We report new STAR measurements of mid-rapidity yields for the $\Lambda$, $\bar{\Lambda}$, $K^{0}_{S}$, $\Xi^{-}$, $\bar{\Xi}^{+}$, $\Omega^{-}$, $\bar{\Omega}^{+}$ particles in Cu+Cu collisions at \sNN{200}, and mid-rapidity yields for the $\Lambda$, $\bar{\Lambda}$, $K^{0}_{S}$ particles in Au+Au at \sNN{200}. We show that at a given number of participating nucleons, the production of strange hadrons is higher in Cu+Cu collisions than in Au+Au collisions at the same center-of-mass energy. We find that aspects of the enhancement factors for all particles can be described by a parameterization based on the fraction of participants that undergo multiple collisions.
The enhancement factor for (multi-) strange particles in Cu+Cu $\sqrt{s_{NN}} = 200$ GeV collisions, where $|y| < 0.5$. The $\Lambda$, and $\bar{\Lambda}$ yields have been feed-down subtracted in all cases. The black bars show the normalization uncertainties, and the uncertainties for the heavy-ion points are the combined statistical and systematic errors. Curves described in the text, where $B_{K} = 2.0$, $B_{\Lambda} = 2.4$, $B_{\Xi} = 5.0$ and $B_{\Omega} = 12.1$.
The enhancement factor for (multi-) strange particles in Au+Au $\sqrt{s_{NN}} = 200$ GeV collisions, where $|y| < 0.5$. The $\Lambda$, and $\bar{\Lambda}$ yields have been feed-down subtracted in all cases. The black bars show the normalization uncertainties, and the uncertainties for the heavy-ion points are the combined statistical and systematic errors. Curves described in the text, where $B_{K} = 2.0$, $B_{\Lambda} = 2.4$, $B_{\Xi} = 5.0$ and $B_{\Omega} = 12.1$.
From a sample of 2.36 million minimum bias events produced in p p collisions at s =630 GeV in the UA1 experiment and from other published data at the CERN S p p S collider we have estimated the relative production of π ± , π 0 , K ± , K S 0 , Λ, Λ , p and p . We obtain a meson over baryon ratio M B = 6.4 ± 1.1 . From the K S 0 π ± ratio we measure the strangeness suppression factor λ = 0.29 ± 0.02 ± 0.01 which, combining with other available data provides a new world average of 0.29 ± 0.015. Both the K S 0 π ± ratio and the strangeness suppression factor λ as a function of s are investigated, and an extrapolation to the LHC energy is performed.
CONST is strangeness suppression factor, extracted from KS/PI+- ratio (see text).
The reaction pp → K + Λp was measured exclusively at the cooler synchrotron COSY at beam momenta of p Beam = 2.50 GeV/c and p Beam = 2.75 GeV/c using the TOF detector. Angular and momentum distributions were obtained for the full phase space of the reaction products. Total cross sections were extracted to be (2.7 ± 0.3) μ b and (12.0 ± 0.4) μ b, respectively. The polarization of the Λ -hyperon was determined as a function of its transversal momentum and was found to be negative for transverse momentum transfers of p T ≥ 0.3 GeV/c. The results together with existing data are compared with phenomenological parametrizations and model calculations on the basis of meson exchange.
Λ , Ξ and Ω yields and transverse mass spectra have been measured in Pb-Pb and p-Pb collisions at 158 A GeV/ c . The yields in Pb-Pb interactions are presented as a function of the collision centrality and compared with those obtained from p-Pb collisions. Strangeness enhancement is observed which increases with centrality and with the strangeness content of the hyperon.
Neutral kaon to negative pion production ratios fromvp and\(\bar vp\) charged current interactions in BEBC are presented and compared with LUND fragmentation model predictions. Good agreement is obtained with a strangeness suppression factor λ=0.203±0.014(stat)±0.010(sys). No evidence is seen for an energy dependence of λ in our kinematic region.
We have made the first direct measurement of the parity-violating coupling of the Z^0 boson to the strange quark, A_s, using ~550,000 e^+e^- ->Z^0->hadrons events produced with a polarized electron beam and recorded by the SLD experiment. Z^0 -> s-sbar events were tagged by the absence of B or D hadrons and the presence in each hemisphere of a high-momentum K^+- or K^0_s. From the polar angle distributions of the strangeness-signed thrust axis, we obtained A_s=0.895+-0.066(stat.)+-0.062(syst.). The analyzing power and u-ubar plus d-dbar background were constrained using the data.
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NUCLEUS IS P, C, AL, CU. BARYUNIUM WITH HIDDEN STRANGENESS.
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.
A search for baryonia with negative and positive strangeness decaying respectively into\(\Lambda+ \bar p + pions\) and\(\bar \Lambda+ p + pions\) has been carried out in a neutron beam with a mean momentum of ≅40 GeV/c in an experiment performed at the Serpukhov accelerator. There is a strong indication of the existence of these baryonia. The following four charge states are observed for negative and positive strangeness: neutral, negative, positive and doubly charged. Their mean mass is 3055±25 MeV/c2 and the width Γ≦36±15 MeV/c2. The data show that the isotopic spin of the baryonia is ≧3/2. The baryonia production cross sections in the acceptable kinematic regionXF≧0.2 andPT≦1 GeV/c times the branching ratios of the observed decays are of the order of 1 μb per nucleon.
We report the first multi-differential measurements of strange hadrons of $K^{-}$, $\phi$ and $\Xi^{-}$ yields as well as the ratios of $\phi/K^-$ and $\phi/\Xi^-$ in Au+Au collisions at ${\sqrt{s_{\rm NN}} = \rm{3\,GeV}}$ with the STAR experiment fixed target configuration at RHIC. The $\phi$ mesons and $\Xi^{-}$ hyperons are measured through hadronic decay channels, $\phi\rightarrow K^+K^-$ and $\Xi^-\rightarrow \Lambda\pi^-$. Collision centrality and rapidity dependence of the transverse momentum spectra for these strange hadrons are presented. The $4\pi$ yields and ratios are compared to thermal model and hadronic transport model predictions. At this collision energy, thermal model with grand canonical ensemble (GCE) under-predicts the $\phi/K^-$ and $\phi/\Xi^-$ ratios while the result of canonical ensemble (CE) calculations reproduce $\phi/K^-$, with the correlation length $r_c \sim 2.7$ fm, and $\phi/\Xi^-$, $r_c \sim 4.2$ fm, for the 0-10% central collisions. Hadronic transport models including high mass resonance decays could also describe the ratios. While thermal calculations with GCE work well for strangeness production in high energy collisions, the change to CE at $\rm{3\,GeV}$ implies a rather different medium property at high baryon density.
$K^-$ (a), invariant yields as a function of $m_T-m_0$ for various rapidity regions in 0--10\% central Au+Au collisions at ${\sqrt{s_{\mathrm{NN}}} = \mathrm{3\,GeV}}$. Statistics and systematic uncertainties are added quadratic here for plotting. Solid and dashed black lines depict $m_T$ exponential function fits to the measured data points with arbitrate scaling factors in each rapidity windows.
$\phi$ meson (b) invariant yields as a function of $m_T-m_0$ for various rapidity regions in 0--10\% central Au+Au collisions at ${\sqrt{s_{\mathrm{NN}}} = \mathrm{3\,GeV}}$. Statistics and systematic uncertainties are added quadratic here for plotting. Solid and dashed black lines depict $m_T$ exponential function fits to the measured data points with arbitrate scaling factors in each rapidity windows.
$\Xi^-$ (c) invariant yields as a function of $m_T-m_0$ for various rapidity regions in 0--10\% central Au+Au collisions at ${\sqrt{s_{\mathrm{NN}}} = \mathrm{3\,GeV}}$. Statistics and systematic uncertainties are added quadratic here for plotting. Solid and dashed black lines depict $m_T$ exponential function fits to the measured data points with arbitrate scaling factors in each rapidity windows.
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