Unit 1.5 Flashcards by L G

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

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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

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How else can the K meson be produced

by an accelerator

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What are hadrons

Particles and antiparticles that can interact through the (weak and) strong interaction e.g. protons, neutrons, pi mesons and K mesons.

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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.

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Leptons interact through the ____ interaction and through the _______ interaction if _____

weak
electromagnetic
charged

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Hadrons interact through the ____ interaction and through the _______ interaction if _____

strong

electromagnetic

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Hadrons decay through the ____ interaction apart from the ____ because…

Weak
Proton
It is stable

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What two particles both interact through the electromagnetic interaction and both are negatively charged

A muon and a pi meson

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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

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1 similarity and 1 difference between the K^0 meson and neutron

no charge

neutron is a baryon and kaon is a meson

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Hadrons are divided into two groups called…

mesons and baryons

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Kaons decay into

pions, muons and antineutrinos, antimuons and neutrinos

Via the weak interaction

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Charged pions decay into

muons and muon antineutrinos
or
antimuons and muon neutrinos

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The pi^0 meson decays into

high energy photons

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Muons and antimuons decay into

electrons and antineutrinos and muon neutrino
or
positrons and neutrinos and electron antimuon

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The decays always obey the conservation rules for…

energy
momentum
charge

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What are baryons

protons and all other hadrons (including neutrons) that decay into protons

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What are mesons

all hadrons that do not include protons in their decay products

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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

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total energy of the particles and antiparticles before the collision =

rest energy+kinetic energy

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The rest energy of the products +

total energy before – the kinetic energy of the products

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Proton interaction

Strong, weak decay

Electromagnetic

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Neutron interaction

Strong, weak decay

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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

Sigma particles strangeness

-1

Pion strangeness

antiK0 and K- strangeness

-1

K0 K+ strangeness

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)