compositeness at ilc250 - ilc agenda (indico)...•ilc250 gives as many ee->bb events than lep1...

Compositeness at ILC250 ?

F. Richard LAL-Orsay

International workshop on future linear colliders

LCWS Strasbourg 23-27 October 2017

F. Richard LAL-Orsay October 2017 1

Introduction

• There are various interpretations of the hierarchy problem: • SUSY • Compositeness (specifically the Randal Sundrum model)• Cosmology (multiverses, relaxions, intelligent design…)• … • Since LEP, there is some experimental evidence that the b quark and therefore,

very likely, the t quark, could be composite objects• ILC250 gives as many ee->bb events than LEP1 and 200 time more events than

LEP2 • Accuracies on Zbb couplings have been recently estimated with ILC250 assuming

500 fb-1 and found to surpass LEP1, providing a final answer on the Zbb anomaly• B factories seem to indicate a similar message


Purpose of this talk

• I will recall the various anomalies observed in the b sector atLEP and B factories

• I will specifically present what can be done at ILC250 on e+e- -> bb

• I will then go through the various RS models and show how they can give a global interpretation on these anomalies

• I will finally discuss what can be expected in the future with emphasis on the radion search at ILC250 (direct & indirect)


The b/t anomalies at LEP


0607280

• Can be reproduced in a RS approach

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What can be expect at ILC250 on ee->bb

• dgRZ/gRZ ~2% sufficient to confirm at >5s or to discard the LEP1 effect which is at the 25% level

• Recall the sign uncertainty on LEP1 solutions dgRZ/gRZ=25% or dgRZ/gRZ=-225%

• Not a problem at 250 GeV to make the right choice for the sign

• ILC measurements with beam polarisationprovide model independent access to vectorand tensor couplings


1709.04289

Anomalies


~-2.5s B->K*µµ vs B->K*ee RK*

RJ/y~-2s B->J/ytn vs Bc->J/yµn

Comments on these anomalies

• None of these effects is fully significant and some may go away as for h->µt

• These results need therefore confirmation

• g-2 is going to be re-measured at FNAL with better accuracy

• More data, coming soon from LHCb Run2, should help (already ~4s for RD*)

• It is fair to say that no model has consistently predicted these effects (composite µ not observed at LEP1)

• From past experience: beware of anomalies ! But also recall that some anomalies turned out to be true: e.g. 1st indications of a H(125) at Tevatron

• Guidance from a global theory is indispensable to gain confidence when several indications appear


Compositeness within RS

• Has the great merit to solve the hierarchy problem

• In its simplest version RS predicts KK excitations of bosons and fermions

• Mkk>10 TeV for bosons to satisfy S,T constraints therefore outside the reach of LHC but testable with e+e- precision accuracy using b and t final states 0603105

• To reduce Mkk lower bound various tricks were tried

• Custodial symmetry with additional Z’/W’ particles Mkk>3-5 TeV at the limit of visibility of LHC 0308036

• Modified IR brane, the so called soft-wall SW scenario then Mkk down to 2 TeV still not excluded by LHC explains B factory anomalies with µ composite 1011.2205


Softwall RS

• Basic idea : keep the main feature of RS to generate the mass hierarchy MW=MPlanckexp(-2kDy) k~1/MP 2kDy~35 , k is the curvature and Dy is the size of the extra dimension

• Modify the Higgs shape near the EW brane to avoid S & T

• Mkk down to 2 TeV

• Radion below 0.5 TeV

• Anomalies (including g-2) can be explained assuming b µ t are distributed differently than e

• Can be made compatible with LEP1 constraints on ZffF. Richard LAL-Orsay October 2017 9

1011.2205

What can we hope for ?

• A significant confirmation of anomalies and of the g - 2 effect

• New anomalies are predicted (not discussed here)

• A discovery of a new resonance at LHC, in particular a discovery of a light radion (<500 GeV) in the WW/ZZ or gg modes

• ILC250 should confirm/dismiss the Zbb anomaly and be able to distinguish between the models

• Higgs BR should show deviations measurable at ILC (not discussed here)

• ILC250 would be unique to observe the radion with a mass below the WW threshold

• …F. Richard LAL-Orsay October 2017 10

1709.10308

The radion

• Could be the lightest particle of the RS model

• Its couplings depends on three parameters mR, x and L

• Can be discovered at LHC if MR > 2MW

• ILC250 is unique to cover lighter masses using the recoil mass method with Z+R up to ~2MW

(complementary to LHC)

• LEP luminosity was insufficient to achieve this goal

• Higgs BR measurements at ILC250 cover a large region parameters and complement direct searches

• 1702.03984


Possible hint

• An indication was present at LEP2 at ~98 GeV (3 fb-1) 0306033

• At LHC, a signal could be observed in gg

• CMS provides a 3 sd signal at 95 GeV at 13 TeV CMS PAS HIG-17-013

• ATLAS has not yet released its analysis at 13 TeV

• ILC250 in ZX would be able to measurebb and gg modes which allow to distinguish a radion from an NMSSMscalar 1210.1976

Stay tuned !


Conclusion• There are various anomalies indicating that the b quark could be composite

• This may also be true for µ and t leptons

• It is possible to give a complete interpretation of these phenomena in the SW version of RS

• If true, this interpretation predicts various new signals to be observed in B factories and at ATLAS/CMS

• ILC250 offers the best sensitivity, well beyond LHC, to observe these effects and select the underlying model

• ILC250 could also be unique to discover a new scalar which offers the best signature for a RS scenario


F. Richard LAL-Orsay October 2017

BACK UP SLIDES

14

RS for pedestrians

• Extra dimension with warped space between two branes in the extra dimension

• Solves hierarchy : MW=MPexp(-2kDy) where kDy~35 with k~1/MP, Dy distance between the two branes

• Describes geometrically the hierarchybetween fermion masses: light fermions close to the Planck brane are light and elementary, the heavy ones see the Higgs on the other brane called the EW brane

• The need to stabilize this brane requires an extra scalar field called the radion


Radion at LHC

• For mR <2MW can also discover the radion but leaves large regions uncovered

• The two photon decay only helps for x>0 MR>70 GeV

• Higgs BR measurements at ILC250 cover large parts of these regions


Radion at LHC and ILC


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