R. A. Briere

Polarization of Λ and Λ produced by 800-GeV protons☆

Abstract We have measured the polarization of Λ and Λ hyperons produced by 800 GeV protons on a Be target at a fixed targeting angle of 4.8 mrad. Comparison with previous data at 400 GeV production energy and twice the targeting angle shows no significant energy dependence for the Λ polarization. This is in striking contrast to the energy dependence found for σ+ and Ξ− polarizations. We find no evidence for Λ polarization at 800 GeV.

Simultaneous measurement of KS and KL decays into π+π-γ

With the E731 apparatus at Fermilab, we have simultaneously collected 6859 [ital K][sub [ital L]] and [ital K][sub [ital S]] decays into [pi][sup +][pi][sup [minus]][gamma]. Using our sample of over 370 000 [pi][sup +][pi][sup [minus]] decays for normalization we have determined that the ratio [Gamma]([ital K][sup 0][r arrow][pi][sup +][pi][sup [minus]][gamma])/[Gamma]([ital K][sup 0][r arrow][pi][sup +][pi][sup [minus]]) is (23.0[plus minus]0.7)[times]10[sup [minus]3] for [ital K][sub [ital L]] and (7.10[plus minus]0.22)[times]10[sup [minus]3] for [ital K][sub [ital S]], for photon energies greater than 20 MeV in the kaon center of mass. After removing the inner-bremsstrahlung contribution, we find that the photon energy spectrum of the direct emission decay of the [ital K][sub [ital L]] is consistent with the presence of a vector meson propagator in the form factor.

Studies of dE/dx measurements with the BESIII

The Beijing Spectrometer III (BESIII) is a general-purpose detector used for the study of τ-charm physics at the Beijing Electron-Positron Collider II (BEPCII). This paper presents our studies of the dE/dx measurement in the drift chamber of BESIII, which is important for the identification of charged particles. Corrections applied to the dE/dx measurement in data reconstruction are discussed. After our current dE/dx calibration, a resolution of about 6% has been obtained for minimum ionization particles, and a 3σ K/π separation is obtained for momenta up to 760 MeV/c. These results meet the design goals of the BESIII drift chamber.

Search for the lepton-family number violating decays KL→π0μ±e∓

Abstract We have carried out at Fermilab the first search for the lepton-family number violating decay K L → π 0 μ ± e ∓ . There were no events observed. By normalizing to K L → π + π − π 0 decays collected simultaneously, the 90% confidence level upper limit on 1 2 [ BR (K L →π 0 μ + e − )+ BR (K L →π 0 μ − e + )] was determined to be 3.1×10 −9 .

Limit on the branching ratio of KL → π0e+e-

We report the results of a search for the decay [ital K][sub [ital L]][r arrow][pi][sup 0][ital e+][ital e[minus]] conducted by E799 at Fermilab. The largest contribution to this decay mode is expected to be [ital CP] violating. Observations of this decay could either confirm the standard model mechanisms for [ital CP] violation or point to physics beyond the standard model. No such events were seen in our search. The 90% confidence level upper limit is determined to be [ital B]([ital K][sub [ital L]][r arrow][pi][sup 0][ital e+][ital e[minus]])[lt]4.3[times]10[sup [minus]9].

Search for the decay KL→π0νν

This thesis describes a search for KL → πνν̄ decay, carried out as a part of E799-II experiment at Fermilab. Within the Standard Model, the KL → πνν̄ decay is dominated by the direct CP violating processes, and thus a discovery of the decay implies confirmation of the direct CP violation. Due to theoretically clean calculations, a measurement of Br(KL → πνν̄) is one of the best ways to determine the CKM parameter, and is one of the most sensitive probes for a new physics. No such events were observed, and we set an upper limit Br(KL → πνν̄) < 5.9× 10−7 , at the 90% confidence level. This result represents an improvement of a factor of 98 over the current limit listed by Particle Data Group, and of a factor of 3 over the recent preliminary result.

A limit on the lepton-family number violating process π0 → μ±e∓

Abstract A FNAL E799 Collaboration has carried out a search for the lepton-family number violating decay π0 → μ±e∓ using π0s produced from KL → π0π0π0 decays in flight. No events were observed. Assuming that lepton-family number violation is charge independent, the 90% confidence level upper limit on 1 2 [ BR (π 0 → μ + e − ) + BR (π 0 → μ − e + )] was determined to be 8.6 × 10−9.

Measurement of the branching ratio and form factor of KL→μ+μ- γ

We report on a measurement of the decay

Measurement of the branching ratio of KLe+e-

K_Lrightarrowmu^+mu^-gamma

Search for the decay KL0→π0π0γ

from Fermilab experiment E799. We observe