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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.
This paper proposes that we can predict which adverbs cannot adjoin to the right in headinitial languages by means of a particular semantic property, that of being a "subjective" adverb, one which maps an event or proposition onto a scale with the high degree of indeterminacy and context-dependence. Such adverbs, such as 'probably' or 'luckily', cannot adjoin to the right with non-manner readings, while other adverbs (like 'politically', 'often', or 'deliberately') may. This supports the view that the distribution of adverbs depends heavily, and subtly, on their lexicosemantic properties.
Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at sqrt(s_NN)=130 GeV using the STAR TPC at RHIC. The elliptic flow signal, v_2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.
Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at sqrt[sNN] = 130 GeV using the STAR Time Projection Chamber at the Relativistic Heavy Ion Collider. The elliptic flow signal, v2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.
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.
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.
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.
Rapidity distributions for Lambda and anti-Lambda hyperons in central Pb-Pb collisions at 40, 80 and 158 AGeV and for K 0 s mesons at 158 AGeV are presented. The lambda multiplicities are studied as a function of collision energy together with AGS and RHIC measurements and compared to model predictions. A different energy dependence of the Lambda/pi and anti-Lambda/pi is observed. The anti-Lambda/Lambda ratio shows a steep increase with collision energy. Evidence for a anti-Lambda/anti-p ratio greater than 1 is found at 40 AGeV.
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 are shown and compared to measurements at lower and higher energies.
Rapidity distributions for $\Lambda$ and $\bar{\Lambda}$ hyperons in central Pb-Pb collisions at 40, 80 and 158 A$\cdot$GeV and for ${\rm K}_{s}^{0}$ mesons at 158 A$\cdot$GeV are presented. The lambda multiplicities are studied as a function of collision energy together with AGS and RHIC measurements and compared to model predictions. A different energy dependence of the $\Lambda/\pi$ and $\bar{\Lambda}/\pi$ is observed. The $\bar{\Lambda}/\Lambda$ ratio shows a steep increase with collision energy. Evidence for a $\bar{\Lambda}/\bar{\rm p}$ ratio greater than 1 is found at 40 A$\cdot$GeV.