The Discovery of the Top Quark and Newer Gossp：頂夸克的發(fā)現(xiàn)和新的八卦

1、the discovery of the top quarkand newer gossipdon lincolnfermilab, university of michiganquarks come in six (known) flavorsd = downs = strangeb = bottomu = upc = charmt = topu uu ud du ud dd dprotonneutronparticle vocabulary1 ev (electron volt) is the amount of energy carried by aparticle with the s

2、ame charge as an electron, when accelerated by a 1 volt battery.electron1 kev (kilo electron volt) 1,000 x-rays, tv1 mev (mega electron volt) 1,000,000 gamma rays1 gev (giga electron volt) 1,000,000,000 big gamma rays1 tev (tera electron volt) 1,000,000,000,000 fermilab!particle linear accelerator (

3、linac)particleaccelerationelectric fieldsynchrotron (fermilab)electric fielde = m c2energy is mattermatter is energylots of energy makes lots of matterand vice versa!a short history of high energy physicsh before 1930s discovery of proton, neutron, electronh 1950s early hep experiments discover many

4、 particles, including strange onesh 1964 quark model proposed (sorry ace)h early 1970s quarks discovered (up, down and strange)h 1974 charm quark discoveredh 1977 bottom quark discovered (fermilab!)h 1984 top quark discovered 40 gev (oops!)h late 1980s series of lower limit measurementsh late 1980s

5、other measurements give upper limitsh 1995 discovery of top quark at fermilabthe 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 colli

6、sion, 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. weve identified 50 top quark events and expect 50 more which look like top, but arent.why is there more than in the unive

7、rse?hfact: in hep experiments, matter and antimatter are created in equal quantitieshfact: we observe (essentially) only matter when we look at the world.hfact: this is pretty bizarre. something doesnt jive.experimental approaches at hpossibility: perhaps anti-matter is unstable and decays.hpossibil

8、ity: perhaps matter and anti-matter arent 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 decayhproton lifetime greater than 10,000,000,

9、000,000,000,000,000,000,000,000 yearshuniverse lifetime about 10,000,000,000 yearshbefore fermilabs tests, anti-proton lifetime measured to be greater than about 3 days.hso a better measurement of the anti-proton lifetime is important.: slippery little suckershneutrinos are almost impossible to see.

10、 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.hbottom line: problems associated(?) with neutrinoshnot enough electron neutrinos coming from the sun.hexcept for neu

11、trinos 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 solutionhcurrent limits have

12、 the electron-type neutrino mass more than 100,000 times less massive than the electron 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 reca

13、ll there are three types of neutrinos if neutrinos have mass, they can change into each other. analogy: its 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