Particle Reactions and Decays - I [Secs 16.1, 16.2 Dunlap]
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Transcript of Particle Reactions and Decays - I [Secs 16.1, 16.2 Dunlap]
Particle Reactions and Decays - I
[Secs 16.1, 16.2 Dunlap]
CAN IT HAPPEN ?Check B, Li, Qc
No
Yes
IS IT WEAK?T, S, C violation ?
Yes
WEAK
W+, or W- involved.
Flavor change occurs with one unit of charge change.
QUARKS LINK UP?
γ in products
Yes
No
REACTIONDECAY
enough energy
Q>0
Q<0
No
STRONG
No No
?
Yes
?
Yes
E.M.
Classification of Decays
ee
p
K
eepn
p
No Type of Decay Particles Guage Bosons Example
1 Leptonic decay leptonleptons weak
2 Hadronic lepton decay
leptonlepton+hadron weak
3 Hadronic decay hadronhadrons strong
4 Nonleptonic hadron decay
hadronhadrons strong+weak
5 Semileptonic hadron decay
hadronhadron+leptons weak
6 Leptonic hadron decay
hadronleptons weak
7 Electromagnetic hadron decay
hadronhadron+photon EM
TO
LE
PT
ON
ST
O
HA
DR
ON
S
LEPTON DECAYS(i.e. decay into leptons)
LEPTONIC DECAY
HADRONIC – LEPTON DECAY
HADRONIC DECAYS
HADRONIC DECAY LEPTONIC HADRON DECAY
SEMI-LEPTONIC HADRON DECAY NON-LEPTONIC HADRON DECAY
ELECTROMAGNETIC HADRON DECAY
In 1963 The UFI is back
In 1963 theoretical physicist Nicolo Cabibbo gave an explanation in terms of quark state mixing and introduced an angle - The Cabibbo angle
The quarks can exist either as eigenstates of the WEAK interaction or the STRONG interaction.
Indeed it is best to think of the QUARKS as being fundamentally having FLAVOR STATES determined via the WEAK interaction. Then comes along the STRONG interaction which MIXES these flavors into.
cos sin
sin cos
w w
w w
d d s
s d s
and w wd s
How the Quark Mixing works
ws
wd
θc
θc
s
d
cos sin
sin cos
w c w c
w c w c
d d s
s d s
After switching on the STRONG interaction – these are the new quark states.
The Cabibbo Angle turns out to be ~15°
Cabbibo allowed – Cabibbo Surpressed
Cabibbo Allowed
Cabibbo Surpressed
d
d
s
d
u
s
d
d
s
d
d
u
W+
u
d
W+
u
s
K+
22
2
sintan
cos
from which one finds
tan 0.075
cKc
c
c
MEASURING THE CABIBBO ANGLE
Example 1
eepn
BETA MINUS DECAY
All the primary conservation laws (above the line) are ok, so the reaction should go. But is it S, W, or EM? There are two things that indicate the primary classification is WEAK. These are (i) the fact that this T of the final state is N.D (not defined) and (ii) the fact that leptons are present in the final state. Having established that it is a W (weak) decay we then make the inference:
WEAK DECAY INVOLVEMENT OF “W” PARTICLE
Example 1 BETA MINUS DECAY
eepn
FEYNMAN DIAGRAM
CLASSIFICATION = Semileptonic Hadron Decay
Example 2 Kn 0
ASSOCIATED PRODUCTION
All the primary conservation laws (above the line) are ok. Also the secondary conservation laws (obeyed by the strong interaction, ones below the line) are ok. This means the reaction must be mediated by the STRONG force. There will be NO Ws
All quarks will “link up”.
Example 2 Kn 0
ASSOCIATED PRODUCTION
FEYNMAN DIAGRAM
CLASSIFICATION = PURE HADRONIC
Example 3
K
K- MESON DECAY
All the primary conservation laws (above the line) are ok. But here the secondary conservation laws (obeyed by the strong interaction, ones below the line) are NOT OK. This is a clear indication that this cannot be a strong process. The presence of leptons also confirms that this must be a WEAK interaction process. the presence of W particles.
Example 3
K
K- MESON DECAY
FEYNMAN DIAGRAM
DECAY CLASSIFICATION = LEPTONIC HADRON DECAY
Example 4 LAMDA ZERO DECAY
As with the K+ decay we see failure on isospin and strangeness. Again this is clear indication that the WEAK interaction is responsible. [We saw in the lecture on strangeness that a strong interaction could only occur if the strange quark that had been produced could find another strange quark for pairing up with – and annihilating with] W PARTICLE involved in FLAVOR changing
Example 4 LAMDA ZERO DECAY
FEYNMAN DIAGRAM
DECAY CLASSIFICATION = Nonleptonic Hadron decay
Example 5 DELTA ++ PRODUCTION
So all is OK for an allowed reaction and one going by the STRONG interaction. This a fully hadronic process.
Example 5 DELTA ++ PRODUCTION
FEYNMAN DIAGRAM
CLASSIFICATION = Hadronic Reaction
Example 6 D ZERO DECAY
All is ok above the line – so the process is possible. Below the line we see a violation of strangeness and charm. Thus it looks as if we have a charmed quark changing into a strange quark. Involvement of a W boson. This is a WEAK process.
Example 6 D ZERO DECAY
FEYNMAN DIAGRAM
DECAY CLASSIFICATION = Nonleptonic Hadron decay
Example 7 D ZERO DECAY
We see again an allowed decay but one which involves flavor changing on a quark. Here, however the presence of leptons in the final state makes finding the Feynman diagram easy.
Example 7 D ZERO DECAY
FEYNMAN DIAGRAM
DECAY CLASSIFICATION = Semileptonic Hadron decay
Example 8
ee
0