1. Lecture 04 - Hadrons Quarks multiplets Hadron decays Resonances
Conservation laws
Resonances
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2. The fundamental forces
Different exchange particles mediate the forces:
electromagnetic
strong
weak
Interaction
Relative strength
Range
Exchange
Mass (GeV)
Charge
Spin
Strong 1
Short ( fm)
Gluon
Electromagnetic
1/137
Long (1/r2)
Photon
Weak
10-9
Short ( 10-3 fm)
W+ W-,Z
80.4,80.4 , 91.2
+e,-e,0
Gravitational
10-38
Long (1/r2)
Graviton ? 2
No quantum field
theory yet for gravity
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3. The quarks Spin ½ particles FK7003 Quark Q (e) Mass (GeV) u- up 2/3
0.003
d- down
-1/3
0.005
s- strange
0.15
c- charm
1.2
b- bottom
4.2
t-top
171
Spin ½ particles
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4. Hadrons Full particle listings from the Review of Particle Physics:
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5. The quarks Spin ½ particles + antiparticles FK7003 Quark Q (e)
Mass (GeV) B S C T
u- up
2/3
0.003
1/3
d- down
-1/3
0.005
s- strange
0.15 -1
c- charm
1.2 1
b- bottom
4.2
t-top
171
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6. Hadron quantum numbers
Particle
Mass (MeV) B Q S C
p (uud)
938 1
n (udu)
940
L (uds)
1116 -1
Lc (udc)
2285
Lb (udb)
5624
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7. Hadron properties Particle Mass (MeV) B Q S C p+ (ud) 140 1 K- (su)1
K- (su)
494 -1
D- (cd)
1869
1971
 (bb)
9460
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8. Evidence for a new quantum number: colour
(4.03)
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9. Hadrons and the strong force
q (R)
q (G)
Gluon (RG)
q(R)
q (G)
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10. Colour combinations We have never seen a quark or gluon!
Nature abhors naked colour.
Every particle in nature is colourless/colour singlet
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11. A strong reaction:
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12. QCD Description of the Strong Nuclear Force
Yukawa model proposed pion exchange
Interaction results from internal gluon lines and
quark exchange
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13. Some words about decays
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14. Strong decay p+ u d u r u d p- u u u p+ d r d p- u u
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15. OZI rule
f decays preferentially to K+K- than p+ p0 p- even though it is less energetically favourable.
Decays in which all gluon lines can be ”cut” are
suppressed.
Rule proposed by Okubo, Zweig and Iizuka in 1960s
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16. FK7003

17. } Weak decays of hadrons s d u L p-
Strangeness (and the other flavour quantum numbers, C,B) are not conserved in weak decays.
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18. Conserved quantities/symmetries
Quantity
Strong
Weak
Electromagnetic
Energy 
Linear momentum
Angular momentum
Baryon number
Lepton number
Isospin -
Flavour (S,C,B)
Charges (em, strong and weak forces)
Parity (P)
C-parity (C)
G-parity (G) CP T
CPT
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19. Short-lived particles
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20. - Breit Wigner Seen in decays of nuclear and atomic energy levels.
Nmax
0.5 Nmax
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21. Resonances Shape of excited state mass distribution follows
Breit-Wigner distribution
770 MeV – ”nominal” mass
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22. Summary Hadrons introduced Decays via em, weak and strong forces.
Conservation laws
Width of a resonance provides a lifetime
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