Implications of D-Mixing for New Physics

1. Implications of D-Mixing for New Physics Meson mixing has historical significance • Charm quark (and mass) inferred from Kaon mixing • Top mass predicted from Bd mixing • Strong constraints on New Physics (SUSY, LRM, …) that has affected collider searches Each meson is different (x = m/): And thus each measurement is important J. Hewett SLAC DOE 07

2. The observation of D-mixing is exciting! • 1st Observation of Flavor Changing Neutral Currents in the up-quark sector! • 1st Glimpse of flavor physics in the up-quark sector • 1st Constraints on flavor violation in up-quark sector • Sparked much interest in the community • Catalogue of New Physics Contributions • Golowich, JLH, Pakvasa, Petrov arXiv:0705.3650

3. Compilation of Predictions for D-Mixing • D-Mixing provides important constraints for model building • Flavor physics provides strong constraints on models • Many models poorly tested in +2/3 quark sector • Many models shove flavor violation into up-quark sector in order to satisfy K mixing  large effects in D mixing H. Nelson, Lepton-Photon 1999

4. D-Mixing in the Standard Model: Short Distance • Box diagram is tiny • GIM is efficient! • b-quark contribution is CKM suppressed • s-quark contribution is suppressed by SU(3) breaking • xbox ~ 10-5 , ybox ~ 10-7 • Higher orders in the OPE may give larger results Georgi; Bigi

5. D Mixing in the Standard Model: Long Distance • Charm is neither light or heavy, so well-developed theoretical techniques don’t apply. • Sum over all possible, multi-particle, intermediate hadronic states • yD is less model-dependent; calculate yD and use dispersion relations to obtain xD • Results in: yD ~ xD ~ 1% Possible that experimental result is explained by SM effects

6. Constraining New Physics • Assume no interference between SM & NP • NP alone does not exceed measured value of xD Use 1 value: xD < 11.7 x 10-3 Allow for 2 and for future exp’t improvements: xD < 3, 5, 8, 15 x 10-3

7. New Physics in D-mixing: Formalism Compute LO QCD corrections Use the OPE to define an effective Hamiltonian Complete set of independent operators: Evolve matching conditions to the charm scale Evaluate hadronic matrix elements

8. Heavy Q=-1/3 Quark Present in, e.g., • E6 GUTS • 4th generation Constraints in mass-mixing plane Removes strong GIM suppression Of SM 3 Unitarity of CKM matrix gives |Vub’Vcb’|< 0.02 5 8 D-mixing improves this constraint by one order of magnitude! 11.7 15 x 10-3

9. Heavy Q=2/3 Singlet Quarks • Induces FCNC couplings of the Z • Violation of Glashow-Weinberg-Paschos conditions • Tree-level contribution to D mixing Constraints on mixing improved over CKM unitarity bounds by TWO orders of magnitude!

10. Little Higgs Models Arkani-Hamed, Cohen, Katz, Nelson Sample particle spectrum These models contain heavy vector-like T-quark Strongest bounds on this sector! Will affect T-quark decays and collider signatures

11. Supersymmetry (MSSM) Large contribution from squark-gluino exchange in box diagram helicity index • Super-CKM basis: • squark and quark fields rotated by • same matrices to get mass eigenstates • Squark mass matrices non-diagonal • Squark propagators expanded to • include non-diagonal mass insertions mass insertion Strong constraints from K mixing has historically lead to assumption of degenerate squarks in collider production

12. Constraints on up/charm-squark mass difference LL,RR LL=RR LR,RL LR=RL

13. Compare to constraints on down/strange-squark mass difference from Kaon mixing (green curve) Bagger, Matchev, Zhang   LL,RR LL=RR   LR,RL LR=RL

14. Supersymmetry (MSSM) • 1st two generations of squark masses now constrained to be degenerate to same level of precision in both Q=+2/3 and -1/3 sectors! • Historically used as a theoretical assumption, now determined experimentally • Degenerate squarks lead to large squark production cross section @ Tevatron/LHC

15. Supersymmetry with Alignment Nir, Seiberg • Quark & squark mass matrices are approximately aligned and diagonalized such that gluino interactions are flavor diagonal • Squark mass differences are not constrained • Bounds from Kaon mixing prevent generation of Cabibbo angle in the down-sector ~ Sets mq≥ 2 TeV Difficult @ LHC!

16. Extra Dimensions • Split fermion scenario: • Fermions localized at • specific locations in • extra flat dimension • Suppresses proton • decay • Generates fermion • hierarchy • Generates tree-level FCNC for gauge boson Kaluza Klein states via overlap of wavefunctions Arkani-Hamed, Schmaltz

17. Constraints on Split Fermion Scenario Compactification scale Distance between u- & c-quarks in 5th dimension u- & c-quarks are localized very close or extra dimensions unobservable @ VLHC

18. Warped Extra Dimensions Based on Randall-Sundrum models Bulk = Slice of AdS5 • SM in the bulk • Induces tree-level FCNC • Result dependent on • fermion localization • 1st gauge KK state • M > 2-3 TeV • Restricts LHC search range

19. Summary of Model Constraints

20. Conclusions • Observation of D-mixing yields stringent bounds on New Physics • These bounds surpass or compete with other constraints • These bounds affect collider(LHC) physics • Look forward to future experimental refinements! • Observation of CP Violation would be clear signal of New Physics…