DirectCPviolation in two-body hadronic charmed meson decays

Abstract

Motivated by the recent observation of CP violation in the charm sector by LHCb, we study direct CP asymmetries in the standard model (SM) for the singly Cabibbo-suppressed two-body hadronic decays of charmed mesons using the topological-diagram approach. In this approach, the magnitude and the phase of topological weak annihilation amplitudes, which arise mainly from final-state rescattering, can be extracted from the data. Consequently, direct CP asymmetry a ðtreeÞ dir at tree level can be reliably estimated. In general, it lies in the range 10 À4 < a ðtreeÞ dir < 10 À3 . Short-distance QCD penguins and penguin annihilation are calculated using QCD factorization. Their effects are generally small, especially for D ! VP modes. Since weak penguin annihilation receives long-distance contributions from the colorallowed tree amplitude followed by final-state rescattering, it is expected to give the dominant contribution to the direct CP violation in the decays D 0 ! K þ K À and D 0 ! þ À , in which a ðtreeÞ dir is absent. The maximal Áa dir CP , the direct CP asymmetry difference between the above-mentioned two modes, allowed in the SM is around À0:25%, more than 2 away from the current world average of Àð0:645 AE 0:180Þ%.

Charm Reflects Poorly on Anticharm

“…In summary, this Letter reports the first observation of a nonzero CP asymmetry in charm decays, using large samples of D 0 → K − K þ and D 0 → π − π þ decays collected with the LHCb detector. The result is consistent with, although in magnitude at the upper end of, SM expectations, which lie in the range 10 −4 − 10 −3 [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. In particular, the result challenges predictions based on firstprinciple QCD dynamics [19,33].…”

“…Charm hadrons provide a unique opportunity to measure CP violation with particles containing only up-type quarks. The size of CP violation in charm decays is expected to be tiny in the SM, with asymmetries typically of the order of 10 −4 − 10 −3 , but due to the presence of low-energy strong-interaction effects, theoretical predictions are difficult to compute reliably [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. Motivated by the fact that contributions of beyond-the-SM virtual particles may alter the size of CP violation with respect to the SM expectation, a number of theoretical analyses have been performed [19,27,32,35].…”

SupersymmetricΔACP

“…The standard model (SM) contribution to the individual asymmetries is suppressed by a Cabibbo-Kobayashi-Maskawa (CKM) factor of order 2Imð V ub V Ã cb V us V Ã cs Þ % 1:2 Â 10 À3 , and by a loop factor of order s ðm c Þ= $ 0:1. While one cannot exclude an enhancement factor of order 30 from hadronic physics [13][14][15][16][17][18][19][20][21], in which case (1) will be accounted for by SM physics, it is interesting to explore the possibility that new physics contributes a major part of ÁA CP .…”

Search for CP Violation in Ds+→KS0π+ , Aaij1, Beteta2, Adeva3 et al. 2019Phys. Rev. Lett.8050View full textAdd to dashboardCite

“…However, the expected SM contribution is difficult to compute due to the presence of low-energy strong-interaction effects, with current predictions spanning several orders of magnitude [9][10][11][12][13]. A promising handle to determine the origin of possible CP-violation signals are correlations between CP asymmetries in flavor-SUð3Þ related decays [14][15][16][17][18][19][20][21][22]. Particularly interesting in this respect are D þ s and D þ decays to two-body (or quasitwo-body) final states, such as…”