185 research outputs found
One-neutron removal reactions on light neutron-rich nuclei
A study of high energy (43--68 MeV/nucleon) one-neutron removal reactions on
a range of neutron-rich psd-shell nuclei (Z = 5--9, A = 12--25) has been
undertaken. The inclusive longitudinal and transverse momentum distributions
for the core fragments, together with the cross sections have been measured for
breakup on a carbon target. Momentum distributions for reactions on tantalum
were also measured for a subset of nuclei. An extended version of the Glauber
model incorporating second order noneikonal corrections to the JLM
parametrisation of the optical potential has been used to describe the nuclear
breakup, whilst the Coulomb dissociation is treated within first order
perturbation theory. The projectile structure has been taken into account via
shell model calculations employing the psd-interaction of Warburton and Brown.
Both the longitudinal and transverse momentum distributions, together with the
integrated cross sections were well reproduced by these calculations and
spin-parity assignments are thus proposed for B, C, N,
O, F. In addition to the large spectroscopic amplitudes for
the s intruder configuration in the N=9 isotones,B and
C, significant s admixtures appear to occur in the
ground state of the neighbouring N=10 nuclei B and C. Similarly,
crossing the N=14 subshell, the occupation of the s orbital is
observed for O, F. Analysis of the longitudinal and transverse
momentum distributions reveals that both carry spectroscopic information, often
of a complementary nature. The general utility of high energy nucleon removal
reactions as a spectroscopic tool is also examined.Comment: 50 pages, 19 figures, submitted to Phys. Rev.
Polarization Phenomena in Small-Angle Photoproduction of e+e- Pairs and the Gerasimov-Drell-Hearn Sum Rule
Photoproduction of pairs at small angles is investigated as a tool
to determine the functions and entering the real-photon forward
Compton scattering amplitude. The method is based on an interference of the
Bethe-Heitler and the virtual Compton scattering mechanisms, generating an
azimuthal asymmetry in the versus yield. The general case of a
circularly polarized beam and a longitudinally polarized target allows one to
determine both the real and imaginary parts of as well as . The
imaginary part of requires target polarization only. We calculate cross
sections and asymmetries of the reaction , estimate
corrections and backgrounds, and propose suitable kinematical regions to
perform the experiment. Our investigation shows that photoproduction of
-pairs off the proton and light nuclei may serve as a rather sensitive
test of the validity of the Gerasimov-Drell-Hearn sum rule.Comment: 22 pages; revtex; 5 postscript figures included in submission;
submitted to Phys. Rev.
High precision position measurements at high counting rates with drift chambers and multi-hit electronics
11 pages, 7 figure
One-neutron removal reactions on neutron-rich psd-shell nuclei
A systematic study of high energy, one-neutron removal reactions on 23
neutron-rich, psd--shell nuclei (Z=5-9, A=12-25) has been carried out. The
longitudinal momentum distributions of the core fragments and corresponding
single-neutron removal cross sections are reported for reactions on a carbon
target. Extended Glauber model calculations, weighted by the spectroscopic
factors obtained from shell model calculations, are compared to the
experimental results. Conclusions are drawn regarding the use of such reactions
as a spectroscopic tool and spin-parity assignments are proposed for 15B, 17C,
19-21N, 21,23O, 23-25F. The nature of the weakly bound systems 14B and 15,17C
is discussed.Comment: 11 pages + 2 figure
Virtual coupling potential for elastic scattering of Be on proton and carbon targets
International audienceThe 10;11Be(p,p) and (12C, 12C) reactions were analyzed to determine the in uence of the weak binding energies of exotic nuclei on their interaction potential. The elastic cross sections were measured at GANIL in inverse kinematics using radioactive 10;11Be beams produced at energies of 39:1 A and 38:4A MeV. The elastic proton scattering data were analyzed within the framework of the microscopic Jeukenne-Lejeune-Mahaux (JLM) nucleon-nucleus potential. The angular distributions are found to be best reproduced by reducing the real part of the microscopic optical potential, as a consequence of the coupling to the continuum. These effects modify deeply the elastic potential. Including the Virtual Coupling Potential (VCP), we show the ability of the general optical potentials to reproduce the data for scattering of unstable nuclei, using realistic densities. Finally, the concepts needed to develop a more general and microscopic approach of the VCP are discussed
Coupling effects in the elastic scattering of He on C
To study the effect of the weak binding energy on the interaction potential between a light exotic nucleus and a target, elastic scattering of 6He at 38.3 MeV/nucleon on a 12C target was measured at Grand Accélérateur National d'Ions Lourds (GANIL). The 6He beam was produced by fragmentation. The detection of the scattered particles was performed by the GANIL spectrometer. The energy resolution was good enough to separate elastic from inelastic scattering contributions. The measured elastic data have been analyzed within the optical model, with the real part of the optical potential calculated in the double-folding model using a realistic density-dependent nucleon-nucleon interaction and the imaginary part taken in the conventional Woods-Saxon (WS) form. A failure of the "bare" real folded potential to reproduce the measured angular distribution over the whole angular range suggests quite a strong coupling of the higher-order breakup channels to the elastic channel. To estimate the strength of the breakup effects, a complex surface potential with a repulsive real part (designed to simulate the polarization effects caused by the projectile breakup) was added to the real folded and imaginary WS potentials. A realistic estimate of the polarization potential caused by the breakup of the weakly bound 6He was made based on a parallel study of 6He+12C and 6Li+12C optical potentials at about the same energies
A new measurement of J/psi suppression in Pb-Pb collisions at 158 GeV per nucleon
We present a new measurement of J/psi production in Pb-Pb collisions at 158
GeV/nucleon, from the data sample collected in year 2000 by the NA50
Collaboration, under improved experimental conditions with respect to previous
years. With the target system placed in vacuum, the setup was better adapted to
study, in particular, the most peripheral nuclear collisions with unprecedented
accuracy. The analysis of this data sample shows that the (J/psi)/Drell-Yan
cross-sections ratio measured in the most peripheral Pb-Pb interactions is in
good agreement with the nuclear absorption pattern extrapolated from the
studies of proton-nucleus collisions. Furthermore, this new measurement
confirms our previous observation that the (J/psi)/Drell-Yan cross-sections
ratio departs from the normal nuclear absorption pattern for semi-central Pb-Pb
collisions and that this ratio persistently decreases up to the most central
collisions.Comment: 19 pages, 10 figures. Submitted to Eur. Phys. J.
Mass Measurements near N=Z
Abstract After an outline of the physics motivations, that illustrate why we think it is important to measure masses in the region NâZ, we report on on experiments performed at Ganil. An experiment aimed at measuring the masses of proton-rich nuclei in the mass region A â 60â80 has been performed, using a direct time-of-flight technique in conjunction with SISSI and the SPEG spectrometer at GANIL. The nuclei were produced via the fragmentation of a 78 Kr beam (73 meV/nucleon). A novel technique for the purification of the secondary beams, based on the stripping of the ions and using the α and the SPEG spectrometers, was succesfully checked. It allows for good selectivity without altering the beam quality. Secondary ions of 100 Ag, 100 Cd, 100 In and 100 Sn were produced via the fusion-evaporation reaction 50 Cr + 58 Ni at an energy of 5.1 MeV/nucleon, and were accelerated simultaneously in the second cyclotron of GANIL (CSS2). About 10 counts were observed from the production and acceleration of 100 Sn 22+ . The masses of 100 Cd, 100 In and 100 Sn were measured with respect to 100 Ag using the CSS2 cyclotron, with precisions of 2 Ă 10 â6 , 3 Ă 10 â6 and 10 â5 respectively
J/psi azimuthal anisotropy relative to the reaction plane in Pb-Pb collisions at 158 GeV per nucleon
The J/ azimuthal distribution relative to the reaction plane has been
measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various
physical mechanisms related to charmonium dissociation in the medium created in
the heavy ion collision are expected to introduce an anisotropy in the
azimuthal distribution of the observed J/ mesons at SPS energies. Hence,
the measurement of J/ elliptic anisotropy, quantified by the Fourier
coefficient v of the J/ azimuthal distribution relative to the
reaction plane, is an important tool to constrain theoretical models aimed at
explaining the anomalous J/ suppression observed in Pb-Pb collisions. We
present the measured J/ yields in different bins of azimuthal angle
relative to the reaction plane, as well as the resulting values of the Fourier
coefficient v as a function of the collision centrality and of the
J/ transverse momentum. The reaction plane has been estimated from the
azimuthal distribution of the neutral transverse energy detected in an
electromagnetic calorimeter. The analysis has been performed on a data sample
of about 100 000 events, distributed in five centrality or p
sub-samples. The extracted v values are significantly larger than zero
for non-central collisions and are seen to increase with p.Comment: proceedings of HP08 conference corrected a typo in one equatio
Bottomonium and Drell-Yan production in p-A collisions at 450 GeV
The NA50 Collaboration has measured heavy-quarkonium production in p-A
collisions at 450 GeV incident energy (sqrt(s) = 29.1 GeV). We report here
results on the production of the Upsilon states and of high-mass Drell-Yan muon
pairs (m > 6 GeV). The cross-section at midrapidity and the A-dependence of the
measured yields are determined and compared with the results of other
fixed-target experiments and with the available theoretical estimates. Finally,
we also address some issues concerning the transverse momentum distributions of
the measured dimuons.Comment: 18 pages, 9 figures, to be published in Phys. Lett.
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