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Register a new userDeep sub-threshold {phi} production and implications for the K+/K- freeze-out in Au+Au collisions
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We present data on charged kaons (K+-) and {phi} mesons in Au(1.23A GeV)+Au collisions. It is the first simultaneous measurement of K and {phi} mesons in central heavy-ion collisions below a kinetic beam energy of 10A GeV. The {phi}/K- multiplicity ratio is found to be surprisingly high with a value of 0.52 +- 0.16 and shows no dependence on the centrality of the collision. Consequently, the different slopes of the K+ and K- transverse-mass spectra can be explained solely by feed- down, which substantially softens the spectra of K- mesons. Hence, in contrast to the commonly adapted argumentation in literature, the different slopes do not necessarily imply diverging freeze- out temperatures of K+ and K- mesons caused by different couplings to baryons.
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We present first data on sub-threshold production of K0 s mesons and {Lambda} hyperons in Au+Au collisions at $sqrt{s_{NN}}$ = 2.4 GeV. We observe an universal <Apart> scaling of hadrons containing strangeness, independent of their corresponding production thresholds. Comparing the yields, their <Apart> scaling, and the shapes of the rapidity and the pt spectra to state-of-the-art transport model (UrQMD, HSD, IQMD) predictions, we find that none of the latter can simultaneously describe all observables with reasonable c{hi}2 values.
We report on the first multi-differential measurement of $phi$ meson and $Xi^{-}$ hyperon production as well as the $phi/K^-$ and $phi/Xi^-$ ratio in Au+Au collisions at ${sqrt{s_{rm NN}} = rm{3,GeV}}$ with the STAR experiment under its fixed targ et configuration at RHIC. $phi$ mesons and $Xi^{-}$ hyperons are measured through their hadronic decay channels, $phirightarrow K^+K^-$ and $Xi^-rightarrow Lambdapi^-$. The transverse kinetic energy spectra of $K^-$, $phi$ and $Xi^{-}$ are presented in different centrality and rapidity intervals. The total production yields and the ratios within a $4pi$ coverage are calculated and compared to thermal model predictions. A calculation within the grand canonical ensemble framework shows a clear discrepancy from our measurement. Our data favor the canonical ensemble approach employing local strangeness conservation with a small strangeness correlation length ($r_c leq 4.2$ fm) in 0--10% central Au+Au collisions at ${sqrt{s_{rm NN}} = rm{3,GeV}}$.
We report on K*0 production at mid-rapidity in Au+Au and Cu+Cu collisions at sqrt{s_{NN}} = 62.4 and 200 GeV collected by the Solenoid Tracker at RHIC (STAR) detector. The K*0 is reconstructed via the hadronic decays K*0 to K+ pi- and bar{K*0} to K-pi+. Transverse momentum, pT, spectra are measured over a range of pT extending from 0.2 GeV/c to 5 GeV/c. The center of mass energy and system size dependence of the rapidity density, dN/dy, and the average transverse momentum, <pT>, are presented. The measured N(K*0)/N(K) and N(phi)/N(K*0) ratios favor the dominance of re-scattering of decay daughters of K*0 over the hadronic regeneration for the K*0 production. In the intermediate pT region (2.0 < pT < 4.0 GeV/c), the elliptic flow parameter, v2, and the nuclear modification factor, RCP, agree with the expectations from the quark coalescence model of particle production.
The properties of the phi-meson have been measured via its e+e- and K+K- decay channels in Au+Au collisions at sqrt{s_NN} = 200 GeV by the PHENIX experiment. The preliminary yields and temperatures derived for the minimum bias and several centrality bins in both decay channels are presented.
Rapidity-odd directed flow measurements at midrapidity are presented for $Lambda$, $bar{Lambda}$, $K^pm$, $K^0_s$ and $phi$ at $sqrt{s_{NN}} =$ 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4 and 200 GeV in Au+Au collisions recorded by the STAR detector at the Relativistic Heavy Ion Collider. These measurements greatly expand the scope of data available to constrain models with differing prescriptions for the equation of state of quantum chromodynamics. Results show good sensitivity for testing a picture where flow is assumed to be imposed before hadron formation and the observed particles are assumed to form via coalescence of constituent quarks. The pattern of departure from a coalescence-inspired sum-rule can be a valuable new tool for probing the collision dynamics.
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