9,870 research outputs found
Shadowing and Absorption Effects on J/psi Production in dA Collisions
We study medium modifications of J/psi production in cold nuclear media in
deuterium-nucleus collisions. We discuss several parameterizations of the
modifications of the parton densities in the nucleus, known as shadowing, an
initial-state effect. We also include absorption of the produced J/psi by
nucleons, a final-state effect. Both spatially homogeneous and inhomogeneous
shadowing and absorption are considered. We use the number of binary
nucleon-nucleon collisions as a centrality measure. Results are presented for
d+Au collisions at sqrt{S_{NN}} = 200 GeV and for d+Pb collisions at
sqrt{S_{NN}} = 6.2 TeV. To contrast the centrality dependence in pA and dA
collisions, we also present pPb results at sqrt{S_{NN}} = 8.8 TeV.Comment: 22 pages, 11 figures, uses revte
Congener speciïŹc analysis of polychlorinated terphenyls
In order to identify and to quantify polychlorinated terphenyls (PCT) in environmental matrices, the chro-
matographic behavior of coplanar and non-coplanar congeners was evaluated. A mixture of 16 single PCT
congeners was used for method development. Four of these compounds were synthesized for the ïŹrst
time by SUZUKI-coupling reaction. These were p-PCT (2,200
,6,600
-tetrachloro-, 20
,3,300
,4,400
,50
,-hexachloro-,
20
,3,300
,5,50
,500
-hexachloro-) and m-PCT (2,200
,3,300
,5,500
-hexachloro-). They were characterized by NMR
(
1
H,
13
C) spectroscopy. By means of the new column chromatographic clean-up reported here, a good
matrix removal and the separation of the coplanar PCT congeners from the non-coplanar ones was
obtained. The recovery rates for all congeners were good for the PCT in different test matrices like fat,
charcoal, and soil. The quality of the clean-up, the separation and the recovery rates were determined
by GC/MS analysis. The method was applied for the ïŹrst time to a real sample from a ïŹre accident, where
different PCT, obviously formed during the combustion process, were found. The conclusion is drawn that
this method is suitable for the analysis of PCT in different environmental samples
Impingement of Water Droplets on NACA 65A004 Airfoil at 8 deg Angle of Attack
The trajectories of droplets in the air flowing past an NACA 65AO04 airfoil at an angle of attack of 8 deg were determined.. The amount of water in droplet form impinging on the airfoil, the area of droplet impingement, and the rate of droplet impingement per unit area on the airfoil surface were calculated from the trajectories and presented to cover a large range of flight and atmospheric conditions. These impingement characteristics are compared briefly with those previously reported for the same airfoil at an angle of attack of 4 deg
Dissociation rates of J/psi's with comoving mesons - thermal vs. nonequilibrium scenario
We study J/psi dissociation processes in hadronic environments. The validity
of a thermal meson gas ansatz is tested by confronting it with an alternative,
nonequilibrium scenario. Heavy ion collisions are simulated in the framework of
the microscopic transport model UrQMD, taking into account the production of
charmonium states through hard parton-parton interactions and subsequent
rescattering with hadrons. The thermal gas and microscopic transport scenarios
are shown to be very dissimilar. Estimates of J/psi survival probabilities
based on thermal models of comover interactions in heavy ion collisions are
therefore not reliable.Comment: 12 pages, 6 figure
Sea flavor content of octet baryons and intrinsic five-quark Fock states
Sea quark contents of the octet baryons are investigated by employing an
extended chiral constituent quark approach, which embodies higher Fock
five-quark components in the baryons wave-functions. The well-known flavor
asymmetry of the nucleon sea , is used as input to predict the
probabilities of , and in the nucleon, ,
and baryons, due to the intrinsic five-quark components in the
baryons wave functions.Comment: 22 page
Bottomonium Production at RHIC and LHC
Properties of bottomonia (Upsilon, chi_b and Upsilon') in the Quark-Gluon
Plasma (QGP) are investigated by assessing inelastic reaction rates and their
interplay with open-bottom states (b-quarks or B-mesons) and color-screening.
The latter leads to vanishing quarkonium binding energies at sufficiently high
temperatures (close to the dissolution point), which, in particular, renders
standard gluo-dissociation, g+Upsilon -> b + b-bar, inefficient due to a
substantial reduction in final-state phase space. This problem is overcome by
invoking a "quasifree" destruction mechanism, g,q,q-bar + Upsilon -> g,q,q-bar
+ b + b-bar, as previously introduced for charmonia. The pertinent reaction
rates are implemented into a kinetic theory framework to evaluate the time
evolution of bottomonia in heavy-ion reactions at RHIC and LHC within an
expanding fireball model. While bottom quarks are assumed to be exclusively
produced in primordial nucleon-nucleon collisions, their thermal relaxation
times in the QGP, which importantly figure into Upsilon-formation rates, are
estimated according to a recent Fokker-Planck treatment. Predictions for the
centrality dependence of Upsilon production are given for upcoming experiments
at RHIC and LHC. At both energies, Upsilon suppression turns out to be the
prevalent effect.Comment: 16 Pages, 21 figures, 1 table v2: Manuscript reorganized, several
sections moved to appendices, additional comments included, contents
unchange
Shadowing Effects on the Nuclear Suppression Factor, R_dAu, in d+Au Interactions
We explore how nuclear modifications to the nucleon parton distributions
affect production of high transverse momentum hadrons in deuteron-nucleus
collisions. We calculate the charged hadron spectra to leading order using
standard fragmentation functions and shadowing parameterizations. We obtain the
d+Au to pp ratio both in minimum bias collisions and as a function of
centrality. The minimum bias results agree reasonably well with the BRAHMS data
while the calculated centrality dependence underestimates the data and is a
stronger function of p_T than the data indicate.Comment: 18 pages, 3 figures, final version, Phys. Rev. C in pres
Open Charm Production at STAR
We present the open charm spectra at mid-rapidity from direct reconstruction
of D0, D* and D+/- in d+Au collisions at sqrt(sNN)=200 GeV using the STAR
detector at RHIC. The indirect electron/positron measurements via charm
semileptonic decays in p+p and d+Au collisions are also reported. The total
c\bar(c) cross section per nucleon-nucleon collision is extracted from both
direct and indirect measurements and are consistent with each other. By
combining the D0 and semileptonic measurements together, the cross section of
1.4+/-0.2+/-0.4 mb is higher than expectations from PYTHIA and other pQCD
calculations. The open charm pT distribution from direct measurements covers
the pT range up to ~10 GeV/c and follows a power-law distribution.Comment: 7 pages, 4 figures, proceedings for Hot Quark 04 Conference.
submitted to J. Phys. G: Nucl. Phy
An interval logic for higher-level temporal reasoning
Prior work explored temporal logics, based on classical modal logics, as a framework for specifying and reasoning about concurrent programs, distributed systems, and communications protocols, and reported on efforts using temporal reasoning primitives to express very high level abstract requirements that a program or system is to satisfy. Based on experience with those primitives, this report describes an Interval Logic that is more suitable for expressing such higher level temporal properties. The report provides a formal semantics for the Interval Logic, and several examples of its use. A description of decision procedures for the logic is also included
- âŠ