Charm Results on CP Violation and Mixing.pdf

a r X i v : h e p - e x / 0 0 0 2 0 2 2 v 1 7 F e b 2 0 0 0 Frascati Physics Series Vol. XVI (2000), pp. 000-000 PHYSICS AND DETECTORS FOR DAΦNE – Frascati, Nov. 16-19, 1999 CHARM RESULTS ON CP VIOLATION AND MIXING Jeffrey A. Appel Fermilab, Batavia, IL, 60510, USA ABSTRACT The most recent results on CP violation and mixing in the charm system are reviewed as a guide to the future. While no surprising results are reported so far, charm provides a unique window to physics beyond the Standard Model. The results reported here come from four sources: ALEPH at LEP, E791 and FOCUS/E831 at Fermilab, and CLEO II.V at CESR. Results beyond these sources may be expected as a byproduct of B-motivated experiments. 1 Introduction So far, there is no evidence for either CP violation or particle-antiparticle mixing in the charm-quark sector. This is as expected in the context of the Standard Model of particle physics. Predictions for CP violation and particle- antiparticle mixing are orders of magnitude below the sensitivities of current experiments. This remains true even though today’s experiments are part of the march toward Standard-Model sensitivities, a march which has seen a couple of orders of magnitude increase in sensitivity in each of the last two decades. 1.1 The Present as a Guide to the Future What would be really exciting is the observation of CP violation or particle- antiparticle mixing in current charm experiments. The Standard-Model pre- dictions which explain these effects for strange and bottom quarks typically predict (so far) unmeasurable effects for charm. In that case, experimental charm signatures have no Standard-Model background, no relevant hadronic uncertainty in background estimates. Any sighting of CP violation or mixing in the charm sector would be evidence of new physics. Since no such sighting has been made, we must settle, for now, simply to use the current experimental efforts as guides to future possibilities. How can we best pursue the se