Active Amplification of the Terrestrial Albedo to Mitigate Climate Change: An Exploratory Study

This study explores the potential to enhance the reflectance of solar insolation by the human settlement and grassland components of the Earth's terrestrial surface as a climate change mitigation measure. Preliminary estimates derived using a static radiative transfer model indicate that such efforts could amplify the planetary albedo enough to offset the current global annual average level of radiative forcing caused by anthropogenic greenhouse gases by as much as 30 percent or 0.76 W/m2. Terrestrial albedo amplification may thus extend, by about 25 years, the time available to advance the development and use of low-emission energy conversion technologies which ultimately remain essential to mitigate long-term climate change. However, additional study is needed to confirm the estimates reported here and to assess the economic and environmental impacts of active land-surface albedo amplification as a climate change mitigation measure.Comment: 21 pages, 3 figures. In press with Mitigation and Adaptation Strategies for Global Change, Springer, N

Centrality dependence of charged antiparticle to particle ratios near mid-rapidity in d+Au collisions at sqrt(s_NN)=200 GeV

The ratios of the yields of charged antiparticles to particles have been obtained for pions, kaons, and protons near mid-rapidity for d+Au collisions at sqrt(s_NN) = 200 GeV as a function of centrality. The reported values represent the ratio of the yields averaged over the rapidity range of 0.1<y_pi<1.3 and 0<y_(K,p)<0.8, where positive rapidity is in the deuteron direction, and for transverse momenta 0.1<p_(T)^(pi,K)<1.0 GeV/c and 0.3<p_(T)^(p)<1.0 GeV/c. Within the uncertainties, a lack of centrality dependence is observed in all three ratios. The data are compared to results from other systems and model calculations.Comment: 6 pages, 4 figures, submitted to PR

Energy dependence of particle multiplicities in central Au+Au collisions

We present the first measurement of the pseudorapidity density of primary charged particles in Au+Au collisions at sqrt(s_NN) = 200GeV. For the 6% most central collisions, we obtain dN_ch/deta|_|eta|<1 = 650 +/- 35 (syst). Compared to collisions at sqrt(s_NN) = 130GeV, the highest energy studied previously, an increase by a factor of 1.14 +/- 0.05 is found. The energy dependence of the pseudorapidity density is discussed in comparison with data from proton-induced collisions and theoretical predictions.Comment: 4 pages, 6 figures, submitted to PR

Collision geometry scaling of Au+Au pseudorapidity density from sqrt(s_NN) = 19.6 to 200 GeV

The centrality dependence of the midrapidity charged particle multiplicity in Au+Au collisions at sqrt(s_NN) = 19.6 and 200 GeV is presented. Within a simple model, the fraction of hard (scaling with number of binary collisions) to soft (scaling with number of participant pairs) interactions is consistent with a value of x = 0.13 +/- 0.01(stat) +/- 0.05(syst) at both energies. The experimental results at both energies, scaled by inelastic p(pbar)+p collision data, agree within systematic errors. The ratio of the data was found not to depend on centrality over the studied range and yields a simple linear scale factor of R_(200/19.6) = 2.03 +/- 0.02(stat) +/- 0.05(syst).Comment: 5 pages, 4 figures, submitted to PRC-R

Pseudorapidity and centrality dependence of the collective flow of charged particles in Au+Au collisions at sqrt{s_NN} = 130 GeV

This paper describes the measurement of collective flow for charged particles in Au+Au collisions at sqrt{s_NN}} = 130 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). An azimuthal anisotropy is observed in the charged particle hit distribution in the PHOBOS multiplicity detector. This anisotropy is presented over a wide range of pseudorapidity (eta) for the first time at this energy. The size of the anisotropy (v_{2}) is thought to probe the degree of equilibration achieved in these collisions. The result here,averaged over momenta and particle species, is observed to reach 7% for peripheral collisions at mid-rapidity, falling off with centrality and increasing |eta|. Data are presented as a function of centrality for |eta|<1.0 and as a function of eta, averaged over centrality, in the angular region -5.0<eta<5.3. These results call into question the common assumption of longitudinal boost invariance over a large region of rapidity in RHIC collisions.Comment: 5 pages, 4 figures, submitted to Physical Review Letter

System size and centrality dependence of charged hadron transverse momentum spectra in Au+Au and Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV

We present transverse momentum distributions of charged hadrons produced in Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV. The spectra are measured for transverse momenta of 0.25 < p_T < 5.0 GeV/c at sqrt(s) = 62.4 GeV and 0.25 < p_T < 7.0 GeV/c at sqrt(s) = 200 GeV, in a pseudo-rapidity range of 0.2 < eta < 1.4. The nuclear modification factor R_AA is calculated relative to p+p data at both collision energies as a function of collision centrality. At a given collision energy and fractional cross-section, R_AA is observed to be systematically larger in Cu+Cu collisions compared to Au+Au. However, for the same number of participating nucleons, R_AA is essentially the same in both systems over the measured range of p_T, in spite of the significantly different geometries of the Cu+Cu and Au+Au systems.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let

Pseudorapidity Distributions of Charged Particles in d + Au and p + p Collisions at sNN\sqrt{s_{_{NN}}} = 200GeV

The measured pseudorapidity distributions of primary charged particles are presented for d + Au and p + p collisions at ${\sqrt{s_{_{NN}}} =}$ 200 GeV over a wide pseudorapidity range of ${\rm \mid \eta \mid \le}$ 5.4. The results for d + Au collisions are presented for minimum-bias events and as a function of collision centrality. The measurements for p + p collisions are shown for minimum-bias events. The ratio of the charged particle multiplicity in d + Au and p + A collisions relative to that for inelastic p + p collisions is found to depend only on ${}$, and it is remarkably independent of collision energy and system mass. The deuteron and gold fragmentation regions in d + Au collisions are in good agreement with proton nucleus data at lower energies.Comment: 4 pages, 3 figures. To appear in the proceedings of Seventeenth International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2004), Oakland, California from January 11-17, 2004. Submitted to Journal of Physics G: Nuclear and Particle Physic

System Size, Energy and Centrality Dependence of Pseudorapidity Distributions of Charged Particles in Relativistic Heavy Ion Collisions

We present the first measurements of the pseudorapidity distribution of primary charged particles in Cu+Cu collisions as a function of collision centrality and energy, \sqrtsnn = 22.4, 62.4 and 200 GeV, over a wide range of pseudorapidity, using the PHOBOS detector. Making a global comparison of Cu+Cu and Au+Au results, we find that the total number of produced charged particles and the rough shape (height and width) of the pseudorapidity distributions are determined by the number of nucleon participants. More detailed studies reveal that a more precise matching of the shape of the Cu+Cu and Au+Au pseudorapidity distributions over the full range of pseudorapidity occurs for the same Npart/2A value rather than the same Npart value. In other words, it is the collision geometry rather than just the number of nucleon participants that drives the detailed shape of the pseudorapidity distribution and its centrality dependence at RHIC energies.Comment: Submitted to Physical Review Letter

Cluster properties from two-particle angular correlations in p+p collisions at s\sqrt{s} = 200 and 410 GeV

We present results on two-particle angular correlations in proton-proton collisions at center of mass energies of 200 and 410 GeV. The PHOBOS experiment at the Relativistic Heavy Ion Collider has a uniquely large coverage for charged particles, giving the opportunity to explore the correlations at both short- and long-range scales. At both energies, a complex two-dimensional correlation structure in $\Delta \eta$ and $\Delta \phi$ is observed. In the context of an independent cluster model of short-range correlations, the cluster size and its decay width are extracted from the two-particle pseudorapidity correlation function and compared with previous measurements in proton-proton and proton-antiproton collisions, as well as PYTHIA and HIJING predictions.Comment: 10 pages, 10 figures, submitted to Phys. Rev.

Identified charged antiparticle to particle ratios near midrapidity in Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV

Antiparticle to particle ratios for identified protons, kaons and pions at sqrt(s) = 62.4 and 200 GeV in Cu+Cu collisions are presented as a function of centrality for the midrapidity region of 0.2 < eta < 1.4. No strong dependence on centrality is observed. For the / ratio at ~ 0.51 GeV/c, we observe an average value of 0.50 +/- 0.003_(stat) +/- 0.04_(syst) and 0.77 +/- 0.008_(stat) +/- 0.05_(syst) for the 10% most central collisions of 62.4 and 200 GeV Cu+Cu, respectively. The values for all three particle species measured at sqrt(s) = 200 GeV are in agreement within systematic uncertainties with that seen in both heavier and lighter systems measured at the same RHIC energy. This indicates that system size does not appear to play a strong role in determining the midrapidity chemical freeze-out properties affecting the antiparticle to particle ratios of the three most abundant particle species produced in these collisions.Comment: 5 Pages, 4 figures Made changes to the figures to include the panel numbers. Slight changes to the text. Updated data points from other experiment