Search Results (29 total)

Experiment 865 at the Brookhaven AGS has observed the decay K⁺→e⁺ν_eμ⁺μ^-. The branching ratio extracted is (1.72±0.37(stat)±0.17(syst)±0.19(model))×10^-8 where the third term in the error results from the use of a model to extrapolate into a kinematic region dominated by background.

Based on results of a search for the lepton-family-number-violating decay K⁺→π⁺μ⁺e^- with data collected by experiment E865 at the Alternating Gradient Synchrotron of Brookhaven National Laboratory, we place an upper limit on the branching ratio at 2.1×10^-11 (90% C.L.). Combining the results with earlier E865 data and those of a previous experiment, E777, an upper limit on the branching ratio of 1.3×10^-11 (90% C.L.) is obtained.

E865 at the Brookhaven National Laboratory AGS collected about 70 000 K_e3⁺ events to measure the K_e3⁺ branching ratio relative to the observed K⁺→π⁺π⁰, K⁺→π⁰μ⁺ν, and K⁺→π⁺π⁰π⁰ decays. The π⁰ in all the decays was detected using the e⁺e^- pair from π⁰→e⁺e^-γ decay and no photons were required. Using the 2002 Particle Data Group branching ratios for the normalization decays, we obtain BR(K_e3(γ)⁺)=(5.13±0.02_stat±0.09_syst±0.04_norm)%, where K_e3(γ)⁺ includes the effect of virtual and real photons. This result is ≈2.3σ higher than the current Particle Data Group value. Implications for the V_us element of the CKM matrix, and the matrix’s unitarity are discussed.

We report experimental details and results of a new measurement of the decay K⁺→π⁺π^-e⁺ν_e(K_e4). A sample of more than 400,000 K_e4 events with low background has been collected by Experiment 865 at the Brookhaven Alternate Gradient Synchrotron. From these data, the branching ratio (4.11±0.01±0.11)×10^-5 and the ππ invariant mass dependence of the form factors F, G, and H of the weak hadronic current as well as the phase shift difference δ₀⁰-δ₁¹ for ππ scattering were extracted. Using constraints based on analyticity and chiral symmetry, a new value with considerably improved accuracy for the s-wave ππ scattering length a₀⁰ has been obtained also: a₀⁰=0.216±0.013 (stat)±0.002 (syst)±0.002 (theor).

A measurement of the deflection of a laser beam in a modulated magnetic field with a prototype apparatus has produced an upper limit on the charge of the photon of 8.5×10^-17e. It is shown that an improved apparatus could attain a sensitivity of 10^-21e.

Experiment 865 at the Brookhaven Alternating Gradient Synchrotron obtained 410 K⁺→e⁺νe⁺e^- and 2679 K⁺→μ⁺νe⁺e^- events including 10% and 19% background. The branching ratios were measured to be [2.48±0.14(stat)±0.14(syst)]×10^-8 (m_ee>150   MeV) and (7.06±0.16±0.26)×10^-8 (m_ee>145   MeV), respectively. Results for the decay form factors are presented.

A novel, single shot, nondestructive scheme to measure the bunch length of submillimeter relativistic electron bunches using the electro-optical method is described. In this scheme, the birefringence induced by the electric field of the electrons converts the temporal characteristics of the bunch to a spatial intensity distribution of an optical pulse. Electric field characteristics, induced birefringence, and retardation are calculated for a few typical electron beam parameters and criteria limiting the resolution are established.

A sample of 4×10⁵ events from the decay K⁺→π⁺π^-e⁺ν_e  (K_e4) has been collected in experiment E865 at the Brookhaven Alternating Gradient Synchrotron. The analysis of these data yields new measurements of the K_e4 branching ratio [(4.11±0.01±0.11)×10^-5], the s-wave ππ scattering length [a₀⁰  =  0.216±0.013(stat)±0.004(syst)±0.005(theor)], and the form factors F, G, and H of the hadronic current and their dependence on the invariant ππ mass.

A search for lepton flavor violating decays, K⁺→μ⁺μ⁺π^-, K⁺→e⁺e⁺π^-, K⁺→π⁺e⁺μ^-, K⁺→μ⁺e⁺π^-, and π⁰→e⁺μ^-, was performed using the data collected in Experiment E865 at the Brookhaven Alternating Gradient Synchrotron. No signal was found in any of the decay modes. At the 90% confidence level, the branching ratios are less than 3.0×10^-9, 6.4×10^-10, 5.2×10^-10, 5.0×10^-10, and 3.4×10^-9, respectively.

We report results of a search for the lepton-family number violating decay K⁺→π⁺μ⁺e^- from data collected by experiment E865 in 1996 at the Alternating Gradient Synchroton of Brookhaven National Laboratory. We place an upper limit on the branching ratio at 3.9×10^-11 ( 90% C.L.). Together with results based on data collected in 1995 and an earlier experiment, E777, this result establishes a combined 90% confidence level upper limit on the branching ratio at 2.8×10^-11. We also report a new upper limit on the branching ratio for π⁰→μ⁺e^- of 3.8×10^-10 ( 90% C.L.).

More than 400 K⁺→π⁺μ⁺μ^- events were observed in a rare K⁺ decay experiment at the Brookhaven Alternating Gradient Synchrotron. Normalized to the K⁺→π⁺π⁺π^- decay, the branching ratio is determined to be [9.22±0.60(stat)±0.49(syst)]×10^-8. This branching ratio and the μμ mass spectrum is in very good agreement with the measurement of the K⁺→π⁺e⁺e^- decay, but deviates significantly from the previous measurement.

A low-background sample of 10 300 events has been collected for the decay mode K⁺→π⁺e⁺e^- by experiment E865 at the Brookhaven Alternating Gradient Synchrotron. The branching ratio is measured to be [2.94±0.05(stat)±0.13(syst)±0.05(model)]×10^-7, the vector nature of this decay is firmly established, and the decay form factor f(z)  =  f₀(1+δz) (z  =  M_ee²/m_K²) is determined to have δ  =  2.14±0.13±0.15. The experiment is described and results discussed in the context of chiral perturbation theory.

Employing the decay chain K⁺→π⁺π⁰, π⁰→e⁺e^- we have observed the decay π⁰→e⁺e^-. With a signal sample of ≊21 events we measure the branching ratio for π⁰→e⁺e^- to be (6.9±2.3±0.6)×10^-8, normalized to the decay K⁺→π⁺π⁰, π⁰→e⁺e^-γ. This result is consistent with the unitarity lower bound and the published 90% confidence level upper limit of 13×10^-8.

We have searched for light scalar and/or pseudoscalar particles that couple to two photons by studying the propagation of a laser beam (λ=514 nm) through a transverse magnetic field. A limit of 3.5×10^-10 rad was set on a possible optical rotation of the beam polarization for an effective path length of 2.2 km in a 3.25 T magnetic field. We find that the coupling g_αγγ<3.6×10^-7 GeV^-1 at the 95% confidence level, provided m_a<10^-3 eV. Similar limits can be set from the absence of ellipticity in the transmitted beam. We also searched for photon regeneration in a magnetic field and found the limit g_αγγ<6.7×10^-7 GeV^-1 for the same range of particle mass.

We have searched for a flux of axions produced in the Sun by exploiting their conversion to x rays in a static magnetic field. The signature of a solar axion flux would be an increase in the rate of x rays detected in a magnetic telescope when the Sun passes within its acceptance. From the absence of such a signal we set a 3σ limit on the axion coupling to two photons g_aγγ≡1/M<3.6×10^-9 GeV^-1, provided the axion mass m_a<0.03 eV and <7.7×10^-9 GeV^-1 for 0.03 <m_a<0.11 eV.

We present results of an experiment in which approximately 500 events of the decay K⁺→π⁺e⁺e^- were observed. We have measured the branching ratio for K_πee⁺ to be (2.75±0.23±0.13)×10^-7 assuming a vector interaction with a form factor of λ=0.105±0.035±0.015. We have also found the branching ratio times decay probability for K⁺→π⁺X⁰, X⁰→e⁺e^- to be less than 1.5×10^-8 (99% C.L.) over an X⁰ invariant mass range from 150 to 340 MeV/c².

A search for the lepton-flavor number-violating decay K⁺→π⁺μ⁺e^- has been conducted at the Brookhaven Alternating Gradient Synchrotron. No candidates have been found which would be consistent with this decay mode. An upper limit on the branching ratio is placed at 2.6×10^-10, which can be combined with our previous result to yield an upper limit of 2.1×10^-10 at the 90% confidence level. A limit on the branching ratio for π⁰→μ⁺e^- of 1.6×10^-8 (90% C.L.) is also established.

We report here on a search for the lepton-family-number-violating decay K⁺→π⁺μ⁺e^-. We found no evidence for this decay mode and we establish an upper limit on its branching ratio of 1.1×10^-9 at the 90% confidence level (C.L.) for a uniform phase-space decay distribution. We also use this result to establish an upper limit for the branching ratio of the decay π⁰→μ⁺e^- of 7.8×10^-8 (90% C.L.).

We have searched for the decay process K⁺→π⁺A⁰, where A⁰ is any particle of mass less than 100 MeV/c² decaying into e⁺e^-. Upper limits for the branching ratio are given as a function of mass and lifetime of the A⁰. For lifetimes shorter than 10^-13 sec, a limit of 4.5×10^-7 at the 90% confidence level is obtained.

We present measurements of kaon and antiproton production cross sections in the momentum region of 700 MeV/c from 0° to 10° by 28.4-GeV/c protons on complex nuclei. A model to describe the A dependence of these cross sections is discussed and compared with these and other data.

Results of measurements of the polarization parameter in K⁺p elastic scattering at 650, 700, 845, and 940 MeV/c are presented. Details of the measurements are described and results are compared with previous measurements and partial-wave parametrizations of the data. The implication of the existence of Z^* resonances in light of these results is discussed.

Total and annihilation cross sections for p̅ p and p̅ d have been measured over the momentum range 355-1066 MeV/c at closely spaced momenta and with good energy resolution. No evidence is seen for the narrow structure reported by other experiments in the vicinity of 500 MeV/c. The present measurements indicate a broader enhancement in this region, which, if interpreted as a resonance, would have a height of ∼ 3 mb and a width of ∼ 20 MeV. This structure appears only in the p̅ p data.

Charge-exchange cross section for antiprotons on protons has been measured in closely spaced momentum intervals from 0.119 to 1.046 GeV/c. The regions of the reported resonances at 1936 and 2020 MeV were scanned in 10-MeV/c steps with a typical statistical error of ≈ 1% and an rms mass resolution of ± 1.5 MeV. No enhancements were observed.

In this paper we report measurements of the backward K^-p differential cross section at 49 momenta covering the momentum range 476-1084 MeV/c. The statistical precision achieved, typically 2.5%, is an order of magnitude better than previous measurements. The systematic errors for this reaction are about 1%. The differential cross section for the reaction K^-p→Σ^-π⁺ where the π⁺ emerges at 0° has also been measured at 32 momenta with comparable improvement in precision over previous experiments. A partial-wave analysis of the K̅ N channels including the new K^-p backward elastic data is presented.