Production of heavy neutron-rich nuclei “south" of lead

The production of heavy neutron-rich nuclei is investigated using cold-fragmentation reactions. More than 25 new heavy neutron-rich nuclei were produced in the fragmentation of ²⁰⁸Pb projectiles at 1 A GeV impinging a beryllium target. The precise measurement of their production cross sections enables to benchmark the predictive power of different model calculations and make reliable predictions of the production rates expected in future radioactive beam facilities.     

Search for deconfinement in NA49 at the CERN SPS

Experiment NA49 at the CERN SPS uses a large acceptance detector for a systematic study of particle yields and correlations in nucleus-nucleus, nucleon-nucleus and nucleon-nucleon collisions. Preliminary results for Pb+Pb collisions at 40, 80 and 158 A⋅GeV beam energy shown and compared to measurements at lower and higher energies.     

Suppression of high-p{T} neutral pion production in central Pb+Pb collisions at sqrt[S{NN}]=17.3 GeV relative to p+C and p+Pb collisions

Neutral pion transverse momentum spectra were measured in p+C and p+Pb collisions at sqrt[S{NN}]=17.4 GeV at midrapidity (2.3 less than or approximately equal eta{lab} less than or approximately equal 3.0) over the range 0.7 less than or approximately equal p{T} less than or approximately equal 3.5 GeV/c. The spectra are compared to pi{0} spectra measured in Pb+Pb collisions at sqrt[S{NN}]=17.3 GeV in the same experiment. For a wide range of Pb+Pb centralities (N{part} less than or approximately equal 300), the yield of pi{0}'s with p{T} greater than or approximately equal 2 GeV/c is larger than or consistent with the p+C or p+Pb yields scaled with the number of nucleon-nucleon collisions (N{coll}), while for central Pb+Pb collisions with N{part}greater than or approximately equal 350, the pi{0} yield is suppressed.     

Strangeness enhancement at midrapidity in Pb–Pb collisions at 158 A GeV/c: A comparison with VENUS and RQMD models

Recently the WA97 Collaboration has measured , , , and negative particle yields and transverse mass spectra at central rapidity in Pb–Pb and p–Pb collisions at 158 A GeV/c. These results are compared with the predictions of two of the most widely used event generators for heavy-ion collisions: VENUS 4.12 and RQMD 2.3. Both models predict that enhancements increase with the strangeness content of the particle. They fail, however, to reproduce completely the measured values of yields at central rapidity. In particular, for multistrange particles, VENUS fails to reproduce both the p–Pb and the Pb–Pb data, while RQMD works for p–Pb collisions but seems to be unable to reproduce the data in Pb–Pb collisions. Moreover, the predicted behavior for strangeness production as a function of the centrality of the collision appears to be different from the observed behavior. Received: 29 April 1999 / Published online: 14 October 1999     

Measurement of light mesons at RHIC by the PHENIX experiment

The PHENIX experiment at RHIC has measured a variety of light neutral mesons (π ⁰, K _S ⁰, η, ω, η ^′, φ) via multi-particle decay channels over a wide range of transverse momentum. A review of the recent results on the production rates of light mesons in p + p and their nuclear modification factors in d + Au, Cu + Cu and Au + Au collisions at different energies is presented.     

Investigation of the high-p<Subscript>T</Subscript> strange baryon anomalies at RHIC

Results from RHIC have shown that there is an enhanced baryon/meson ratio in the intermediate transverse momentum range (2<p_T<6 GeV/c) in Au+Au collisions at both  =130 and 200 GeV. This was initially demonstrated by measurements of the p̄/π^- ratio which was then extended in p_T by the Λ/K⁰ _S ratio. The data were successfully described by models utilising different hadronization mechanisms: those having recombination of quarks and others having an interplay between flow, jet quenching and incorporating baryon junction loops. The strange particle data from the first Au+Au run at  =200 GeV gave tantalising hints that the observed enhancement of baryons compared to mesons was diminished by a p_T of 6 GeV/c, but a lack of statistics in this range made a definitive statement impossible. Here we present an extended analysis of identified strange baryons and mesons in Au+Au collisions at  =200 GeV using data obtained by the STAR experiment from the 2004 running period. The increase in statistics extends the measurement of Λ hyperons out to at least 7 GeV/c and K⁰ _S mesons out to 9 GeV/c. This data allows us to place limits on the range where in-vacuum fragmentation functions are applicable and the effect of baryon dominance is reduced. We also discuss the prospects for making these measurements using multiply-strange baryons and mesons (Ω and ϕ).     

What can we learn from high-p<Subscript>T</Subscript> correlations of neutral strange baryons and mesons at RHIC?

We present results on two-particle azimuthal correlations of neutral strange baryons (Λ, Λ̄) and mesons (K_S ⁰) for p_T=2–6 GeV/c associated with non-identified charged particles in d+Au and Au+Au collisions at  =200 GeV measured by the STAR experiment. We investigate in detail the associated yield of charged particles as a function centrality of the collision and transverse momentum of trigger and associated particles to look for possible flavor, baryon/meson and particle/anti-particle differences. We compare our results to the proton and pion triggered correlations as well as to a fragmentation and recombination model. PACS 25.75.-q; 25.75.Gz     

Large-angle production of charged pions by 3-12.9?GeV/c protons on beryllium, aluminium and lead targets

Measurements of the double-differential π^± production cross-section in the range of momentum 100 MeV/c≤p< 800 MeV/c and angle 0.35 rad ≤θ<  2.15 rad in proton–beryllium, proton–aluminium and proton–lead collisions are presented. The data were taken with the HARP detector in the T9 beam line of the CERN PS. The pions were produced by proton beams in a momentum range from 3 GeV/c to 12.9 GeV/c hitting a target with a thickness of 5% of a nuclear interaction length. The tracking and identification of the produced particles was performed using a small-radius cylindrical time projection chamber (TPC) placed inside a solenoidal magnet. Incident particles were identified by an elaborate system of beam detectors. Results are obtained for the double-differential cross-sections d²σ/dpdθ at six incident proton beam momenta (3 GeV/c, 5 GeV/c, 8 GeV/c, 8.9 GeV/c (Be only), 12 GeV/c and 12.9 GeV/c (Al only)) and compared to previously available data.     

ψ′ production in Pb–Pb collisions at 158?GeV/nucleon

ψ^′ production is studied in Pb–Pb collisions at 158 GeV/c per nucleon incident momentum. Absolute cross-sections are measured and production rates are investigated as a function of the centrality of the collision. The results are compared with those obtained for lighter colliding systems and also for the J/ψ meson produced under identical conditions. PACS 25.75.Dw     

Two-kaon correlations in central Pb+Pb collisions at 158 a GeV/c

Two-particle interferometry of positive kaons is studied in Pb+Pb collisions at mean transverse momenta approximately 0.25 and 0.91 GeV/c. A three-dimensional analysis was applied to the lower p(T) data, while a two-dimensional analysis was used for the higher p(T) data. We find that the source-size parameters are consistent with the m(T) scaling curve observed in pion-correlation measurements in the same collisions, and that the duration time of kaon emission is consistent with zero within the experimental sensitivity.     

First fragmentation function measurements from full jet reconstruction in heavy-ion collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV by STAR

Measurements of inclusive hadron suppression and di-hadron azimuthal correlations in ultra-relativistic nuclear collisions at RHIC have provided important insights into jet quenching in hot QCD matter, but are limited in their sensitivity due to well-known biases. Full jet reconstruction in heavy-ion collisions would conceptually provide a direct measurement of the energy of the scattered parton before energy loss, alleviating such biases and allowing a measurement of the energy loss probability distribution in a model-independent way from hard probes. In these proceedings we utilize recent progress in the reconstruction of jets in the heavy ion environment and present the first measurement of the fragmentation function from fully reconstructed jets in heavy ion collisions. The fragmentation function measured in central Au + Au collisions at  GeV will be presented and discussed with respect to p + p reference measurements.     

K*0 and φ meson production in proton–nucleus interactions at ?s=41.6\textGeV\sqrt{s}=41.6\text{GeV}

The inclusive production cross sections of the strange vector mesons K^*0, K̄^*0, and φ have been measured in interactions of 920 GeV protons with C, Ti, and W targets with the HERA-B detector at the HERA storage ring. Differential cross sections as a function of rapidity and transverse momentum have been measured in the central rapidity region and for transverse momenta up to p_T = 3.5 GeV/c. The atomic number dependence is parametrised as σ_pA=σ_pN*A^α, where σ_pN is the proton–nucleon cross section. Within the phase space accessible, α(K^*0)=0.86±0.03, α(K̄^*0)=0.87±0.03, and α(φ)=0.96±0.02. The total proton–nucleon cross sections, determined by extrapolating the differential measurements to full phase space, are σ_pN→K*0=(5.06±0.54) mb, σ_pN→K̄*0=(4.02±0.45) mb, and σ_pN→φ=(1.17±0.11) mb. For all resonances the Cronin effect is observed; compared to the measurements of Cronin et al. for K^± mesons, the measured values of α for φ mesons coincide with those of K⁺ mesons for all transverse momenta, while the enhancement for K^*0/K̄^*0 mesons is smaller.     

Test of quantum mechanics by neutron interferometry

Measurements of the π⁰ and direct photon nuclear modification factors in p+p and A+A collisions in the PHENIX experiment at RHIC will be reviewed and recent results at  GeV will be presented. Using for the first time the p+p reference measured in the same experiment instead of averaging world data the π⁰ suppression turns out to be almost as large at  GeV as at  GeV, implying gluon densities dN^g/dy>800. Possible origins of photon suppression at high p_T in  GeV are discussed in light of the new results on photon R_AA at  GeV.     

Charged particle multiplicities in A+A and p+p collisions in the constituent quarks framework

Charged particle multiplicities in A+A and p(p̄)+p collisions as a function of pseudorapidity, centrality and energy are studied in both the nucleon and the constituent quark frameworks. In the present work, the calculation using the nuclear overlap model takes into account the fact that for the peripheral A+A and p+p collisions the number of nucleon and constituent quark participants cannot be smaller than two. A striking agreement is seen between the particle density in A+A and p(p̄)+p collisions, both at mid-rapidity and in the fragmentation regions, when normalized to the number of participating constituent quarks. The observations presented in this paper imply that the number of constituent quark pairs participating in the collision controls the particle production. PACS 25.75.-q; 25.75.Dw; 25.75.Nq; 24.10.Jv     

What can we learn from the decay of NX(1625) in the molecule picture?

Considering two assumptions on the molecular state, i.e. the S-wave Λ̄–K^- and S-wave Σ̄⁰–K^- molecular states, we study the possible decays of N̄_X(1625) that include N̄_X(1625)→K^-Λ̄,π⁰p̄,ηp̄,π^-n̄. Our results indicate that (1) if N̄_X(1625) is the Λ̄–K^- molecular state, K^-Λ̄ is the main decay mode of N̄_X(1625), and the branching ratios of the rest decay modes are tiny; (2) if N̄_X(1625) is the Σ̄⁰–K^- molecular state, the branching ratio of N̄_X(1625)→K^-Λ̄ is one or two orders smaller than that of N̄_X(1625)→π⁰p̄,ηp̄,π^-n̄. Thus the search for N̄_X(1625)→π⁰p̄,ηp̄,π^-n̄ will be helpful to shed light on the nature of N̄_X(1625). PACS 13.30.Eg, 13.75.Jz     

Particle production in Pb+Pb collisions at the SPS

Experiment NA49 at the CERN SPS employs a large acceptance detector to study particle spectra, yields and correlations in nucleus-nucleus, nucleon-nucleus and nucleon-nucleon collisions. Preliminary results on pion, kaon, A and ā production in central Pb+Pb collisions at 40, 80 and 158 A·GeV beam energy are shown and compared to measurements at lower and higher energies.     

Measurement of the production cross-section of positive pions in the collision of 8.9 GeV/c protons on beryllium

The double-differential production cross-section of positive pions, , measured in the HARP experiment is presented. The incident particles are 8.9 GeV/c protons directed onto a beryllium target with a thickness of 5% of a nuclear interaction length. The measured cross-section has a direct impact on the prediction of neutrino fluxes for the MiniBooNE and SciBooNE experiments at Fermilab. After cuts, 13 million protons on target produced about 96000 reconstructed secondary tracks which were used in this analysis. Cross-section results are presented in the kinematic range 0.75 GeV/c≤p_π≤ 6.5 GeV/c and 30 mrad≤θ_π≤ 210 mrad in the laboratory frame.     

Partonic effect on anisotropic flows of Ω baryon for Au+Au at 62.4 and 200 GeV/c

The elliptic flow v₂ and the fourth order anisotropic flow v₄ of (Ω+Ω̄) have been studied in the framework a parton–hadronic transport model, namely a multi-phase transport (AMPT) model, for ¹⁹⁷Au+¹⁹⁷Au collisions at = 200 GeV and 62.4 GeV. The transverse momentum (p_T) and the transverse kinetic energy (m_T-m₀) dependence of v₂ and v₄ are presented. The calculation in the AMPT model seems consistent with the STAR data. The results show that the v₂ of (Ω+Ω̄) in 200 GeV obeys the constituent quark number scaling that has been observed for other mesons and baryons. Comparison of (Ω+Ω̄) elliptic flow v₂ in the default version of AMPT, the melting version of AMPT and the RQMD model calculation, shows that the parton cascade process is important to reproduce the sizeable v₂, and the string melting AMPT model preferably reproduces (Ω+Ω̄) elliptic flow v₂ in ¹⁹⁷Au+¹⁹⁷Au collisions at = 200 GeV. The v₂ of (Ω+Ω̄) in the 62.4 and 200 GeV collisions seem similar, and the p_T dependence of (Ω+Ω̄) baryons’ v₄ in 62.4 GeV and 200 GeV looks also similar in the string melting AMPT model, which indicates that a similar partonic matter phase has been reached in both energies.     

Protons flow in Pb+Pb collisions at 40 <Emphasis Type="Italic">A</Emphasis> GeV energy

For Pb+Pb collisions at 40 A GeV energy, we calculate the side-ward and elliptic differential flow of protons in the microscopic relativistic transport simulation model. We compare our results with the recent data from the NA49 Collaboration as a function of transverse momenta, rapidity and centrality. We find that the side-ward and elliptic flow agree reasonably well with the experimental data with and without momentum-dependent potentials in the simulation model.     

Measurement of the W boson mass and width in e+e- collisions at LEP

The mass of the W boson is determined from the direct reconstruction of W decays in WW→qq̄qq̄ and WW→ℓνqq̄ events in e⁺e^- collisions at LEP. The data sample corresponds to an integrated luminosity of 683 pb^-1 collected with the ALEPH detector at centre-of-mass energies up to 209 GeV. To minimise any effect from colour reconnection a new procedure is adopted in which low energy particles are not considered in the mass determination from the qq̄qq̄ channel. The combined result from all channels is where FSI represents the possible effects of final state interactions in the qq̄qq̄ channel and LEP indicates the uncertainty in the beam energy. From two-parameter fits to the W mass and width, the W width is found to be