1 Introduction - Caltech High Energy Physics - California Institute of ...

408 New Physics
CP violation from µ and At phases
Let us first discuss minimal flavor violation models with effective SUSY spectra. In this model, flavor
violation comes through the CKM matrix, whereas CP violation originates from the µ and At phases, as
well as the CKM phase. The one loop electric dipole moment (EDM) constraint is evaded in the effective
SUSY model due to the decoupling of the first/second generation sfermions, but there are potentially large
two loop contribution to electron/neutron EDM’s through Barr-Zee type diagrams in the large tan β region
[208]. Imposing this two-loop EDM constraint and direct search limits on Higgs and SUSY particles, we find
that [209, 210]
• There are no new phase shifts in B 0 B 0 and B 0 sB 0
s mixing: Time-dependent CP asymmetries in Bd →
J/ψ K 0 S still measure the CKM angle β = φ1 [Fig. 5-36 (a)]
• ∆MBd can be enhanced up to ∼ 80% compared to the Standard Model prediction [Fig. 5-36 (b)]
• Direct CP asymmetry in B → Xsγ (A b→sγ
CP ) can be as large as ±15% [see Fig. 5-37]
• Rµµ can be as large as 1.8
• ɛK can differ from the Standard Model value by ∼ 40%
One can therefore anticipate substantial deviations in certain observables in the B system in SUSY models
with minimal flavor violation and complex µ and At parameters. This class of models include electroweak
baryogenesis (EWBGEN) within the MSSM and some of its extensions (such as NMSSM), where the chargino
and stop sectors are the same as in the MSSM. In the EWBGEN scenario within the MSSM, the current
lower limit on the Higgs mass requires a large radiative correction from the stop loop. Since ˜tR has to be
light to have a sufficiently strong 1st order electroweak phase transition, one has to have heavy ˜tL to induce
a large ∆m2 h . After considering B → Xsγ, one expects a very small deviations in A b→sγ
CP and ∆MBd [211].
However, in some extensions of the MSSM, the tension between mh and m˜tL becomes significantly diluted
in EWBGEN scenarios, because there could be tree level contributions to m2 h . Therefore, the predictions
made in Refs. [209, 210] will be still valid in EWBGEN scenarios beyond the MSSM.
Super B Factoriesshould be able to measure A b→sγ
CP to higher accuracy, and will impose a strong constraint
on a new CP -violating phase that could appear in B → Xsγ. Also the forward-backward asymmetries in
B → Xsℓ + ℓ− with ℓ = e or µ are equally important probes of new CP -violating phases, and important
observables to be measured at Super B Factories, for which LHCb or BTeV cannot compete.
CP violation from gluino-squark loops
In effective SUSY scenarios, it is possible that the gluino-mediated b → s transition is dominant over other
SUSY contributions. Cohen et al. have described qualitative features of such scenarios in B physics [212]; a
more quantitative analysis was presented by other groups. In Ref. [213], effects of possible new CP -violating
phases on B → Xsγ and B → Xsℓ + ℓ− were considered both in a model-independent manner, and in gluino
mediation dominance scenario. In effective SUSY models, A b→sγ
CP
can be as large as ±10%, if the third
generation squarks are light enough m˜ b � (100 − 200) GeV (see Fig. 5-38), whereas B → Xsℓ + ℓ − is almost
the same as the Standard Model prediction [213].
How to distinguish the µ or At phase from the δ d 23 phase
Should we find deviations in sin 2βφK0 or Ab→sγ
S CP , it will be very important to figure out the origin of new CP -
violating phases. In an effective SUSY context, one has complex At, µ or (δd AB )23 (with A, B = L, R). The
effects of these new complex parameters on some oservables in the B system are shown in Table 5-16. The
only process which is not directly affected by gluino-mediated FCNC is B → Xsνν. All the other observables
The Discovery Potential of a Super B Factory