119390534
Use of W-boson longitudinal-transverse interferencein top quark spin-correlation functions
Abstract.Most of this paper consists of the derivation of general beam-referenced stage-two spin-correlation functions for the analysis of top-antitop pair production at the Tevatron, at the Large Hadron Collider, and/or at an International Linear Collider. However, for the charged-lepton plus jets reaction $q \bar{q} \rightarrow t \bar{t} \rightarrow (W^ + b) (W^- \bar{b} ) \rightarrow (l^{ + } \nu b ) (W^- \bar{b} )$, there is a simple three-angle spin-correlation function for the determination of the relative sign of or for the measurement of a possible non-trivial phase between the two dominant λb=-1/2 helicity amplitudes for the t → W+b decay mode. For the CP-conjugate case, there is an analogous function and tests for $\bar{t} \rightarrow W^{-} \bar{b}$ decay. These results make use of W-boson longitudinal-transverse interference.
73531680
Diffractive vector meson cross sections from BK evolution with impact parameter
The solution of the Balitsky-Kovchegov evolution equation with impact parameter dependence is used to compute cross sections for J/Ψ, ρ and φ vector meson production. These calculations are then compared with data from HERA and good agreement is found for the J/Ψ and φ mesons while the ρ has a low normalization. The phenomenological corrections needed to bring the calculations into agreement with the data are discussed. The work presented here may be found in the publication [1].
118876778
Use of W-boson longitudinal–transverse interference in top quark spin-correlation functions: II
This continuation of the derivation of general beam-referenced stage-two spin-correlation functions is for the analysis of top–antitop pair-production at the Tevatron and at the Large Hadron Collider. Both the gluon-production and the quark-production contributions are included for the charged-lepton-plus-jets reaction pp or $p\bar{p}\rightarrow t\bar{t}\rightarrow(W^+b)(W^-\bar{b})\rightarrow(l^+\nu b)(W^-\bar{b})$. There is a simple 4-angle beam-referenced spin-correlation function for determination of the relative sign of or for measurement of a possible non-trivial phase between the two dominant $\lambda_b=-1/2$ helicity amplitudes for the $t\rightarrow W^+b$ decay mode. There is an analogous function and tests for $\bar{t}\rightarrow W^-\bar{b}$ decay. This signature requires use of the $(t\bar{t})_{\text{c.m.}}$ energy of the hadronically decaying W-boson, or the kinematically equivalent cosine of the polar angle of $W^\mp$ emission in the antitop (top) decay frame. Spinors and their outer-products are constructed so that the helicity-amplitude phase convention of Jacob and Wick can be used throughout for the fixing of the signs associated with this large W-boson longitudinal–transverse interference effect.
122779026
NONLINEAR EVOLUTION AT SMALL x WITH IMPACT PARAMETER DEPENDENCE
Nonlinear evolution at small x was evaluated numerically with full dependence on impact parameter using the BK equation. several distinct behaviors were found and are presented for the leading logarithmic kernel in the BK evolution equation with both fixed and running coupling. The value of the saturation scale at various dipole sizes was found to agree with analytic expectations. Calculation of the F2 structure function from the numerical solution of the evolution with running coupling were then compared to the HERA data and qualitative agreement found. The agreement is improved with inclusion of soft contributions and these are discussed.
119217412
System overview of the VLTI Spectro-Imager
The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 night and with a maximum angular resolution of 1 milliarcsecond, making best use of the Very Large Telescope Interferometer capabilities. To fulfill the scientific goals (see Garcia et. al.), the system requirements are: a) combining 4 to 6 beams; b) working in spectral bands J, H and K; c) spectral resolution from R= 100 to 12000; and d) internal fringe tracking on-axis, or off-axis when associated to the PRIMA dual-beam facility. The concept of VSI consists on 6 sub-systems: a common path distributing the light between the fringe tracker and the scientific instrument, the fringe tracker ensuring the co-phasing of the array, the scientific instrument delivering the interferometric observables and a calibration tool providing sources for internal alignment and interferometric calibrations. The two remaining sub-systems are the control system and the observation support software dedicated to the reduction of the interferometric data. This paper presents the global concept of VSI science path including the common path, the scientific instrument and the calibration tool. The scientific combination using a set of integrated optics multi-way beam combiners to provide high-stability visibility and closure phase measurements are also described. Finally we will address the performance budget of the global VSI instrument. The fringe tracker and scientific spectrograph will be shortly described.
17402120
FIRST VISUAL ORBIT FOR THE PROTOTYPICAL COLLIDING-WIND BINARY WR 140
Wolf-Rayet (WR) stars represent one of the final stages of massive stellar evolution. Relatively little is known about this short-lived phase and we currently lack reliable mass, distance, and binarity determinations for a representative sample. Here we report the first visual orbit for WR 140 (= HD193793), a WC7+O5 binary system known for its periodic dust production episodes triggered by intense colliding winds near periastron passage. The Infrared-Optical Telescope Array and Center for High Angular Resolution Astronomy interferometers resolved the pair of stars in each year from 2003 to 2009, covering most of the highly eccentric, 7.9 year orbit. Combining our results with the recently improved double-line spectroscopic orbit of Fahed et al., we find the WR 140 system is located at a distance of 1.67 ± 0.03 kpc, composed of a WR star with M WR = 14.9 ± 0.5 M_☉ and an O star with M O = 35.9 ± 1.3 M_☉. Our precision orbit yields key parameters with uncertainties ~6× smaller than previous work and paves the way for detailed modeling of the system. Our newly measured flux ratios at the near-infrared H and Ks bands allow a spectral energy distribution decomposition and analysis of the component evolutionary states.
39932805
Hot circumstellar material resolved around β Pic with VLTI/PIONIER
Aims. We aim at resolving the circumstellar environment around β Pic in the near-infrared in order to study the inner planetary system (<200 mas, i.e., ~4 AU). 
 
Methods. Precise interferometric fringe visibility measurements were obtained over seven spectral channels dispersed across the H band with the four-telescope VLTI/PIONIER interferometer. Thorough analysis of interferometric data was performed to measure the stellar angular diameter and to search for circumstellar material. 
 
Results. We detected near-infrared circumstellar emission around β Pic that accounts for 1.37% ± 0.16% of the near-infrared stellar flux and that is located within the field-of-view of PIONIER (i.e., ~200 mas in radius). The flux ratio between this excess and the photosphere emission is shown to be stable over a period of 1 year and to vary only weakly across the H band, suggesting that the source is either very hot (≳1500 K) or dominated by the scattering of the stellar flux. In addition, we derive the limb-darkened angular diameter of β Pic with an unprecedented accuracy (θ_LD= 0.736 ± 0.019 mas). 
 
Conclusions. The presence of a small H-band excess originating in the vicinity of β Pic is revealed for the first time thanks to the high-precision visibilities enabled by VLTI/PIONIER. This excess emission is likely due to the scattering of stellar light by circumstellar dust and/or the thermal emission from a yet unknown population of hot dust, although hot gas emitting in the continuum cannot be firmly excluded.
118593802
Imaging the spotty surface of Betelgeuse in the H band
Aims. This paper reports on H-band interferometric observations of Betelgeuse made at the three-telescope interferometer IOTA. We image Betelgeuse and its asymmetries to understand the spatial variation of the photosphere, including its diameter, limb darkening, effective temperature, surrounding brightness, and bright (or dark) star spots. Methods. We used different theoretical simulations of the photosphere and dusty environment to model the visibility data. We made images with parametric modeling and two image reconstruction algorithms: MIRA and WISARD. Results. We measure an average limb-darkened diameter of 44.28 ± 0.15 mas with linear and quadratic models and a Rosseland diameter of 45.03 ± 0.12 mas with a MARCS model. These measurements lead us to derive an updated effective temperature of 3600 ± 66 K. We detect a fully-resolved environment to which the silicate dust shell is likely to contribute. By using two imaging reconstruction algorithms, we unveiled two bright spots on the surface of Betelgeuse. One spot has a diameter of about 11 mas and accounts for about 8.5% of the total flux. The second one is unresolved (diameter < 9 mas) with 4.5% of the total flux. Conclusions. Resolved images of Betelgeuse in the H band are asymmetric at the level of a few percent. The MOLsphere is not detected in this wavelength range. The amount of measured limb-darkening is in good agreement with model predictions. The two spots imaged at the surface of the star are potential signatures of convective cells.
30825403
First Surface-resolved Results with the IOTA Imaging Interferometer: Detection of Asymmetries in AGB stars
We have measured non-zero closure phases for about 29% of our sample of 56 nearby Asymptotic Giant Branch (AGB) stars, using the 3-telescope Infrared Optical Telescope Array (IOTA) interferometer at near-infrared wavelengths (H band) and with angular resolutions in the range 5-10 milliarcseconds. These nonzero closure phases can only be generated by asymmetric brightness distributions of the target stars or their surroundings. We discuss how these results were obtained, and how they might be interpreted in terms of structures on or near the target stars. We also report measured angular sizes and hypothesize that most Mira stars would show detectable asymmetry if observed with adequate angular resolution.