arXiv subjects

NA49 Collaboration

Publications and source records attributed to NA49 Collaboration.

At least 19 recordsLinked to original sources

arXiv2016

Production of deuterium, tritium, and $^3$He in central Pb+Pb collisions at 20A, 30A, 40A, 80A, and 158A GeV at the CERN SPS

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.

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arXiv2015

Measurement of event-by-event transverse momentum and multiplicity fluctuations using strongly intensive measures $Δ[P_T, N]$ and $Σ[P_T, N]$ in nucleus-nucleus collisions at the CERN Super Proton Synchrotron

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 $Φ_{p_T}$ by a study of the recently proposed strongly intensive measures of fluctuations $Δ[P_T, N]$ and $Σ[P_T, N]$. 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 $Δ[P_T, N]$ and $Σ[P_T, N]$, 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.

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arXiv2012

System-size and centrality dependence of charged kaon and pion production in nucleus-nucleus collisions at 40A GeV and158A GeV beam energy

Measurements of charged pion and kaon production are presented in centrality selected Pb+Pb collisions at 40A GeV and 158A GeV beam energy as well as in semi-central C+C and Si+Si interactions at 40A GeV. Transverse mass spectra, rapidity spectra and total yields are determined as a function of centrality. The system-size and centrality dependence of relative strangeness production in nucleus-nucleus collisions at 40A GeV and 158A GeV beam energy are derived from the data presented here and published data for C+C and Si+Si collisions at 158A GeV beam energy. At both energies a steep increase with centrality is observed for small systems followed by a weak rise or even saturation for higher centralities. This behavior is compared to calculations using transport models (UrQMD and HSD), a percolation model and the core-corona approach.

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arXiv2009

Search for the QCD critical point at SPS energies

Lattice QCD calculations locate the QCD critical point at energies accessible at the CERN Super Proton Synchrotron (SPS). We present average transverse momentum and multiplicity fluctuations, as well as baryon and anti-baryon transverse mass spectra which are expected to be sensitive to effects of the critical point. The future CP search strategy of the NA61/SHINE experiment at the SPS is also discussed.

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arXiv2009

System-size dependence of Lambda and Xi production in nucleus--nucleus collisions at 40A and 158A GeV measured at the CERN Super Proton Synchrotron

Results on Lambda, Anti-lambda, and Xi- production in centrality selected Pb+Pb reactions at 40A and 158A GeV and in near-central C+C and Si+Si reactions at 158A GeV are presented. Transverse mass spectra, rapidity spectra, and multiplicities in dependence of the system size are discussed. Comparisons to transport models (UrQMD2.3 and HSD) and to the core-corona approach are performed. While Lambda and Anti-lambda production can be described by transport models reasonably well, these models do not agree with the Xi- measurements. On the other hand, the core-corona picture fits very well the system-size dependence of Lambda and Xi-, while it agrees less well with the Anti-lambda data.

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arXiv2009

Energy dependence of particle ratio fluctuations in central Pb+Pb collisions from $\sqrt{s_{_{NN}}} =$~6.3 to 17.3 GeV

We present measurements of the energy dependence of event-by-event fluctuations in the K/pi and (p + \bar{p})/pi multiplicity ratios in heavy ion collisions at the CERN SPS. The particle ratio fluctuations were obtained for central Pb+Pb collisions at five collision energies, \sqrt{s_{_{NN}}}, between 6.3 and 17.3 GeV. After accounting for the effects of finite-number statistics and detector resolution, we extract the strength of non-statistical fluctuations at each energy. For the K/pi ratio, larger fluctuations than expected for independent particle production are found at all collision energies. The fluctuations in the (p + \bar{p})/pi ratio are smaller than expectations from independent particle production, indicating correlated pion and proton production from resonance decays. For both ratios, the deviation from purely statistical fluctuations shows an increase towards lower collision energies. The results are compared to transport model calculations, which fail to describe the energy dependence of the K/pi ratio fluctuations.

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arXiv2009

Inclusive production of protons, anti-protons and neutrons in p+p collisions at 158 GeV/c beam momentum

New data on the production of protons, anti-protons and neutrons 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 charged baryons are identified by energy loss measurement in a large TPC tracking system. Neutrons are detected in a forward hadronic calorimeter. Inclusive invariant cross sections are obtained in intervals from 0 to 1.9 GeV/c (0 to 1.5 GeV/c) in transverse momentum and from -0.05 to 0.95 (-0.05 to 0.4) in Feynman x for protons (anti-protons), respectively. pT integrated neutron cross sections are given in the interval from 0.1 to 0.9 in Feynman x. The data are compared to a wide sample of existing results in the SPS and ISR energy ranges as well as to proton and neutron measurements from HERA and RHIC.

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arXiv2008

Energy dependence of Lambda and Xi production in central Pb+Pb collisions at 20A, 30A, 40A, 80A, and 158A GeV measured at the CERN Super Proton Synchrotron

Results on $Λ$, $\barΛ}$, $Ξ^{-}$, and $\barΞ^{+}$ 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 $Ξ^{-}$, and $\barΞ^{+}$ multiplicities.

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arXiv2008

High Transverse Momentum Hadron Spectra at sqrt{s_{NN}}=17.3 GeV, in Pb+Pb and p+p Collisions

Transverse momentum spectra up to 4.5 GeV/c around midrapidity of pi^{+/-}, p, pbar, K^{+/-} in Pb+Pb reactions were measured at sqrt{s_{NN}}=17.3 GeV by the CERN-NA49 experiment. The nuclear modification factors R_{AA} for pi^{+/-} and R_{CP} for pi^{+/-},p,pbar,K^{+/-} were extracted and are compared to RHIC results at sqrt{s_{NN}}=200 GeV. The modification factor R_{AA} shows a rapid increase with transverse momentum in the covered region. This indicates that the Cronin effect is the dominating effect in our energy range. The modification factor R_{CP}, in which the contribution of the Cronin effect is reduced, shows a saturation well below unity in the pi^{+/-} channel. The extracted R_{CP} values follow the 200 GeV RHIC results closely in the available transverse momentum range, except for pi^{+/-} above 2.5 GeV/c transverse momentum. There the measured suppression is smaller than that observed at RHIC.

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arXiv2007

Pion and kaon production in central Pb+Pb collisions at 20A and 30A GeV: Evidence for the onset of deconfinement

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.

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arXiv2007

Bose-Einstein correlations of pion pairs in central Pb+Pb collisions at CERN SPS energies

Measurements of Bose-Einstein correlations of pion pairs in central Pb+Pb collisions were performed with the NA49 detector at the CERN SPS for beam energies of 20A, 30A, 40A, 80A, and 158A GeV. Correlation functions were measured in the longitudinally co-moving ``out-side-long'' reference frame as a function of rapidity and transverse momentum in the forward hemisphere of the reaction. Radius and correlation strength parameters were obtained from fits of a Gaussian parametrization. The results show a decrease of the radius parameters with increasing transverse momentum characteristic of strong radial flow in the pion source. No striking dependence on pion-pair rapidity or beam energy is observed. Static and dynamic properties of the pion source are obtained from simultaneous fits with a blast-wave model to radius parameters and midrapidity transverse momentum spectra. Predictions of hydrodynamic and microscopic models of Pb+Pb collisions are discussed.

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arXiv2007

Rapidity and energy dependence of the electric charge correlations in A+A collisions at the SPS energies

Results from electric charge correlations studied with the Balance Function method in A+A collisions from 20\emph{A} to 158\emph{A} GeV are presented in two different rapidity intervals: In the mid-rapidity region we observe a decrease of the width of the Balance Function distribution with increasing centrality of the collision, whereas this effect vanishes in the forward rapidity region. Results from the energy dependence study in central Pb+Pb collisions show that the narrowing of the Balance Function expressed by the normalised width parameter \textit{W} increases with energy towards the highest SPS and RHIC energies. Finally we compare our experimental data points with predictions of several models. The hadronic string models UrQMD and HIJING do not reproduce the observed narrowing of the Balance Function. However, 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 Balance Function analysis to the time of hadronization.

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arXiv2007

Centrality and system size dependence of multiplicity fluctuations in nuclear collisions at 158 AGeV

The centrality and system size dependence of multiplicity fluctuations of charged particles produced in nuclear collisions at $158 A$ GeV was studied by the NA49 collaboration. Centrality selected Pb+Pb collisions, semi-central 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 ($1.1 <y_{c.m.} <2.6$) shows a significant increase towards 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 towards 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.

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arXiv2006

Inclusive production of charged pions in p+C collisions at 158 GeV/c beam momentum

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 x. 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.

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arXiv2006

Energy and centrality dependence of antiproton and proton production and the antilambda to antiproton ratio in Pb+Pb collisions between 20A GeV and 158A GeV

The transverse mass 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, inverse slope parameter and mean transverse mass derived from the transverse mass 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 transverse mass distributions of antiproton and proton are very similar. The ratios of the particle yields, antiproton/proton and antilambda/antiproton, are also analysed. The antiproton to proton ratio exhibits an increase with decreasing centrality and a steep rise with increasing beam energy. The antilambda to antiproton ratio increases beyond unity with decreasing beam energy.

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arXiv2005

Energy and rapidity dependence of electric charge correlations at 20-158GeV beam energies at the CERN SPS (NA49)

Electric charge correlations are studied with the Balance Function method for central Pb + Pb collisions at the CERN - SPS. The results on centrality selected Pb + Pb interactions at 40 and 158 AGeV are presented for the first time for two different rapidity intervals. In the mid-rapidity region a decrease of the width with increasing centrality of the collision is observed whereas in the forward rapidity region this effect vanishes. This could suggest a delayed hadronization scenario. In addition, the results from a first attempt to study the energy dependence of the Balance Function throughout the whole SPS energy range, are presented. The suitably scaled decrease of the width is approximately constant for the intermediate energies (30 to 80 AGeV) and gets stronger for the highest SPS and RHIC energies. On the other hand, both URQMD and HSD simulation results show no dependence on the collision energy.

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arXiv2005

Upper Limit of D0 Production in Central Pb-Pb Collisions at 158A GeV

Results are presented from a search for the decays D0 -> Kmin piplus and D0bar -> Kplus pimin in a sample of 3.8x10^6 central Pb-Pb events collected with a beam energy of 158A GeV by NA49 at the CERN SPS. No signal is observed. An upper limit on D0 production is derived and compared to predictions from several models.

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arXiv2004

System Size and Centrality Dependence of the Electric Charge Correlations in A+A and p+p Collisions at the SPS Energies

The Balance Function analysis method was developed in order to study the long range correlations in pseudo-rapidity of charged particle. The final results on p+p, C+C, Si+Si and centrality selected Pb+Pb collisions at $\sqrt{s_{NN}} = 17.2$ GeV and the preliminary data at $\sqrt{s_{NN}} = 8.8$ GeV are presented. The width of the Balance Function decreases with increasing system size and centrality of the collisions. This could suggest a delayed hadronization scenario.

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