Experimental HEP Seminar

Bottomonium: recent results

Gérard Bonneaud

Paris VI-VII

The bottomonium mesons are bound quark-antiquark pairs of the bottom quark b. They all have masses near 10 GeV, roughly the mass of a boron atom. In the final run of its fruitful decade-long operation, the PEPII electron-positron collider at SLAC has revealed the lowest-energy state of bottomonium, the heaviest family of mesons.

Computational tricks based on QCD are presumed to do best with the heaviest quarks. Because top quarks are too short-lived to form mesons or any other particles, b-quark states afford the best opportunity for comparing theory with measurement.

Having discovered the spin-singlet ground state, labeled η_b, the BaBar detector collaboration at PEPII has measured its mass to lie just 71±4 MeV below that of Y(1S), the lowest-mass spin-triplet state, whose discovery in 1977 first revealed the existence of the b quark. BaBar's measurement of this hyperfine mass splitting provides an important validation of the lattice-QCD computational technique that predicted 61±14 MeV.

We will review properties of the bottomonium system as recently published by the BABAR, the Belle and the CLEO Collaborations.