119302438
The rise and fall of the ridge in heavy ion collisions
Abstract Recent data from heavy ion collisions at RHIC show unexpectedly large near-angle correlations that broaden longitudinally with increasing centrality. The amplitude of this ridge-like correlation rises rapidly, reaches a maximum, and then falls in the most central collisions. In this Letter we explain how this behavior can be uniquely explained by initial-state coordinate-space anisotropies converted into final-state momentum-space correlations. We propose v n 2 / e n , part 2 as a useful way to study length scales and provide a prediction for the ridge in Pb + Pb collisions at s NN = 2.76 TeV .
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.
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.
125578392
Azimuthal anisotropy of K0(S) and Lambda + anti-Lambda production at mid-rapidity from Au + Au collisions at S(NN)**(1/2) = 130-GeV
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.
17495479
Identified Particle Measurements at RHIC: Elucidating Hadronization Mechanisms for Bulk Partonic Matter
Measurements of identified particle momentum spectra at √{sNN} = 200 GeV are reviewed. Emphasis is placed on the azimuthal dependence and the centrality dependence of hadron yields at intermediate transverse momentum (1.5 < pT < 5 GeV/c). The first measurements of the fourth harmonic term (v4) in the azimuthal variation of identified particle yields are shown. The recombination mechanism of hadron formation provides a consistent description of the dependence of these measurements on particle-type.
120972199
Do quarks propagate
Abstract Processes with coloured particles in the initial state are generally infrared divergent. We investigate the effect of this on processes with colourless particles in the initial state, when the amplitude is near an intermediate quark pole. The result is a characteristics logarithmic dependence on the “binding energy” (even though spectator interactions are taken into account), and the result is gauge-invariant. Summed to all orders, the logarithms could perhaps suppress the quark pole.
118466778
Towards energy resolution at the statistical limit from a negative ion time projection chamber
Abstract We make a proof-of-principle demonstration that improved energy resolution can be obtained in a negative-ion time projection chamber, by individually counting each electron produced by ionizing radiation.
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.
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.
14131974
First direct detection limits on sub-GeV dark matter from XENON10.
The first direct detection limits on dark matter in the MeV to GeV mass range are presented, using XENON10 data. Such light dark matter can scatter with electrons, causing ionization of atoms in a detector target material and leading to single- or few-electron events. We use 15  kg day of data acquired in 2006 to set limits on the dark-matter-electron scattering cross section. The strongest bound is obtained at 100 MeV where σ(e)<3×10(-38)  cm2 at 90% C.L., while dark-matter masses between 20 MeV and 1 GeV are bounded by σ(e)<10(-37)  cm2 at 90% C.L. This analysis provides a first proof of principle that direct detection experiments can be sensitive to dark-matter candidates with masses well below the GeV scale.