A Closer Look At Hadrons (2)
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Hadrons are elementary particles that are subject to both the strong and the weak force..

Hadrons are not really elementary particles however. They appear to occupy a finite space and are thus not dimensionless 'points' like leptons appear to be. The quark theory has attempted to account for the array of observed hadrons and mesons by postulating that they are composed of fundamental constituents termed 'Quarks'. Particle physics  (1985) attributes all known hadrons and mesons to combinations of six kinds of these fundamental entities and their corresponding 'Antiquarks'. The 'truth' quark is a hypothetical particle.



The diagram shows a second family of hadrons with very short lifetimes except for W- . These are termed resonances and may be thought of as 'excited states' like for excited atoms.Typical lifetimes are 10-19 to 10-23seconds so they cannot be observed directly in bubble chamber photographs and their creation and annihilation has to be inferred from other events. Charmed mesons have been observed .

Eg (J , - (c c )) termed 'Charmonium'.

Q9) Examine the diagram carefully and with the help of the quark table below interpret it fully. What is the difference between this supermultiplet of baryons and the one we encountered earlier ?


Q10) Calculate the time it takes light to cross an atom and comment on the lifetimes of the spin 3/2 baryons. The particle W- has a lifetime of 1.2 x 10-10 seconds. How far could it travel at speed 0.5c in this time ?
 

Q11) Using the quark properties in the table deduce the quark structure of the hadrons in the supermultiplet that includes the nucleons. Remember that antiparticles have baryon number (- 1/3 )and an antistrange quark has strangeness +1.

Q12) Calculate the kinetic energy of a proton travelling at 0.1 , 0.5 , 0.9 , 0.95 , 0.99 , 0.995 times the speed of light. Compare these energies with that of a 'truth' quark
 

Q13) For a two body decay, A -- > B + C , show ,using relativistic mechanics that in a frame of reference in which A is at rest, the Kinetic Energy of particle B is given by

Use this result to determine the kinetic energy of each decay product for the following decays:

(a) K+ --> p+ + po
(b) S+ --> p + po

CHARMONIUM
The J particle is interpreted as a bound state termed charmonium. Here is a Feynmann diagram for its production and possible decay:

Q14) Interpret these diagrams and write equations for them. What is the total charm of charmonium ?

Is it a lepton, meson or baryon ?

The most massive charmed baryon is ccc. Its mass is about 5 GeV. Repeat the analysis of Q10 and compare.

In actual fact 'Quarkonium' states are so massive that relativity can be ignored in analysing their motion. Why?.

Suggest some other Quarkonium states.

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