physics-subatomic-particles

deduce the general relatio n7, Pr .The shape of the cross-section - energy graph at resonance is given by the Breit-Wigne rformula6, = 1/((E-Fr)1+ (7/ 2 )2 ) ,where n is the energy at renorace, and 8 is the energy at which the width of th ecurve, V, has beer measured . The spin of a resonance is measured by the carefu lobservation of the angular distribution of its d e cay products, and, in the case of th eit is 3/2 . We know that the orbital angular momentum, 1, of the pion and nucleon i nthe A. particle is 1 . Thus we know that its parity i sP(11) P(N) (-1)~ 43 -The A. particle was the first resonance discovered in a formation experiment ,using cross-section - energy graphs . However, its statue as a resonance was no tconfirmed until it was also detected in a production experiment, where it acted as aparticle, rather than a favourite interaction energy . It was not, in fact, the firs tresonance to be revealed in a production experiment, but, for the sake of homogeneitywe will discuss its production experiment . We consider the reactio nPP — anA'" --a. nprt '.If there were no intermediate stage, then the neutron produced ahould have a complet erange of different energies . However, when protons of 2 .8 GeV were used, only a verysmall spread of value ., corre sp onding to the macs uncertainty of the 0 , peaked aroun d1 .62 GeV was found . It can be shown that this corresponds to the neutrons recoilin gfrom a single particle of mass 12.36 MeV, which is an acceptable experimental error .The first particle to be discovered in a resonance production experiment was th eY* particle . In late 1960, Alston, Alvarez, 3berhard, Good, Graziano, Ticho, and Wojkick iset out, using the accelerator at the Lawrence radiation Laboratory, to study th eprocessK 7+ p -4/47+7 7to see if any resonances could be produced . They allowed a magnetically-separate dkaon beam to enter a liquid hydrogen bubble chamber, and steadily increased its energy .Every 20 - 100 MeV, batches of photographs were taken of the reactions in the bubbl echamber . By 1960, there was good evidence from decay product momentum analysis, t oshow that the processK-+ p —~ - +1T -+ —~ +-++r 4. -was occurring . The mass of the Y " resonance was found to be about 1385 MeV and it sbandwidth to be about 60 MeV .We will not, at this point, follow the historical development of resonancephysics, but we will consider our current knowledge of the baryon resonances . No tonly have a considerable number of S• 0 and S= -1 baryon resonances been found, bu talso a few S .-2 ones . An example of one of these is the particle with a mass o f1530 MeV discovered by Bertanza et al . in 1962 . They showed that the proces sK +p--,=* K --s1T Ktook place by measuring the recoil energies of the K particle, and demonstrating tha tthey were consistent with recoil from one rather than tKo other particles . Theangular distribution of the decay products favoured a J of 3/ 2 + or 5/2 , but the