Rare Charm Processes and Supersymmetry Kwong Lau University of Houston PRC-US Workshop Beijing, June 11-18, 2006

Outline of talk Why are rare charm processes important in searching for new physics outside the Standard Model? Why rare charm processes are sensitive to supersymmetry? Two benchmark charm rare processes: FCNC decay D 0 ->  +  - and D 0 mixing Prospects at BES III Summary

Brief summary of rare charm searches ProcessPresent limit BR < 1.3x10 -6 MM  M <4.6x MeV  =0.016+/ x=  M/  < 0.03

General Comments Rare charm processes proceed in the Standard Model via box diagrams in the short distance limit The GIM mechanism suppresses FCNC in the Standard model The GIM mechanism is broken by non-degenerate quark masses The FCNC box amplitude in the charm sector is undetectably small because of the smallness and/or degeneracy of the quark masses in the down-type quarks (d, s, and b) Supersymmetric quarks (squarks) and wino can contribute to the box amplitude, and dominate if the squarks masses are not degenerate Squark masses are a priori not degenerate unless there is additional symmetry Fractional squark mass differences at O( ) will enhance the box amplitudes to a detectable level. –For example, the CCNC decay D   branching ratio can be enhanced to level The purpose of this talk is to explore the relationship between the two main CCNC processes (rare decay and mixing) in the context of a generic supersymmetric model

The effective CCNC amplitude c   Reference: Inami and Lim, NPB 207, 533 (1982).

The effective CCNC amplitude (cont.)

The f and g functions

CCNC predictions The two rare processes share common parameters through the C and E functions. One can do a parametric study by evaluating both process numerically as a function of model parameters (assumed free).

D ->  decay rate in supersymmetric models Supersymmetric particles with natural mass differences (O(10 -3 )) can boost the rare D ->  decay rate by 6-7 orders of magnitude

D0 mixing rate in supersymmetric models Supersymmetric particles with natural mass differences (O(10 -3 )) can boost the D mixing rate by 6-7 orders of magnitude

FCNC decay searches in E771 High rate hadroproduction of D0’s at hadron colliders and precision vertex measurement of D0 decays are both necessary, a challenging task.

Prospects at BESIII BESIII expects to produce a few x 10 7 D0’s per year It is unlikely that BESIII can improve the D0->  limit BESIII can reconstruct a large sample of low-multiplicity D0 decays, e.g., D0 -> K  decays to search for mixing The fact that D0’s are produced at threshold at BESIII is a challenge

Mixing vs FCNC decay rate

D0 mixing vs D ->  decay rate in supersymmetric models The next generation charm experiment at BES III can search D0 CCNC decay rates of order , probing squark mass up to TeV scale

Mixing vs FCNC decay rate in supersymmetric models

D0 mixing vs D to mumu decay rate in supersymmetric models

Mixing vs FCNC decay rate in supersymmetric models