We report the first observation of $K^{\star}(892)^{0}\to\pi K$ in relativistic heavy ion collisions. The transverse momentum spectrum of $(K^{\star0}+\bar{K}^{\star0})/2$ from central Au+Au collisions at $\sqrt{s_{_{NN}}}=130$ GeV is presented. The ratios of the $K^{\star0}$ yield derived from these data to the yields of negative hadrons, charged kaons, and $\phi$ mesons have been measured in central and minimum bias collisions and compared with model predictions and comparable $e^{+}e^{-}$, $pp$, and $\bar{p}p$ results. The data indicate no dramatic reduction of $K^{\star0}$ production in relativistic heavy ion collisions despite expected losses due to rescattering effects.
Transverse mass spectrum of K*0 with YRAP = -0.5 to 0.5 for the 14 PCT most central interactions. Numerical values requested from the authors.
K*0 to negative hadron ratio using hadron data from Adler et al PRL 87,112303(2001).
K*0 to kaon ratio using STAR kaon data.
We present results for the charged-particle multiplicity distribution at mid-rapidity in Au - Au collisions at sqrt(s_NN)=130 GeV measured with the PHENIX detector at RHIC. For the 5% most central collisions we find $dN_{ch}/d\eta_{|\eta=0} = 622 \pm 1 (stat) \pm 41 (syst)$. The results, analyzed as a function of centrality, show a steady rise of the particle density per participating nucleon with centrality.
130 GeV is sqrt(S) per nucleon-nucleon collision. N(C=N_NUCLEONS) and N(C=N_COLLISONS) are the number of participating nucleons and binary collisions. The statistical errors are negligible and only systematic errors are quoted. COL(NAME=CENTRALITY) is centrality.
The elastic electroproduction of phi mesons is studied at HERA with the H1 detector for photon virtualities 1 < Q^2 < 15 GeV^2 and hadronic centre of mass energies 40 < W < 130 GeV. The Q^2 and t dependences of the cross section are extracted (t being the square of the four-momentum transfer to the target proton). When plotted as function of (Q^2 + M_V^2) and scaled by the appropriate SU(5) quark charge factor, the phi meson cross section agrees within errors with the cross sections of the vector mesons V = rho, omega and J/psi. A detailed analysis is performed of the phi meson polarisation state and the ratio of the production cross sections for longitudinally and transversely polarised phi mesons is determined. A small but significant violation of s-channel helicity conservation (SCHC) is observed.
The measured ratio of PHI to RHO0 production.
The cross section for elastic PHI meson electro-production calculated by multiplying the PHI/RHO0 cross section ratio by the RHO0 cross section accurately measured in the earlier H1 publication (EPJ C13,371).
The corrected T distribution of elastic PHI meson production for W around 75 GeV and Q2 in the range 2.5 to 15 GeV**2 (mean = 4.8 GeV**2). Statistical error only.
Yields and phase space distributions of φ -mesons emitted from p+p (minimum bias trigger), p+Pb (at various centralities) and central Pb+Pb collisions are reported ( E beam =158 A GeV). The decay φ →K + K − was used for identification. The φ / π ratio is found to increase by a factor of 3.0±0.7 from inelastic p+p to central Pb+Pb. Significant enhancement in this ratio is also observed in subclasses of p+p events (characterized by high charged-particle multiplicity) as well as in the forward hemisphere of central p+Pb collisions. In Pb+Pb no shift or significant broadening of the φ -peak is seen.
Transverse mass distribution for PHI mesons produced in PB PB collisions averaged over the rapidity region 3.0 to 3.8.
Transverse mass distribution for PHI mesons produced in P P collisions averaged over the rapidity region 2.9 to 4.5.
Rapidity distributions for PHI mesons produced in PB PB collisions.
Deep-inelastic ep scattering data, taken with the H1 detector at HERA, are used to study the event shape variables thrust, jet broadening, jet mass, C parameter and two kinds of differential two-jet rate. The data cover a large range of the four-momentum transfer Q, which is considered to be the relevant energy scale, between 7 GeV and 100 GeV. The Q dependences of the mean values are compared with second order calculations of perturbative QCD applying power law corrections proportional to 1/Q^p to account for hadronization effects. The concept of power corrections is investigated by fitting simultaneously a non-perturbative parameter alpha_p and the strong coupling constant alpha_s.
Corrected mean values of the (1-THRUST) distribution (w.r.t.current hemisphere axis) as a function of Q.
Corrected mean values of the Jet Broadenning (B) distribution (w.r.t.current hemisphere axis) as a function of Q.
Corrected mean values of the (1-THRUST) distribution (w.r.t.max long. momentum axis) as a function of Q.
The electroproduction of J/psi and psi(2S) mesons is studied in elastic, quasi-elastic and inclusive reactions for four momentum transfers 2 < Q^2 < 80 GeV^2 and photon-proton centre of mass energies 25 < W < 180 GeV. The data were taken with the H1 detector at the electron proton collider HERA in the years 1995 to 1997. The total virtual photon-proton cross section for elastic J/psi production is measured as a function of Q^2 and W. The dependence of the production rates on the square of the momentum transfer from the proton (t) is extracted. Decay angular distributions are analysed and the ratio of the longitudinal and transverse cross sections is derived. The ratio of the cross sections for quasi-elastic psi(2S) and J/psi meson production is measured as a function of Q^2. The results are discussed in terms of theoretical models based upon perturbative QCD. Differential cross sections for inclusive and inelastic production of J/psi mesons are determined and predictions within two theoretical frameworks are compared with the data, the non-relativistic QCD factorization approach including colour octet and colour singlet contributions, and the model of Soft Colour Interactions.
Cross section for elastic J/PSI photoproduction in W bins.
Cross section for elastic J/PSI photoproduction in W bins.
Cross section for elastic J/PSI photoproduction in W bins.
The elastic electroproduction of rho mesons is studied at HERA with the H1 detector for a photon virtuality in the range 1 < Q^2 < 60 GeV^2 and for a hadronic centre of mass energy in the range 30 < W < 140 GeV. The shape of the pipi mass distribution in the rho resonance region is measured as a function of Q^2. The full set of rho spin density matrix elements is determined, and evidence is found for a helicity flip amplitude at the level of 8 +- 3 % of the non-flip amplitudes. Measurements are presented of the dependence of the cross section on Q^2, W and t (the four-momentum transfer squared to the proton). They suggest that, especially at large Q^2, the gamma^*p cross section develops a stronger W dependence than that expected from the behaviour of elastic and total hadron-hadron cross sections.
Average values of the spin density matrix elements measured for the 1996 data sample.
Spin density matrix elements measured for 3 Q**2 values for the 1996 data sample.
Spin density matrix elements measured for 3 W values for the 1996 data sample.
Events with a (2+1) jet topology in deep-inelastic scattering at HERA are studied in the kinematic range 200 < Q^2< 10,000 GeV^2. The rate of (2+1) jet events has been determined with the modified JADE jet algorithm as a function of the jet resolution parameter and is compared with the predictions of Monte Carlo models. In addition, the event rate is corrected for both hadronization and detector effects and is compared with next-to-leading order QCD calculations. A value of the strong coupling constant of alpha_s(M_Z^2)= 0.118+- 0.002 (stat.)^(+0.007)_(-0.008) (syst.)^(+0.007)_(-0.006) (theory) is extracted. The systematic error includes uncertainties in the calorimeter energy calibration, in the description of the data by current Monte Carlo models, and in the knowledge of the parton densities. The theoretical error is dominated by the renormalization scale ambiguity.
Y2 distribution corrected for detector effects.
Y2 distribution corrected for both detector and hadronization effects.
Y2 distribution using the E, E0 and P variants of the JADE alogrithm, corrected for both detector and hadronization effects. Statistical errors only.
The multiplicity structure of the hadronic system X produced in deep-inelastic processes at HERA of the type ep -> eXY, where Y is a hadronic system with mass M_Y< 1.6 GeV and where the squared momentum transfer at the pY vertex, t, is limited to |t|<1 GeV^2, is studied as a function of the invariant mass M_X of the system X. Results are presented on multiplicity distributions and multiplicity moments, rapidity spectra and forward-backward correlations in the centre-of-mass system of X. The data are compared to results in e+e- annihilation, fixed-target lepton-nucleon collisions, hadro-produced diffractive final states and to non-diffractive hadron-hadron collisions. The comparison suggests a production mechanism of virtual photon dissociation which involves a mixture of partonic states and a significant gluon content. The data are well described by a model, based on a QCD-Regge analysis of the diffractive structure function, which assumes a large hard gluonic component of the colourless exchange at low Q^2. A model with soft colour interactions is also successful.
The multiplicity moment MULT as a function of the mass of the charged hadron system in the full phase space and separately in the forward and backward hemispheres.
The multiplicity moment DISPERSION as a function of the mass of the charged hadron system in the full phase space and separately in the forward and backward hemispheres.
The multiplicity moment R2 as a function of the mass of the charged hadron system in the full phase space and separately in the forward and backward hemispheres.
The shape of the transverse momentum distribution of W bosons (p_T(W)) produced in pbarp collisions at sqrt(s)= 1.8 TeV is measured with the DO detector at Fermilab. The result is compared to QCD perturbative and resummation calculations over the p_T(W) range from 0-200 GeV/c. The shape of the distribution is consistent with the theoretical prediction.
The first error is statistical, the first systematic (DSYS) error is the uncertainty in the background and efficiencies, the second is the systematic errorin the detector modelling.
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