Chapter 13folk.uio.no/farido/fys3510/SomeOutstandingQuestions13.pdf · 2016-05-30 · • 3 massive gauge bosons of WI, W+, W-, Z0 • 1 mass-less gauge boson of EM, γ SU (3) C ×

Chapter13

9.5BeyondtheStandardModel:UnificationSchemes.9.5.1GrandUnification9.5.2Supersymmetry9.5.3Stringsandthings

9.3TheOriginofMass:theHiggsBosonètreatedinpreviouschapters

TheoreticalbackgroundExperimentalsearchesDiscoveryFutureprospects

9.4TheNatureoftheNeutrinoètreatedinChapter14aspartofBetadecay

9.4.1DiracorMajorana?9.4.2Neutrinolessdoublebdecay

29/05/16 F. Ould-Saada 2


1.  Spin-1-gaugebosonsector•  SU(3)CrepresentsQCD

–  Thegaugebosons–8mass-lesscoloredgluons–coupleonlytocolor-chargedparticles,quarks&gluons

•  SU(2)LxU(1)YrepresentsEWinteraction–  LindicatesthatSU(2)couplesonly

toleft-handedparticles,fermions=quarksandleptons

–  YindicatesthatU(1)couplestoweakhypercharge

–  AfterSSBà•  3massivegaugebosonsofWI,

W+,W-,Z0•  1mass-lessgaugebosonof

EM,γ

YLC USUSU )1()2()3( ××

2.  Spin-1/2-fermionscomein3familiesorgenerations–  5multipletsperfamily,

accordingtohowtheytransformundergaugesymmetries•  Particleswithineach

multipletaretransformedintoeachotherbygaugesymmetries

•  Particlesindifferentmultipletsarenot

–  Hyperchargeassignmentslookratherad-hocàbeyondSM?

–  Intotal15particlesà45for3families!


YLC USUSU )1()2()3( ××

€

Q = I3 +Y2

3.Spin-0-Higgssector• EWSSB• HowmanyHiggsbosons?

¡  SMsuccessfulindescribingnearlyallexistingexperimentaldata§  àvariousattemptstoextendElectroWeakunificationtoincludeQCDà

GrandUnification(GUT)?Lepton-QuarkSymmetry§  àincludingGravityinlargerunificationschemes?

¡  GrandUnification¡  Supersymmetry¡  Superstrings


¡  AlthoughagreementbetweenSMandexperimentsisnotfarfrombeingperfect§  SMcontainsmanyparameterstobedeterminedexperimentally▪  Couplingconstants,mixingangles,particlemasses(fermions,gaugebosons,Higgsboson),…

§  Manyofsuchparametershavenothingtodowiththesymmetriesofthetheory

§  SMleavesseveralquestionsunanswered▪  Whyarethereexactly3independentsymmetrygroups?▪  Whataboutreducingthenumberoffreeparameters?▪  Whyarethere3familiesofquarksandleptons?▪  Whatistheoriginofthesymmetrybetweenquarksandleptons?▪  Arefermionscompositeobjects?

¡  Whyiselectricchargequantizedandprotonandelectronhaveexactlyoppositecharge?§  Whyarequarkchargesfractional?

¡  Whatisthesolutiontothehierarchyproblem,thattheEWscaleissosmallcomparedtothePlanckscale?§  MW~10-17MPl?

¡  Whatisthesolutiontothefinetuningproblem?§  LoopcorrectionsinvolvingHiggsarequadraticallydivergent,

suchthatcorrectionstoHiggsmassaremanyordersofmagnitudelargerthanthemassitself!

§  Unnaturalfinetuningisneeded,whichconsistsinadjustingcountertermsorderbyorderinperturbationtheorytocancelthedivergences

¡  17thcentury,Newtonrealized1stunificationbetweenfallingbodiesandplanetmovements

¡  19thcentury,Maxwell,inhisEMtheoryoflight,unifiedelectricityandmagnetism,ononehand,andopticsontheotherhand

¡  20thcentury,GSWdescribedweakforceinthesameformalismasEM§  Oneparameter,θW,relatesthe2couplingconstants

¡  TowardsGrandunificationalsoincludingstrongforce?§  WithSupersymmetry?

¡  Or?§  Gravity+GUT+SUSY=SuperStrings?

¡  Letushopethattimescaleunitwon’tbe100years!

¡  CurrentdatahintataunificationbetweenStrongandElectroweakforces...atmuchlargerenergies,GUTscale.

¡  GUTisasymmetrybetweenLeptonsandQuarks§  unifiesstrongandelectroweak

forces§  Requiresnewgaugebosonsand

baryonnumberviolation¡  SUSYunifies“matterandforce

particles”:“matter-forceduality”§  relatesparticlesofdifferentspins:

Fermions-Bosons§  introducessuper-partnerstoeach

SMparticle§  requires5Higgsparticles§  providesDMcandidate

29/05/16 F.Ould-Saada:HEPP&ATLAS 9

GUT

...SUSY...

¡  EW+QCDàgrandunifiedtheories


¡  GiventhemeasurementuncertaintiesSupersymmetryorsomethingelseisneededtoachieveunificationatMX~1016GeV

g = esinθW

; g ' = ecosθW

gs = 4παs

!

"#

$#

?%→%αU ≡

gU2

4π≈142

MX ~1015GeV

)

*#

+#

cosθW =MW

MZ

GUGUT! ⊃ SU(3)C

QCD!"# $# ⊗ SU(2)L ⊗U(1)Y

EW! "## $##

29/05/16 F. Ould-Saada: HEPP & ATLAS 11

Strong

Weak

Electromagnetic

¡  SU(5)multiplets

SU(5) 1015GeV! →!! SU(3)C ⊗ SU(2)L ⊗U(1)Y102GeV! →!! SU(3)C ⊗U(1)QED

¡  Green–SMinteractions¡  Red–SU(5)interactionsmediatedbyXandYgaugebosons

dRred dR

green dRblue eR

+ νe~

dRred g,γ,Z gr+g gr+b X-4/3

red Y-1/3red

dRgreen gg+r g,γ,Z gg+b X-4/3

green Y-1/3green

dRblue gb+r gb+g g,γ,Z X-4/3

blue Y-1/3blue

eR+ X4/3

red X4/3green X4/3

blue γ,Z W+

νe~ Y1/3

red Y1/3green Y1/3

blue W- Z

¡  Quarkfractionalcharges,withinmultiplets

¡  SU(2)doubletstructure¡  Weakmixingangle

§  Z/γmixing§  Z/γcouplingtofermions

3qd + e+ 0 = 0⇒ qp = 2qu + qd = e

(νe,e− )L, (u,d ')L : Q(ν )-Q(e)=Q(u)-Q(d)

Q(I3 −Qsin2θW5∑ ) = 0

Z 0 γ = 0

#$%

&%⇒ sin2θW =

QI35∑

Q25∑= 3 / 8→ 0.21

sin2θW (MZ ) ~ 0.23 ;

¡  τ(exp)>8.2x1033y

¡  SO(10)-basedGUTs§  Moreparameters,combinationwithsupersymmetry§  Lifetimesof~1033formostprobablepàK+ν(exp:τ>6.7x1032y)

¡  TestingGUTs§  X,Yvertices§  àreactionswhere

LandBviolated§  àproton

unstable!

p→ π 0 + e+

p→ π + +νe

"#$

%$ R ≡ B − Ll

l∑ conserved

yrτ

)c(Mg)c(Mτ

p

pU

Xp

130

524

42

10 ±≈

≈

29/05/16 16

Proton decay: p à e+ π˚Ø  To achieve lifetime limits of 1033-1034

Ø  need to control 1034 protons ...

Ø  Super Kamiokande: Water Cerenkov technique

Ø After 7 years, exposure= MΔt=138 000 t yr à NpΔt=45 X 1033

€

Np = M(kg) 103kg /g( )NA1018( ) = 2.25 ×107 ×103 × 6 ×1023 10

18( ) = 7.5 ×1033

-  50 000 t of pure water (22 500 t fiducial volume)-  readout by ½- m photomultipliers, 1000 m underground

Ø  Super Kamiokande: Water Cerenkov technique

Ø  Detection efficiency: not all protons detected

Ø  efficiency ~40%

yrepB 330 104.8)( ××→≥ +πτ

pMeMep

MM

=→

=→++ )(

)(00

00

ππ

γγγγππ

¡  MMscanbecreatedatthetimeofGUSBà…,U(1)

¡  Magnetic§  chargegandmassMMhuge

¡  IntroductionofMMsintoMaxwellequations§  Completesymmetrybetweenelectricandmagneticfields§  SymmetrybrokenbylargegandMM

¡  Read§  13.1.3Cosmology.FirstmomentoftheUniverse§  13.4Particles,AstrophysicsandCosmology§  13.6TheBigBangandtheprimordialUniverse

MM ~MX

αGU

~ 1015

0.03~ 3×1016

eg = n!c ; n =1→ g = 68.5e

¡  Introductionofnewparticles–sparticles-ensurescancellationinhigherorderdiagrams


R-parity = (-1)2s+3B+L

R=+1 for particles R= -1 for s-particles

¡  Ifexactsymmetryàparticlesandsparticleswouldhavesamemasses¡  SUSYmustbebroken!

¡  U|fermion>=|boson>¡  U|boson>=|fermion>

¡  a)SM¡  b)SUSY

¡ 

SUSY (WIKIpedia) SUSY Spectrum

Supersymmetry facing experiment: much ado (already) about nothing (yet) Weak Scale Supersymmetry

¡  Ine+e-


!"#$p E/missing

000

~~~~

~~χχ

χ+→

⎭⎬⎫

+→

→ −+−+

±±

−+−+

eeeeee

eeee

−+−+

−+

→

→

χχ

χχ~~~~ 00

eeee

gravity

EM

Stre

ngth

r


¡  Oneofmainchallengesinparticlephysics§  UnderstandEWsymmetrybreakingandoriginofmass§  Solution?ExistenceofScalarHiggsboson

¡  MotivationsforHiggs¡  Experimentalsearch¡  Discovery


The material on Higgs has been treated in previous chapters

¡  Forcesaredictatedby(gauge)symmetries§  Fermionsin3!=SU(3)C*[SU(2)L*U(1)Y] àQCD+Electroweak(“=“QED+Weak)

29/05/16 PhysicswithATLAS 26

§  Symmetriesoflawsdonotnecessarilyleadtosymmetriesofoutcomesú  Electroweaksymmetryspontaneouslybroken–BroutEnglertHiggsmechanismú  BEH“hides”EWsymmetry,givesmassestoweakgaugebosonsand“approves”

fermionmasses,predictscouplingsofparticlestoHiggs,andmore§  HiggsbosonmassisnotpredictedbytheSM§  èMustbemeasured!

¡  Higgscouplingtomassiveparticlespredicted§  Hcouplesveryweaklyto

lightparticles,likee,µ, ν,u,d,s

§  HcouplesmorestronglytoW,Z,t,b

§  Couplingtofermions~mf

§  Couplingtobosons~mV2



ttHMMZZHMMWWHMM

jetbbHMM

tH

ZH

WH

HMHMHffgbbH

WH

→≥

→≥

→≥

−→→<

−+

−Ο=Ο=→Γ

:2:2

:2

2:2

00

)410()2()(

⎟⎟⎠

⎞⎜⎜⎝

⎛=

W

fWHff Mm

gg 2

¡  RareHiggsdecaymodes

¡  TotalwidthdependsstronglyonHiggsmass§  Noteincreaseduetogaugeboson

channelopening§  Width~massatTeV!


20

3

/150110:10

cGeVMffZHBRH

H −→−

≈→− −γγ

¡  Higgsbosonhasrichspectrumofdecaymodes¡  BranchingratiosdependstronglyonHiggsmass



2

00

/114

208

cGeVMbbHZHee

GeVs

H >⇒

→→

≤−+

€

−M H < 2MW

H →bb ,τ +τ−

−M H ≥ 2MW

H →W +W − → l+l−ν lν l−M H ≥ 2MZ

H →Z 0Z 0 → l+l−l+l−ATLAS, CMS optimized to search up to 1 TeV masses


29/05/16 Higgs and more - F. Ould-Saada 34

¡  125GeV…arathergoodcompromise

¡  4/5productionprocesses

¡  ≥5decaychannels

29/05/16 Higgs and more - F. Ould-Saada 35

§  Understandingof“background”isimportantú  Mostofwhichisduetoimportantphysicsatthe

heartofthegaugestructure/symmetryofelectroweakinteraction

ú  Higgsshowedupbetween2relativelybusyregions!

36

¡  HowtoincorporateGravity?§  Nosuccessfulstand-alonequantumtheoryofGravity

¡  Replacepoint-likeparticlesby1-dimentionalquantumstringsformulatedin10or11space-timedimensions

¡  Superstringtheorieshave1parameter–stringtension§  However,weleavein4dimensions§  Allextradimensionshavetobecompactified§  Toomanytheories,nopredictivepower...yet

¡  Higherdimensionalbranesin11dimensions§  M-theoriesàunificationofall5Superstringtheories

¡  OperateatPlanckmass-scale§  Gravity~EW~QCD


219 /102.1 cGeVGcMP ×==!

¡  See-sawmechanism§  Notheoreticalunderstandingofleptonandquarkmasspattern§  Neutrinomassesfromoscillationsmuchlowerthanthoseofchargedleptons§  PossibleexplanationincontextofGUTswherebothtypesofneutrinos–

MajoranaandDirac–couldco-exist§  Massmatrix

See-Sawmechanism:onemassgoesuptheotherdown!


€

M =0 mD

mD mM

"

# $

%

& ' mD ≈ MEW ; mM ≈ MGUT

mM >> mD ⇒ λ+ ≈ mM

very heavy neutrino! " # $ # , λ− ≈

mD2

mM

observed neutrinos~1eV! " # $ #

Documents

Chapter 13folk.uio.no/farido/fys3510/SomeOutstandingQuestions13.pdf · 2016-05-30 · • 3 massive gauge bosons of WI, W+, W-, Z0 • 1 mass-less gauge boson of EM, γ SU (3) C ×