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Register a new userMeasurements of $Xileft(1530right)^{0}$ and $overline{Xi}left(1530right)^{0}$ production in proton-proton interactions at $sqrt{s_{NN}}$ = 17.3 GeV in the NA61/SHINE experiment
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Double-differential yields of $Xileft(1530right)^{0}$ and $overline{Xi}left(1530right)^{0}$ resonances produced in pp interactions were measured at a laboratory beam momentum of 158~GeVc. This measurement is the first of its kind in pp interactions below LHC energies. It was performed at the CERN SPS by the NASixtyOne collaboration. Double-differential distributions in rapidity and transverse momentum were obtained from a sample of 26$cdot$10$^6$ inelastic events. The spectra are extrapolated to full phase space resulting in mean multiplicity of $Xileft(1530right)^{0}$ (6.73 $pm$ 0.25 $pm$ 0.67)$times10^{-4}$ and $overline{Xi}left(1530right)^{0}$ (2.71 $pm$ 0.18 $pm$ 0.18)$times10^{-4}$. The rapidity and transverse momentum spectra and mean multiplicities were compared to predictions of string-hadronic and statistical model calculations.
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The production of $Xi(1321)^{-}$ and $overline{Xi}(1321)^{+}$ hyperons in inelastic p+p interactions is studied in a fixed target experiment at a beam momentum of 158 GeV/textit{c}. Double differential distributions in rapidity y and transverse momentum $p_{T}$ are obtained from a sample of 33M inelastic events. They allow to extrapolate the spectra to full phase space and to determine the mean multiplicity of both $Xi^{-}$ and $overline{Xi}^{+}$. The rapidity and transverse momentum spectra are compared to transport model predictions. The $Xi^{-}$ mean multiplicity in inelastic p+p interactions at 158~GeVc is used to quantify the strangeness enhancement in A+A collisions at the same centre-of-mass energy per nucleon pair.
The momentum correlation between protons and lambda particles emitted from central Pb+Pb collisions at sqrt(s_{NN}) = 17.3 GeV was studied by the NA49 experiment at the CERN SPS. A clear enhancement is observed for small relative momenta (q_{inv} < 0.2 GeV). By fitting a theoretical model, which uses the strong interaction between the proton and the lambda in a given pair, to the measured data a value for the effective source size is deduced. Assuming a static Gaussian source distribution we derive an effective radius parameter of R_G = 3.02 pm 0.20$(stat.)^{+0.44}_{-0.16}(syst.) fm.
We report the first measurement of rapidity-odd directed flow ($v_{1}$) for $D^{0}$ and $overline{D^{0}}$ mesons at mid-rapidity ($|y| < 0.8$) in Au+Au collisions at $sqrt{s_{rm NN}}$ = 200,GeV using the STAR detector at the Relativistic Heavy Ion Collider. In 10--80% Au+Au collisions, the slope of the $v_{1}$ rapidity dependence ($dv_{1}/dy$), averaged over $D^{0}$ and $overline{D^{0}}$ mesons, is -0.080 $pm$ 0.017 (stat.) $pm$ 0.016 (syst.) for transverse momentum $p_{rm T}$ above 1.5~GeV/$c$. The absolute value of $D^0$-meson $dv_1/dy$ is about 25 times larger than that for charged kaons, with 3.4$sigma$ significance. These data give a unique insight into the initial tilt of the produced matter, and offer constraints on the geometric and transport parameters of the hot QCD medium created in relativistic heavy-ion collisions.
Pentaquark states have been extensively investigated theoretically in the context of the constituent quark model. In this paper results of an experimental search for pentaquarks in the Ximpim, Ximpip, Xippim and Xippip invariant mass spectra in proton-proton interactions at $sqrt{s}$=17.3~GeV are presented. Previous possible evidence from the NA49 collaboration of the existence of a narrow Ximpim baryon resonance in p+p interactions is not confirmed with almost 10 times greater event statistics. The search was performed using the NASixtyOne detector which reuses the main components of the NA49 apparatus. No signal was observed with either the selection cuts of NA49 or newly optimised cuts.
Due to the large masses, heavy-flavor quarks are dominantly produced in initial hard scattering processes and experience the whole evolution of the medium produced in heavy-ion collisions at RHIC energies. They are also expected to thermalize slower than light-flavor quarks. Thus the measurement of heavy quark production and azimuthal anisotropy can provide important insights into the medium properties through their interactions with the medium. In these proceedings, we report measurements of $D^0$ production and elliptic flow ($v_2$) via topological reconstruction using STARs recently installed Heavy Flavor Tracker (HFT). The new measurement of the nuclear modification factor ($R_{AA}$) of $D^0$ mesons in central Au+Au collisions at $sqrt{s_{NN}}$ = 200 GeV confirms the strong suppression at high transverse momenta ($p_{T}$) reported in the previous publication with much improved precision. We also report the measurement of elliptic flow for $D^0$ mesons in a wide transverse momentum range in 0-80% minimum-bias Au+Au collisions. The $D^0$ elliptic flow is finite for $p_{T}$ $>$ 2 GeV/c and is systematically below that of light hadrons in the same centrality interval. Furthermore, several theoretical calculations are compared to both $R_{AA}$ and $v_2$ measurements, and the charm quark diffusion coefficient is inferred to be between 2 and $sim$12.
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