First observation of the $P$-wave spin-singlet bottomonium states $h_b(1P)$ and $h_b(2P)$.

Abstract

Wereportthefirstobservationsofthespin-singletbottomoniumstateshb ð1PÞandhb ð2PÞ.Thestates areproducedinthereactioneþe!hb ðnPÞþusinga121:4fb1datasamplecollectedatenergies neartheð5SÞresonancewiththeBelledetectorattheKEKBasymmetric-energyeþecollider.We determineM½hb ð1PÞ¼ð9898:2þ1:1þ1:0 1:01:1 ÞMeV=c2andM½hb ð2PÞ¼ð10259:80:6þ1:4 1:0 ÞMeV=c2, whichcorrespondtoP-wavehyperfinesplittingsMHF ¼ðþ1:71:5Þandðþ0:5þ1:6 1:2 ÞMeV=c2,respectively. Thesignificancesofthehb ð1PÞandhb ð2PÞare5:5and11:2,respectively.Wefindthatthe productionofthehb ð1PÞandhb ð2PÞisnotsuppressedrelativetotheproductionoftheð1SÞ,ð2SÞ,and ð3SÞ.