Colliding beams

We will be rather brief in describing the principles of the experimental methods that are most commonly used in studies of dissociative recombination, afterglows and colliding beams (merged beams and ion storage rings). It should suffice to recount some of their generic properties. 

Figure 1 shows three configurations for colliding-beam experiments that have been used for studies of dissociative recombination. These are the inclined-beam apparatus at the University of Newcastle-upon-Tyne,30 the merged-electron—ion-beam experiment (MEIBE) at the University of Western Ontario,31 and an electron-cooler apparatus at the Manne Siegbahn laboratory in Stockholm.32 In the inclined-beam method (Figure la), the ion beam is accelerated to an energy of 30... 

Figure 3 shows another example where colliding-beam experiments have produced results in excellent agreement with each other. This particular reaction is the recombination of ions with electrons producing ion-pair products, i.e. ... 

As an example of Ya.B. s role in the development of particle physics we quote from an article by G. I. Budker on colliding beams, The idea of antiparallel particles is not new it is a trivial consequence of the theory of relativity, As far as I know, it was first expressed by Academician Zeldovich, though in a very pessimistic context. His pessimism is quite understandable [53]. As is well known, G. I. Budker and his collaborators and their foreign colleagues were able to overcome the enormous difficulties which caused this pessimism. The role of colliding beams in particle physics is impossible to overestimate. 

Polanyi, John C. (1929-). Awarded the Nobel Prize in chemistry in 1986 jointly with Herschbach and Lee. Herschbach reported that the energies of reactions of colliding beams of isolated alkali metal atoms and alkyl halide molecules appeared mostly as vibrational excited states of products. Polanyi characterized the excited states by the infrared light emitted by product molecules. His work also led to the development of lasers. Bom in Germany, Polanyi studied in England and later became a Canadian citizen. Doctorate awarded by Manchester Universi-ty, England, in 1952. 

The encounter of two particles belonging to two colliding beams has a very low probability, because the number density of the colliding particles is very low. Two beams see each other almost transparent, and for one collision event to occur, the beams should be driven at each other many times, that is, the beams should be stored and they should have a suitably long life. 

The term luminosity is used in connection with colliding beam experiments to determine the production rate of a collision. The instantaneous luminosity is proportional to the overlap integral to the densities of the two beams. The total number of individual collisions in an experiment is given by the cross section of the collision process times the integrated luminosity, which is defined as the instantaneous luminosity integrated over the total time of the experiment. More details can be found in the work of Conte and Mackay (1991b). 

In crossed molecular beam scattering experiments, the direction of approach of the reactants is fixed by the configuration of the colliding beams [41]. Since by convention the incoming flux vector is directed along the space-fixed z-axis (and parallel to the field vectors E and B), we have = 0, and the general expression for the scattering amplitude (4.14) reduces to... 

In the CM system, both the projectile (first particle) and the target atoms (second particle) are supposed to move in the opposite directions (as in the case of colliding beams) whereas in the laboratory frame, the target atoms are at rest. Referring to Fig. B.l, let v and be the velocities of the projectile and target atoms in the opposite directions such that E = and... 

The ideal tools for studying the spectroscopy of the new vector meson particles have undoubtedly been the various e" e colliding beam machines SPEAR at SLAC, DORIS at DESY (Deutsches Elektronen Synchrotron), PETRA at DESY and, more recently, SLC at Stanford and LEP 1 at CERN though the actual discovery (Aubert et al, 1974 Herb et al, 1977 UAl, 1983 UA2, 1983) of some of these particles occurred on the proton machines (Brookhaven, Fermilab and CERN). 

Colliding-beam e" e machines were first advocated by B. Touschek in the late fifties, but not even the greatest optimist could have foreseen the development that took place after the early days of the single ring device ADA (Anello Di Accumulazione) whose operation began in 1960. 

Richter, B. (1976). In Physics with Very High Energy e+e" Colliding Beams, p. 237. CERN Report 76-18. 

Gatto,R, Theoretical Aspects of Colliding Beam Experiments (Vol. 39)... 

---