ar X iv : h ep - e x / 99 02 02 6 v 1 1 8 Fe b 19 99 UGVA - DPNC 1998 / 11 - 180 Nov . 1998 B and D Spectroscopy at LEP

Results from the four LEP experiments ALEPH, DELPHI, L3, and OPAL on the spectroscopy of B and charmed mesons are presented. The predictions of Heavy Quark Effective Theory (HQET) for the masses and the widths of excited L = 1 B mesons are supported by a new measurement from L3. A few Bc candidate events have masses consistent with the recent CDF observation and the predictions. New results on D production and B → Dlν are also presented. The evidence for a D ′ meson reported recently by DELPHI is not supported by OPAL and CLEO. INTRODUCTION Detailed understanding of the spectroscopy of orbitally excited heavy mesons containing a b or a c quark provides important information regarding the underlying theory. A flavor-spin symmetry arises from the fact that the mass of a heavy quark Q is large relative to ΛQCD. In this approximation, the spin ~sQ of the heavy quark Q is conserved in the interactions, independently of the total angular momentum ~jq = ~sq+~ L of the light quark q. Corrections to this symmetry are a series expansion in 1/mQ, 1/m 2 Q, calculable in Heavy Quark Effective Theory (HQET) [1]. TABLE 1. L = 1 B mesons containing a u or a d light quark with corresponding spin states, relative production rates, prediction for masses and widths, and two-body decay modes. Name jq J P Production Mass [MeV] Width [MeV] Decay Mode B∗0 1/2 0 + 1/12 B1 − 12 ∼ 150 Bπ S-wave B∗1 1/2 1 + 3/12 B2 ± 100 ∼ 150 Bπ S-wave B1 3/2 1 + 3/12 5759 21 Bπ D-wave B∗2 3/2 2 + 5/12 5771 25 Bπ,Bπ D-wave The L = 0 mesons, for which jq = 1/2, have two possible spin states: a pseudoscalar P (J = 0−) and a vector V (J = 1−). If the spin of the heavy quark is conserved independently, the relative production rate of these states is expected to be V/(V + P ) = 0.75. Corrections due to the decay of higher excited states are predicted to be small. Recent measurements of this rate for the B system [2,3] agree well with this ratio. In the case of L = 1 orbitally excited B mesons two sets of doublets are expected: the B∗0 and B ∗ 1 (jq = 1/2) and the B1 and B ∗ 2 (jq = 3/2) mesons (see Table 1). Their relative production rate follows from spin state counting (2J+1 states) [4]. For the dominant two-body decays, the jq = 1/2 states can decay via an S-wave transition and their decay widths are expected to be broad in comparison to those of the jq = 3/2 states which must decay via a D-wave transition. Many measurements exist for L = 1 orbitally excited charm mesons. All six narrow states, a doublet (D∗2 and D1) for each quark content (cū, cd̄ and cs̄) are well established [17]. The wide L = 1 states are hard to measure and have not been clearly identified. Several models based on HQET and on the charmed L = 1 meson data, have made predictions for the masses and widths of orbitally excited B∗∗ mesons [5–9] (see Table 1). Some of these models place the average mass of the jq = 3/2 states above that of the jq = 1/2 states, while others predict the opposite (“spin-orbit inversion”). The mass splitting within each doublet is predicted to be 12 MeV.