A 4th generation scenario

F. Richard ECFA Study June 2008F. Richard ECFA Study June 2008

A 4th generation scenarioA 4th generation scenario

F. Richard LAL/OrsayF. Richard LAL/Orsay

http://ecfa2008.fuw.edu.pl/welcome.html


IntroductionIntroduction

In view of the LHC start, it seems worthwhile In view of the LHC start, it seems worthwhile to envisage unexpected (but well motivated) to envisage unexpected (but well motivated) scenarios which would strongly impact on ILC scenarios which would strongly impact on ILC

Examples:Examples: Discovery of a heavy Higgs Discovery of a heavy Higgs Discovery of heavy fermions with or without Discovery of heavy fermions with or without

SUSYSUSY This talk is presenting one of these scenarios This talk is presenting one of these scenarios


OutlineOutline

Is a 4th generation Is a 4th generation allowed by allowed by LEP/SLC/TeVatron PM ?LEP/SLC/TeVatron PM ?

Is it useful and why ?Is it useful and why ? What does it predict ? What does it predict ?


4th & PM4th & PM

Common wisdom (PDG): 4Common wisdom (PDG): 4thth chiral chiral generation is excluded by S/T generation is excluded by S/T constraints.constraints.

Excluded only for the mass degenerate Excluded only for the mass degenerate casecase

T=0 T=0 S=3/4S=3/4 One can play with the >0 correlation One can play with the >0 correlation

between these variables and easily pass between these variables and easily pass the constraints when fermions are the constraints when fermions are partially degenerate in mass partially degenerate in mass

²~

(150 )²m

TGeV

²~

(150 )²m

TGeV


An exampleAn example

G. Kribs et al G. Kribs et al hhttp://arxiv.org/abs/0706.3718vttp://arxiv.org/abs/0706.3718v11

Heavy Higgs Heavy Higgs allowedallowed

http://arxiv.org/abs/0706.3718v1




Motivation for >3 generationsMotivation for >3 generations

Baryogenesis needs C+CP violation & Baryogenesis needs C+CP violation & strong EW 1st order transition strong EW 1st order transition

SM alone SM alone Not enough CPV Not enough CPV Insufficient EW transitionInsufficient EW transition MSSM aloneMSSM alone New phases but severely constrained by New phases but severely constrained by

EDMEDM EW transition not strong enough unless EW transition not strong enough unless

very FT (light stop ?)very FT (light stop ?) -> extra particles needed, strongly coupled -> extra particles needed, strongly coupled

to the Higgs field, scalars or fermions to the Higgs field, scalars or fermions (cf. M. Carena et al hep-ph 0410352) (cf. M. Carena et al hep-ph 0410352)


4th generation 4th generation

CPV fine (2 extra phases in CKM; Jarlskog CPV fine (2 extra phases in CKM; Jarlskog determinant >> SM)determinant >> SM)

Large Yukawa couplings Large Yukawa couplings yyt’t’ to Higgs field to Higgs field (NB: (NB: yyt’t’ and quartic coupling and quartic coupling become become strongstrong at scale at scale ~TeV)~TeV)

However not enough to get the right EW However not enough to get the right EW transitiontransition

Works including SUSY, hence Works including SUSY, hence 4MSSM4MSSM R. Fok G. Kribs R. Fok G. Kribs arXiv:0803.4207arXiv:0803.4207


Predictions:Predictions:

300<Mt’,b’<450 GeV + lighter leptons300<Mt’,b’<450 GeV + lighter leptons Squarks ~ mass degenerate with quarksSquarks ~ mass degenerate with quarks Higgs could be heavyHiggs could be heavy through RC through RC Spectacular & early signals at LHCSpectacular & early signals at LHC Accessible at a TeV LC (heavy leptons)Accessible at a TeV LC (heavy leptons) Note that Tevatron already excludes Note that Tevatron already excludes

mt’<260 GeV & 140<mH<180 GeV mt’<260 GeV & 140<mH<180 GeV The latter is due to X9 cross section in gg->HThe latter is due to X9 cross section in gg->H


Search at TeVatronSearch at TeVatron

Recent CDF update 2.3fb-Recent CDF update 2.3fb-11

http://http://www-cdf.fnal.govwww-cdf.fnal.gov / /physicsphysics/new/top/2008//new/top/2008/tproptprop /Tprime2.3/cdf9234_tprime_23_pub.pdf /Tprime2.3/cdf9234_tprime_23_pub.pdf

Mt’>284 GeVMt’>284 GeV Slight excess above this Slight excess above this

limitlimit Assumes t’->Wq with Assumes t’->Wq with mt’-mb’<Mwmt’-mb’<Mw Should therefore add the Should therefore add the

b’ b’ contribution X2 ? contribution X2 ? -> mt’,b’>330 GeV ?-> mt’,b’>330 GeV ?

X2

http://www-cdf.fnal.gov/physics/new/top/2008/tprop/Tprime2.3/cdf9234_tprime_23_pub.pdf








The flavour sectorThe flavour sector

Bs Bs SM mixing goes like ~mtVtb without CPV SM mixing goes like ~mtVtb without CPV mt’Vt’b could be of similar sizemt’Vt’b could be of similar size

Vt’bVt’b complex, then complex, then CPVCPV present in Bs mixing present in Bs mixing More generally CPV present in b->s transitions More generally CPV present in b->s transitions

while are almost absent in the SMwhile are almost absent in the SM Has it been seen ?Has it been seen ?

' ' '1

t t b t s

t ts

NP m V VSM m V


b->s with 4 generationsb->s with 4 generations

Several indications Several indications b->sb->s ‘penguin’ ‘penguin’ transitions but plagued by usual QCD transitions but plagued by usual QCD uncertainties uncertainties

cf. e.g. cf. e.g. KKpuzzle puzzle G. Hou G. Hou arXiv:0710.5424arXiv:0710.5424 For the 1st time Tevatron is measuring the For the 1st time Tevatron is measuring the

time dependence of the ‘gold plated’ time dependence of the ‘gold plated’ mode mode J/J/ with tagged events with tagged events

Could provide an unambiguous answer Could provide an unambiguous answer with sufficient statisticswith sufficient statistics

Watch carefullyWatch carefully


UTfitUTfit Recent but unofficial (UTfit Recent but unofficial (UTfit

collaboration) combination of CDF collaboration) combination of CDF (1.35 fb-1)+D0 gives ~3 (1.35 fb-1)+D0 gives ~3 effect with effect with 2 solutions 2 solutions

One of them has NP/SM<1One of them has NP/SM<1 http://fr.arxiv.org/abs/0803.0659v1http://fr.arxiv.org/abs/0803.0659v1


msms

The UTfit negative phase The UTfit negative phase predicts a destructive predicts a destructive interference SM-NP with interference SM-NP with reduction on reduction on msms

Indicated by the CKM fit Indicated by the CKM fit Other interpretations are Other interpretations are

obviously possible within obviously possible within SUSY (one of them gave SUSY (one of them gave NP>>SM but not CPV !)NP>>SM but not CPV !)

Keep an eye on these Keep an eye on these developmentsdevelopments


Possible scenarioPossible scenario

At LHC an early discovery of the new At LHC an early discovery of the new fermions + SUSY squarksfermions + SUSY squarks

A heavy Higgs very easily observed or A heavy Higgs very easily observed or a light Higgs as difficult as SM a light Higgs as difficult as SM

(same 2(same 2 rate but H->2 g prominent) rate but H->2 g prominent) Rich and confusingRich and confusing ILC very powerful in particular for ILC very powerful in particular for

leptons and for a light Higgsleptons and for a light Higgs


Final remarksFinal remarks

For simplicity one assumes a 4th For simplicity one assumes a 4th generation, simple replica of the first 3generation, simple replica of the first 3

It seems that this is an unnecessary It seems that this is an unnecessary limitation limitation

What matters is the occurrence of extra What matters is the occurrence of extra heavy quarks which provide the extra heavy quarks which provide the extra degrees of freedom needed for degrees of freedom needed for baryogenesis and CPV in the b sectorbaryogenesis and CPV in the b sector

Models predicting KK extra fermions e.g. Models predicting KK extra fermions e.g. on the basis of ND>4 could also provide on the basis of ND>4 could also provide similar mechanismssimilar mechanisms


ConclusionConclusion

A reasonably well motivated scenarioA reasonably well motivated scenario Requires SUSY but cannot be extrapolated Requires SUSY but cannot be extrapolated

to GUT because of the large Yukawa to GUT because of the large Yukawa constants constants

Early signalsEarly signals expected at LHC (or even at expected at LHC (or even at Tevatron with full luminosity) Tevatron with full luminosity)

Allows for a Allows for a heavy Higgsheavy Higgs within SUSY within SUSY Rich physics for a TeV LCRich physics for a TeV LC Watch for the Bs sector @ TevatronWatch for the Bs sector @ Tevatron -> Could serve as an illustration of LHC/LC -> Could serve as an illustration of LHC/LC

complementaritycomplementarity


BeyondBeyond thethe 3SM 3SM generationgeneration atat thethe LHC LHC eraera

4-5 September 20084-5 September 2008

http://indico.cern.ch/conferenceDisplay.py?confId=33285














Mh=115

c/T=1

A 4th generation scenario

Documents

Transcript of A 4th generation scenario