Search Results (36 total)

A search for TeV-PeV muon neutrinos from unresolved sources was performed on AMANDA-II data collected between 2000 and 2003 with an equivalent live time of 807 days. This diffuse analysis sought to find an extraterrestrial neutrino flux from sources with nonthermal components. The signal is expected to have a harder spectrum than the atmospheric muon and neutrino backgrounds. Since no excess of events was seen in the data over the expected background, an upper limit of E²Φ_90%C.L.<7.4×10^-8  GeV cm^-2 s^-1 sr^-1 is placed on the diffuse flux of muon neutrinos with a Φ∝E^-2 spectrum in the energy range 16 TeV to 2.5 PeV. This is currently the most sensitive Φ∝E^-2 diffuse astrophysical neutrino limit. We also set upper limits for astrophysical and prompt neutrino models, all of which have spectra different from Φ∝E^-2.

The IceCube neutrino detector is a cubic kilometer TeV to PeV neutrino detector under construction at the geographic South Pole. The dominant population of neutrinos detected in IceCube is due to meson decay in cosmic-ray air showers. These atmospheric neutrinos are relatively well understood and serve as a calibration and verification tool for the new detector. In 2006, the detector was approximately 10% completed, and we report on data acquired from the detector in this configuration. We observe an atmospheric neutrino signal consistent with expectations, demonstrating that the IceCube detector is capable of identifying neutrino events. In the first 137.4 days of live time, 234 neutrino candidates were selected with an expectation of 211±76.1(syst)±14.5(stat) events from atmospheric neutrinos.

We report the results of a five-year survey of the northern sky to search for point sources of high energy neutrinos. The search was performed on the data collected with the AMANDA-II neutrino telescope in the years 2000 to 2004, with a live time of 1001 days. The sample of selected events consists of 4282 upward going muon tracks with high reconstruction quality and an energy larger than about 100 GeV. We found no indication of point sources of neutrinos and set 90% confidence level flux upper limits for an all-sky search and also for a catalog of 32 selected sources. For the all-sky search, our average (over declination and right ascension) experimentally observed upper limit Φ⁰=(E / 1  TeV)^γ·dΦ / dE to a point source flux of muon and tau neutrino (detected as muons arising from taus) is Φ_{νμ+ν̅ μ}⁰+Φ_{ντ+ν̅ τ}⁰=11.1×  10^-11  TeV^-1 cm^-2 s^-1, in the energy range between 1.6 TeV and 2.5 PeV for a flavor ratio Φ_{νμ+ν̅ μ}⁰/Φ_{ντ+ν̅ τ}⁰=1 and assuming a spectral index γ=2. It should be noticed that this is the first time we set upper limits to the flux of muon and tau neutrinos. In previous papers we provided muon neutrino upper limits only neglecting the sensitivity to a signal from tau neutrinos, which improves the limits by 10% to 16%. The value of the average upper limit presented in this work corresponds to twice the limit on the muon neutrino flux Φ_{νμ+ν̅ μ}⁰=5.5×10^-11  TeV^-1 cm^-2 s^-1. A stacking analysis for preselected active galactic nuclei and a search based on the angular separation of the events were also performed. We report the most stringent flux upper limits to date, including the results of a detailed assessment of systematic uncertainties.

On 27 December 2004, a giant γ flare from the Soft Gamma-Ray Repeater 1806-20 saturated many satellite gamma-ray detectors, being the brightest transient event ever observed in the Galaxy. AMANDA-II was used to search for down-going muons indicative of high-energy gammas and/or neutrinos from this object. The data revealed no significant signal, so upper limits (at 90% C.L.) on the normalization constant were set: 0.05(0.5)  TeV^-1 m^-2 s^-1 for γ=-1.47 (-2) in the gamma flux and 0.4(6.1)  TeV^-1 m^-2 s^-1 for γ=-1.47 (-2) in the high-energy neutrino flux.

A recently developed standard-model extension (SME) formalism for neutrino oscillations that includes Lorentz and CPT violation is used to analyze the sidereal time variation of the neutrino event excess measured by the liquid scintillator neutrino detector (LSND) experiment. The LSND experiment, performed at Los Alamos National Laboratory, observed an excess, consistent with neutrino oscillations, of ν̅ _e in a beam of ν̅ _μ. It is determined that the LSND oscillation signal is consistent with no sidereal variation. However, there are several combinations of SME coefficients that describe the LSND data; both with and without sidereal variations. The scale of Lorentz and CPT violation extracted from the LSND data is of order 10^-19  GeV for the SME coefficients a_L and E×c_L. This solution for Lorentz and CPT violating neutrino oscillations may be tested by other short baseline neutrino oscillation experiments, such as the MiniBooNE experiment.

We observe a net beam excess of 8.7±6.3(stat)±2.4(syst) events, above 160 MeV, resulting from the charged-current reaction of ν_μ and/or ν̅ _μ on C and H in the LSND detector. No beam-related muon background is expected in this energy regime. Within an analysis framework of π⁰→ν_μν̅ _μ, we set a direct upper limit for this branching ratio of Γ(π⁰→ν_μν̅ _μ)/Γ(π⁰→all)<1.6×10^-6 at 90% confidence level.

Charged current scattering of ν_μ on ¹²C has been studied using a π⁺ decay-in-flight ν_μ beam at the Los Alamos Neutron Science Center. A sample of 66.9±9.1 events satisfying criteria for the exclusive reaction ¹²C(ν_μ,μ^-)¹²N_g.s. was obtained using a large liquid scintillator neutrino detector. The observed flux-averaged cross section (5.6±0.8±1.0)×10^-41 cm² agrees well with reliable theoretical expectations. A measurement was also obtained for the inclusive cross section to all accessible ¹²N states ¹²C(ν_μ,μ^-)X. This flux-averaged cross section is (10.6±0.3±1.8)×10^-40 cm² which is lower than present theoretical calculations.

Charged current reactions of ν_e on ¹²C have been studied using a μ⁺ decay-at-rest ν_e beam at the Los Alamos Neutron Science Center. The cross section for the exclusive reaction ¹²C(ν_e,e^-)¹²N_g.s. was measured to be (8.9±0.3±0.9)×10^-42 cm². The observed energy dependence of the cross section and angular distribution of the outgoing electron agree well with theoretical expectations. Measurements are also presented for inclusive transitions to ¹²N excited states, ¹²C(ν_e,e^-)¹²N^* and compared with theoretical expectations. The measured cross section, (4.3±0.4±0.6)×10^-42 cm², is somewhat lower than previous measurements and than a continuum random phase approximation calculation. It is in better agreement with a recent shell model calculation.

A search for ν̅ _μ→ν̅ _e oscillations was conducted by the Liquid Scintillator Neutrino Detector at the Los Alamos Neutron Science Center using ν̅ _μ from μ⁺ decay at rest. A total excess of 87.9±22.4±6.0 events consistent with ν̅ _ep→e⁺n scattering was observed above the expected background. This excess corresponds to an oscillation probability of (0.264±0.067±0.045)%, which is consistent with an earlier analysis. In conjunction with other known limits on neutrino oscillations, the LSND data suggest that neutrino oscillations occur in the 0.2–10 eV²/c⁴ Δm² range, indicating a neutrino mass greater than 0.4 eV/c².

The cross section for the elastic scattering reaction ν_e+e^-→ν_e+e^- was measured by the Liquid Scintillator Neutrino Detector using a μ⁺ decay-at-rest ν_e beam at the Los Alamos Neutron Science Center. The standard model of electroweak physics predicts a large destructive interference between the charge current and neutral current channels for this reaction. The measured cross section, σ_νee^-=[10.1±1.1(stat)±1.0(syst)]×E_νe (MeV)×10^-45 cm², agrees well with standard model expectations. The measured value of the interference parameter, I=-1.01±0.13(stat)±0.12(syst), is in good agreement with the standard model expectation of I^SM=-1.09. Limits are placed on neutrino flavor-changing neutral currents. An upper limit on the muon-neutrino magnetic moment of 6.8×10^-10μ_Bohr is obtained using the ν_μ and ν̅ _μ fluxes from π⁺ and μ⁺ decay.

A search for ν_μ→ν_e oscillations has been conducted at the Los Alamos Meson Physics Facility using ν_μ from π⁺ decay in flight. An excess in the number of beam-related events from the ν_e C→e^- X inclusive reaction is observed. The excess is too large to be explained by normal ν_e contamination in the beam at a confidence level greater than 99%. If interpreted as an oscillation signal, the observed oscillation probability of (2.6±1.0±0.5)×10^-3 is consistent with the previously reported ν̅ _μ→ν̅ _e oscillation evidence from LSND.

A search for ν_μ→ν_e oscillations has been conducted with the LSND apparatus using ν_μ from π⁺ decay in flight. Two analyses observe a total of 40 beam-on high-energy (60–200 MeV) electron events consistent with the ν_e C→e^- X inclusive reaction. This number is significantly above the 21.9±2.1 events expected from the ν_e contamination in the beam and the beam-off background. If interpreted as an oscillation signal, the observed oscillation probability of (2.6±1.0±0.5)×10^-3 is consistent with the previously reported ν̅ _μ→ν̅ _e oscillation evidence from LSND.

Charged current scattering of ν_μ on ¹²C has been studied using a π⁺ decay-in-flight ν_μ beam at the Los Alamos Meson Physics Facility. A sample of 56.8 ±9.6 events satisfying criteria for the exclusive reaction ¹²C(ν_μ,μ^-)¹²N_g.s. was obtained using a large liquid scintillator neutrino detector. The observed flux-averaged cross section (6.6±1.0±1.0)×10^-41 cm² agrees well with reliable theoretical expectations. A measurement was also obtained for the inclusive cross section to all accessible ¹²N states ¹²C(ν_μ,μ^-)X. This flux-averaged cross section is (11.2±0.3±1.8)×10^-40 cm², which is approximately half of that given by a recent continuum random-phase approximation calculation.

Charged current reactions of ν_e on ¹²C have been studied using a μ⁺ decay-at-rest ν_e beam from the Los Alamos Meson Physics Facility. More than 500 events from the exclusive reaction ¹²C(ν_e,e^-)¹²N_g.s. were measured in a large Liquid Scintillator Neutrino Detector (LSND). The observed energy dependence of the cross section and the angular distribution of the outgoing electron agree well with theoretical expectations. Measurements are also presented for inclusive transitions to ¹²N excited states, ¹²C(ν_e,e^-)¹²N^* and compared with theoretical expectations. Results are consistent with a recent continuum random phase approximation (CRPA) calculation.

A search for ν¯_μ→ν¯_e oscillations has been conducted at the Los Alamos Meson Physics Facility using ν¯_μ from μ⁺ decay at rest. The ν¯_e are detected via the reaction ν¯_ep→e⁺n, correlated with the 2.2 MeV γ from np→dγ. The use of tight cuts to identify e⁺ events with correlated γ rays yields 22 events with e⁺ energy between 36 and 60 MeV and only 4.6±0.6 background events. The probability that this excess is due entirely to a statistical fluctuation is 4.1×10^-8. A χ² fit to the entire e⁺ sample results in a total excess of 51.0_-19.5^+20.2±8.0 events with e⁺ energy between 20 and 60 MeV. If attributed to ν¯_μ→ν¯_e oscillations, this corresponds to an oscillation probability (averaged over the experimental energy and spatial acceptance) of (0.31±0.12±0.05)%. © 1996 The American Physical Society.

A search for ν̅ _μ→ν̅ _e oscillations has been conducted at the Los Alamos Meson Physics Facility by using ν̅ _μ from μ⁺ decay at rest. The ν̅ _e are detected via the reaction ν̅ _e p→e⁺ n, correlated with a γ from np→dγ ( 2.2 MeV). The use of tight cuts to identify e⁺ events with correlated γ rays yields 22 events with e⁺ energy between 36 and 60 MeV and only 4.6±0.6 background events. A fit to the e⁺ events between 20 and 60 MeV yields a total excess of 51.0_-19.5^+20.2±8.0 events. If attributed to ν̅ _μ→ν̅ _e oscillations, this corresponds to an oscillation probability of ( 0.31±0.12±0.05)%.

Cross-section excitation-energy spectra and angular distributions were measured for the ²H(p,n)2p reaction at 135 MeV in 6° steps from 0° to 30° (laboratory), using the beam swinger facility at the Indiana University Cyclotron Facility. The target was a 12.8 mg/cm² foil of CD₂. Neutron energies were measured by the time-of-flight method using large-volume plastic scintillator arrays at flight paths of 91 m. The overall energy resolution was 260 keV. The 0° spectrum is dominated by a large peak near 0 MeV of relative energy in the final 2p system; this peak corresponds to the two protons in the ¹S₀ state. The wider-angle spectra are dominated by a broad peak centered at 10 to 20 MeV of excitation which is the quasifree scattering peak. The spectra are compared with impulse approximation and three-body Faddeev calculations. © 1996 The American Physical Society.

We report observations from the (p,n) reaction on ¹²C at 135 MeV. The experiment was performed with the beam-swinger neutron time-of-flight system at the Indiana University Cyclotron Facility. Neutrons were detected in large-volume plastic scintillation detectors located in three detector stations at 0°, 24°, and 45° with respect to the undeflected beam line; the flight paths were 91 m, 91 m, and 74 m, respectively. Overall time resolutions of about 825 ps provided energy resolutions of about 350 keV in the first two stations and about 425 keV in the third station. The angular distributions for states with excitation energies up to 10 MeV are presented and comparisons are made with DWIA calculations that use one-body density matrices from 0ħω and 1ħω shell-model calculations. New information is deduced on the excitation energies, widths, and spin-parity assignments for several energy levels of ¹²N. © 1996 The American Physical Society.

A search for ν̅ _e's in excess of the number expected from conventional sources has been made using the Liquid Scintillator Neutrino Detector, located 30 m behind the Los Alamos Meson Physics Facility beam stop. The ν̅ _e are detected via ν̅ _e p→e⁺ n with e⁺ energy between 36 and 60 MeV, followed by a γ ray from np→dγ ( 2.2 MeV). Using strict cuts to identify γ rays correlated with e⁺ yields 9 events with only 2.1±0.3 background expected. A likelihood fit to the entire e⁺ sample results in a total excess of 16.4_-8.9^+9.7±3.3 events. If attributed to ν̅ _μ→ν̅ _e oscillations, this corresponds to an oscillation probability of ( 0.34_-0.18^+0.20±0.07)%.

Pion-induced double charge exchange (π⁺,π^-) on ^76,78,80,82Se, leading to the double isobaric analog states (DIAS) and the ground states of ^76,78,80,82Kr, has been studied at a laboratory angle of 5⁰ and incident pion kinetic energy of 293.2 MeV. Cross sections for these transitions have been extracted, and those for the DIAS are compared to two simple models of pion double charge exchange.

The reaction ¹²C(ν_μ,μ^-)X has been measured near threshold using a π⁺ decay-in-flight ν_μ beam from the Los Alamos Meson Physics Facility and a massive liquid scintillator neutrino detector (LSND). In the energy region 123.7<E_ν<280 MeV, the measured spectral shape is consistent with that expected from the Fermi-gas model (FGM). However, the measured flux-averaged inclusive cross section {[8.3±0.7(stat)±1.6(syst)]×10^-40 cm²} is more than a factor of 2 lower than that predicted by the Fermi-gas model and by a recent random phase approximation calculation.

Measurements of the differential cross section for the ¹⁶O(p,n)¹⁶F and ¹⁸O(p,n)¹⁸F reactions are made at θ_lab= 0°, 1°, 2°, 3°, 4°, 6°, and 8° with a bombardment energy of 494 MeV. Multipole decomposition methods based on the measured angular distributions are used to extract ΔL=0, ΔL=1, and ΔL=2 contributions to the cross sections. The summed Gamow-Teller strength B(GT) is computed for the excitation energy region 0–30 MeV in ¹⁶F, and 0–12.5 MeV in ¹⁸F. Difficulties with the decomposition methods are discussed.

A 20-ton neutrino detector located near the Los Alamos Meson Physics Facility beam stop is used search for ν̅ _e generated via neutrino oscillations from any of the three neutrino types, ν_μ, ν̅ _μ, and ν_e, which radiate from the beam stop. The analysis of three years of data provides limits on the oscillation modes ν̅ _μ→ν̅ _e, ν_e→ν̅ _e, and ν_μ→ν̅ _e, and the lepton-number-violating decay process μ⁺→e⁺+ν̅ _e+ν_μ. The 90%-confidence-level limits for ν̅ _μ→ν̅ _e oscillations are δm²≤0.14 eV² for maximal mixing, and sin²2θ≤0.024 for large δm².

Measurements were made of pion double charge exchange on ^128,130Te at θ_lab=5° and T_π=292 MeV. Observations were made of the double isobaric analog, the giant dipole resonance built upon the isobaric analog, and the giant dipole resonance built upon itself. Cross sections for these states were found and compared with all previously known cross sections at T_π=292 MeV, and new mass dependences were fitted to these data. A new state below the double isobaric analog state in ¹²⁸Te was observed and its cross section and width were determined.