The reaction e + e − → e + e − γ ∗ γ ∗ → e + e − hadrons is analysed using data collected by the L3 detector during the LEP runs at s = 130−140 GeV and s = 161 GeV . The cross sections σ(e + e − → e + e − hadrons) and σ(γγ → hadrons) are measured in the interval 5 ≤ W γγ ≤ 75 GeV. The energy dependence of the σ(γγ → hadrons) cross section is consistent with the universal Regge behaviour of total hadronic cross sections.
No description provided.
No description provided.
Inclusive photoproduction of $\dspm$ in ep collisions at HERA has been measured with the ZEUS detector for photon-proton centre of mass energies in the range \linebreak \wrang and photon virtuality Q~2 < 4 \g2. The cross section $\sigma_{ep \to \ds X} $ integrated over the kinematic region \ptrangand \etarang is {\xsecs}. Differential cross sections as functions of $p_{\perp}~{\ds}$, $\eta~{\ds}$ and W are given. The data are compared with two next-to-leading order perturbative QCD predictions. For a calculation using a massive charm scheme the predicted cross sections are smaller than the measured ones. A recent calculation using a massless charm scheme is in agreement with the data.
Data from the (Kpi)pi channel.
Data from the (Kpipipi)pi channel.
Data from the (Kpi)pi channel.
Diffractive scattering of $\gamma~* p \to X + N$, where $N$ is either a proton or a nucleonic system with $M_N<4$GeV has been measured in deep inelastic scattering (DIS) at HERA. The cross section was determined by a novel method as a function of the $\gamma~* p$ c.m. energy $W$ between 60 and 245GeV and of the mass $M_X$ of the system $X$ up to 15GeV at average $Q~2$ values of 14 and 31GeV$~2$. The diffractive cross section $d\sigma~{diff} /dM_X$ is, within errors, found to rise linearly with $W$. Parameterizing the $W$ dependence by the form $d\sigma~{diff}/dM_X \propto (W~2)~{(2\overline{\mbox{$\alpha_{_{I\hspace{-0.2em}P}}$}} -2)}$ the DIS data yield for the pomeron trajectory $\overline{\mbox{$\alpha_{_{I\hspace{-0.2em}P}}$}} = 1.23 \pm 0.02(stat) \pm 0.04 (syst)$ averaged over $t$ in the measured kinematic range assuming the longitudinal photon contribution to be zero. This value for the pomeron trajectory is substantially larger than $\overline{\mbox{$\alpha_{_{I\hspace{-0.2em}P}}$}}$ extracted from soft interactions. The value of $\overline{\mbox{$\alpha_{_{I\hspace{-0.2em}P}}$}}$ measured in this analysis suggests that a substantial part of the diffractive DIS cross section originates from processes which can be described by perturbative QCD. From the measured diffractive cross sections the diffractive structure function of the proton $F~{D(3)}_2(\beta,Q~2, \mbox{$x_{_{I\hspace{-0.2em}P}}$})$ has been determined, where $\beta$ is the momentum fraction of the struck quark in the pomeron. The form $F~{D(3)}_2 = constant \cdot (1/ \mbox{$x_{_{I\hspace{-0.2em}P}}$})~a$ gives a good fit to the data in all $\beta$ and $Q~2$ intervals with $a = 1.46 \pm 0.04 (stat) \pm
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No description provided.
No description provided.
Results on the cross section for the production of electron pairs in p p collisions at √ s = 630 GeV are presented. The measured value is σ = 405 ± 51 (syst.) ± 84 (syst.) pb, in the invariant mass interval 10 < m < 70 GeV. The results are compared to recent theoretical calculations which include O( α s 2 ) QCD contributions. The comparison of these data with those of lower energy experiments show approximate scaling as a function of the variable √τ = m √s .
No description provided.
Statistical and systematic errors combined.
Statistical errors only.
Two-jet mass distributions have been measured as a function of centre-of-mass scattering angle for high-mass jet pairs produced in proton-antiproton collisions at the CERN collider operating at a centre-of-mass energy of 630 GeV. The agreement between QCD expectations and the experimental measurements has been used to place limits on the production cross section of an object X decaying into two jets. In particular we consider the existence of a massive colour octet of vector gauge bosons (axigluons). We exclude axigluons with a width Λ A < 0.4 m A and a mass m A in the range 150 < m A < 310 GeV/ c 2 (95% CL).
No description provided.
The production of very large transverse momentum hadron jets has been measured in the UA2 experiment at the CERN p p Collider for s = 540 GeV using a highly segmented calorimeter. The range of previously available cross sections for inclusive jet production is extended to p T = 150 GeV and the two-jet invariant mass distribution to m jj = 280 GeV with the largely increased data sample collected during the 1983 running period. The results are compared with the predictions of QCD models.
LISTED ERRORS INCLUDE STATISTICAL AND THE PT-DEPENDENT UNCERTAINTIES. THE ADDITIONAL OVERALL SYSTEMATIC UNCERTAINTY IS 45PCT.
LISTED ERRORS INCLUDE STATISTICAL AND THE M-DEPENDENT UNCERTAINTIES. THE ADDITIONAL OVERALL SYSTEMATIC UNCERTAINTY IS 45PCT.
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