Study of Λc+ Cabibbo favored decays containing a Λ baryon in the final state

Using data from the FOCUS experiment (FNAL–E831), we study the decay of Λc+ baryons into final states containing a Λ hyperon. The branching fractions of Λc+ into Λπ+, Λπ+π+π− and ΛK¯0K+ relative to that into pK−π+ are measured to be 0.217±0.013±0.020, 0.508±0.024±0.024 and 0.142±0.018±0.022, respectively. We also report new measurements of Γ(Λc+→Σ0π+)Γ(Λc+→Λπ+)=1.09±0.11±0.19, Γ(Λc+→Σ0π+π+π−)Γ(Λc+→Λπ+π+π−)=0.26±0.06±0.09 and Γ(Λc+→Ξ(1690)0(ΛK¯0)K+)Γ(Λc+→ΛK¯0K+)=0.32±0.10±0.04. Further, an analysis of the subresonant structure for the Λc+→Λπ+π+π− decay mode is presented

Search for T violation in charm meson decays

Using data from the FOCUS (E831) experiment, we have searched for T violation in charm meson decays using the four-body decay channels D0→K−K+π−π+, D+→KS0K+π−π+, and Ds+→KS0K+π−π+. The T violation asymmetry is obtained using triple-product correlations and assuming the validity of the CPT theorem. We find the asymmetry values to be ATviol(D0)=0.010±0.057(stat.)±0.037(syst.), ATviol(D+)=0.023±0.062(stat.)±0.022(syst.), and ATviol(Ds+)=−0.036±0.067(stat.)±0.023(syst.). Each measurement is consistent with no T violation. New measurements of the CP asymmetries for some of these decay modes are also presented

Measurement of the branching ratio of the decay D0→π−μ+ν relative to D0→K−μ+ν

We present a new measurement of the branching ratio of the Cabibbo suppressed decay D0→π−μ+ν relative to the Cabibbo favored decay D0→K−μ+ν and an improved measurement of the ratio |f+π(0)/f+K(0)|. Our results are 0.074±0.008±0.007 for the branching ratio and 0.85±0.04±0.04±0.01 for the form factor ratio, respectively

Study of the Cabibbo-suppressed decay modes D0→π−π+ and D0→K−K+

Using data from the FOCUS (E831) experiment at Fermilab, we present a new measurement for the branching ratios of the Cabibbo-suppressed decay modes D0→π−π+ and D0→K−K+. We measured: Γ(D0→K−K+)/Γ(D0→π−π+)=2.81±0.10(stat)±0.06(syst), Γ(D0→K−K+)/Γ(D0→K−π+)=0.0993±0.0014(stat)±0.0014(syst), and Γ(D0→π−π+)/Γ(D0→K−π+)=0.0353±0.0012(stat)±0.0006(syst). These values have been combined with other experimental data to extract the ratios of isospin amplitudes and the phase shifts for the D→KK and D→ππ decay channels

Measurement of the isolated photon cross section in pp¯ collisions at s=1.96 TeV

The cross section for the inclusive production of isolated photons has been measured in pp¯ collisions at s=1.96 TeV with the DØ detector at the Fermilab Tevatron Collider. The photons span transverse momenta 23 to 300 GeV and have pseudorapidity |η|\u3c0.9. The cross section is compared with the results from two next-to-leading order perturbative QCD calculations. The theoretical predictions agree with the measurement within uncertainties

Charm–anticharm baryon production asymmetries in photon–nucleon interactions

We report measurements of the charm–anticharm production asymmetries for Λc+, Σc++, Σc0, Σc++∗, Σc0∗, and Λc+(2625) baryons from the Fermilab photoproduction experiment FOCUS (E831). These asymmetries are integrated over the region where the spectrometer has good acceptance. In addition, we have obtained results for the photoproduction asymmetries of the Λc baryons as functions of pL, pT2, and xF. The integrated asymmetry for Λc+ production, (σΛc+−σΛc−)/(σΛc++σΛc−), is 0.111±0.018±0.012, significantly different from zero. The asymmetries of the excited states are consistent with the Λc asymmetry

Measurement of the ratio of the vector to pseudoscalar charm semileptonic decay rate Γ(D+→K¯*0μ+νμ)/Γ(D+→K¯0μ+νμ)

Using a high statistics sample of photo-produced charm particles from the FOCUS experiment at Fermilab, we report on the measurement of the ratio of semileptonic rates Γ(D+→Kπμ+νμ)/Γ(D+→K¯0μ+νμ)=0.625±0.045±0.034. Allowing for the Kπ S-wave interference measured in [J.M. Link, et al., FOCUS Collaboration, Phys. Lett. B 544 (2002) 89], we extract the vector to pseudoscalar ratio Γ(D+→K¯*0μ+νμ)/Γ(D+→K¯0μ+νμ)=0.594±0.043±0.033 and the ratio Γ(D+→K¯0μ+νμ)/Γ(D+→K−π+π+)=1.019±0.076±0.065. Our results show a lower ratio for Γ(D→K*ℓν)/Γ(D→Kℓν) than has been reported recently and indicate the current world average branching fractions for the decays D+→K¯0(μ+,e+)νμ,e are low. Using the world average B(D+→K−π+π+) [K. Hagiwara, et al., Particle Data Group Collaboration, Phys. Rev. D 66 (2002) 010001, and 2003 partial update for edition 2004 (http://pdg.lbl.gov)] we extract B(D+→K¯0μ+ν)=(9.27±0.69±0.59±0.61)%

Hadronic mass spectrum analysis of D+→K−π+μ+ν decay and measurement of the K∗(892)0 mass and width

We present a Kπ mass spectrum analysis of the four-body semileptonic charm decay D+→K−π+μ+ν in the range of 0.65 GeV/c

Search for the lightest scalar top quark in events with two leptons in pp¯ collisions at s=1.96 TeV

Data collected by the D0 detector at a pp¯ center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider have been used to search for pair production of the lightest supersymmetric partner of the top quark decaying into bℓν˜. The search is performed in the ℓℓ′=eμ and μμ final states. No evidence for this process has been found in data samples of approximately 400 pb−1. The domain in the [M(t˜1),M(ν˜)] plane excluded at the 95% C.L. is substantially extended by this search