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

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

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

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

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

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

New Physics in D-mixing: Formalism

Use the OPE to define an

effective Hamiltonian

Complete set ofindependent operators:

Compute LO QCD corrections

Evolve matching conditions to the charm scale

Evaluate hadronic matrixelements

Heavy Q=-1/3 Quark

Present in, e.g.,

• E6 GUTS

• 4th generation

Removes strong GIM suppression Of SM

Constraints in mass-mixing plane

Unitarity of CKM matrix gives |Vub’Vcb’|< 0.02D-mixing improves this constraint by one order of magnitude!

3

5

8

11.7

15 x 10-3

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!

Little Higgs Models

These models contain heavy vector-like T-quark

Strongest bounds on this sector!

Will affect T-quark decays and collider signatures

Arkani-Hamed, Cohen, Katz, Nelson

Sample particle spectrum

Supersymmetry (MSSM)

Large contribution from squark-gluino exchange in box diagram

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 insertionsStrong constraints from K mixing has historically

lead to assumption of degenerate squarks in collider production

mass insertion

helicity index

Constraints on up/charm-squark mass difference

LL,RR LL=RR

LR,RL

LR=RL

Compare to constraints on down/strange-squark mass difference from Kaon mixing (green curve)

LL,RR LL=RR

LR,RL

LR=RL

Bagger, Matchev, Zhang

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

Supersymmetry with Alignment

• 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

Nir, Seiberg

Sets mq ≥ 2 TeV

Difficult @ LHC!

~

Extra Dimensions

• Generates tree-level FCNC for gauge boson Kaluza Klein states via overlap of wavefunctions

Split fermion scenario:

•Fermions localized at specific locations in extra flat dimension•Suppresses proton decay•Generates fermion hierarchy

Arkani-Hamed, Schmaltz

Constraints on Split Fermion Scenario

Distance between u- & c-quarks in 5th dimension

Compactification scale

u- & c-quarks are localized very close or extra dimensions unobservable @ VLHC

Warped Extra Dimensions

Based on Randall-Sundrum modelsBulk = 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

Summary of Model Constraints

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…