Particle Physics

Question 1

The K– meson has strangeness –1.

(i) State the quark composition of a meson.

Answer 1

quark antiquark pair

Question 2

The K– meson has strangeness –1.

State the baryon number of the K– meson.

Answer 2

0

Question 3

What is the quark composition of the K– meson?

Answer 3

anti-up strange

Question 4

State the quark composition of a proton

Answer 4

uud

Question 5

A change in quark identity is involved in electron capture.

(i) Explain what is meant by electron capture.

Answer 5

an atomic/orbital/shell electron

interacts with a proton in the nucleus (via the weak interaction)

Question 6

Give an example of an exchange particle other than a W+
or W– particle, and
state the fundamental force involved when it is produced.

Answer 6

Z0 with the weak interaction
gluons or pions with the strong nuclear force
γ photons with electromagnetic interaction
gravitons with gravity

Question 7

State what roles exchange particles can play in an interaction.

Answer 7

transfers energy
transfers momentum
transfers force
(sometimes) transfers charge any two

Question 8

State the quark structure of an antibaryon

Answer 8

consists of 3 antiquarks

Question 9

Give one property of an antiparticle that is the same for its corresponding particle and
one property that is different.

Answer 9

same (rest) mass (energy)

difference eg baryon number/charge

Question 10

Name two baryons

Answer 10

any two eg proton, neutron

Question 11

State the quark structure of the pion

Answer 11

up, antidown

Question 12

The K+ kaon is a strange particle. Give one characteristic of a strange particle that
makes it different from a particle that is not strange.

Answer 12

contains a strange quark
or longer half life than expected
or decays by weak interaction

Question 13

name the particles in the following list that may be affected by the weak
interaction.

Answer 13

positron, neutron, neutrino, positive pion

Question 14

name the particles in the following list that may be affected by the
electromagnetic force.

Answer 14

electron, proton, negative muon

Question 15

Sub-atomic particles can either be hadrons or leptons.

State one difference between these two groups of particles.

Answer 15

leptons do not experience the strong interaction but
hadrons do or hadrons not fundamental/made of quarks
and leptons are not

Question 16

Give an example of a non-strange hadron and an example of a lepton.

Answer 16

hadron eg proton, neutron, pion (1)

lepton eg electron, neutrino

Question 17

Hadrons can be further divided into two groups. Name these two groups and state a
difference between them.

Answer 17

baryons (1)
mesons (1)
baryons made from three quarks (or 3 antiquarks),
mesons a quark, antiquark pair or baryons, baryon
number is +1 or –1 mesons 0

Question 18

What property defines a hadron?

Answer 18

particles that experience the strong (nuclear) force/interaction

Question 19

What is the quark structure of a baryon?

Answer 19

particles composed of three quarks

Question 20

What is the quark structure of a meson?

Answer 20

particles composed of a quark and an antiquark

Question 21

State one similarity and one difference between a particle and its antiparticle.

Answer 21

similarity: but the same (rest) mass or rest energy
difference: opposite quantum states eg charge

Question 22

The quark model was developed to help understand hadrons. Quarks cannot exist
separately, they form combinations.
(a) (i) List the three combinations that quarks can form.

Answer 22

q anti-q, q q q, anti-q anti-q anti-q

Question 23

Give the quark combination for a positive pion, π

+ and an antiproton,

Answer 23

i) up anit-d

ii) anti-d anti-u anti-u

Question 24

What is the virtual exchange particle used by electromotive force?

Answer 24

γ photon

Question 25

State two differences between the exchange particles used by the weak interaction
and used by the electromagnetic force.

Answer 25

γ is massless
γ has infinite range
γ does not carry charge

Question 26

State what is meant by an antiparticle.

Answer 26

all properties/quantum numbers (e.g. charge, strangeness)

are opposite