LHCb

Abstract:

A search for pair production of neutral heavy Higgs bosons decaying into {Mathematical expression} has been carried out in a study of hadronic decays of the Z boson into four jet final states using data taken by DELPHI in 1991 and 1992. The two production mechanisms present in the two Higgs doublets scheme, bremsstrahlung production of hZ* and associated production of hA, may lead to four beauty jets well recognizable using the precise microvertex detector measurements. No evidence for a signal was found, leading to limits on BR(Z→hA→4b) from 3.5 to 5.5×10-4 at 95% contidence level, depending on the mass of the ligthest Higgs. When combined with the results of the recent DELPHI standard Higgs search, this result allows the kinematical limit to be reached for the masses of h and A in the minimal supersymmetric extension of the Standard Model (MSSM) scheme. It also allows the tanβ≤1 domain to be explored, and a region above the kinematic limit for direct hA production is constrained by considering virtual hA production. Results are also given in the general two-doublet scheme. © 1995 Springer-Verlag.

Abstract:

For the first time, multihadronic production from single tagged γγ collisions has been studied, where one of the scattered leptons was tagged at very low virtual photon absolute mass squared (〈Q2〉 = 0.06 (GeV/c2)2). Data collected during 1991 and 1992 in the DELPHI experiment at LEP are shown to agree well with predictions which included the non-perturbative vector meson dominance model in which the interacting photons are assumed to have converted into a vector meson (ρ{variant}, ω or π), a quark-parton model which describes direct photon interactions and a QCD-based model which considers the photon to have quark and gluon structure functions. Five different parametrizations of these structure functions were used and the predictions compared with the data. This study confirms recent results from no-tag experiments in requiring a QCD-based component to successfully describe the data, indicating that the photon has a significant partonic content. © 1995.

Abstract:

Inclusive jet differential cross sections for the reaction ep → jet + X at Q2below 4 GeV2have 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 < ηjet< 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 < ηjet(λp CMS) < 0. These measurements cover a new kinematic regime of the partonic structure of the photon, at typical scales up to ∼300 GeV2and photon fractional momenta down to xγ∼ 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 ηjetand Etjetdistributions. © 1995.

Abstract:

Deep inelastic e-p scattering has been studied in both the charged current (CC) and neutral current (NC) reactions at momentum transfers squared Q2 above 400 GeV2 using the ZEUS detector at the HERA ep collider. The CC and NC total cross sections, the NC to CC cross section ratio, and the differential cross sections d/dQ2 are presented. From the Q2 dependence of the CC cross section, the mass term in the CC propagator is determined to be MW=76 16 13 GeV. © 1995 The American Physical Society.

Abstract:

The forward-backward asymmetries for the processes {Mathematical expression} and {Mathematical expression} at the Z resonance are measured using identified D^*± mesons. In 905,000 selected hadronic events, taken in 1991 and 1992 with the DEL-PHI detector at LEP, 4757 D^*+→D⁰π⁺ decays are reconstructed. The c and b quark forward-backward asymmetries are determined to be: {Mathematical expression} Constraining the b asymmetry to the value measured by DELPHI using independent analyses, the charm asymmetry is determined to be: {Mathematical expression}. This result corresponds to an effective electroweak mixing angle measured using charm quark events of: {Mathematical expression} © 1995 Springer-Verlag.