Distinguishing $B$ and $\overline B$ Hadrons

Abstract

Distinguishing the flavor of $B$ and $\overline B$ hadrons is critical in studies of CP-violation, $B^0 -\overline{B^0}$ mixing, and the underlying $b$-decay mechanisms. Methods of $b$ ``flavor tagging" are broadly divided into ``opposite $b$" tagging and self-tagging of the signal $b$ hadron. The former, while understood, has the perceived drawback of low efficiency. The latter, while having the potential for an order of magnitude higher efficiency, has yet to be demonstrated for neutral $B$ hadrons. In this article we review opposite $b$ tagging in light of methods whose efficacy has only recently been demonstrated or suggested. In addition, we recommend a number of tagging methods for the opposite $b$ including: $K^{*0}$ and $K^{*\pm}$ with large inclusive yields of 15\% and 18\%; $\overline Λ$ and $\overline Λp $; partially reconstructed charmed hadrons; sophisticated jet charge techniques, etc. We also recommend the use of self-tagging for the $opposite$ $b$ hadron. Such an inversion of self-tagging could conceivably increase the efficiency of opposite $b$ tagging and even mitigate the effects of neutral $B$ mixing. Self-tagging of the signal hadron, when possible, could be used either by itself or to confirm the result from the opposite $b$ tag. We suggest that all methods be weighted by their dilutions and combined to yield efficient tagging. For a given detector, this requires that the dilution of each tag be well measured. We therefore review the determination of the dilution $D_T$ for a general tag $T$ in some detail. Finally, we briefly consider $B$ sector and suggest a number of exclusive modes which can be combined for higher statistics probes of the unitarity angles. While ambitious from an experimental perspective, the program of flavor identification outlined here has the potential to yield important fundamental results in the near future.