Particle Physics Questions

 

1.  C

2.  C

 

 

  3.     (a)

	hadron	baryon	lepton
neutron	y	y
proton	y	y
electron			y
neutrino			y

          4 lines correct 2/2: 3 lines correct 1/2: 2 or 1 line correct 0/2 (2)                           2

 

3.  Three from:

a.       Proton turns into a neutron and positron

b.       Positron is released

c.       Up quark turns to down quark

d.       Electron neutrino released

[3]

 

5.       (i)      up down down / udd;                                                                                          1

  (ii)           Q                B                 S
        u   (+)2/3          (+)1/3              0                                               u values (1)
        d    –1/3           (+)1/3              0                                                d values (1)        2

  (iii)  so for neutron     Q = 0
                          B = 1
                          S = 0                                                                                       1

[4]

 

6.       (i)      leptons;                                                                                                             1

(ii)     neutrino / muon / tau(on);                                                                                   1

[2]

7.       lepton: two examples:  electron; (1)
                                    positron; (1)
                                    neutrino; (1) any 2 (2)
                                    (allow muon, tauon)
3 particles including one wrong gets 1 only

          composition: fundamental (- no quark components); (1)

          forces: weak force / interaction; (1)
            electron / positron - (also) electromagnetic / electrostatic force; (1)

          where found: electron - in atom, outside nucleus or in β– decay; (1)

                               positron (rarely) emerging from (high mass) radioisotopes /
                     in β + decay / accelerating-colliding machines; (1)

                               neutrino - travelling in space eg from Sun
                     or emitted (with electron / positron) in beta decay; (1)

          allow ONCE ‘resulting from high energy particle collisions’                                   any 6

[6]

 

 8.      baryon: two examples proton; (1)
                                    neutron; (1)
3 particles quoted, including one wrong gets 1/2 only

          quark composition:    proton         uud; (1)
                                 neutron       udd; (1)

          (aware consists of 3 quarks, unspecified, gets 1/2)

          stability:   proton stable inside (stable) nucleus; (1)
                 proton possible decay / half life = 1032 years when free; (1)
                 allow any half life > 1030 years

                          neutron stable inside (stable) nucleus; (1)

                          neutron half life = 10/15 minutes when free; (1)                                     any 5

[6]

 

9.       neutron is udd / proton is uud; (1)
quarks are: up down strange top bottom charm; (1)
either up / u has Q = (+)2/3, B = (+)1/3;
or down / d has Q = –1/3, B = (+)1/3; (1)

          quarks are fundamental particles; (1)
for every quark there is an antiquark; (1)
antiquarks have opposite values of Q, B and S (compared to quark) (1)
quarks are held together by strong force / gluons (1)
Q, B and S are conserved in (quark) reactions (1) any 2                                                  5

[5]

 

10

THREE FROM:

the strong interaction ✔

has short range OR mention range (less than 5 fm) ✔

attraction up to 5 fm ✔

repulsive (any distance below 1fm) ✔

is zero/negligible beyond 5 fm ✔

only affects hadrons/ baryons and mesons ✔

mediated by gluons/pions ✔

If wrong interaction identified then zero marks

If refer to strong interaction correctly then ignore any subsequent reference to other interactions