PP16 Seminar 1 - Particle Physics Question Sheet PDF

Preview

Summary

Particle Physics Question Sheet ...

Description

Seminar(Sheet(PP1:(Identifying(Particles(and(Interactions.( ! Reminder:( When( trying( to( figure( out( which( interaction( is( responsible( for( a( particular( observed( reaction,(there(are(several(clues(to(consider:( • Conservation(laws((Consider(Q, B, L,(I3 and(quark(&(lepton(flavours.( Ignore(parity,(c-parity,( spin(and(IT(which(are(much(harder(to(use,(due(to(complications(with(collision(angles(etc.)( • Reaction(probability/rate:( Strong(>(Electromagnetic(>(Weak( • Only(electromagnetic(interactions(involve(photons( • Only(weak(interactions(involve(neutrinos.( • Strong(interactions(only(involve(quarks.(

Examples:! Example!1:(Identify(the(interactions((strong,(electromagnetic,(weak(or(forbidden)(involved(here:( Λ0

(dus)

→ π-

( du)

+

p+

p+

(duu )

(duu )

+1 Q ( ( ( +1 B 0 S 1 0 −1 + I3 2 Charge( &( baryon( numbers( conserved,( but( flavour( S(and( I3(are(not(conserved(=>(A(weak( interaction( ( 0 +1 −1

−1 0 0

(du )

→ κ 0 + Λ0 ds (dus)

( )

+1 −1 0 0 Q ( +1 0 0 +1 B 1 1 −1 − + 0 I3 2 2 0 0 −1 +1 S Only(quarks,(no(violated(quantum(numbers.( Could( be( electromagnetic,( but( strong( contribution(larger((=>(Strong( ( ( p+ → π 0 + e+ +1 0 +1 Q OK ( +1 0 0 B No! Baryon(numbers(not(conserved(=>(forbidden!(

n 0 + γ → e− + e+ + n 0 0 0 −1 +1 0 Q ( 0 0 +1 −1 0 L ( 1 0 0 0 1 B 1 1 0 0 0 − − I3 2 2 All(quantum(numbers(conserved,(and(involves( photons(=>(must(be(electromagnetic(

Example!2:!Identify(the(unknown(particle(“?(“in( ( p + → n 0 + π + + .... ? uud → udd ud .... uu + dd +1 → 0 + +1 + .... 0 Q ( +1 → +1 + 0 + .... 0 B 0 → 0 + 0 + .... 0 L ( (

+ π-

p + → n + π + + ? ((Assume(the(lightest(possible.) ( Charge(conservation(means(“?”(has(charge(0.( Baryon(number(conservation(means(“?”(has( baryon(number(+0((lepton(or(meson).( Lepton(number(conservation(means(“?”(has( lepton(number(+0(( !0 =>!Therefore!it!is!a!light!charge!+0!meson:!π (

! 1

Section!A!(Questions!to!do!now):! ( 1.( For(each(of(these,(write(out(the(particles((leptons+quarks),(and(all(relevant(quantum(numbers( involved.(From(this,(try(to(classify(them(into(strong,(electromagnetic(and(weak(reactions.( ( (

( a)(( π − + p+ → π − + π + + n 0 (

(

c)( K + →π o + µ + +ν µ (

b)( γ + p+ → π + + n 0 ( d)( ν µ + n 0 → µ− + p+ (

(

e)( Λ 0 → e− + π + +e ν e (

f)(

π0 → e− + e+ + e − + e + (

( g)( p+ + p → π − + π + + π o ((Note:(could(also(be(written(as( p+ + p− → π − + π + + π o )( ( h)( τ - →e - + γ ( ( 2.( For(each(of(these,(identify(the(unknown(particle,(assuming(that(the(reaction(is(allowed.(Where( more(than(one(possibility(exists,(choose(the(lowest(mass(alternative.( ( (

( ( ( ( ( ( (

+ − 0 a)(( p + K → ? + η (A(strong(interaction(–(2(possible(solutions.)(

−

(

−

b)( ν µ + τ → µ + ? ( c)( ? + π+ → K − + π + + n 0 ((A(strong(interaction)( d)( Ω− → ? + e − + ν e (

Section!B!(Example!exam!questions):! ! This%is%a%part%of%a%question%from%section%A%(short%answer%section)%of%the%exam%paper:% 3.( a)( (

b)( ( (

We%haven’t%covered%the%material%for%this%question%part%yet.% ( (

(

(

(8%marks)(

For(each(of(the(following,(state(whether(it(is(a(boson(or(a(fermion,(and(list(the( interactions((strong,(weak,(electromagnetic)(that(it(is(sensitive(to/involved(in.( ( ( ( p+( ( ( ( W- ( ( ( ( g( ( ( ( ( ( ( ( ( ( ( π+( Ξ+( ( ντ ( ( ( ( ( (12%marks)(

% This%is%two%parts%of%a%question%from%section%B%(long%answer%section)%of%the%exam%paper:%

! 4.( The( “LHCb”( detector( at( the( Large( Hadron( Collider( is( designed( to( examine( the( differences( between(matter(and(antimatter.(In(particular(the(researchers(want(to(better(understand(why( our(universe(is(dominated(by(matter,(rather(than(antimatter.( ( a) i)((What(do(the(“Parity”((P)(and(“C-Parity”((C)(operations(do?( ii) What( is( CP( symmetry,( and( how( might( its( violation( explain( the( matter( dominance( of( the(universe?( 2

iii)(Is(there(a(related(symmetry(combination(that(is(not(believed(to(be(violated,(and(if(so,(( what(is(it?( ( ( ( (7%marks)( b)( We%haven’t%covered%the%material%for%this%question%part%yet.( (9%marks)( ( c)( For(each(of(the(following,(write(out(the(particles(involved((at(lepton+quark(level)(and(all( relevant(quantum(numbers(involved,(determining(which(quantum(numbers(are(conserved,( and(which(are(not.(Then(state,(with(reason(s),(whether(the(interaction(is(strong,( electromagnetic,(weak(or(forbidden.( ( ( i)(( B− + p+ → B 0 + n 0 (

( ( (

( (

ii)( Λ b0 + e+ → p+ + ν e ( iii)( B + → π + + π 0 (

( (9%marks)(

! ! Section!C!(Extra!questions):! ( 5.( For( each( of( these,( write( out( the( particles( (leptons+quarks),( and( quantum( numbers( involved.( From(this,(try(to(classify(them(into(strong,(electromagnetic(and(weak(reactions.( ( b)( τ − → π − + ν τ ( ( a)( µ+ →e+ + νe + ν µ ( − + − − D → K +π +π (

(

c)(

( ( ( 6.(

− + 0 + e)( π + π → p + n + p ( g)( ν µ + p+ → µ + + n 0 (

d)( π − → π 0 + e− + νe ( Λ 0 + p+ → K − + p+ + p+ ( h)( ν e + p+ → e− + π + + p+ ( f)(

(

For(each(of(these,(identify(the(unknown(particle,(assuming(that(the(reaction(is(allowed.(Where( more(than(one(possibility(exists,(choose(the(lowest(mass(alternative.( (

(

+ + a)(( λ c →? + µ +ν µ ((((Choose(the(most(likely/fastest(decay.)((

(

b)( ? → µ− + ν µ + ν τ (

( ( (

c)( K + + π − →? + π 0 (((A(strong(interaction)( d)( λ 0 → ? + ? + ν e (((((Choose(the(mostly(likely/fastest(decay)(

3...