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Home , Delta baryon

From Last Time… Something unexpected • are quanta of a quantum field • Raise the momentum and the and see – Represent excitations of the associated field what we can make. – Particles can appear and disappear • Might expect that we make a and an • Particles interact by exchanging other particles antiquark. The particles that make of the . – Electrons interact by exchanging – Guess that they are 1/3 the of the proton 333MeV • This is the Coulomb interaction µ, mass: 100MeV/c2, • Electrons are excitations of the field electron mass 0.5 MeV/c2 • Photons are excitations of the field • Today e- µ- Instead we get a More particles! muon, acts like a heavy version of Essay due Friday µ + the electron e+ Phy107 Fall 2006 1 Phy107 Fall 2006 2

Accelerators CERN (Switzerland)

• What else can we make with more energy? •CERN, Geneva Switzerland • Electrostatic accelerator: Potential difference V accelerate electrons to 1 MeV • LHC Cyclic accelerator • Linear Accelerator: Cavities that make EM waves • 27km, 14TeV surf the waves - SLAC 50 GeV electrons 27 km 7+7=14 • Cyclic Accelerator: Circular design allows particles to be accelerated by cavities again and again – LEP 115 GeV electrons – Tevatron 1 TeV – LHC 7 TeV protons(starts next year)

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Measuring particle collisions Fundamental Particles Detectors are required to determine the results of In the the basic building blocks are the collisions. said to be ‘fundamental’ or not more up of constituent parts. Which particle isn’t ‘fundamental’:

A. electron B. muon • CDF: Collider C. photon Detector Facility at Fermilab D. proton

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1 What have we learned? • Neutrino was first detected in 1956 is made of • The neutrino has –Zero charge, 1/2, almost zero mass • Electron has – Charge -e, spin 1/2, Atoms are made of and mass 0.5 Mev/c2 “ Atoms are made of leptons and quarks “  u • Electron and neutrino Leptons e Quarks generically called leptons e d Fred Reines, Clyde Cowan, at the Hanford nuclear reactor Interact via different forces carried by particles, Seen before in the weak interaction. photons… Phy107 Fall 2006 7 Phy107 Fall 2006 8

Protons/ are composite Protons, neutrons, and quarks

• Protons and neutrons are made up of – ‘up’ quarks and ‘down’ quarks

Charge Spin Mass (MeV/c2) Up +(2/3)e 1/2 3 Down -(1/3)e 1/2 6

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Question Protons & Neutrons

A is a composite particle consisting of three quarks (up=charge +2/3e, and down = To make a proton: We bind 2 up quarks of Q = +2/3 charge -1/3e). Which is the structure of the and 1 of Q = -1/3. neutron. The total charge is Total charge: 2/3 + 2/3 + (-1/3) = +1 ! A. up, up, up +2e To make a neutron: B. up, up, down +e We bind 2 down quarks of Q= -1/3 C. up, down, down with 1 of Q = +2/3 to get: 0 (-1/3) + (-1/3) + (2/3) = 0 !

Neutron has zero total charge

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2 Hierarchy of structure What about the muon? -15 R ~ 10 m (strong) • The muon found early on. protons and neutrons are – Heavy version of the electron. made from quarks  u • Otherwise would have been fairly simple! Leptons e Quarks e d µ, Muon mass: 100MeV/c2, R ~ 10-10 m (electromagnetic) electron mass 0.5 MeV/c2 Atoms are made from protons, neutrons, and electrons e- µ-

R > 106 m (gravitational) We’ll talk about the rest of µ + e+ the universe later

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More particles The particle garden • In 1975, the was discovered at SLAC.(Nobel prize, 1995) • at this point has settled on a Just like the electron and muon, but 3500 times countable number of ‘fundamental particles’. heavier than the electron – Same charge, • The bad news - there are: same spin, but different mass. – (6 leptons +6 quarks)+ (4 electroweak +8 +1 ) =25 • Made this particle by fundamental particles, not counting ! creating more energy. • The good news: – These are not just random, but have some relationships Both the muon and tau have that let us understand the ideas without thinking Muon-neutrino immediately about all the particles. Tau-neutrino Stanford linear (detected in 2000) accelerator center (SLAC) Phy107 Fall 2006 15 Phy107 Fall 2006 16

Three electron-like particles Three

Charge Spin Mass (MeV/c2) Charge Spin Mass (MeV/c2) Electron -e 1/2 0.5 Electron-neutrino 0 1/2 ~0 Muon -e 1/2 106 Muon-neutrino 0 1/2 ~0 Tau -e 1/2 1,777 Tau-neutrino 0 1/2 ~0

These are referred to as three These are referred to as three ‘generations’ of particles. ‘generations’ of particles. Difference between them is only mass Difference between them is only mass

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3 Six quarks Quarks: Heavy, Heavier, Heaviest  6 different kinds of quarks. 2 1000 Charge Spin Mass (MeV/c ) Gold top  Matter is composed mainly ]

2 100 Up +(2/3)e 1/2 3 of up quarks and down quarks Silver atom bound in the nuclei of atoms. 10 Down -(1/3)e 1/2 6 bottom Proton charm 1  vary dramatically Mass [GeV/c 2 strange Top +(2/3)e 1/2 1,300 (from ~0.005 to 175 [GeV/c ]) 0.1

Bottom -(1/3)e 1/2 100  Heavier quarks are unstable, 0.01 down up rapidly decay to lighter quarks 0.001 01234567 Charmed +(2/3)e 1/2 175,000 Strange -(1/3)e 1/2 4,300 Example: t  b (~10-23 [s]) b  c (~10-12 [s]) More on quark decays c  s (~10-12 [s]) later… Phy107 Fall 2006 19 su Phy107(~10 -7-Fall10 2006-10 [s]) 20

Three ‘generations’ of particles The generations of ‘matter particles’ • Three generations differentiated primarily by mass (energy). • First generation Light – One pair of leptons, one pair of quarks Heavier • Leptons: – Electron, electron- neutrino. Heaviest •Quarks: Up, down.

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Antiparticles Making more composite particles • Each of these has an , different only by charge. • The forces which hold the protons and neutrons together in the nucleus are VERY strong. • Electron antiparticle •They interact via the STRONG FORCE. = • Muon antiparticle • Protons and neutrons are among a class of particles called = anti-muon “” (Greek for strong). • Particles made of quarks. • Tau antiparticle = anti-tau • are hadrons which contain 3 quarks (no anti-quarks). Matter and anti-matter can • Anti-baryons are hadrons which contain annihilate creating energy 3 anti-quarks (no quarks).

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4 Use up and down quarks Are there baryons other than Quark up down strange protons and neutrons? Charge Q +2/3 -1/3 -1/3 Mass ~5 [MeV/c2] ~10 [MeV/c2] ~200 [MeV/c2] Other quarks can combine to form other baryons. u u u d d d s s s For example:

u This combination is called a u u 0 s Lambda , or  for short d d d u d Charge 0: (2/3) + (-1/3) + (-1/3) = 0 Proton Neutron Q = +1 Q = 0 M=938 MeV/c2 M=940 MeV/c2

Most of the mass is in the binding energy.

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More Baryons Another baryon: Quark up down strange Q +2/3 -1/3 -1/3 u What’s this baryon’s electric 2 2 2 charge? Mass ~5 [MeV/c ] ~10 [MeV/c ] ~200 [MeV/c ] u u u u u d d d s s s Delta baryon, or ++ for short. Charge: +2 Excited state - Higher energy/mass (2/3) + (2/3) + (2/3) = +2 !

u u u d A. 0 s d s u s d s d B. +1 Lambda () Sigma (+) Sigma (0) Sigma () C. +2 Q = 0 Q = +1 Q = 0 Q = -1 M=1116 MeV/c2 M=1189 MeV/c2 M=1192 MeV/c2 M=1197 MeV/c2

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Mesons Leptons and quarks: • They are formed when a quark and an anti-quark what’s the difference? “bind” together. • One important difference is how they interact. • So far we’ve only seen 3 quark combinations. There are also 2 quark combinations. • We said the Coulomb interaction is between • The hadrons: 2 quarks, and 3 quarks, baryon. particles with electrical charge. • Understood by exchanging photons. d d d • The other interactions: u c s –Weak –Strong What’s the charge What’s the charge What’s the charge of this particle? of this particle? of this particle? – Gravitational • Particles understood/defined by how they Q=+1, and it’s Q= -1, and this charm Q= 0, this strange interact called a + meson is called a D- meson is called a K0  Phy107 Fall 2006 29 Phy107 Fall 2006 30

5 Electromagnetic Force Interactions between particles • The modern view of forces In the Standard Model particles are often classified is in terms of particle exchange. by what forces they interact via. • These are ‘virtual’ particles of the fields Which of these particle does not interact with the created by the particle charges. electromagnetic force: This shows Coulomb A. electron repulsion between two electrons. It is B. muon described as the C. photon exchange of a photon. D. quark

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Four Gauge forces Exchange bosons • Each interaction has one or more associated particles that mediate the interaction. • The exchange particles are associated with the known interactions Interaction Mediating particle(s) Number Electro- photon (1) magnetic Weak W+, W- and Zo (3) Strong gluons (8) Gravity graviton (1) • These all have integer spins, hence are bosons

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Bosons

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