Helena Bialkowska

Measurements of charged pion and kaon production in central Pb+Pb collisions at 40, 80, and 158 A GeV are presented. These are compared with data at lower and higher energies as well as with results from p+p interactions. The mean pion multiplicity per wounded nucleon increases approximately linearly with s1/4NN with a change of slope starting in the region 15–40 A GeV. The change from pion suppression with respect to p+p interactions, as observed at low collision energies, to pion enhancement at high energies occurs at about 40A GeV. A nonmonotonic energy dependence of the ratio of K+ to π+ yields is observed, with a maximum close to 40A GeV and an indication of a nearly constant value at higher energies. The measured dependences may be related to an increase of the entropy production and a decrease of the strangeness to entropy ratio in central Pb+Pb collisions in the low SPS energy range, which is consistent with the hypothesis that a transient state of deconfined matter is created above these energies. Other interpretations of the data are also discussed.Received 6 May 2002DOI:https://doi.org/10.1103/PhysRevC.66.054902©2002 American Physical Society

Results on charged pion and kaon production in central Pb+Pb collisions at 20A and 30A GeV are presented and compared to data at lower and higher energies. A rapid change of the energy dependence is observed around 30A GeV for the yields of pions and kaons as well as for the shape of the transverse mass spectra. The change is compatible with the prediction that the threshold for production of a state of deconfined matter at the early stage of the collisions is located at low SPS energies.

Directed and elliptic flow measurements for charged pions and protons are reported as a function of transverse momentum, rapidity, and centrality for 40 and 158A GeV Pb + Pb collisions as recorded by the NA49 detector. Both the standard method of correlating particles with an event plane, and the cumulant method of studying multiparticle correlations are used. In the standard method the directed flow is corrected for conservation of momentum. In the cumulant method elliptic flow is reconstructed from genuine 4, 6, and 8-particle correlations, showing the first unequivocal evidence for collective motion in A+A collisions at SPS energies.

The NA49 detector is a wide acceptance spectrometer for the study of hadron production in p+p, p+A, and A+A collisions at the CERN SPS. The main components are 4 large-volume TPCs for tracking and particle identification via dE/dx. TOF scintillator arrays complement particle identification. Calorimeters for transverse energy determination and triggering, a detector for centrality selection in p+A collisions, and beam definition detectors complete the set-up. A description of all detector components is given with emphasis on new technical realizations. Performance and operational experience are discussed in particular with respect to the high track density environment of central Pb+Pb collisions.

Results of resonance searches in the Xi(-)pi(-), Xi(-)pi(+), Xi;(+)pi(-), and Xi;(+)pi(+) invariant mass spectra in proton-proton collisions at sqrt[s]=17.2 GeV are presented. Evidence is shown for the existence of a narrow Xi(-)pi(-) baryon resonance with mass of 1.862+/-0.002 GeV/c(2) and width below the detector resolution of about 0.018 GeV/c(2). The significance is estimated to be above 4.2sigma. This state is a candidate for the hypothetical exotic Xi(--)(3/2) baryon with S=-2, I=3 / 2, and a quark content of (dsdsū). At the same mass, a peak is observed in the Xi(-)pi(+) spectrum which is a candidate for the Xi(0)(3/2) member of this isospin quartet with a quark content of (dsus[-]d). The corresponding antibaryon spectra also show enhancements at the same invariant mass.

Net proton and negative hadron spectra for central Pb+Pb collisions at 158 GeV per nucleon at the CERN Super Proton Synchrotron were measured and compared to spectra from lighter systems. Net baryon distributions were derived from those of net protons. Stopping (rapidity shift with respect to the beam) and mean transverse momentum ⟨pT⟩ of net baryons increase with system size. The rapidity density of negative hadrons scales with the number of participant nucleons for nuclear collisions, whereas their ⟨pT⟩ is independent of system size. The ⟨pT⟩ dependence upon particle mass and system size is consistent with larger transverse flow velocity at midrapidity for Pb+Pb compared to S+S central collisions.Received 22 October 1998DOI:https://doi.org/10.1103/PhysRevLett.82.2471©1999 American Physical Society

The directed and elliptic flow of protons and charged pions has been observed from the semicentral collisions of a 158 GeV͞nucleon Pb beam with a Pb target.The rapidity and transverse momentum dependence of the flow has been measured.The directed flow of the pions is opposite to that of the protons but both exhibit negative flow at low p t .The elliptic flow of both is fairly independent of rapidity but rises with p t .

First results from ultrarelativistic 16O+Pb collisions at 200 GeV/nucleon are presented. The transverse energy ET in average central collisions is ≈ 75 GeV for the interval 2.2⩽y⩽3.8. A 16-fold convolution of the inelastic p+Au transverse energy spectrum, also measured at 200 GeV, reproduces the mean ET of 16O+Pb. The amount of nuclear stopping power appears to be high.

φ meson production is studied by the NA49 Collaboration in central Pb + Pb collisions at 20A, 30A, 40A, 80A, and 158A GeV beam energy.The data are compared with measurements at lower and higher energies and with microscopic and thermal models.The energy dependence of yields and spectral distributions is compatible with the assumption that partonic degrees of freedom set in at low SPS energies.

Yields and phase space distributions of φ-mesons emitted from p+p (minimum bias trigger), p+Pb (at various centralities) and central Pb+Pb collisions are reported (Ebeam=158AGeV). The decay φ→K+K− was used for identification. The φ/π ratio is found to increase by a factor of 3.0±0.7 from inelastic p+p to central Pb+Pb. Significant enhancement in this ratio is also observed in subclasses of p+p events (characterized by high charged-particle multiplicity) as well as in the forward hemisphere of central p+Pb collisions. In Pb+Pb no shift or significant broadening of the φ-peak is seen.

We present first data on event-by-event fluctuations in the average transverse momentum of charged particles produced in Pb+Pb collisions at the CERN SPS. This measurement provides previously unavailable information allowing sensitive tests of microscopic and thermodynamic collision models and to search for fluctuations expected to occur in the vicinity of the predicted QCD phase transition. We find that the observed variance of the event-by-event average transverse momentum is consistent with independent particle production modified by the known two-particle correlations due to quantum statistics and final state interactions and folded with the resolution of the NA49 apparatus. For two specific models of non-statistical fluctuations in transverse momentum limits are derived in terms of fluctuation amplitude. We show that a significant part of the parameter space for a model of isospin fluctuations predicted as a consequence of chiral symmetry restoration in a non-equilibrium scenario is excluded by our measurement.

Measurements of the forward and the transverse energy in 158 GeV per nucleon $^{208}\mathrm{Pb}$ + Pb collisions are presented. A total transverse energy of about 1 TeV is created in central collisions. An energy density of about 3 GeV/${\mathrm{fm}}^{3}$ is estimated for near head-on collisions. Only statistical fluctuations are seen in the ratio of electromagnetic to hadronic transverse energy.

The transverse mass m t distributions for antiprotons are measured at midrapidity for minimum bias Pb+Pb collisions at 158A GeV and for central Pb+Pb collisions at 20A, 30A, 40A, and 80A GeV beam energies in the fixed target experiment NA49 at the CERN SPS.The rapidity density dn/dy, inverse slope parameter T, and mean transverse mass m t derived from the m t distributions are studied as a function of the incident energy and the collision centrality and compared to the relevant data on proton production.The shapes of the m t distributions of p and p are very similar.The ratios of the particle yields, p/p and ¯ / p, are also analyzed.The p/p ratio exhibits an increase with decreasing centrality and a steep rise with increasing beam energy.The ¯ / p ratio increases beyond unity with decreasing beam energy.

The transverse mass m t distributions for deuterons and protons are measured in Pb+ Pb reactions near midrapidity and in the range 0 Ͻ m t -m Ͻ 1.0 ͑1.5͒ GeV/ c 2 for minimum bias collisions at 158A GeV and for central collisions at 40 and 80 A GeV beam energies.The rapidity density dn / dy, inverse slope parameter T and mean transverse mass ͗m t ͘ derived from m t distributions as well as the coalescence parameter B 2 are studied as a function of the incident energy and the collision centrality.The deuteron m t spectra are significantly harder than those of protons, especially in central collisions.The coalescence factor B 2 shows three systematic trends.First, it decreases strongly with increasing centrality reflecting an enlargement of the deuteron coalescence volume in central Pb+ Pb collisions.Second, it increases with m t .Finally, B 2 shows an increase with decreasing incident beam energy even within the SPS energy range.The results are discussed and compared to the predictions of models that include the collective expansion of the source created in Pb+ Pb collisions.

In a study of π+ p, K+ p and pp collisions at √s=22GeV in the european hybrid spectrometer (EHS), the maximum charged particle density per given rapidity interval is found to rise linearly with charged particle multiplicity, independent of beam particle type and practically independent of energy between 22 and 900 GeV. An anomalous π+ p event is found with ten particles within the very narrow rapidity interval Δy=0.098.

With its large acceptance and particle identification coverage the NA49 experiment (Fig. 1) can study hadron production in a wide range of high energy reactions [1]. Originally aimed at examining central Pb+Pb collisions for signatures of quark-gluon plasma formation, the scope of the experiment has been enhanced with a systematic study of impact parameter and projectile size dependence, as well as the inclusion of the more elementary p+p and p+A interactions. The question is: are predicted signals of the quark-gluon plasma observed and are there discontinuities which would support the concept of hadronic phase transition?

Results on $\Lambda$, $\bar{\Lambda}}$, $\Xi^{-}$, and $\bar{\Xi}^{+}$ production in central Pb+Pb reactions at 20A, 30A, 40A, 80A, and 158A GeV are presented. The energy dependence of transverse mass spectra, rapidity spectra, and multiplicities is discussed. Comparisons to string hadronic models (UrQMD and HSD) and statistical hadron gas models are shown. While the latter provide a reasonable description of all particle yields, the first class of models fails to match the $\Xi^{-}$, and $\bar{\Xi}^{+}$ multiplicities.

The production of charged pions in minimum bias p+C interactions is studied using a sample of 377000 inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. The data cover a phase space area ranging from 0 to 1.8 GeV/c in transverse momentum and from -0.1 to 0.5 in Feynman xF. Inclusive invariant cross sections are given on a grid of 270 bins per charge, thus offering for the first time a dense coverage of the projectile hemisphere and of the cross-over region into the target fragmentation zone.

Production of $d$, $t$, and $^3$He nuclei in central Pb+Pb interactions was studied at five collision energies ($\sqrt{s_{NN}}=$ 6.3, 7.6, 8.8, 12.3, and 17.3 GeV) with the NA49 detector at the CERN SPS. Transverse momentum spectra, rapidity distributions, and particle ratios were measured. Yields are compared to predictions of statistical models. Phase-space distributions of light nuclei are discussed and compared to those of protons in the context of a coalescence approach. The coalescence parameters $B_2$ and $B_3$, as well as coalescence radii for $d$ and $^3$He were determined as a function of transverse mass at all energies.

Preliminary inclusive spectra of negative hadrons, net protons and neutral strange particles are presented, measured by the NA49 experiment in central Pb+Pb collisions at 158 GeV per nucleon. Comparison of their yields with those from the lighter S+S system suggests that the yields scale approximately with the number of participating nucleons.

Production of Lambda and Antilambda hyperons was measured in central Pb-Pb collisions at 40, 80, and 158 A$\cdot$GeV beam energy on a fixed target. Transverse mass spectra and rapidity distributions are given for all three energies. The $\Lambda/\pi$ ratio at mid-rapidity and in full phase space shows a pronounced maximum between the highest AGS and 40 A$\cdot$GeV SPS energies, whereas the $\bar{\Lambda}/\pi$ ratio exhibits a monotonic increase.

The transverse momentum and rapidity distributions of negative hadrons and participant protons have been measured for central S + S collisions at p~, b = 200 GeV/c per nucleon.The proton mean rapidity shift (b, y) 1.6 and mean transverse momentum (pT ) 0.6 GeV/c ire much higher than in py or peripheral AA collisions and indicate an increase in the nuclear stopping power.All pT spectra exhibit similar source temperatures.Including previous results for K~, A, and A, we account for all important contributions to particle production.

The results on spectra of negative particles produced in16O+Au andp-Au collisions at 200 GeV/nucleon and16O+Au at 60 GeV/nucleon are presented. The correlations of average rapidity and average transverse momentum with event multiplicity are studied. Spectral shapes are similar for central16O+Au andp-Au collisions. The transverse momentum and rapidity distributions for central16O+Au andp-Au collisions differ strongly from corresponding distributions forp+p interactions. The FRITIOF model fails to describe the shapes of the transverse momentum distributions. The simple thermodynamical model of a single fireball does not fit the midrapidity transverse momentum distributions, and the rapidity distributions.

Results are presented on event-by-event fluctuations in transverse momentum of charged particles, produced at forward rapidities in p+p, C+C, Si+Si and Pb+Pb collisions at 158 AGeV. Three different characteristics are discussed: the average transverse momentum of the event, the Phi_pT fluctuation measure and two-particle transverse momentum correlations. In the kinematic region explored, the dynamical fluctuations are found to be small. However, a significant system size dependence of Phi_pT is observed, with the largest value measured in peripheral Pb+Pb interactions. The data are compared with predictions of several models.

We report results from a pion interferometry analysis of 200 GeV/nucleon 16O+Au collisions. Both a gaussian source model and a model based on the inside-outside cascade are used to fit the experimental correlation function, giving transverse and longitudinal shape parameters, a freeze-out time parameter, and a chaoticity parameter for the pion emitting source. We find a transverse source size consistent with the projectile radius except at the CM rapidity, where significantly larger transverse and longitudinal sizes and a longer freeze-out time are measured suggesting a thermalized source. Calculation of correlation lengths, and comparisons with a simple freeze-out model and other pion interferometry experiments are presented.

Recent results from the NA35 Collaboration are presented for the reactions of 60 and 200 GeV/nucleon p and 16O, and 200 GeV/nucleon 32S with various targets ranging from S to Au. Midrapidity transverse energy distributions and forward energy flow, p⊥ spectra and rapidity distributions of hadrons are presented. Two-pion interferometry results are discussed. Neutral strange particle yields and p⊥ distributions are presented. Conclusions are drawn from the experimental results.

Multiplicity distributions of all charged and of negative particles for non (single)-diffractive events in π+p and pp collisions at 250 GeV/c (s=22 GeV) are presented for various rapidity intervals. The data are well described by the negative binomial distribution. The π+p and pp data are different for full phase space, but similar for the central region. In the central region, the relation kch≈12 k− holds for all charged and negative multiplicities. This favours the interpretation in terms of cascade models above (partial) stimulated emission models.

The yields of (anti)protons were measured by the NA49 Collaboration in centrality-selected Pb $+$ Pb collisions at $40A$ and $158A$ GeV. Particle identification was obtained in the laboratory momentum range from 5 to 63 GeV$/c$ by measuring the energy loss $dE/dx$ in the time projection chamber detector gas. The corresponding rapidity coverage extends 1.6 units from midrapidity into the forward hemisphere. Transverse-mass spectra, the rapidity dependences of the average transverse mass, and rapidity density distributions were studied as a function of collision centrality. The values of the average transverse mass as well as the midrapidity yields of protons normalized to the number of wounded nucleons show only modest centrality dependences. In contrast, the shape of the rapidity distribution changes significantly with collision centrality, especially at $40A$ GeV. The experimental results are compared to calculations of the hadron-string dynamics and the ultrarelativistic quantum-molecular-dynamics transport models.

New data on the production of charged kaons in p+p interactions are presented. The data come from a sample of 4.8 million inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. The kaons are identified by energy loss in a large TPC tracking system. Inclusive invariant cross sections are obtained in intervals from 0 to 1.7 GeV/c in transverse momentum and from 0 to 0.5 in Feynman x. Using these data as a reference, a new evaluation of the energy dependence of kaon production, including neutral kaons, is conducted over a range from 3 GeV to $\mathrm{p}+\overline{\mathrm{p}}$ collider energies.

We look for fluctuations expected for the QCD critical point using an intermittency analysis in the transverse momentum phase space of protons produced around midrapidity in the 12.5 % most central C+C, Si+Si and Pb+Pb collisions at the maximum SPS energy of 158A GeV. We find evidence of power-law fluctuations for the Si+Si data. The fitted power-law exponent $$\phi _{2} = 0.96^{+0.38}_{-0.25}\text { (stat.)}$$ $$\pm $$ $$0.16\text { (syst.)}$$ is consistent with the value expected for critical fluctuations. Power-law fluctuations had previously also been observed in low-mass $$\pi ^+ \pi ^-$$ pairs in the same Si+Si collisions.

We present the first measurement of fluctuations from event to event in the production of strange particles in collisions of heavy nuclei. The ratio of charged kaons to charged pions is determined for individual central Pb+Pb collisions. After accounting for the fluctuations due to detector resolution and finite number statistics we derive an upper limit on genuine nonstatistical fluctuations, which could be related to a first- or second-order QCD phase transition. Such fluctuations are shown to be very small.

Results are presented on Omega production in central Pb+Pb collisions at 40 and 158 AGeV beam energy. Given are transverse-mass spectra, rapidity distributions, and total yields for the sum Omega+Antiomega at 40 AGeV and for Omega and Antiomega separately at 158 AGeV. The yields are strongly under-predicted by the string-hadronic UrQMD model and are in better agreement with predictions from a hadron gas models.

The energy dependence of hadron production in central Pb+Pb collisions is presented and discussed. In particular, midrapidity $m_T$-spectra for $\pi^-$, $K^-$, $K^+$, $p$, $\bar{p}$, $d$, $\phi$, $\Lambda$ and $\bar{\Lambda}$ at 40, 80 and 158 $A$GeV are shown. In addition $\Xi$ and $\Omega$ spectra are available at 158 $A$GeV. The spectra allow to determine the thermal freeze-out temperature $T$ and the transverse flow velocity $\beta_T$ at the three energies. We do not observe a significant energy dependence of these parameters; furthermore there is no indication of early thermal freeze-out of $\Xi$ and $\Omega$ at 158 $A$GeV. Rapidity spectra for $\pi^-$, $K^-$, $K^+$ and $\phi$ at 40, 80 and 158 $A$GeV are shown, as well as first results on $\Omega$ rapidity distributions at 158 $A$GeV. The chemical freeze-out parameters $T$ and $\mu_B$ at the three energies are determined from the total yields. The parameters are close to the expected phase boundary in the SPS energy range and above. Using the total yields of kaons and lambdas, the energy dependence of the strangeness to pion ratio is discussed. A maximum in this ratio is found at 40 $A$GeV. This maximum could indicate the formation of deconfined matter at energies above 40 $A$GeV. A search for open charm in a large sample of 158 $A$GeV events is presented. No signal is observed. This result is compared to several model predictions.

Results of the production of Xi and Xi-bar hyperons in central Pb+Pb interactions at 158 GeV/c per nucleon are presented. This analysis utilises a global reconstruction procedure, which allows a measurement of 4pi integrated yields to be made for the first time. Inverse slope paramters, which are determined from an exponential fit to the transverse mass spectra, are shown. Central rapidity densities are found to be 1.49 +- 0.08 and 0.33 +- 0.04 per event per unit of rapidity for Xi and Xi-bar respectively. Yields integrated to full phase space are 4.12 +- 0.02 and 0.77 +- 0.04 for Xi and Xi-bar. The ratio of Xi-bar/Xi at mid-rapidity is 0.22 +- 0.03.

Emission of pi+/-, K+/-, phi, and Lambda was measured in near-central C+C and Si+Si collisions at 158 AGeV beam energy. Together with earlier data for p+p, S+S, and Pb+Pb, the system-size dependence of relative strangeness production in nucleus-nucleus collisions is obtained. Its fast rise and the saturation observed at about 60 participating nucleons can be understood as the onset of the formation of coherent systems of increasing size.

The charged particle multiplicity distribution has been studied for non-single-diffractive π+ p andpp collisions at $$\sqrt s = 22$$ GeV, for full phase space as well as for intervals in rapidity, azimuthal angle and transverse momentum. In general, the multiplicity distribution is well described by a negative binomial. From comparison of the distribution for negative or positive particles to that of all charged particles, cascading is favoured as an interpretation over stimulated emission. Interesting consequences follow from a comparison of our results to those at collider energies and toe + e − data at comparable energy. Furthermore, evidence is given that the multiplicity distribution is not exactly of negative binomial type in every (connected or disconnected) phase space region.

The centrality and system size dependence of multiplicity fluctuations of charged particles produced in nuclear collisions at $158A$ GeV was studied by the NA49 Collaboration. Centrality selected Pb+Pb collisions, semicentral C+C and Si+Si collisions as well as inelastic $p$+$p$ interactions were analyzed. The number of projectile participants determined on an event-by-event basis was used to characterize the collision centrality. The scaled variance of the multiplicity distribution obtained in the forward rapidity region ($1.1<{y}_{\mathrm{c.m.}}<2.6$) shows a significant increase toward peripheral collisions. The results are similar for negatively and positively charged particles and about 50% larger for all charged particles. String-hadronic models of nuclear reactions without the fusion process do not reproduce the rise of fluctuations from central toward peripheral collisions. The measured centrality dependence can be reproduced in superposition models with the assumption of contributions from target participants to particle production in the forward hemisphere or in string models with fusion.

Inelastic cross sections at 60 and 200 GeV/nucleon are determined in a streamer chamber for 16O on several nuclear targets. Charged particle multiplicity distributions for inelastic and central collisions are studied and compared with theoretical predictions. The inelastic cross section exhibit a geometrical dependence on nuclear radii. The multiplicity data are governed by the collision geometry. They are consistent with a picture of superposition of independent nucleon-nucleus interactions.

Production of the $K^{\ast}(892)^0$ and $\bar{K}^{\ast}(892)^0$ resonances was studied via their $K^+ \pi^-$ and $K^- \pi^+$ decay modes in central Pb+Pb, Si+Si, C+C and inelastic p+p collisions at 158\agev ($\sqrt{s_{NN}}$ = 17.3 GeV) with the NA49 detector at the CERN SPS. Transverse momentum and rapidity distributions were measured and total yields were estimated. The yield of $K^{\ast}$ exceeds that of $\bar{K}^{\ast}$ by about a factor of two in nucleus-nucleus reactions. The total yield ratios $< K^{\ast} >/< K^+ >$ and $< \bar{K}^{\ast} >/< K^->$ are strongly suppressed in central Pb+Pb compared to p+p, C+C and Si+Si collisions in agreement with the expected attenuation of these short-lived resonance states in the hadronic phase of the expanding fireball. The UrQMD model, although incorporating such a scenario, does not provide a quantitative description of the experimental results. The statistical hadron gas model assuming the same freeze-out parameters for stable hadrons and resonances overestimates the $< K^{\ast} >/< K >$ ratios in central Pb+Pb collisions by about a factor of 2.5.

Results are presented on event-by-event electric charge fluctuations in central Pb+Pb collisions at 20, 30, 40, 80 and 158 AGeV. The observed fluctuations are close to those expected for a gas of pions correlated by global charge conservation only. These fluctuations are considerably larger than those calculated for an ideal gas of deconfined quarks and gluons. The present measurements do not necessarily exclude reduced fluctuations from a quark-gluon plasma because these might be masked by contributions from resonance decays.

In the vicinity of the quark-hadron critical point, in the phase diagram, simple power-law relations constrain the mid-rapidity net-baryon density, for different heavy-ion processes, in a unifying scheme. These relations reveal a characteristic trend of the SPS experiments (S + S, S + Ag, S + Au, Pb + Pb) supporting the hypothesis of a critical point of second order, at nonzero baryon density. However, the central events in these experiments stay outside the critical area, especially in Pb + Pb collisions, suggesting the absence of strong critical fluctuations in these processes. The role of noncentral events and the possibility to reach the QCD critical point at RHIC and LHC, is also discussed.

Rapidity spectra of pions and participant protons in S + S collisions at 200 GeV/nucleon are compared with N + N data. The average energy loss of the participating nucleons increases by 23% and is balanced by the energy of the final state particles, through a twofold increase of strange particle production and a similar enhancement, assumed for baryon-antibaryon pairs.

The production of neutral strange particlesK s o , Λ and % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaacciGaf83MdW% Kbaebaaaa!3780! $$\bar \Lambda $$ has been studied in 60 and 200 GeV per nucleon OAu and pAu collisions with the streamer chamber vertex spectrometer of the NA35 experiment at the CERN-SPS accelerator. Ratios of neutral strange particle production to negatively charged particle production in selected regions of phase space were measured to be the same in OAu and pAu reactions. The rates of strange particle production in central OAu collisions are about a factor of 16 higher than in pAu collisions when compared in the same regions of phase space. If an enhancement of strange particle production in OAu collisions relative to pAu collisions is considered to be a signature for quark-gluon plasma formation, no evidence supporting it is observed. The experimental results are compared to the Lund FRITIOF model.

Terbium (Tb3+) binding to skeletal muscle troponin C was studied by fluorescence spectroscopy and circular dichroism. Titrations indicate that Tb3+, like Ca2+, preferentially binds to the two high affinity Ca2+-Mg2+ sites (III and IV) inducing structural changes similar to those induced by Ca2+. Tb3+ readily displaces Ca2+ from these sites suggesting a K(Tb3+) ≥ 109 M−1 In 6 M urea, both Ca2+ and Tb3+ bind preferentially to a single site on troponin C. The spectral changes suggest this to be site III.

The reactions p + p → p + X and p + p → Δ++ + X at 69 GeV/c are studied in the Mirabelle bubble chamber at Serpukhov. The distribution of x and missing masses M2 to the identified proton are shown for different topologies as well as t′ distributions for different M2 intervals. The cross section for the single diffractive process is evaluated. Peripheral production of a low-mass Δ++π− system is observed.

We report measurements of Ξ− and Ξ+ hyperon absolute yields as a function of rapidity in 158 GeV/c Pb+Pb collisions. At midrapidity, dN/dy=2.29±0.12 for Ξ−, and 0.52±0.05 for Ξ+, leading to the ratio of Ξ+/Ξ−=0.23±0.03. Inverse slope parameters fitted to the measured transverse mass spectra are of the order of T≈300 MeV near mid-rapidity. The estimated total yield of Ξ− particles in Pb+Pb central interactions amounts to 7.4±1.0 per collision. Comparison to Ξ− production in properly scaled p+p reactions at the same energy reveals a dramatic enhancement (about one order of magnitude) of Ξ− production in Pb+Pb central collisions over elementary hadron interactions.

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 Λp near midrapidity is approximately 1.4 on average, significantly larger than the corresponding ratio observed in proton-proton and proton-nucleus collisions.

We discuss preliminary data on stopping for central Pb + Pb collisions at 158 GeV/nucleon. The (net) proton rapidity density measured by the NA49 Time Projection Chambers, NA49 Time of Flight and the NA44 spectrometer is presented. Slightly higher stopping is observed relative to S + S at 200 GeV/nucleon. The rapidity density exhibits a plateau around mid-rapidity which is qualitatively different from results at the AGS and BEVALAC/SIS energies. The second part of the paper discusses the azimuthal correlation of the energy flow. Preliminary results reveal that the ‘fireball’ preserves the information of the collision geometry even at SPS energies.

Recent results on hadron production in central nucleus-nucleus collisions obtained by the experiment NA35 at the CERN SPS are reviewed. The first preliminary results on central Pb+Pb collisions obtained by the NA49 experiment, the successor of NA35, are also discussed. Their impact on our understanding of the properties of strongly interacting matter at different stages of the collision is underlined.

In this review we first outline the basics of transport theory and its recent generalization to off-shell transport. We then present in some detail the main ingredients of any transport method using in particular the Giessen Boltzmann–Uehling–Uhlenbeck (GiBUU) implementation of this theory as an example. We discuss the potentials used, the ground state initialization and the collision term, including the in-medium modifications of the latter. The central part of this review covers applications of GiBUU to a wide class of reactions, starting from pion-induced reactions over proton and antiproton reactions on nuclei to heavy-ion collisions (up to about 30AGeV). A major part concerns also the description of photon-, electron- and neutrino-induced reactions (in the energy range from a few 100MeV to a few 100GeV). For this wide class of reactions GiBUU gives an excellent description with the same physics input and the same code being used. We argue that GiBUU is an indispensable tool for any investigation of nuclear reactions in which final-state interactions play a role. Studies of pion–nucleus interactions, nuclear fragmentation, heavy-ion reactions, hypernucleus formation, hadronization, color transparency, electron–nucleus collisions and neutrino–nucleus interactions are all possible applications of GiBUU and are discussed in this article.

Electric charge correlations were studied for p+p, C+C, Si+Si, and centrality selected Pb+Pb collisions at $\sqrt{{s}_{\mathrm{NN}}}=17.2$ GeV with the NA49 large acceptance detector at the CERN SPS. In particular, long-range pseudorapidity correlations of oppositely charged particles were measured using the balance function method. The width of the balance function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions.

Kaons and protons carry large parts of two conserved quantities, strangeness and baryon number. It is argued that their correlation and thus also fluctuations are sensitive to conditions prevailing at the anticipated parton-hadron phase boundary. Fluctuations of the $(\mathrm{K}^+ + \mathrm{K}^-)/(\mathrm{p}+\bar{\mathrm{p}})$ and $\mathrm{K}^+/\mathrm{p}$ ratios have been measured for the first time by NA49 in central Pb+Pb collisions at 5 SPS energies between $\sqrt{s_{NN}}$= 6.3 GeV and 17.3 GeV. Both ratios exhibit a change of sign in $\sigma_{\mathrm{dyn}}$, a measure of non-statistical fluctuations, around $\sqrt{s_{NN}}$ = 8 GeV. Below this energy, $\sigma_{\mathrm{dyn}}$ is positive, indicating higher fluctuation compared to a mixed event background sample, while for higher energies, $\sigma_{\mathrm{dyn}}$ is negative, indicating correlated emission of kaons and protons. The results are compared to UrQMD calculations which which give a good description at the higher SPS energies, but fail to reproduce the transition to positive values.

A novel approach, the identity method, was used for particle identification and the study of fluctuations of particle yield ratios in Pb + Pb collisions at the CERN Super Proton Synchrotron (SPS).This procedure allows one to measure the moments of the multiplicity distributions of protons (p), kaons (K), pions (π ), and electrons (e) in case of incomplete particle identification.Using these moments the excitation function of the fluctuation measure ν dyn [A,B] was measured, with A and B denoting different particle types.The obtained energy dependence of ν dyn agrees with previously published NA49 results on the related measure σ dyn .However, ν dyn [K,p] and ν dyn [K,π ] were found to depend on the phase-space coverage.This feature most likely explains the reported differences between measurements of NA49 and those of STAR in central Au + Au collisions.

New data with a minimum bias trigger for 158 GeV/nucleon Pb + Pb have been analyzed. Directed and elliptic flow as a function of rapidity of the particles and centrality of the collision are presented. The centrality dependence of the ratio of elliptic flow to the initial space elliptic anisotropy is compared to models.

The NA35 experiment has collected a high statistics set of momentum analyzed negative hadrons near and forward of midrapidity for central collisions of $200A\phantom{\rule{0ex}{0ex}}\mathrm{GeV}/c$ $^{32}S+\mathrm{S}$, Cu, Ag, and Au. Using momentum space correlations to study the size of the source of particle production, the transverse source radii are found to decrease by $\ensuremath{\sim}$40% at midrapidity and $\ensuremath{\sim}$20% at forward rapidity while the longitudinal radius ${R}_{L}$ is found to decrease by $\ensuremath{\sim}$50% as ${p}_{T}$ increases over the interval $50&lt;{p}_{T}&lt;600\phantom{\rule{0ex}{0ex}}\mathrm{MeV}/c$. Calculations using a microscopic phase space approach (relativistic quantum molecular dynamics) reproduce the observed trends of the data.

Production of charged kaons in proton-sulphur, proton-gold, sulphur-sulphur and oxygen-gold collisions at 200 GeV/nucleon has been studied in the NA35 Streamer Chamber experiment. Rapidity and transverse mass distributions as well as mean multiplicities were obtained. The results are compared with nucleon-nucleon data and with model predictions.

The NA49 large-acceptance hadron spectrometer has measured strange and multi-strange hadrons from Pb + Pb and p + p collisions at the CERN SPS. Preliminary results for the transverse mass and rapidity distributions for Ξ- and from central Pb + Pb collisions at 158 GeV c-1/nucleon are presented. Fully integrated yields per event of 4.42 ± 0.31 and 0.74 ± 0.04 are found for Ξ- and , respectively, leading to a 4π /Ξ- ratio of 0.17 ± 0.02. The ratio /Ξ- at mid-rapidity is found to be 0.22 ± 0.04, agreeing with previously published values. In addition, preliminary data on the Λ(1520) and ϕ (1020) resonances are presented. The Λ(1520) multiplicity for p + p collisions is found to be 0.012 ± 0.003. No signal is observed for Pb + Pb collisions and a production upper limit of 1.36 Λ(1520) per event indicates an apparent suppression when comparing with scaled p + p data. Integrated ϕ(1020) yields per event are found to be 7.6 ± 1.1 for Pb + Pb and 0.012 ± 0.0015 for p + p collisions. No significant shift or broadening of the ϕ(1020) invariant mass distribution is observed in central Pb + Pb collisions.

The dependence of the K+ and K− production on the number of nucleons involved in the annihilation process is investigated experimentally in the p¯ annihilation at rest on hydrogen, deuterium, 3He and 4He gas targets. Annihilations with any number of prongs (charged pions and kaons, protons and deuterons) are analyzed. Events with and without production of neutral mesons and with and without emission of fast neutrons (that is neutrons involved in the annihilation process) are recognized. The results are consistent with our previous ones on a more restricted sample of annihilation reactions and put in evidence that the strangeness production is lower or higher depending on the reaction channel. As a general trend, the strangeness production is higher in events without neutral mesons and still higher in events with the involvement of a higher number of nucleons. Both K+ and K− productions increase with the number of involved nucleons, but K+ much more. The maximum K+ production is observed in the reaction K+2π+2π−3n on 4He (with the involvement of 3–4 nucleons); compared with the production on hydrogen in the reaction K+π+2π−, the production on 4He is higher by a factor of 31.7±5.5. In the light of some theoretical speculations, this enhancement factor is too high to be explainable in terms of hadronic interactions and could be interpreted as a signature of quark deconfinement and of formation of a quark–gluon plasma.

Enhanced strange particle production, nonstatistical multiplicity fluctuations and two-pion Bose-Einstein correlations were measured in O, S-nucleus reactions at 60 and 200 GeV/nucleon. The results indicate significant collective effects in high-energy nucleus-nucleus collisions.

In this paper we present recent results from the NA49 experiment for Λ and hyperons produced in central Pb + Pb collisions at 40, 80 and 158 A GeV. Transverse mass spectra and rapidity distributions for Λ are shown for all three energies. The shape of the rapidity distribution becomes flatter with increasing beam energy. The multiplicities at mid-rapidity as well as the total yields are studied as a function of collision energy including AGS measurements. The ratio Λ/π at mid-rapidity and in 4π has a maximum around 40 A GeV. In addition, rapidity distributions have been measured at 40 and 80 A GeV, which allows us to study the /Λ ratio.

The large acceptance and high momentum resolution as well as the significant particle identification capabilities of the NA49 experiment at the CERN SPS allow for a broad study of fluctuations and correlations in hadronic interactions. In the first part recent results on event-by-event charge and p_t fluctuations are presented. Charge fluctuations in central Pb+Pb reactions are investigated at three different beam energies (40, 80, and 158 AGeV), while for the p_t fluctuations the focus is put on the system size dependence at 158 AGeV. In the second part recent results on Bose Einstein correlations of h-h- pairs in minimum bias Pb+Pb reactions at 40 and 158 AGeV, as well as of K+K+ and K-K- pairs in central Pb+Pb collisions at 158 AGeV are shown. Additionally, other types of two particle correlations, namely pi p, Lambda p, and Lambda Lambda correlations, have been measured by the NA49 experiment. Finally, results on the energy and system size dependence of deuteron coalescence are discussed.

Results from the NA49 experiment at the CERN SPS are presented on event-by-event transverse momentum and multiplicity fluctuations of charged particles, produced at forward rapidities in central Pb+Pb interactions at beam momenta 20$A$, 30$A$, 40$A$, 80$A$, and 158$A$ GeV/c, as well as in systems of different size ($p+p$, C+C, Si+Si, and Pb+Pb) at 158$A$ GeV/c. This publication extends the previous NA49 measurements of the strongly intensive measure $\Phi_{p_T}$ by a study of the recently proposed strongly intensive measures of fluctuations $\Delta[P_T, N]$ and $\Sigma[P_T, N]$. In the explored kinematic region transverse momentum and multiplicity fluctuations show no significant energy dependence in the SPS energy range. However, a remarkable system size dependence is observed for both $\Delta[P_T, N]$ and $\Sigma[P_T, N]$, with the largest values measured in peripheral Pb+Pb interactions. The results are compared with NA61/SHINE measurements in $p+p$ collisions, as well as with predictions of the UrQMD and EPOS models.

Results from electric charge correlations studied with the Balance Function (BF) method in $A+A$ collisions from $20A$ to $158A$ GeV are presented in two different rapidity intervals: In the midrapidity region we observe a decrease of the width of the BF distribution with increasing centrality of the collision, whereas this effect vanishes in the forward rapidity region. Results from the energy dependence study in central $\mathrm{Pb}+\mathrm{Pb}$ collisions show that the narrowing of the BF expressed by the normalized width parameter $W$ increases with energy toward the highest CERN Super Proton Synchrotron and BNL Relativistic Heavy Ion Collider energies. Finally we compare our experimental data points with the predictions of several models. The hadronic string models Ultra-relativistic Quantum Molecular Dynamics and Heavy Ion Jet INteraction Generator (HIJING) do not reproduce the observed narrowing of the BF. However, A MultiPhase Transport medel (AMPT), which contains a quark-parton transport phase before hadronization, can reproduce the narrowing of the BF's width with centrality. This confirms the proposed sensitivity of the BF analysis to the time of hadronization.

Abstract We investigate the main features of the reaction pp → ppπ+π− at 69 GeV/c from data obtained in the Mirabelle bubble chamber at Serpukhov. A search for a double pomeron exchange mechanism contribution leads to an upper limit of ⋍20 μ b for M(π + π − ) ⩽ 0.7 GeV under reasonable assumptions. The four-body final state is dominated by proton diffractive dissociation p → pπ+π− (mostly Δ++π−). The cross section for this process, as well as the t production slope and the decay distributions (of the Δ++) show little variation in comparison with lower energy data.

We report on a systematic study of midrapidity transverse energy production and forward energy flow in interactions of16O and32S projectiles with S, Cu, Ag and Au targets at 60 and 200 GeV/nucleon. The variation of the shape of theE T distributions with target and projectile mass can be understood from collision geometry. AverageE T values determined for central collisions show an increasing stopping power for heavier target nuclei. A higher relative stopping is observed at 60 GeV/nucleon than at 200 GeV/nucleon. Bjorken estimates of the energy density reach approximately 3 GeV/fm3 in highE T events at 200 GeV/nucleon with16O and32S projectiles. The systematics of the data and the shapes ofE T and pseudorapidity distributions are well described by the Lund model Fritiof.

Using data from several bubble chamber experiments, we have studied the inclusive reactions π±p → π− + X, K−p → K0 + X and K−p → Λ + X at incident momenta ranging from 8 to 16 GeV/c. Single particle spectra are given as functions of the transverse energy E⊥ = (p⊥2 + m2)12 for selected intervals of the longitudinal rapidity y. Using these two variables we find a simple, mass independent, representation of all particle spectra. Within a large range of y, non-Lorentz-invariant E⊥ distributions are nearly exponential and, over several orders of magnitude in cross section, can be fitted well with the single-parameter function (eE⊥/T −1)−1. The slope parameter T is shown to depend on y but, in the central region, it appears to be independent of the particle mass and gives indications of approaching a limiting value of approximately 120 MeV. Implications of these results with regard to thermodynamic models are briefly discussed.

Experimental results on deuteron emission from central Pb+Pb collisions (Ebeam=158A GeV, fixed target), obtained by NA49 at the CERN SPS accelerator, are presented. The transverse mass mt distribution was measured near mid-rapidity (2.0<y<2.5) in the range of 0<mt−m0<0.9 GeV/c2 (0<pt<2.0 GeV/c) for the 4% most central collisions. An exponential fit gives an inverse slope Td=(450±30) MeV and a yield dNd/dy=0.34±0.03. The coalescence factor B2(mt=m0)=(3.5±1.0)·10−4 GeV2 and its mt-dependence are determined and discussed in terms of a model that includes the collective expansion of the source created in a collision. The derived Gaussian size parameter RG of the emission volume is consistent with earlier HBT results on the source of pion emission.

The two-proton correlation function at midrapidity from Pb+Pb central collisions at 158 A GeV has been measured by the NA49 experiment. The results are compared to model predictions from static thermal Gaussian proton source distributions and transport models rqmd and venus. An effective proton source size is determined by minimizing χ2/ndf between the correlation functions of the data and those calculated for the Gaussian sources, yielding σeff=3.85±0.15(stat.)+0.60−0.25(syst.) fm. Both the rqmd and the venus model are consistent with the data within the error in the correlation peak region.

Pion interferometry is the unique tool to study the space-time evolution of the systems created in the ultrarelativistic nuclear collisions. Five different data sets have been analyzed in terms of cylindrical coordinates, and all yield consistent results. We conclude that the system expands longitudinally, the decoupling proper time is ∼5 fm/c, the duration of particle emission is very short <2 fm/c, and the transverse decoupling size is 1.5 to 2 times larger than the one corresponding to the collision geometry. That gives a causally consistent space-time evolution picture.

Bose-Einstein correlations of charged kaons were measured near mid-rapidity in central Pb+Pb collisions at 158 A$\cdot$GeV by the NA49 experiment at the CERN SPS. Source radii were extracted using the Yano-Koonin-Podgoretsky and Bertsch-Pratt parameterizations. The results are compared to published pion data. The measured $m_\perp$ dependence for kaons and pions is consistent with collective transverse expansion of the source and a freeze-out time of about 9.5 $fm$.

New measurements by the NA49 experiment of the centrality dependence of event-by-event fluctuations of the particle yield ratios $({K}^{+}+{K}^{\ensuremath{-}})/({\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}})$, $(p+\overline{p})/({\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}})$, and $({K}^{+}+{K}^{\ensuremath{-}})/(p+\overline{p})$ are presented for Pb+Pb collisions at 158$A$ GeV. The absolute values of the dynamical fluctuations of these ratios, quantified by the measure ${\ensuremath{\sigma}}_{\text{dyn}}$, increase by about a factor of two from central to semiperipheral collisions. Multiplicity scaling scenarios are tested and found to apply for both the centrality and the previously published energy dependence of the $({K}^{+}+{K}^{\ensuremath{-}})/({\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}})$ and $(p+\overline{p})/({\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}})$ ratio fluctuations. A description of the centrality and energy dependence of $({K}^{+}+{K}^{\ensuremath{-}})/(p+\overline{p})$ ratio fluctuations by a common scaling prescription is not possible since there is a sign change in the energy dependence.

Similarly as in lepton-hadron scattering, but less pronounced than in e+e− annihilation at comparable energies, we observe a rise of the “sea-gull” wings with CMS energy. The large average transverse momenta around Feynman |xF|=0.4 are mainly due to high multiplicity events, for which also a tail develops in the multiplicity distribution. Neither of these effects can be reproduced by currently used low-pT fragmentation models.

Data on inclusive reactions π−p → π± + … and π−n → π± + … at 40 GeV/c are presented. Inclusive cross sections of the reactions π−p → π± + … at x = 0 normalized to the inelastic cross section coincide with the ISR results for pp interactions at 500 – 1500 GeV. A similar result has been obtained for the inclusive process π−p → γ + … as well.

Source imaging methodology is used to provide a three-dimensional two-pion source function for mid-rapidity pion pairs with $p_T<70$ MeV/c in central ($0-7%$) Pb+Pb collisions at $\sqrt s_{NN}$=17.3 GeV. Prominent non-Gaussian tails are observed in the pion pair transverse momentum (outward) and in the beam (longitudinal) directions. Model calculations reproduce them with the assumption of Bjorken longitudinal boost invariance and transverse flow blast-wave dynamics coupled with "outside-in burning" in the transverse direction; they also yield a proper time for breakup and emission duration for the pion source.

One of the key physics goals of the LHCb experiment at the LHC is the measurement of mixing induced CP violation in decays of B s → J/ψφ.The interference between mixing and decay gives rise to a CP-violating phase, φ J/ψφ s .Assuming a proper-time resolution and tagging performance as observed in simulated data, together with an expected luminosity of 1 fb -1 by the end of 2011, LHCb is expected to be able to measure φ J/ψφ s with an error of 0.07 rad.

Multiplicity distributions of negatively charged particles have been studied in restricted phase space intervals for central S+S, O+Au and S+Au collisions at 200 GeV/nucleon. It is shown that multiplicity distributions are well described by a negative binomial form irrespectively of the size and dimensionality of phase space domain. A clan structure analysis reveals interesting similarities between complex nuclear collisions and a simple partonic shower. The lognormal distribution agrees reasonably well with the multiplicity data in large domains, but fails in the case of small intervals. No universal scaling function was found to describe the shape of multiplicity distributions in phase space intervals of varying size.

Multiplicity distributions, observed inK + interactions with Al and Au nuclei at 250 GeV/c incident momentum are presented. They are analyzed in the framework of multiple collisions of the incident particle inside a nucleus. The probability distribution of the number of grey tracks is well described by the model of Andersson et al., if a negative binomial distribution is assumed for the distribution of the number of grey protons produced per elementary collision instead of the usual geometrical distribution. The analysis of the average and dispersion of the charge multiplicity distribution supports the validity of the multiple collision model, including results on correlations between forward and backward multiplicities.

We have measured the inclusive cross section for the reaction π−n→pX−− at 21, 205 and 360 GeV/c in the kinematic region |tnp|<1.0 (GeV/c)2. The differential cross sections can be described qualitatively by the reggeized one-pion-exchange amplitude at all momenta studied; however, there is evidence for the contribution of other amplitudes. The extracted π−π− total cross section for 4⪅sππ⪅340 GeV2 is of the order of 10–12 mb. The average number of charged particles and dispersion of the charged particle multiplicity distributions for various sππ intervals are compatible with results observed in hadron-proton interactions.

Data on φ-production obtained by the CERN NA49 experiment for central Pb+Pb collisions at 158 GeV/u are presented. Compared with pp interactions the φ-yield shows substantial strangeness enhancement: the φ/π ratio is found to increase by a factor of 2.6 ± 0.6, which is approximately the square of the K/π enhancement.

Abstract The average transverse momentum 〈Pt〉 has been studied as a function of the charge multiplicity n in π+p, K+p and pp collisions at 250 GeV /c ( s ≈ 22 GeV ) and compared to that at other energies. The effect of cuts in rapidity and pT is demonstrated. A comparison to currently used low-pT models shows that the two-chain dual parton model underestimates the experimentally observed correlation at large pT. The new version of the two-chain LUND-FRITIOF model is better than the first version of this model, but still overestimates the correlation.