Search Results (87 total)

We demonstrate that zero-field β-detected nuclear quadrupole resonance and spin relaxation of low energy ⁸Li can be used as a sensitive local probe of structural phase transitions near a surface. We find that the transition near the surface of a SrTiO₃ single crystal occurs at T_c∼150  K, i.e., ∼45  K higher than T_c^bulk, and that the tetragonal domains formed below T_c are randomly oriented.

Fermilab experiment E835 has studied reactions p̅ p→π⁰π⁰,π⁰η,ηη, π⁰η^′ and ηη^′ in the energy region of the χ_c0(1³P₀) from 3340 MeV to 3470 MeV. Interference between resonant and continuum production is observed in the π⁰π⁰ and ηη channels, and the product of the input and output branching fractions is measured. Limits on resonant production are set for the π⁰η and π⁰η^′ channels. An indication of interference is observed in the ηη^′ channel. The technique for extracting resonance parameters in an environment dominated by continuum production is described.

We report evidence for the h_c state of charmonium in its η_cγ decay mode and lack of evidence in the J/ψπ⁰ mode. We studied these channels in p̅ p annihilations near the center of gravity of the ³P_J states, where the h_c was reported in the J/ψπ⁰ mode by E760, our previous experiment, at 3526.2±0.15±0.2  MeV, with Γ_R≤1  MeV. We observe an event excess in the η_cγ mode near 3526 MeV. Testing the null hypothesis of a linearly varying background cross section against the alternate hypothesis that includes a resonance near 3526 MeV, we reject the null hypothesis with P∼0.001. The resonance mass is 3525.8±0.2±0.2  MeV and the resonance width ≤1  MeV. We estimate 10.0±3.5<Γ_{p̅ p}B_ηcγ<12.0±4.5  eV, corresponding to fixed values 0.5<Γ_R<1.0  MeV. We find no event excess within the search region in the J/ψπ⁰ mode.

We have measured several branching ratios for ψ^′ decay using the data collected by the FNAL E835 experiment during the year 2000, obtaining B(ψ^′→e⁺e^-)=0.0068±0.0001±0.0004, B(ψ^′→J/ψπ⁺π^-)=0.292±0.005±0.018, B(ψ^′→J/ψπ⁰π⁰)=0.167±0.005±0.014, and B(ψ^′→J/ψη)=0.028±0.002±0.002. We also present a measurement of the dipion mass distribution in the decays ψ^′→J/ψππ.

Fermilab experiment E835 has observed p̅ p annihilation production of the charmonium state χ_c0 and its subsequent decay into π⁰π⁰. Although the resonant amplitude is an order of magnitude smaller than that of the nonresonant continuum production of π⁰π⁰, an enhanced interference signal is evident. A partial wave expansion is used to extract physics parameters. The amplitudes J=0 and 2, of comparable strength, dominate the expansion. Both are accessed by L=1 in the entrance p̅ p channel. The product of the input and output branching fractions is determined to be B(p̅ p→χ_c0)×B(χ_c0→π⁰π⁰)=(5.09±0.81±0.25)×10^-7.

We report on a study of the angular distributions in the radiative decay of the χ_c1 and χ_c2 states formed in p̅ p annihilations. These distributions depend on the dynamics of the formation process and the multipole structure of the radiative decay. Using 2090 χ_c1 and 5908 χ_c2 events, we have measured the fractional magnetic quadrupole amplitude to be a₂(χ_c1)≃M2/E1=0.002±0.032, and a₂(χ_c2)=-0.093_-0.041^+0.039. We have also measured the square of the helicity 0 fractional amplitude in the χ_c2 formation process to be B₀²=0.13±0.08.

We report on a search by Fermilab experiment E835 for the η_c^′ (2 ¹S₀) charmonium resonance in the process p̅ p→η_c^′→γγ. No signal was observed and, based on 34 pb^-1 integrated luminosity, we determine the following upper limits (90% confidence level) to the product of the branching ratios for a resonance mass in the region 3575–3660 MeV/c²: Br(η_c^′→p̅ p)×Br(η_c^′→γγ)<12.0×10^-8 for Γ=5 MeV; <5.9×10^-8 for Γ=10 MeV; <4.8×10^-8 for Γ=15 MeV. Combining the present data with those of the predecessor experiment, E760, the upper limits become 8.0×10^-8, 5.0×10^-8, and 4.5×10^-8, respectively. In the restricted region 3589–3599 MeV/c², where a candidate was reported by the Crystal Ball experiment, we obtain the following limits from the combined E760–E835 experiments: Br(η_c^′→p̅ p)×Br(η_c^′→γγ)<5.6×10^-8 for Γ=5 MeV; <3.7×10^-8 for Γ=8 MeV. A comparison of these with other experimental results is presented.

We report the branching ratios of the χ_c2(1³P₂) and χ_c0(1³P₀) charmonium resonances to two photons using event samples collected by Fermilab experiment E835 in the reactions p̅ p→χ_c2(1³P₂)[χ_c0(1³P₀)]. Our result for the χ_c2 is B(χ_c2→γγ)=(1.35±0.25±0.12)×10^-4. We set a 95% upper limit for the χ_c0 branching ratio B(χ_c0→γγ) at 2.09×10^-4.

The first measurement of B(D⁰→φX⁰) and an upper limit for B(D⁺→φX⁺) are determined from 22.3 pb^-1 of e⁺e^- annihilation data at a c.m. energy of 4.03 GeV. The data were recorded by the Beijing Spectrometer (BES) at BEPC. A recoil charge method is applied to charm threshold data to determine the charge of the D meson in the recoil from 9054±309±416 reconstructed D⁰, D⁺ mesons. The branching fractions B(D⁰→φX⁰)=(1.71_-0.71^+0.76±0.17)%, and B(D⁺→φX⁺)<1.8% are determined from 10 events with a reconstructed D and a recoiling φ. In addition, a 90% C.L. upper limit of B(D⁺→φe⁺X⁰)<1.6% is determined from a search for semileptonic decays of the D⁺.

We have determined the following ψ^′ branching ratios using the large event sample collected by Fermilab experiment E835 in the reaction pp̅ →ψ^′: B(ψ^′→e⁺e^-)=(7.4±0.2±0.7)×10^-3, B(ψ^′→J/ψπ⁰π⁰)=(18.7±0.9±1.3)% and B(ψ^′→J/ψη)=(4.1±0.3±0.5)%.

The cross section for charmed meson production at sqrt[s]=4.03 and 4.14 GeV has been measured with the Beijing Spectrometer. The measurement was made using 22.3 pb^-1 of e⁺e^- data collected at 4.03 GeV and 1.5 pb^-1 of e⁺e^- data collected at 4.14 GeV. Inclusive observed cross sections for the production of charged and neutral D mesons and momentum spectra are presented. Observed cross sections were radiatively corrected to obtain tree level cross sections. Measurements of the total hadronic cross section are obtained from the charmed meson cross section and an extrapolation of results from below the charm threshold.

The resonance parameters of χ_c0, the ³1P₀ resonance of charmonium, have been measured at the Fermilab Antiproton Accumulator by means of the reaction p̅ p→χ_c0→γJ/ψ→γ(e⁺e^-). The results are M(χ_c0)  =  3417.4_-1.9^+1.8±0.2 MeV/c², Γ(χ_c0)  =  16.6_-3.7^+5.2±0.1 MeV, and Γ(χ_c0→p̅ p)×B(χ_c0→J/ψγ)×B(J/ψ→e⁺e^-)  =  2.89_-0.53^+0.67±0.14 eV. Using known branching ratios we also obtain Γ(χ_c0→p̅ p)  =  8.0_-1.5-1.9^+1.9+3.5 keV. These results are discussed in relation to the other χ_cJ states and to theoretical predictions.

The cross section for the reaction p̅ p→e⁺e^- has been measured at s=8.8, 10.8, 12.4, 13.1, and 14.4 GeV² by Fermilab experiment E835. A non-magnetic spectrometer is used to identify the e⁺e^- final states generated by the antiproton beam intersecting an internal hydrogen gas jet target. From the analysis of the 144 observed events, new high-precision measurements of the proton magnetic form factor for timelike momentum transfers are obtained.

The IMB-3 experiment was a large water Cherenkov ring imaging detector with a fiducial mass of 3.3 kton. During a 7.6-kton-year exposure (∼4.6×10³³ nucleon yr) 935 contained events were observed. The observed rate and characteristics are consistent with the expected backgrounds from atmospheric neutrinos. Lower limits on the nucleon lifetime are set for a wide variety of proposed decay modes.

We propose an experiment to measure the Lamb shift and fine structure (the intervals 2s_1/2-2p_1/2 and 2p_1/2-2p_3/2) in antihydrogen. A sample of 10 000 antihydrogen atoms at a momentum of 8.85 GeV/c suffices to measure the Lamb shift to 5% and the fine structure to 1%. Atomic collisions excite antihydrogen atoms to states with n=2; field ionization in a Lorentz-transformed laboratory magnetic field then prepares a particular n=2 state, and is used again to analyze that state after it is allowed to oscillate in a region of zero field. This experiment is feasible at Fermilab.

We report the background-free observation of atomic antihydrogen, produced by interactions of an antiproton beam with a hydrogen gas jet target in the Fermilab Antiproton Accumulator. We measure the cross section of the reaction p̅ p→H̅ e^-p for p̅ beam momenta between 5203 and 6232 MeV/ c to be 1.12±0.14±0.09 pb.

A search is performed for the production of the ψ(2S) in e⁺e^- annihilation at a center-of-mass energy of 4.03 GeV using the BES detector operated at the Beijing Electron Positron Collider (BEPC). The kinematic features of the reconstructed ψ(2S) signal are consistent with its being produced only in association with an energetic photon resulting from initial state radiation (ISR). Limits are placed on ψ(2S) production from the decay of unknown charmonia or metastable hybrids that might be produced in e⁺e^- annihilations at 4.03 GeV. Under the assumption that the observed cross section for ψ(2S) production is due entirely to ISR, the partial width Γ_ee of the ψ(2S) is measured to be 2.07±0.32 keV.

The absolute inclusive branching fraction of D_s⁺→φX⁺ has been measured from data collected by the BES detector at a center-of-mass energy of 4.03 GeV, corresponding to an integrated luminosity of 22.3 pb^-1. At this energy, direct pair production e⁺e^-→D_s⁺D_s^- has been observed. We have selected D_s candidate events by reconstructing five hadronic decay modes D_s⁺→φπ⁺, K^0*K⁺, K⁰K⁺, f₀π⁺ and K⁰K^-π⁺π⁺ and have searched for inclusive φ’s in the recoiling D_s^-. We observed three recoiling φ’s in the 166.4 ± 31.8 D_s candidate events, which leads to the absolute branching fraction B(D_s⁺→φX⁺)=(17.8_{- 7.2}^+15.1 _-6.3^+0.6) % and B(D_s⁺→φπ⁺)=(3.6_-1.6^+3.1 _-1.3^+0.4) %.

The absolute inclusive semileptonic branching fraction of the D_s meson has been measured based on 22.3 pb^-1 of e⁺e^- collision data collected with the Beijing Spectrometer at sqrt[s]=4.03 GeV. At this energy, the D_s are produced in pairs: e⁺e^-→D_s⁺D_s^-. We reconstructed 171±21±15 D_s events in five hadronic decay modes. In the recoil system of these events, several D_s inclusive semileptonic decays were observed and the branching fraction is estimated to be B(D_s⁺→e⁺X)=(7.7_-4.3-2.1^+5.7+2.4)%.

We have performed an experiment in the Antiproton Accumulator at Fermilab to study two-body neutral final states formed in p̅ p annihilations. Differential cross sections are determined in the center-of-mass energy range 2.911<sqrt[s]<3.686 GeV for the final states π⁰π⁰, ηπ⁰, ηη, π⁰γ, and γγ. The energy dependence of differential cross sections at 90° in the center of mass is studied to test the predictions of phenomenological QCD scaling hypotheses which predict power-law dependence.

A 2.1 kton yr exposure of data from the Irvine-Michigan-Brookhaven detector has yielded 72 atmospheric neutrino events with a vertex contained inside the fiducial volume and at least 0.95 GeV of visible Čerenkov energy. The ratio of these two ratios (muonlike / total)_Data/(muonlike / total)_MC was found to be 1.1_-0.12^+0.07(stat)±0.11(syst). The zenith angle dependence of this ratio of ratios is consistent with being flat. The region of sin²(2θ)>0.5 and δm²>9.8×10^-3 eV² has been excluded to the 90% confidence level for ν_μ→ν_e oscillations while the region of sin²(2θ)>0.7 and δm²>1.5×10^-2 eV² has been excluded to the 90% confidence level for ν_μ→ν_τ oscillations.

We have observed exclusive decays of the ψ^′ in an experiment where the ψ^′ is formed in antiproton-proton annihilations. We report the branching ratios B(ψ^′→e⁺e^-)=(8.3±0.5_stat±0.7_syst)×10^-3, B(ψ^′→J/ψπ⁺π^-)=0.283±0.021_stat±0.020_syst, B(ψ^′→J/ψπ⁰π⁰)=0.184±0.019_stat±0.013_syst, B(ψ^′→J/ψη)=0.032±0.010_stat±0.002_syst.

We report the first observation of the (radiative) decay J / ψ→e⁺e^-γ. Our data are from an experiment in which J / ψ is formed in antiproton-proton annihilations. The observed rate is consistent with a QED calculation based on final state radiation. Our measurement gives a branching ratio for this mode of (8.8±1.3±0.4)×10^-3 for γ energy>100 MeV.