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.
119288740
Analyzing the Power Spectrum of the Little Bangs
Abstract In this talk we discuss the analogy between data from heavy-ion collisions and the Cosmic Microwave Background. We identify p T correlations data as the heavy-ion analogy to the CMB and extract a power-spectrum from the heavy-ion data. We define the ratio of the final state power-spectrum to the initial coordinate-space eccentricity as the transfer-function. From the transfer-function we find that higher n terms are suppressed and we argue that the suppression provides information on length scales like the mean-free-path. We make a rough estimate of the mean-free-path and find that it is larger than estimates based on the centrality dependence of ν 2 .
118375394
Coalescence Models for Hadron Formation from Quark-Gluon Plasma
We review hadron formation from a deconfined quark-gluon plasma (QGP) via coalescence or recombination of quarks and gluons. We discuss the abundant experimental evidence for coalescence from the R...
121208134
Dependence of the non-photonic electron spectrum on the charmed baryon-to-meson ratio
Abstract In this talk I argue that a substantial fraction of the non-photonic electron suppression in Au+Au collisions could arise as a result of an enhanced Λc/D ratio rather than purely from jet-quenching. At intermediate transverse momentum (2<pT<6 GeV/c), the baryon-to-meson ratio in Au+Au collisions is enhanced compared to p+p collisions. Since charm-baryon decays produce electrons less frequently than charm-meson decays, the non-photonic electron spectrum is sensitive to the Λc/D ratio. I show the dependence of the non-photonic electron spectrum on the baryon-to-meson ratio for charm hadrons. As an example, I assume that the Λc/D ratio is the same as the Λ/K0S ratio. I show that even if the total charm quark yield in Au+Au collisions scales with the number of binary nucleon-nucleon collisions (Nbin), the electron spectrum at 2<pT<5 GeV/c will be suppressed relative to Nbin scaled p+p collisions by as much as 20%.  
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.
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 .
120475304
An eikonal line-integral model and factorization in QCD
We study an approximation to perturbative QCD in which all quarks (active and spectator) move along eikonal lines. These eikonal lines are described by matrix operatorsU defined by time-ordered and path-ordered integrals. All known examples of Bloch-Nordsieck cancellations follow simply from the unitary properties ofU. In particular, when the eikonal lines are space-like, the time-ordering can be omitted and the unitarity ofU is evident. In this model, it is possible to examine rather explicitly the soft and very-soft gluons whose effects must cancel if factorization is hold (to leading twist). We can show such cancellation if there is a smooth continuation from space-like eikonal lines to time-like ones. We give some examples relevant to this conjecture, but we are unable to prove it in general.
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.
18747581
An early‐time infrared and optical study of the Type Ia Supernova 1998bu in M96
We present first-season infrared (IR) and optical photometry and spectroscopy of the Type Ia Supernova 1998bu in M96. We also report optical polarimetry of this event. SN 1998bu is one of the closest type Ia supernovae of modern times, and the distance of its host galaxy is well determined. We find that SN 1998bu is both photometrically and spectroscopically normal. However, the extinction to this event is unusually high, with A(V) = 1.0 +/- 0.11. We find that SN 1998bu peaked at an intrinsic M-V = -19.37 +/- 0.23. Adopting a distance modulus of 30.25 (Tanvir et al.) and using Phillips et al.'s relations for the Hubble constant, we obtain H-0 = 70.4 +/- 4.3 km s(-1) Mpc(-1). Combination of our IR photometry with those of Jha et al. provides one of the most complete early-phase IR light curves for a SN Ia published so far. In particular, SN 1998bu is the first normal SN Ia for which good pre-t(Bmax) IR coverage has been obtained. It reveals that the J, H and K light curves peak about 5 days earlier than the flux in the B-band curve.
119103405
Low-energy (<10keV) electron ionization and recombination model for a liquid argon detector
Abstract Detailed understanding of the ionization process in noble liquid detectors is important for their use in applications such as the search for dark matter and coherent elastic neutrino-nucleus scattering. The response of noble liquid detectors to low-energy ionization events is poorly understood at this time. We describe a new simulation tool which predicts the ionization yield from electronic energy deposits ( E 10 keV ) in liquid Ar, including the dependence of the yield on the applied electric drift field. The ionization signal produced in a liquid argon detector from 37Ar beta decay and 55Fe X-rays has been calculated using the new model.
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.