The idea that hadrons might be combinations of simpler more fundamental particles occurred to a number of physicists.In 1964 Gell-Mann and Zweig suggested that the meson nonet and baryon octet and decuplet could all be derived by combining three distinct spin – 1/2 particles, and their associated antiparticles. These new fundamental particles were called quarks. In 1967 Feynman suggested an intuitive model of what hapens when protons conteining quarks collide with other particles. He was able to derive certain characteristics of scattering that could be related back to the quark/parton model. In 1968 Freidman, Kendall and Taylor directed high-energy electrons at protons at SLAC(Stanford Linear Accelerator Center).One thing stood out, the pattern of scattering was the same at all collision energies. They discovered that they could account for the scattering by identifying the partons with quarks and introducing some additional particles moving between the quarks.1
Deep inelastic scattering – when high-energy electron beams were fired at fixed targets some of electrons suffered large angle scatterings rather like those of the alfa particles in original Rutherford scattering experiment.
The electrons must be interacting with highly concentrated charged particles inside the protons.The scattering takes place via the exchange ofhigh-energy photon.3
The 1990 Nobel Prize for Physics was shared by Friedman, kenall and Taylor for their pioneering investigations concerning deep inelastic scattering of electrons on protons and bound neutrons, which have been of essential importance for the development of quark model in particle physics….
Quark is hypothetical particle that carries a fractional charge. There are four different kinds of quarks, each having antiparticle called Antiquark. These quarks are called:
The Up Quark (u)
The Down Quark (d)
The Strange Quark (s)
The Charm Quark (c)
The charges on the four quarks u, d, s, c are +2/3, -1/3, -1/3, +2/3 that of the electron charge. Antiquarks have opposite charges. All quarks and antiquarks have equal spins which is ½. These quarks combine to form different elementary particles. For example: Protonsare composed of three quarks (uud) and neutrons (udd). Each meson can be conceived as the union of a quark and an antiquark.



Particles, particles…

untitledThere are two main types of particle: fermion (with half-integer spin) and bosons (with integer spin). Particles can also be classified by their interactions:
– hadrons (baryons and mesons) interact by the strong force.Half-integer spin hadrons (such as protons and neutrons) are called baryons and integer spin hadrons are called mesons (such as the pion)
– leptons not affected by strong interaction.
The first generation of leptons – electron (electron – neutrino).
The second generation of leptons – muons (don’t take part in the strong interaction but do behave just like electrons would if their mass was increased 207 times, except that they are unstable. When they decay they do so by creating an electron and anti-neutrino which is not the same as the anti-neutrino emitted in beta decay).
The third generation of leptons discovered in 1974 Martin Perl -the tau particle (tau – neutrino).
The 1988 Nobel Prize for Physics was awarded to Lederman, Schwartz and Steinberger for the neutrino beam method and the demonstration of the doublet structure of the leptons through the discovery of the muon-neutrino.
In 1995 the Nobel Prize was awarded to Martin Perl for the discovery of the tau lepton and Frederick Reines for the detection of the neutrino.
O divine neutrino!
“Neutrinos they are very small.
They have no charge and have no mass
And don’t interact at all.
The earth is just a silly ball
To them,through which they simply pass
Like dustmaids down a drafty hall…”
The problem with neutrinos is that they only interact with matter through the weak force, so they are extremely difficult to detect:

– spin (-1/2) hadrons such as the proton and neutron called baryons
– integer spin hadrons like the pion called mesons
Baryon decay always results in a proton and some other particles since the proton is the lightest and probably stable. Baryons cannot decay to mesons, so protons don’t decay to pions.
untitled1Mesons decay to lepton.
Rochester and Butler discovered in 1946 heavy meson – the kaon. The ions are formed by the strong interaction and decay by the weak interaction.Kaon were called “strange particles” because of this.
Kaons were created in collisions between pions and protons, the kaon was always accompanied by another strange particle it never came with a pion….