Kaon CP Violation Research Articles

Charged Kaons semi-leptonic form factors from NA48/2

The NA48/2 experiment collected unprecedent statistics of charged kaon decays in 2003 and 2004. The main purpose of the experiment was to measure direct CP violation in kaon decays to three pions while an extensive physics program was carried out together with the main goal. The huge statistics collected allowed to test with a high accuracy the predictions of low energy QCD theories in several charged kaon decay processes. The precise measurement of the charged kaon semileptonic form factors are reported here, based on data collected in 2004 with a dedicated minimum bias trigger.

CP violation and material interaction of neutral kaons in measurements of the CKM angle \u03b3 using B\xb1 \u2192 DK\xb1 decays where D \u2192 Ks0\u03c0+\u03c0\u2212

As measurements of the CKM angle γ in decays of b-hadrons become increasingly precise, it is important to consider the impact of processes that affect secondary and tertiary decay products and can contribute to the observed CP violation. The golden decay mode used to measure γ is B → DK, where D → Ks0π+π−. Due to the presence of a Ks0 meson in the final state, γ measurements based on this mode are affected by neutral kaon CP violation and matter regeneration, and this study examines the potential size of the impact. Previous studies determine the impact of kaon CP violation to be a few degrees in size, but make simplifying assumptions about how experimental measurements are implemented. These assumptions are lifted in the present study, and the matter regeneration effect is included for the first time. The results are presented within the context of γ measurements to be made using the LHCb and Belle II detectors. It is found that the expected biases due to ignoring the effects of CP violation and matter regeneration in neutral kaons is small and less than 0.5° degrees in all experimental scenarios considered.

Present and futureKandBmeson mixing constraints on TeV scale left-right symmetry

We revisit the $\Delta F=2$ transitions in the $K$ and $B_{d,s}$ neutral meson systems in the context of the minimal Left-Right symmetric model. We take into account, in addition to up-to-date phenomenological data, the contributions related to the renormalization of the flavor-changing neutral Higgs tree-level amplitude. These contributions were neglected in recent discussions, albeit formally needed in order to obtain a gauge independent result. Their impact on the minimal LR model is crucial and twofold. First, the effects are relevant in $B$ meson oscillations, for both CP conserving and CP violating observables, so that for the first time these imply constraints on the LR scenario which compete with those of the $K$ sector (plagued by long-distance uncertainties). Second, they sizably contribute to the indirect kaon CP violation parameter $\varepsilon$. We discuss the bounds from $B$ and $K$ mesons in both cases of LR symmetry: generalized parity ($\mathcal P$) and charge conjugation ($\mathcal C$). In the case of $\mathcal P$, the interplay between the CP-violation parameters $\varepsilon$ and $\varepsilon'$ leads us to rule out the regime of very hierarchical bidoublet vacuum expectation values $v_2/v_1<m_b/m_t\simeq 0.02$. In general, by minimizing the scalar field contribution up to the limit of the perturbative regime and by definite values of the relevant CP phases in the charged right-handed currents, we find that a right-handed gauge boson $W_R$ as light as 3 TeV is allowed at the 95% CL. This is well within the reach of direct detection at the next LHC run. If not discovered, within a decade the upgraded LHCb and Super B factories may reach an indirect sensitivity to a Left-Right scale of 8 TeV.

Combining direct & indirect kaon CP violation to constrain the warped KK scale

The Randall–Sundrum (RS) framework has a built in protection against flavour violation, but still generically suffers from little CP problems. The most stringent bound on flavour violation is due to ϵK, which is inversely proportional to the fundamental Yukawa scale. Hence the RS ϵK problem can be ameliorated by effectively increasing the Yukawa scale with a bulk Higgs, as was recently observed in arXiv:0810.1016. We point out that incorporating the constraint from ϵ′/ϵK, which is proportional to the Yukawa scale, raises the lower bound on the KK scale compared to previous analyses. The bound is conservatively estimated to be 5.5 TeV, choosing the most favorable Higgs profile, and 7.5 TeV for the profile which roughly reproduces the two site case. Relaxing this bound might require some form of RS flavour alignment. As a by-product of our analysis, we also provide the leading order flavour structure of the theory with a bulk Higgs.

The beam and detector for the NA48 neutral kaon CP violation experiment at CERN

The beam and detector, used for the NA48 experiment, devoted to the measurement of Re ( ε ′ / ε ) , and for the NA48/1 experiment on rare K S and neutral hyperon decays, are described.

Kaon physics and CP violation calculations on QCDOC

The violation of charge conjugation (C) and parity (P) in kaon decays, first observed in Nobel-prize winning experiments at Brookhaven National Lab in 1964, is allowed by the Standard Model of particle physics. Predicting indirect CP violation in kaon decays requires the values for standard model parameters and the evaluation of a four-quark matrix element inside a kaon. Using lattice QCD with domain wall fermions and the current QCDOC computers, calculations are underway that will yield, among other results, the value for this matrix element, allowing more precise comparisons between theory and experiment for CP violation in kaon decays.

CP VIOLATION AND ΔI=1/2 ENHANCEMENT FOR K→ππ, K→ππγ WEAK DECAYS

Data indicate that ΔI=3/2 transitions account for 4.5–4.7% of both CP conserving and CP violating K→2π decays, as well as CP conserving radiative K→ππγ processes. Observed K→ππγ/ππ branching ratios are shown to scale near α/π or α/2π. The KL–KS mixing angle ϕ and the semileptonic weak-rate asymmetry δ are reviewed, and theory is shown to be consistent with data. Also, K→2π ΔI=1/2 dominance is studied in the context of the chiral constituent quark model, displaying again excellent agreement with data. Finally, indirect and direct kaon CP violation (CPV) are successfully described in the framework of photon-mediated quark-loop graphs. This suggests that kaon CPV can be understood via second-order weak transitions, radiatively corrected.

Alternative solution of strong CP

In this talk I begin with some general discussion of the history of CP violation, then move on to aspects of a spontaneous CP violation model including the production of new particles at LHC, implications for B decay, generalized Cabibbo mixing and a reevaluation of kaon CP violation. Finally there is a summary.

Cosmological baryon number and kaon CP violation from a common source.

We extend an earlier model for radiatively generated fermion masses based on the Pati-Salam group to include CP violation. Spontaneous CP violation in the early universe gives rise to a complex mass matrix for heavy sterile neutrinos. The out-of-equilibrium decay of these neutrinos generates a B-L asymmetry. The sterile neutrinos also act as a mass seed in generating one-loop (complex) mass matrices for the quarks. Thus, the two low energy manifestations of CP violation, the CKM phase and the baryon number asymmetry, can both be traced in a calculable way to a common source. \textcopyright{} 1996 The American Physical Society.

Pattern of quark mass matrices and the mixing-angle hierarchy.

By expressing the quark masses, as well as the quark-mixing angles, in powers of the Cabibbo angle (\ensuremath{\lambda}) we show that the up- and down-quark mass matrices are proportional to each other up to terms of order ${\ensuremath{\lambda}}^{2}$. This implies that the mass ratio of these two types of quarks should be roughly the same in each generation except for the lightest quarks. We then demonstrate that this is the key ingredient that enables the Fritzsch ansatz for quark mass matrices to reproduce the observed pattern of Kobayashi-Maskawa (KM) mixings and predict that the KM angle ${\mathrm{theta}}_{3}$=O(${\ensuremath{\lambda}}^{3}$). Some of the phenomelogical implications, including that for the kaon CP-violation parameter \ensuremath{\epsilon}, are worked out.