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We report a new measurement of the production of electrons from open heavy-flavor hadron decays (HFEs) at mid-rapidity (|y| < 0.7) in Au+Au collisions at √sNN = 200 GeV. Invariant yields of HFEs are measured for the transverse momentum range of 3.5 < pT < 9 GeV/c in various configurations of the collision geometry. The HFE yields in head-on Au+Au collisions are suppressed by approximately a factor of 2 compared to that in p + p collisions scaled by the average number of binary collisions, indicating strong interactions between heavy quarks and the hot and dense medium created in heavy-ion collisions. Comparison of these results with models provides additional tests of theoretical calculations of heavy quark energy loss in the quark-gluon plasma.
We present the first measurements of charge-dependent correlations on angular difference variables η1 − η2 (pseudorapidity) and φ1 − φ2 (azimuth) for primary charged hadrons with transverse momentum 0.15 <= pt <= 2 GeV/c and |η| <= 1.3 from Au–Au collisions at √sNN = 130 GeV. We observe correlation structures not predicted by theory but consistent with evolution of hadron emission geometry with increasing centrality from one-dimensional fragmentation of color strings along the beam direction to an at least two-dimensional hadronization geometry along the beam and azimuth directions of a hadron-opaque bulk medium.
Mid-rapidity transverse mass spectra and multiplicity densities of charged and neutral kaons are reported for Au + Au collisions at √sNN = 130 GeV at RHIC. The spectra are exponential in transverse mass, with an inverse slope of about 280 MeV in central collisions. The multiplicity densities for these particles scale with the negative hadron pseudo-rapidity density. The charged kaon to pion ratios are K+/π− = 0.161± 0.002(stat) ± 0.024(syst) and K−/π− = 0.146± 0.002(stat) ± 0.022(syst) for the most central collisions. The K+/π− ratio is lower than the same ratio observed at the SPS while the K−/π− is higher than the SPS result. The ratios are enhanced by about 50% relative to p + p and p¯ + p collision data at similar energies.
We report high-precision measurements of the longitudinal double-spin asymmetry, 𝐴𝐿𝐿, for midrapidity inclusive jet and dijet production in polarized 𝑝𝑝 collisions at a center-of-mass energy of √𝑠=200 GeV. The new inclusive jet data are sensitive to the gluon helicity distribution, Δ𝑔(𝑥,𝑄2), for gluon momentum fractions in the range from 𝑥≃0.05 to 𝑥≃0.5, while the new dijet data provide further constraints on the 𝑥 dependence of Δ𝑔(𝑥,𝑄2). The results are in good agreement with previous measurements at √𝑠=200 GeV and with recent theoretical evaluations of prior world data. Our new results have better precision and thus strengthen the evidence that Δ𝑔(𝑥,𝑄2) is positive for 𝑥>0.05.
Measurement of inclusive J/ψ polarization in p + p collisions at √s=200 GeV by the STAR experiment
(2020)
We report on new measurements of inclusive 𝐽/𝜓 polarization at midrapidity in 𝑝+𝑝 collisions at √𝑠=200 GeV by the STAR experiment at the Relativistic Heavy Ion Collider. The polarization parameters, 𝜆𝜃, 𝜆𝜙, and 𝜆𝜃𝜙, are measured as a function of transverse momentum (𝑝T) in both the helicity and Collins-Soper (CS) reference frames within 𝑝T<10 GeV/𝑐. Except for 𝜆𝜃 in the CS frame at the highest measured 𝑝T, all three polarization parameters are consistent with 0 in both reference frames without any strong 𝑝T dependence. Several model calculations are compared with data, and the one using the Color Glass Condensate effective field theory coupled with nonrelativistic QCD gives the best overall description of the experimental results, even though other models cannot be ruled out due to experimental uncertainties.
The family Dendrodorididae has a global distribution, with prevalence in tropical and subtropical intertidal zones. Three species of Dendrodorididae were collected from the intertidal zone of the northern coast of the Persian Gulf in Iran. Based on anatomical, histological, and molecular investigations they can be assigned to Dendrodoris fumata, Dendrodoris nigra, and a new species of Doriopsilla, D. aroni sp. nov. Molecular analyses of CO1 and 16S, including all genera of Dendrodorididae, members of the sister taxon Phyllidiidae, and other dorid outgroups resulted in a polyphyletic genus Dendrodoris, which is in contrast to the nuclear gene studies. Our molecular results confirm the differentiation between Dendrodoris rubra and D. fumata. Dendrodoris nigra, D. fumata, and D. krusensternii each consist of several clades, indicating cryptic species complexes requiring further investigation. We describe the presence of bacteria for the first time in the vestibular gland of D. fumata. Validation of the specimens of Doriopsilla from the Persian Gulf as a new species is supported by haplotype networking, genetic distance, and ABGD analyses of mitochondrial genes. Our CO1 analysis confirms a previous hypothesis that Cariopsilla is a junior synonym of Doriopsilla.
The genus Tekellina Levi, 1957 is currently composed of ten species, six of which are Neotropical. They are small-sized spiders (0.9 to 1.5 mm), with a wide distribution, with a great diversity in the Neotropical Region and well represented in Brazil. In this article, males and females of the species Tekellina bella Marques & Buckup, 1993 and T. crica Marques & Buckup, 1993 are redescribed and illustrated. The female of Tekellina minor Marques & Buckup, 1993 is described and illustrated for the first time. New records are included for Neotropical species. Tekellina guaiba Marques & Buckup, 1993 is synonymized with T. pretiosa Marques & Buckup, 1993. Three new species are described for Brazil: Tekellina picurrucha Rodrigues & Estol sp. nov. (São Paulo, Paraná and Rio Grande do Sul), Tekellina miuda Rodrigues & Estol sp. nov. (São Paulo and Paraná) and Tekellina miudinha Rodrigues & Estol sp. nov. (São Paulo). Distribution maps with new records and an identification key of the Neotropical species are also presented.
Nerillids are small marine annelids, once placed at the artificial group ‘Archiannelida’, which contained all families of the exclusively interstitial polychaetes. Nerillidae is the most species rich family among them, with 71 species grouped into 15 genera, and represents an important component of the interstitial fauna, occupying a wide bathymetric range. Despite its problematic placement among the ‘Archiannelida’ families, the group per se is considered monophyletic. Currently, only two species of Paranerilla are valid, both being reported from the northern hemisphere. It is presented herein as the first description of a species of Paranerilla from tropical waters, named as Paranerilla schiavettii sp. nov., which is also considered as a unique record by the presence of a modified acicular spine in noto- and neuropodia from chaetiger 3–7, not mentioned in its congeners descriptions. Hence, we also propose an emendation on the genus diagnosis to embrace the presence of acicular spines within Paranerilla. So, the presented information complements the current knowledge about the group’s taxonomy and expands its distribution to South Atlantic waters.
Search for the lepton number violating decay Σ⁻ → pe⁻e⁻ and the rare inclusive decay Σ⁻ → Σ⁺X
(2021)
Using a data sample of (1310.6±7.0)×106 𝐽/𝜓 events taken with the BESIII detector at the center-of-mass energy of 3.097 GeV, we search for the first time for the lepton number violating decay Σ−→𝑝𝑒−𝑒− and the rare inclusive decay Σ−→Σ+𝑋, where 𝑋 denotes any possible particle combination. The Σ− candidates are tagged in 𝐽/𝜓→¯Σ(1385)+Σ− decays. No signal candidates are found, and the upper limits on the branching fractions at the 90% confidence level are determined to be ℬ(Σ−→𝑝𝑒−𝑒−)<6.7×10−5 and ℬ(Σ−→Σ+𝑋)<1.2×10−4.
Using 10.1 × 109 J/ψ events produced by the Beijing Electron Positron Collider (BEPCII) at a center-of-mass energy √s = 3.097 GeV and collected with the BESIII detector, we present a search for the rare semi-leptonic decay J/ψ → D−e+νe + c.c. No excess of signal above background is observed, and an upper limit on the branching fraction B(J/ψ → D−e +νe + c.c.) < 7.1 × 10−8 is obtained at 90% confidence level. This is an improvement of more than two orders of magnitude over the previous best limit.