Search

This paper describes how data from a new type of air shower detector, MILAGRO, can shed light on a variety of interesting problems in astrophysics. MILAGRO has the capability to make observations of VHE/UHE emission from the recently discovered TeV gamma‐ray source Markarian 421, an Active Galactic Nucleus (AGN). An observation of the attenuation of this signal in the range of 1–20 TeV can be used to make the first measurement of the intergalactic infrared radiation. We will also describe how MILAGRO can improve the existing limits on the density of Primordial Black Holes (PBH) by three orders of magnitude. In addition, MILAGRO will have a large aperture and continuous operation which gives it the capability to search for VHE gamma ray bursts.

In this paper we describe a new proposed water‐Cerenkov detector called MILAGRO, for observing cosmic gamma rays over a broad energy range of 1–1000 TeV. This detector will have an angular resolution better than 0.5° and an energy threshold near 1 TeV.

The 11 ‘‘in‐phase’’ source events from the 1986 muon‐rich bursts associated with Hercules X‐1 (previously reported by this group) have been studied for indications of further anomalous behavior. The most significant effect observed resulted from an analysis of the showerfront time‐structures of these events. This analysis was then applied a priori to the rest of the source day, where an additional ∼9 signal events are expected to remain. The same effect was observed at a chance probability level of ∼0.1%.

A new method of searching for UHE point source has been developed. With a data sample of 150 million events, we have surveyed the sky for point sources over 3314 locations (1.4°

We report here the preliminary results of our observations of the sporadic X‐binary system 4U0115+63. The CYGNUS air shower array has been collecting data since April 1986. No significant excess is seen from the direction of this source, nor any correlation with its 24‐day orbital period. A 90% confidence‐level upper limit on the flux from 4U0115+63 is 2.8×10−13 cm−2 s−1 above 50 TeV. This flux limit is considerably lower than those reported by other UHE experiments. Search for periodicity at the neutron star frequency is in progress.

Data from the CYGNUS extensive air shower experiment at Los Alamos, NM has been analyzed to study the angular resolution of the array, and to search for point sources in the galaxy. Results on searches for steady emission from Cyg X‐3, Her X‐1 and the Crab nebula are presented.

New experimental upper limits for the branching ratios of the lepton‐family‐number nonconserving decays μ+ → e+γ and μ+ → e+γγ are presented. A new determination of γ, the ratio of pion axial‐vector to vector form factors, from radiative pion decay is also reported. These results are from data taken with the Crystal Box detector at LAMPF.

A search has been performed for the decays μ → eee, μ → eγ, and μ → eγγ with a sensitivity in the branching ratios at the level of 10−10. The experiment used a surface muon beam at LAMPF with an average intensity of 300 kHz. A total of ≳1011 muon decays was examined for the present result. The detector for the experiment is the Crystal Box which consists of a cylindrical drift chamber surrounded by 396 NaI(T1) crystals. A layer of scintillation counters in front of the crystals provided timing for electrons and a veto for photons. The energy resolution for electrons and photons is ∼6% (FWHM). The position resolution of the drift chamber is 350 μm leading to a vertex cut with a rejection of 103 for μ → eee. The timing resolution is ∼400 ps from the scintillators and ∼1 ns from the crystals. From these values, the eee and eγγ limits are expected to be background free.

The Cygnus experiment at Los Alamos National Laboratory has been designed to study, with high angular accuracy, point sources of gamma rays above 1014 eV. The experimental detector consists of an air shower array to observe gamma ray showers and a shielded, large area track detector to study the muon content of the showers. In this paper we present preliminary data from the array and describe its performance.

We measure a helicity dependence in the p‐H20 cross section at 6 GeV/c. The result is (σ+−σ−)/(σ++σ−) =−(15.0±2.8) ×10−6 where σ+ (σ−) is approximately the p‐H2O total cross section for positive (negative) beam helicity. The helicity dependence may be due to background from weakly decaying hyperons produced in the H2O target.

Development of the Crystal Box Spectrometer at the Clinton P. Anderson Meson Physics Facility in Los Alamos has been completed. And a search for the rare muon decays mu to e−gamma, to e−2gamma, and to 3e is ready to start taking data. (AIP)

We have measured the parity‐violating longitudinal asymmetry A=(σ+−σ)/(σ++σ−) in the total cross section for 6 GeV/c protons on a water target. Our present data yield a value of (1.94±71)×10−6 from our scintillation detectors, (3.57±85)×10−6 from our ionization chambers, and (2.61±.55)×10−6 from a combined fit to both. Quoted errors include statistical and systematic contributions.