Flavour violating gluino three-body decays at LHC

1. Flavour violating gluino three-body decays at LHC K. Hidaka Tokyo Gakugei University In collaboration with A. Bartl, H. Eberl, E. Ginina, B. Herrmann, W. Majerotto and W. Porod (arXiv:1107.2775 [hep-ph]) SUSY2011, 1 Sep 2011, Fermilab

2. Contents 1. Introduction 2. MSSM with Quark Flavour Violation (QFV) 3. Constraints on the MSSM 4. QFV Benchmark Scenario 5. Impact of squark generation mixing on gluino 3-body decays 6. Impact on gluino Signatures at LHC 7. Conclusion

3. 1. Introduction (1) Motivation; • Discovery of all SUSY partners and study of their properties are essential for testing the MSSM. • Here we focus on SUSY partners of gluons and quraks (i.e gluinos and squarks). • With the start of the Large Hadron Collider (LHC) at CERN a new era of particle physics has begun. • If weak scale SUSY is realized in nature, gluinos and squarks will have high production rates for masses up to O(1) TeV at LHC. • The main decay modes of gluinos and squarks are usually assumed to be quark-flavour conserving (QFC). • However, the squarks are not necessarily quark-flavour eigenstates. The flavour mixing in the squark sector may be stronger than that in the quark sector. In this case quark-flavour violating (QFV) decays of gluinos and squarks could occur. • Here we study the effect of the mixing of charm-squark and top-squark on the gluino 3-body decays at LHC.

4. In this work we study the effect of scharm-stop mixing on • the gluino 3-body decays at LHC in the general MSSM. • We show that branching ratio of QFVgluino 3-body decays • due to the squark generation mixing can be very large in a • significant part of the MSSM parameter space despite the • very strong experimental constraints from QFV processes. • This could have an important impact on the search for • gluinos and the MSSM parameter determination at LHC. (2)Purpose of this work;

5. 2. MSSM with QFV • The basic parameters of the MSSM with QFV: {tanb, mA ,M1 , M2 , M3,m ,M2Q,ab , M2U,ab , M2D,ab , TUab , TDab } (at Q = 1TeV scale (SPA convention)) (a,b = 1,2,3 = u, c, t or d, s, b) tanb : ratio of VEV of the two Higgs doublets <H02>/<H01> mA : CP odd Higgs boson mass (pole mass) M1, M2 ,M3 : U(1), SU(2),SU(3) gaugino masses m : higgsino mass parameter M2Q,ab: left squarksoft mass matrix M2Uab : right up-type squarksoft mass matrix M2Dab : right down-type squarksoft mass matrix TUab : trilinear coupling matrix of up-type squark and Higgs boson TDab: trilinear coupling matrix of down-type squark and Higgs boson

6. Here we study mixing effect. • QFV parameters in our study are: • M2Q,23:mixing term（mixing term) • M2U23:mixing term • TU23 :mixing term • TU32 :mixing term • (Note) We work in the super-CKM basis of squarks: • . • In this basis we have due to the SU(2) symmetry, • where is the soft mass matrix of left up-type squarks • is the soft mass matrix of left down-type squarks and • K is the CKM matrix. • (Note) We have as . • Here we study mixing case. LFV parameters in our study are: :mixing term（mixing term) :mixing term :mixing term :mixing term • (note) We assume that all the basic parameters are real. • (note) The basic parameters determine all of the physics here.

7. 3. Constraints on the MSSM Recent ATLAS and CMS SUSY searches at 7TeV with ~1 fb-1 In a simplified model; gluino masse > 800 GeV squark mass > 850 GeV (for 1st & 2nd generation squarks) In the context of the constrained MSSM (mSUGRA); gluino masse > 700 GeV squark mass > 1050 GeV We assume a gluino mass of about 1 TeV and squark masses significantly larger than 1 TeV in our analysis (Note) We also respect the constraint on (mA , tanb) from the recent MSSM Higgs boson search at LHC.

8. 3. Constraints on the MSSM (continued) The following constraints are imposed in our analysis in order to respect experimental and theoretical constraints: (a)Constraints from the B-physics experiments : (b)LEP limits on sparticle masses (ex) etc. (c)The experimental limit on SUSY contributions to the electroweak r parameter: (d)Vacuum stability conditions on trilinear couplings (see J.A. Casas and S. Dimopoulos, Phys. Lett. B 387 (1996) 107 [hep-ph/9606237].) (ex) etc. etc. with

9. (Note) We find that these constraints are very important: and data => strongly constrain the QFV squark parameters data => strongly constrain Vacuum stability conditions => strongly constrain QFV trilinear couplings TUab,TDab (Note) We use the public code SPheno v3.0 in the calculation of the B-physics observables.

10. 4. QFV Benchmark Scenario We take the following scenario as our prototype QFV scenario: We add QFV parameters (i.e. squark-generation mixing parameters) to this scenario: M2Q,ab , M2U,ab , M2D,ab , TUab , TDab (ab)

11. Physical masses in the prototype QFV scenario These masses are fairly insensitive to the QFV parameters.

12. Prototype QFV scenario < up-squark sector > < down-squark sector > We add mixing to this scenario

13. “Prototype QFV scenario” + “large mixing” < up-squark sector > < down-squark sector > mass-splitting due to large mixing In this large mixing scenario all squarks other than are very heavy. So, gluino decay is dominated by virtual exchange.

14. “Prototype QFV scenario” + “large mixing” (continued) In this large mixing scenario; • Gluino decay is dominated by virtual exchange contribution. • is a strong mixture of and . • QFV branching ratiocould be very large!

15. 5. Impact of squark generation mixing on gluino 3-body decays We study the effect of squark generation mixing on gluino production and decays at LHC for the case that the gluino is lighter than all squarks and dominantly decays into three particles: In case of mixing, gluino could decay as follows:

16. Gluino decay branching ratios in our scenario: QFV decay BR BR(gluino → 3-body) mixing parameter QFV gluino decay branching ratio can be very large (up to ~40%) for large mixing parameter !

17. Contour plots of QFV BR in our scenario contours mixing parameter The QFV decay branching ratio can be very large in a significant part of the plane allowed by all of the constraints. mixing parameter This can lead to large QFV effects at LHC!

18. Contour plots of QFV BR in our scenario contours excluded by data excluded by data mixing parameter The QFV decay branching ratio can be very large in a significant part of the plane allowed by all of the constraints. mixing parameter This can lead to large QFV effects at LHC!

19. We have obtained a similar result for the QFV 3-body decay branching ratio : It can be as large as ~35%!

20. Neutralino/chargino parameter dependence of QFV BR contours in m – M2 plane The branching ratios of the QFV 3-particle gluino decays depend quite strongly on the parameters of the neutralino/chargino sector!

21. Large mixing Large QFV BR 6. Impact on gluino signatures at LHC The signature of the QFV gluino decay at LHC: ' top-quark + jet + missing-energy'

22. Gluino pair production and the QFV gluino 3-body decay lead to QFV gluino signature at LHC : 6. Impact on gluino signatures at LHC (continued) ‘top-quark + top-quark + 2 jets + missing-ET + beam-jets‘ ‘isolated same sign dilepton + 4 jets + missing-ET + beam-jets‘

23. Example of QFV gluino signature at LHC isolated same sign dilepton QFV gluino decay ‘isolated same sign dilepton + 4 jets + missing-ET + beam-jets‘

24. Example of QFV gluino signature at LHC isolated same sign dilepton ‘isolated same sign dilepton + 4 jets + missing-ET + beam-jets‘

25. QFV Signal rates at LHC QFV signal rates such as can be significant for large mixing parameter at LHC! mixing parameter

26. Impact on gluino search at LHC • Our analyses suggest the following: • One should take into account the possibility of significant contributions from QFV gluino 3-body decays in the gluino • search at LHC. • Moreover, one should also include QFV squark parameters • (i.e. squark–generation mixing parameters) in the determination • of the basic SUSY parameters at LHC.

27. 7. Conclusion • We have studied production and decays of gluinos in the MSSM with squark generation mixing, especially mixing. • We have shown that QFV gluino 3-body decay branching ratio can be very large (up to ~40%) due to the mixing despite the very strong constraints on QFV from experimental data on B mesons . • This can result in remarkable QFV gluino signal events such as ‘ + beam-jets' with a significant rate at LHC. • We have obatined a similar result for QFV gluino 3-body decay branching ratio : It can be as large as ~35%.

28. These could have an important impact on the search for gluinos and the MSSM parameter determination at LHC.

29. Backup Slides