1. Compositeness at ILC250 ? F. Richard LAL-Orsay
International workshop on future linear colliders
LCWS Strasbourg October 2017
F. Richard LAL-Orsay October 2017

2. F. Richard LAL-Orsay October 2017
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
F. Richard LAL-Orsay October 2017

3. F. Richard LAL-Orsay October 2017
Purpose of this talk
I will recall the various anomalies observed in the b sector at LEP 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)
F. Richard LAL-Orsay October 2017

4. The b/t anomalies at LEP
Can be reproduced in a RS approach
F. Richard LAL-Orsay October 2017

5. 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 polarisation provide model independent access to vector and tensor couplings
F. Richard LAL-Orsay October 2017

6. F. Richard LAL-Orsay October 2017
Anomalies
RK*
~-2.5s B->K*µµ vs B->K*ee
~-2s B->J/ytn vs Bc->J/yµn
RJ/y
F. Richard LAL-Orsay October 2017

7. 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
F. Richard LAL-Orsay October 2017

8. 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
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
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
F. Richard LAL-Orsay October 2017

9. F. Richard LAL-Orsay October 2017
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 Zff
F. Richard LAL-Orsay October 2017

10. F. Richard LAL-Orsay October 2017
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

11. F. Richard LAL-Orsay October 2017
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
F. Richard LAL-Orsay October 2017

12. F. Richard LAL-Orsay October 2017
Possible hint
An indication was present at LEP2 at ~98 GeV (3 fb-1)
At LHC, a signal could be observed in gg
CMS provides a 3 sd signal at 95 GeV at 13 TeV CMS PAS HIG
ATLAS has not yet released its analysis at 13 TeV
ILC250 in ZX would be able to measure bb and gg modes which allow to distinguish a radion from an NMSSM scalar
Stay tuned !
F. Richard LAL-Orsay October 2017

13. F. Richard LAL-Orsay October 2017
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

14. F. Richard LAL-Orsay October 2017
BACK UP SLIDES
F. Richard LAL-Orsay October 2017

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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 hierarchy between 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
F. Richard LAL-Orsay October 2017

16. F. Richard LAL-Orsay October 2017
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
F. Richard LAL-Orsay October 2017

17. F. Richard LAL-Orsay October 2017
Radion at LHC and ILC
F. Richard LAL-Orsay October 2017