Bubble-Chamber Study of Dimuon Production by Neutrinos Using the Phase-2 EMI and a Dichromatic Beam

The authors propose to examine in detail, using the 15-foot bubble chamber and an improved (Phase II) EMI, the characteristics of 'dimuon' events produced by neutrinos. A light neon-hydrogen filling (30% neon atoms) provides adequate target mass, good track measurements, and high detection efficiency for photons and electrons. Thus e-{mu} and e-e dileptons, as well as dimuons, can be observed with good efficiency. They estimate a yield of 100 detected dimuons in a 200 K picture expoture. They assume 400 GeV operation, 1 x 10{sup 13} protons/pulse, and a two-horn dichromatic beam focusing 100 {+-} 10 GeV/c mesons. If dimuons are made by neutrinos {ge} 30 GeV, then the yield from this dichromatic beam is about half the yield from a wide-band beam. Knowledge of neutrino energy is important in dimuon analysis. An improved two-plane EMI, as proposed by the UH-LBL group, would provide about 1 kg/cm{sup 2} absorption thickness for particles above 10 GeV/c, thus ensuring excellent dimuon identification. Another proposed EMI improvement, the Internal Picket Fence (IPF), is designed to eliminate EMI random background (mainly neutrino-induced in the internal coil-absorber). this should greatly simplify EMI analysis and reduce the misidentification of low momentum hadrons as muons. Thus they also expect improved efficiency for identification of neutral current events and slow (wide-angle) muons with this Phase II EMI

Multi-messenger Observations of a Binary Neutron Star Merger

International audienceOn 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of $\sim 1.7\,{\rm{s}}$ with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of ${40}_{-8}^{+8}$ Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 $\,{M}_{\odot }$. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at $\sim 40\,{\rm{Mpc}}$) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position $\sim 9$ and $\sim 16$ days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta