2014/04/15 by Andrzej J. Buras, Buras, Andrzej J., Fulvia De Fazio +3
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #High Energy Physics - Lattice (hep-lat) #High Energy Physics - Phenomenology (hep-ph) #High-Energy Particle Collisions Research #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #hep-ex #hep-lat #hep-ph
paper · pdf · doi:10.48550/arxiv.1404.3824
63 pages, 20 figures; clarifying comments added; version accepted for publication in EPJC
openalex publication_date 2014/04/15 · arxiv created 2014/07/09 · arxiv updated 2014/07/10 · openalex created_date 2022/10/03 · openalex updated_date 2026/07/28
The experimental value for the isospin amplitude Re(A2) in K->pi pi decays has been successfully explained within the Standard Model, both within large N approach to QCD and by QCD lattice calculations. On the other hand in both approaches the theoretical values of Re(A0) are by at least 30% below the data so that the Delta I=1/2 rule in K->pi pi decays is not fully explained. While this deficit could be the result of present theoretical uncertainties in both approaches, it cannot be excluded that the missing piece in Re(A0) comes from New Physics. We demonstrate that this deficit can be significantly softened by tree-level FCNC transitions mediated by a heavy colourless Z' gauge boson with particularly chosen flavour violating couplings assuring negligible NP contributions to Re(A2) and significantly enhancing the contribution of the leading QCD penguin operator Q6 to Re(A0). A large fraction of the missing piece in the Delta I=1/2 rule can be explained in this manner for MZ' in the reach of the LHC, while satisfying constraints from epsilonK, epsilon'/epsilon, Delta MK, LEP-II and the LHC. We identify quartic correlation between Z' contributions to Re(A0), epsilon'/epsilon, epsilonK and Delta MK. We present correlations between epsilon'/epsilon and rare decays K->pi nu barnu with and without the Delta I=1/2 rule constraint and generalize the whole analysis to Z' with colour (G') and Z with FCNC couplings. In the latter case no improvement on Re(A0) can be achieved without destroying the agreement of the SM with the data on Re(A2). Moreover, this scenario is very tightly constrained by epsilon'/epsilon. On the other hand in the context of the Delta I=1/2 rule G' is even more effective than Z': it provides the missing piece in Re(A0) for MG'=(3.5-4.0) TeV.