arXiv subjects
Publications and source records attributed to A. J. Schwartz.
We review results from searches for mixing and CP violation in the D0-D0bar system. No evidence for mixing or CP violation is found, and limits are set for the mixing parameters x, y, x', y', and several CP-violating parameters.
The Belle experiment has used several methods to measure or constrain the angles phi_1, phi_2, and phi_3 (or beta, alpha, and gamma) of the CKM unitarity triangle. The results are sin(2phi_1) = 0.728 \pm 0.056 (stat) \pm 0.023 (syst) or phi_1= (23.4 +2.7 -2.4) degrees from B0 -> J/psi K0 decays (140 fb-1); phi_2 = 0-19 degrees or 71-180 degrees at 95.4% CL from B0 -> pi+pi- decays (253 fb-1); and phi_3 = [68 +14 -15 (stat) \pm 13 (syst) \pm 11 (model)] degrees from B+ -> (D0, D0bar) K+, (D0,D0bar) -> K0_S pi+ pi- decays (253 fb-1). These values satisfy the triangle relation phi_1 + phi_2 + phi_3 = 180 degrees within their uncertainties. The angle phi_1 is also determined from several b -> s qbar q penguin-dominated decay modes; the value obtained by taking a weighted average of the individual results differs from the B0 -> J/psi K0 result by more than two standard deviations. The angle phi_2 is constrained by measuring a CP asymmetry in the decay time distribution; the asymmetry observed is large, and the difference in the yields of B0,B0bar -> pi+ pi- decays constitutes the first evidence for direct CP violation in the B system.
The Belle experiment has measured branching fractions and CP asymmetries for the charmless decays B0->pi+pi- and B0->rho+-pi-+. From these measurements, constraints upon the CKM angle phi_2 can be obtained. These constraints indicate that phi_2 is around 100 degrees.
We have searched for mixing in the D0-D0bar system by measuring the decay-time distribution of D0->K+pi- decays. The analysis uses 90 fb^{-1} of data collected by the Belle detector at the KEKB e+e- collider. We fit the decay-time distribution for the mixing parameters x' and y' and also for the parameter R_D, which is the ratio of the rate for the doubly-Cabibbo-suppressed decay D0->K+pi- to that for the Cabibbo-favored decay D0->K-pi+. We do these fits both assuming CP conservation and allowing for CP violation. We use a frequentist method to obtain a 95% C.L. region in the x'^2 - y' plane. Assuming no mixing, we measure R_D = (0.381 \pm 0.017 +0.008 -0.016) %.
The Belle and BaBar experiments have measured branching fractions and CP asymmetries in the charmless decay modes B0->pi+pi-, B0->rho+pi-/rho-pi+, and B0->rho+rho-. From these measurements, constraints upon the CKM angle phi_2 can be obtained. These constraints consistently indicate that phi_2 is around 100 degrees.
We present recent results from the Belle experiment on rare hadronic B meson decays. The results are based on a 78 fb^{-1} data sample and consist of branching fractions, CP asymmetries, and polarization amplitudes. The decays studied include two-body pseudoscalar-pseudoscalar final states (B -> pi pi, K pi, KK, and D^0 K^\pm); pseudoscalar-vector final states (B -> omega pi, omega K, and phi K); and vector-vector final states (B -> phi K* and rho^+ rho^0).
From Dalitz-plot analyses of $D^+\toπ^-π^+π^+$ and $D^+\to K^-π^+π^+$ decays, we find evidence for light and broad scalar resonances sigma(500) and kappa(800). From a Dalitz-plot analysis of $D^+_s\toπ^-π^+π^+$ decays, we measure the masses and decay widths of the scalar resonances f_0(980) and f_0(1370).
We review results from FNAL E791 concerning D0-D0bar mixing and CP violation in D meson decays. We have searched for mixing in semileptonic D0 -> K+\ell-\barν decays and in hadronic D0 -> K+π- and D0 -> K+π-π+π- decays. We have searched for CP violation in D0 -> K+K- / π+π- and D+ -> ϕπ+ / \bar{K}^{*0}K+ / K+K-π+ / π+π-π+ decays. Finally, we have measured the difference in decay widths ΔΓbetween the two mass-eigenstates of the D0-D0bar system. This parameter affects the rate of D0-D0bar mixing. We combine our results with those from other experiments to obtain confidence intervals incorporating all published experimental data.
We review results on rare and forbidden decays of D^0, D^+, and D^+_s mesons from experiments at FNAL. The decay modes studied have two leptons in the final state and, if observed, would constitute evidence for flavor-changing neutral-current, lepton-flavor-violating, or lepton-number-violating processes. To date, no evidence for these decays has been observed and upper limits are obtained for their branching fractions. These limits can constrain various extensions to the Standard Model. We present new upper limits from FNAL E791 on the branching fractions for more than two dozen three- and four-body decay modes.
We calculate the time dependence of B0->f decays (and analogously D0->f decays) and use this result to obtain expressions for the time dependence of: an untagged sample (B0->f and Bbar->f decays combined), a sample containing charge-conjugate final states (B0->f and B0->fbar decays combined), and a sample containing all four decay modes together. For simplicity we assume CP violating effects are negligible.
HERA-B is a hadroproduction experiment located at DESY in Hamburg, Germany. The experiment produces B mesons and baryons by inserting thin wire targets into the halo of the proton beam circulating in the HERA storage ring. The B decays are studied to search for evidence of CP violation and constrain the angle $β$ and possibly $γ$ and $α$ of the CKM unitarity triangle. The experiment also produces B_s mesons; these decays are studied to measure or constrain the mass difference $Δm_s$ and width difference $ΔΓ_s$ between the two $B^0_s/\bar{B}_s^0$ mass eigenstates. Finally, the large number of B's produced allows HERA-B to search for rare and forbidden decays such as $B\to K^{(*)}\ell^+_1\ell^-_2$. The experiment is scheduled to begin running in early 2000.
Fermilab experiment E791 studied weak decays of D+, D_s, and D^0 mesons produced in collisions of 500 GeV/c negative pions with Pt and C targets. The experiment collected over 200,000 fully reconstructed charm decays. Four recent results are discussed here: (a) measurement of the form factor ratios V/A_1, A_2/A_1, and A_3/A_1 in D->K*-l-nu and Ds->phi-l-nu decays; (b) measurement of the difference in decay widths $ΔΓ$ between the two D^0/D^0-bar mass eigenstates; (c) search for rare and forbidden D decays to dilepton final states; and (d) search for a ``Pentaquark,'' a bound state of c-bar-suud.
We have developed a straw tube chamber with pickup-pad readout. The mechanism for signal pickup, the size of the pickup signal, and the distribution of signals among neighboring pads are discussed. We have tested a prototype chamber in a beamtest at Brookhaven National laboratory and have measured chamber efficiencies in excess of 99%.
We describe the development and testing of a novel beam stop for use in a rare kaon decay experiment at the Brookhaven AGS. The beam stop is located inside a dipole spectrometer magnet in close proximity to straw drift chambers and intercepts a high-intensity neutral hadron beam. The design process, involving both Monte Carlo simulations and beam tests of alternative beam-stop shielding arrangements, had the goal of minimizing the leakage of particles from the beam stop and the resulting hit rates in detectors, while preserving maximum acceptance for events of interest. The beam tests consisted of measurements of rates in drift chambers, scintilation counter hodoscopes, a gas threshold Cherenkov counter, and a lead glass array. Measurements were also made with a set of specialized detectors which were sensitive to low-energy neutrons, photons, and charged particles. Comparisons are made between these measurements and a detailed Monte Carlo simulation.
We present asymmetries between the production of D+ and D- mesons in Fermilab experiment E791 as a function of xF and pt**2. The data used here consist of 74,000 fully-reconstructed charmed mesons produced by a 500 GeV/c pi- beam on C and Pt foils. The measurements are compared to results of models which predict differences between the production of heavy-quark mesons that have a light quark in common with the beam (leading particles) and those that do not (non-leading particles). While the default models do not agree with our data, we can reach agreement with one of them, PYTHIA, by making a limited number of changes to parameters used.