Inclusive π±, K± and\((p,\bar p)\) differential cross-sections in hadronic decays of the Z have been measured as a function ofz=Phadron/Pbeam, the scaled momentum. The results are based on approximately 520 000 events measured by the ALEPH detector at LEP during 1992. Charged particles are identified by their rate of ionization energy loss in the ALEPH Time Projection Chamber. The position, ξ*, of the peak in the ln(1/z) distribution is determined, and the evolution of the peak position with centre-of-mass energy is compared with the prediction of QCD.
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We have studied the production of D*± mesons in a sample of 1.25 million multihadronic decays of the Z0, in which 1969 candidates have been identified. We have determined the total multiplicity of charged D* mesons in multihadronic Z0 decays to be
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Multiplicity data uncorrected for decay branching ratios.
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Experimental evidence for the existence of orbitally excited B meson states is presented in an analysis of the Bπ and B ∗ π distribution of Q = m(B ∗∗ ) − m(B (∗) ) − m(π) using Z 0 decay data taken with the DELPHI detector at LEP. The mean Q-value of the decays B ∗∗ → B (∗) π is measured to be 284 ± 5 (stat.) ± 15 (syst.) MeV/c 2 , and the Gaussian width of the signal is 79 ± 5 (stat.) ± 8 (syst.) MeV/c 2 . This signal can be described as a single resonance of mass m = 5732 ± 5 (stat.) ± 20 (syst.) MeV/c 2 and full width Γ = 145 ± 28 MeV/c 2 . The observed shape is also consistent with the production of several broad and narrow states as predicted by the quark model and partly observed in the D-meson sector. The production rate of B ∗∗ per b-jet is found to be 0.27 ± 0.02 (stat.) ± 0.06 (syst.).
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Jet rates in deep inelastic electron proton scattering are studied with the H1 detector at HERA for momentum transfers squared between 10 and 4000 GeV 2 . It is shown that they can be quantitatively described by perturbative QCD in next to leading order making use of the parton densities of the proton and with the strong coupling constant α s as a free parameter. The measured value, α s ( M Z 2 ) = 0.123 ± 0.018, is in agreement both with determinations from e + e − annihilation at LEP using the same observable and with the world average.
Determination of ALP_S(MZ**2). Error contains both statistics and systematics.
We present the results of a search in p¯p collisions at s=1.8 TeV for the top quark decaying to a charged Higgs boson (H±). We search for dilepton final states from the decay chain tt¯→HH (or HW, or WW) + bb¯→ll+X. In a sample of 19.3 pb−1 collected during 1992-93 with the Collider Detector at Fermilab, we observe 2 events with a background estimation of 3.0 ± 1.0 events. Limits at 95% C.L. in the (Mtop,MH±) plane are presented. For the case Mtop<MW+Mb, we exclude at 95% C.L. the entire (Mtop,MH±) plane for the branching ratio B(H→τν) larger than 75%. We also interpret the results in terms of the parameter tan β of two-Higgs-doublet models.
Upper limits on the cross section at 95PCT CL. CONST(TAN(BETA)) is model parameter describing the charged Higgs decay (see text).
Upper limits on the cross section at 95PCT CL. CONST(TAN(BETA)) is model pameter describing the charged Higgs decay (see text).
Upper limits on the cross section at 95PCT CL. CONST(TAN(BETA)) is model pameter describing the charged Higgs decay (see text).
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.
The gluon momentum density xg ( x , Q 2 ) of the proton was extracted at Q 2 = 20 GeV 2 for small values of x between 4 × 10 −4 and 10 −2 from the scaling violations of the proton structure function F 2 measured recently by ZEUS in deep inelastic neutral current ep scattering at HERA. The extraction was performed in two ways. Firstly, using a global NLO fit to the ZEUS data on F 2 at low x constrained by measurementsfrom NMC at larger x ; and secondly using published approximate methods for the solution of the GLAP QCD evolution equations. Consistent results are obtained. A substantial increase of the gluon density is found at small x in comparison with the NMC result obtained at larger values of x .
Values of F2 and slope of F2 obtained from fits to the ZEUS paper used in the extraction of the gluon momentum distributions.
Gluon momenta distribution at Q**2 = 20.
Inclusive jet differential cross sections for the reaction ep → jet + X at Q 2 below 4 GeV 2 have been measured with the ZEUS detector at HERA using an integrated luminosity of 0.55 pb −1 . These cross sections are given in the kinematic region 0.2 < y < 0.85, for jet pseudorapidities in the ep -laboratory range −1 < η jet < 2 and refer to jets at the hadron level with a cone radius of one unit in the η - θ plane. These results correspond to quasi-real photoproduction at centre-of-mass energies in the range 130–270 GeV and, approximately, for jet pseudorapidities in the interval −3 < η jet ( λp CMS) < 0. These measurements cover a new kinematic regime of the partonic structure of the photon, at typical scales up to ∼300 GeV 2 and photon fractional momenta down to x γ ∼ 10 −2 . Leading logarithm parton shower Monte Carlo calculations, which include both resolved and direct processes and use the predictions of currently available parametrisations of the photon parton distributions, describe in general the shape and magnitude of the measured η jet and E t jet distributions.
Second systematic error is uncertainty in the ET scale.
Second systematic error is uncertainty in the ET scale.
Second systematic error is uncertainty in the ET scale.
The strong coupling alpha_s(M_Z^2) has been measured using hadronic decays of Z^0 bosons collected by the SLD experiment at SLAC. The data were compared with QCD predictions both at fixed order, O(alpha_s^2), and including resummed analytic formulae based on the next-to-leading logarithm approximation. In this comprehensive analysis we studied event shapes, jet rates, particle correlations, and angular energy flow, and checked the consistency between alpha_s(M_Z^2) values extracted from these different measures. Combining all results we obtain alpha_s(M_Z^2) = 0.1200 \pm 0.0025(exp.) \pm 0.0078(theor.), where the dominant uncertainty is from uncalculated higher order contributions.
Final average value of alpha_s. The second (DSYS) error is from the uncertainty on the theoretical part of the calculation.
TAU is 1-THRUST.
RHO is the normalized heavy jet mass MH**2/EVIS**2.
The charge asymmetry has been measured using $19,039W$ decays recorded by the CDF detector during the 1992-93 run of the Tevatron Collider. The asymmetry is sensitive to the ratio of $d$ and $u$ quark distributions to $x<0.01$ at $Q~2 \approx M_W~2$, where nonperturbative effects are minimal. It is found that of the two current sets of parton distributions, those of Martin, Roberts and Stirling (MRS) are favored over the sets most recently produced by the CTEQ collaboration. The $W$ asymmetry data provide a stronger constraints on $d/u$ ratio than the recent measurements of $F_2~{\mu n}/F_2~{\mu p}$ which are limited by uncertainties originating from deutron corrections.
Charge asymmetry defined as (DSIG(Q=L+)/DYRAP - DSIG(Q=L-)/DYRAP)/ (DSIG(Q=L+)/DYRAP + DSIG(Q=L-)/DYRAP). Here LEPTON are E and MU.
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