[show abstract][hide abstract] ABSTRACT: We describe a silicon microstrip detector interleaved with segments of a beryllium oxide target which was used in the FOCUS photoproduction experiment at Fermilab. The detector was designed to improve the vertex resolution and to enhance the reconstruction efficiency of short-lived charm particles.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 01/2004;
[show abstract][hide abstract] ABSTRACT: Using a high statistics sample of photo-produced charm particles from the FOCUS experiment at Fermilab, we report results of a search for eight rare and Standard-Model-forbidden decays: D+, Ds+→h±μ∓μ+ (with h=π,K). Improvement over previous results by a factor of 1.7–14 is realized. Our branching ratio upper limit D+→π+μ−μ+ of 8.8×10−6 at the 90% C.L. is below the current MSSM R-parity violating constraint.
[show abstract][hide abstract] ABSTRACT: We study the decay of D+ and D+s mesons into charged five-body final states, and report the discovery of the decay mode D+→K+K−π+π+π−, as well as measurements of the decay modes D+→K−π+π+π+π−, Ds+→K+K−π+π+π−, Ds+→φπ+π+π− and D+/Ds+→π+π+π+π−π−. An analysis of the resonant substructure for D+→K−π+π+π+π− and Ds+→K+K−π+π+π− is included, with an indication that both decays proceed primarily through an a1 vector resonance.
[show abstract][hide abstract] ABSTRACT: We describe the algorithm used to identify charged tracks in the fixed-target charm-photoproduction experiment FOCUS. We begin by describing the new algorithm and contrast this approach with that used in our preceding experiment — E687. We next illustrate the algorithm's performance using physics signals. Finally, we briefly describe some of the methods used to monitor the quantum efficiency and noise of the Cherenkov cells.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 01/2002;
[show abstract][hide abstract] ABSTRACT: A high statistics sample of photoproduced charm particles from the FOCUS (E831) experiment at Fermilab has been used to search for CP violation in the Cabibbo suppressed decay modes D+→K−K+π+, D0→K−K+ and D0→π−π+. We have measured the following CP asymmetry parameters: ACP(K−K+π+)=+0.006±0.011±0.005, ACP(K−K+)=−0.001±0.022±0.015 and ACP(π−π+)=+0.048±0.039±0.025 where the first error is statistical and the second error is systematic. These asymmetries are consistent with zero with smaller errors than previous measurements.
[show abstract][hide abstract] ABSTRACT: Using a high statistics sample of photoproduced charm particles from the FOCUS experiment at Fermilab, we compare the lifetimes of neutral D mesons decaying via to measure the lifetime differences between CP even and CP odd final states. These measurements bear on the phenomenology of mixing. If the D0→K−π+ is an equal mixture of CP even and CP odd eigenstates, we measure .
[show abstract][hide abstract] ABSTRACT: Using data from the FOCUS (E831) experiment at Fermilab, we present a new measurement of the branching ratio for the Cabibbo-favored decay mode D0→K−K−K+π+. From a sample of 143±19 fully reconstructed D0→K−K−K+π+ events, we measure Γ(D0→K−K−K+π+)/Γ(D0→K−π−π+π+)=0.00257±0.00034(stat.)±0.00024(syst.). A coherent amplitude analysis has been performed to determine the resonant substructure of this decay mode. This analysis reveals a dominant contribution from φ and states.
[show abstract][hide abstract] ABSTRACT: Using the FOCUS spectrometer with photon beam energies between 20 and 160 GeV, we confirm the existence of a diffractively photoproduced enhancement in K+K− at 1750 MeV/c2 with nearly 100 times the statistics of previous experiments. Assuming this enhancement to be a single resonance with a Breit–Wigner mass shape, we determine its mass to be 1753.5±1.5±2.3 MeV/c2 and its width to be 122.2±6.2±8.0 MeV/c2. We find no corresponding enhancement at 1750 MeV/c2 in K∗K, and again neglecting any possible interference effects we place limits on the ratio Γ(X(1750)→K∗K)/Γ(X(1750)→K+K−). Our results are consistent with previous photoproduction experiments, but, because of the much greater statistics, challenge the common interpretation of this enhancement as the φ(1680) seen in e+e− annihilation experiments.
[show abstract][hide abstract] ABSTRACT: Using data collected by the FOCUS experiment at Fermilab, we report the discovery of the decay modes D0→K−π+π+π+π−π− and D0→π+π+π+π−π−π−. With a sample of 48±10 reconstructed D0→K−π+π+π+π−π− decays and 149±17 reconstructed D0→π+π+π+π−π−π− decays, we measure the following relative branching ratios: Γ(D0→K−π+π+π+π−π−)/Γ(D0→K−π+π+π−)=(2.70±0.58±0.38)×10−3,Γ(D0→π+π+π+π−π−π−)/Γ(D0→K−π+π+π−)=(5.23±0.59±1.35)×10−3,Γ(D0→π+π+π+π−π−π−)/Γ(D0→K−π+π+π+π−π−)=1.93±0.47±0.48. The first errors are statistical and the second are systematic. The branching fraction of the Cabibbo suppressed six-body decay mode is measured to be a factor of two higher than the branching fraction of the Cabibbo favored six-body decay mode.
[show abstract][hide abstract] ABSTRACT: We report measurements of the charm–anticharm production asymmetries for Λc+, 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.
[show abstract][hide abstract] ABSTRACT: The FOCUS experiment (FNAL-E831) has used two channels, Ω−π+ and Ξ−K−π+π+, to measure the lifetime of the charmed baryon. From a sample of 64±14 signal events at a mass of 2.698 GeV/c2, we measure an lifetime of 72±11 (stat.) ±11 (sys.) fs, substantially improving upon the current world average.