Physics 116 Session 40 Particle physics Dec 6, 2011 Email: ph116@u.washington.edu
Announcements • � Final exam: Monday 12/12, 2:30-4:20 pm • � Same length/format as previous exams (but you can have 2 hrs) • � Kyle Armour is away this week; see TAs in study center • � JW will have extra office hours Thu-Fri this week: • � 12:45-1:15pm before class, • � 2:30-3pm after class (my office B303 PAB, or B305 conf room next door) • � Practice questions will be posted tomorrow (Weds) evening TODAY: YOUR CHANCE FOR REVENGE – COURSE EVALUATION Pick up now: bubble sheet, yellow sheet and pencil but wait to fill out until I leave the room (or, if you must leave early, leave forms with a neighbor to turn in) Leave completed forms in box at front of room, at end of class. News items worth reading: Today’s NY Times, see • � Astronomers Find Biggest Black Holes Yet, By DENNIS OVERBYE (more on this today) • � Quantum Computing Promises New Insights, Not Just Supermachines, By SCOTT AARONSON (contemporary atomic physics)
Lecture Schedule (to end of term) Today 3
What’s a black hole? “Not on exam” • � Stars die in 3 ways: – � Mass smaller that 1.4 Sun’s mass: as nuclear fuel burns out, becomes a “brown dwarf” (blob of frozen gas) – � Mass between 1.4 and about 3 Msun : supernova explosion • � As fusion fuel runs out, star collapses under its own gravity • � Eventually density/temperature so great it reignites in a massive sudden explosion: supernova • � Most of its mass (heavy elements!) is expelled into its galaxy • � Remnant is a neutron star (solid blob of neutrons*!!) or other “compact object”, typically radiates lots of energy (“pulsar”) – � Mass greater than about 3 Msun: collapses too quickly for the supernova stage, into a “black hole” • � General relativity says light is bent by strong gravity • � When density is so big, g field gets so intense that light cannot escape: black hole • � Black hole’s intense g field sucks up all nearby matter… • � Most galaxies have a BH at their center * Density >10 17 kg/m 3 = Earth crushed to size of Manhattan 4
What is required to make gravitational escape velocity = speed of light? Recall from PHYS 114: v ESC = 2 GM EARTH 2 GM BH � c = “Not on exam” R EARTH R BH ? We used classical physics, but GR BH = 2 GM BH Schwarzschild radius: R calculation gives the same result c 2 “horizon” of BH of mass M Most BHs have spin – stars spiral into them our solar system on the same scale “event horizon” = radius such that nothing can escape (all light cones bend into the BH; “future” of any object there lies entirely inside the BH Today’s NY Times Artists’ conception of Black Hole with M=10 10 M sun
Some terminology... yesterday • � "Elementary particles" = objects that make up atoms (n,p,e) or are produced when atoms are smashed (over 200 identified) – � "elementary" because thought to be fundamental in 1950s • � "Fundamental" particles or constituents of matter – � Truly no known substructure (as of today!) • � Hadrons = elementary particles subject to strong nuclear force (Greek: hadros = strong) – � protons, neutrons; plus pions, kaons, lambda particles...etc – � now known to be made of fundamental particles: quarks • � Leptons = elementary particles subject to weak nuclear force (Greek: leptos = weak) – � responsible for radioactive decays – � electrons, plus muons, taus and associated neutrinos • � All leptons are considered fundamental (as of today!) 6
But that’s not all... • � Antimatter : Each elementary particle has an “antiparticle” counterpart Electron � Antielectron (Positron) Proton � Antiproton Neutron � Antineutron etc . � anti-etc . Antiparticles have opposite electric charge (and other properties) but are otherwise identical • � E = mc 2 says matter and energy are interchangeable – � It’s just as easy to make antimatter as matter • � Happens all the time in nature - and we can do it in labs – � But: if particle and antiparticle meet – annihilation! – � How come we live in a universe where there is almost no antimatter? (luckily - or we might not survive long…) What caused the Big Bang to create much more matter than antimatter? 7
The “Standard Model” of Particle Physics Basic ingredients of matter are the Fundamental fundamental forces are particles: quarks and mediated by leptons photons, gluons, 6 quarks Z’s and W’s 6 leptons These types of particles are + their antiparticles called 'bosons' (Symmetry!) !"#$%&'(( These types of particles are called (after 'fermions' Satrendyanath Bose) (after Enrico Fermi) (from http://www.fnal.gov) 8
Fundamental particles: graphic where size is proportional to rest energy (mass) (Neutrinos are invisibly tiny on this scale) 9
All Forces are Mediated by Exchanged Particles • � Electrical and Magnetic forces – photon (massless) • � Strong nuclear force – “gluons” (massless – but have 3 “colors”) • � Weak nuclear force – W, Z (massive) • � Gravity – graviton (massless, although no one has yet seen one) – � LIGO experiment in Hanford, WA will try! • � search for gravity waves • � Laser beams in 4km-long tunnels • � Look for changes in length of 10 -15 m! LIGO Hanford Observatory http://www.ligo-wa.caltech.edu/ • � The range (reach) of the force depends on the mass of the exchanged particle – � Gravity and electromagnetic forces extend infinitely far (though weaken with increased distance) – � Strong and weak nuclear forces are remote from everyday experience: only come into play at distances like nuclear size 10
Hot Quark Soup • � 6 quarks, in 3 'generations' with increasing mass – � up/down, charm/strange, top/bottom • � Combinations of quarks make up (explain properties of) the entire 'zoo' of particles cataloged since the 1950s – � 6 quarks, 6 anti-quarks, grouped in twos and threes • � baryons = 3 quarks • � mesons = quark + antiquark – � Many dozens of combinations, but only 1 or 2 stable – � Charges always come out as multiples of e charge! – � Model explained newly discovered particles too! • � For example: – � Up, charm, top quarks have +2/3 charge – � Down, strange, bottom quarks have –1/3 charge – � 2u + 1d (uud) � proton, with +1 charge • � 2(+2/3) + 1(-1/3) = 3/3 = +1 – � 2d + 1u (ddu) � neutron, with 0 charge • � 2(-1/3) + 1(+2/3) = 0/3 = 0 11
Need heavy-duty equipment to make high energy particle beams! Photo of CERN (EU particle physics lab) near Geneva, Switzerland See http://public.web.cern.ch/ CERN proton accelerator and p/anti-p collider rings (LHC = Large hadron collider) Geneva airport CERN, Switzerland 12
ATLAS detector @ LHC UW members: Profs. Henry Lubatti, Anna Goussiou, and Gordon Watts and their students Size of humans! 13
Data from ATLAS: p+anti-p go to Z boson + 2 electrons 14
What are they looking for? • � Ideally, all quarks should have zero mass: perfect symmetry!! • � How come we live in a Universe where things have mass? • � Symmetry must be broken somehow… • � “Higgs boson” = as-yet undetected particle that is the “messenger” of the symmetry-breaking that gives everything else mass • � Higgs is expected to be very massive itself: beyond energy reach of previous generations of particle accelerators Hot results expected from LHC next week… 15
What to look for in the news… If p+anti-p make a Higgs, we expect to see a bump in the probability vs total energy graph. The rumor mill says the bump below has become much bigger (>3 � ) with more data. Actual data (as of early November � = std. deviations 16
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