Parameters of scalar resonances from the combined analysis of data on processes ππ→ππ,KKˉ,ηη\pi\pi\to\pi\pi,K\bar{K},\eta\eta and J/ψJ/\psi decays

A combined analysis of data on isoscalar S-wave processes $\pi\pi\to\pi\pi,K\overline{K},\eta\eta$ and on decays $J/\psi\to\phi\pi\pi,\phi K\overline{K}$ from the DM2, Mark III and BESIII collaborations is performed to study $f_0$ mesons. The method of analysis is based on analyticity and unitarity and uses an uniformization procedure. In the analysis limited only to the multi-channel $\pi\pi$-scattering data, two possible sets of parameters of the $f_0(500)$ were found: in both cases the mass was about 700 MeV but the total width was either about 600 or 930 MeV. The extension of the analysis using only the DM2 and Mark III data on the $J/\psi$ decays does not allow to choose between these sets. However, the data from BESIII on the di-pion mass distribution in the decay $J/\psi\to\phi\pi^+\pi^-$ clearly prefers the wider $f_0(500)$ state. Spectroscopic implications from results of the analysis are also discussed.Comment: the formalism is also described (text overlap) in arXiv:1108.3725; new extended analysis of data; revised PRD versio

The interstellar oxygen-K absorption edge as observed by XMM-Newton

High resolution X-ray spectra of the Reflection Grating Spectrometer (RGS) on board the XMM satellite are used to resolve the oxygen K absorption edge. By combining spectra of low and high extinction sources, the observed absorption edge can be split in the true interstellar (ISM) extinction and the instrumental absorption. The detailed ISM edge structure closely follows the edge structure of neutral oxygen as derived by theoretical R-matrix calculations. However, the position of the theoretical edge requires a wavelength shift. In addition the detailed instrumental RGS absorption edge structure is presented. All results are verified by comparing to a subset of Chandra LETG-HRC observations.Comment: LaTeX2e A&A style, 10 pages, 12 postscript figures, accepted for publication in Astronomy and Astrophysic

Physical Properties of Complex C Halo Clouds

Observations from the Galactic Arecibo L-Band Feed Array HI (GALFA-HI) Survey of the tail of Complex C are presented and the halo clouds associated with this complex cataloged. The properties of the Complex C clouds are compared to clouds cataloged at the tail of the Magellanic Stream to provide insight into the origin and destruction mechanism of Complex C. Magellanic Stream and Complex C clouds show similarities in their mass distributions (slope = -0.7 and -0.6, respectively) and have a common linewidth of 20 - 30 km/s (indicative of a warm component), which may indicate a common origin and/or physical process breaking down the clouds. The clouds cataloged at the tail of Complex C extend over a mass range of 10^1.1 to 10^4.8 solar masses, sizes of 10^1.2 to 10^2.6 pc, and have a median volume density of 0.065 cm^(-3) and median pressure of (P/k) = 580 K cm^{-3}. We do not see a prominent two-phase structure in Complex C, possibly due to its low metallicity and inefficient cooling compared to other halo clouds. From assuming the Complex C clouds are in pressure equilibrium with a hot halo medium, we find a median halo density of 5.8 x 10^(-4) cm^(-3), which given a constant distance of 10 kpc, is at a z-height of ~3 kpc. Using the same argument for the Stream results in a median halo density of 8.4 x 10^(-5) x (60kpc/d) cm^(-3). These densities are consistent with previous observational constraints and cosmological simulations. We also assess the derived cloud and halo properties with three dimensional grid simulations of halo HI clouds and find the temperature is generally consistent within a factor of 1.5 and the volume densities, pressures and halo densities are consistent within a factor of 3.Comment: Accepted for publication in AJ. 54 pages, including 6 tables and 16 figure

Extended HI Rotation Curve and Mass Distribution of M31

New HI observations of Messier 31 (M31) obtained with the Effelsberg and Green Bank 100-m telescopes make it possible to measure the rotation curve of that galaxy out to ~35 kpc. Between 20 and 35 kpc, the rotation curve is nearly flat at a velocity of ~226 km/s. A model of the mass distribution shows that at the last observed velocity point, the minimum dark-to-luminous mass ratio is \~0.5 for a total mass of 3.4 10^11 Msol at R < 35 kpc. This can be compared to the estimated MW mass of 4.9 10^11 Msol for R < 50 kpc.Comment: 4 pages, 2 figures, accepted for publication in ApJ Letter

A High Galactic Latitude HI 21cm-line Absorption Survey using the GMRT: I. Observations and Spectra

We have used the Giant Meterwave Radio Telescope (GMRT) to measure the Galactic HI 21-cm line absorption towards 102 extragalactic radio continuum sources, located at high (|b| >15deg.) Galactic latitudes. The Declination coverage of the present survey is Decl. ~ -45deg.. With a mean rms optical depth of ~0.003, this is the most sensitive Galactic HI 21-cm line absorption survey to date. To supplement the absorption data, we have extracted the HI 21-cm line emission profiles towards these 102 lines of sight from the Leiden Dwingeloo Survey of Galactic neutral hydrogen. We have carried out a Gaussian fitting analysis to identify the discrete absorption and emission components in these profiles. In this paper, we present the spectra and the components. A subsequent paper will discuss the interpretation of these results.Comment: 46 pages, Accepted for publication in Journal of Astrophysics & Astronom

A Very Sensitive 21cm Survey for Galactic High-Velocity HI

Very sensitive HI 21cm observations have been made in 860 directions at dec >= -43deg in search of weak, Galactic, high-velocity HI emission lines at moderate and high Galactic latitudes. One-third of the observations were made toward extragalactic objects. The median 4-sigma detection level is NHI = 8x10^{17} cm^-2 over the 21' telescope beam. High-velocity HI emission is detected in 37% of the directions; about half of the lines could not have been seen in previous surveys. The median FWHM of detected lines is 30.3 km/s. High- velocity HI lines are seen down to the sensitivity limit of the survey implying that there are likely lines at still lower values of NHI. The weakest lines have a kinematics and distribution on the sky similar to that of the strong lines, and thus do not appear to be a new population. Most of the emission originates from objects which are extended over several degrees; few appear to be compact sources. At least 75%, and possibly as many as 90%, of the lines are associated with one of the major high-velocity complexes. The Magellanic Stream extends at least 10 deg to higher Galactic latitude than previously thought and is more extended in longitude as well. Although there are many lines with low column density, their numbers do not increase as rapidly as NHI^-1, so most of the HI mass in the high-velocity cloud phenomenon likely resides in the more prominent clouds. The bright HI features may be mere clumps within larger structures, and not independent objects.Comment: 88 pages includes 22 figures Accepted for Publication in ApJ Suppl. June 200

Learning object relationships which determine the outcome of actions

Peer reviewedPublisher PD

On the size of the sigma meson and its nature

In this work the nature of the \sigma or f_0(600) resonance is discussed by evaluating its quadratic scalar radius, \la r^2\ra_s^\sigma. This allows one to have a quantitative estimate for the size of this resonance. We obtain that the \sigma resonance is a compact object with \la r^2\ra_s^\sigma=(0.19\pm0.02)-i(0.06\pm0.02) fm^2. Within our approach, employing unitary chiral perturbation theory, the \sigma is a dynamically generated resonance that stems from the pion-pion interactions. Given its small size we conclude that the two pions inside the resonance are merged. A four-quark picture is then more appropriate. However, when the pion mass increases, for pion masses somewhat above 400 MeV, the picture of a two-pion molecule is the appropriate one. The \sigma is then a spread \pi\pi bound state. These results are connected with other recent works that support a non standard nature of the \sigma as well, while fulfilling strong QCD constraints, as well as with lattice QCD. We offer a detailed study of the low-energy S-wave \pi\pi scattering data from where we extract our values for the threshold parameters of S-wave \pi\pi phase shifts, the {\cal O}(p^4) chiral perturbation theory low energy constants as well as the \sigma pole position. From the comparison with other accurate determinations in the literature we obtain the average values for the isospin 0 S-wave \pi\pi threshold parameters, $a_0^0=0.220\pm0.003$, $b_0^0=0.279\pm 0.003 M_\pi^{-2}$, and for the real and imaginary parts of the \sigma pole position in \sqrt{s}, $458\pm14-i(261\pm17)$ MeV. The quark mass dependence of the size of the \sigma, its mass and width are considered too. The latter agree accurately with a previous lattice QCD calculation. The fact that the mass of this resonance tends to follow the threshold of two pions is a clear indication that the \sigma is a dynamically generated meson-meson resonance.Comment: 31 pages, 21 figure