1. 8/5/2002Ulrich Heintz - Quarknet 20021 Particle Physics what do we know? Ulrich Heintz Boston University

2. 8/5/2002Ulrich Heintz - Quarknet 20022 Particle Physics What associations does the word particle physics bring to your mind?

3. 8/5/2002Ulrich Heintz - Quarknet 20023 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?

4. 8/5/2002Ulrich Heintz - Quarknet 20024 Particle Physics it’s fun and fascinating

5. 8/5/2002Ulrich Heintz - Quarknet 20025 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

6. 8/5/2002Ulrich Heintz - Quarknet 20026 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

7. 8/5/2002Ulrich Heintz - Quarknet 20027 and... 1927 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 1956 1936-1947 the muon and the pions (  +,  0,  - ) –Rabi: “who ordered that?”

8. 8/5/2002Ulrich Heintz - Quarknet 20028 The ascent of accelerators previous discoveries used –cosmic rays –“natural accelerators” (radioactivity) after WWII –accelerators

9. 8/5/2002Ulrich Heintz - Quarknet 20029 The particle “Zoo” 1947: strange particles –K 0   +  -, K +   +  +  - –p+ -–p+ - – ,  –long lifetime  ¼ 10 -10 s more particles... –p,–p, –    –short lifetime  ¼ 10 -24 s

10. 8/5/2002Ulrich Heintz - Quarknet 200210 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

11. 8/5/2002Ulrich Heintz - Quarknet 200211 The quark model –only colorless (“white”) combinations of quarks and antiquarks can form particles qqq qq no others observed

12. 8/5/2002Ulrich Heintz - Quarknet 200212 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

13. 8/5/2002Ulrich Heintz - Quarknet 200213 Quark confinement What holds quarks/antiquarks together? –strong force –acts between all “colored” objects –short range –independent of distance

14. 8/5/2002Ulrich Heintz - Quarknet 200214 So what is the world made of? e e ud 0.511 MeV0a few MeV  cs 106 MeV01100 MeV150 MeV  tb 1.8 GeV0175 GeV4.2 GeV leptons quarks spin = ½ (fermions) The Standard Model

15. 8/5/2002Ulrich Heintz - Quarknet 200215 Are these fundamental? As far as we know.... –we can measure structure as small as 10 -18 m Accelerators are like huge microscopes –To measure smaller distances –go to higher energies

16. 8/5/2002Ulrich Heintz - Quarknet 200216 How do particles interact? particles attract or repel each other by exchanging “messenger” particles (field quanta) e e    Feynman diagram

17. 8/5/2002Ulrich Heintz - Quarknet 200217 What holds the world together? force acts between relative strength field quantum strong quarks 10 g electro- magnetic charged particles 10 -2  weak all particles 10 -13 W § Z 0 gravity all particles 10 -42 G spin = 1 (bosons)

18. 8/5/2002Ulrich Heintz - Quarknet 200218 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

19. 8/5/2002Ulrich Heintz - Quarknet 200219 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

20. 8/5/2002Ulrich Heintz - Quarknet 200220 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

21. 8/5/2002Ulrich Heintz - Quarknet 200221 What might we find? Super Symmetry –fermions  bosons –we have already found half the particles.... electronselectron neutrinosneutrino quarksquark photonphotino gluongluino WWino ZZino