Modern Physics

 Quarks colour The problem associated with the idea that baryons are composed of quarks is that two or three same type of quarks are contain in a particular particle for example two u quarks in proton and three s quarks in 𝝮⁻ baryons violates the exclusion principle. Quarks must follow exclusion principle because they are fermions and have half integral spin (1/2). To solve this problem, it was considered that quarks have an additional property called colours and its possibilities are red, green and blue. The antiquark colours are antired, antigreen and antiblue. According to colour hypothesis, each baryon consist of three quarks of different colours which satisfies the exclusion principle, since all quarks have different states even if two or three particles are identical, such combination is thought to be white. The antibaryon is made of antired, antigreen and antiblue quarks. The meson is consist of quark of one colour and an antiquark of corresponding anticolour and thus cance...

Quarks Gellmann and independently George Nishijina propose that all baryons consist of three fundamental particles. Gellmann named these particles 'quarks' from the phrase 'three quarks for Muster Mark' appear in the novel Finnegann's Wake. The three fundamental quarks are up, down and strange. The up and down quarks have strangeness number zero and the strange quark have strangeness number -1. Since each baryon (B = 1) consist of three quarks, thus each quark has baryon number B = 1/3. Each antibaryon (B = -1) consist of three antiquarks, thus each antiquark have B = -1/3.  A meson (B = 0) is supposed to consist of a quark and an antiquark. Quarks and antiquarks have spin equal to 1/2. Each quark have fractional charge. No particle in nature have fractional charge, so quark hypothesis was hard to accept at the beginning. The existence of quark was proved by the simple experiment which involved scattering of high energy electrons by protons.  Flavour of quarks There...

Quantum numbers; In case of elementary particles, while considering reactions, we must consider various parameters. One of the major parameter is quantum numbers.  Baryon and lepton numbers A set of quantum numbers is used to characterise baryons and three families of leptons. Baryon and lepton numbers.   The significance of these numbers is that in any kind of reaction the total baryon numbers (B) and lepton numbers are conserved. Baryon and lepton quantum numbers are conserved. Strangeness number (S) Gellmann and Nishijina introduced a new quantum number called strangeness quantum number. Strangeness number is assigned to strange particles, which are named due to their strange behaviour i.e they are produced via strong interaction or electromagnetic interaction, but they decay via weak interaction. Another fact about these particles is that they are always produced in pairs. The assignment of strangeness number to particle is shown in Table below. Strangeness number of hadro...