124593536
Highlights from the Relativistic Heavy Ion Collider
119402907
Suppression of nonphotonic electrons from enhancement of charm baryons in heavy ion collisions
In Au+Au collisions at 2<p{sub T}<6 GeV/c baryon production is enhanced compared to p+p collisions. Since charm baryon decays produce electrons less frequently than charm meson decays, the nonphotonic electron spectrum is sensitive to the {lambda}{sub c}/D ratio. In this report we study the dependence of the nonphotonic electron spectrum on the baryon-to-meson ratio for charm hadrons. As an example, we take the {lambda}{sub c}/D ratio to have the same form as the {lambda}/K{sub S}{sup 0} ratio. In this case, even if the total charm quark yield in Au+Au collisions scales with the number of binary nucleon-nucleon collisions (N{sub bin}), the electron spectrum at 2<p{sub T}<5 GeV/c is suppressed by as much as 20% relative to N{sub bin} scaled p+p collisions.
118502088
The Sound of the Little Bangs
Measurements of particles emitted from collisions of heavy ions at relativistic energies show evidence for temperature-fluctuations on the freeze-out surface of the expanding fireball. These can be understood as remnants of the density inhomogeneities in the initial collision overlap region. In this paper we present an analysis of heavy-ion collisions analogous to the analysis of the cosmic microwave background radiation. We use data on transverse momentum correlations to extract a power-spectrum from heavy-ion collisions and use a Glauber model for eccentricity to extract the transfer function needed to produce the observed correlations. We also discuss the acoustic signal, the sound that an observer inside the matter would hear.
17939619
RHIC CRITICAL POINT SEARCH: ASSESSING STARs CAPABILITIES.
In this report we discuss the capabilities and limitations of the STAR detector to search for signatures of the QCD critical point in a low energy scan at RHIC. We find that a RHIC low energy scan will cover a broad region of interest in the nuclear matter phase diagram and that the STAR detector--a detector designed to measure the quantities that will be of interest in this search--will provide new observables and improve on previous measurements in this energy range.
8293894
Particle dependence of elliptic flow in Au + Au collisions at s(NN)**(1/2) = 200-GeV
The elliptic flow parameter (v 2 ) for K 0 S and Λ+Λ has been measured at mid-rapidity in Au+Au collisions at √s NN = 200 GeV by the STAR Collaboration. The υ 2 values for both K 0 S and Λ+Λ saturate at moderate p T , deviating from the hydrodynamic behaviour observed in the lower p T region. The saturated v 2 values and the p T scales where the deviation begins are particle dependent. The particle-type dependence of v 2 shows features expected from the hadronization of a partonic ellipsoid by coalescence of co-moving quarks. These results will be discussed in relation to the nuclear modification factor (R CP ) which has also been measured for K 0 S and Λ+Λ by the STAR Collaboration.
118478180
Implications of space–momentum correlations and geometric fluctuations in heavy-ion collisions
The standard picture of heavy-ion collisions includes a collective expansion. If the initial energy density in the collisions is lumpy, then the expansion can convert the spatial lumpiness into correlations between final-state particles. Correlations in heavy-ion collisions show prominent features not present in p+p collisions. I argue that many features of these correlations are related to the transference of over-densities from the initial overlap region into momentum–space during the QGP phase of the expansion. I show results from a toy Monte Carlo model to illustrate the consequences of lumpy initial conditions and a collective expansion.
119106969
A coherent understanding of low-energy nuclear recoils in liquid xenon
Liquid xenon detectors such as XENON10 and XENON100 obtain a significant fraction of their sensitivity to light (10 GeV) particle dark matter by looking for nuclear recoils of only a few keV, just above the detector threshold. Yet in this energy regime a correct treatment of the detector threshold and resolution remains unclear. The energy dependence of the scintillation yield of liquid xenon for nuclear recoils also bears heavily on detector sensitivity, yet numerous measurements have not succeeded in obtaining concordant results. In this article we show that the ratio of detected ionization to scintillation can be leveraged to constrain the scintillation yield. We also present a rigorous treatment of liquid xenon detector threshold and energy resolution. Notably, the effective energy resolution differs significantly from a simple Poisson distribution. We conclude with a calculation of dark matter exclusion limits, and show that existing data from liquid xenon detectors strongly constrain recent interpretations of light dark matter.
119186611
Anisotropic diffusion of electrons in liquid xenon with application to improving the sensitivity of direct dark matter searches
Electron diffusion in a liquid xenon time projection chamber has recently been used to infer the z coordinate of a particle interaction, from the width of the electron signal. The goal of this technique is to reduce the background event rate by discriminating edge events from bulk events. Analyses of dark matter search data which employ it would benefit from increased longitudinal electron diffusion. We show that a significant increase is expected if the applied electric field is decreased. This observation is trivial to implement but runs contrary to conventional wisdom and practice. We also extract a first measurement of the longitudinal diffusion coefficient, and confirm the expectation that electron diffusion in liquid xenon is highly anisotropic under typical operating conditions.
14779676
SPECTRAL FEATURES OF PRESOLAR DIAMONDS IN THE LABORATORY AND IN CARBON STAR ATMOSPHERES
Laboratory analyses on ne-grained diamond residues from primitive meteorites have shown that nano- diamonds represent the most abundant form of presolar dust preserved in meteoritic samples. The presolar diamonds carry isotopic anomalies which indicate a very complex formation history. Several groups of diamonds may exist with origin in different types of stars. In order to identify the sites of for- mation observationally, we have extracted presolar diamonds from the Allende meteorite and measured the monochromatic absorption coefcient in a form which is useful for stellar atmo- sphere calculations. The monochromatic absorption coefcient was measured in the wavelength ranges 400{4000cm 1 (2.5{ 25m) and 12200{52600cm 1 (190{820nm). We have made identical laboratory measurements on CVD diamonds as on the meteoritic diamonds, in order to get a more solid basis for the interpretationofthediamondspectrum.Themonochromaticab- sorption coefcient for the presolar diamonds was incorporated in self-consistent carbon star photospheric models. The main influence of the diamond dust in our photospheric models is a heating of the upper photospheric layers and a reduction of the C2H2 abundance. Due to the relatively small absorption coef- cientofthediamondscomparedtootherstellardustgrains,their spectral appearance is weak. However, the weak interaction of the diamonds with the radiation eld may give them an impor- tant role in the dust nucleation process. The gas pressure will stay high and the gas will be much closer to hydrostatic equilib- rium during possible diamond nucleation than is normally the case in dust forming stellar regions, and therefore allow ample time for the nucleation process.
46522188
The spin-orbit angles of the transiting exoplanets WASP-1b, WASP-24b, WASP-38b and HAT-P-8b from Rossiter–McLaughlin observations
We present observations of the Rossiter-McLaughlin effect for the transiting exoplanet systems WASP-1, WASP-24, WASP-38 and HAT-P-8, and deduce the orientations of the planetary orbits with respect to the host stars’ rotatio n axes. The planets WASP-24b, WASP-38b and HAT-P-8b appear to move in prograde orbits and be well aligned, having sky-projected spin orbit angles consistent with zero: � = 4:7 ± 4:0 � , � =15 +33 � −43� and� = 9:7 +9.0 � −7.7� , respectively. The host stars have Teff < 6250 K and conform with the trend of cooler stars having low obliquities. WASP-38b is a massive planet on a moderately long period, eccentric orbit so may be expected to have a misaligned orbit given the high obliquities measured in similar systems. However, we find no evidence for a large spinorbit angle. By contrast, WASP-1b joins the growing number of misaligned systems and has an almost polar orbit, � = 79:0 +4.5 � −4.3� . It is neither very massive, eccentric nor orbiting a hot host star, and therefore does not share the properties of many other misaligned systems.
123170953
An Investigation of the Infrared Behaviour of the Gluon Propagator in the Axial Gauge
In the axial gauge an integral equation for the gluon propagator of a pure Yang-Mills theory is derived based on the Dyson-Schwinger equation and the Slavnov-Taylor identities. Dimensional regularization is used. The solution of this equation is investigated in the case where the variable γ = (nk)2/n2k2 is different from zero and it is seen that the nice properties of the confining solution D(k) ~ 1/k4 are lost in this case.