The production of beauty and charm quarks in ep interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared 5 < Q^2 < 1000 GeV^2 using an integrated luminosity of 354 pb^{-1}. The beauty and charm content in events with at least one jet have been extracted using the invariant mass of charged tracks associated with secondary vertices and the decay-length significance of these vertices. Differential cross sections as a function of Q^2, Bjorken x, jet transverse energy and pseudorapidity were measured and compared with next-to-leading-order QCD calculations. The beauty and charm contributions to the proton structure functions were extracted from the double-differential cross section as a function of x and Q^2. The running beauty-quark mass, m_b at the scale m_b, was determined from a QCD fit at next-to-leading order to HERA data for the first time and found to be 4.07 \pm 0.14 (fit} ^{+0.01}_{-0.07} (mod.) ^{+0.05}_{-0.00} (param.) ^{+0.08}_{-0.05} (theo) GeV.
Differential cross sections for inclusive jet production in beauty events as a function of ET(JET) for ET(JET) > 5 GeV. The measurements are given together with their statistical and systematic uncertainties. Hadronisation and QED radiative corrections, CHAD and CRAD, respectively, are also shown.
Differential cross sections for inclusive jet production in charm events as a function of ET(JET) for ET(JET) > 4.2 GeV. The measurements are given together with their statistical and systematic uncertainties. Hadronisation and QED radiative corrections, CHAD and CRAD, respectively, are also shown.
Differential cross sections for inclusive jet production in beauty events as a function of ETARAP(JET) for -1.6 < ETARAP(JET) < 2.2. The measurements are given together with their statistical and systematic uncertainties. Hadronisation and QED radiative corrections, CHAD and CRAD, respectively, are also shown.
Diffractive photoproduction of D*+/-(2010) mesons was measured with the ZEUS detector at the ep collider HERA, using an integrated luminosity of 78.6 pb^{-1}. The D* mesons were reconstructed in the kinematic range: transverse momentum p_T(D*) > 1.9 GeV and pseudorapidity |eta(D*)| < 1.6, using the decay D*+ -> D0 pi+_s followed by D0 -> K- pi+ (+c.c.). Diffractive events were identified by a large gap in pseudorapidity between the produced hadronic state and the outgoing proton. Cross sections are reported for photon-proton centre-of-mass energies in the range 130 < W < 300 GeV and for photon virtualities Q^2 < 1 GeV^2, in two ranges of the Pomeron fractional momentum x_pom < 0.035 and x_pom < 0.01. The relative contribution of diffractive events to the inclusive D*+/-(2010) photoproduction cross section is about 6%. The data are in agreement with perturbative QCD calculations based on various parameterisations of diffractive parton distribution functions. The results are consistent with diffractive QCD factorisation.
Total cross section integrated over the given kinematic range.
Ratio of diffractive to inclusive D* cross section.
Differential cross sections for diffractive photoproduction of D*+- mesons as a function of X(NAME=POMERON).
Production of D*+/-(2010) mesons in diffractive deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb^{-1}. Diffractive events were identified by the presence of a large rapidity gap in the final state. Differential cross sections have been measured in the kinematic region 1.5 < Q^2 < 200 GeV^2, 0.02 < y < 0.7, x_{IP} < 0.035, beta < 0.8, p_T(D*+/-) > 1.5 GeV and |\eta(D*+/-)| < 1.5. The measured cross sections are compared to theoretical predictions. The results are presented in terms of the open-charm contribution to the diffractive proton structure function. The data demonstrate a strong sensitivity to the diffractive parton densities.
Total cross section for diffractive D*+- production in the stated kinematicregion.. The second DSYS uncertainty arises from the subtraction of the proton-dissociative background.
The differential cross section as a function of X(NAME=POMERON).
The differential cross section as a function of transverse momentum.
Diffractive production of D*+-(2010) mesons in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 44.3 pb-1. Diffractive charm production is identified by the presence of a large rapidity gap in the final state of events in which a D*+-(2010) meson is reconstructed in the decay channel D*+ -> (D0 -> K-pi+) pi+ (+ charge conjugate). Differential cross sections when compared with theoretical predictions indicate the importance of gluons in such diffractive interactions.
Measurment of total diffractive cross section and ratio to inclusive DIS cross section.
Ratio of diffractive to inclusive D*+- production w.r.t. Q**2.
Ratio of diffractive to inclusive D*+- production w.r.t. W.
Production of Sigma- and Lambda(1520) in hadronic Z decays has been measured using the DELPHI detector at LEP. The Sigma- is directly reconstructed as a charged track in the DELPHI microvertex detector and is identified by its Sigma -> n pi decay leading to a kink between the Sigma- and pi-track. The reconstruction of the Lambda(1520) resonance relies strongly on the particle identification capabilities of the barrel Ring Imaging Cherenkov detector and on the ionisation loss measurement of the TPC. Inclusive production spectra are measured for both particles. The production rates are measured to be <N_{Sigma-}/N_{Z}^{had}> = 0.081 +/- 0.002 +/- 0.010, <N_{Lambda(1520)}/N_{Z}^{had}> = 0.029 +/- 0.005 +/- 0.005. The production rate of the Lambda(1520) suggests that a large fraction of the stable baryons descend from orbitally excited baryonic states. It is shown that the baryon production rates in Z decays follow a universal phenomenological law related to isospin, strangeness and mass of the particles.
The measured differential cross section for SIGMA- production.
The total production rate of SIGMA-. The second systematic (DSYS) error is due to the extrapolation to the fullx-range.
The measured differential cross section for LAMBDA(1520) production. The first error is the fit error.
DELPHI results are presented on the inclusive production of the neutral mesons ρ 0 , f 0 (980), f 2 (1270), K ∗0 2 (1430) and f ′ 2 (1525) in hadronic Z 0 decays. They are based on about 2 million multihadronic events collected in 1994 and 1995, using the particle identification capabilities of the DELPHI Ring Imaging Cherenkov detectors and measured ionization losses in the Time Projection Chamber. The total production rates per hadronic Z 0 decay have been determined to be: 1.19±0.10 for ρ 0 ; 0.164±0.021 for f 0 (980); 0.214±0.038 for f 2 (1270); 0.073±0.023 for K ∗0 2 (1430) ; and 0.012±0.006 for f ′ 2 (1525). The total production rates for all mesons and differential cross-sections for the ρ 0 , f 0 (980) and f 2 (1270) are compared with the results of other LEP experiments and with models.
Differential production cross sections. The error is the quadratic combination of the errors from the fits and the systematic uncertainty.
Integrated rates extrapolated to the full x range.
The cross section for the photoproduction of events containing three jets with a three-jet invariant mass of M_3J > 50 GeV has been measured with the ZEUS detector at HERA. The three-jet angular distributions are inconsistent with a uniform population of the available phase space but are well described by parton shower models and O(alpha alpha_s^2) pQCD calculations. Comparisons with the parton shower model indicate a strong contribution from initial state radiation as well as a sensitivity to the effects of colour coherence.
Cross section in the specified kinematic range.
The measured 3-jet cross-section w.r.t. the 3-jet invariant mass.
The measured distribution in THETA(P=3).
The splitting processes in identified quark and gluon jets are investigated using longitudinal and transverse observables. The jets are selected from symmetric three-jet events measured in Z decays with the Delphi detector in 1991-1994. Gluon jets are identified using heavy quark anti-tagging. Scaling violations in identified gluon jets are observed for the first time. The scale energy dependence of the gluon fragmentation function is found to be about two times larger than for the corresponding quark jets, consistent with the QCD expectation CA/CF. The primary splitting of gluons and quarks into subjets agrees with fragmentation models and, for specific regions of the jet resolution y, with NLLA calculations. The maximum of the ratio of the primary subjet splittings in quark and gluon jets is 2.77±0.11±0.10. Due to non-perturbative effects, the data are below the expectation at small y. The transition from the perturbative to the non-perturbative domain appears at smaller y for quark jets than for gluon jets. Combined with the observed behaviour of the higher rank splittings, this explains the relatively small multiplicity ratio between gluon and quark jets.
Scaled energy distribution of charged hadrons produced in Quark jets in 'Y'topology 3-JET events.
Scaled energy distribution of charged hadrons produced in Gluon jets in 'Y'topology 3-JET events.
Scaled energy distribution of charged hadrons produced in Quark jets in 'Mercedes' topology 3-JET events.
The transverse, longitudinal and asymmetric components of the fragmentation function are measured from the inclusive charged particles produced in$e^+e^-$collisi
Transverse component of the differential cross section.
Longitudinal component of the differential cross section.
Asymmetric component of the differential cross section.
Helicity density matrix elements for inclusive K*(892)^0 mesons from hadronic Z^0 decays have been measured over the full range of K^*0 momentum using data taken with the OPAL experiment at LEP. A preference for occupation of the helicity zero state is observed at all scaled momentum x_p values above 0.3, with the matrix element rho_00 rising to 0.66 +/- 0.11 for x_p > 0.7. The values of the real part of the off-diagonal element rho_1-1 are negative at large x_p, with a weighted average value of -0.09 +/- 0.03 for x_p > 0.3, in agreement with new theoretical predictions based on Standard Model parameters and coherent fragmentation of the qq(bar) system from the Z^0 decay. All other helicity density matrix elements measured are consistent with zero over the entire x_p range. The K^*0 fragmentation function has also been measured and the total rate determined to be 0.74 +/- 0.02 +/- 0.02 K*(892)^0 mesons per hadronic Z^0 decay.
Inclusive K*= cross section.
Helicity density matrices elemnts.
Ratios of helicity density matrices elements.