Compositeness at ILC250?

Transcription

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

2 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

3 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

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

5 What can be expect at ILC250 on ee->bb dg RZ /g RZ ~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 dg RZ /g RZ =25% or dg RZ /g RZ =-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

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

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. 1 st 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

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

9 Softwall RS Basic idea : keep the main feature of RS to generate the mass hierarchy M W =M Planck exp(-2kdy) k~1/m P 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

10 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

11 The radion Could be the lightest particle of the RS model Its couplings depends on three parameters m R, x and L Can be discovered at LHC if M R > 2M W ILC250 is unique to cover lighter masses using the recoil mass method with Z+R up to ~2M W (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

12 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

13 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

14 BACK UP SLIDES F. Richard LAL-Orsay October

15 RS for pedestrians Extra dimension with warped space between two branes in the extra dimension Solves hierarchy : M W =M P exp(-2kdy) where kdy~35 with k~1/m P, 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

16 Radion at LHC For m R <2M W can also discover the radion but leaves large regions uncovered The two photon decay only helps for x>0 M R >70 GeV Higgs BR measurements at ILC250 cover large parts of these regions F. Richard LAL-Orsay October

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