Within the framework of three lepton families we have derived an exact and compact formula to describe the matter effect on neutrino mixing and CP violation. This model- and parametrization-independent result can be particularly useful for recasting the fu

andthusenhance(orsuppress)thegenuinesignalsofCPorTviolation.Asforthelong-baselineneutrinoexperimentunderconsideration,thematter-inducede ectintheT-violatingasymmetryATisnegligiblysmall.Themattere ectontheCP-violatingasymmetryinvacuumcannotbeneglected,buttheformerisunlikelytofakethelattercompletely.Wecon rmnumericallythattherelationshipAT=ACPinvacuumbecomesviolatedinmatter.

Iftheearth-inducedmattere ectscanwellbecontrolled,itispossibletorecastthefundamental avormixingmatrixVfromavarietyofmeasurementsofneutrinooscillations.Suchagoalisexpectedtobereachedintheneutrinofactories[5].

Insummary,wehavederivedanexactandcompactformulatoshowtheanalyticalrelationshipbetweenthefundamentalneutrinomixingmatrixandthematter-correctedonewithintheframeworkofthreeleptonfamilies.Thismodel-andparametrization-independentresultcanbeparticularlyusefulforthestudyof avormixingandCPviolationinthelong-baselineneutrinoexperiments.Anextensionofthepresentwork,inwhichthemixingofasterileneutrinowiththreeactiveneutrinoscanbeincorporated,isinprogress.

Acknowledgment:TheauthorwouldliketothankH.Fritzschforusefuldiscussions.