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We present the first measurement of midrapidity vector meson phi production in Au+Au collisions at RHIC (sqrt[sNN]=130 GeV) from the STAR detector. For the 11% highest multiplicity collisions, the slope parameter from an exponential fit to the transverse mass distribution is T=379±50(stat)±45(syst) MeV, the yield dN/dy=5.73±0.37(stat)±0.69(syst) per event, and the ratio N phi /Nh- is found to be 0.021±0.001(stat)±0.004(syst). The measured ratio N phi /Nh- and T for the phi meson at midrapidity do not change for the selected multiplicity bins.
We report results on the ratio of midrapidity antiproton-to-proton yields in Au+Au collisions at sqrt[sNN] = 130 GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of | y|<0.5 and 0.4<pt<1.0 GeV/c, the ratio is essentially independent of either transverse momentum or rapidity, with an average of 0.65±0.01(stat)±0.07(syst) for minimum bias collisions. Within errors, no strong centrality dependence is observed. The results indicate that at this RHIC energy, although the p-p-bar pair production becomes important at midrapidity, a significant excess of baryons over antibaryons is still present.
The high energy loss of heavy ions in matter as well as the small angular scattering makes heavy ion beams an excellent tool to produce almost cylindrical and homogeneously excited volumes in matter. This aspect can be used to pump short wavelength lasers. In an experiment performed at the GSI (Gesellschaft für Schwerionenforschung, Darmstadt, Germany) ion accelerator facility in December 2005 the well-known KrF* excimer laser was pumped with an intense high energy uranium beam. Pulses of an uranium beam with initial particle energy of 250 MeV per nucleon, provided by heavy-ion-synchrotron SIS-18, were delivered to the HHT-target station and then stopped inside a gas laser cell. The maximum beam intensity reached in the experiment was 2,5·109 particles per pulse, which resulted in 34 J/g specific energy deposited in the laser gas. By applying electron cooling and a bunch compression technique at SIS-18, the beam pulses were compressed down to 110 ns (FWHM). A mixture of an excimer laser premix gas (95,5% Kr + 0,5% F2) and a buffer gas (Ar 4.8) was used as the laser gas in proportions of 35/65 and 60/40, respectively. The gas pressure inside the laser cell was varied in the range of 1,2÷2 bar in continues flow mode. The experimental setup consisted of a 1 m long stainless steel tube with a number of diagnostic viewports and two mirror adjustment units. The optical cavity was formed by a flat, Alcoated mirror at the beam entrance and a second dielectrically coated, highly reflective mirror with 3 m radius of curvature at a distance of 1,3 m. A beam of heavy ions has been used to pump a short wavelength gas laser for the first time. Laser effect on the KrF* laser transition (λ = 248 nm) has been successfully demonstrated. Laser threshold for this specific setup was reached with a beam intensity of 1,2·109 particles per pulse. Laser action has been clearly proofed by the following methods: appearance of the laser line, spectral narrowing of the laser line, temporal narrowing of the laser signal, non-linear response of the laser output intensity on the pumping power, and cavity disalignment effect. An energy of the laser pulse of about 2 mJ was measured for an ion beam intensity of 2·109 particles per pulse. The time delay of the onset of the laser emission with respect to the pumping pulse was measured as a function of ion beam intensity. The dependence of spontaneous emission spectra on the gas pressure in a range of 1,3÷2 bar was observed and the optimal gas pressure for laser experiments in the sense of laser efficiency was concluded. As a next step in studying short wavelength lasers pumped with heavy ion beams it is planned to reduce the laser wavelength down to the VUV region of the spectrum, and to proceed to the excimer lasers of the pure rare gases: Xe2 * (λ = 172 nm), Kr2 * (λ = 146 nm), Ar2 * (λ = 126 nm), Ne2 * (λ = 83 nm) and He2 * (λ = 80 nm). We believe that the use of heavy ion beams as a pumping source may lead to new pumping schemes on the higher lying level transitions and considerably shorter wavelengths (XUV and X-ray spectral region), which rely on the high cross sections for multiple ionization of the target species.
We present measurements of ρ0, ω and K∗0 spectra in π−+ C production interactions at 158 GeV / c and ρ0 spectra at 350 GeV / c using the NA61/SHINE spectrometer at the CERN SPS. Spectra are presented as a function of the Feynman’s variable xF in the range 0<xF<1 and 0<xF<0.5 for 158 and 350 GeV / c respectively. Furthermore, we show comparisons with previous measurements and predictions of several hadronic interaction models. These measurements are essential for a better understanding of hadronic shower development and for improving the modeling of cosmic ray air showers.
his Erratum replaces incorrect plots shown in Fig. 7 with the corrected ones. In the publication, the NA57 [1] ratios of Ξ− and Ξ¯¯¯¯+ to the number of wounded nucleons at ⟨NW⟩=349 by mistake were plotted at the wrong values. The ratios were calculated and plotted by mistake using ⟨NW⟩=249.
The correct normalization does not change the conclusions of the paper. The correctly normalized results are presented in Fig. 7.
The production of Ξ(1321)− and Ξ¯¯¯¯(1321)+ hyperons in inelastic p+p interactions is studied in a fixed target experiment at a beam momentum of 158 GeV/c. Double differential distributions in rapidity y and transverse momentum pT are obtained from a sample of 33M inelastic events. They allow to extrapolate the spectra to full phase space and to determine the mean multiplicity of both Ξ− and Ξ¯¯¯¯+. The rapidity and transverse momentum spectra are compared to transport model predictions. The Ξ− mean multiplicity in inelastic p+p interactions at 158 GeV/c is used to quantify the strangeness enhancement in A+A collisions at the same centre-of-mass energy per nucleon pair.
A measurement of charged hadron pair correlations in two-dimensional ηφ space is presented. The analysis is based on total 30 million central Be + Be collisions observed in the NA61/SHINE detector at the CERN SPS for incident beam momenta of 19A, 30A, 40A, 75A, and 150A GeV/c. Measurements were carried out for unlike-sign and like-sign charge hadron pairs independently. The C(η, φ) correlation functions were compared with results from a similar analysis on p + p interactions at similar beam momenta per nucleon. General trends of the backto-back correlations are similar in central Be + Be collisions and p + p interactions, but are suppressed in magnitude due to the increased combinatorial background. Predictions from the Epos and UrQMD models are compared to the measurements. Evolution of an enhancement around (η, φ) = (0, 0) with incident energy is observed in central Be + Be collisions. It is not predicted by both models and almost non-existing in proton–proton collisions at the same momentum per nucleon.
Bose-Einstein correlations of charged kaons were measured near mid-rapidity in central Pb+Pb collisions at 158 A 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.
Measurements of charged pion and kaon production in central Pb+Pb collisions at 40, 80 and 158 AGeV 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 s_NN^1/4 with a change of slope starting in the region 15-40 AGeV. 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 40 AGeV. A non-monotonic energy dependence of the ratio of K^+ to pi^+ yields is observed, with a maximum close to 40 AGeV 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.
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 non-statistical fluctuations, perhaps related to a first or second order QCD phase transition. Such fluctuations are shown to be very small.
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.
Cold target recoil ion momentum spectroscopy (COLTRIM) has been employed to image the momentum distributions of continuum electrons liberated in the impact of slow He2+ on He and H2. The distributions were measured for fully determined motion of the nuclei that is as a function of the impact parameter and in a well de ned scattering plane The single ionization (SI) of H2 leading to H2+ recoil ions in nondissociative states (He2+ + H+ -> He2+ + H+ + e-) and the transfer ionization (TI) of H2 leading to H2 dissociation into two free protons (He2+ H2 -> He+ + H+ + H+ + e-) were investigated. Similar measurements have been carried out for He target, the corresponding atomic two electron system, i.e. the single ionization (SI) (He2+ + He -> He+ + He2+ e- and the transfer ionization (TI) (He2+ + He -> He+ + He2+ + e-). These measurements have been exploited to understand the results obtained for H target. In comparing the continuum electron momentum distributions for H2 with that for He, a high degree of similarity is observed. In the case of transfer ionization of H2, the electron momentum distributions generated for parallel and perpendicular molecular orientations revealed no orientation dependence. The in scattering plane electron momentum distributions for the transfer ionization of H2 by He2+ and for the transfer ionization of He by He2e showed that the salient feature of these distributions for both collisions systems consists in the appearance of two groups of electrons with difeerent structures. In addition to the group of the saddle electrons forming two jets separated by a valley along the projectile axis we nd a new group of electrons moving with a velocity higher than the projectile velocity These new fast forward electrons result from a narrow range of impact parameters and appear as image saddle in the projectile frame. In contrast to the transfer ionization of He, the fast forward electrons group disappears in the in scattering plane electron momentum distribution generated for the single ionization of He. Instead of this group another new group of electrons appear These electrons exhibit an amount of backscattering These backward elec trons appear as image saddle in the target frame The structures that the saddle electrons show are owing to the quasi molecular nature of the collision process For the TI of H2, the TI of He and the SI of He, a pi-orbital shape of the electron momentum distribution is observed This indicates the importance of the rotational coupling 2-p-theta -> 2p-pi in the initial promotion of the ground state followed by further promotions to the continuum The backward electrons as well as the fast forward electrons are not discussed in the theoretical literature at all. However, a number of obvious indications of the existence of the backward and fast forward electrons could be seen in the experimental works of Abdallah et al. as well as in the theoretical calculations of Sidky et al One might speculate that electrons which are promoted on the saddle for some time during the collision could finally swing around the He+ ion in the way out of the collision, i.e. either around the projectile in the forward direction as in the TI case forming the fast forward electrons or around the recoil ion in the backward direction as in the SI case forming the backward electrons. This might be a result of the strong gradient, and hence the large acceleration of the screened He+ potential.
Partial wave analysis of the reaction p(3.5 GeV) + p → pK +Λ to search for the "ppK−" bound state
(2015)
Employing the Bonn–Gatchina partial wave analysis framework (PWA), we have analyzed HADES data of the reaction p(3.5 GeV) + p → pK +Λ. This reaction might contain information about the kaonic cluster “ppK −” (with quantum numbers J P = 0− and total isospin I = 1/2) via its decay into pΛ. Due to interference effects in our coherent description of the data, a hypothetical KNN (or, specifically “ppK −”) cluster signal need not necessarily show up as a pronounced feature (e.g. a peak) in an invariant mass spectrum like pΛ. Our PWA analysis includes a variety of resonant and non-resonant intermediate states and delivers a good description of our data (various angular distributions and two-hadron invariant mass spectra) without a contribution of a KNN cluster. At a confidence level of CLs = 95% such a cluster cannot contribute more than 2–12% to the total cross section with a pK +Λ final state, which translates into a production cross-section between 0.7 μb and 4.2 μb, respectively. The range of the upper limit depends on the assumed cluster mass, width and production process.
We present measurements of exclusive ensuremathπ+,0 and η production in pp reactions at 1.25GeV and 2.2GeV beam kinetic energy in hadron and dielectron channels. In the case of π+ and π0 , high-statistics invariant-mass and angular distributions are obtained within the HADES acceptance as well as acceptance-corrected distributions, which are compared to a resonance model. The sensitivity of the data to the yield and production angular distribution of Δ (1232) and higher-lying baryon resonances is shown, and an improved parameterization is proposed. The extracted cross-sections are of special interest in the case of pp → pp η , since controversial data exist at 2.0GeV; we find \ensuremathσ=0.142±0.022 mb. Using the dielectron channels, the π0 and η Dalitz decay signals are reconstructed with yields fully consistent with the hadronic channels. The electron invariant masses and acceptance-corrected helicity angle distributions are found in good agreement with model predictions.
Abstract Geant4 is a toolkit for simulating the passage of particles through matter. It includes a complete range of functionality including tracking, geometry, physics models and hits. The physics processes offered cover a comprehensive range, including electromagnetic, hadronic and optical processes, a large set of long-lived particles, materials and elements, over a wide energy range starting, in some cases, from 250 eV and extending in others to the TeV energy range. It has been designed and constructed to expose the physics models utilised, to handle complex geometries, and to enable its easy adaptation for optimal use in different sets of applications. The toolkit is the result of a worldwide collaboration of physicists and software engineers. It has been created exploiting software engineering and object-oriented technology and implemented in the C++ programming language. It has been used in applications in particle physics, nuclear physics, accelerator design, space engineering and medical physics. PACS: 07.05.Tp; 13; 23
Nuclear transport models including density- and momentum-dependent mean-field effects are compared to intranuclear-cascade models and tested on recent data on inclusive p-like cross sections for 800A-MeV La+La. We find a remarkable agreement between most model calculations but a systematic disagreement with the measured yield at 20°, possibly indicating a need for modification of nuclear transport properties at high densities.
There is little doubt that Quantumchromodynamics (QCD) is the theory which describes strong interaction physics. Lattice gauge simulations of QCD predict that in the m,T plane there is a line where a transition from confined hadronic matter to deconfined quarks takes place. The transition is either a cross over (at low m) or of first order (at high m). It is the goal of the present and future heavy ion experiment at RHIC and FAIR to study this phase transition at different locations in the m,T plane and to explore the properties of the deconfined phase. It is the purpose of this contribution to discuss some of the observables which are considered as useful for this purpose.
We demonstrate that momentum-dependent nuclear interactions (MDI) have a large effect on the dynamics and on the observables of high-energy heavy-ion collisions: A soft potential with MDI suppresses pion and kaon yields much more strongly than a local hard potential and results in transverse momenta intermediate between soft and hard local potentials. The collective-flow angles and the deuteron-to-proton ratios are rather insensitive to the MDI. Only simultaneous measurements of these observables can give clues on the nuclear equation of state at densities of interest for supernova collapse and neutron-star stability.