95016103
A Liquid Helium Bubble Chamber
1) To provide an efficient dewar with large windows on two sides which allow for illuminating and photo­ graphing the bubble chamber tracks without the difficulty of any intervening liquid nitrogen or helium baths in the light path between the bubble chamber and the room temperature photographic system. At the same time heat losses due to room temperature radiation must be reduced several hundred times below that expected from two such room temperature windows.
119446389
Pseudopotential approximation in a harmonic trap
The pseudopotential method @1,2# is an important tool for the study of interacting particles. The key idea is to replace the actual, possibly complicated interaction potential by a much simpler pseudopotential operator, such that the exact energy eigenvalues of the interacting system are reproduced at least to the lowest few orders in a suitable expansion parameter. This approach now is of central importance for the theoretical description of Bose-Einstein condensates @3‐5#, where the approximate pseudopotential mimics the real twobody interaction solely through its s-wave scattering length. However, the condensates are subjected to a trapping potential, and one expects some influence of this external potential on the pseudopotential at least with tight traps, i.e., when the distance over which the trapping potential varies significantly becomes comparable to the scattering length. In this paper we investigate the influence of the trap in detail for a hard-sphere interaction potential, and quantify the accuracy of the standard pseudopotential approximation in an isotropic harmonic trap. Let us briefly recapitulate the essence of the pseudopotential approach @2# for two identical particles of mass m which interact, in the absence of an additional external trapping potential, via a finite-range potential V(uru) without twobody bound states, so that the Hamiltonian is given by
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.
118613941
Ultrahigh energy neutrino scattering: an update
We update our estimates of charged and neutral current neutrino total cross sections on isoscalar nucleons at ultrahigh energies using a global (x, Q 2 ) fit, motivated by the Froissart bound [1], to the F2 (electron-proton) structure function utilizing the most recent analysis [2] of the complete ZEUS and H1 data sets from HERA I. Using the large Q 2 , small Bjorken-x limits of the “wee” parton model, we connect the ultrahigh energy neutrino cross sections directly to the large Q 2 , small x extrapolation of our new fit, which we assume saturates the Froissart bound [1]. We compare both to our previous work [3], which utilized only the smaller ZEUS [4] data set, as well as to recent results [5] of a calculation using the ZEUS-S based global perturbative QCD parton distributions using the combined HERA I results as input. Our new results substantiate our previous conclusions [3], again predicting significantly smaller cross sections than those predicted by extrapolating pQCD calculations to neutrino energies above 10 9 GeV.
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)
119358581
A global test of factorization for nucleon-nucleon, gamma p and gamma gamma scattering
The purpose of this note is to show that the cross section factorization relation $\sigma_{nn}(s)/\sigma_{\gamma p}(s) = \sigma_{\gamma p}(s)/ \sigma_{\gamma\gamma}(s)$ is satisfied experimentally in the energy domain $8\le\sqrt s\le 2000$ GeV, where the $\sigma$'s are total cross sections and $nn$ denotes the even portion of the $pp$ and $\pbar p$ total cross section. A convenient phenomenological paramaterization for a global simultaneous fit to the $pp$, $\pbar p$, $\gamma p$ and $\gamma\gamma$ total cross section data together with the $\rho$-value data for $pp$ and $\pbar p$ is provided by using real analytic amplitudes. Within experimental errors, we show that factorization is satisfied when we unfold the published $\gamma\gamma$ data which had averaged the cross sections obtained by using the two different PHOJET and PYTHIA Monte Carlo results. Our analysis clearly favors the PHOJET results and suggests that the additive quark model, together with vector meson dominance, allows one to compute $\sigma_{\gamma p}(s)$ and $\sigma_{\gamma\gamma}(s)$ from $\sigma_{nn}(s)$ with essentially no free parameters. The universal $\rho$-value predicted by our fit, {\em i.e.,} $\rho_{nn} = \rho_{\gamma p} = \rho_{\gamma\gamma}$, is compared to the $\rho$-value obtained by a QCD-inspired analysis of $\pbar p$ and $pp$ data, including the p-air cross sections from cosmic rays. The $\rho$-values obtained from the two techniques are essentially indistinguishable in the energy region $8\le\sqrt s\le 2000$ GeV, giving us increased confidence in our parameterization of the cross sections needed for the factorization relation.
10030510
DUST PRODUCTION AND MASS LOSS IN THE GALACTIC GLOBULAR CLUSTER NGC 362
We investigate dust production and stellar mass loss in the Galactic globular cluster NGC 362. Due to its close proximity to the Small Magellanic Cloud (SMC), NGC 362 was imaged with the Infrared Array Camera and Multiband Imaging Photometer cameras onboard the Spitzer Space Telescope as part of the Surveying the Agents of Galaxy Evolution (SAGE-SMC) Spitzer Legacy program. We detect several cluster members near the tip of the red giant branch (RGB) that exhibit infrared excesses indicative of circumstellar dust and find that dust is not present in measurable quantities in stars below the tip of the RGB. We modeled the spectral energy distribution (SED) of the stars with the strongest IR excess and find a total cluster dust mass-loss rate of 3.0{sup +2.0}{sub -1.2} x 10{sup -9} M{sub sun} yr{sup -1}, corresponding to a gas mass-loss rate of 8.6{sup +5.6}{sub -3.4} x 10{sup -6} M{sub sun} yr{sup -1}, assuming [Fe/H] =-1.16. This mass loss is in addition to any dustless mass loss that is certainly occurring within the cluster. The two most extreme stars, variables V2 and V16, contribute up to 45% of the total cluster dust-traced mass loss. The SEDs of the more moderate stars indicate themore » presence of silicate dust, as expected for low-mass, low-metallicity stars. Surprisingly, the SED shapes of the stars with the strongest mass-loss rates appear to require the presence of amorphous carbon dust, possibly in combination with silicate dust, despite their oxygen-rich nature. These results corroborate our previous findings in omega Centauri.« less