Properties of the X(3872)Guillelmo
IntroductionThe mesons containing one heavy quark are a useful laboratory to test QCD models. In the limit of heavy quark mass m Q → ∞, heavy mesons' properties are governed by the dynamics of the light quark. As such, these states become "hydrogen atoms" of hadron physics. In this Heavy Quark Symmetry approach (see References [1,2,3,4,5]) the quantum numbers of the heavy and light quarks are separately conserved by the strong interaction. For the charmed D-mesons the heavy charmed quark spin, s Q , couples with the light quark momentum j q = s q + L, where s q is the spin of the light quark and L is its angular momentum. Hence for P -wave (L = 1) mesons we obtain two j q = 3/2 + states, the J P = 2 + , 1 + states, and two j q = 1/2 + states, the J P = 0 + , 1 + states. In the Heavy Quark Symmetry limit, conservation of parity and j q requires that the strong decaysand again via D-wave. D 1 (J P = 1 + , j q = 1/2 + ) converts only into D * (J P = 1 − ) emitting a pseudoscalar π in S-wave, while D * 0 (J P = 0 + , j q = 1/2 + ) decays only to D(J P = 0 − )π(J P = 0 − ) and only in S-wave. States decaying via S-wave are expected to be broad while those decaying via D-wave are expected to be narrow.The first observation of excited charmed mesons was made by the ARGUS Collaboration (see References [6,7,8,9,10]) and immediately confirmed by CLEO [11] and the Tagged Photon Spectrometer (FNAL) [12] Collaborations. The states have also been studied at LEP [13,14,15]. A high statistics analysis has been done with the CLEO-II detector [16,17]. The most recent measurements by the CLEO-II [18], BELLE [19], and FOCUS [20,21] experiments have improved the previous ones and extracted the contributions of broad D 1 and D * 0 states.