Charm Meson Mixing: An Experimental Review

We review current experimental results on charm mixing and CP violation. We survey experimental techniques, including time-dependent, time-independent, and quantum-correlated measurements. We review techniques that use a slow pion tag from D*+ --> pi+ D0 + c.c. decays and those that do not, and cover two-body and multi-body D0 decay modes. We provide a summary of D-mixing results to date and comment on future experimental prospects at the LHC and other new or planned facilities.Comment: 53 pages, 29 figures, 8 table

G28.17+0.05: An unusual giant HI cloud in the inner Galaxy

New 21 cm HI observations have revealed a giant HI cloud in the Galactic plane that has unusual properties. It is quite well defined, about 150 pc in diameter at a distance of 5 kpc, and contains as much as 100,000 Solar Masses of atomic hydrogen. The outer parts of the cloud appear in HI emission above the HI background, while the central regions show HI self-absorption. Models which reproduce the observations have a core with a temperature <40 K and an outer envelope as much as an order of magnitude hotter. The cold core is elongated along the Galactic plane, whereas the overall outline of the cloud is approximately spherical. The warm and cold parts of the HI cloud have a similar, and relatively large, line width of approximately 7 km/s. The cloud core is a source of weak, anomalously-excited 1720 MHz OH emission, also with a relatively large line width, which delineates the region of HI self-absorption but is slightly blue-shifted in velocity. The intensity of the 1720 MHz OH emission is correlated with N(H) derived from models of the cold core. There is 12CO emission associated with the cloud core. Most of the cloud mass is in molecules, and the total mass is > 200,000 Solar Masses. In the cold core the HI mass fraction may be 10 percent. The cloud has only a few sites of current star formation. There may be about 100 more objects like this in the inner Galaxy; every line of sight through the Galactic plane within 50 degrees of the Galactic center probably intersects at least one. We suggest that G28.17+0.05 is a cloud being observed as it enters a spiral arm and that it is in the transition from the atomic to the molecular state.Comment: 35 pages, inludes 12 figure

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

On the structure of the scalar mesons f0(975)f_0(975) and a0(980)a_0(980)

We investigate the structure of the scalar mesons $f_0(975)$ and $a_0(980)$ within realistic meson-exchange models of the $\pi\pi$ and $\pi\eta$ interactions. Starting from a modified version of the J\"ulich model for $\pi\pi$ scattering we perform an analysis of the pole structure of the resulting scattering amplitude and find, in contrast to existing models, a somewhat large mass for the $f_0(975)$ ($m_{f_0}=1015$ MeV, $\Gamma_{f_0}=30$ MeV). It is shown that our model provides a description of $J/\psi\rightarrow\phi\pi\pi/\phi KK$ data comparable in quality with those of alternative models. Furthermore, the formalism developed for the $\pi\pi$ system is consistently extended to the $\pi\eta$ interaction leading to a description of the $a_0(980)$ as a dynamically generated threshold effect (which is therefore neither a conventional $q\overline{q}$ state nor a $K\overline{K}$ bound state). Exploring the corresponding pole position the $a_0(980)$ is found to be rather broad ($m_{a_0}=991$ MeV, $\Gamma_{a_0}=202$ MeV). The experimentally observed smaller width results from the influence of the nearby $K\overline{K}$ threshold on this pole.Comment: 25 pages, 15 Postscript figure

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

Carbon Recombination Lines from the Galactic Plane at 34.5 & 328 MHz

We present results of a search for carbon recombination lines in the Galaxy at 34.5 MHz (C$575\alpha$) made using the dipole array at Gauribidanur near Bangalore. Observations made towards 32 directions, led to detections of lines in absorption at nine positions. Followup observations at 328 MHz (C$272\alpha$) using the Ooty Radio Telescope detected these lines in emission. A VLA D-array observation of one of the positions at 330 MHz yielded no detection implying a lower limit of 10' for the angular size of the line forming region. The longitude-velocity distribution of the observed carbon lines indicate that the line forming region are located mainly between 4 kpc and 7 kpc from the Galactic centre. Combining our results with published carbon recombination line data near 76 MHz (\nocite{erickson:95} Erickson \et 1995) we obtain constraints on the physical parameters of the line forming regions. We find that if the angular size of the line forming regions is $\ge 4^{\circ}$, then the range of parameters that fit the data are: \Te $= 20-40$ K, \ne $\sim 0.1-0.3$ \cm3 and pathlengths $\sim 0.07-0.9$ pc which may correspond to thin photo-dissociated regions around molecular clouds. On the other hand, if the line forming regions are $\sim 2^{\circ}$ in extent, then warmer gas (\Te $\sim 60-300$ K) with lower electron densities (\ne $\sim 0.03-0.05$ \cm3) extending over several tens of parsecs along the line of sight and possibly associated with atomic \HI gas can fit the data. Based on the range of derived parameters, we suggest that the carbon line regions are most likely associated with photo-dissociation regions.Comment: To appear in Journal of Astrophysics & Astronomy, March 200

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