8/5/2002Ulrich Heintz - Quarknet Particle Physics what do we know? Ulrich Heintz Boston University

8/5/2002Ulrich Heintz - Quarknet Particle Physics What associations does the word particle physics bring to your mind?

8/5/2002Ulrich Heintz - Quarknet Particle Physics What are the fundamental building blocks of the universe? What are the interactions between them? How can we explain the universe? –its history –its present form –its future Is there a theory of everything?

8/5/2002Ulrich Heintz - Quarknet Particle Physics it’s fun and fascinating

8/5/2002Ulrich Heintz - Quarknet What is a particle? a small piece of matter... characterized by –charge –mass –lifetime –spin particles can scatter off each other like billiard balls unlike billiard balls, most particles are unstable and decay particles can be produced by colliding other particles

8/5/2002Ulrich Heintz - Quarknet What was the world made of in 1932? electrons (1897) –orbit atomic nucleus proton (1911) –nucleus of lightest atom neutron (1932) –neutral constituent of the nucleus photon (1905) –quantum of the electromagnetic field

8/5/2002Ulrich Heintz - Quarknet and Dirac’s relativistic quantum mechanics 1931 the positive electron (positron) –antiparticles: for every particle there exists an antiparticle with same mass, lifetime, spin, but opposite charge 1930 Pauli’s neutrino –energy conservation in beta decay requires the existence of a light, neutral particle –n  p + + e - + –observed in the muon and the pions (  +,  0,  - ) –Rabi: “who ordered that?”

8/5/2002Ulrich Heintz - Quarknet The ascent of accelerators previous discoveries used –cosmic rays –“natural accelerators” (radioactivity) after WWII –accelerators

8/5/2002Ulrich Heintz - Quarknet The particle “Zoo” 1947: strange particles –K 0   +  -, K +   +  +  - –p+ -–p+ - – ,  –long lifetime  ¼ s more particles... –p,–p, –    –short lifetime  ¼ s

8/5/2002Ulrich Heintz - Quarknet The quark model 1964 Gell-Mann, Zweig –there are three quarks and their antiparticles –each quark can carry one of three colors red blue green –antiquarks carry anticolor anti-red anti-blue anti-green QuarkUpDownStrange Charge+2/3-1/3

8/5/2002Ulrich Heintz - Quarknet The quark model –only colorless (“white”) combinations of quarks and antiquarks can form particles qqq qq no others observed

8/5/2002Ulrich Heintz - Quarknet The 8-fold way K0K0 -- K+K+ ++ 0  0   K-K- K0K0 sd ud su du ds us uu,dd,ss 00 -- ++ ++ 0 0  -- 00 uss uus dss dds udd uud uds -- ddd  ++ uuu -- sss n p mesons qq baryons qqq

8/5/2002Ulrich Heintz - Quarknet Quark confinement What holds quarks/antiquarks together? –strong force –acts between all “colored” objects –short range –independent of distance

8/5/2002Ulrich Heintz - Quarknet So what is the world made of? e e ud MeV0a few MeV  cs 106 MeV01100 MeV150 MeV  tb 1.8 GeV0175 GeV4.2 GeV leptons quarks spin = ½ (fermions) The Standard Model

8/5/2002Ulrich Heintz - Quarknet Are these fundamental? As far as we know.... –we can measure structure as small as m Accelerators are like huge microscopes –To measure smaller distances –go to higher energies

8/5/2002Ulrich Heintz - Quarknet How do particles interact? particles attract or repel each other by exchanging “messenger” particles (field quanta) e e    Feynman diagram

8/5/2002Ulrich Heintz - Quarknet What holds the world together? force acts between relative strength field quantum strong quarks 10 g electro- magnetic charged particles  weak all particles W § Z 0 gravity all particles G spin = 1 (bosons)

8/5/2002Ulrich Heintz - Quarknet The Higgs boson the standard model requires the existence of one more particle Higgs boson –uncharged –unknown mass (>115 GeV) –spin = 0 required to be able to describe massive fermions and bosons

8/5/2002Ulrich Heintz - Quarknet Is this the theory of everything? NO –Standard Model doesn’t work at all energies –Standard Model does not include gravity –we haven’t found the Higgs yet... unification Electricity Magnetism Weak force Strong force Gravity string theory... electromagnetism electroweak force GUTs

8/5/2002Ulrich Heintz - Quarknet Accelerators 1983: CERN pp collider –E = 540 GeV  W § (80 GeV), Z 0 (91 GeV) 1995: Fermilab Tevatron pp collider –E=1.8 TeV  top quark (175 GeV) ¼ 2008: CERN LHC pp collider –E=14 TeV  discover Higgs? ????: Linear e + e - Collider –E=1-2 TeV  study Higgs in detail

8/5/2002Ulrich Heintz - Quarknet What might we find? Super Symmetry –fermions  bosons –we have already found half the particles.... electronselectron neutrinosneutrino quarksquark photonphotino gluongluino WWino ZZino