447 research outputs found
Thermal and electromagnetic properties of 166-Er and 167-Er
The primary gamma-ray spectra of 166-Er and 167-Er are deduced from the
(3-He,alpha gamma) and (3-He,3-He' gamma) reaction, respectively, enabling a
simultaneous extraction of the level density and the gamma-ray strength
function. Entropy, temperature and heat capacity are deduced from the level
density within the micro-canonical and the canonical ensemble, displaying
signals of a phase-like transition from the pair-correlated ground state to an
uncorrelated state at Tc=0.5 MeV. The gamma-ray strength function displays a
bump around E-gamma=3 MeV, interpreted as the pygmy resonance.Comment: 21 pages including 2 tables and 11 figure
Gamma-ray strength function and pygmy resonance in rare earth nuclei
The gamma-ray strength function for gamma energies in the 1-7 MeV region has
been measured for 161,162-Dy and 171,172-Yb using the (3-He,alpha gamma)
reaction. Various models are tested against the observed gamma-ray strength
functions. The best description is based on the Kadmenskii, Markushev and
Furman E1 model with constant temperature and the Lorentzian M1 model. A
gamma-ray bump observed at E_gamma=3 MeV is interpreted as the so-called pygmy
resonance, which has also been observed previously in (n,gamma) experiments.
The parameters for this resonance have been determined and compared to the
available systematics.Comment: 11 pages, including 4 figures and 2 table
Centrality dependence of charged-particle pseudorapidity distributions from d+Au collisions at sqrt(s_{NN})=200 GeV
Charged-particle pseudorapidity densities are presented for the d+Au reaction
at sqrt{s_{NN}}=200 GeV with -4.2 <= eta <= 4.2$. The results, from the BRAHMS
experiment at RHIC, are shown for minimum-bias events and 0-30%, 30-60%, and
60-80% centrality classes. Models incorporating both soft physics and hard,
perturbative QCD-based scattering physics agree well with the experimental
results. The data do not support predictions based on strong-coupling,
semi-classical QCD. In the deuteron-fragmentation region the central 200 GeV
data show behavior similar to full-overlap d+Au results at sqrt{s_{NN}}=19.4
GeV.Comment: 4 pages, 3figures; expanded discussion of uncertainties; added 60-80%
centrality range; added additional discussion on centrality selection bia
Scanning the phases of QCD with BRAHMS
BRAHMS has the ability to study relativistic heavy ion collisions from the
final freeze-out of hadrons all the way back to the initial wave-function of
the gold nuclei. This is accomplished by studying hadrons with a very wide
range of momenta and angles. In doing so we can scan various phases of QCD,
from a hadron gas, to a quark gluon plasma and perhaps to a color glass
condensate.Comment: 8 pages, 6 figures, proceedings of plenary talk at Quark Matter 2004
conferenc
High Pt Hadron Spectra at High Rapidity
We report the measurement of charged hadron production at different
pseudo-rapidity values in deuteron+gold as well as proton+proton collisions at
= 200GeV at RHIC. The nuclear modification factors and
are used to investigate new behaviors in the deuteron+gold system as
function of rapidity and the centrality of the collisions respectively.Comment: Nine pages 4 figures to be published in the QM2004 Proceedings, typos
corrected and one reference adde
Charged particle densities from Au+Au collisions at sqrt{s_{NN}}=130 GeV
We present charged particle densities as a function of pseudorapidity and
collision centrality for the 197Au+197Au reaction at sqrt{s_{NN}}=130 GeV. An
integral charged particle multiplicity of 3860+/-300 is found for the 5% most
central events within the pseudorapidity range -4.7 <= eta <= 4.7. At
mid-rapidity an enhancement in the particle yields per participant nucleon pair
is observed for central events. Near to the beam rapidity, a scaling of the
particle yields consistent with the ``limiting fragmentation'' picture is
observed. Our results are compared to other recent experimental and theoretical
discussions of charged particle densities in ultra-relativistic heavy-ion
collisions.Comment: 14 pages, 4 figures; to be published in Phys. Lett.
Nuclear Modification Factor for Charged Pions and Protons at Forward Rapidity in Central Au+Au Collisions at 200 GeV
We present spectra of charged pions and protons in 0-10% central Au+Au
collisions at GeV at mid-rapidity () and forward
pseudorapidity () measured with the BRAHMS experiment at RHIC. The
spectra are compared to spectra from p+p collisions at the same energy scaled
by the number of binary collisions. The resulting nuclear modification factors
for central Au+Au collisions at both and exhibit suppression
for charged pions but not for (anti-)protons at intermediate . The
ratios have been measured up to GeV/ at the two
rapidities and the results indicate that a significant fraction of the charged
hadrons produced at intermediate range are (anti-)protons at both
mid-rapidity and
Forward and midrapidity like-particle ratios from p+p collisions at sqrt(s)=200 GeV
We present a measurement of pi-\pi+, K-/K+ and pbar/p from p+p collisions at
sqrt(s) = 20 0GeV over the rapidity range 0<y<3.4. For pT < 2.0 GeV/c we see no
significant transverse momentum dependence of the ratios. All three ratios are
independent of rapidity for y ~< 1.5 and then steadily decline from y ~ 1.5 to
y ~ 3. The pi-\pi+ ratio is below unity for y > 2.0. The pbar/p ratio is very
similar for p+p and 20% central Au+Au collisions at all rapidities. In the
fragmentation region the three ratios seem to be independent of beam energy
when viewed from the rest frame of one of the protons. Theoretical models based
on quark-diquark breaking mechanisms overestimate the pbar/p ratio up to y ~<
3. Including additional mechanisms for baryon number transport such as baryon
junctions leads to a better description of the data.Comment: 15 pages, 4 figures, uses elsart.sty. Changes to references and
discussion based on referee comments, resubmitted to Phys. Lett.
The New Physics at RHIC. From Transparency to High p Suppression
Heavy ion collisions at RHIC energies (Au+Au collisions at
GeV) exhibit significant new features as compared to
earlier experiments at lower energies. The reaction is characterized by a high
degree of transparency of the collisions partners leading to the formation of a
baryon-poor central region. In this zone, particle production occurs mainly
from the stretching of the color field. The initial energy density is well
above the one considered necessary for the formation of the Quark Gluon Plasma,
QGP. The production of charged particles of various masses is consistent with
chemical and thermal equilibrium. Recently, a suppression of the high
transverse momentum component of hadron spectra has been observed in central
Au+Au collisions. This can be explained by the energy loss experienced by
leading partons in a medium with a high density of unscreened color charges. In
contrast, such high jets are not suppressed in d+Au collisions suggesting
that the high suppression is not due to initial state effects in the
ultrarelativistic colliding nuclei.Comment: 15 pages, 11 figures. to appear in Nucl. Physics A. Invited talk at
'Nucleus-Nucleus Collisions 2003' conference, Mosco
New results from the NA57 experiment
We report results from the experiment NA57 at CERN SPS on hyperon production
at midrapidity in Pb-Pb collisions at 158 GeV/ and 40 GeV/.
, and yields are compared with those from the STAR
experiment at the higher energy of the BNL RHIC. , , \
and preliminary transverse mass spectra are presented and interpreted
within the framework of a hydro-dynamical blast wave model.Comment: 8 pages, 3 figures, contribution to the proceedings of The XXXVIIIth
Rencontres de Moriond "QCD and High Energy Hadronic Interactions
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