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Register a new userThe Final Measurement of Epsilon/Epsilon from KTeV
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E.T. Worcester
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We present precise measurements of CP and CPT symmetry based on the full dataset of K to 2pi decays collected by the KTeV experiment at FNAL. We measure the direct CP violation parameter Re(epsilon/epsilon) = (19.2 pm 2.1)x10-4. We also report the KL-KS mass difference, the KS lifetime, the phase of epsilon, and the phase difference (phi00)-(phi+-). These results are consistent with other experimental results and with CPT symmetry.
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The ratio $epsilon/epsilon$ measures the size of the direct CP violation in $K_Ltopipi$ decays $(epsilon^prime)$ relative to the indirect one described by $epsilon$ and is very sensitive to new sources of CP violation. As such it played a prominent role in particle physics already for 45 years. Due to the smallness of $epsilon/epsilon$ its measurement required heroic efforts in the 1980s and the 1990s on both sides of the Atlantic with final results presented by NA48 and KTeV collaborations 20 years ago. Unfortunately, even 45 years after the first calculation of $epsilon/epsilon$ we do not know to which degree the Standard Model agrees with this data and how large is the room left for new physics contributions to this ratio. This is due to significant non-perturbative (hadronic) uncertainties accompanied by partial cancellation between the QCD penguin contributions and electroweak penguin contributions. While the significant control over the short distance perturbative effects has been achieved already in the early 1990s, with several improvements since then, different views on the non-perturbative contributions to $epsilon/epsilon$ have been expressed by different authors over last thirty years. In fact even today the uncertainty in the room left for NP contributions to $epsilon/epsilon$ is very significant. My own work on $epsilon/epsilon$ started in 1983 and involved both perturbative and non-perturbative calculations. This writing is a non-technical recollection of the steps which led to the present status of $epsilon/epsilon$ including several historical remarks not known to everybody. The present status of the $Delta I=1/2$ rule is also summarized. This story is dedicated to Jean-Marc Gerard on the occasion of the 35th anniversary of our collaboration and his 64th birthday.
We review the current status of calculations of the two pion decays of the kaon using the first-principles methods of lattice gauge theory and the significant challenges that these calculations pose. While a calculation with controlled errors at even the 10-20% level has not yet been performed, present results suggest that such a calculation of the real and imaginary parts of the Delta I = 3/2 amplitude should be accomplished within the next two years. The more difficult Delta I = 1/2 amplitude may also be now within reach.
Three years after the completion of the next-to-leading order calculation, the status of the theoretical estimates of $epsilon/epsilon$ is reviewed. In spite of the theoretical progress, the prediction of $epsilon/epsilon$ is still affected by a 100% theoretical error. In this paper the different sources of uncertainty are critically analysed and an updated estimate of $epsilon/epsilon$ is presented. Some theoretical implications of a value of $epsilon/epsilon$ definitely larger than $10^{-3}$ are also discussed.
We report on progress and future plans for calculating kaon weak matrix elements for epsilon/epsilon using staggered fermions.
Recently, the standard model prediction of $epsilon/epsilon$ was improved, and a discrepancy from the experimental results was reported at the $2.9sigma$ level. We study the chargino contributions to $Z$ penguin especially with the vacuum stability constraint. The vacuum decay rate is investigated, and it is shown that the discrepancy can be explained if superparticles are lighter than 4-6 TeV. Correlations with $mathcal{B}(K_Ltopi^0 ubar u)$ and other experimental constraints are also discussed.
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