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12 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Nucleon-gold collisions at 200A GeV using tagged d + Au interactions in the PHOBOS detector

Forward calorimetry in the PHOBOS detector has been used to study charged hadron production in d+Au, p+Au, and n+Au collisions at √s NN =200GeV. The forward proton calorimeter detectors are described and a procedure for determining collision centrality with these detectors is detailed. The deposition of energy by deuteron spectator nucleons in the forward calorimeters is used to identify p+Au and n+Au collisions in the data. A weighted combination of the yield of p+Au and n+Au is constructed to build a reference for Au+Au collisions that better matches the isospin composition of the gold nucleus. The p T and centrality dependence of the yield of this improved reference system is found to match that of d+Au. The shape of the charged-particle transverse momentum distribution is observed to extrapolate smoothly from p+p¯ to central d+Au as a function of the charged-particle pseudorapidity density. The asymmetry of positively and negatively charged hadron production in p+Au is compared to that of n+Au. No significant asymmetry is observed at midrapidity. In conclusion, these studies augment recent results from experiments at the CERN Large Hadron Collider and BNL Relativistic Heavy Ion Collider facilities to give a more complete description of particle production in p+A and d+A collisions, essential for the understanding the medium produced in high-energy nucleus-nucleus collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

PHOBOS AS A D-TYPE CAPTURED ASTEROID, SPECTRAL MODELING FROM 0.25 TO 4.0 μm

This paper describes the spectral modeling of the surface of Phobos in the wavelength range between 0.25 and 4.0 μm. We use complementary data to cover this spectral range: the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System on board the ESA Rosetta spacecraft) reflectance spectrum that Pajola et al. merged with the VSK-KRFM-ISM (Videospectrometric Camera (VSK)-Combined Radiometer and Photometer for Mars (KRFM)-Imaging Spectrometer for Mars (ISM) on board the USSR Phobos 2 spacecraft) spectra by Murchie and Erard and the IRTF (NASA Infrared Telescope Facility, Hawaii, USA) spectra published by Rivkin et al. The OSIRIS data allow the characterization of an area of Phobos covering from 86.°8 N to 90° S in latitude and from 126° W to 286° W in longitude. This corresponds chiefly to the trailing hemisphere, but with a small sampling of the leading hemisphere as well. We compared the OSIRIS results with the Trojan D-type asteroid 624 Hektor and show that the overall slope and curvature of the two bodies over the common wavelength range are very similar. This favors Phobos being a captured D-type asteroid as previously suggested. We modeled the OSIRIS data using two models, the first one with a composition that includes organic carbonaceous material, serpentine, olivine, and basalt glass, and the second one consisting of Tagish Lake meteorite and magnesium-rich pyroxene glass. The results of these models were extended to longer wavelengths to compare the VSK-KRFM-ISM and IRTF data. The overall shape of the second model spectrum between 0.25 and 4.0 μm shows curvature and an albedo level that match both the OSIRIS and Murchie and Erard data and the Rivkin et al. data much better than the first model. The large interval fit is encouraging and adds weight to this model, making it our most promising fit for Phobos. Since Tagish Lake is commonly used as a spectral analog for D-type asteroids, this provides additional support for compositional similarities between Phobos and D-type asteroids.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Measuring the Elemental Composition of Phobos: The Mars-moon Exploration with GAmma rays and NEutrons (MEGANE) Investigation for the Martian Moons eXploration (MMX) Mission

The Mars-moon Exploration with GAmma rays and NEutrons (MEGANE) investigation will use gamma-ray and neutron spectroscopy to measure the elemental composition of Mars' moon Phobos. MEGANE is part of the Japanese Martian Moons eXploration (MMX) mission that will make comprehensive remote sensing measurements of both of Mars' moons Phobos and Deimos. MMX will also return to Earth regolith samples of Phobos. The science goals of the MEGANE investigation mirror those of the MMX mission. MEGANE will use elemental composition measurements to determine if Phobos is a captured asteroid or the end result of a giant impact event on Mars, study Phobos surface processes, provide reconnaissance to support the sample site selection, and supply compositional context for the returned samples. To accomplish its measurements, MEGANE will use a high-purity Ge gamma-ray spectrometer (GRS), and a neutron spectrometer (NS) that consists of two 3He gas proportional neutron sensors. The GRS derives heritage from similar instruments from NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission and the Psyche mission that is currently in development; the NS is based on similar instruments used for NASA's Lunar Prospector and Psyche missions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Excavating Stickney crater at Phobos

Stickney crater, at 9 km across, dominates the morphology of ~22 km Phobos, the larger of the two moons of Mars. The Stickney impact event had global repercussions for Phobos, including extensive resurfacing and fracturing of the moon. Understanding the initial conditions and dynamical consequences of the collision is necessary to test competing hypotheses for the origin of peculiar grooved terrain that striates much of the surface. Previous modeling of the impact event was unable to replicate Stickney without globally fragmenting the satellite. We also describe high-resolution numerical simulations that successfully generate Stickney crater while maintaining the large-scale structure of Phobos. Target porosity, which is estimated to be significant, aids in keeping the moon intact. Damage follows patterns centered on Stickney that are inconsistent with the observed alignment of grooved terrain on Phobos. We ejected low-velocity boulders at shallow angles in sufficient numbers to support a rolling-boulder origin for grooved terrain.

58 GEOSCIENCES↗
DOE OSTI2015

PHOBOS in the LHC era

The PHOBOS experiment ran at the RHIC collider from 2000 to 2005, under the leadership of Wit Busza. These proceedings summarize selected PHOBOS results, highlighting their continuing relevance amidst the wealth of new results from the lead–lead program at the Large Hadron Collider (LHC)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

On the Impact Origin of Phobos and Deimos. I. Thermodynamic and Physical Aspects

Phobos and Deimos are the two small moons of Mars. Recent works have shown that they can accrete within an impact-generated disk. However, the detailed structure and initial thermodynamic properties of the disk are poorly understood. In this paper, we perform high-resolution SPH simulations of the Martian moon-forming giant impact that can also form the Borealis basin. This giant impact heats up the disk material (around ∼2000 K in temperature) with an entropy increase of ∼1500 J K{sup −1} kg{sup −1}. Thus, the disk material should be mostly molten, though a tiny fraction of disk material (<5%) would even experience vaporization. Typically, a piece of molten disk material is estimated to be meter sized owing to the fragmentation regulated by their shear velocity and surface tension during the impact process. The disk materials initially have highly eccentric orbits (e ∼ 0.6–0.9), and successive collisions between meter-sized fragments at high impact velocity (∼1–5 km s{sup −1}) can grind them down to ∼100 μm sized particles. On the other hand, a tiny amount of vaporized disk material condenses into ∼0.1 μm sized grains. Thus, the building blocks of the Martian moons are expected to be a mixture of these different sized particles from meter-sized down to ∼100 μm sized particles and ∼0.1 μm sized grains. Our simulations also suggest that the building blocks of Phobos and Deimos contain both impactor and Martian materials (at least 35%), most of which come from the Martian mantle (50–150 km in depth; at least 50%). Our results will give useful information for planning a future sample return mission to Martian moons, such as JAXA’s MMX (Martian Moons eXploration) mission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Radiation damage and annealing of three coaxial n-type germanium detectors: Preparation for spaceflight missions to asteroid 16 Psyche and Mars’ moon Phobos

Three n-type high-purity germanium (HPGe) detectors were irradiated with protons at solar and galactic cosmic ray energies, with fluences corresponding to 3 years of exposure to the interplanetary radiation environment. Following 1 GeV proton irradiations (8x10 8 protons cm –2 ), annealing of the detectors at 105° and 115 °C resulted in full energy resolution recovery after 240 and 140 h of annealing, respectively. A second irradiation, consisting of 7.25x10 9 protons cm –2 with a solar-proton-like energy spectrum, resulted in full recovery within <316 h of annealing at 105 °C. Prior spaceflight experience raised concerns about annealing-induced leakage currents. During this study, one of the three detectors was annealed for a cumulative time of 57 days, and there was no evidence for increased leakage currents. However, gamma-ray photopeak detection efficiency was found to be strongly anti-correlated with cumulative anneal time for all three detectors. The energy- and time-dependence of the efficiency loss is consistent with the loss of active volume at the inner borehole, which we attribute to thermal diffusion of the lithium contact during annealing. The data collected during this study validate aspects of the design of two in-development planetary gamma-ray spectrometers; one to the asteroid (16) Psyche and one to Mars’ moon Phobos. The annealing strategy and operations concepts for these two instruments are informed by the results of this study.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Improved version of the PHOBOS Glauber Monte Carlo

“Glauber” models are used to calculate geometric quantities in the initial state of heavy ion collisions, such as impact parameter, number of participating nucleons and initial eccentricity. Experimental heavy-ion collaborations, in particular at RHIC and LHC, use Glauber Model calculations for various geometric observables for determination of the collision centrality. In this document, we describe the assumptions inherent to the approach, and provide an updated implementation (v2) of the Monte Carlo based Glauber Model calculation, which originally was used by the PHOBOS collaboration. The main improvement w.r.t. the earlier version (v1) (Alver et al. 2008) is the inclusion of Tritium, Helium-3, and Uranium, as well as the treatment of deformed nuclei and Glauber–Gribov fluctuations of the proton in p +A collisions. A users’ guide (updated to reflect changes in v2) is provided for running various calculations.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

Participant and spectator scaling of spectator fragments in Au + Au and Cu + Cu collisions at s N N = 19.6 and 22.4 GeV

Spectator fragments resulting from relativistic heavy ion collisions, consisting of single protons and neutrons along with groups of stable nuclear fragments up to nitrogen (Z = 7), are measured in PHOBOS. These fragments are observed in Au+Au ( s N N = 19.6 GeV) and Cu+Cu (22.4 GeV) collisions at high pseudorapidity (η). The dominant multiply-charged fragment is the tightly bound helium (α), with lithium, beryllium, and boron all clearly seen as a function of collision centrality and pseudorapidity. In this paper, we observe that in Cu+Cu collisions, it becomes much more favorable for the α fragments to be released than lithium. The yields of fragments approximately scale with the number of spectator nucleons, independent of the colliding ion. The shapes of the pseudorapidity distributions of fragments indicate that the average deflection of the fragments away from the beam direction increases for more central collisions. Finally, a detailed comparison of the shapes for α and lithium fragments indicates that the centrality dependence of the deflections favors a scaling with the number of participants in the collision.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Tarda and Tagish Lake: Samples from the same outer Solar System asteroid and implications for D- and P-type asteroids

Here, we report a comprehensive study of the ungrouped type 2 carbonaceous chondrite, Tarda, which fell in Morocco in 2020. This meteorite exhibits substantial similarities to Tagish Lake, Wisconsin Range 91600, and Meteorite Hills 00432, which are generally considered to have originated from a D-type asteroid(s). We constrain the compositions and petrologies of the materials present in a potential sample of a D-type asteroid by reporting the petrography, bulk chemical compositions, bulk H, C, N, Cr, and Ti isotopic compositions, reflectance spectra, and in situ chemical compositions of metals, sulfides, carbonates, and FeO-poor and FeO-rich chondrule silicates of Tarda. We also present new data for Tagish Lake. We then compare Tarda with the other Tagish Lake-like meteorites. Tarda and Tagish Lake appear to be from the same parent body, as demonstrated by their similar petrologies (modal abundances, chondrule sizes), mineral compositions, bulk chemical and isotopic compositions, and reflectance spectra. While the two other Tagish Lake-like meteorites, Wisconsin Range 91600 and Meteorite Hills 00432, show some affinities to Tagish Lake and Tarda, they also share similar characteristics to the Mighei-like carbonaceous (CM) chondrites, warranting further study. Similarities in reflectance spectra suggest that P-type asteroids 65 Cybele and 76 Freia are potential parent bodies of Tarda and the Tagish Lake-like meteorites, or at least have similar surface materials. Since upcoming spacecraft missions will spectrally survey D-type, P-type, and C-type Trojan asteroids (NASA's Lucy) and spectrally study and return samples from Mars' moon Phobos (JAXA's Martian Moons eXploration mission), which is spectrally similar to D-type asteroids, these meteorites are of substantial scientific interest. Furthermore, since Tarda closely spectrally matches P-type asteroids (but compositionally matches the D-type asteroid like Tagish Lake meteorite), P-type and D-type asteroids may represent fragments of the same or similar parent bodies.

58 GEOSCIENCES↗
DOE OSTI2019

Squeezing Marsquakes Out of Groundwater

Pore pressure in aquifers confined below a cryosphere will increase as Mars cools and the cryosphere thickens. Increased pore pressure decreases the effective stress and hence promotes seismicity. We calculate the rate of pore pressure change from cooling of Mars's interior and the modulation of pore pressure from solar and Phobos tides and barometric loading. Using the time-varying pressure and tidal stresses, we compute Coulomb stress changes and the expected seismicity rate from a rate-and-state friction model. Seismicity rate will vary by several tens of percent to 2 orders of magnitude if the mean pore pressure is within 0.2 and 0.01 MPa of lithostatic, respectively. Seismic events promoted by high pore pressure may be tremor-like. Documenting (or not) tidally modulated shallow seismicity would provide evidence for (or against) water-filled confined aquifers, that pore pressure is high, and that the state of stress is close to failure—with implications for processes that can deliver water to the Martian surface.

58 GEOSCIENCES↗
DOE OSTI2025

Measurement of directed flow in Au + Au collisions at $\sqrt{s{NN}}$ = 19.6 and 27 GeV with the STAR event plane detector

In heavy-ion collision experiments, the global collectivity of final-state particles can be quantified by anisotropic flow coefficients (𝑣 𝑛 ) . The first-order flow coefficient, also referred to as the directed flow (𝑣 1 ), describes the collective sideward motion of produced particles and nuclear fragments in heavy-ion collisions. It carries information on the very early stage of the collision, especially at large pseudorapidity (𝜂), where it is believed to be generated during the nuclear passage time. Directed flow therefore probes the onset of bulk collective dynamics during thermalization, providing valuable experimental guidance to models of the pre-equilibrium stage. In 2018, the Event Plane Detector (EPD) was installed in STAR and used for the Beam Energy Scan phase-II (BES-II) data taking. The combination of EPD (2.1 < |𝜂| < 5.1) and high-statistics BES-II data enables us to extend the 𝑣 1 measurement to the forward and backward 𝜂 regions. In this paper, we present the measurement of 𝑣 1 over a wide 𝜂 range in Au + Au collisions at $\sqrt{s_{NN}}$ = 19.6 and 27 GeV using the STAR EPD. The results of the analysis at $\sqrt{s_{NN}}$ = 19.6 GeV exhibit excellent consistency with the previous PHOBOS measurement, while elevating the precision of the overall measurement. The increased precision of the measurement also revealed finer structures in heavy-ion collisions, including a potential observation of the first-order event-plane decorrelation. Multiple physics models were compared to the experimental results. Only a transport model and a three-fluid hybrid model can reproduce a sizable 𝑣 1 at large 𝜂 as was observed experimentally. The model comparison also indicates 𝑣 1 at large 𝜂 might be sensitive to the QGP phase transition.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗