J. Graham

Search for the decay

Abstract Data collected in Fermilab experiment E731 was used to perform the first search for the decay K L →π 0 ν ν . This decay is dominated by short distance effects and is almost entirely direct CP violating within the standard model. Cuts were developed to reject the background processes Λ→nπ0 and KL→π+e−γν. No candidate events were seen. We find BR (K L →π 0 ν ν ) −4 at the 90% confidence level.We report on a search for the rare decay K_L -> pi^0 nu nubar in the KTeV experiment at Fermilab. We searched for two-photon events whose kinematics were consistent with an isolated pi^0 coming from the decay K_L -> pi^0 nu nubar. One candidate event was observed, which was consistent with the expected level of background. An upper limit on the branching ratio was determined to be B(K_L -> pi^0 nu nubar) < 1.6E-6 at the 90% confidence level.We report on a search for the rare decay K_L -> pi^0 nu nubar in the KTeV experiment at Fermilab. We searched for two-photon events whose kinematics were consistent with an isolated pi^0 coming from the decay K_L -> pi^0 nu nubar. One candidate event was observed, which was consistent with the expected level of background. An upper limit on the branching ratio was determined to be B(K_L -> pi^0 nu nubar) < 1.6E-6 at the 90% confidence level.

Measurements of direct CP violation, CPT symmetry, and other parameters in the neutral kaon system

The authors present precision measurements of the direct CP violation parameter, Re({epsilon}{prime}/{epsilon}), the kaon parameters, {Delta}m and {tau}{sub S}, and the CPT tests, {phi}{sub {+-}} and {Delta}{phi}, in neutral kaon decays. These results are based on the full dataset collected by the KTeV experiment at Fermi National Accelerator Laboratory during 1996, 1997, and 1999. This dataset contains {approx} 15 million K {yields} {pi}{sup 0}{pi}{sup 0} decays and {approx} 69 million K {yields} {pi}{sup +}{pi}{sup -} decays. They describe significant improvements to the precision of these measurements relative to previous KTeV analyses. They find Re({epsilon}{prime}/{epsilon}) = [19.2 {+-} 1.1(stat) {+-} 1.8(syst)] x 10{sup -4}, {Delta}m = (5265 {+-} 10) x 10{sup 6} hs{sup -1}, and {tau}{sub S} = (89.62 {+-} 0.05) x 10{sup -12} s. They measure {phi}{sub {+-}} = (44.09 {+-} 1.00){sup o} and {Delta}{phi} = (0.29 {+-} 0.31){sup o}; these results are consistent with CPT symmetry.

Observation of CP violation in K(L) ---> pi+ pi- e+ e- decays

We report the first observation of a manifestly CP violating effect in the K(L)->pi+pi-e+e- decay mode. A large asymmetry was observed in the distribution of these decays in the CP-odd and T-odd angle phi between the decay planes of the e+e- and pi+pi- pairs in the K(L) center of mass system. After acceptance corrections, the overall asymmetry is found to be 13.6+-2.5 (stat) +-1.2 (syst)%. This is the largest CP-violating effect yet observed integrating over the entire phase space of a mode and the first such effect observed in an angular variable.

A determination of the cabibbo-kobayashi-maskawa parameter |VUS| using KL decays

We present a determination of the CKM parameter |Vus| based on new measurements of the six largest KL branching fractions and semileptonic form factors by the KTeV (E832) experiment at Fermilab. We find |Vus| = 0.2252 +- 0.0008(KTeV) +- 0.0021(ext), where the errors are from KTeV measurements and from external sources. We also use the measured branching fractions to determine the CP violation parameter |eta+-| = [2.228 +- 0.005(KTeV) +- 0.009(ext)]E-3.

Measurements of K(L) branching fractions and the CP violation parameter |eta+-|

We present new measurements of the six largest branching fractions of the KL using data collected in 1997 by the KTeV experiment (E832) at Fermilab. The results are B(KL -> pi e nu) = 0.4067 +- 0.0011 B(KL -> pi mu nu) = 0.2701 +- 0.0009 B(KL -> pi+ pi- pi0) = 0.1252 +- 0.0007 B(KL -> pi0 pi0 pi0) = 0.1945 +- 0.0018 B(KL -> pi+ pi-) = (1.975 +- 0.012)E-3, and B(KL -> pi0 pi0) = (0.865 +- 0.010)E-3, where statistical and systematic errors have been summed in quadrature. We also determine the CP violation parameter |eta+-| to be (2.228 +- 0.010)E-3. Several of these results are not in good agreement with averages of previous measurements.

A Measurement of the K(L) charge asymmetry

We present a measurement of the charge asymmetry delta(L) in the mode K(L)-->pi(+/-)e(-/+)nu based on 298 x 10(6) analyzed decays. We measure a value of delta(L) = [3322+/-58(stat)+/-47(syst)]x10(-6), in good agreement with previous measurements and 2.4 times more precise than the current best published result. The result is used to place more stringent limits on CPT and DeltaS = DeltaQ violation in the neutral kaon system.

Measurement of the decay K(L) ---> pi0 gamma gamma

We report on a new measurement of the decay KL -> pi0 gamma gamma by the KTeV experiment at Fermilab. We determine the KL -> pi0 gamma gamma branching ratio to be (1.68 +/- 0.07 +/- 0.08)x10**-6. Our data shows the first evidence for a low-mass gamma gamma signal as predicted by recent O(p**6) chiral perturbation calculations that include vector meson exchange contributions. From our data, we extract a value for the effective vector coupling aV = -0.72 +/- 0.05 +/- 0.06.

Search for the decay KL → π0e+e-

We report on a search for the decay Kl -> pi0 e+ e- carried out by the KTeV/E799 experiment at Fermilab. This decay is expected to have a significant CP violating contribution and the measurement of its branching ratio could support the CKM mechanism for CP violation or could point to new physics. Two events were observed in the 1997 data with an expected background of 1.06 +-0.41 events, and we set an upper limit Br(Kl -> pi0 e+ e-) < 5.1 x 10^-10 at the 90% confidence level.

Search for the weak decay of a lightly bound H0 dibaryon

We present results of a search for a neutral, six-quark, dibaryon state called the \h, a state predicted to exist in several theoretical models. Observation of such a state would signal the discovery of a new form of hadronic matter. Analyzing data collected by experiment E799-II, using the KTeV detector at Fermilab, we searched for the decay

First measurement of form-factors of the decay Xi0 ---> Sigma+ e- anti-nu(e)

H^0 \to \Lambda p \piminus