Andrei Solodsky- 2001


Observation of diffractive J/Psi production


The best way to present Andrei Solodsky is to explain briefly what question he answered in his thesis and how he went about it. After all, you only REALLY know people by what they do!

Our Universe is full of mysteries. Finding answers to mysteries satisfies our inherent thirst for knowledge and benefits society. Remember Archimedes jumping out of his bathtub shouting "eureka"? Well, Andrei did not find the answer to his thesis topic in the bathtub. It wasn't that easy, but there are similarities! When one day, after several years of dedicated and hard work he finally had the answer to his mystery and walked into my office to share it with me, in his excitement he did look like he had just taken a bath!

From his thesis title you wouldn't guess that Andrei addressed a key question about the birth of the Universe, not to mention guessing about possible spin-offs to society. Well then, listen to the story behind the title, and please do listen carefully, because at the end of the story I am going to ask YOU to answer the question about benefits to society.

The Universe is made up of two kinds of fundamental constituents: quarks and leptons. An example of a lepton is the well known electron. Electrons are used abundantly in communications - when electrons move, the world listens! Quarks, however, are not found free in nature. They are confined in groups of two or three inside particles like the pion and the proton. Even school children today know that the proton is made up of three quarks. But is this the whole story?

There would be no Universe if the quarks and leptons did not interact among themselves. The three "valence" quarks inside the proton interact with one another by exchanging gluons, which are the quanta of the "strong force" that binds quarks together. The gluons themselves emit quark-antiquark pairs, which emit other gluons, and ... the beat goes on! So, the energy of a fast moving proton is shared by a "sea" of quarks and gluons, which we call partons. We know all this from experiments in which an individual parton is knocked out of a proton in a high energy head-on collision with an electron or another proton. A struck parton emerges from the collision as a jet of ordinary particles carrying the parton's energy.

But how are the partons organized inside the proton? In particular, do they form states that are energy bundles with vacuum quantum numbers? By studying such states we could learn something about the properties of the vacuum from which the Universe was created in the big bang. But how can this be done in practice?

A high energy collision between a proton and an antiproton at the Tevatron, Fermilab's powerful particle accelerator, is like an explosion creating on average about 100 particles of all kinds. In two dimensions, this firework-like spectacle looks like a beautiful pie. But in some collisions a large piece of the pie is missing! Who got it? Apparently, in these cases a piece of energy with vacuum quantum numbers escaped from, say, the proton and collided with the antiproton producing an asymmetric firework of particles. Such collisions are called "diffractive". The next question is whether the ingredients in the partially eaten pie are in the same proportion as in the full pie. In other words, does a collision with the vacuum produce the same variety of particles? In earlier studies, our group had found that this is indeed the case for particles made up of the ordinary up and down quarks. Andrei studied the production of J/Psi particles, which are made up of "charm" quarks, and found that this is true in this rather exotic case as well. In a pecan pie analogy, Andrei found that whoever ate the missing piece of the pie did not also eat the pecans from the rest of the pie! The vacuum is well behaved!

And now the question: how could possibly such a seemingly obscure discovery benefit society? Well, I couldn't blame you if you don't yet have the answer. By explaining how electrons behave inside semiconductors, quantum mechanics changed the world in a way that nobody could have imagined. So, perhaps it would be unfair for me to ask anyone to imagine what benefits could come from understanding the true nature of the force that confines quarks inside protons.

Andrei did his work in collaboration with about 500 other pysicists from 50 institutions. It took all these people several years to build a state of the art particle detector, and five years to collect data of proton-antiproton collisions at Fermilab. But for Andrei, it was just as if all these people were working for him! He did the data analysis alone with dedication and high standards. He truly deserves the credit for this discovery, and I am proud to present him today for the degree of Doctor of Philosophy.