119228766
Constraints on cosmological dark matter annihilation from the Fermi-LAT isotropic diffuse gamma-ray measurement
The first published Fermi large area telescope (Fermi-LAT) measurement of the isotropic diffuse gamma-ray emission is in good agreement with a single power law, and is not showing any signature of a dominant contribution from dark matter sources in the energy range from 20 to 100 GeV. We use the absolute size and spectral shape of this measured flux to derive cross section limits on three types of generic dark matter candidates: annihilating into quarks, charged leptons and monochromatic photons. Predicted gamma-ray fluxes from annihilating dark matter are strongly affected by the underlying distribution of dark matter, and by using different available results of matter structure formation we assess these uncertainties. We also quantify how the dark matter constraints depend on the assumed conventional backgrounds and on the Universe's transparency to high-energy gamma-rays. In reasonable background and dark matter structure scenarios (but not in all scenarios we consider) it is possible to exclude models proposed to explain the excess of electrons and positrons measured by the Fermi-LAT and PAMELA experiments. Derived limits also start to probe cross sections expected from thermally produced relics (e.g. in minimal supersymmetry models) annihilating predominantly into quarks. For the monochromatic gamma-ray signature, the current measurement constrains only dark matter scenarios with very strong signals.
118693667
Gamma ray observations of the orion molecular clouds with the fermi large area telescope
We report on the gamma-ray observations of giant molecular clouds Orion A and B with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The gamma-ray emission in the energy band between ∼100 MeV and ∼100 GeV is predicted to trace the gas mass distribution in the clouds through nuclear interactions between the Galactic cosmic rays (CRs) and interstellar gas. The gamma-ray production cross-section for the nuclear interaction is known to ∼10% precision which makes the LAT a powerful tool to measure the gas mass column density distribution of molecular clouds for a known CR intensity. We present here such distributions for Orion A and B, and correlate them with those of the velocity-integrated CO intensity (WCO) at a 1◦ × 1◦ pixel level. The correlation is found to be linear over a WCO range of ∼10-fold when divided in three regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The WCO-to-mass conversion factor, XCO, is found to be ∼2.3 × 1020 cm−2 (K km s−1)−1 for the high-longitude part of Orion A (l > 212◦), ∼1.7 times higher than ∼1.3 × 1020 found for the rest of Orion A and B. We interpret the apparent high XCO in the high-longitude region of Orion A in the light of recent works proposing a nonlinear relation between H2 and CO densities in the diffuse molecular gas. WCO decreases faster than the H2 column density in the region making the gas "darker" to WCO.
118924226
Analysis Methods for Milky Way Dark Matter Satellite Detection
The Gamma Ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) Dark Matter and New Physics Working group has been developing approaches for the indirect detection of in situ annihilation of dark matter. Our work has assumed that a significant component of dark matter is a new type of Weakly Interacting Massive Particle (WIMP) in the 100GeV mass range. The annihilation of two WIMPs results in the production of a large number of high energy gamma rays (>1GeV) that can be well measured by the GLAST LAT. The cold dark matter model implies a significant number of as yet unobserved dark matter satellites in our galaxy. The spectra of these galactic satellites are considerably harder than most, if not all, astrophysical sources, have an endpoint at the mass of the WIMP, and are not power laws. We describe a preliminary feasibility study for the indirect detection of dark matter satellites in the Milky Way using the GLAST LAT.
119304648
RADIO AND γ-RAY CONSTRAINTS ON THE EMISSION GEOMETRY AND BIRTHPLACE OF PSR J2043+2740
We report on the first year of Fermi gamma-ray observations of pulsed high-energy emission from the old PSR J2043+2740. The study of the gamma-ray efficiency of such old pulsars gives us an insight into the evolution of pulsars' ability to emit in gammma rays as they age. The gamma-ray lightcurve of this pulsar above 0.1 GeV is clearly defined by two sharp peaks, 0.353+/-0.035 periods apart. We have combined the gamma-ray profile characteristics of PSR J2043+2740 with the geometrical properties of the pulsar's radio emission, derived from radio polarization data, and constrained the pulsar-beam geometry in the framework of a Two Pole Caustic and an Outer Gap model. The ranges of magnetic inclination and viewing angle were determined to be {alpha,zeta}~{52-57,61-68} for the Two Pole Caustic model, and {alpha,zeta}~{62-73,74-81} and {alpha,zeta}~{72-83,60-75} for the Outer Gap model. Based on this geometry, we assess possible birth locations for this pulsar and derive a likely proper motion, sufficiently high to be measurable with VLBI. At a characteristic age of 1.2 Myr, PSR J2043+2740 is the third oldest of all discovered, non-recycled, gamma-ray pulsars: it is twice as old as the next oldest, PSR J0357+32, and younger only than the recently discovered PSR J1836+5925 and PSR J2055+25, both of which are at least 5 and 10 times less energetic, respectively.
47886823
Fermi-LAT Study of Gamma-ray Emission in the Direction of Supernova Remnant W49B
We present an analysis of the gamma-ray data obtained with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the direction of SNR W49B (G43.3-0.2). A bright unresolved gamma-ray source detected at a significance of 38 sigma is found to coincide with SNR W49B. The energy spectrum in the 0.2-200 GeV range gradually steepens toward high energies. The luminosity is estimated to be 1.5x10^{36} (D/8 kpc)^2 erg s^-1 in this energy range. There is no indication that the gamma-ray emission comes from a pulsar. Assuming that the SNR shell is the site of gamma-ray production, the observed spectrum can be explained either by the decay of neutral pi mesons produced through the proton-proton collisions or by electron bremsstrahlung. The calculated energy density of relativistic particles responsible for the LAT flux is estimated to be remarkably large, U_{e,p}>10^4 eV cm^-3, for either gamma-ray production mechanism.
27791621
The radio/gamma-ray connection in active galactic nuclei in the era of the Fermi large area telescope
We present a detailed statistical analysis of the correlation between radio and gamma-ray emission of the active galactic nuclei (AGNs) detected by Fermi during its first year of operation, with the largest data sets ever used for this purpose. We use both archival interferometric 8.4 GHz data (from the Very Large Array and ATCA, for the full sample of 599 sources) and concurrent single-dish 15 GHz measurements from the Owens Valley Radio Observatory (OVRO, for a sub sample of 199 objects). Our unprecedentedly large sample permits us to assess with high accuracy the statistical significance of the correlation, using a surrogate data method designed to simultaneously account for common-distance bias and the effect of a limited dynamical range in the observed quantities. We find that the statistical significance of a positive correlation between the centimeter radio and the broadband (E > 100 MeV) gamma-ray energy flux is very high for the whole AGN sample, with a probability of < 10(-7) for the correlation appearing by chance. Using the OVRO data, we find that concurrent data improve the significance of the correlation from 1.6 x 10(-6) to 9.0 x 10(-8). Our large sample size allows us to study the dependence of correlation strength and significance on specific source types and gamma-ray energy band. We find that the correlation is very significant (chance probability < 10(-7)) for both flat spectrum radio quasars and BL Lac objects separately; a dependence of the correlation strength on the considered gamma-ray energy band is also present, but additional data will be necessary to constrain its significance.
2306101
Phase transition from hadronic matter to quark matter
We study the phase transition from two-flavor nuclear matter to quark matter. A mean field model, constructed at the quark level, is used to give the equation of state for nuclear matter, while the equation of state for color superconducting quark matter is calculated within the NJL model. It is found that at low temperature, the phase transition from nuclear to color superconducting quark matter will take place when the density is of order 2.5{rho}{sub 0}-5{rho}{sub 0}. At zero density, the quark phase will appear when the temperature is larger than about 148 MeV. Within the mean field treatment, the phase transition from nuclear matter to quark matter is always first order, whereas the transition between color superconducting quark matter and normal quark matter is second order.
210003711
Search for $B^{0}$ decays to invisible final states
We report a search for $B^{0}$ decays into invisible final states using a data sample of $657 \times 10^{6}$ $B\bar{B}$ pairs collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^{+}e^{-}$ collider. The signal is identified by fully reconstructing a hadronic decay of the accompanying $B$ meson and requiring no other particles in the event. No significant signal is observed, and we obtain an upper limit of $1.3 \times 10^{-4}$ at the 90% confidence level for the branching fraction of invisible $B^{0}$ decay.
125575431
Measurement of the branching ratios for J / psi --> gamma pi0, gamma eta, gamma eta' --> 3gamma on the BES
124550490
Study of $J/ψ → ωp\overline{p}$ at BESIII
124682883
A geometric factor calculation method based on the isotropic flux assumption
One of the instruments onboard the China Seismic Electromagnetic Satellite (CSES) is the Low Energy Particle Detector (LEPD). The primary objective of LEPD is to provide measurements of the fluxes, energy spectra and pitch angles of 100 keV to 10 MeV electrons and protons from 2 to 50 MeV in the Earth's magnetosphere. The geometric factor is one of the principle parameters of a detector, which converts the physical quantity count rate to the particle quantity-flux. In this paper, we calculated the geometric factor of LEPD via computer modeling of an isotropic radiation environment. It was first demonstrated that the radiation intensity related should obey a cosine-law, then a general sampling method of generating this distribution via CPS of GEANT4 was explained. Furthermore, combined with flux normalization, a comparison of the geometric factor calculation of a set of 2-layer detectors with different shapes (cylinder, truncated cone and rectangle) was performed. Results show a generally good agreement between simulation and analytical calculations for the cylinder and truncated cone detectors, and the result of the rectangular one, for which there is no accurate analytical formula, is consistent with the previous simulated results by others. As a practical instance of the 2-layer rectangle detector, the geometric factor of LEPD is 10.336 +/- 0.036 cm(2).sr for 10 MeV proton and 8.211 +/- 0.032 cm(2).sr for 8 MeV electron.