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Register a new user$K^{ast}(892)^0$ and $bar{K}^{ast}(892)^0$ production in central Pb+Pb, Si+Si, C+C and inelastic p+p collisions at 158$A$~GeV
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Production of the $K^{ast}(892)^0$ and $bar{K}^{ast}(892)^0$ resonances was studied via their $K^+ pi^-$ and $K^- pi^+$ decay modes in central Pb+Pb, Si+Si, C+C and inelastic p+p collisions at 158agev ($sqrt{s_{NN}}$ = 17.3 GeV) with the NA49 detector at the CERN SPS. Transverse momentum and rapidity distributions were measured and total yields were estimated. The yield of $K^{ast}$ exceeds that of $bar{K}^{ast}$ by about a factor of two in nucleus-nucleus reactions. The total yield ratios $< K^{ast} >/< K^+ >$ and $< bar{K}^{ast} >/< K^->$ are strongly suppressed in central Pb+Pb compared to p+p, C+C and Si+Si collisions in agreement with the expected attenuation of these short-lived resonance states in the hadronic phase of the expanding fireball. The UrQMD model, although incorporating such a scenario, does not provide a quantitative description of the experimental results. The statistical hadron gas model assuming the same freeze-out parameters for stable hadrons and resonances overestimates the $< K^{ast} >/< K >$ ratios in central Pb+Pb collisions by about a factor of 2.5.
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The measurement of $K^{*}(892)^0$ resonance production via its $K^{+}pi^{-}$ decay mode in inelastic p+p collisions at beam momentum 158 GeV/$c$ ($sqrt{s_{NN}}=17.3$ GeV) is presented. The data were recorded by the NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. The textit{template} method was used to extract the $K^{*}(892)^0$ signal and double differential transverse momentum and rapidity spectra were obtained. The full phase-space mean multiplicity of $K^{*}(892)^0$ mesons was found to be $(78.44 pm 0.38 mathrm{(stat)} pm 6.0 mathrm{(sys)) cdot 10^{-3}}$. The NA61/SHINE results are compared with the EPOS1.99 and Hadron Resonance Gas models as well as with world data from p+p and nucleus-nucleus collisions.
Using data samples of 89 fb$^{-1}$, 703 fb$^{-1}$, and 121 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider at center-of-mass energies 10.52 GeV, 10.58 GeV, and 10.876 GeV, respectively, we study the exclusive reactions $e^+e^- to omegapi^0$, $K^{ast}(892)bar{K}$, and $K_2^{ast}(1430)bar{K}$ (Charge-conjugate modes are included implicitly). Significant signals of $omegapi^0$, $K^{ast}(892)^0bar{K}^0$, and $K_2^{ast}(1430)^-K^+$ are observed for the first time at these energies, and the energy dependencies of the cross sections are presented. On the other hand, no significant excesses for $K^{ast}(892)^-K^+$ and $K_2^{ast}(1430)^0 bar{K}^0$ are found, and we set limits on the cross section ratios $R_{rm VP} = frac{sigma_B(e^+e^-to K^{ast}(892)^0bar K^0)} {sigma_B(e^+e^-to K^{ast}(892)^-K^+)}>$ 4.3, 20.0, and 5.4, and $R_{rm TP} = frac{sigma_B(e^+e^-to K_2^{ast}(1430)^0bar K^0)} {sigma_B(e^+e^-to K_2^{ast}(1430)^-K^+)}<$ 1.1, 0.4, and 0.6, for center-of-mass energies of 10.52 GeV, 10.58 GeV, and 10.876 GeV, respectively, at the 90% C.L.
Results are presented on hyperon and antihyperon production in Pb-Pb, pPb and pBe collisions at 158 GeV/c per nucleon. Lambda, Xi and Omega yields have been measured at central rapidity and medium transverse momentum as functions of the centrality of the collision. Comparing the yields in Pb-Pb to those in pBe interactions, strangeness enhancement is observed. The enhancement increases with the centrality and with the strangeness content of the hyperons, reaching a factor of about 20 for the Omega in the central Pb-Pb collisions.
We present a measurement of angular observables, $P_4$, $P_5$, $P_6$, $P_8$, in the decay $B^0 to K^ast(892)^0 ell^+ ell^-$, where $ell^+ell^-$ is either $e^+e^-$ or $mu^+mu^-$. The analysis is performed on a data sample corresponding to an integrated luminosity of $711~mathrm{fb}^{-1}$ containing $772times 10^{6}$ $Bbar B$ pairs, collected at the $Upsilon(4S)$ resonance with the Belle detector at the asymmetric-energy $e^+e^-$ collider KEKB. Four angular observables, $P_{4,5,6,8}$ are extracted in five bins of the invariant mass squared of the lepton system, $q^2$. We compare our results for $P_{4,5,6,8}$ with Standard Model predictions including the $q^2$ region in which the LHCb collaboration reported the so-called $P_5$ anomaly.
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.
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