A measurement is presented of dijet and 3-jet cross sections in low-|t| diffractive deep-inelastic scattering interactions of the type ep -> eXY, where the system X is separated by a large rapidity gap from a low-mass baryonic system Y. Data taken with the H1 detector at HERA, corresponding to an integrated luminosity of 18.0 pb^(-1), are used to measure hadron level single and double differential cross sections for 4<Q^2<80 GeV^2, x_pom<0.05 and p_(T,jet)>4 GeV. The energy flow not attributed to jets is also investigated. The measurements are consistent with a factorising diffractive exchange with trajectory intercept close to 1.2 and tightly constrain the dominating diffractive gluon distribution. Viewed in terms of the diffractive scattering of partonic fluctuations of the photon, the data require the dominance of qqbarg over qqbar states. Soft colour neutralisation models in their present form cannot simultaneously reproduce the shapes and the normalisations of the differential cross sections. Models based on 2-gluon exchange are able to reproduce the shapes of the cross sections at low x_pom values.
Average values, over the specified interval, of the differential hadron level dijet cross section as a function of Q**2.
Average values, over the specified interval, of the differential hadron level dijet cross section as a function of the average transverse momentum of the two jets in the c.m.frame.
Average values, over the specified interval, of the differential hadron level dijet cross section as a function of the average pseudorapidity of the two jets in the lab frame.
The production of hard di-jet events in photoproduction at HERA is dominated by resolved photon processes in which a parton in the photon with momentum fraction x_gamma is scattered from a parton in the proton. These processes are sensitive to the quark and gluon content of the photon. The differential di-jet cross-section dsigma/dlog(x_gamma) is presented here, measured in tagged photoproduction at HERA using data taken with the H1 detector, corresponding to an integrated luminosity of 7.2 pb^(-1). Using a restricted data sample at high transverse jet energy, E_(T,jet)>6 GeV, the effective parton density f_gamma,eff(x_gamma) = [q(x_gamma) + bar(q)(x_gamma) +9/4g(x_gamma)] in the photon in leading order QCD is measured down to x_gamma=0.05 from which the gluon density in the photon is derived.
The di-jet photoproduction cross section for ET > 4 GeV.
The di-jet photoproduction cross section for ET > 6 GeV after pedestal energy subtraction.
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.
High transverse momentum pi0-mesons have been measured with the H1 detector at HERA in deep-inelastic ep scattering events at low Bjorken-x, down to x <~ 4.10^{-5}. The measurement is performed in a region of small angles with respect to the proton remnant in the laboratory frame of reference, namely the forward region, and corresponds to central rapidity in the centre of mass system of the virtual photon and proton. This region is expected to be particularly sensitive to QCD effects in hadronic final states. Differential cross-sections for inclusive pi0-meson production are presented as a function of Bjorken-x and the four-momentum transfer Q^2, and as a function of transverse momentum and pseudorapidity. A recent numerical BFKL calculation and predictions from QCD models based on DGLAP parton evolution are compared with the data.
Axis error includes +- 5/5 contribution (Trigger efficiency).
Axis error includes +- 5/5 contribution (Trigger efficiency).
Axis error includes +- 5/5 contribution (Trigger efficiency).
With the H1 detector at the ep collider HERA, D* meson production cross sections have been measured in deep inelastic scattering with four-momentum transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88 GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe the differential cross sections within theoretical and experimental uncertainties. Using these calculations, the NLO gluon momentum distribution in the proton, x_g g(x_g), has been extracted in the momentum fraction range 7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon momentum fraction x_g has been obtained from the measured kinematics of the scattered electron and the D* meson in the final state. The results compare well with the gluon distribution obtained from the analysis of scaling violations of the proton structure function F_2.
Total cross section for DIS D*+- production in the specified kinemtaic range.
DIS cross section as a function of the transverse D* momentum in the laboratory frame.
DIS cross section as a function of the transverse D* momentum in the hadronic centre-of-mass frame.
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.
Single particles and jets in deeply inelastic scattering at low x are measured with the H1 detector in the region away from the current jet and towards the proton remnant, known as the forward region. Hadronic final state measurements in this region are expected to be particularly sensitive to QCD evolution effects. Jet cross-sections are presented as a function of Bjorken-x for forward jets produced with a polar angle to the proton direction, theta, in the range 7 < theta < 20 degrees. Azimuthal correlations are studied between the forward jet and the scattered lepton. Charged and neutral single particle production in the forward region are measured as a function of Bjorken-x, in the range 5 < theta < 25 degrees, for particle transverse momenta larger than 1 GeV. QCD based Monte Carlo predictions and analytical calculations based on BFKL, CCFM and DGLAP evolution are compared to the data. Predictions based on the DGLAP approach fail to describe the data, except for those which allow for a resolved photon contribution.
Forward Jet cross section. Axis error includes +- 7/7 contribution (Dependence of the model used to correct the data).
Forward Di-jet cross section. Axis error includes +- 7/7 contribution (Dependence of the model used to correct the data).
Data from Figure 3a on charged particle production
Interactions of the type ep -> eXY are studied, where the component X of the hadronic final state contains two jets and is well separated in rapidity from a leading baryonic system Y. Analyses are performed of both resolved and direct photoproduction and of deep-inelastic scattering with photon virtualities in the range 7.5 < Q^2 < 80 GeV^2. Cross sections are presented where Y has mass M_Y < 1.6 GeV, the squared four-momentum transferred at the proton vertex satisfies |t| < 1 GeV^2 and the two jets each have transverse momentum p^jet_T > 5 GeV relative to the photon direction in the rest frame of X. Models based on a factorisable diffractive exchange with a gluon dominated structure, evolved to a scale set by the transverse momentum p^hat_T of the outgoing partons from the hard interaction, give good descriptions of the data. Exclusive qqbar production, as calculated in perturbative QCD using the squared proton gluon density, represents at most a small fraction of the measured cross section. The compatibility of the data with a breaking of diffractive factorisation due to spectator interactions in resolved photoproduction is investigated.
Transverse momentum distribution for two jet production in photoproduction events (one entry per jet).
Transverse momentum distribution for two jet production in DIS events (one entry per jet).
Differential pseudo rapidity distribution in the lab frame for photoproduction data (one entry per jet).
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.
Forum