HFAG Charm Mixing Averages

Almost since the discovery of charm mesons, mixing of D −D 0 mesons have been sought in analogy to the well-known K−K 0 mixing. Due to very effective GIM suppression, the expected mixing rate in the charm system is much smaller than for kaons. Only very recently, the BaBar [1] and Belle [2] collaborations have reported the first evidence of charm mixing. These results have renewed the interest from the theory community as the observed mixing rate could be caused by physics beyond the standard model or at least provide additional constraints on new physics. None of the mixing measurement have a significance above four standard deviations, but several have similar precision for the mixing parameters. By combining the measurements we therefore obtain more precise values for the mixing parameters and exclude the nomixing hypothesis with larger confidence. Combining the different mixing measurements is not completely straightforward, since not all measurements are sensitive to the same charm mixing parameters. The Heavy Flavor Averaging Group (HFAG) in 2006 created a subgroup with the responsibility of providing averages of charm physics measurements. One of the high priority tasks of this group is to combine the charm mixing measurements into world-average values for the fundamental mixing parameters. The first average assuming CP conservation was shown at FPCP [3]. Besides those results, we here report the first results of combining mixing measurements where we allow for CP violation.