377 research outputs found
Projectilelike fragments from N14 beams at 15, 25, and 35 MeV/nucleon
Momentum distributions of projectilelike fragments produced in the interaction of 15, 25, and 35 MeV/nucleon N14 beams on targets of C12, Mg24, Al27, Ti48, and Ni58 have been measured. Widths and centroids of the quasielastic component of the distributions have been extracted for fragments ranging from He4 to N13. The widths are compared with published data and several theoretical predictions. The Friedman model correctly predicts the charge and isotope dependence of the widths at the highest beam energy. At 15 MeV/nucleon some deviations from the trend of the published data suggest the possibility of a different reaction mechanism for the projectile-target combinations studied in the present work
System-size dependence of the pion freeze-out volume as a potential signature for the phase transition to a Quark Gluon Plasma
Hanburry-Brown-Twiss (HBT) correlation functions and radii of negatively
charged pions from C+C, Si+Si, Cu+Cu, and In+In at lower RHIC/SPS energies are
calculated with the UrQMD transport model and the CRAB analyzing program. We
find a minimum in the excitation function of the pion freeze-out volume at low
transverse momenta and around GeV which can be related to
the transition from hadronic to string matter (which might be interpreted as a
pre-cursor of the QGP). The existence of the minimum is explained by the
competition of two mechanisms of the particle production, resonance decays and
string formation/fragmentation.Comment: 12 pages, 4 fig
Silicon Pad Detectors for the PHOBOS Experiment at RHIC
The PHOBOS experiment is well positioned to obtain crucial information about
relativistic heavy ion collisions at RHIC, combining a multiplicity counter
with a multi-particle spectrometer. The multiplicity arrays will measure the
charged particle multiplicity over the full solid angle. The spectrometer will
be able to identify particles at mid-rapidity. The experiment is constructed
almost exclusively of silicon pad detectors. Detectors of nine different types
are configured in the multiplicity and vertex detector (22,000 channels) and
two multi-particle spectrometers (120,000 channels). The overall layout of the
experiment, testing of the silicon sensors and the performance of the detectors
during the engineering run at RHIC in 1999 are discussed.Comment: 7 pages, 7 figures, 1 table, Late
Evaporation residue cross sections and average neutron multiplicities in the 64Ni+92Zr and 12C+144Sm reactions leading to 156Er
Evaporation residue cross sections and neutron multiplicity distributions have been measured for the 12C + 144Sm and 64Ni + 92Zr reactions leading to the same compound nucleous 156Er. Statistical model calculations can account for the data in the 12C-induced reaction. In contrast, the inhibition of neutron emission with respect to statistical model predictions seen in 64Ni + 92Zr cannot be explained even with the inclusion of the broad angular momentum distributions required to describe the fusion cross section data
C10 and 11B+ 12C reactions from 4 to 9 MeV/nucleon
Reaction products arising from the interaction of 11B+ 12C and 10B+ 13C have been studied in the energy range 4<Elab(B)<9 MeV/nucleon. From the total fusion cross sections for the two entrance channels, the critical angular momenta have been extracted and then compared as a function of compound nucleus excitation energy. Even though a limitation in the fusion cross section was observed, no common limitation was found in the critical angular momenta for these two systems up to at least a Na23 excitation energy of 60 MeV. Above this excitation energy, the experimental uncertainties make this point less clear. Up to an excitation energy of 60 MeV in Na23, a fusion limitation based on reaching a critical density of compound nucleus states like the yrast or ''statistical'' yrast line cannot be responsible for the fusion cross section limitations observed for these entrance channels. The present data suggest that competing entrance channel processes are responsible for the observed fusion cross section limitations
Velocity and angular distributions of evaporation residues from induced32 reactions
Velocity distributions of mass-resolved evaporation residues from reactions of S32 with C12, Mg24, Al27, Si28, and Ca40 have been measured at bombarding energies of 194, 239, and 278 MeV using time-of-flight techniques. In all cases, the observed shifts in the velocity centroids relative to the values expected for complete fusion are consistent with a previously reported parametrization of a threshold for onset of incomplete fusion. Angular distributions were measured and total cross sections extracted for the Mg32 system at all three energies. A comparison with existing results for Mg32 at lower energies, and with other systems leading to the Ni56 compound nucleus, suggests two different types of compound-nuclear limitations to complete fusion at higher energies
Fusion evaporation-residue cross sections for Si28+40Ca at E(28Si)=309, 397, and 452 MeV
Velocity distributions of mass-identified evaporation residues produced in the Si28+40Ca reaction have been measured at bombarding energies of 309, 397, and 452 MeV using time-of-flight techniques. These distributions were used to identify evaporation residues and to separate the complete-fusion and incomplete-fusion components. Angular distributions and upper limits for the total evaporation-residue and complete-fusion evaporation-residue cross sections were extracted at all three bombarding energies. The complete-fusion evaporation-residue cross sections and the deduced critical angular momenta are compared with earlier measurements and the predictions of existing models. The ratios of the complete-fusion evaporation-residue cross section to the total evaporation-residue cross section, along with those measured for the Si28+12C and Si28+28Si systems at the same energies, support the entrance-channel mass-asymmetry dependence of the incomplete-fusion evaporation-residue process reported earlier
Evidence of Final-State Suppression of High-p_T Hadrons in Au + Au Collisions Using d + Au Measurements at RHIC
Transverse momentum spectra of charged hadrons with 6 GeV/c have
been measured near mid-rapidity (0.2 1.4) by the PHOBOS experiment
at RHIC in Au + Au and d + Au collisions at . The spectra for different collision centralities are compared to collisions at the same energy. The resulting nuclear modification
factor for central Au + Au collisions shows evidence of strong suppression of
charged hadrons in the high- region ( GeV/c). In contrast, the d +
Au nuclear modification factor exhibits no suppression of the high-
yields. These measurements suggest a large energy loss of the high-
particles in the highly interacting medium created in the central Au + Au
collisions. The lack of suppression in d + Au collisions suggests that it is
unlikely that initial state effects can explain the suppression in the central
Au + Au collisions.Comment: 3 pages, 4 figures, International Europhysics Conference on High
Energy Physics EPS (July 17th-23rd 2003) in Aachen, German
Au+Au Reactions at the AGS: Experiments E866 and E917
Particle production and correlation functions from Au+Au reactions have been
measured as a function of both beam energy (2-10.7AGeV) and impact parameter.
These results are used to probe the dynamics of heavy-ion reactions, confront
hadronic models over a wide range of conditions and to search for the onset of
new phenomena.Comment: 12 pages, 14 figures, Talk presented at Quark Matter '9
Influence of nucleon Fermi motion on incomplete fusion
Velocity spectra were measured for evaporation residues produced in fusion reactions induced by 5-35 MeV/A14N. The results, together with published data for 16O and 20Ne induced fusion, are shown to reveal a projectile dependence of incomplete fusion processes. The data can be qualitatively described in terms of a picture which takes into account the vector addition of the center-of-mass velocities of the interacting nuclei with the intrinsic Fermi velocities of the nucleons
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