NEW PHASES IN CP-VIOLATING B-DECAY ASYMMETRIES FROM MIXING TO SINGLETDOWN QUARKS

Groups such as E6 with extra SU(2)L Singlet down quarks give rise to f lavor-changing neutral currents (FCNC's) through the mixing of four or more down quarks. These currents may substantially contribute to the processes of B(d)0-B(d)0BAR and B(s)0-(B)s0BAR mixing, within the allo wed range of nonzero values for the four quark mixing parameters. Thes e would then introduce new angles and phases into the CP-violating B d ecay asymmetries. Other, negative FCNC experiments put limits on these angles. Using a maximum likelihood analysis with contributions from b oth the standard model and the FCNC's, we find large regions for new p hysics phases contributing to CP-violating B decay asymmetries. From t he bound on the mixing elements, the new singlet down quark might have a mass above the 500 GeV range.