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…