We review the main results obtained by the BRAHMS Collaboration on the properties of hot and dense hadronic and partonic matter produced in ultrarelativistic heavy ion collisions at RHIC. A ...particular focus of this paper is to discuss to what extent the results collected so far by BRAHMS, and by the other three experiments at RHIC, can be taken as evidence for the formation of a state of deconfined partonic matter, the so-called quark–gluon plasma (QGP). We also discuss evidence for a possible precursor state to the QGP, i.e., the proposed color glass condensate.
Transverse momentum spectra of protons and anti-protons measured in the rapidity range 0<y<3.1 from 0–10% central Au+Au collisions at sNN=62.4 GeV are presented. The rapidity densities, dN/dy, of ...protons, anti-protons and net-protons (Np–Np¯) have been deduced from the spectra over a rapidity range wide enough to observe the expected maximum net-baryon density. From mid-rapidity to y=1 the net-proton yield is roughly constant (dN/dy∼10), but rises to dN/dy∼25 at 2.3<y<3.1. The mean rapidity loss is 2.01±0.14±0.12 units from beam rapidity. The measured rapidity distributions are compared to model predictions. Systematics of net-baryon distributions and rapidity loss vs. collision energy are discussed.
The BRAHMS collaboration has measured transverse momentum spectra of pions, kaons, protons, and antiprotons at rapidities 0 and 3 for Cu+Cu collisions at s NN =200 GeV. As the collisions become more ...central the collective radial flow increases while the temperature of kinetic freeze-out decreases. The temperature is lower and the radial flow weaker at forward rapidity. Pion and kaon yields with transverse momenta between 1.5 and 2.5 GeV/c are suppressed for central collisions relative to scaled p + p collisions. This suppression, which increases as the collisions become more central, is consistent with jet quenching models and is also present with comparable magnitude at forward rapidity. At such rapidities, initial state effects may also be present and persistence of the meson suppression to high rapidity may reflect a combination of jet quenching and nuclear shadowing. In conclusion, the ratio of protons to mesons increases as the collisions become more central and is largest at forward rapidities.
Angular distributions for the
163Dy(
t
,
p
) and
177Hf(
t
,
p
) reactions were measured using 17 MeV tritons from the McMaster University Tandem Van de Graaff accelerator. Reaction products were ...analyzed with a magnetic spectrograph and detected with photographic emulsions. Favored
L
=
0
transitions confirmed assignments of the
5
/
2
−
523
band in
165Dy and
7
/
2
−
514
band in
179Hf. Additional
L
=
0
transitions in each nuclide identified previously unknown
5
/
2
−
levels in
165Dy and
7
/
2
−
ones in
179Hf. Overall trends of
L
=
0
strengths support the existence of subshell closures at neutron numbers 98 and 108. On the basis of a relatively strong
L
=
2
transition, the
K
π
=
11
/
2
−
γ-vibration based on the
7
/
2
−
514
state is identified at 1689 keV in
179Hf, about 440 keV above its previously-assigned
K
π
=
3
/
2
−
partner.
The WA97 experiment has measured the transverse mass \(({m_{\mathrm T}})\) spectra for negative hadrons (\(\mathrm{h}^-\)) and strange particles produced at mid–rapidity in Pb–Pb collisions. The ...increased statistics of analysed data samples allowed us to perform a study of the spectra of \({\rm K_S^0}\), \(\mathrm{\Lambda}\), \(\mathrm{\Xi}\), \(\mathrm{\Omega}\) and \(\mathrm{h}^-\) as a function of the collision centrality. The data, which correspond to the most central 40% of the total inelastic cross section, have been divided into four centrality classes according to the estimated number of nucleons taking part in the collision. The \(m_{\mathrm T}\) spectra, analysed separately for each centrality bin, exhibit only weak (\(\leq\) 15%) centrality dependence. The deviation of the \(\mathrm{\Omega}\) inverse slope from the linear dependence on the particle mass is confirmed even for the most central Pb–Pb collisions.
There is lack of knowledge of the structure of the 231Ac nucleus located in the upper border of the island of octupole deformation centered around A = 225. We have populated the excited states in ...231Ac by beta-decay from the parent 231Ra produced at ISOLDE, CERN. The low-energy structure of 231Ac has been investigated by means of gamma, conversion electrons, gamma-gamma and gamma-e- spectroscopy. We report here in the precise determination in 231Ac of the half-life of the most intensively populated states by the Advanced Time Delayed betabetagamma(t) technique.
A measurement of strange baryon and antibaryon production in Pb–Pb collisions has been carried out by the NA57 experiment at the CERN SPS, with 40 and 158 AGeV/c beam momentum. Results on Λ, Ξ and Ω ...hyperon yields at mid-rapidity in the most central 53% of Pb–Pb collisions at 40 AGeV/c are presented and compared with those obtained at higher energy, in the same collision centrality range.
The Λ and Ξ− yields per unit rapidity stay roughly constant while those of Ω−, Λ̄, Ξ̄+ and Ω̄+ increase when going to the higher SPS energy. Hyperon yields at the SPS are compared with those from the STAR experiment in sNN=130 GeV Au–Au collisions at RHIC.
We report the main results from experiment WA97 on the production of strange and multistrange hadrons at midrapidity in Pb+Pb, p+Pb and p+Be collisions at 158
A GeV/
c. A comparison with some of the ...available models is presented.
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