Tau (particle) Tau (particle) The tau (τ), also called the tau lepton, tau particle, or tauon, is an elementary particle similar to the electron, with negative electric charge and a spin of. Together with the electron, the muon, and the three neutrinos, it is a lepton. Like all elementary particles with half-integer spin, the tau has a corresponding antiparticle of opposite charge but equal mass and spin, which in the tau's case is the antitau (also called the "positive tau"). Tau particles are denoted by and the antitau by . Tau leptons have a lifetime of and a mass of (compared to
Cassidy (given name) Cassidy (given name) Cassidy is a given name derived from an Irish surname and ultimately from the Gaelic given name "Caiside", meaning "clever" or "curly-haired." The name "Caiside" comes from the Gaelic word element "cas", according to "Behindthename.com" Cassidy was the 244th most popular name for girls born in the United States in 2009. It was most popular in 1999, when it was the 99th most popular name for American girls. It first appeared among the 1,000 most popular names for American girls in 1981. Kassidy, an alternate spelling, was ranked as the 443rd most popular name for girls in