Sulphur-nucleus Collisions Research Articles

Charged kaon and pion production at midrapidity in proton-nucleus and sulphur-nucleus collisions

The NA44 collaboration has measured charged kaon and pion distributions at midrapidity in sulphur and proton collisions with nuclear targets at 200 and 450 GeV/c per nucleon, respectively. The inverse slopes of kaons are larger than those of pions. The difference in the inverse slopes of pions, kaons and protons, all measured in our spectrometer, increases with system size and is consistent with the buildup of collective flow for larger systems. The target dependence of both the yields and inverse slopes is stronger for the sulphur beam suggesting the increased importance of secondary rescattering for SA reactions. The rapidity density, dN/dy, of both K+ and K- increases more rapidly with system size than for pi+ in a similar rapidity region. This trend continues with increasing centrality, and according to RQMD, it is caused by secondary reactions between mesons and baryons. The K-/K+ ratio falls with increasing system size but more slowly than the pbar/p ratio. The pi-/pi+ ratio is close to unity for all systems. From pBe to SPb the K+/p ratio decreases while K-/pbar increases and ({K+*K-}/{p*pbar})**1/2 stays constant. These data suggest that as larger nuclei collide, the resulting system has a larger transverse expansion, baryon density and an increasing fraction of strange quarks.

Charged particle production in proton-, deuteron-, oxygen- and sulphur-nucleus collisions at 200 GeV per nucleon

The transverse momentum and rapidity distributions of net protons and negatively charged hadrons have been measured for minimum bias proton–nucleus and deuteron–gold interactions, as well as central oxygen–gold and sulphur–nucleus collisions at 200 GeV per nucleon. The rapidity density of net protons at midrapidity in central nucleus–nucleus collisions increases both with target mass for sulphur projectiles and with the projectile mass for a gold target. The shape of the rapidity distributions of net protons forward of midrapidity for d+Au and central S+Au collisions is similar. The average rapidity loss is larger than 2 units of rapidity for reactions with the gold target. The transverse momentum spectra of net protons for all reactions can be described by a thermal distribution with ‘temperatures’ between $145 \pm 11$ MeV (p+S interactions) and $244 \pm 43$ MeV (central S+Au collisions). The multiplicity of negatively charged hadrons increases with the mass of the colliding system. The shape of the transverse momentum spectra of negatively charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and central nucleus-nucleus collisions. The mean transverse momentum is almost constant in the vicinity of midrapidity and shows little variation with the target and projectile masses. The average number of produced negatively charged hadrons per participant baryon increases slightly from p+p, p+A to central S+S,Ag collisions.

Proton and antiproton distributions at midrapidity in proton-nucleus and sulphur-nucleus collisions

Experiment NA44 has measured proton and antiproton distributions at midrapidity in sulphur and proton collisions with nuclear targets at 200 and 450GeV/c per nucleon respectively. The inverse slopes of transverse mass distributions increase with system size for both protons and antiprotons but are slightly lower for antiprotons. This could happen if antiprotons are annihilated in the nuclear medium. The antiproton yield increases with system size and centrality and is largest at midrapidity. The proton yield also increases with system size and centrality, but decreases from backward rapidity to midrapidity. The stopping of protons at these energies lies between the full stopping and nuclear transparency scenarios. The data are in reasonable agreement with RQMD predictions except for the antiproton yields from sulphur-nucleus collisions.Received 25 August 1997DOI:https://doi.org/10.1103/PhysRevC.57.837©1998 American Physical Society

Charged particle production in proton-, deuteron-, oxygen- and sulphur-nucleus collisions at 200 GeV per nucleon

The transverse momentum and rapidity distributions of net protons and negatively charged hadrons have been measured for minimum bias proton-nucleus and deuteron-gold interactions, as well as central oxygen-gold and sulphur-nucleus collisions at 200 GeV per nucleon. The rapidity density of net protons at midrapidity in central nucleus-nucleus collisions increases both with target mass for sulphur projectiles and with the projectile mass for a gold target. The shape of the rapidity distributions of net protons forward of midrapidity for d+Au and central S+Au collisions is similar. The average rapidity loss is larger than 2 units of rapidity for reactions with the gold target. The transverse momentum spectra of net protons for all reactions can be described by a thermal distribution with `temperatures' between 145 +- 11 MeV (p+S interactions) and 244 +- 43 MeV (central S+Au collisions). The multiplicity of negatively charged hadrons increases with the mass of the colliding system. The shape of the transverse momentum spectra of negatively charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and central nucleus-nucleus collisions. The mean transverse momentum is almost constant in the vicinity of midrapidity and shows little variation with the target and projectile masses. The average number of produced negatively charged hadrons per participant baryon increases slightly from p+p, p+A to central S+S,Ag collisions.

Strange antibaryon production data and reduction of strangeness suppression in sulphur-nucleus collisions at 200A GeV

We have used the event generator LUCIAE to analyse NA35 data of the $\bar p$ and $\bar{\Lambda}$ yields, the ratio $\bar{\Lambda}/\bar p$, and the transverse mass distributions of $\bar p$ and $\bar{\Lambda}$ in pp and central sulphur-nucleus collisions at 200A GeV. The NA35 data could be reproduced reasonably if one assumes that the s quark pair suppression factor and concerns in nucleus-nucleus collisions are larger than the nucleon-nucleon collision. It seems to indicate that NA35 data might imply the reduction of strangeness suppression in ultrarelativistic nucleus-nucleus collisions comparing to the nucleon-nucleon collision at the same energy. However, the ratio $\bar{\Lambda}/\bar p$ approaching to unity in AA collisions comparing to the pp collision does not necessarily mean a flavor symmetry since hadronic rescattering plays a role as well.

Strangeness enhancement in sulphur—Nucleus collisions at 200 A GeV/c

The NA35 experiment used several independent methods to determine the strange particle production in p+S and S+A collisions. The different techniques show consistent results. Strangeness conservation in full phase space is used as an additional check of the consistency of the data. On the base of the analysis in full phase space it could be shown that strangeness conservation is fullfilled. The NA35 K$^0_S$ in S+S and S+Ag are consistent with the NA44 results for K$^+$ and K$^-$. The results of the NA36 collaboration for S+Pb collisions were extrapolated to full phase space. The comparison with the NA35 results shows more than two times lower yields. The ratio of $\Lambda$ to $\overline{\Lambda}$ at midrapidity of NA36 is inconsistent with the high baryon density determind by NA35. The strange particle production is compared to the abundance of non strange particles, especially negatively charged pions which are measured in full phase space in the same experiment. A clear enhanced strange hadron production relative to $\pi^-$ is observed in S+Ag collisions compared to p+S reactions at the same energy. The K$^0_S$ multiplicity in full phase space per negative hadron (h$^-$) in S+S, S+Ag and Pb+Pb is enhanced by about a factor 1.6 compared to N+N and p+S collisions. The NA36 result for the K$^0_S$ multiplicity per h$^-$ in S+Pb is below the N+N value.

Antibaryon production in sulphur-nucleus collisions at 200 GeV per nucleon

Antiproton production near midrapidity has been studied in central collisions of 32S with sulphur, silver and gold nuclei at 200 GeV per nucleon. The measured transverse mass distributions can be described by an exponential with inverse slope parameters of about 200 MeV, similar to those obtained from Λ spectra. The rapidity density increases weakly with the target mass, ranging from 0.4 to 0.7. The ratio Λ p near midrapidity is approximately 1.4 on average, significantly larger than the corresponding ratio observed in proton-proton and proton-nucleus collisions.

Antibaryon production in 32S+nucleus collisions at 200 GeV/nucleon

The antibaryon production ( p and Λ ) near midrapidity in central sulphur-nucleus collisions has been measured by the NA35 experiment at the CERN SPS. Antiprotons ( p ) and antilambdas ( Λ ) may be used to study production and annihilation processes in ultrarelativistic heavy ion collisions. The transverse mass spectra of p and Λ show the same inverse slope parameter around 220 MeV. The rapidity densities increase weakly with the target mass. The ratio of Λ to p may be used as a measure of relative strangeness production. It is found to be approximately 1 near midrapidity for central sulphur-nucleus collisions, which is significantly larger than in p + p and p + A interactions at the same energy per nucleon.

A high speed Fastbus-VME data acquisition system for the CERN NA36 experiment

A high speed data acquisition system was used to record events from sulphur-nucleus collisions at 200 GeV/ c per nucleon at the CERN NA36 experiment. The system was designed to accept up to 12 Mbytes of raw data per beam spill. A multicrate Fastbus-CAMAC system was used to acquire the data during the beam spill and thereafter event-building and transfer to IBM 3480 cartridges were accomplished by means of two processors in a VME crate which processed data between spills. Communication between Fastbus and VME crates was provided by a fast link developed at CERN.