physics-subatomic-particles

have strangeness of opposite sign, so as to mace their total strangeness zero, and t oallow such reactions a sp-err-.fl+K° .They also postulated that in the weak decays of these so-called 'strange' particles ,strangeness is not conserved, thus inhibiting and slowing down the decays . It is anexperimental fact that the difference between the initial and final strangeness ofweakly interacting system is ± 1 . This type of rule is known as a 'partial' conservatio nlaw .We say that a group of particles of roughly the same mass is a multiplet . P•;ember sof the same multiplet are denoted by the same Greek letter, upper-case for baryon sand lower-case for mesons . Let us consider the average charges, Q, or centres o fcharge, of these multiplets . If we double the values of the average charges, we obtai na useful quantum number known as hypercharge, Y . The average charge of the nucleo nmultiplet is ;., but that of, for example, the n is O . Thus we say that the n i sdisplaced from the normal by -'> units . Let us call this displacement A . We find tha tA= . z and A, . -1 . For mesons, we say that the normal is the average charge of th epion multiplet, which is zero . Thus, ;iK z . If we double all our values for A, w efind that we have no other quantum number than strangeness, and so we see tha tstrangeness is given by:S = Y B .We might also have achieved this results by consider reactions which do and do no ttake place . For example, since the reactionp4 p'-a p+p+ K °does not take place, and we arbitrarily assign 3 .0 for the nucleons, we may say thatthe K° has nonzero strangeness .Soon after the discovery of the strong nuclear force, which is charge independent ,W.Heisenberg suggested the idea that the proton and neutron are simply differentfacets of the same particle, the ' nucleon' . He realised that, so far as the stronginteraction was concerned, they did behave in exactly the same way . An analogou ssystem to that of subatomic particles is to be found in atomic spectra . A givenspectral line depends upon the orbital quantum number, 1, and the magnetic quantu mnumber, m . We find that m aan take any integral value between -1 and 1 . When no magneti cfield is applied to the atom in question, spectral lines corresponding to differen tvalues of m have the same energy, and are said to be degenerate . However, if a weakmagnetic field is applied to the atom, spectral lines with different values of mform small groups called multiplets . This term has been borrowed by particle physics .If similarly, we could 'turn off' all electric charge in the universe, then, jus tlike spectral lines with differing values of m, the proton and neutron would appea ridentical .Heisenberg suggested the assignment of a new quantum number to each multi pl et ,which could, like ordinary spin, be projected according to the charge of a give nparticle . HP argued that if we are to call the proton and neutron truly differen tparticles because of their difference in charge, then we should also call proton swith spins of different particles from those with spins of 4 . He denoted theproton by the vector (1` and the neutron by the vector (0) . Using the Paul i0 1matrices, which are defined2,4 (0 1 0 -i1 0) ,26 s' (i 0) , 263410 -1,a