Unit 1.5 Flashcards
What happens when a cosmic particle enters the Earth’s atmosphere
it creates new short-lived particles and antiparticles, as well as photons by colliding with gas atoms in the atmosphere including: the muon, the pion and the kaon
Why is the K meson called a strange particle
It is produced via the strong interaction but interacts via the weak interaction, but decay products include the pi meson
How else can the K meson be produced
by an accelerator
What are hadrons
Particles and antiparticles that can interact through the (weak and) strong interaction e.g. protons, neutrons, pi mesons and K mesons.
What are leptons
Particles and antiparticles that only act through the weak interaction and not interact through the strong interaction e.g. electrons, muons and neutrinos.
Leptons interact through the ____ interaction and through the _______ interaction if _____
weak
electromagnetic
charged
Hadrons interact through the ____ interaction and through the _______ interaction if _____
strong
electromagnetic
Hadrons decay through the ____ interaction apart from the ____ because…
Weak
Proton
It is stable
What two particles both interact through the electromagnetic interaction and both are negatively charged
A muon and a pi meson
1 similarity and 1 difference between the pion and the kaon
both interact through the strong nuclear interaction but the pi meson involves protons in its decay
1 similarity and 1 difference between the K^0 meson and neutron
no charge
neutron is a baryon and kaon is a meson
Hadrons are divided into two groups called…
mesons and baryons
Kaons decay into
pions, muons and antineutrinos, antimuons and neutrinos
Via the weak interaction
Charged pions decay into
muons and muon antineutrinos
or
antimuons and muon neutrinos
The pi^0 meson decays into
high energy photons
Muons and antimuons decay into
electrons and antineutrinos and muon neutrino
or
positrons and neutrinos and electron antimuon
The decays always obey the conservation rules for…
energy
momentum
charge
What are baryons
protons and all other hadrons (including neutrons) that decay into protons
What are mesons
all hadrons that do not include protons in their decay products
What is the LHC and what does it do
large hadron collider is a accelerator that boosts the kinetic energy of the charged particles and causes collision s
total energy of the particles and antiparticles before the collision =
rest energy+kinetic energy
The rest energy of the products +
total energy before – the kinetic energy of the products
Proton interaction
Strong, weak decay
Electromagnetic
Neutron interaction
Strong, weak decay
Electron interaction
Weak, electromagnetic
Neutrino interaction
Weak
Muon m- interaction
Weak, electromagnetic
Pi meson interaction
Strong, electromagnetic (if charged)
K meson interaction
Strong, electromagnetic (if charged)
Where do muons, pions and kaons come from
Cosmic ray collisions
What are pions and kaons
Bosons and mesons
Muon half life
1.5 microseconds
Pion half life
18 nanoseconds
What two types do leptons come in
Charged (ionising particles with easily detectable tracks) And uncharged (neutrinos)
Why are leptons elementary
No internal structure so are not made of anything therefore is elementary
What is the half life of a kaon
12 nanoseconds
Where were neutrinos discovered
Nuclear reactors
Leptons change into other leptons via the _____ nuclear force
Weak
In any interaction, lepton number is ____
Conserved meaning the reaction/decay is permitted
Particle lepton number
Antiparticle lepton number
1
-1
Ve + p —> n + e-
Permitted or not?
L 1 0 |||| 0 1
Le 1 0 |||| 0 1
Lm 0 0 |||| 0 0
Lepton number is conserved so reaction is permitted
Ve + n —> p- + e+
Permitted or not?
L: 1 0 |||| 0 -1 X
Le: 1 0 |||| 0 -1 X
Lm: 0 0 |||| 0 0 _/
Lepton number is not conserved so reaction/decay is not permitted
Muon decay and the interaction
Weak interaction
Muon –> electron + muon neutrino + electron antineutrino
Muon antineutrino + proton —>
Antimuon and neutron
One similarity and one difference between electron and muon
- equal charge
- different mass
One similarity and one difference between electron neutrino and muon neutrino
- equal rest mass
- a muon cannot decay into an electron neutrino whereas an electron can, and an electron cannot decay into a muon neutrino whereas a muon can
Electron Positron L Le Lμ
Electron: L 1 Le 1 Lμ 0 Positron L -1 Le -1 Lμ 0
Electron neutrino Electron antineutrino L Le Lμ
Electron neutrino: L 1 Le 1 Lμ 0 Electron antineutrino: L -1 Le -1 Lμ 0
Muon Antimuon L Le Lμ
Muon L 1 Le 0 Lμ 1 Antimuon L -1 Le 0 Lμ -1
Muon neutrino Muon antineutrino L Le Lμ
Muon neutrino L 1 Le 0 Lμ 1 Muon antineutrino L -1 Le 0 Lμ -1
What type of particle are quarks and what do they make up
Elementary
Hadrons (baryons and mesons)
What type of quarks make up protons and neutrons
Up quarks
And down quarks
How were quarks discovered
High energy electrons collide with stationary protons and neutrons which caused deep inelastic scattering (energy was being lost from the scattered protons) and because energy is conserved there must have been other particles carrying the ‘lost’ energy (quarks)
Baryon’s generalised quark structure
3 quarks
Meson’s generalised quark structure
Quark/antiquark pairs
π+
π-
π0
Quark structure
u(anti)d
d(anti)u
Any quark/antiquark pair
u(anti)u d(anti)d s(anti)s
Beta decay with quark changes
d=neutron –> u=proton
W-
Electron antineutrino –> electron
Positron decay with quark structure
u=proton—>neutron=d
W+
Electron neutrino -> positron
How is the Σ+ particle created (heavier than proton)
π0+ρ+ –> Σ+ + Κ0
Strangeness means
Decays into a π meson
How does the Σ+ particle decay
Σ+ –> π0 + ρ+
The Σ particle is a
The K particle is a
Two similarities between them
Baryon
Meson
Both hadrons
Both interact via the strong nuclear interaction so strangeness is conserved
The Σ particle and K meson decay via the
weak interaction
Is strangeness conserved in all cases
No, only in the strong interaction not the weak interactions
Beta decay is what type of interaction
weak
Explain how we know beta decay is weak interaction
Because quark flavour is not conserved in the weak interaction and during beta decay the quark flavour changes from a down quark (neutron) to an up quark (proton) therefore it isn’t conserved
Building quarks - charge and strangeness of quarks/antiquarks
Antiquarks have exact opposite charge and strangeness to quarks on data sheet
Neutron strangeness
0
Sigma particles strangeness
-1
Pion strangeness
0
antiK0 and K- strangeness
-1
K0 K+ strangeness
+1
K mesons are
Strange particles that decay into pions
The quark structure of an antiparticle of any meson is a
quark/antiquark pair
K+ K- K0 AntiK0 Quark structure
up anti strange
Strange anti up
Down anti strange
Strange anti down
Σ+
Σ0
Σ-
Quark structure
uus
uds
dds
Proton Neutron Antiproton Antineutron Quark structure
uud
udd
Anti(uud)
Anti(udd)
One difference between kaon and pion
Kaon is strange whereas pion isn’t
If strangeness is not conserved then it is what type of interaction
Weak
What is always conserved
Baryon, lepton and quark number
Charge
Strangeness
Baryon number for baryons, anti-baryons, mesons, leptons, protons, neutrons sigma particles
+1 for baryon (proton,neutron,sigma)
-1 for anti-baryon
0 for meson or lepton
Mesons are not conserved because they are
Exchange particles for the strong interaction
What are the exchange particles for the WNF and EMF
W+/W-
γ
Baryon number for a quark and anti-quark is
1/3
-1/3
1GeV =
1000MeV
1x10^9eV
Is
p+p–>n+K++Σ+
Allowed
Baryon = 2/2 Lepton = 0/0 Strangeness = 0/0 Charge = 2/2 All conserved therefore allowed
What are baryons and anti-baryons
Hadrons consisting of 3 quarks or anti-quarks
Neutrinos are
leptons
When does strangeness occur
When there are multiple possibilities for decay
Electron proton collision and electron capture
Electron capture is w+ to the right
Electron proton collision is w- to left towards proton (very high speeds)
