ParticleZoo

September 01 W. Udo Schröder: History NS 2 Nucleons Are Not Elementary Particles! p e-e- e-e- hadron jet Scatter high-energy electrons off protons. If there is no internal structure of e - or p, then well- defined “elastic” e - energy for each angle. See structure!! elastic x1/8.5 Each line in the energy spectrum of scattered electrons corresponds to a different energy state of the proton. Bartel etal. PL28B, 148 (1968) scatter probability energy of scattered electron ground state of the proton excited states of the proton

September 01 W. Udo Schröder: History NS 3 The Quark Model The quark model represents a relatively simple picture of the internal structure of subatomic particles and makes predictions of their production and decay. It uses a minimum of adjusted quark parameters and has great predictive power, e.g., for the composite-particle masses, magnetic moments, and lifetimes. There are no contradictions to this model known so far, (but many questions remain).

September 01 W. Udo Schröder: History NS 4 Internal Nucleonic Structure The proton has internal structure, so-called quarks (u,u,d). Quarks combine to nucleon states of different excitations. Proton is the (u,u,d) ground state p e-e- e-e- 938 MeV 1200 MeV N  S=½ S= 3/2 135 MeV  S=0 Mesons N: one doublet with a splitting of only  m = 1.3 MeV  : one quadruplet with a splitting of only  m = 8 MeV

September 01 W. Udo Schröder: History NS 5 The Quark-Lepton Model of Matter Nucleons (q,q,q) Mesons (q, q-bar) q-bar:anti-quark families of quarks (3 “colors” each) and associated leptons. All are spin-1/2 particles, quarks have non-integer charges Explains the consistency of the known particles in all of their states. 3

September 01 W. Udo Schröder: History NS 6 Particle Spectrum Spin ½ ½ 3/2 0 1 Leptons Baryons Mesons Hadrons      Y*      J  ''  '’ Mass (GeV/c2)  e Simplified scheme of stable or unstable subatomic particles. Families have different interactions, Leptons: weak+elm, Hadrons: weak+elm+strong Each particle also has an anti-particle, with inverse quantum numbers. “strange”

September 01 W. Udo Schröder: History NS 7 Quark Quantum Numbers Flavor Q/eM/ GeVc -2 TT3T3 SCB*Top u+2/30.005½½0000 d-1/30.009½- ½0000 s-1/ c+2/ b-1/ t+2/ T,T 3 : isospin; S: strangeness; C: charm; B*: bottom qu.#, Top: top qu.# All: spin=1/2, baryon number B=1/3

September 01 W. Udo Schröder: History NS 8 0 T3T3 Structure of Composite Particles There are only 3-quark (q,q,q)  Baryons and quark-antiquark configurations. No free quarks or higher quark multiplicities. _d_d _u_u _s_s u d s quarks antiquarks d d u u u d d s u u s s u s d s s d u s _s_s d d _u_u d _u_u _u_u s _u_u s _s_s u d _d_d u _u_u s _s_s d n p -- 00 00 ++ -- 00 ++ -- K0K0 K+K+ K-K- _K0_K0 00  ’’ S s= 1/2 s= 0

September 01 W. Udo Schröder: History NS 9 0 S T3T3 d d d u u u d d u u d u d s d d s u u s u d s s u s s s s s           s = 3/2

September 01 W. Udo Schröder: History NS 10 Meson Wave Functions Examples to interpret the graphic shorthand in these figures: Meson spins are integer, vector sum of half- integer quark and anti-quark spins, and their integer orbital angular momentum l. In ground state, mostly l =0.

September 01 W. Udo Schröder: History NS 11 Baryon Wave Functions Examples to interpret the graphic shorthand: These Baryon and Meson wave functions are schematic, do not have proper (anti-)symmetry property required by Pauli Principle : The total particle wave function must be antisymmetric under quark exchange (quarks are fermions)

September 01 W. Udo Schröder: History NS 12 Pauli Principle and Color Coordinate have both 3 identical fermions (same quarks) with same spins (S=3/2) and isospin (T 3 =+3/2) states Quarks are Fermions  no two same quarks can be in the same state d d d  u u u   s 3,T 3 Conclusion: There must be an additional quantum number (degree of freedom), “color”. Need 3 colors and their anti-colors Color and complementary color (anti-color) add up to color-less (white) d d d _d_d _d_d _d_d d quarks anti-d quarks Violates Pauli Principle !?

September 01 W. Udo Schröder: History NS 13 Color Wave Function  ++ : Flavor and spin configurations symmetric, spatial configuration symmetric (no orbital angular momentum, l =0) All physical particles are “white.”  color configuration must be antisymmetric. All colors are present with equal weights. All physical particles are “white.” d d d _d_d _d_d _d_d d quarks anti-d quarks Necessity of color rules out combinations such as Confinement There are no free quarks  Confinement

September 01 W. Udo Schröder: History NS 14Gluons Bound quark systems (physical particles) by q-q interactions. Gluons Field quanta: 8 Gluons (not actually pions!) Spin and parity 1 - like a photon. qcqc q c’ q _q_q gluon emission q-qbar creation self coupling changes color of the color charges Usual conservation laws apply to reactions between quarks. Gluons carry color and the corresponding anticolor. Color can be transferred but particle remains colorless.

September 01 W. Udo Schröder: History NS 15 Gluon Exchange u _d_d r b g b _r_r _b_b _g_g _b_b  _ r,b _ b,g u r b g b _ r,g g g g r b u d p Gluons are exchanged back and forth between q-q, changing q colors and momenta dynamically r, g, and b are visited with equal probability time

September 01 W. Udo Schröder: History NS 16 Baryon Production with Strong Interactions Typically: Energetic projectile hits nucleon/nucleus, new particles are produced. Rules for strong interactions: Energy, momentum, s, charge, baryon numbers, etc., conserved q existing in system are rearranged, no flavor is changed q-q-bar pairs can be produced u u u d _d_d u u u s _s_s p    annihilation creation d, d-bar s, s-bar time 

September 01 W. Udo Schröder: History NS 17 Baryon Resonances Typically: Energetic projectile hits nucleon/nucleus, intermediate particle is produced and decays into other particles. u u u  ++ u u d _ d u time  u u d _ d u p ++ p ++  ++ produced as short-lived intermediate state,  = 0.5· s corresp. width of state:  = ħ/  = 120 MeV This happens with high probability when a nucleon of 300 MeV/c, or a relative energy of 1232 MeV penetrates into the medium of a nucleus.  Resonance

September 01 W. Udo Schröder: History NS 18 Confinement and Strings Why are there no free quarks? Earlier: symmetry arguments. Property of gluon interaction between color charges (“string- like character). Q: Can one dissociate a qq pair? energy in strings proportional to length 0.9GeV/fm field lines: color strings successive q/q-bar creation, always in pairs!

September 01 W. Udo Schröder: History NS 19 Leptons Leptons have their own quantum number, L, which is conserved. It seems likely, but is not yet known, whether electronic, muonic and tau lepton numbers are independently conserved in reactions and decays.

September 01 W. Udo Schröder: History NS 20 Conservation Laws Quantum numbers are additive. Anti-quarks have all signs of quark quantum numbers reversed, except spin and isospin. Derived quantities: In a reaction/transmutation, decay, the following quantities are conserved (before=after): The total energy, momentum, angular momentum (spin), The total charge, baryon number, lepton number

September 01 W. Udo Schröder: History NS 21 Conservation Laws in Decays Decay A  B + C possible, if m A c 2 ≥ m B c 2 + m C c 2 Otherwise, balance must be supplied as kinetic energy. Example: Conservation of charge, baryon number, lepton number in neutron decay.

September 01 W. Udo Schröder: History NS 22 Weak Interactions weaker than strong interaction, small probabilities for reaction/decays. Mediated by heavy (mass ~100GeV) intermediate bosons W ±,Z 0. Weak bosons can change quark flavor u d W+W+ W-W- Z0Z0 u s u u up-downstrange-non-strange no flavor change conversion conversion carries +e carries –e carries no charge

September 01 W. Udo Schröder: History NS 23 Decays of W ± and Z 0 Bosons Hadronic decays to quark pair are dominant (>90%), leptonic decays are weak. All possible couplings:

September 01 W. Udo Schröder: History NS 24 Examples of Weak Decays Can you predict, which (if any) weak boson effects the change? n ? ? ? p p e-e- _ e p   e-e- e time n-decay? neutrino scattering neutrino-induced off protons? reaction off e - ?

September 01 W. Udo Schröder: History NS 25 Examples of Weak Decays Answer: Yes, all processes are possible. These are the bosons, n W-W- W+W+ Z0Z0 p p e-e- _ e p   e-e- e time n-decay neutrino scattering neutrino-induced off protons reaction off e - Method: Balance conserved quantities at the vortex, where boson originates. Remember W ± carries away charge ±|e|. Balance conserved quantities at lepton vortex.

September 01 W. Udo Schröder: History NS 26 Particle Production  e-e- e+e+ -- ++  e-e- e+e+ fermion e-e- e+e+ -- ++  anti- fermion electromagnetic weak example In electron-positron collisions, particle-anti-particle pairs can be created out of collision energy, either via electromagnetic or weak interaction.  collision energy (GeV) probability

September 01 W. Udo Schröder: History NS 27 The Standard Model The body of currently accepted views of structure and interactions of subatomic particles. Interaction Coupling Charge Field Boson Mass/ GeVc -2 JJ strongcolorgluons (8)01-1- elmgnelectric (e)photon (  )01-1- weak W +, W -, Z Interactions FermionsFamilyQ/eColorSpin Weak Isospin Quarks u c t d s b +2/3 -1/3 r, b, g½½ Leptons e   e  0 none½½ Particles Weak interactions violate certain symmetries (parity, helicity) see later

September 01 W. Udo Schröder: History NS 28 The Standard Model ct’d Combine weak and elm interactions  “electro-weak” Type of isospin-symmetry : same particles carry weak and elm charge. Force range Electromagnetic: ∞ Weak: fm Strong qq force increases with distance 2m q c 2 V qq r 1 fm 0 There are no free quarks. All free physical particles are colorless.

September 01 W. Udo Schröder: History NS 29 The End