arXiv subjects

H. A. Rubin

Publications and source records attributed to H. A. Rubin.

32 records · Page 2Linked to original sources

arXiv2011

Search for the disappearance of muon antineutrinos in the NuMI neutrino beam

We report constraints on antineutrino oscillation parameters that were obtained by using the two MINOS detectors to measure the 7% muon antineutrino component of the NuMI neutrino beam. In the Far Detector, we select 130 events in the charged-current muon antineutrino sample, compared to a prediction of 136.4 +/- 11.7(stat) ^{+10.2}_{-8.9}(syst) events under the assumption |dm2bar|=2.32x10^-3 eV^2, snthetabar=1.0. Assuming no oscillations occur at the Near Detector baseline, a fit to the two-flavor oscillation approximation constrains |dm2bar|<3.37x10^-3 eV^2 at the 90% confidence level with snthetabar=1.0.

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arXiv2011

Improved search for muon-neutrino to electron-neutrino oscillations in MINOS

We report the results of a search for $ν_{e}$ appearance in a $ν_μ$ beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of $8.2\times10^{20}$ protons on the NuMI target at Fermilab, we find that $2\sin^2(θ_{23})\sin^2(2θ_{13})<0.12\ (0.20)$ at 90% confidence level for $δ\mathord{=}0$ and the normal (inverted) neutrino mass hierarchy, with a best fit of $2\sin^2(θ_{23})\sin^2(2θ_{13})\,\mathord{=}\,0.041^{+0.047}_{-0.031}\ (0.079^{+0.071}_{-0.053})$. The $θ_{13}\mathord{=}0$ hypothesis is disfavored by the MINOS data at the 89% confidence level.

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arXiv2010

Forward Neutron Production at the Fermilab Main Injector

We have measured cross sections for forward neutron production from a variety of targets using proton beams from the Fermilab Main Injector. Measurements were performed for proton beam momenta of 58 GeV/c, 84 GeV/c, and 120 GeV/c. The cross section dependence on the atomic weight (A) of the targets was found to vary as $A^(alpha)$ where $α$ is $0.46\pm0.06$ for a beam momentum of 58 GeV/c and 0.54$\pm$0.05 for 120 GeV/c. The cross sections show reasonable agreement with FLUKA and DPMJET Monte Carlos. Comparisons have also been made with the LAQGSM Monte Carlo.

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arXiv2010

Study of the rare hyperon decay Omega \to Xi π^+ π^-

We report a new measurement of the decay Ω^- \to Ξ^- π^+ π^- with 76 events and a first observation of the decay Ω^+ \to Ξ^+ π^+ π^- with 24 events, yielding a combined branching ratio (3.74 ^{+0.67}_{-0.56}) \times 10^{-4}. This represents a factor 25 increase in statistics over the best previous measurement. No evidence is seen for CP violation, with B(Ω^- \to Ξ^- π^+ π^-)=4.04^{+0.83}_{-0.71} \times 10^{-4} and B(Ω^+ \to Ξ^+ π^+ π^-)=3.15^{+1.12}_{-0.89} \times 10^{-4}. Contrary to theoretical expectation, we see little evidence for the decays Ω^- \to Ξ_{1530}^{*0} π^- and Ω^+ \to Ξ_{1530}^{*0} π^+ and place a 90% C.L. upper limit on the combined branching ratio B(Ω^-(Ω^+) \to Ξ^{*0}_{1530}(Ξ^{*0}_{1530}) π^\mp)<7.0 \times 10^{-5}.

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arXiv2005

Search for the Lepton-Number-Violating Decay $Ξ^- \to p μ^- μ^-$

A sensitive search for the lepton-number-violating decay $Ξ^-\to p μ^-μ^-$ has been performed using a sample of $\sim10^9$ $Ξ^-$ hyperons produced in 800 GeV/$c$ $p$-Cu collisions. We obtain $\mathcal{B}(Ξ^-\to p μ^-μ^-)< 4.0\times 10^{-8}$ at 90% confidence, improving on the best previous limit by four orders of magnitude.

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arXiv2005

Observation of Parity Violation in the Omega-minus -> Lambda + K-minus Decay

The alpha decay parameter in the process Omega-minus -> Lambda + K-minus has been measured from a sample of 4.50 million unpolarized Omega-minus decays recorded by the HyperCP (E871) experiment at Fermilab and found to be [1.78 +/- 0.19(stat) +/- 0.16(syst)]{\times}10^{-2}. This is the first unambiguous evidence for a nonzero alpha decay parameter, and hence parity violation, in the Omega-minus -> Lambda + K-minus decay.

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arXiv2005

delta S = 2 nonleptonic hyperon decays

A sensitive search for the rare decays Ω^- \to Λπ^- and Ξ^0 \to p π^- has been performed using data from the 1997 run of the HyperCP (Fermilab E871) experiment. Limits on other such processes do not exclude the possibility of observable rates for |ΔS| = 2 nonleptonic hyperon decays, provided the decays occur through parity-odd operators. We obtain the branching-fraction limits B(Ω^- \to Λπ^-)< 2.9 x 10^{-6} and B(Ξ^0 \to p π^-)< 8.2 x 10^{-6}, both at 90% confidence level.

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arXiv2005

Measurement of the Alpha Asymmetry Parameter for the Omega- to Lambda K- Decay

We have measured the alpha parameter of the Omega- to Lambda K- decay using data collected with the HyperCP spectrometer during the 1997 fixed-target run at Fermilab. Analyzing a sample of 0.96 million Omega- to Lambda K^-, Lambda to p pi- decays, we obtain alpha_Omega*alpha_Lambda = [1.33+/-0.33(stat)+/-0.52(syst)] x 10^{-2}. With the accepted value of alpha_Lambda, alpha_Omega is found to be [2.07+/-0.51(stat)+/-0.81(syst)] x 10^{-2}.

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arXiv2005

Evidence for the Decay Sigma+ -> p mu+ mu-

We report the first evidence for the decay Sigma+ -> p mu+ mu- from data taken by the HyperCP experiment(E871) at Fermilab. Based on three observed events, the branching ratio is B(Sigma+ -> p,mu+,mu-) = [8.6 +6.6,-5.4(stat) +/-5.5(syst)] x 10**-8. The narrow range of dimuon masses may indicate that the decay proceeds via a neutral intermediate state, Sigma+ -> p P0, P0 -> mu+ mu-, with a P0 mass of 214.3 +/- 0.5 MeV/c**2 and branching ratio B(Sigma+ -> p P0; P0 -> mu+ mu-) = [3.1 +2.4,-1.(stat) +/-1.5(syst)] x 10**-8.

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arXiv2004

Search for CP Violation in Charged-Xi and Lambda Hyperon Decays

We have compared the proton and antiproton angular distributions in 117 million Xi-minus -> Lambda + pi-minus -> proton + pi-minus + pi-minus and 41 million anti-Xi-minus -> anti-Lamba + pi-plus -> antiproton + pi-plus + pi-plus decays using a subset of the data from the HyperCP experiment (E871) at Fermilab. We find no evidence of CP violation, with the direct-CP-violating parameter $A_{ΞΛ} = \frac{α_Ξα_Λ - \barα_Ξ\barα_Λ}{α_Ξα_Λ + \barα_Ξ\barα_Λ} = [0.0+/-5.1(stat)+/-4.4(syst)]{\times}10^{-4}$.

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arXiv2004

High Statistics Search for the Theta+(1.54) Pentaquark State

We have searched for Theta+(1.54) -> K0,p decays using data from the 1999 run of the HyperCP experiment at Fermilab. We see no evidence for a narrow peak in the K0,p mass distribution near 1.54 GeV/c among 106,000 K0,p candidates, and obtain an upper limit for the fraction of Theta+(1.54) to K0,p candidates of <0.3% at 90% confidence.

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arXiv2004

HyperCP: A high-rate spectrometer for the study of charged hyperon and kaon decays

The HyperCP experiment (Fermilab E871) was designed to search for rare phenomena in the decays of charged strange particles, in particular CP violation in $Ξ$ and $Λ$ hyperon decays with a sensitivity of $10^{-4}$. Intense charged secondary beams were produced by 800 GeV/c protons and momentum-selected by a magnetic channel. Decay products were detected in a large-acceptance, high-rate magnetic spectrometer using multiwire proportional chambers, trigger hodoscopes, a hadronic calorimeter, and a muon-detection system. Nearly identical acceptances and efficiencies for hyperons and antihyperons decaying within an evacuated volume were achieved by reversing the polarities of the channel and spectrometer magnets. A high-rate data-acquisition system enabled 231 billion events to be recorded in twelve months of data-taking.

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arXiv2003

Measurement of Decay Parameters for $Ξ^{-} \to Λπ^{-}$ Decay

Based on 1.35 million polarized $Ξ^{-}$ events, we measure the parameter $ϕ_Ξ$ to be $-1.61^{\circ} \pm 2.66^{\circ} \pm 0.37^{\circ}$ for $Ξ^{-} \to Λπ^{-}$ decay. New results for the parameters $β_Ξ$ and $γ_Ξ$ are also presented. Assuming that the CP-violating phase-shift difference is negligible, we deduce the strong phase-shift difference between the P-wave and S-wave amplitudes of the $Λπ$ final state to be $3.17^{\circ} \pm 5.28^{\circ} \pm 0.73^{\circ}$. This strong phase-shift difference reduces the theoretical uncertainty in estimating the level of CP violation in $Ξ$-hyperon decay.

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arXiv1996

Asymmetries between the production of D+ and D- mesons from 500 GeV/c pi- nucleon interactions as a function of xF and pt**2

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.

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