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

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

Ulrich Heintz - Quarknet 2002 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? 8/5/2002 Ulrich Heintz - Quarknet 2002

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

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

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 8/5/2002 Ulrich Heintz - Quarknet 2002

Ulrich Heintz - Quarknet 2002 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?” 8/5/2002 Ulrich Heintz - Quarknet 2002

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

Ulrich Heintz - Quarknet 2002 The particle “Zoo” 1947: strange particles K0+ -, K++ + - p+ - ,  long lifetime  ¼ 10-10 s more particles... p,  short lifetime  ¼ 10-24 s 8/5/2002 Ulrich Heintz - Quarknet 2002

Ulrich Heintz - Quarknet 2002 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 Quark Up Down Strange Charge +2/3 -1/3 8/5/2002 Ulrich Heintz - Quarknet 2002

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

Ulrich Heintz - Quarknet 2002 The 8-fold way baryons qqq mesons qq 0 - + + 0  - 0 uss uus dss dds udd uud uds - ddd ++ uuu - sss n p K0 - K+ + 0   K- sd ud su du ds us uu,dd,ss 8/5/2002 Ulrich Heintz - Quarknet 2002

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

So what is the world made of? The Standard Model e e u d 0.511 MeV a few MeV   c s 106 MeV 1100 MeV 150 MeV   t b 1.8 GeV 175 GeV 4.2 GeV spin = ½ (fermions) leptons quarks 8/5/2002 Ulrich Heintz - Quarknet 2002

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

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

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§ Z0 gravity all particles 10-42 G spin = 1 (bosons) 8/5/2002 Ulrich Heintz - Quarknet 2002

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

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 electromagnetism electroweak force GUTs string theory... 8/5/2002 Ulrich Heintz - Quarknet 2002

Ulrich Heintz - Quarknet 2002 Accelerators 1983: CERN pp collider E = 540 GeV  W§ (80 GeV), Z0 (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 8/5/2002 Ulrich Heintz - Quarknet 2002

Ulrich Heintz - Quarknet 2002 What might we find? Super Symmetry fermions  bosons we have already found half the particles.... electron selectron neutrino sneutrino quark squark photon photino gluon gluino W Wino Z Zino 8/5/2002 Ulrich Heintz - Quarknet 2002