We present measurements of the differential cross section for the production of massive muon pairs in 225-GeV/c π−-nucleus collisions. We have used the data between the ψ and ϒ resonances in the framework of the Drell-Yan quark-antiquark annihilation model to predict the behavior of the cross section in the high-mass (mμμ>11 GeV/c2) region. The data are consistent with this extrapolation provided that a QCD leading-logarithmic evolution is included in the structure functions.
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We report on a measurement of the ratio of the differential cross sections for W and Z boson production as a function of transverse momentum in proton-antiproton collisions at sqrt(s) = 1.8 TeV. This measurement uses data recorded by the D0 detector at the Fermilab Tevatron in 1994-1995. It represents the first investigation of a proposal that ratios between W and Z observables can be calculated reliably using perturbative QCD, even when the individual observables are not. Using the ratio of differential cross sections reduces both experimental and theoretical uncertainties, and can therefore provide smaller overall uncertainties in the measured mass and width of the W boson than current methods used at hadron colliders.
The measured W and Z0 cross sections used to compute the ratio.
The measured ratios of W+-/Z0 cross sections, corrected for the branching ratios BR(W-->e-nue)=0.1073+-0.0025 and BR(Z0-->E+E-)=0.033632+-0.000059 (PDG 2000). The error given is the total error, but note that the 4.3pct error in the luminosity cancels completely in the ratio.
We present a measurement of angular observables, $P_4'$, $P_5'$, $P_6'$, $P_8'$, in the decay $B^0 \to K^\ast(892)^0 \ell^+ \ell^-$, where $\ell^+\ell^-$ is either $e^+e^-$ or $\mu^+\mu^-$. The analysis is performed on a data sample corresponding to an integrated luminosity of $711~\mathrm{fb}^{-1}$ containing $772\times 10^{6}$ $B\bar B$ pairs, collected at the $\Upsilon(4S)$ resonance with the Belle detector at the asymmetric-energy $e^+e^-$ collider KEKB. Four angular observables, $P_{4,5,6,8}'$ are extracted in five bins of the invariant mass squared of the lepton system, $q^2$. We compare our results for $P_{4,5,6,8}'$ with Standard Model predictions including the $q^2$ region in which the LHCb collaboration reported the so-called $P_5'$ anomaly.
Results of the angular analysis of $B^0 \to K^\ast(892)^0 \ell^+ \ell^-$ (where $\ell = e,\mu$) in five bins of $q^2$, the di-lepton invariant mass squared.
An updated analysis using about 1.5 million events recorded at $\sqrt{s} = M_Z$ with the DELPHI detector in 1994 is presented. Eighteen infrared and collinear safe event shape observables are measured as a function of the polar angle of the thrust axis. The data are compared to theoretical calculations in ${\cal O} (\alpha_s^2)$ including the event orientation. A combined fit of $\alpha_s$ and of the renormalization scale $x_{\mu}$ in $\cal O(\alpha_s^2$) yields an excellent description of the high statistics data. The weighted average from 18 observables including quark mass effects and correlations is $\alpha_s(M_Z^2) = 0.1174 \pm 0.0026$. The final result, derived from the jet cone energy fraction, the observable with the smallest theoretical and experimental uncertainty, is $\alpha_s(M_Z^2) = 0.1180 \pm 0.0006 (exp.) \pm 0.0013 (hadr.) \pm 0.0008 (scale) \pm 0.0007 (mass)$. Further studies include an $\alpha_s$ determination using theoretical predictions in the next-to-leading log approximation (NLLA), matched NLLA and $\cal O(\alpha_s^2$) predictions as well as theoretically motivated optimized scale setting methods. The influence of higher order contributions was also investigated by using the method of Pad\'{e} approximants. Average $\alpha_s$ values derived from the different approaches are in good agreement.
The weighted value of ALPHA-S from all the measured observables using experimentally optimized renormalization scale values and corrected for the b-mass toleading order.
The value of ALPHA-S derived from the JCEF and corrected for heavy quark mass effects. The quoted errors are respectively due to experimental error, hadronization, renormalization scale and heavy quark mass correction uncertainties.
Energy Energy Correlation EEC.
Dijet cross sections as functions of several jet observables are measured in photoproduction using the H1 detector at HERA. The data sample comprises e^+p data with an integrated luminosity of 34.9 pb^(-1). Jets are selected using the inclusive k_T algorithm with a minimum transverse energy of 25 GeV for the leading jet. The phase space covers longitudinal proton momentum fraction x_p and photon longitudinal momentum fraction x_gamma in the ranges 0.05
Differential ep cross section for dijet production as a function of the invariant mass of the two jets.
Differential ep cross section for dijet production as a function of the average transverse energy the two jets.
Differential ep cross section for dijet production as a function of the maximum transverse energy the leading 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.
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The cross section limits are set using two methods. The first (C=COUNT) is a simple counting experiment, and the second (C=SHAPE) use the shape of the dij et mass spectrum input to a likelihood fit.
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Upper limit at the 95% C.L.
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Cross section times the branching ratio for decay into dimuons.
We have calculated the double and triple differential cross sections for electron ejection with energy of 14.6 eV in single ionization of H2 by 75 keV proton impact. A molecular version of the continuum distorted wave-eikonal initial state approach is applied, where the interaction between the projectile and the residual molecular ion is considered more properly than in previous applications of the method. For triple differential cross sections, the present results are in better agreement with the experimental data than those of other descriptions when large momentum transfer values are considered. For double differential cross sections the experimental data are reproduced quite well for both coherent and incoherent proton beams.
No description provided.
No description provided.
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