25621201
Experimental confirmation that the proton is asymptotically a black disk.
Although experimentally accessible energies cannot probe "asymptopia", recent measurements of inelastic pp cross sections at the LHC at 7000 GeV and by Auger at 57,000 GeV allow us to conclude that (i) both σ(inel) and σ(tot), the inelastic and total cross sections for pp and pp interactions, saturate the Froissart bound of ln(2)s, (ii) when s→∞, the ratio σ(inel)/σ(tot) is experimentally determined to be 0.509 ± 0.021, consistent with the value 0.5 required by a black disk at infinite energies, and (iii) when s→∞, the forward scattering amplitude becomes purely imaginary, another requirement for the proton to become a totally absorbing black disk. Experimental verification of the hypotheses of analyticity and unitarity over the center of mass energy range 6 ≤ √s ≤ 57000 GeV are discussed. In QCD, the black disk is naturally made of gluons; our results suggest that the lowest-lying glueball mass is 2.97 ± 0.03 GeV.
121023736
PHASE-SPACE INTEGRALS FOR MULTIPARTICLE SYSTEMS
The total phase-space integrals, occurring in the Fermi statistical theory of meson production, for 2-, 3-, 4-, and 5-body final states are reduced to forms suitable for numerical evaluation by hand computation. In addition, the momentum spectrum of any one particle, as derived from the statistical factor, is evaluated. For the 3- and 4-body systems, the $Q$ distribution for any two of the particles (effective mass minus the rest masses of the 2-particle subsystem) is derived. Numerical results are presented for nucleon-nucleon collisions at 0.8-, 1.5-, and 2.7-Bev bombarding kinetic energies.
120614937
Elastic scattering in nucleon-nucleon collisions
Recently, E811 has measured[1] the total cross section for pp scattering at √s = 1800 GeV. In this paper, we refit the experimental data for σtot, ϱ and B for both pp and pp to a QCD-inspired eikonal model, including the new σtot measurement.
122464578
Measurements of the proton--proton total cross section by means of Coulomb scattering at the CERN Intersecting Storage Rings.
Abstract Proton-proton elastic scattering has been measured at the CERN Intersecting Storage Rings in the four-momentum transfer range 0.001 ⩽… t …⩽ 0.015 GeV 2 at centre-of-mass energies of 23 and 31 GeV. The detection of Coulomb scattering and of its interference with nuclear scattering leads to the determination of the real part of the nuclear amplitude and of the total proton-proton cross section by the optical theorem.
9426399
Implications from analyticity constraints used in a Landshoff-Donnachie fit
Landshoff and Donnachie[hep/ph 0509240, (2005)] parametrize the energy behavior of pp and pp̄ scattering cross sections with five parameters, using: σ = 56.08s + 21.70s for pp, (1) σ = 98.39s + 21.70s for pp̄. (2) Using the 4 analyticity constraints of Block and Halzen[M. M. Block and F. Halzen, Phys. Rev. D 72, 036006 (2005)], we simultaneously fit the Landshoff-Donnachie form to the same “sieved” set of pp and pp̄ cross section and ρ data that Block and Halzen used for a very good fit to a ln s parametrization. We show that the satisfaction of the analyticity constraints will require complicated modifications of the LandshoffDonnachie parametrization for lower energies, greatly altering its inherent appeal of simplicity and universality. Landshoff and Donnachie[1, 2, 3] parameterize the scattering cross section with five parameters, using: σ = 56.08s + 21.70s for pp, (3) σ = 98.39s + 21.70s for pp̄, (4) where s is in GeV. Using the high energy limit s → 2mν, where ν is the laboratory energy and m is the proton mass, we rewrite these equations, as well as ρ, the ratio of the real part to the imaginary part of the forward scattering amplitude, more generally as σ = A ( ν m )α−1 + B ( ν m )β−1 ± D ( ν m )α−1 , (5) dσ d(ν/m) = A(α − 1) ( ν m )α−2 + B(β − 1) ( ν m )β−2 ± D(α − 1) ( ν m )α−2 , (6)
13499391
New evidence for the saturation of the Froissart bound
Fits to high energy data alone cannot cleanly discriminate between asymptotic lns and ln{sup 2}s behavior of total hadronic cross sections. We demonstrate that this is no longer true when we require that these amplitudes also describe, on average, low energy data dominated by resonances. We simultaneously fit real analytic amplitudes to high energy measurements of: (i) the {pi}{sup +}p and {pi}{sup -}p total cross sections and {rho}-values (ratio of the real to the imaginary portion of the forward scattering amplitude), for {radical}(s){>=}6 GeV, while requiring that the asymptotic fits smoothly join the {sigma}{sub {pi}{sup +}}{sub p} and {sigma}{sub {pi}{sup -}}{sub p} total cross sections at {radical}(s)=2.6 GeV--both in magnitude and slope, and (ii) separately simultaneously fit the pp and pp total cross sections and {rho}-values for {radical}(s){>=}6 GeV, while requiring that their asymptotic fits smoothly join the the {sigma}{sub pp} and {sigma}{sub pp} total cross sections at {radical}(s)=4.0 GeV--again both in magnitude and slope. In both cases, we have used all of the extensive data of the Particle Data Group [K. Hagiwara et al. (Particle Data Group), Phys. Rev. D 66, 010001 (2002).]. However, we then subject these data to a screening process, the Sieve algorithm [M. M. Block,more » physics/0506010.], in order to eliminate outliers that can skew a {chi}{sup 2} fit. With the Sieve algorithm, a robust fit using a Lorentzian distribution is first made to all of the data to sieve out abnormally high {delta}{chi}{sub i}{sup 2}, the individual ith point's contribution to the total {chi}{sup 2}. The {chi}{sup 2} fits are then made to the sieved data. Both the {pi}p and nucleon-nucleon systems strongly favor a high energy ln{sup 2}s fit of the form: {sigma}{sup {+-}}=c{sub 0}+c{sub 1}ln(({nu}/m))+c{sub 2}ln{sup 2}(({nu}/m))+{beta}{sub P{sup '}}(({nu}/m)){sup {mu}}{sup =} -{sup 1}{+-}{delta}(({nu}/m)){sup {alpha}}{sup -1}, basically excluding a lns fit of the form: {sigma}{sup {+-}}=c{sub 0}+c{sub 1}ln(({nu}/m))+{beta}{sub P{sup '}}(({nu}/m)){sup {mu}}{sup -1}{+-}{delta}(({nu}/m)){sup {alpha}}{sup -1}. The upper sign is for {pi}{sup +}p (pp) and the lower sign is for {pi}{sup -}p (pp) scattering, where {nu} is the laboratory pion (proton) energy, and m is the pion (proton) mass.« less
12656398
SPITZER ANALYSIS OF H II REGION COMPLEXES IN THE MAGELLANIC CLOUDS: DETERMINING A SUITABLE MONOCHROMATIC OBSCURED STAR FORMATION INDICATOR
H II regions are the birth places of stars, and as such they provide the best measure of current star formation rates (SFRs) in galaxies. The close proximity of the Magellanic Clouds allows us to probe the nature of these star forming regions at small spatial scales. To study the H II regions, we compute the bolometric infrared flux, or total infrared (TIR), by integrating the flux from 8 to 500 ?m. The TIR provides a measure of the obscured star formation because the UV photons from hot young stars are absorbed by dust and re-emitted across the mid-to-far-infrared (IR) spectrum. We aim to determine the monochromatic IR band that most accurately traces the TIR and produces an accurate obscured SFR over large spatial scales. We present the spatial analysis, via aperture/annulus photometry, of 16 Large Magellanic Cloud (LMC) and 16 Small Magellanic Cloud (SMC) H II region complexes using the Spitzer Space Telescope's IRAC (3.6, 4.5, 8 ?m) and MIPS (24, 70, 160 ?m) bands. Ultraviolet rocket data (1500 and 1900 ?) and SHASSA H? data are also included. All data are convolved to the MIPS 160 ?m resolution (40 arcsec full width at half-maximum), and apertures have a minimum radius of 35''. The IRAC, MIPS, UV, and H? spatial analysis are compared with the spatial analysis of the TIR. We find that nearly all of the LMC and SMC H II region spectral energy distributions (SEDs) peak around 70 ?m at all radii, from ~10 to ~400?pc from the central ionizing sources. As a result, we find the following: the sizes of H II regions as probed by 70 ?m are approximately equal to the sizes as probed by TIR (70?pc in radius); the radial profile of the 70 ?m flux, normalized by TIR, is constant at all radii (70 ?m ~ 0.45TIR); the 1? standard deviation of the 70 ?m fluxes, normalized by TIR, is a lower fraction of the mean (0.05-0.12 out to ~220?pc) than the normalized 8, 24, and 160 ?m normalized fluxes (0.12-0.52); and these results are the same for the LMC and the SMC. From these results, we argue that 70 ?m is the most suitable IR band to use as a monochromatic obscured star formation indicator because it most accurately reproduces the TIR of H II regions in the LMC and SMC and over large spatial scales. We also explore the general trends of the 8, 24, 70, and 160 ?m bands in the LMC and SMC H II region SEDs, radial surface brightness profiles, sizes, and normalized (by TIR) radial flux profiles. We derive an obscured SFR equation that is modified from the literature to use 70 ?m luminosity, SFR(M ? yr?1) = 9.7(0.7) ? 10?44 L 70(ergs s?1), which is applicable from 10 to 300?pc distance from the center of an H II region. We include an analysis of the spatial variations around H II regions between the obscured star formation indicators given by the IR and the unobscured star formation indicators given by UV and H?. We compute obscured and unobscured SFRs using equations from the literature and examine the spatial variations of the SFRs around H II regions.
29749856
SPATIAL VARIATIONS OF DUST ABUNDANCES ACROSS THE LARGE MAGELLANIC CLOUD
Using the data obtained with the Spitzer Space Telescope as part of the Surveying the Agents of a Galaxy's Evolution (SAGE) legacy survey, we have studied the variations of the dust composition and abundance across the Large Magellanic Cloud (LMC). Such variations are expected, as the explosive events which have lead to the formation of the many H I shells observed should have affected the dust properties. Using a model and comparing with a reference spectral energy distribution from our Galaxy, we deduce the relative abundance variations of small dust grains across the LMC. We examined the infrared color ratios as well as the relative abundances of very small grains (VSGs) and polycyclic aromatic hydrocarbons (PAHs) relative to the big grain abundance. Results show that each dust component could have different origins or evolution in the interstellar medium (ISM). The VSG abundance traces the star formation activity and could result from shattering of larger grains, whereas the PAH abundance increases around molecular clouds as well as in the stellar bar, where they could have been injected into the ISM during mass loss from old stars.
119268816
Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud (SAGE-SMC). II. Cool Evolved Stars
We investigate the infrared (IR) properties of cool, evolved stars in the Small Magellanic Cloud (SMC), including the red giant branch (RGB) stars and the dust-producing red supergiant (RSG) and asymptotic giant branch (AGB) stars using observations from the Spitzer Space Telescope Legacy program entitled Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity SMC, or SAGE-SMC. The survey includes, for the first time, full spatial coverage of the SMC bar, wing, and tail regions at IR wavelengths (3.6-160 μm). We identify evolved stars using a combination of near-IR and mid-IR photometry and point out a new feature in the mid-IR color-magnitude diagram that may be due to particularly dusty O-rich AGB stars. We find that the RSG and AGB stars each contribute 20% of the global SMC flux (extended + point-source) at 3.6 μm, which emphasizes the importance of both stellar types to the integrated flux of distant metal-poor galaxies. The equivalent SAGE survey of the higher-metallicity Large Magellanic Cloud (SAGE-LMC) allows us to explore the influence of metallicity on dust production. We find that the SMC RSG stars are less likely to produce a large amount of dust (as indicated by the [3.6] – [8] color). There is a higher fraction of carbon-rich stars in the SMC, and these stars appear to reach colors as red as their LMC counterparts, indicating that C-rich dust forms efficiently in both galaxies. A preliminary estimate of the dust production in AGB and RSG stars reveals that the extreme C-rich AGB stars dominate the dust input in both galaxies, and that the O-rich stars may play a larger role in the LMC than in the SMC.
8901792
LABOCA observations of giant molecular clouds in the southwest region of the Small Magellanic Cloud
Context. The amount of molecular gas is a key for understanding the future star formation in a galaxy. Because H2 is diffi cult to observe directly in dense and cold clouds, tracers like the CO molecule are used. However, at low metallicities especially, CO only traces the shielded interiors of the clouds. In this context , millimeter dust emission can be used as a tracer to unveil the total dense gas masses. However, the comparison of masses deduced from the continuum SIMBA 1.2 mm emission and virial masses (thought to trace the whole potential of the clouds) in a sample of giant molecular clouds in the Small Magellanic Cloud (SMC) by Rubio et al. (2004) and Bot et al. (2007) showed a discrepancy between these two quantities that is in need of an explanation. Aims. This study aims at better assessing possible uncertainties on the dust emission observed in the sample of giant molecular clouds from the SMC. It focuses on the mass comparison in the densest parts of the giant molecular clouds where CO is detected in order to confirm the mass discrepancy observed. Methods. New observations of the south-west region of the SMC were obtained with the LABOCA camera on the APEX telescope. All the giant molecular clouds previously observed in CO are detected and their emission at 870� m is compared to ancillary data. The different contributions to the sub-millimeter emission are est imated, as well as dust properties (temperatures, emissivi ties), in order to deduce molecular cloud masses precisely. Results. The (sub-)millimeter emission observed in the giant molecular clouds in the south west region of the SMC is dominated by dust emission and masses are deduced for the part of each cloud where CO is detected and compared to the virial masses. The mass discrepancy between both methods is confirmed at 870� m with the LABOCA observations: the virial masses are on average 4 times smaller than the masses of dense gas deduced from dust emission, contrary to what is observed for equivalent clouds in our Galaxy. Conclusions. At present, the origin of this mass discrepancy in the SMC remains unkown. The direct interpretation of this effect is that the CO linewidth used to compute virial masses do not measure the full velocity distribution of the gas. Geometrical effects and uncertainties on the dust properties are also discussed.