Sixth type quark was discovered

Discovery of Higgs boson

Standard Model of Particle Physics

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The best current theory of particle physics is the so called standard model, a modest name for the most successful physical theory ever constructed. The standard model is concerned with the different interactions between the elementary particles. The standard model asserts that the material in the Universe is made up of elementary fermions interacting through fields, of which they are the sources. The particles associated with the interaction fields are bosons. The elementary fermions of the standard model are of two types: leptons and quarks. Leptons interact only through the electromagnetic interaction and the weak interaction. Quarks interact through the electromagnetic and weak interactions and also through the strong interaction.

Subatomic Particles

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Subatomic particles are very small particles than an atom, which is known as the fundamental particle. It is of two types, elementary particle and composite particle. Elementary particles are the basic building block of any matter. These subatomic particles follow the law of quantum mechanics. Some of the elementary particles are described in next section.

Quarks and Leptons

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The known quarks are up, down, strange, charm, top and bottom.In the standard model, quarks like leptons are spin 1/2 Dirac fermions, but the electric charges they carry are 2e/3, -e/3. Quarks carry quark number, anti quarks being counted negatively. The net quark number of an isolated system has never been observed to charge. However, the number of different types or flavours of quark are not separately conserved: charges are possible through the weak interaction.

Types of Quarks

The different leptons are electron, electron neutrino, muon, muon neutrino, tau and tau neutrino. The Dirac equation for a charged fermion predicts the existence of an antiparticle of the same mass and spin, but their charge and magnetic moment are opposite. Of the charged leptons, only the electrons, only the electron carrying charge -e and its antiparticle are stable. The muon and tau and their antiparticles, differ from the electron and positron only in their masses and their finite life times. They appear to be elementary particles.


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Antimatter exist in the universe for every matter. We can convert energy from radiation to a matter or antimatter according to the right conditions given. If the antimatter particle meets the corresponding matter, they can transfer the energy as radiations and get disappear. Thus, any antimatter particles produced in the laboratory or in naturally occurring high energy processes, disappear again very shortly. In a matter dominated environment their chances for longevity are very slim.


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Muons are unstable elementary particles of two charge types having a spin of 1/2, an unusual mass intermediate between the proton mass and the electron mass and 2.2 μs lifetime. The muon has the second longest lifetime among all the fundamental unstable particles after the neutron and has the second smallest mass among all the fundamental particles after the electron.

Particle Detector

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Particle detectors have contributed significantly to the advancement of science. New detection techniques like cloud chambers, bubble chambers, multiwire proportional and drift chambers and micropattern detectors allowed essential discoveries. The application of particle detectors in nuclear physics, elementary particle physics, in the physics of cosmic rays, astronomy, astrophysics and astroparticle physics as well as in biology and medicine or other applied fields.
Particle Detector