The Discovery of the Top Quark and Newer Gossip Don Lincoln Fermilab, University of Michigan

Quarks come in six (known) `flavors’ d = down s = strange b = bottom u = up c = charm t = top u u d u d d protonneutron

Acceleration Particle Acceleration Vocabulary 1 eV(electron volt) is the amount of energy carried by a particle with the same charge as an electron, when accelerated by a 1 volt battery. electron 1 keV (kilo electron volt) 1,000 x-rays, TV 1 MeV (mega electron volt) 1,000,000 Gamma rays 1 GeV (giga electron volt) 1,000,000,000 Big gamma rays 1 TeV (tera electron volt) 1,000,000,000,000 Fermilab!

Acceleration Particle Acceleration Linear Accelerator (LINAC) Particle Acceleration Electric Field Synchrotron (Fermilab) Electric Field

E = m c 2 Energy is Matter Matter is Energy Lots of energy makes lots of matter and vice versa!!!!!!

A Short History of High Energy Physics HBefore 1930’s Discovery of proton, neutron, electron H1950’s Early HEP experiments discover many particles, including ‘strange’ ones H1964 Quark model proposed (sorry Ace) HEarly 1970’s Quarks discovered (up, down and strange) H1974 Charm quark discovered H1977 Bottom quark discovered (Fermilab!) H1984 Top quark ‘discovered’ 40 GeV (oops!) Hlate 1980’s Series of lower limit measurements Hlate 1980’s Other measurements give upper limits H1995 Discovery of top quark at Fermilab

The Needle in the Haystack There are 2,000,000,000,000,000 possible collisions per second. There are 300,000 actual collisions per second, each of them scanned. We write 4 per second to tape. For each top quark making collision, there are 10,000,000,000 other types of collisions. Even though we are very picky about the collisions we record, we have 30,000,000 on tape. Only 500 are top quark events. We’ve identified 50 top quark events and expect 50 more which look like top, but aren’t.

matter anti-matter Why is there more matter than anti-matter in the Universe? HFact: In HEP experiments, matter and antimatter are created in equal quantities HFact: We observe (essentially) only matter when we look at the world. HFact: This is pretty bizarre. Something doesn’t jive.

Fermilab Experimental Approaches at Fermilab HPossibility: Perhaps anti-matter is unstable and decays. HPossibility: Perhaps matter and anti-matter aren’t quite created equally. Maybe there is a little more matter made than anti-matter. HPossibility: There are chunks of the universe which are entirely anti-matter. HPossibility: Something else is going on.

Anti-matter Decay HProton lifetime greater than 10,000,000,000,000,000,000,000,000,000,000 years HUniverse lifetime about 10,000,000,000 years HBefore Fermilab’s tests, anti-proton lifetime measured to be greater than about 3 days. HSo a better measurement of the anti-proton lifetime is important.

Neutrinos Neutrinos: Slippery little suckers HNeutrinos are almost impossible to see. HNeutrinos are involved in some kinds of nuclear radiation. HA neutrino from nuclear decay has a 50/50 shot of punching through 750 light-years of lead. HNeutrinos have nearly no mass. They’re almost not there. HBottom line: They’re almost not there.

Problems Associated(?) with Neutrinos HNot enough electron neutrinos coming from the sun. HExcept for neutrinos coming from the sun, there should be two muon-type neutrinos for each electron-type neutrino. Observed ratio is more like one to one. HAstrophysics studies show that there is more gravitational force in the universe than can be explained by observed matter.

Possible Solution HCurrent limits have the electron-type neutrino mass more than 100,000 times less massive than the electron H IF H IF the electron neutrino is no more than about 500,000 times less massive than the electron, all of these effects can be explained. HConclusion: Measure the mass of the neutrinos.

Measuring if neutrinos have mass Recall there are three types of neutrinos If neutrinos have mass, they can change into each other. Analogy: It’s as if you have three kinds of people: (boys, girls, and other) Start with a population of boys. If after some time you see some girls in the population, some must have changed.

Summary The discovery of the top quark is the biggest discovery in particle physics since Fermilab is now exploring many more interesting topics, with preliminary results becoming available within the year. Come on out and visit!!! The geese, buffalo and even the scientists are waiting....