The production rates for 2-, 3-, 4- and 5-jet hadronic final states have been measured with the DELPHI detector at the e + e − storage ring LEP at centre of mass energies around 91.5 GeV. Fully corrected data are compared to O(α 2 s ) QCD matrix element calculations and the QCD scale parameter Λ MS is determined for different parametrizations of the renormalization scale ω 2 . Including all uncertainties our result is α s ( M 2 Z )=0.114±0.003[stat.]±0.004[syst.]±0.012[theor.].
Corrected jet rates.
Second systematic error is theoretical.
A leading order determination of the gluon density in the proton has been performed in the fractional momentum range $1.9 \cdot 10~{-3} < x_{g/p} < 0.18$ by measuring multi-jet events from boson-gluon fusion in deep-inelastic scattering with the H1 detector at the electron-proton collider HERA. This direct determination of the gluon density was performed in a kinematic region previously not accessible. The data show a considerable increase of the gluon density with decreasing fractional momenta of the gluons.
FG is gluon structure function. XPARTON here means the X of the gluon. For the experimental definitions of the XPARTON see paper.
The value of the strong coupling constant,$$\alpha _s (M_{Z^0 } )$$, is determined from a study of 15 d
Differential jet mass distribution for the heavier jet using method T. The data are corrected for the finite acceptance and resolution of the detector and for initial state photon radiation.
Differential jet mass distribution for the jet mass difference using methodT. The data are corrected for the finite acceptance and resolution of the detec tor and for initial state photon radiation.
Differential jet mass distribution for the heavier jet using method M. The data are corrected for the finite acceptance and resolution of the detector and for initial state photon radiation.
The production rate of final state photons in hadronic Z 0 decays is measured as a function of y cut = M ij 2 / E cm 2 the jet resolution parameter and minimum mass of the photon-jet system. Good agreement with the theoretical expectation from an O( αα s ) matrix element calculation is observed. Comparing the measurement and the prediction for y cut = 0.06, where the experimental systematic and statistical errors and the theoretical uncertainties are small, and combining this measurement with our result for the hadronic width of the Z 0 , we derived partial widths of up and down type quarks to be Γ u = 333 ± 55 ± 72 MeV and Γ d = 358 ± 37 ± 48 MeV in agreement with the standard model expectations. We compare our yield with the QCD shower models including photon radiation. At low γ cut JETSET underestimates the photon yield, and ARIADNE describes the production rate well.
It is assumed that the couplings of various up quarks to be the same.
It is assumed that the couplings of various down type quarks to be the same.
A search for excited states of the standard model fermions was performed using the ZEUS detector at the HERA electron-proton collider, operating at a centre of mass energy of 296 GeV. In a sample corresponding to an integrated luminosity of 0.55 pb−1, no evidence was found for any resonant state decaying into final states composed of a fermion and a gauge boson. Limits on the coupling strength times branching ratio of excited fermions are presented for masses between 50 GeV and 250 GeV, extending previous search regions significantly.
The cross sections times branching ratio.
We have searched for signatures of polarization in hadronic jets from $Z~0 \rightarrow q \bar{q}$ decays using the ``jet handedness'' method. The polar angle asymmetry induced by the high SLC electron-beam polarization was used to separate quark jets from antiquark jets, expected to be left- and right-polarized, respectively. We find no evidence for jet handedness in our global sample or in a sample of light quark jets and we set upper limits at the 95\% C.L. of 0.063 and 0.099 respectively on the magnitude of the analyzing power of the method proposed by Efremov {\it et al.}
Polarized E- beam. Events were classified as being of light or heavy flavors based on impact parameters of charged tracks measured in the vertex detector. Jet handedness are measured for helicity-based and chirality-based analysis (seetext). C=95PCT CL indicates the upper limits at the 95 PCT C.L. on the magnitudes.
Relative production rates of multijet hadronic final states of Z 0 boson decays, observed in e + e − annihilation around 91 GeV centre of mass energy, are presented. The data can be well described by analytic O( α s 2 ) QCD calculations and by QCD shower model calaculations with parameters as determined at lower energies. A first judgement of Λ MS and of the renormalization scale μ 2 in O( α s 2 ) QCD results in values similar to those obtained in the continuum of e + e − annihilations. Significant scaling violations are observed when the 3-jet fractions are compared to the corresponding results from smaller centre of mass energies. They can be interpreted as being entirely due tot the energy dependence of α s , as proposed by the nonabelian nature of QCD, The possibility of an energy independent coupling constant can be excluded with a significance of 5.7 standard deviations.
Data are corrected for final acceptance and resolution of the detector. No explicit corrections for hadronisation effects are applied.
This paper describes an analysis of sub-jet multiplicities, which are expected to be sensitive to the properties of soft gluon radiation, in hadronic decays of theZ0. Two- and three-jet event samples are selected using thek⊥ jet clustering algorithm at a jet resolution scaley1. The mean sub-jet multiplicity as a function of the sub-jet resolution,y0, is determined separately for both event samples by reapplying the same jet algorithm at resolution scalesy0<y1. These measurements are compared with recent perturbative QCD calculations based on the summation of leading and next-to-leading logarithms, and with QCD Monte Carlo models. The analytic calculations provide a good description of the sub-jet multiplicity seen in three- and two-jet mvents in the perturbative region (y0≈y1)), and the measured form of the data is in agreement with the expectation based on coherence of soft gluon radiation. The analysis provides good discrimination between Monte Carlo models, and those with a coherent parton shower are preferred by the data. The analysis suggests that coherence effects are present in the data.
Ratio of multiplicities of sub-jets from 3 and 2 jet samples. Data are corrected to the hadron level and have combined statistical and systematic errors.
Sub-jet multiplicity for 3 jet sample. Data corrected to the hadron level and have combined statistical and systematic errors.
Sub-jet multiplicity for 2 jet sample. Data corrected to the hadron level and have combined statistical and systematic errors.
The error includes the experimental uncertainties (±0.003), uncertainties of hadronisation corrections and of the degree of parton virtualities to which the data are corrected, as well as the uncertainty of choosing the renormalisation scale.
Jet production rates using the E0 recombination scheme.
Jet production rates using the E recombination scheme.
Jet production rates using the p0 recombination scheme.
We present a study of 43 000 3-jet events from Z 0 boson decays. Both the measured jet energy distributions and the event orientation are reproduced by second order QCD. An alternative model with scalar gluons fails to describe the data.
Jets are ordered according their energy: E1 > E2 > E3.
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