Keith Jarrett, Jan Garbarek, Palle Danielsson, Jon Christensen, ‘Sleeper’

Terje Mosnes/ECM Records

Keith Jarrett’s European Quartet played only sporadically between 1974 and 1979 and produced just four albums. But the group achieved a singular unity of freedom, rhythmic groove, and open-hearted lyricism that made it deeply influential and left an impact that can still be heard across jazz today. That alone would make the release of “Sleeper’’ — a complete recording of an April 1979 Tokyo concert, discovered in the ECM archives by the label’s founder, Manfred Eicher — a significant event. But it’s much more, documenting this brilliant group in its final, exploratory phase. Jarrett (pictured), saxophonist Jan Garbarek, bassist Palle Danielsson, and drummer Jon Christensen don’t swing quite as fiercely as they would a month later on “Nude Ants,” still the best live document of this band. But the material sounds fresher, as if the players were just unearthing the possibilities in Jarrett’s compositions.

The angular “Personal Mountains” has a driving, corkscrew solo by Garbarek, and “Chant of the Soil” features Jarrett’s piano comping at its funky best. The 28-minute “Oasis” opens with a spontaneous flute-bass-percussion prologue and morphs into a tune of strange, wandering beauty. Perhaps the greatest moment on the entire album is the emergence of the quiet coda to “So Tender,” which arrives out of nowhere and leaves a listener spellbound. These are flashes of this band at its very best, raising hopes that more such gems lie waiting to be discovered. (Out Tuesday)