LHCb

Abstract:

Charged particle production has been measured in Deep Inelastic Scattering (DIS) events using the ZEUS detector over a large range of Q2 from 10 to 1280 GeV2. The evolution with Q of the charged multiplicity and scaled momentum has been investigated in the current fragmentation region of the Breit frame. The data are used to study QCD coherence effects in DIS and are compared with corresponding e+e- data in order to test the universality of quark fragmentation. © 1995 Springer-Verlag.

Abstract:

This paper presents measurements of K⁰ and Λ production in neutral current, deep inelastic scattering of 26.7 GeV electrons and 820 GeV protons in the kinematic range 102<640 GeV², 0.00030.04. Average multiplicities for K⁰ and Λ production are determined for transverse momenta pT>0.5 GeV and pseudorapidities |η|<1.3. The multiplicities favour a stronger strange to light quark suppression in the fragmentation chain than found in e⁺e^- experiments. The production properties of K^0' s in events with and without a large rapidity gap with respect to the proton direction are compared. The ratio of neutral K^0' s to charged particles per event in the measured kinematic range is, within the present statistics, the same in both samples. © 1995 Springer-Verlag.

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.