The properties of two-, three-, four-, five-, and six-jet events with multijet masses >600 GeV /c2 are compared with QCD predictions. The shapes of the multijet-mass and leading-jet-angular distributions are approximately independent of jet multiplicity and are well described by the NJETS matrix element calculation and the HERWIG parton shower Monte Carlo predictions. The observed jet transverse momentum distributions for three- and four-jet events discriminate between the matrix element and parton shower predictions, the data favoring the matrix element calculation.
Exclusive 2-jet mass distribution.
Exclusive 3-jet mass distribution.
Exclusive 4-jet mass distribution.
The inclusive production of D ∗± mesons in photon-photon collisions has been measured by the Aleph experiment at LEP with a beam energy of 45 GeV. The D ∗+ are detected in their decay to D 0 π + with the D 0 observed in three separate decay modes: (1) K − π + , (2) K − π + π 0 and (3) K − π + π − π + , and analagously for the D ∗− modes. A total of 33 events was observed from an integrated luminosity of 73 pb −1 which corresponds to a cross section for Σ( e + e − → e + e − D ∗± X ) of 155 ± 33 ± 21 pb. This result is compatible with both the direct production γγ → c c in the Born approximation and with a more complete calculation which includes both radiative QCD corrections and contributions in which one of the photons is first resolved into its quark and gluon constituents. The shapes of distributions for events containing a D ∗+ are found to be better described by the latter.
No description provided.
We have compared a new QCD calculation by Clay and Ellis of energy-energy correlations (EEC’s) and their asymmetry (AEEC’s) in e+e− annihilation into hadrons with data collected by the SLD experiment at SLAC. From fits of the new calculation, complete at O(αs2), we obtained αs(MZ2)=0.1184±0.0031(expt)±0.0129(theory) (EEC) and αs(MZ2)=0.1120±0.0034(expt)±0.0036(theory) (AEEC). The EEC result is significantly lower than that obtained from comparable fits using the O(αs2) calculation of Kunszt and Nason.
The data are compared to the predictions of Monte-Carlo. Two values of ALPHA_S are corresponded the two theoretical models used in the comparison.
A measurement is presented, using data taken with the H1 detector at HERA, of the contribution of diffractive interactions to deep-inelastic electron-proton scattering. The diffractive contribution to the proton structure function is evaluated as a function of the appropriate deep-inelastic scattering variables using a class of deep-inelastic ep scattering events with no hadronic energy flow in an interval of pseudo-rapidity adjacent to the proton beam direction. The dependence of this contribution on x-pomeron is consistent with both a diffractive interpretation and a factorisable ep diffractive cross section. A first measurement of the deep-inelastic structure of the pomeron in the form of a factorised structure function is presented. This structure function is observed to be consistent with scale invariance.
No description provided.
No description provided.
No description provided.
Using about 950000 hadronic events collected during 1991 and 1992 with the ALEPH detector, the ratios r b = α s b α s udsc and r uds = α s uds α s cb have been measured in order to test the flavour independence of the strong coupling constant α s . The analysis is based on event-shape variables using the full hadronic sample, two b -quark samples enriched by lepton tagging and lifetime tagging, and a light-quark sample enriched by lifetime antitagging. The combined results are r b = 1.002±0.023 and r uds = 0.971 ± 0.023.
No description provided.
We have measured the charge-changing cross sections of 10.6 GeV/nucleon Au197 nuclei interacting in targets of CH2 (polyethylene), C, Al, Cu, Sn, and Pb. Cross sections for H are calculated from those measured in C and CH2. The total charge-changing cross sections are higher than those measured at energies of ≤1 GeV/nucleon. The measured cross sections for the heavier targets are somewhat larger than those predicted by a model based on data taken at lower energies with lighter targets. Partial charge-changing cross sections for the production of fragments from the incident Au projectiles were measured for charge changes (ΔZ) from ΔZ=+1,80Hg, down to approximately ΔZ=-29,50Sn. In comparison to lower energy measurements, these partial cross sections are found to be smaller for small ΔZ and larger or the same for large ΔZ. The H partial cross sections are found to follow a power law in ΔZ similar to that for heavier targets, instead of the exponential form observed at lower energies. Factorization is found to hold for all partial cross sections with ΔZ greater than two. In the heavier targets, the cross sections for one and two proton removal have significant contributions from electromagnetic dissociation. The electromagnetic dissociation contribution to the total cross section is derived and found to be relatively small, but with a strong dependence on the charge of the target nuclei of the form ZT1.75±0.01.
TARGET NUCLEUS=CH2(POLYETHYLENE).
TARGET NUCLEUS=CH2(POLYETHYLENE).
We have conducted a search for bound states of a negative pion and a number of neutrons (pineuts) using the E814 spectrometer. A beam of Si28 at a momentum of 14.6A GeV/c was used to bombard targets of Al, Cu, Sn, and Pb. We describe our experimental technique, present measured upper limits for pineut production, and discuss the significance of our results.
AUTHORS NAMED CHARGED- BY PINEUT. Here ALL means the total number of interactions.
An investigation of the production of neutron-rich isotopes from the fragmentation of Si28 projectiles at plab=14.6 GeV/c per nucleon was performed using the BNL-AGS-E814 spectrometer. We have measured the inclusive production cross sections of neutron-rich fragments (6He, He8, Li8, Li9, Be10, Be11, and B13). We have also measured the transverse momentum distributions for He6 and Li9, and the forward and transverse energy distributions associated with He6 production. The momentum distributions were analyzed in the context of the Goldhaber model. The question of whether the fragments are produced in the decay of the projectile following its electromagnetic excitation was also investigated.
No description provided.
The photon structure function F 2 γ has been measured at average Q 2 values of 73 and 390 GeV 2 using data collected by the AMY detector at the TRISTAN e + e − collider. F 2 γ is observed to be increasing as ln Q 2 . The x -dependence of F 2 γ , where x is the momentum fraction carried by the parton inside the photon, is also measured. The measurements are compared with several parton density models.
No description provided.
No description provided.
Errors contain both statistics and systematics.
We have used 19 pb**-1 of data collected with the Collider Detector at Fermilab to search for new particles decaying to dijets. We exclude at 95% confidence level models containing the following new particles: axigluons with mass between 200 and 870 GeV, excited quarks with mass between 80 and 570 GeV, and color octet technirhos with mass between 320 and 480 GeV.
Here UNSPEC refers to axigluons, excited quarks, colour octet technirhos, ngauge bosons (W' and Z') and diquarks (D and Dc). M is the mass of the new particle (axigluon, q*, ...). Measurements are given to the 95% confidence limit.
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