Flavour violating gluino three-body decays at the LHC

1. Flavour violating gluino three-body decays at the LHC Helmut Eberl In collaboration with A. Bartl, B. Herrmann, K. Hidaka, W. Majerotto and W. Porod Phys. Rev. D84 (2011) 115026 (arXiv:1107.2775 [hep-ph]) SUSY 2012,Peking University, Beijing, China, 17th August 2012

2. Content • Introduction • MSSM with Quark Flavour Violation (QFV) • Constraints on the MSSM • Squark generation mixing in gluino three-body decays • Influence of neutralino/chargino parameters • Measurability • Conclusions SUSY 2012, Beijing

3. Motivation • With the start of the LHC at CERN a new era of particle physics has begun. • Discovery of all SUSY partners and study of their properties are essential for testing the MSSM. • If weak scale SUSY is realized in nature, squarks and gluinos will have high production rates for masses up to O(1) TeV at LHC. • The decay modes of three-body gluino decays 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. Then quark-flavour violating (QFV) decays can occur with a significant rate. SUSY 2012, Beijing

4. Quark Flavour Violation in the MSSM In the Standard Model, all quark flavour-violating terms are prop. to CKM-matrix Beyond Standard Model, e.g. Minimal Supersymmetric Standard Model (MSSM) Non-minimal flavour-violation (NMFV) Minimal flavour-violation (MFV) • new sources of flavour violation can appear within SUSY-GUTs • e.g. gravity-mediation, messenger- matter mixing, flavour symmetry, ... • corresponding flavour-violating entries not related to CKM-matrix • considered as free parameters • no new sources of flavour violation • in super-CKM basis squarks undergo same rotations as quarks • all flavour-violating entries related to CKM-matrix • Example: interaction proportional to The flavour-violating terms are incorporated in the mass matrices at the electroweak scale, e.g. SUSY 2012, Beijing

5. Quark Flavour Violation in the MSSM The 3x3 soft-breaking matrices can include off-diagonal, i.e. flavour-violating, entries Introduce dimensionless parametrization for flavour-violating entries Diagonalization through 6x6 rotation matrix leads to mass eigenstates SUSY 2012, Beijing

6. Rather insensitive to QFV elements Highly sensitive to QFV elements Constraints on the MSSM parameter space • Mass limits from collider searches • only mixing between second and third generation squarks considered • Electroweak precision and low-energy measurements • Cosmological constraints due to cold dark matter [WMAP 2010] SUSY 2012, Beijing

7. QFV gluino three-body decays • The gluino is lighter than all squarks Only three-body decays to quark pairs + chargino/neutralino possible • If squark generation mixing occurs only between 2nd and 3rd gen, then one can have these QFV three-body decays of gluino into quarks and neutralinos: • We will mainly focus on decays to the lightest neutralino. SUSY 2012, Beijing

8. Numerical scenario • Input parameters: • QFV parameters: • Reference scenario (we used Spheno v3.0) up-squark sector down-squark sector For this point the “ino”-masses are Note, they are fairly insensitive to QFV parameters SUSY 2012, Beijing

9. Relevant QFV parameters • In our case QFV left-right mixing effects are not relevant: SUSY 2012, Beijing

10. Squark mass matrices up-squark sector down-squark sector SUSY 2012, Beijing

11. QFV gluino three-body decays • Effective mixing and consequences: Suppression of this cancellation requires large mass splitting and hence large values of the mixing term (other QFV parameters being zero) SUSY 2012, Beijing

12. QFV gluino three-body decays SUSY 2012, Beijing

13. QFV gluino three-body decays (other QFV parameters being zero) SUSY 2012, Beijing

14. Influence of neutralino/chargino parameters SUSY 2012, Beijing

15. Measurability of these QFV decays (other QFV parameters being zero) Unique QFV signature, e.g. two isolated same sign leptons SUSY 2012, Beijing

16. Mass distribution • A characteristic feature of a three-particle decay of the gluino is the invariant mass distribution of the two produced quarks. • In contrast to the case where the squarks are lighter than the gluino and the gluino decays via real squarks [Bartl et al. 2009], no edge structure appears. However, the thresholds and the shapes of the distributions are very different. SUSY 2012, Beijing

17. Lightest Higgs mass SUSY 2012, Beijing

18. Conclusions • We have studied the effect of squark generation mixing on gluino three-body decays together with gluino production at LHC in the MSSM with focus on mixing between 2nd and 3rd generation squarks. • Taking into account the constraints from B-physics experiments, we have shown that various regions in the parameter space exist where three-body decays of gluinos into flavour violating final states can have large branching ratios of up to ~ 40%. • Rates of corresponding signals, e.g. , can be significant at LHC (at 14 TeV) • We conclude that the inclusion of flavour mixing effects can be important for the search of squarks and gluinos and the determination of the MSSM parameters at LHC. SUSY 2012, Beijing

19. Thank you for your attention! SUSY 2012, Beijing