Measurements of inclusive production of the Lambda, Xi- and Xi*(1530) baryons in two-photon collisions with the L3 detector at LEP are presented. The inclusive differential cross sections for Lambda and Xi- are measured as a function of the baryon transverse momentum, pt, and pseudo-rapidity, eta. The mean number of Lambda, Xi- and Xi*(1530) baryons per hadronic two-photon event is determined in the kinematic range 0.4 GeV < pt< 2.5 GeV, |eta| < 1.2. Overall agreement with the theoretical models and Monte Carlo predictions is observed. A search for inclusive production of the pentaquark theta+(1540) in two-photon collisions through the decay theta+ -> proton K0s is also presented. No evidence for production of this state is found.
Differential cross section for LAMBDA production.
Differential cross section for LAMBDA production.
Differential cross section for XI- production.
Ratios of the Psi' over the J/psi production cross sections in the dilepton channel for C, Ti and W targets have been measured in 920 GeV proton-nucleus interactions with the HERA-B detector at the HERA storage ring. The Psi' and J/psi states were reconstructed in both the mu+mu- and the e+e- decay modes. The measurements covered the kinematic range -0.35 < x_F < 0.1 with transverse momentum p_T < 4.5 GeV/c. The Psi' to J/psi production ratio is almost constant in the covered x_F range and shows a slow increase with p_T. The angular dependence of the ratio has been used to measure the difference of the Psi' and J/psi polarization. All results for the muon and electron decay channels are in good agreement: their ratio, averaged over all events, is R_psi'(mu)/R_psi'(e)=1.00+-0.08+-0.04. This result constitutes a new, direct experimental constraint on the double ratio of branching fractions, (B'(mu)*B(e))/(B(mu)*B'(e)), of Psi' and J/psi in the two channels.
Ratio of PSI(3685) and J/PSI cross sections for both muon and electron channels combined, obtained for different cos theta in the s-channel helicity frame.
Ratio of PSI(3685) and J/PSI cross sections for both muon and electron channels combined, obtained for intervals inpT using the data from all targets.
Ratio of PSI(3685) and J/PSI production cross sections per nucleus.
We present strange particle spectra and yields measured at mid-rapidity in $\sqrt{\text{s}}=200$ GeV proton-proton ($p+p$) collisions at RHIC. We find that the previously observed universal transverse mass ($\mathrm{m_{T}}\equiv\sqrt{\mathrm{p_{T}}^{2}+\mathrm{m}^{2}}$) scaling of hadron production in $p+p$ collisions seems to break down at higher \mt and that there is a difference in the shape of the \mt spectrum between baryons and mesons. We observe mid-rapidity anti-baryon to baryon ratios near unity for $\Lambda$ and $\Xi$ baryons and no dependence of the ratio on transverse momentum, indicating that our data do not yet reach the quark-jet dominated region. We show the dependence of the mean transverse momentum (\mpt) on measured charged particle multiplicity and on particle mass and infer that these trends are consistent with gluon-jet dominated particle production. The data are compared to previous measurements from CERN-SPS, ISR and FNAL experiments and to Leading Order (LO) and Next to Leading order (NLO) string fragmentation model predictions. We infer from these comparisons that the spectral shapes and particle yields from $p+p$ collisions at RHIC energies have large contributions from gluon jets rather than quark jets.
Corrected mid-rapidity (|y| < 0.5) pT spectra for $K^{+}$, $K^{−}$, $K^{0}_{S}$, Λ, Ξ, and Ω. Λ spectra that have been corrected for feed-down are shown as open symbols in the Λ panel. The dashed lines are fits using Equation 11 except for the $\Omega+\overline{\Omega}$ where the fit uses Equation 9. The error bars displayed include systematic errors while the fits were done using statistical errors only for all species except the charged kaons.
Corrected mid-rapidity (|y| < 0.5) pT spectra for $K^{+}$, $K^{−}$, $K^{0}_{S}$, Λ, Ξ, and Ω. Λ spectra that have been corrected for feed-down are shown as open symbols in the Λ panel. The dashed lines are fits using Equation 11 except for the $\Omega+\overline{\Omega}$ where the fit uses Equation 9. The error bars displayed include systematic errors while the fits were done using statistical errors only for all species except the charged kaons.
Corrected mid-rapidity (|y| < 0.5) pT spectra for $K^{+}$, $K^{−}$, $K^{0}_{S}$, Λ, Ξ, and Ω. Λ spectra that have been corrected for feed-down are shown as open symbols in the Λ panel. The dashed lines are fits using Equation 11 except for the $\Omega+\overline{\Omega}$ where the fit uses Equation 9. The error bars displayed include systematic errors while the fits were done using statistical errors only for all species except the charged kaons.
The STAR collaboration at RHIC reports measurements of the inclusive yield of non-photonic electrons, which arise dominantly from semi-leptonic decays of heavy flavor mesons, over a broad range of transverse momenta ($1.2 < \pt < 10$ \gevc) in \pp, \dAu, and \AuAu collisions at \sqrtsNN = 200 GeV. The non-photonic electron yield exhibits unexpectedly large suppression in central \AuAu collisions at high \pt, suggesting substantial heavy quark energy loss at RHIC. The centrality and \pt dependences of the suppression provide constraints on theoretical models of suppression.
Non photonic electron yield in P+P collisions versus $p_{T}$. To obtain a differential cross-section in mb/(GeV$^2$), multiply listed data by 30.
Non photonic electron yield in minimum bias D+AU collisions versus $p_{T}$.
Non photonic electron yield in Au+Au collisions versus $p_{T}$, for a centrality range of 40-80%.
We report charged-particle pair correlation analyses in the space of Delta -phi (azimuth) and Delta -eta (pseudo-rapidity), for central Au + Au collisions at sqrt{s_{NN}} = 200 GeV in the STAR detector. The analysis involves unlike-sign charge pairs and like-sign charge pairs, which are transformed into charge-dependent (CD) signals and charge-independent (CI) signals. We present detailed parameterizations of the data. A model featuring dense gluonic hot spots as first proposed by van Hove predicts that the observables under investigation would have sensitivity to such a substructure should it occur, and the model also motivates selection of transverse momenta in the range 0.8 < p_t < 2.0$ GeV/c. Both CD and CI correlations of high statistical significance are observed and possible interpretations are discussed.
FIG. 1: a) left side: The $\Delta\phi$ - $\Delta\eta$ correlation data for unlike-sign charge particle pairs from the Star central trigger dataset shown in a 2-dimensional (2-D) perspective plot. The particle tracks have 0.8 GeV/c < $p_t$ < 2.0 GeV/c and |$\eta$| < 1.0. The structure that looks like tiles on a roof is due to the readout boundary effects of the 12 sector TPC. b) right side: The similar correlation data for like-sign charge particle pairs is shown.
FIG. 1: a) left side: The $\Delta\phi$ - $\Delta\eta$ correlation data for unlike-sign charge particle pairs from the Star central trigger dataset shown in a 2-dimensional (2-D) perspective plot. The particle tracks have 0.8 GeV/c < $p_t$ < 2.0 GeV/c and |$\eta$| < 1.0. The structure that looks like tiles on a roof is due to the readout boundary effects of the 12 sector TPC. b) right side: The similar correlation data for like-sign charge particle pairs is shown.
FIG. 2: a) left side: The correlation data for the ratio of the histograms of same-event-pairs to mixed-event-pairs for unlike-sign charged pairs, shown in a two-dimensional (2-D) perspective plot $\Delta\phi$ - $\Delta\eta$. The plot was normalized to a mean of 1. b) right side: The similar correlation data for like-sign charge pairs.
New results on quasi-free $\eta$ photoproduction on the neutron and proton bound in a deuteron target are presented. The $\gamma n \to \eta n$ quasi-free cross section reveals a bump-like structure which is not seen in the cross section on the proton. This structure may signal the existence of a relatively narrow ($M\sim 1.68$ GeV, $\Gamma \leq 30$ MeV) baryon state.
Quasi free differential cross section for the reaction GAMMA N --> ETA N at COS(THETA(CM)) from -0.9 to -0.5.
Quasi free differential cross section for the reaction GAMMA N --> ETA N at COS(THETA(CM)) from -0.3 to 0.1.
Quasi free differential cross section for the reaction GAMMA N --> ETA N at COS(THETA(CM)) from 0.1 to 0.5.
A detailed analysis is presented of the diffractive deep-inelastic scattering process $ep\to eXY$, where $Y$ is a proton or a low mass proton excitation carrying a fraction $1 - \xpom > 0.95$ of the incident proton longitudinal momentum and the squared four-momentum transfer at the proton vertex satisfies $|t|<1 {\rm GeV^2}$. Using data taken by the H1 experiment, the cross section is measured for photon virtualities in the range $3.5 \leq Q^2 \leq 1600 \rm GeV^2$, triple differentially in $\xpom$, $Q^2$ and $\beta = x / \xpom$, where $x$ is the Bjorken scaling variable. At low $\xpom$, the data are consistent with a factorisable $\xpom$ dependence, which can be described by the exchange of an effective pomeron trajectory with intercept $\alphapom(0)= 1.118 \pm 0.008 {\rm (exp.)} ^{+0.029}_{-0.010} {\rm (model)}$. Diffractive parton distribution functions and their uncertainties are determined from a next-to-leading order DGLAP QCD analysis of the $Q^2$ and $\beta$ dependences of the cross section. The resulting gluon distribution carries an integrated fraction of around 70% of the exchanged momentum in the $Q^2$ range studied. Total and differential cross sections are also measured for the diffractive charged current process $e^+ p \to \bar{\nu}_e XY$ and are found to be well described by predictions based on the diffractive parton distributions. The ratio of the diffractive to the inclusive neutral current $ep$ cross sections is studied. Over most of the kinematic range, this ratio shows no significant dependence on $Q^2$ at fixed $\xpom$ and $x$ or on $x$ at fixed $Q^2$ and $\beta$.
Reduced cross section from the Minimum Bias data sample taken in 1997.
Reduced cross section from the Minimum Bias data sample taken in 1997.
Reduced cross section from the complete ('all') data sample taken in 1997.
We present a measurement of the top quark pair production cross section in ppbar collisions at sqrt(s)=1.96 TeV using 318 pb^{-1} of data collected with the Collider Detector at Fermilab. We select ttbar decays into the final states e nu + jets and mu nu + jets, in which at least one b quark from the t-quark decays is identified using a secondary vertex-finding algorithm. Assuming a top quark mass of 178 GeV/c^2, we measure a cross section of 8.7 +-0.9 (stat) +1.1-0.9 (syst) pb. We also report the first observation of ttbar with significance greater than 5 sigma in the subsample in which both b quarks are identified, corresponding to a cross section of 10.1 +1.6-1.4(stat)+2.0-1.3 (syst) pb.
Measured cross section where at least one B quark from the TOP quark decays is identified.
Measured cross section where both B quarks from the TOP quark decays are identified.
The inclusive production cross sections of the strange vector mesons K*0, K*0bar, and phi have been measured in interactions of 920 GeV protons with C, Ti, and W targets with the HERA-B detector at the HERA storage ring. Differential cross sections as a function of rapidity and transverse momentum have been measured in the central rapidity region and for transverse momenta up to pT=3.5 GeV/c. The atomic number dependence is parametrised as sigma(pA) = sigma(pN)*A**alpha, where sigma(pN) is the proton-nucleon cross section. Within the phase space accessible, alpha(K*0) = 0.86+/-0.03, alpha(K*0bar) = 0.87+/-0.03, and alpha(phi) = 0.96+/-0.02. The total proton-nucleon cross sections, determined by extrapolating the differential measurements to full phase space, are sigma(pN->K*0) = 5.06+/-0.54 mb, sigma(pN->K*0bar) = 4.02+/-0.45 mb, and sigma(pN->phi) = 1.17+/-0.11 mb. The Cronin effect is observed for the first time for vector mesons containing strange quarks/ compared to the measurements of Cronin et al. for K+- mesons, the measured values of alpha for phi mesons coincide with those of K- mesons for all transverse momenta, while the enhancement for K*0 / K*0bar mesons is smaller.
Measured rapidity distribution for K*0 production in the accessible phase space.
Measured rapidity distribution for K*BAR0 production in the accessible phase space.
Measured rapidity distribution for PHI production in the accessible phase space.
We present the scaling properties of Lambda, Xi, Omega and their anti-particles produced at mid-rapidity in Au+Au collisions at RHIC at sqrt(s_NN) = 200 GeV. The yield of multi-strange baryons per participant nucleon increases from peripheral to central collisions more rapidly than the Lambda yield, which appears to correspond to an increasing strange quark density of matter produced. The value of the strange phase space occupancy factor gamma_s, obtained from a thermal model fit to the data, approaches unity for the most central collisions. We also show that the nuclear modification factors, R_CP, of Lambda and Xi are consistent with each other and with that of protons in the transverse momentum range 2.0 < p_T < 5.0 GeV/c. This scaling behaviour is consistent with a scenario of hadron formation from constituent quark degrees of freedom through quark recombination or coalescence.
Transverse momentum distributions of (a) $\Lambda(\overline{\Lambda})$ for $|y|<1.0$, (b) $\Xi^{-}(\overline{\Xi}^{+})$ for $|y|<0.75$ and (c) $\Omega^{-}+\overline{\Omega}^{+}$ for $|y|<0.75$ in Au+Au collisions at $\sqrt{s_{NN}}$ as a function of centrality. The $\Lambda$ spectra were corrected for weak decay of $\Xi$, $\Xi^{0}$ and $\Omega$. Scale factors were applied to the spectra for clarity. Only statistical errors are shown. The dashed curves show a Boltzmann fit to the $\Lambda$, $\Xi^{-}$ and $\Omega^{-}+\overline{\Omega}^{+}$ data, the fits to the $\overline{\Lambda}$ and $\overline{\Xi}^{+}$ are omitted for clarity.
Transverse momentum distributions of (a) $\Lambda(\overline{\Lambda})$ for $|y|<1.0$, (b) $\Xi^{-}(\overline{\Xi}^{+})$ for $|y|<0.75$ and (c) $\Omega^{-}+\overline{\Omega}^{+}$ for $|y|<0.75$ in Au+Au collisions at $\sqrt{s_{NN}}$ as a function of centrality. The $\Lambda$ spectra were corrected for weak decay of $\Xi$, $\Xi^{0}$ and $\Omega$. Scale factors were applied to the spectra for clarity. Only statistical errors are shown. The dashed curves show a Boltzmann fit to the $\Lambda$, $\Xi^{-}$ and $\Omega^{-}+\overline{\Omega}^{+}$ data, the fits to the $\overline{\Lambda}$ and $\overline{\Xi}^{+}$ are omitted for clarity.
Transverse momentum distributions of (a) $\Lambda(\overline{\Lambda})$ for $|y|<1.0$, (b) $\Xi^{-}(\overline{\Xi}^{+})$ for $|y|<0.75$ and (c) $\Omega^{-}+\overline{\Omega}^{+}$ for $|y|<0.75$ in Au+Au collisions at $\sqrt{s_{NN}}$ as a function of centrality. The $\Lambda$ spectra were corrected for weak decay of $\Xi$, $\Xi^{0}$ and $\Omega$. Scale factors were applied to the spectra for clarity. Only statistical errors are shown. The dashed curves show a Boltzmann fit to the $\Lambda$, $\Xi^{-}$ and $\Omega^{-}+\overline{\Omega}^{+}$ data, the fits to the $\overline{\Lambda}$ and $\overline{\Xi}^{+}$ are omitted for clarity.
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