LHCb

Abstract:

The 4-jet events collected by the DELPHI experiment at LEP1 in 1992, 1993 and 1994 are analysed to determine the contribution of the triple-gluon vertex. Two of the four jets are tagged as jets from b-or c-quarks using lifetime and lepton transverse momentum information. The 4-jet contributions from double-gluon brems Strahlung, the triple-gluon vertex, and secondary quark-antiquark pair production then yield significantly different two-dimensional distributions in the generalized Nachtmann Reiter angle versus the opening angle of the two secondary jets. These distributions are used to fit CA/CF, the ratio of the coupling strength of the triple-gluon vertex to that of gluon bremsstrahlung, and NC/NA, the ratio of the number of quark colours to the number of gluons, giving CA/CF = 2.51 ± 0.28 and NC/NA = 0.38 ∓ 0.10 in agreement with the values expected from QCD: CA/CF= 9/4 = 2.25 and NC/NA = 3/8 = 0.375. © 1997 Published by Elsevier Science B.V.

Abstract:

Charged particle production has been measured in deep inelastic scattering (DIS) events over a large range of x and Q² using the ZEUS detector. The evolution of the scaled momentum, xp, with Q², in the range 10 to 1280 GeV², has been investigated in the current fragmentation region of the Breit frame. The results show clear evidence, in a single experiment, for scaling violations in scaled momenta as a function of Q². © 1997 Elsevier Science B.V.

Abstract:

Oscillations of B⁰s mesons were studied in events with a large transverse momentum lepton selected from 3.2 million hadronic Z⁰ decays registered by DELPHI between 1991 and 1994. A limit on the mass difference between the physical B⁰s states Δms > 6.5ps^-1 at 95% C.L. was obtained by combining the results obtained in three channels. © 1997 Published by Elsevier Science B.V.

Abstract:

Events containing an isolated prompt photon with high transverse energy, together with a balancing jet, have been observed for the first time in photoproduction at HERA. The data were taken with the ZEUS detector, in a γp centre of mass energy range 120-250 GeV. The fraction of the incoming photon energy participating in the production of the prompt photon and the jet, xγ, shows a strong peak near unity, consistent with LO QCD Monte Carlo predictions. In the transverse energy and pseudorapidity range 5 ≤ E^γ T < 10 GeV, -0.7 ≤ η^γ < 0.8, E^jet T ≥ 5 GeV, and -1.5 ≤ η^jet ≤ 1.8, with x^OBS γ > 0.8, the measured cross section is 15.3 ± 3.8 ± 1.8 pb, in good agreement with a recent NLO calculation. © 1997 Elsevier Science B.V.

Abstract:

The ZEUS Central Tracking Detector utilizes a time difference measurement to provide a fast determination of the z coordinate of each hit. The z-by-timing measurement is achieved by using a Time-to-Amplitude Converter which has an intrinsic timing resolution of 36 ps, has pipelined readout, and has a multihit capability of 48 ns. In order to maintain the required sub-nanosecond timing accuracy, the technique incorporates an automated self-calibration system. The readout of the z-by-timing data utilizes a fully customized timing control system which runs synchronously with the HERA beam-crossing clock, and a data acquisition system implemented on a network of Transputers. Three dimensional space-points provided by the z-by-timing system are used as input to all three levels of the ZEUS trigger and for offline track reconstruction. The average z resolution is determined to be 4.4 cm for multi-track events from positron-proton collisions in the ZEUS detector.