Direct CP, Lepton Flavor and Isospin Asymmetries in the Decays B->K(*)l+l-

TL;DR

This study measures asymmetries in rare B meson decays to test the Standard Model, finding no CP or lepton-flavor asymmetries but observing unexpectedly large isospin asymmetries below the J/psi resonance.

Contribution

First measurement of rate asymmetries in B->K(*)l+l- decays with a large dataset, revealing significant isospin asymmetries inconsistent with Standard Model predictions.

Findings

No evidence for direct CP or lepton-flavor asymmetries.

Large isospin asymmetries observed below J/psi resonance.

Results suggest potential new physics or need for refined theoretical models.

Abstract

We measure rate asymmetries for the rare decays B->K(*)l+l-, where l+l- is either e+e- or mu+mu-, using a sample of 384 million BBbar events collected with the Babar detector at the PEP-II e+e- collider. We find no evidence for direct CP or lepton-flavor asymmetries. For dilepton masses below the J/psi resonance, we find evidence for unexpectedly large isospin asymmetries in both B->Kl+l- and B->K*l+l-, which differ respectively by 3.2 sigma and 2.7 sigma, including systematic uncertainties, from the Standard Model expectations.