ar X iv : h ep - l at / 0 40 80 38 v 1 2 5 A ug 2 00 4 Preliminary results of the heavy - light meson spectrum using chirally improved light quarks

Using a " wall " of quark point sources, we invert the chirally improved Dirac operator to create an " incoherent " collection of quark propagators which originate from all spatial points of the source time slice. The lowest-order NRQCD approximation is used to create heavy-quark propagators from the same wall source. However, since the numerical cost involved in computing such heavy-quark propagators is low, we are able to use a number of source gauge paths to establish coherence between the heavy and light quarks at several spatial separations. The resulting collection of heavy-light meson correlators is analyzed to extract the corresponding mass spectrum. 1. Light-quark source and propagators For the light quarks, we use the chirally improved Dirac operator, constructed via an expansion in gauge paths and the corresponding approximate solution of the Ginsparg-Wilson relation (for details see Ref. [1]). As sources for the light-quark propagators, we use 12 (3 colors × 4 spins) uniform walls, setting the color and spin of the quarks to be the same at all spatial positions and relying upon the random gauges of the ensemble of configurations to cancel any non-gauge-invariant (open) contributions to hadron correlators constructed from these quark propagators. This is similar to the volume source used by others [2] for disconnected correlators, except for the fact that our source sits on only a single time-slice. Connected meson correlators from two of these quarks should exhibit a signal arising from L 3 closed (or gauge-invariant) cor-relators, along with some additional noise from the L 3 (L 3 − 1) open correlators. These sources have been used before for heavy quarkonium cor-relators with some success [3] since the signal-to-noise ratio proved to be surprisingly good. Since we retain our light-quark propagators and the heavy-quark evolution is computationally cheap, we are free to use a number of different gauge paths to create " walls " of extended heavy-light * Presented by T. Burch. meson sources from the light-quark source before we compute the heavy-quark propagators. In this way we can construct a full matrix of correlators with various spatial extents and a collection of starting positions without additional light-quark inversions. 2. Heavy-quark evolution The heavy-quark propagators are created using lowest-order NRQCD, along with some improvements for the lattice version [4]. A single time-step of heavy-quark evolution is achieved via