Particles as fields. Review Chap. 18: Particle Physics. Energy uncertainty. Quantum Electrodynamics: QED. Creating more particles

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1 Final Exam: Thr. Dec. 21, 2:45-4:45 pm, 113 Psycholoy Bilin Exam is cmlative, coverin all material Review Chap. 18: Particle Physics an fiels: a new pictre Qarks an leptons The stron an weak interaction Unification an mass Strin theory Phy107 Fall as fiels Electromanetic fiel sprea ot over space. Stroner near the the sorce of the electric/manetic chare - weaker farther away. Electromanetic raiation, the photon, is the qanta of the fiel. Describe electron particles as fiels: Makes sense - the electron was sprea ot aron the hyroen atom. Wasn t in one place - ha locations it was more or less probable to be. Stroner an weaker like the electromanetic fiel. Electron is the qanta of the electron fiel. Phy107 Fall Qantm Electroynamics: QED Normal electromanetic force comes abot from exchane of photons. Electromanetic replsion via emission of a photon electron photon electron Phy107 Fall Enery ncertainty To make a very short plse in time, nee to combine a rane of freqencies. Freqency relate to qantm enery by E=hf. Heisenber ncertainty relation can also be state (Enery ncertainty)x(time ncertainty) ~ (Planck s constant) In other wors, if a particle of enery E only exists for a time less than h/e, it oesn t reqire any enery to create it! These are the virtal particles that propaate fiels Phy107 Fall Pair proction, annihilation Electron an positron can annihilate to form two photons. An nexpecte preiction! Photon can isappear to form electron-positron pair. Relativity: Mass an enery are the same Go from electron mass to electromanetic/photon enery an back Phy107 Fall Creatin more particles All that is neee to create particles is enery. Enery can be provie by hih-enery collision of particles. An example: Electron an positron annihilate to form a photon. This can then create particles with mc 2 <photon enery. e- e-,µe+ µ, Mon mass: 100MeV/c 2, electron mass 0.5 MeV/c 2 e+,µ+ New particles fon this way Phy107 Fall

2 What have we learne? Matter is mae of atoms Atoms are mae of leptons an qarks Atoms are mae of leptons an qarks Leptons Qarks e Interact via ifferent forces carrie by particles, photons, simple except for the mon Phy107 Fall Three enerations of particles Three enerations ifferentiate primarily by mass (enery). First eneration One pair of leptons, one pair of qarks Leptons: Electron, electron-netrino. Qarks: Up, own. All 3 enerations seen Phy107 Fall Liht Heavier Heaviest The enerations Chare These are the exchane bosons. What are they exchane between? Or on what are the corresponin forces exerte? Example: When a photon is exchane between two particles, there is a electromanetic or Colomb force. We know that only particles with electrical chare interact via the Colomb force Zero chare -> zero Colomb interaction Phy107 Fall Phy107 Fall Many Chares In this lanae, we say that the electrical chare is a sorce of an EM fiel. A mass chare is the sorce of a ravitational fiel A weak chare (sometimes calle flavor ) is the sorce of a weak interaction fiel A stron chare (sometimes calle color ) is the sorce of a stron interaction fiel Qarks an leptons have mltiple chares. Some of the bosons have chares. Electric, flavor, color, mass Flavor Electric, flavor, mass All those chares! Color None Electric, mass Phy107 Fall Phy107 Fall

3 Interactions throh Exchane of Color Chare Initially Emission of Glon After lon emission RED RED-ANTIBLUE + BLUE (qark) (lon) (qark) Re-absorption of Glon Before lon absorption After lon absorption RED-ANTIBLUE + BLUE RED (lon) (qark) (qark) Phy107 Fall Feynman Diarams (Qark Scatterin) Qark-qark Scatterin Col also be Qark-antiqark Scatterin or Antiqark-antiqark Scatterin Qark-antiqark Annihilation Position Phy107 Fall time Glon interactions Since lons carry color chare, they can interact with each other!(photons can t o that) Very important, makes stron interaction stroner an leas to confinement Glon-lon Scatterin Glon-lon Fsion More Baryons Qark p own strane Q +2/3-1/3-1/3 Mass ~5 [MeV/c 2 ] ~10 [MeV/c 2 ] ~200 [MeV/c 2 ] s s s Excite state - Hiher enery/mass s Lamba ( ) Q = 0 M=1116 MeV/c 2 s Sima ( + ) Q = +1 M=1189 MeV/c 2 s Sima ( 0 ) Q = 0 M=1192 MeV/c 2 s Sima ( ) Q = -1 M=1197 MeV/c 2 Phy107 Fall Phy107 Fall Mesons They are forme when a qark an an anti-qark bin toether. So far we ve only seen 3 qark combinations. There are also 2 qark combinations. The harons: 2 qarks, meson an 3 qarks, baryon. Carriers of the weak force Like the Electromanetic & Stron forces, the Weak force is also meiate by force carriers. For the weak force, there are three force carriers: What s the chare of this particle? Q=+1, an it s calle a + c What s the chare of this particle? s What s the chare of this particle? W + W - Z 0 These weak force carriers carry electric chare also! This weak force carrier is electrically netral The chare of the weak interaction Q= -1, an this charm Q= 0, this strane is calle weak chare meson is calle a D - meson is calle a K 0 Phy107 Fall Phy107 Fall

4 Rane of the interaction Electron oesn t have enoh enery to create Z o. Z o only present e to ncertainty relation (Enery ncertainty)x(time ncertainty)~planck cnst It can only exist for a time etermine by Planck cnst Time ncertainty ~ Particle mass Farthest it can travel in that time is Planck cnst Rane ~(Liht Spee)x Particle Mass ~ m Phy107 Fall Scatterin from qarks in a ncles What Ice Cbe looks for is netrinos emerin from collisions as mons. n µ W + µ - p time The netrino interacts with qarks bon insie ncleons in the ncles. Netrino emits W +, chanin flavor into mon. Down qark bon in a netron absorbs W +, chanin into a p qark. The ncleon then has two ps an one own qark, which is a proton. Always look to conserve chare in these interactions Phy107 Fall Similar to nclear beta ecay Interaction via the W explains nclear beta ecay. Lepton ecay Flavor chane can occr spontaneosly if the particle is heavy enoh. n W - _ e - p time qark emits a W-, chanin flavor into a qark. W ecays to an electron an anti-electron netrino. The ncleon then has two ps an one own qark, which is a proton. Similar to the rotate Feynman iaram we sties with the electromanetic force Generation I e Electron is stable Generation II µ µ 2x10-6 secons Generation III 3x10-13 secons Chare -1 0 Phy107 Fall Phy107 Fall Qarks an the weak force Qarks have color chare, electric chare, an weak chare other interactions swamp the weak interaction Bt similar to leptons, qarks can chane their flavor (ecay) via the weak force, by emittin a W particle. Flavor chane between enerations Bt for qarks, not limite to within a eneration! Generation I Generation II Generation III Chare Generation I Generation II Generation III Chare c t +2/3 c t +2/3 s b -1/3 s b -1/3 Emit W + 2x10-12 secons Emit W secons secons secons Phy107 Fall Phy107 Fall

5 & their Interactions (Smmary) qarks Chare leptons (e,µ, ) Netral leptons ( ) Color Chare? Y N N EM Chare? Y Y N Weak Chare? Y Y Y Qarks can participate in Stron, EM & Weak Interactions. All qarks & all leptons carry weak chare. Comparison of the Force Carriers Force Carrier Chare of force carrier Coples to: Rane EM Photon ( ) None w/elect. chare Infinite (1/ 2 ) Stron Glon () Color w/color chare (Qarks,lons) <10-14 m (insie harons) W +, W - Electric & Weak w/weak chare (Qarks, leptons) W,Z) < 2x10-18 m Weak Z 0 None w/weak chare (Qarks, leptons W,Z) < 2x10-18 m Netrinos only carry weak chare. Phy107 Fall Phy107 Fall Key Points Differences between particles connecte to how they interact, what chares they have. Qarks have all the chares. Color chare: Qarks form composite states harons via the stron force. Flavor chare: Heavy qarks ecay to lihter qarks via the weak force. Leptons have no color chane. Don t form any composite states. Netrinos only interact via the weak force which means they rarely interact at all. Phy107 Fall Key Points Cont. Properties of the force carriers etermine the aspects of that force. Glons an the stron force. Glon can interact with other lons. Limits the rane of that force an makes it stroner. W, Z an the weak force. Force carriers are massive. Limits the rane they can travel an makes the force weaker. Photon an the electromanetic force. Happy mile ron between stron an weak. Phy107 Fall Netral weak Zero chare Mass=91 GeV/c 2 Rane ~ m Electroweak Unification Electromanetic Zero chare Mass=0 GeV/c 2 Rane ~ inf. These two both exchane netral bosons Neither boson chanes the lepton flavor (remains electron) Have the same strenth at hih enery! W + W - e e Pos. weak Pos. chare Mass=80 GeV/c 2 Rane ~ m Ne. weak Ne. chare Mass=80 GeV/c 2 Rane ~ m These two both exchane chare bosons. Both bosons chane the lepton flavor Unification Details of weak interaction sest Diff. qarks are iff. orientations of the same particle. Diff. leptons are iff. orientations of the same particle. Weak an EM interactions are ifferent parts of a sinle electroweak force. Electroweak interaction le to the introction of the His Boson Gran Unifie Theories (GUTs) Will combine leptons an qarks Unify stron an electroweak an ravitational interactions. From one sorce. Electroweak force. Nee His particle to ive Phy107 W, Fall Z 2006 mass - an everythin else. 29 Phy107 Fall

6 Checklist for a theory of everythin Unify all the forces: stron force - ravity Qantize the forces - QFT very sccessfl Unify the particles: qarks, leptons - 3 enerations Explain all the ifferent masses an strenths Explain ark matter Explain why niverse is mostly matter Explain physics at very hih enery - bi ban Phy107 Fall Kalza-Klein: EM & ravity Connect electromanetism an ravity in a classical relativistic theory. Kalza an Klein fon a theory in five imensions (for space & one time) with one interaction (5-imensional ravity). When one of the imensions was compactifie, two interactions reslte: ravity an electromanetism. What appears to s as two istinct interactions oriinate from only one. Kalza & Klein, 1920 Only nifies ravity. Can t be qantize. Doesn t answer all the other qestions! Phy107 Fall Spersymmetry (SSy) Spersymmetry Sccesses Desine to explain behavior at very hih enery Sperpartners (compare to anti-particles) Every fermion has a boson partner an vice versa Phy107 Fall Forces mere in SUSY Same strenth at hih enery. Lihtest SUSY particles on t ecay. Dark Matter Doesn t nifies ravity. Can t explain many of the other qestions! Phy107 Fall Strin theory A strin is a fnamental qantm mechanical object that has a small bt nonzero spatial extent. Jst like a particle has a mass, a strin has a tension that characterizes its behavior. Qantm mechanical vibrations of the strin correspon to the particles we observe Can incle Kalza Klein theory an Spersymmetry. Checklist Strin Theory Unify all the forces: stron force - ravity Qantize the forces - QFT very sccessfl Unify the particles: qarks lepton - 3 enerations Explain all the ifferent masses an strenths Explain ark matter Explain why niverse is mostly matter Explain physics at very hih enery - bi ban Bilin experiments to explore all these theories inclin the Stanar Moel - His not fon yet! Phy107 Fall Phy107 Fall