physics-subatomic-particles

Over 2500 photographs were taken of this proc ess, of which only 800 showed th e neutralpion necessary to conserve momentum if a resonance were to be formed . By computingthe effective mass of thelt'Tr-Ti° resonance by means of high-speed digital computer sthe rerearchers were able to show that in 93 cases a tri-pion resonance, which the ynamed ca had been formed . By momentum-analysis of decay products, the rs mass wa sfixed as 790 ieV . The ca was found to be a singlet with zero isospin .in the formation reactio nr -- d —gyp + p + Tr'+ Tr + TT °the Gross-section - energy graph was found to have two p eaks: a large one with aneffective mass of 790 I•ieV and a bandwidth of about 13 i :eV, and a smaller one with aneffective mass of 550 Ba y and a bandwidth of 2 .6 KeV. The particle represented by th esmaller peak was another singlet, which was named then) . Three of the four possibl edecays of this particle include two or more photons, and it has a long lifetime, s owe conclude that it is not a resonance in the true sense of the word, but decaysvia th eelectromagnetic interaction and is hence meta-stable . As the rl decay has only S= 0particles in it, it is possible to establish a G-parity for this particle, and it isfound to be-el, since there are three pions in its pions-only decay modes .Let us now consider the ex;o:imental methods used in finding mesic resonances .Apart from the bubble chamber method, as used in the search for the 1 meson, thereexists also a piece of apparatus known as a missing; mass spectrometer . The principl eof this is that a beam cf, for example n's with a well-defined momentum hits a liqui dhydrogen target producing the reactionTr ----4. P X,where 1 - represents a whole group of particles produced, whose not charge is -1 .The vector momentum of the recoil proton is than measured and the mass of the resonanc eparticle corrr ponding to h , if such a particle exists, is given b ym Z. _ ( C+ - Er, - (P„_ - Pr ,If no resonance exists, tries: the recoil proton will have a continuous range of energies ,and will not be monoenergetic . The first operational missing-mass spectrometer wa ssot up in 1968 by Kionale at Geneva . Behind the hydrogen target, in lino withthe primary beam of negative pions were two wire chambers, and behind these, therewas a matrix of counters . At an ajustable angle to the target, there were a series o fabout ton sonic spark chambers, which made up a proton telescop e. The whole. piece ofe-,uipment, including the target, was on a turntable, so that the target could pr esentitself to the beam at different angles . Kuch useful work has been done using the C12115 (Misting-' . o Spectrometer) . A slight improvement or the 10.13 is the CBi6ii Boso nSpectrometer (CBS). This can study different en°rgy~ regions from th- i' iS• It analyse sthe momenta of recoil electrons emerging near 0 using a wide-gap magnot and two pair sof wire spark chan gers . Toe whole a .pparat.s can be revolved about the main magnet inorder to study different ;pass regions. The great usefulness of the ills and CBS i stheir extreme speed, so that 100 000 readings can be taken to a very high accuracy i na matter of a few months .We will not discuss the discoveries of the hundreds of mesic resonances nowdiscovered in great detail, but we will consider a few interesting examples . In 196 5the first composite mesic resonance was found . It was named the Buddha, B, and had amass of around 1215 11eV . Its dominant decay mode was the two-stage proces sB —a w co .Another composite resonance, the C° particle, with decayC°( 14 22) --t°K°--*n'n-K