arXiv subjects

FOCUS Collaboration

Publications and source records attributed to FOCUS Collaboration.

At least 19 recordsLinked to original sources

arXiv2007

Study of the D^0 \to pi^-pi^+pi^-pi^+ decay

Using data from the FOCUS (E831) experiment at Fermilab, we present new measurements for the Cabibbo-suppressed decay mode $D^0 \to π^-π^+π^-π^+$. We measure the branching ratio $Γ(D^0 \toπ^+π^- π^+π^-)/Γ(D^0 \to K^-π^+π^-π^+) = 0.0914 \pm 0.0018 \pm 0.0022$. An amplitude analysis has been performed, a first for this channel, in order to determine the resonant substructure of this decay mode. The dominant component is the decay $D^0 \to a_1(1260)^+ π^-$, accounting for 60% of the decay rate. The second most dominant contribution comes from the decay $D^0 \to ρ(770)^0ρ(770)^0$, with a fraction of 25%. We also study the $a_1(1260)$ line shape and resonant substructure. Using the helicity formalism for the angular distribution of the decay $D^0 \to ρ(770)^0ρ(770)^0$, we measure a longitudinal polarization of $P_L = (71 \pm 4\pm 2)$%.

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arXiv2005

A Non-parametric Approach to the D+ to K*0bar mu+ nu Form Factors

Using a large sample of D+ -> K- pi+ mu+ nu decays collected by the FOCUS photoproduction experiment at Fermilab, we present the first measurements of the helicity basis form factors free from the assumption of spectroscopic pole dominance. We also present the first information on the form factor that controls the s-wave interference discussed in a previous paper by the FOCUS collaboration. We find reasonable agreement with the usual assumption of spectroscopic pole dominance and measured form factor ratios.

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arXiv2005

Hadronic Mass Spectrum Analysis of D+ into K- pi+ mu+ nu Decay and Measurement of the K*(892)^0 Mass and Width

We present a Kpi mass spectrum analysis of the four-body semileptonic charm decay D+ into K- pi+ mu+ nu in the range of 0.65 GeV < mKpi < 1.5 GeV. We observe a non-resonant contribution of 5.30 +- 0.74 +0.99 -0.51 % with respect to the total D+ into K- pi+ mu+ nu decay. For the K*(892)^0 resonance, we obtain a mass of 895.41 +- 0.32 +0.35 -0.36 MeV, a width of 47.79 +- 0.86 +1.3 -1.1 MeV, and a Blatt-Weisskopf damping factor parameter of 3.96 +- 0.54 +0.72 -0.90 GeV^(-1). We also report 90 % CL upper limits of 4 % and 0.64 % for the branching ratios of D+ into K*(1680)^0 mu+ nu with respect to D+ into K- pi+ mu+ nu and D+ into K*(1430)^0 mu+ nu with respect to D+ into K- pi+ mu+ nu, respectively.

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arXiv2005

Search for a strongly decaying neutral charmed pentaquark

We present a search for a charmed pentaquark decaying strongly to $D^{(*)-}p$. Finding no evidence for such a state, we set limits on the cross section times branching ratio relative to $D^{*-}$ and $D^-$ under particular assumptions about the production mechanism.

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arXiv2005

A Measurement of the Ds+ Lifetime

A high statistics measurement of the Ds+ lifetime from the Fermilab fixed-target FOCUS photoproduction experiment is presented. We describe the analysis of the two decay modes, Ds+ -> phi(1020)pi+ and Ds+ -> \bar{K}*(892)0K+, used for the measurement. The measured lifetime is 507.4 +/- 5.5 (stat.) +/- 5.1 (syst.) fs using 8961 +/- 105 Ds+ -> phi(1020)pi+ and 4680 +/- 90 Ds+ -> \bar{K}*(892)0K+ decays. This is a significant improvement over the present world average.

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arXiv2005

Dalitz plot analysis of D_s+ and D+ decay to pi+pi-pi+ using the K-matrix formalism

FOCUS results from Dalitz plot analysis of D_s+ and D+ to pi+pi-pi+ are presented. The K-matrix formalism is applied to charm decays for the first time to fully exploit the already existing knowledge coming from the light-meson spectroscopy experiments. In particular all the measured dynamics of the S-wave pipi scattering, characterized by broad/overlapping resonances and large non-resonant background, can be properly included. This paper studies the extent to which the K-matrix approach is able to reproduce the observed Dalitz plot and thus help us to understand the underlying dynamics. The results are discussed, along with their possible implications on the controversial nature of the sigma meson.

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arXiv2005

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 $D^0 \to K^-K^+π^-π^+$, $D^+ \to K^0_SK^+π^-π^+$, and $D^+_s \to K^0_SK^+π^-π^+$. 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 $A_Tviol (D^0) = 0.010 \pm 0.057(stat.) \pm 0.037(syst.)$, $A_Tviol (D^+) = 0.023 \pm 0.062(stat.) \pm 0.022(syst.)$, and $A_Tviol (D^+_s) = -0.036 \pm 0.067(stat.) \pm 0.023(syst.)$. Each measurement is consistent with no T violation. New measurements of the CP asymmetries for some of these decay modes are also presented.

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arXiv2005

Study of Lambda/c+ Cabibbo Favored Decays Containing a Lambda Baryon in the Final State

Using data from the FOCUS experiment (FNAL-E831), we study the decay of $Λ^+_c$ baryons into final states containing a $Λ$ hyperon. The branching fractions of $Λ^+_c$ into $Λπ^+$, $Λπ^+ π^+ π^-$ and $Λ\bar{K} ^0 K^+$ relative to that into $pK^-π^+$ are measured to be $0.217 \pm 0.013 \pm 0.020$, $0.508 \pm 0.024 \pm 0.024$ and $0.142 \pm 0.018 \pm 0.022$, respectively. We also report new measurements of $\frac{Γ(Λ^+_c \to Σ^0 π^+)}{Γ(Λ^+_c \to Λπ^+)} = 1.09 \pm 0.11 \pm 0.19$, $\frac{Γ(Λ^+_c \to Σ^0 π^+π^+ π^-)}{Γ(Λ^+_c \to Λπ^+ π^+ π^-)} = 0.26 \pm 0.06 \pm 0.09$ and $\frac{Γ(Λ^+_c \to Ξ(1690)^0(Λ\bar{K} ^0) K^+)}{Γ(Λ^+_c \to Λ\bar{K} ^0 K^+)} = 0.33 \pm 0.10 \pm 0.04$. Further, an analysis of the subresonant structure for the $Λ^+_c \to Λπ^+π^+π^-$ decay mode is presented.

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arXiv2005

Measurement of the doubly Cabibbo suppressed decay $D^0 \to K^+π^-$ and a search for charm mixing

We present an analysis of the decay $D^0 \to K^+π^-$ based on FOCUS data. From a sample of 234 signal events, we find a branching ratio of $\frac{Γ(D^0 \to K^+π^-)}{Γ(D^0 \to K^-π^+)} = (0.429^{+0.063}_{-0.061}\pm 0.027)%$ under the assumptions of no mixing and no CP violation. Allowing for CP violation, we find a branching ratio of $(0.429 \pm 0.063 \pm 0.028)%$ and a \textit{CP} asymmetry of $0.18 \pm 0.14 \pm 0.04$. The branching ratio for the case of mixing with no CP violation is $(0.381^{+0.167}_{-0.163} \pm 0.092)%$. We also present limits on charm mixing.

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arXiv2004

Measurement of the branching ratio of the decay D^0 -> π^-μ^+νrelative to D^0 -> K^-μ^+ν

We present a new measurement of the branching ratio of the Cabibbo suppressed decay D^0\to π^-μ^+νrelative to the Cabibbo favored decay D^0\to K^-μ^+νand an improved measurement of the ratio |\frac{f_+^π(0)}{f_+^{K}(0)}|. Our results are 0.074 \pm 0.008 \pm 0.007 for the branching ratio and 0.85 \pm 0.04 \pm 0.04 \pm 0.01 for the form factor ratio, respectively.

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arXiv2004

Measurements of Six-Body Hadronic Decays of the D^0 Charmed Meson

Using data collected by the FOCUS experiment at Fermilab, we report the discovery of the decay modes D^0 --> K- pi+ pi+ pi+ pi- pi- and D^0 --> pi+ pi+ pi+ pi- pi- pi-. With a sample of 48 +/- 10 reconstructed D^0 --> K- pi+ pi+ pi+ pi- pi- decays and 149 +/- 17 reconstructed D^0 --> pi+ pi+ pi+ pi- pi- pi- decays, we measure the following relative branching ratios: ${Γ(D^0 \to K^- π^+ π^+ π^+ π^- π^-) / Γ(D^0 \to K^- π^+ π^+ π^-)} = (2.70 \pm 0.58 \pm 0.38) \times 10^{-3}$ ${Γ(D^0 \to π^+ π^+ π^+ π^- π^- π^-) / Γ(D^0 \to K^- π^+ π^+ π^-)} = (5.23 \pm 0.59 \pm 1.35) \times 10^{-3}$ ${Γ(D^0 \to π^+ π^+ π^+ π^- π^- π^-) / Γ(D^0 \to K^- π^+ π^+ π^+ π^- π^-)} = 1.93 \pm 0.47 \pm 0.48$ 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.

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arXiv2003

Charm-anticharm baryon production asymmetries in photon-nucleon interactions

We report measurements of the charm-anticharm production asymmetries for $Λ_c^+$, $Σ_c^{++}$, $Σ_c^0$, $Σ_c^{++*}$, $Σ_c^{0*}$, and $Λ_c^+(2625)$ 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 $Λ_c$ baryons as functions of $p_L$, $p_T^2$, and $x_F$. The integrated asymmetry for $Λ_c^+$ production, $(σ_{Λ_c^+} - σ_{Λ_c^-}) / (σ_{Λ_c^+} + σ_{Λ_c^-})$, is $0.111 \pm 0.018 \pm 0.012$, significantly different from zero. The asymmetries of the excited states are consistent with the $Λ_c$ asymmetry.

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arXiv2003

Study of the decay mode D^0 -> K-K-K+pi+

Using data from the FOCUS (E831) experiment at Fermilab, we present a new measurement of the branching ratio for the Cabibbo-favored decay mode $D^0 \to K^-K^-K^+π^+$. From a sample of $143 \pm 19$ fully reconstructed $D^0 \to K^-K^-K^+π^+$ events, we measure $Γ(D^0 \to K^-K^-K^+π^+)/Γ(D^0 \to K^-π^-π^+π^+) = 0.00257 \pm 0.00034(stat.) \pm 0.00024(syst.)$. 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 $\bar K^{*0}(890)$ states.

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arXiv2003

Search for Rare and Forbidden 3-body Di-muon Decays of the Charmed Mesons D+ and Ds+

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+/- muon-/+ muon+ (with h=pion or Kaon). Improvement over previous results by a factor of 1.7--14 is realized. Our branching ratio upper limit D+ > pion+ muon- muon+ of 8.8E-6 at the 90% C.L. is below the current MSSM R-Parity violating constraint.

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arXiv2003

Studies of correlations between D and ${\bar D}$ mesons in high energy photoproduction

Studies of $D{\bar D}$ correlations for a large sample of events containing fully and partially reconstructed pairs of charmed $D$ mesons recorded by the Fermilab photoproduction experiment FOCUS (FNAL-E831) are presented. Correlations between $D$ and ${\bar D}$ mesons are used to study heavy quark production dynamics. We present results for fully and partially reconstructed charm pairs and comparisons to a recent version of \textsc{Pythia} with default parameter settings. We also comment on the production of $ψ(3770)$ in our data.

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arXiv2003

Study of the Cabibbo-suppressed decay modes D0-->Pi-pi+ 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-->Pi-Pi+ and D0-->K-K+. We measured: Gamma(D0-->K-K+)/Gamma(D0-->Pi-Pi+) = 2.81 +/- 0.10(stat) +/- 0.06(syst), Gamma(D0-->K-K+)/Gamma(D0-->K-Pi+) = 0.0993 +/- 0.0014(stat) +/- 0.0014(syst), and Gamma(D0-->Pi-Pi+)/Gamma(D0-->K-Pi+) = 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-->PiPi decay channels.

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arXiv2002

Observation of a 1750 MeV/c^2 Enhancement in the Diffractive Photoproduction of K^+K^-

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 \mevcc 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 $1753.5\pm 1.5\pm 2.3$ \mevcc and its width to be $122.2\pm 6.2\pm 8.0$ \mevcc. We find no corresponding enhancement at 1750 \mevcc in $K^*K$, and again neglecting any possible interference effects we place limits on the ratio $Γ(X(1750) \to K^*K)/Γ(X(1750) \to K^+K^-)$. 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.

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arXiv2001

Measurement of Natural Widths of Sigma-c-0 and Sigma-c-++ Baryons

In this paper we present a measurement of the natural widths of $Σ_c^0$ and $Σ_c^{++}$. Using data from the FOCUS experiment, we find $Γ(Σ_c^0) = 1.55 +0.41/-0.37 \pm 0.38$ MeV/c^2 and $Γ(Σ_c^0) = 2.05 +0.41/-0.38 \pm 0.38$ MeV/c^2. The first errors are statistical, the second systematic. These results are obtained with a sample of 913 $Σ_c^0 \to Λ_c^+ π^-$ decays and 1110 $Σ_c^++ \to Λ_c^+ π^+$ decays. These results are compared with recent theoretical predictions. PACS numbers: 14.20.Lq 13.30Eg

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