Suren Bagdasarov - 1998


Observation of diffractive W-boson production at the Fermilab Tevatron


Suren came from Armenia, where he studied as an undergraduate at Yerevan University. For his thesis at Rockefeller, he chose to study a very peculiar and extremely interesting class of interactions between subatomic particles. Since you can really get to know a person by what he does, and since his thesis title is not very revealing to the non-specialist, I will say a few words about his thesis.

All interactions among subatomic particles occur through messengers, which transfer energy, momentum and information from one particle to the other. The messengers are themselves particles, and the information they transfer is in the form of quantum numbers.

The violent exchange of energy and momentum fragments the interacting particles into two multi-particle clusters. The space between these two clusters is filled with other particles radiated from the messenger as it travels from one particle to the other. In a typical collision between a proton and an antiproton at the Fermilab Tevatron - an energy equivalent to 2000 times the proton mass - about 100 particles are produced, flying away from the collision point in all directions.

A messenger that carries the quantum numbers of a vacuum does not radiate particles. Events due to "vacuum exchange," called "diffractive", consist of two particle-clusters with no other particles in-between. The study of diffractive events can help us characterize the nature of vacuum exchange. One of the questions to be answered is what fraction of the exhanged energy is in the form of quark-antiquark pairs. This fraction can be measured from the rate of production of "W" particles in diffractive collisions. Suren made the first observation of diffractive W production, and from their production rate concluded that a substantial fraction of the vacuum-exhange energy is in the form of quark-antiquark pairs. This result was unexpected and has been the subject of discussion at every international conference since its discovery.

Suren took his vacuum exploration very seriously. Every time I went to the lab, I found him there. So, I was under the impression that he never went home. Finding the signal we were looking for was very difficult work. Every time I saw him I would ask him:

`did you get anything yet?' The answer was always no, until one day he said:

`I got a baby!'

`Really?' I asked, thinking he was talking about the long-sought signal. `Let me see it.'

`She is at the hospital,' he answered. `She weighs 8 lbs and her name is Lana.'

`Oh!' I said, as I finally understood what he meant. `And how is our wife Jana?'

Well, this is Suren. Trustees, friends, Mr. President, I am very proud to present Suren Bagdasarov for the degree of Doctor of Philosophy.