P. Checchia

DELPHI (DEtector with Lepton, Photon and Hadron Identication) is a detector for e + e physics, designed to provide high granularity o v er a 4 solid angle, allowing an eective particle identication.It has been operating at the LEP (Large Electron-Positron) collider at CERN since 1989.This article reviews its performance.

Weak isosinglet Neutral Heavy Leptons (v m) have been searched for using data collected by the DELPHI detector corresponding to 3.3 × 106 hadronic Z0 decays at LEP1. Four separate searches have been performed, for short-lived v m production giving monojet or acollinear jet topologies, and for long-lived v m giving detectable secondary vertices or calorimeter clusters. No indication of the existence of these particles has been found, leading to an upper limit for the branching ratio BR(Z0 → v m?) of about 1.3 × 10−6 at 95% confidence level for v m masses between 3.5 and 50 GeV/c2. Outside this range the limit weakens rapidly with the v m mass. The results are also interpreted in terms of limits for the single production of excited neutrinos.

First measurements of the mass and width of the Z0 performed at the newly commissioned LEP Collider by the DELPHI Collaboration are presented. The measuements are derived from the study of multihadronic final states produced in e+e− annihilations at several energies around the Z0 mass. The values found for the mass and width are M(Z0)=91.06±0.09 (stat) ±0.045 (syst.) GeV and Γ(Z0)=2.42±0.21 (stat.) GeV respectively, froma three-parameter fit to the line shape. A two-parameter fit in the framework of the standard model yields for the number of light neutrino species Nν=2.4±0.4 (stat.) ±0.5 (syst.).

The production of single- and multi-photon events has been studied in the reaction e+e- -> gamma (gamma) + invisible particles. The data collected with the DELPHI detector during the years 1999 and 2000 at centre-of-mass energies between 191 GeV and 209 GeV was combined with earlier data to search for phenomena beyond the Standard Model. The measured number of light neutrino families was consistent with three and the absence of an excess of events beyond that predicted by the Standard Model processes was used to set limits on new physics. Both model-independent searches and searches for new processes predicted by supersymmetric and extra-dimensional models have been made. Limits on new non-standard model interactions between neutrinos and electrons were also determined.

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The muon tomography technique, based on the Multiple Coulomb Scattering of cosmic ray muons, has been proposed recently as a tool to perform non-destructive assays of large-volume objects without any radiation hazard. In this paper we discuss experimental results obtained with a scanning system prototype, assembled using two large-area CMS Muon Barrel drift chambers. The capability of the apparatus to produce 3D images of objects and to classify them according to their density is presented. We show that the absorption of low-momentum muons in the scanned objects produces an underestimate of their scattering density, making the discrimination of materials heavier than lead more difficult.

Hadronic decays of Z0 bosons are studied in the Delphi detector. Global event variables and singel particles inclusive distributions are compared with QCD-based predictions. The mean charged multiplicity is found to be 20.6±1.0 (stat+syst). The mean values of the sphericity, aplanarity, thrust, minor value, pinT and poutT are compared with values found at lower energy e+e− colliders.

Applications of cosmic-ray muons have grown in numbers in the last decades. This was possible thanks to the development of detectors and techniques employed in particle and nuclear physics. Indeed the first famous application, the scanning of the Chephren's pyramid, was performed by L. W. Alvarez, that was a great expert in particle detectors and indeed was awarded a Nobel prize for his work on the hydrogen bubble chambers. After a first period in which the applications exploited mainly the absorption of the cosmic-ray muons when crossing a structure under investigation, more recently also the deflection of the muons has been used to design new applications. Nowadays more and more groups around the world are working on this research field. In the present review, after an introduction on cosmic-ray muons, the principles of the interaction of muons with matter will be briefly summarised. This description is important to classify the applications in three main categories: muon radiography, muon tomography and muon metrology. In the following, for each class, an overview of the basic ideas and a detailed description of the technologies will be presented along with a list of past and present applications.

The correlations in rapidity in hadron production from e+e− annihilation near the Z0 resonance were studied by means of the method of factorial moments, using data taken with the DELPHI detector at LEP. The parton shower hadronization model was found to be in quantitative agreement with the data, in contrast with previous results at lower energies.

Bose-Einstein correlation between pairs of like-sign charged particles produced in e+e− annihilations near the Z0 peak have been studied using data taken with the DELPHI detector at LEP. An enhancement is found in the production of pairs of identical pions of similar moments, with respect to a reference sample. Under the hypothesis that the pions are emitted by a spherically symmetrical source with gaussian density, the data indicate a radius of the source of r = 0.62±0.04(stat.)±0.20(syst.) fm. The large systematic uncertainty reflects the sensitivity of r to the choice of the reference sample.

The inclusive cross sections for forward D meson production at s=26 GeV in π−p interactions have been measured to be: σ(π−p→D0/D0+X)xF>0 = (10.1±2.2)μb, σ(π−p→D±+X)xF>0 = (5.7±1.6)μb. The distribution in xF for all D and for xF>0 has the form dσ/dxF=107−37+39(1−xF)7.5−1.7+2.5+5.4−3.8+6.0(1−xF)0.7−0.71.0μ b, with evidence for leading D production. The pT2 distribution is exponential with slope parameter [−1.18−0.16+0.18](GeV/ c)−2. The data are compared with predictions from first-order quark/gluon fusion calculations.

A study of the properties of charm particles produced in 400 GeV/cpp interactions is reported. The experiment was performed using the high resolution hydrogen bubble chamber LEBC in association with the European Hybrid Spectrometer at the CERN SPS. Details of the experimental set-up and operational procedures are given and the methods to extract samples of charm decays are discussed. Results are presented on the intrinsic properties of charm particles (masses, lifetimes, decay modes and branching ratios), adding, whenever appropriate, the relevant information obtained in a similar study made with 360 GeV/cπ − p interactions. The hadroproduction properties of charm states (total and differential cross sections, correlations) are presented and discussed in the context of current QCD inspired phenomenology.

From measurements of the cross sections for e+e−→ hadrons and the cross sections and forward-backward charge-asymmetries for ee−→e+e−, μ+μ− and π+π− at several centre-of-mass energies around the Z0 pole with the DELPHI apparatus, using approximately 150 000 hadronic and leptonic events from 1989 and 1990, one determines the following Z0 parameters: the mass and total width MZ = 91.177 ± 0.022 GeV, ΓZ = 2.465 ± 0.020 GeV, the hadronic and leptonic partial widths Γh = 1.726 ± 0.019 GeV, Γl = 83.4 ± 0.8 MeV, the invisible width Γinv = 488 ± 17 MeV, the ratio of hadronic over leptonic partial widths RZ = 20.70 ± 0.29 and the Born level hadronic peak cross section σ0 = 41.84±0.45 nb. A flavour-independent measurement of the leptonic cross section gives very consistent results to those presented above (Γl = 83.7 ± 0.8rmMeV). From these results the number of light neutrino species is determined to be Nv = 2.94 ±0.10. The individual leptonic widths obtained are: Γe = 82.4±_1.2 MeV, Γu = 86.9±2.1 MeV and Γτ = 82.7 ± 2.4 MeV. Assuming universality, the squared vector and axial-vector couplings of the Z0 to charged leptons are: V̄l2 = 0.0003±0.0010 andĀl2 = 0.2508±0.0027. These values correspond to the electroweak parameters: ϱeff = 1.003 ± 0.011 and sin2θWeff = 0.241 ± 0.009. Within the Minimal Standard Model (MSM), the results can be expressed in terms of a single parameter: sin2θWM̄S = 0.2338 ± 0.0027. All these values are in good agreement with the predictions of the MSM. Fits yield 43<mtop < 215 GeV at the 95% level. Finally, the measured values of ΓZ and Γinv are used to derived lower mass bounds for possible new particles.

The production rates for 2-, 3-, 4- and 5-jet hadronic final states have been measured with the DELPHI detector at the e+e− storage ring LEP at centre of mass energies around 91.5 GeV. Fully corrected data are compared to O(α2s) QCD matrix element calculations and the QCD scale parameter ΛMS is determined for different parametrizations of the renormalization scale ω2. Including all uncertainties our result is αs(M2Z)=0.114±0.003[stat.]±0.004[syst.]±0.012[theor.].

Using a data sample corresponding to 10 000 hadronic Z0 decays, we have searched for the production of sleptons and gauginos in the two-prong decays of Z0. No candidate remains after straightforward selections. For neutralinos, we use selection methods developed in our previous search for neutral Higgs particles. The negative results are translated into improved mass limits and parameter constraints on the minimal supersymmetric extension of the standard model.

Searches for the Standard Model Higgs boson have been performed in the data collected by the DELPHI experiment at LEP in the year 2000 at centre-of-mass energies between 200 and 209 GeV corresponding to a total integrated luminosity of 224 pb−1. No evidence for a Higgs signal is observed in the kinematically accessible mass range, and a 95% CL lower mass limit of 114.3 GeV/c2 is set, to be compared with an expected median limit of 113.5 GeV/c2 for these data.

A search for pair-produced doubly charged Higgs bosons has been performed using the data collected by the DELPHI detector at LEP at centre-of-mass energies between 189 and 209 GeV. No excess is observed in the data with respect to the Standard Model background. A lower limit for the mass of 97.3 GeV/c2 at the 95% confidence level has been set for doubly charged Higgs bosons in left–right symmetric models for any value of the Yukawa coupling between the Higgs bosons and the τ leptons.

During the 1992 running period of the LEP e+e− collider, the DELPHI experiment accumulated approximately 24 pb− of data at the Z0 peak. The decays into hadrons and charged leptons have been analysed to give values for the cross sections and leptonic forward-backward asymmetries which are significantly improved with respect to those previously published by the DELPHI collaboration. Incorporating these new data, more precise values for the Z0 resonance parameters are obtained from model-independent fits. The results are interpreted within the framework of the Standard Model, yielding for the top quark mass mt = 157−48+36(expt.)−20+19(Higgs) GeV, and for the effective mixing angle sin2 θefflept = 0.2328 ± 0.0013 (expt.)−0.0003+0.0001(Higgs), where (Higgs) represents the variation due to Higgs boson mass in the range 60 to 1000 GeV, with central value 300 GeV.

A measurement of the cross section for e+e- → hadrons using 11 000 hadronic decays of the Z boson at ten different center-of-mass energies is presented. A three-parameter fit gives the following values for the Z mass Mz, the total width Γz, the product of the electronic and hadronic partial widths ΓeΓh, and the unfolded pole cross section σ0: MZ=91.171±0.030(stat)±0.030 (beam) GeV, ΓZ=2.511±0.065 GeV, ΓeΓh=0.148±0.006 (stat.)±0.004 (syst.) GeV2, σ0=41.6±0.7(stat.)±1.1 (syst.) nb, Good agreement with the predictions of the standard model is observed. From a two-parameter fit the number of massless neutrino generations is found to be Nν = 2.97±0.26. Thus the hypothesis of a fourth neutrino with mass less than 40 GeV is excluded with 95% confidence level. Combining the cross section measurements with the ratio ΓℓΓh reported in another DELPHI paper [Phys. Lett. B 241 (1990) 425], the hadronic, leptonic and invisible widths are found to be Γh=1741±61 MeV, Γℓ=85.1±2.9 MeV, ΓhΓℓ=20.45±0.98, Γinv=515±54 MeV, in good agreement with the standard model.

We have measured the inclusive production properties of D and D messons produced from pp interactions at s=27.4 GeV. The differential production cross section is well represented by the empirical form d2σdxFdP2T=12[σ (D/D)(n+1)b](1−|xF|)n exp(−bp2T) with n=4.9 ± 0.5, b=(1.0±0.1)(GeV/c)−2, and the inclusive D/D cross section σ(D/D) is (30.2±3.3) ωb. The QCD fusion model predicts D/D production which is in good agreement with our data except for the magnitude of the cross section which depends sensitively on the assumed mass of the charm quark.

The multiplicity distributions of charged particles in restricted rapidity intervals inZ 0 hadronic decays measured by the DELPHI detector are presented. The data reveal a shoulder structure, best visible for intervals of intermediate size, i.e. for rapidity limits around ±1.5. The whole set of distributions including the shoulder structure is reproduced by the Lund Parton Shower model. The structure is found to be due to important contributions from 3-and 4-jet events with a hard gluon jet. A different model, based on the concept of independently produced groups of particles, "clans", fluctuating both in number per event and particle content per clan, has also been used to analyse the present data. The results show that for each interval of rapidity the average number of clans per event is approximately the same as at lower energies.

A study of the properties of charm particles produced in 360 GeV/c π- p interactions is reported. The experiment was performed using the high resolution hydrogen bubble chamber LEBC in association with the European Hybrid Spectrometer at the CERN SPS. Details of the exposure and operation of the spectrometer are given and the methods used to extract the charm data are presented. The essential physics results on the decay properties (lifetime, branching ratios) as well as on the hadroproduction properties (cross sections forD, $$\bar D$$ ,F, Λ c ,D, correlations between charm particles) are given.

A determination of branching ratios for D meson decays into all charged particle final states is reported. The values obtained: (D± → K∓π±π±/all D±) = (14 ± 6)% and (D0/D0 → K±π∓π+π−/all D0/D0) = (10 ± 4)%, are higher than those currently accepted. This result, if confirmed, implies a corresponding reduction in the accepted values for some total cross section measurements. Revised inclusive cross sections for D meson production in the forward hemisphere in π−p and pp interactions at 360 GeV/c, are presented.

The European Hybrid Spectrometer is described in its preliminary version for the NA16 charm experiment. The performance of the small hydrogen bubble chamber LEBC and the detectors of the spectrometer is discussed. In particular the combination of the bubble chamber information with the spectrometer data is described in detail. The track reconstruction efficiency is 90%. The precision with which vertices seen in the bubble chamber are reconstructed is around 10 μm and the two track resolution is 40 μm. Therefore very complex event configurations, in particular charm particle decays, can be reconstructed correctly.

The DELPHI detector at LEP has been used to measure multi-muon bundles originating from cosmic ray interactions with air. The cosmic events were recorded in “parasitic mode” between individual e+e− interactions and the total live time of this data taking is equivalent to 1.6 × 106 s. The DELPHI apparatus is located about 100 m underground and the 84 metres rock overburden imposes a cutoff of about 52 GeV/c on muon momenta. The data from the large volume Hadron Calorimeter allowed the muon multiplicity of 54,201 events to be reconstructed. The resulting muon multiplicity distribution is compared with the prediction of the Monte Carlo simulation based on CORSIKA/QGSJET01. The model fails to describe the abundance of high multiplicity events. The impact of QGSJET internal parameters on the results is also studied.

Single photons detected by the DELPHI experiment at LEP2 in the years 1997–2000 are reanalysed to investigate the existence of a single extra dimension in a modified ADD scenario with slightly warped large extra dimensions. The data collected at centre-of-mass energies between 180 and 209 GeV for an integrated luminosity of ∼650 pb−1 agree with the predictions of the Standard Model and allow a limit to be set on graviton emission in one large extra dimension. The limit obtained on the fundamental mass scale M D is 1.69 TeV/c 2 at 95% CL, with an expected limit of 1.71 TeV/c 2.

A measurement of the W boson mass and width has been performed by the DELPHI collaboration using the data collected during the full LEP2 programme (1996–2000). The data sample has an integrated luminosity of 660 pb-1 and was collected over a range of centre-of-mass energies from 161 to 209 GeV. Results are obtained by applying the method of direct reconstruction of the mass of the W from its decay products in both the W+W-→ℓν̄ℓqq̄’ and W+W-→qq̄’q̄q’ channels. The W mass result for the combined data set is $M_W = 80.336 \pm0.055 ({\text{Stat.}}) \pm0.028 ({\text{Syst.}}) \pm0.025 ({\text{FSI}}) \pm0.009 ({\text{LEP}}) \text{GeV}/c^2, $ where FSI represents the uncertainty due to final state interaction effects in the qq̄’q̄q’ channel, and LEP represents that arising from the knowledge of the collision energy of the accelerator. The combined value for the W width is ${\Gamma_{W}} = 2.404 \pm0.140 ({\text{Stat.}}) \pm0.077 ({\text{Syst.}}) \pm0.065 ({\text{FSI}}) \text{GeV}/c^2. $ These results supersede all values previously published by the DELPHI collaboration.

The nature of b-quark jet hadronisation has been investigated using data taken at the Z peak by the DELPHI detector at LEP. Two complementary methods are used to reconstruct the energy of weakly decaying b-hadrons, $E_{\mathrm{B}}^{\mathrm{weak}}$ . The average value of $x^{\mathrm{weak}}_{\mathrm{B}} = E_{\mathrm{B}}^{\mathrm{weak}}/E_{\mathrm{beam}}$ is measured to be 0.699±0.011. The resulting $x^{\mathrm{weak}}_{\mathrm{B}}$ distribution is then analysed in the framework of two choices for the perturbative contribution (parton shower and Next to Leading Log QCD calculation) in order to extract measurements of the non-perturbative contribution to be used in studies of b-hadron production in other experimental environments than LEP. In the parton shower framework, data favour the Lund model ansatz and corresponding values of its parameters have been determined within PYTHIA 6.156 from DELPHI data: $$a= 1.84^{+0.23}_{-0.21}\quad\mbox{and}\quad b=0.642^{+0.073}_{-0.063}~\mathrm{GeV}^{-2},$$ with a correlation factor ρ=92.2%. Combining the data on the b-quark fragmentation distributions with those obtained at the Z peak by ALEPH, OPAL and SLD, the average value of $x^{\mathrm{weak}}_{\mathrm{B}}$ is found to be 0.7092±0.0025 and the non-perturbative fragmentation component is extracted. Using the combined distribution, a better determination of the Lund parameters is also obtained: $$a= 1.48^{+0.11}_{-0.10}\quad\mbox{and}\quad b=0.509^{+0.024}_{-0.023}~\mathrm{GeV}^{-2},$$ with a correlation factor ρ=92.6%.

Muon radiographic methods can be used to explore inaccessible volumes profiting of the property of muons to penetrate thick materials. An extension of the muon radiographic methods, the muon scattering tomography, was proposed for the first time in 2003 and it is based on the measurement of the multiple Coulomb scattering of muons crossing the volume under investigation. In this talk, the principles of tomographic image reconstruction are first outlined and then the experimental setup and the most adequate detectors are described. A review of the possible applications of this technique is reported, with specific reference to security in transports and monitoring of industrial processes. The technique can also be used to provide precise measurements of the properties of various materials. The experimental challenge related to this activity is discussed.

In recent decades, muon imaging has found a plethora of applications in many fields. This technique succeeds to infer the density distribution of big inaccessible structures where conventional techniques cannot be used. The requirements of different applications demand specific implementations of image reconstruction algorithms for either multiple scattering or absorption-transmission data analysis, as well as noise-suppression filters and muon momentum estimators. This paper presents successful results of image reconstruction techniques applied to simulated data of some representative applications. In addition to well-known reconstruction methods, a novel approach, the so-called μCT, is proposed for the inspection of spent nuclear fuel canisters. Results obtained based on both μCT and the maximum-likelihood expectation maximization reconstruction algorithms are presented.This article is part of the Theo Murphy meeting issue 'Cosmic-ray muography'.

An analysis of the data collected in 1997 and 1998 with the DELPHI detector at e+e− collision energies close to 183 and 189 GeV was performed in order to extract the hadronic and leptonic fermion-pair cross-sections, as well as the leptonic forward–backward asymmetries and angular distributions. The data are used to put limit on contact interactions between fermions, the exchange of R-parity violating SUSY sneutrinos, Z′ bosons and the existence of gravity in extra dimensions.

The pair production of the lightest scalar Higgs boson, h, and a pseudoscalar Higgs boson, A, was searched for in a data sample containing 10 000 hadronic Z0 decays. The search involved both leptonic and purely hadronic decay channels of each Higgs boson. No signal was found, and limits on the Higgs boson masses, in the framework of the minimal supersymmetric extension of the standard model, ar reported up to 35 GeV/c2 at 95% CL, for both tan β1 and tan β<1, where tan β is the ratio of the vacuum expectation values of the two Higgs doublets.

A search for the neutral Higgs boson in Z0-decays has been performed using the DELPHI detector at the large Electron Positron collider (LEP) at CERN. We looked for the decay of Z0 into a neutral Higgs particle and a pair of fermions. No events fulfilled the criteria for H0-production. Our results, which are based on an integrated luminosity of 530 nb−1, exclude a minimal Standard Model Higgs boson with a mass in the range 210 MeV/c2 to 14 GeV/c2 at 95% confidence level.

Soft photons inside hadronic jets converted in front of the DELPHI main tracker (TPC) in events of qq̄ disintegrations of the Z0 were studied in the kinematic range 0.2<Eγ<1 GeV and transverse momentum with respect to the closest jet direction pT<80 MeV/c. A clear excess of photons in the experimental data as compared to the Monte Carlo predictions is observed. This excess (uncorrected for the photon detection efficiency) is (1.17±0.06±0.27)×10-3 γ/jet in the specified kinematic region, while the expected level of the inner hadronic bremsstrahlung (which is not included in the Monte Carlo) is (0.340±0.001±0.038)×10-3 γ/jet. The ratio of the excess to the predicted bremsstrahlung rate is then (3.4±0.2±0.8), which is similar in strength to the anomalous soft photon signal observed in fixed target experiments with hadronic beams.

A determination of the single W spin density matrix (SDM) elements in the reaction e+e-→W+W-→lνqq̄(l=e/μ) is reported at centre-of-mass energies between 189 and 209 GeV. The data sample used corresponds to an integrated luminosity of 520 pb-1 taken by DELPHI between 1998 and 2000. The single W SDM elements, ρττ' W± (τ,τ'=± 1 or 0), are determined as a function of the W- production angle with respect to the e- beam direction and are obtained from measurements of the W decay products by the application of suitable projection operators, Λττ', which assume the V-A coupling of the W-boson to fermions. The measured SDM elements are used to obtain the fraction of longitudinally polarised Ws, with the result: $\frac{\sigma_{\text{L}}}{\sigma_{{\text{tot}}}} = 24.9 \pm4.5({\text{stat}}) \pm2.2({\text{syst}})\%$ at a mean energy of 198 GeV. The SDM elements are also used to determine the triple gauge couplings Δg1 Z,Δκγ,λγ and g4 Z, $\tilde{\kappa}_{Z}$ and $\tilde{\lambda}_{Z}$ . For the CP-violating couplings the results of single parameter fits are: $g_4^{{Z}} = -0.39^{+0.19}_{-0.20}$ $\tilde{\kappa}_{{Z}} = -0.09^{+0.08}_{-0.05}$ $\tilde{\lambda}_{{Z}} = -0.08\pm0.07 .$ The errors are a combination of statistical and systematic errors. All results are consistent with the Standard Model.

An analysis is presented of the z distributions of secondary hadrons produced in 5600 charged current events from a BEBC neutrino-hydrogen experiment. Evidence is presented for scaling deviations in the z distributions and a breakdown of factorization in the single particle inclusive cross sections. The results are consistent with the leading order QCD predictions on the q2 dependence of nonsinglet moments of quark fragmentation functions, yielding a value of Λ ≈ 0.6 GeV.

The reaction νp→μ−pπ+ (777 events) is studied at neutrino energies from 5 to 200 GeV. A total of 551 events fit the channel νp→μ−Δ++ (1232) with χ2 probability greater than 2%. Decay angular distributions of the Δ++ are investigated and the density matrix elements are studied as functions of Q2, the square four-momentum transfer. The total Δ++ production cross section and the differential cross section dσ/dQ2 are determined. Using the Schreiner-von Hippel parametrization of the Adler model, the value of the axial mass determined by fitting the total cross sections above 20 GeV is MA = 0.85±0.10 GeV. The model describes the differential cross sections reasonably well above Q2⋍0.2 GeV2. Disagreements, however, are found for some values of the density matrix elements of the Δ++ decay angular distributions and their Q2 dependence. The (pπ+) mass region above the Δ++(1232) contains evidence for the presence of higher mass Δ++ resonances and, above 2 GeV, for the forward emission of fast π+.

An analysis of the direct soft photon production rate as a function of the parent jet characteristics is presented, based on hadronic events collected by the DELPHI experiment at LEP1. The dependences of the photon rates on the jet kinematic characteristics (momentum, mass, etc.) and on the jet charged, neutral and total hadron multiplicities are reported. Up to a scale factor of about four, which characterizes the overall value of the soft photon excess, a similarity of the observed soft photon behaviour to that of the inner hadronic bremsstrahlung predictions is found for the momentum, mass, and jet charged multiplicity dependences. However for the dependence of the soft photon rate on the jet neutral and total hadron multiplicities a prominent difference is found for the observed soft photon signal as compared to the expected bremsstrahlung from final state hadrons. The observed linear increase of the soft photon production rate with the jet total hadron multiplicity and its strong dependence on the jet neutral multiplicity suggest that the rate is proportional to the number of quark pairs produced in the fragmentation process, with the neutral pairs being more effectively radiating than the charged ones.

Infrared and collinear safe event shape distributions and their mean values are determined using the data taken at five different centre of mass energies above MZ with the DELPHI detector at LEP. From the event shapes, the strong coupling αs is extracted in O(αs2), NLLA and a combined scheme using hadronisation corrections evaluated with fragmentation model generators as well as using an analytical power ansatz. Comparing these measurements to those obtained at MZ, the energy dependence (running) of αs is accessible. The logarithmic energy slope of the inverse strong coupling is measured to bedα−1sdlog(Ecm)=1.39±0.34(stat)±0.17(syst),in good agreement with the QCD expectation of 1.27.

An update of the searches for charginos and neutralinos in DELPHI is presented, based mainly on recent data collected at centre-of-mass energies of 161 GeV and 172 GeV. No signal is found. For a sneutrino with mass above 300 GeV/c 2 and a mass difference between the chargino and the lightest neutralino above 10 GeV/c 2, the lower limit at 95% confidence level on the chargino mass ranges from 84.3 GeV/c 2 to the kinematical limit (86.0 GeV/c 2), depending on the mixing parameters. The limit decreases for lower chargino-neutralino mass differences. The limit in the case of a light sneutrino is 67.6 GeV/c 2, provided that that there is no light sneutrino with a mass within 10 GeV/c 2 below the chargino mass. Upper limits on neutralino pair production cross-sections of about a picobarn are derived. The (μ,M 2) domain excluded in the MSSM-GUT scenario is determined by combining the neutralino and chargino searches. These results imply a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 24.9 GeV/c 2 for tanß >- 1. The search has also been extended to the case where the lightest neutralino is unstable and decays into a photon and a gravitino. imply a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 24.9 GeV/c 2 for tanß >- 1. The search has also been extended to the case where the lightest neutralino is unstable and decays into a photon and a gravitino.

The value of the b quark mass at the MZ scale defined in the MS renormalization scheme, mb(MZ), was determined using 2.8 million hadronic Z decays collected during 1992-1994 by the DELPHI detector to bemb(MZ)=2.67±0.25(stat.)±0.34(frag.)±0.27(theo.)GeV/c2.The analysis considers NLO corrections to the three-jet production rate including mass effects, and the result obtained agrees with the QCD prediction of having a running b quark mass at an energy scale equal to MZ. This is the first time that such a measurement is performed far above the bb production threshold. The study also verifies the flavour independence of the strong coupling constant for b and light quarks within 1% accuracy.

An analysis of the production of the Λ baryon in the hadronic decays of the Z0 is presented, based on about 993K multihadronic events collected by the DELPHI detector at LEP during 1991 and 1992. The differencial cross section of the Λ and the correlations between Λ and Λ produced in the same event are compared to current models, based both on string fragmentation and on cluster decay. The predictions of the string fragmentation model are found to give satisfactory agreements with the data, clearly better than those of the cluster model.

This analysis, based on a sample of 170000 hadronic Z0 decays, provides a measurement of the K± and p/p differential cross sections which is compared to string- and cluster fragmentation models. The total multiplicities for K± and p/p per hadronic event were found to be: NK = 2.26 ± 0.18 and Np = 1.07 ± 0.14. The positions ξ* of the maxima of the differential cross sections as a function of ξ = ln(1/xp) for K± and p/p were determined to be 2.63 ± 0.07 and 2.96 ± 0.16 respectively. A comparison of the ξ* values for various identified particles measured at LEP with the prediction of the Modified Leading Logarithm Approximation with Local Parton Hadron Duality model has been performed. The measured ξ* position as a function of the hadron mass, after corrections due to particle decays, is in agreement with the model calculation.

In 1996 LEP ran at a centre-of-mass energy of 161 GeV, just above the threshold of W-pair production. DELPHI accumulated data corresponding to an integrated luminosity of 9.93 pb−1, and observed 29 events that are considered as candidates for W-pair production. From these, a cross-section for the doubly resonant e+e− → WW process of 3.67−0.85+0.97 ± 0.19 pb has been measured. Within the Standard Model, this cross-section corresponds to a mass of the W-boson of 80.40 ± 0.44 (stat.) ± 0.09 (syst.) ± 0.03 (LEP) GeV/c2. Alternatively, if mW is held fixed at its current value determined by other experiments, the observed cross-section is used to obtain limits on trilinear WWV (V ≡ γ, Z) couplings.

Using D∗+ mesons exclusively reconstructed in the DELPHI detector at LEP, an excess of 66±14(stat.) events is observed in the D∗+π+π− final state with a mass of 2637±2(stat.)±6(syst.) MeV/c2 and a full width smaller than 15 MeV/c2 (95% C.L.). This signal is compatible with the expected decay of a radially excited D∗′ (JP=1−) meson.

In four-jet events from e+e− →Z0 →multihadrons one can separate the three principal contributions from the triple-gluon vertex, double gluon-bremsstrahlung and the secondary quark-antiquark production, using the shape of the two-dimensional angular distributions in the generalized Nachtmann-Reiter angle θNR∗ and the opening angle of the secondary jets. Thus one can identify directly the contribution from the triple-gluon vertex without comparison with a specific non-QCD model. Applying this new method to events taken with the DELPHI-detector we get for the ratio of the colour factor Nc to the fermionic Casimir operator CF: NcCF= 2.55 ± 0.55 (stat.) ± 0.4 (fragm. + models) ± 0.2 (error in bias) in agreement with the value 2.25 expected in QCD from Nc=3 and CF=43.

An analysis of the production of strange particles from the decays of the Z0 boson into multihadronic final states is presented. The analysis is based on about 90 000 selected hadronic Z0 decays collected by the DELPHI detector at LEP in 1990. Ks0, K∗±, Λ(Λ) and Ξ− (Ξ+) have been identified by their characteristic decays. The measured production cross sections are compared with predictions of the Lund Monte Carlo tuned to data at PEP/PETRA energies.

A search for single top production (e+e−→tc̄) via flavour changing neutral currents (FCNC) was performed using the data taken by the DELPHI detector at LEP2. The data analyzed have been accumulated at center-of-mass energies ranging from 189 to 208 GeV. Limits at 95% confidence level were obtained on the anomalous coupling parameters κγ and κZ.

This paper presents DELPHI measurements and interpretations of cross-sections, forward-backward asymmetries, and angular distributions, for the e+e- -&gt; ffbar process for centre-of-mass energies above the Z resonance, from sqrt(s) ~ 130 - 207 GeV at the LEP collider. The measurements are consistent with the predictions of the Standard Model and are used to study a variety of models including the S-Matrix ansatz for e+e- -&gt; ffbar scattering and several models which include physics beyond the Standard Model: the exchange of Z' bosons, contact interactions between fermions, the exchange of gravitons in large extra dimensions and the exchange of sneutrino in R-parity violating supersymmetry.

We have studied the energy-energy angular correlations in hadronic final states from Z0 decay using the DELPHI detector at LEP. From a comparison with Monte Carlo calculations based on the exact second order QCD matrix element and string fragmentation we find that Λ(5)MS=104+25-20(stat.)+25-20(syst.)+3000)theor.). MeV, which corresponds to αs(91 GeV)=0.106±0.003(stat.)±0.003(syst.)+0.003-0.000(theor). The theoretical error stems from different choices for the renormalization scale of αs. In the Monte Carlo simulation the scale of αs as well as the fragmentation parameters have been optimized to described reasonably well all aspects of multihadron production.

Using a sample of Z0's corresponding to about 12 000 events, we have searched for the production of charged scalars, primarily charged Higgs particles, decaying into cscs, τν + jets, and τντν. The average detection efficiency is 20%. No candidate was found in the leptonic modes. Masses in the range up to 30–36 GeV/c2 are excluded, extending the mass domain covered by previous e+e− machines.

Results are presented on charm meson lifetimes. The sample of charm particle decays was obtained by exposing the high resolution rapid cycling hydrogen bubble chamber (LEBC) coupled with the European Hybrid Spectrometer to π− and p beams at 360 GeV/c ffrom the CERN SPS. The analysis of ∼850 k pictures has yielded 77 events containing a total of 60 charm decays. From these, an unbiased sample of 31 D decays (15± and 16 D0) is issued in the lifetime analysis. The measured mean lifetimes for D± and D0 are (where the symbol D0 means D0 and D0):τ(D±)=8.4+3.5−2.2 × 10−13sτ(D0)=4.1+1.3−0.9 ×10−13s. Three unambiguous examples of F± decay have also been observed and the corresponding lifetime, based on 2 decays, is τ(F±)=2.1 +3.6−0.8 × 10 −13s

We describe the two gamma detectors built for the European Hybrid Spectrometer (EHS). Their monitoring system is presented in detail. Results from tests and the performance obtained during the first EHS experiment are given.

Charm D-meson production in 360 GeV π−p interactions has been studied using the high-resolution hydrogen bubble chamber LEBC and the European Hybrid Spectrometer. The data show evidence for leading quark effects both in the number of D-meson types and in the Feynman x distributions. The production cross section is of the form d2δdxdpT2∞(1-x)nexp(-apT2) with n = 2.8±0.8 and a = 1.1±0.3 (GeV/c)−2. The x distribution is, however, compatible with the presence of both central (n = 6) and leading (n = 1) D/Dproduction. The fraction of D-messons in the leading component is estimated to be ≈30%. The rapidity gap between members of reconstructed charm pairs is small compared to the available rapidity range. The inclusive cross section for single D-messons in the forward direction is: δ(D/D)=(408+15)μb (forx>0).

We demonstrate that muon tomography can be used to precisely measure the properties of various materials. The materials which have been considered have been extracted from an experimental blast furnace, including carbon (coke) and iron oxides, for which measurements of the linear scattering density relative to the mass density have been performed with an absolute precision of 10%. We report the procedures that are used in order to obtain such precision, and a discussion is presented to address the expected performance of the technique when applied to heavier materials. The results we obtain do not depend on the specific type of material considered and therefore they can be extended to any application.

A sample of 2.2 million hadronic Z decays, selected from the data recorded by the Delphi detector at Lep during 1994–1995 was used for an improved measurement of inclusive distributions of $\pi^+, K^+$ and p and their antiparticles in gluon and quark jets. The production spectra of the individual identified particles were found to be softer in gluon jets compared to quark jets, with a higher multiplicity in gluon jets as observed for inclusive charged particles. A significant proton enhancement in gluon jets is observed indicating that baryon production proceeds directly from colour objects. The maxima, $\xi^*$ , of the $\xi$ -distributions for kaons in gluon and quark jets are observed to be different.

A classifier based on a feed-forward neural network has been used for separating a sample of about 123 500 selected hadronic decays of the Z0, collected by DELPHI during 1991, into three classes according to the flavour of the original quark pair: uu+dd+ss (unresolved), cc and bb. The classification has been used to compute the partial widths of the Z0 into b and c quark pairs. This gave Γcc/Γh= 0.151 ± 0.008 (stat.) ± 0.041 (syst.), Γbb/Γh= 0.232±0.005 (stat.)±0.017 (syst.).

Glueballs, hybrids and multiquark states are predicted as bound states in models guided by quantum chromo dynamics (QCD), by QCD sum rules or QCD on a lattice. Estimates for the (scalar) glueball ground state are in the mass range from 1000 to 1800 MeV, followed by a tensor and a pseudoscalar glueball at higher mass. Experiments have reported evidence for an abundance of meson resonances with 0-+,0++ and 2++ quantum numbers. In particular, the sector of scalar mesons is full of surprises starting from the elusive σ and κ mesons. The a0(980) and f0(980), discussed extensively in the literature, are reviewed with emphasis on their Janus-like appearance as KK¯ molecules, tetraquark states or qq¯ mesons. Most exciting is the possibility that the three mesons f0(1370), f0(1500), and f0(1710) might reflect the appearance of a scalar glueball in the world of quarkonia. However, the existence of f0(1370) is not beyond doubt and there is evidence that both f0(1500) and f0(1710) are flavour octet states, possibly in a tetraquark composition. We suggest a scheme in which the scalar glueball is dissolved into the wide background into which all scalar flavour-singlet mesons collapse.There is an abundance of meson resonances with the quantum numbers of the η. Three states are reported below 1.5GeV/c2 whereas quark models expect only one, perhaps two. One of these states, ι(1440), was the prime glueball candidate for a long time. We show that ι(1440) is the first radial excitation of the η meson.Hybrids may have exotic quantum numbers which are not accessible by qq¯ mesons. There are several claims for JPC=1-+ exotics, some of them with properties as predicted from the flux tube model interpreting the quark–antiquark binding by a gluon string. The evidence for these states depends partly on the assumption that meson–meson interactions are dominated by s-channel resonances. Hybrids with non-exotic quantum numbers should appear as additional states. Light-quark mesons exhibit a spectrum of (squared) masses which are proportional to the sum of orbital angular momentum and radial quantum numbers. Two states do not fall under this classification. They are discussed as hybrid candidates.The concept of multiquark states has received revived interest due to new resonances in the spectrum of states with open and hidden charm. The new states are surprisingly narrow and their masses and their decay modes often do not agree with simple quark-model expectations.Lattice gauge theories have made strong claims that glueballs and hybrids should appear in the meson spectrum. However, the existence of a scalar glueball, at least with a reasonable width, is highly questionable. It is possible that hybrids will turn up in complex multibody final states even though so far, no convincing case has been made for them by experimental data. Lattice gauge theories fail to identify the nonet of scalar mesons. Thus, at the present status of approximations, lattice gauge theories seem not to provide a trustworthy guide into unknown territory in meson spectroscopy.

Inclusive J/psi production in photon-photon collisions has been observed at LEP II beam energies. A clear signal from the reaction gamma gamma -&gt; J/psi+X is seen. The number of observed N(J/psi -&gt; mu+mu-) events is 36 +/- 7 for an integrated luminosity of 617 pb^{-1}, yielding a cross-section of sigma(J/psi+X) = 45 +/- 9 (stat) +/- 17 (syst) pb. Based on a study of the event shapes of different types of gamma gamma processes in the PYTHIA program, we conclude that (74 +/- 22)% of the observed J/psi events are due to `resolved' photons, the dominant contribution of which is most probably due to the gluon content of the photon.

The search in DELPHI data for neutral Higgs bosons is described. No candidate for the Standard Model Higgs is seen in Z0 decays to H0νν, H0μ+μ− or H0τ+τ− after selections that proved efficient for finding simulated H0. One remaining candidate for Z0 → H0e+e− is consistent with background. Together with our earlier studies, these results restrict the H0 mass to be above 38 GeV/c2 at the 95% confidence level. No signal is found for decays of Minimal Supersymmetric Standard Model neutral Higgs bosons to τ+τ−. Limits are obtained for their decays to produce four jets.

Distributions of event shape variables obtained from 120600 hadronicZ decays measured with the DELPHI detector are compared to the predictions of QCD based event generators. Values of the strong coupling constant αs are derived as a function of the renormalization scale from a quantitative analysis of eight hadronic distributions. The final result, αs(M Z), is based on second order perturbation theory and uses two hadronization corrections, one computed with a parton shower model and the other with a QCD matrix element model.

The Compact Muon Solenoid (CMS) experiment prepares its Phase-2 upgrade for the high-luminosity era of the LHC operation (HL-LHC). Due to the increase of occupancy, trigger latency and rates, the full electronics of the CMS Drift Tube (DT) chambers will need to be replaced. In the new design, the time bin for the digitization of the chamber signals will be of around 1 ns, and the totality of the signals will be forwarded asynchronously to the service cavern at full resolution. The new backend system will be in charge of building the trigger primitives of each chamber. These trigger primitives contain the information at chamber level about the muon candidates position, direction, and collision time, and are used as input in the L1 CMS trigger. The added functionalities will improve the robustness of the system against ageing. An algorithm based on analytical solutions for reconstructing the DT trigger primitives, called Analytical Method, has been implemented both as a software C++ emulator and in firmware. Its performance has been estimated using the software emulator with simulated and real data samples, and through hardware implementation tests. Measured efficiencies are 96 to 98% for all qualities and time and spatial resolutions are close to the ultimate performance of the DT chambers. A prototype chain of the HL-LHC electronics using the Analytical Method for trigger primitive generation has been installed during Long Shutdown 2 of the LHC and operated in CMS cosmic data taking campaigns in 2020 and 2021. Results from this validation step, the so-called Slice Test, are presented.

Abstract The BLEMAB European project (BLast furnace stack density Estimation through online Muon ABsorption measurements), the evolution of the previous Mu-Blast European project, is designed to investigate in detail the capability of muon radiography techniques applied to the imaging of the inner zone of a blast furnace. In particular, the goal of this collaboration is to characterize the internal region (so-called cohesive zone) where the slowly downward-moving material begins to soften and melt, which plays an important role in the performance of the blast furnace itself. In this contribution, we describe the state-of-the-art of the muon tracking system which is currently being developed and installed at a blast furnace on the ArcelorMittal site in Bremen (Germany). Moreover, we will present the GEANT4 simulation framework devised for this application together with the simulation results. Finally, we will show the possible contribution of multiple scattering effects to such peculiar applications.

The spin density matrix elements for the ϱ0, K∗0(892) and F produced in hadronic Z0 decays are measured in the DELPHI detector. There is no evidence for spin alignment of the K∗0(892) and F in the region xp ≤ 0.3 (xp = ppbeam), where ϱ00 = 0.33 ± 0.05 and ϱ00 = 0.30 ± 0.04, respectively. In the fragmentation region, xp ≥ 0.4, there is some indication for spin alignment of the ϱ0 and K∗0(892), since ϱ00 = 0.43 ± 0.05 and ϱ00 = 0.46 ± 0.08, respectively. These values are compared with those found in meson-induced hadronic reactions. For the F, ϱ00 = 0.30 ± 0.04 for xp ≥ 0.4 and 0.55 ± 0.10 for xp ≥ 0.7. The off-diagonal spin density matrix element ϱ1-1 is consistent with zero in all cases.

A new precise measurement of |Vcb| and of the branching ratio BR(B̄0→D∗+ℓ−ν̄ℓ) has been performed using a sample of about 5000 semileptonic decays B̄0→D∗+ℓ−ν̄ℓ, selected by the DELPHI detector at LEP I by tagging the soft pion from D∗+→D0π+. The results are: Vcb=(39.0±1.5(stat.)+2.5−2.6(syst. exp.)±1.3(syst. th.))×10−3, BR(B̄0→D∗+ℓ−ν̄ℓ)=(4.70±0.13(stat.)+0.36−0.31(syst. exp.))%. The analytic dependencies of the differential cross-section and of the Isgur–Wise form factor as functions of the variable w=vB0·vD∗ have also been obtained by unfolding the experimental resolution.

A sample of events enriched in bb̄ quark pairs was selected in the data recorded by the DELPHI experiment at LEP during 1992 and 1993, by the presence of secondary decay vertices from short-lived particles. Using this sample, the average multiplicities of Ks0, K±, p(p̄), Λ(Λ) and of charged particles in bb̄ events have been measured, distinguishing the component from fragmentation and the component coming from the decay of b-hadrons. The measurement of the average charge multiplicity in bb̄ events was used to compute the mean fractional beam energy carried by the primary b-hadron, and the difference in charged particle multiplicity between bb̄ events and light quark (uū, dd̄, ss̄) events.

From the combined data of 1990 and 1991 of the DELPHI experiment at LEP, 13057 4-jet events are obtained and used for determining the contribution of the triple-gluon vertex. The relevant variables are the generalized Nachtmann Reiter angle θ * and the opening angle of the two least energetic jets. A fit to their two-dimensional distribution yields $$C_A /C_F = 2.12 \pm 0.35 and N_C /N_A = 0.46 \pm 0.19,$$ whereC A/C F is the ratio of the coupling strength of the triple-gluon vertex to that of gluon bremsstrahlung from quarks, andN C/N A, the ratio of the number of quark colours to the number of gluons. This constitutes a convincing model-independent proof of the existence of the triple-gluon vertex, since its contribution is directly proportional toC A/C F. The results are in agreement with the values expected from QCD:C A/C F=2.25, andN C/N A=3/8.

Measurements are presented of the cross section ratios Rℓ=σℓ(e+e−→ℓ+ℓ−)σh(e+e−→hadrons) for ℓ=e, μ and τ using data taken from a scan around the Z0. The results are Re=(5.09±o.32±0.18)%, Rμ=(0.46±0.35±0.17)% and Rτ=(4.72±0.38±0.29)% where, for the ratio Re, the t-channel contribution has been subtracted. These results are consistent with the hypothesis of lepton universality and test this hypothesis at the energy scale s∼8300 GeV2. The absolute cross sections σℓ(e+e−→ℓ+ℓ−) have also been measured. From the cross sections the leptonic partial widths Γe=(83.2±3.0±2.4) MeV, (ΓeΓμ)12=(84.6±3.0±2.4)MeV and (ΓeΓτ)12=(82.6±3.3±3.2)MeV have been extracted. Assuming lepton universality the ratio ΓℓΓh=(4.89±0.20±0.12) × 10−2 w was obtained, together with Γℓ=(83.6±1.8±2.2) MeV. The number of light neutrino species is determined to be Nv=3.12±0.24±0.25. Al the data are consistent with the predictions of the standard model.

These final results on e+e- -&gt; W+W- production cross-section measurements at LEP2 use data collected by the DELPHI detector at centre-of-mass energies up to 209 GeV. Measurements of total cross-sections, W angular differential distributions and decay branching fractions, and the value of the CKM element |V_{cs}| are compared to the expectations of the Standard Model. These results supersede all values previously published by DELPHI.

Charm-charm correlation properties are studied in detail for the first time using a sample of DD pairs produced in 360 GeV/c π−p interactions. The data are compared with various models of charm production.

The ratio Rp of the neutral current to charged current cross sections has been measured in the BEBC bubble chamber filled with hydrogen and exposed to the CERN SPS wideband neutrino beam. It is found that an event selection in terms of the transverse momentum of the hadronic system is very effective in reducing backgrounds and enables Rp to be determined with an error of less than 10%. Combining the results from hydrrogen and isoscalar targets, the individual values of the coupling constants uL2 and dL2 are determined separately to be uL2 = 0.15 ± 0.06 and dL2 = 0.17 ± 0.08. The results are compatible with the standard SU (2) × U(1) model. The value of sin2θW determined from this experiment is 0.19 ± 0.04.

Based on a sample of 22 four-prong D0/D0 decays produced in hydrogen by 360 GeV/c π−, we present the following new results: mean lifetime τ = (3.5−0.9+1.4) x 10−13s; production cross section for xF > 0.0, σ = (10.3 ± 3.5) ωb; the D → K±π±π+π− branching ratio = (7.1 ± 2.5)%.

Production of charmed mesons has been observed in neutrino-hydrogen interactions in 285 000 photographs of BEBC exposed to the CERN wide-band neutrino beam. In ∼ 6000 charged current events, two events have been found each giving a three-constraint kinematical fit with production of only one strange particle, namely a K−, which is identified by its characteristic reaction K−p→Σ−π+. These events are thus examples of ΔS=−ΔQ reactions corresponding to charm production on a valence quark. For both events the effective mass of a (K− + pions) system is equal to the D0(1863) mass while the effective mass of this system plus a π+ is equal to the D∗+(2009) mass. The mass difference ΔM=M(D∗+)−MD0 is 145.2 ± 0.6 MeV. The first event is interpreted as νp→μ−pD∗+ and the second as νp→μ−pD∗+π+π−, both with D∗+→D0π+. The rate of inclusive D∗+ production has been estimated for all events by assuming that each negative track in turn is a K− and using the fact that the error on ΔM is small. It is found that the cross section σ(νp→μ−D∗++anything) relative to σ(νp→μ− + anything), above the D∗ threshold, is (4.1 ± 2.4)%.

Neutral triple-gauge-boson couplings ZZZ, ZZγ and Zγγ have been studied with the DELPHI detector using data at energies between 183 and 208 GeV. Limits are derived on these couplings from an analysis of the reactions e+e-→Zγ, using data from the final states γff̄, with f=q or ν, from e+e-→ZZ, using data from the four-fermion final states qq̄qq̄, qq̄μ+μ-, qq̄e+e-, qq̄νν̄, μ+μ-νν̄ and e+e-νν̄, and from e+e-→Zγ*, in which the final state γ is off mass-shell, using data from the four-fermion final states qq̄e+e- and qq̄μ+μ-. No evidence for the presence of such couplings is observed, in agreement with the predictions of the Standard Model.

The data taken by DELPHI at centre-of-mass energies between 189 and 209 GeV are used to place limits on the CP-conserving trilinear gauge boson couplings Delta_g1z, lambda_gamma and Delta_kappag associated to W+W- and single W production at LEP2. Using data from the jjlv, jjjj, jjX and lX final states, where j, l and X represent a jet, a lepton and missing four-momentum, respectively, the following limits are set on the couplings when one parameter is allowed to vary and the others are set to their Standard Model values of zero: Delta_g1z = -0.025^{+0.033}_{-0.030}, lambda_gamma = 0.002^{+0.035}_{-0.035} and Delta_kappag = 0.024^{+0.077}_{-0.081} . Results are also presented when two or three parameters are allowed to vary. All observations are consistent with the predictions of the Standard Model and supersede the previous results on these gauge coupling parameters published by DELPHI.

The muon tomography technique, based on multiple Coulomb scattering of cosmic ray muons, has been proposed as a tool to detect the presence of high density objects inside closed volumes. In this paper a new and innovative method is presented to handle the density fluctuations (noise) of reconstructed images, a well known problem of this technique. The effectiveness of our method is evaluated using experimental data obtained with a muon tomography prototype located at the Legnaro National Laboratories (LNL) of the Istituto Nazionale di Fisica Nucleare (INFN). The results reported in this paper, obtained with real cosmic ray data, show that with appropriate image filtering and muon momentum classification, the muon tomography technique can detect high density materials, such as lead, albeit surrounded by light or medium density material, in short times. A comparison with algorithms published in literature is also presented.

A search for events with one jet and at most one isolated lepton used data taken at LEP-2 by the DELPHI detector. These data were accumulated at a center-of-mass energy of 183 GeV and correspond to an integrated luminosity of 47.7 pb−1. Production of single scalar and vector leptoquarks was searched for. Limits at 95% confidence level were derived on the masses (ranging from 134GeV/c2 to 171GeV/c2 for electromagnetic type couplings) and couplings of the leptoquark states. A search for top-charm flavour changing neutral currents (e+e−→t̄c or charge conjugate) used the semileptonic decay channel. A limit on the flavour changing cross-section via neutral currents was set at 0.55pb (95% confidence level).

In a sample of 3.02 million hadronic Z0 decays collected by the DELPHI detector, 270 Jψ→ ℓ+ℓ− candidates have been selected. A search for fully reconstructed Bc± mesons has yielded one Bc±→Jψπ± candidate, no Bc±→Jψℓ±νℓ candidates, and one Bc±→Jψ, π+π−π± candidate, consistent with expected background in each channel. The following 90% confidence level upper limits are determined: Br(Z0→ Bc±X) × Br(Bc±→Jψπ±) < (1.05 to 0.84) × 10−4 and Br(Z0→ Bc±X) × Br(Bc±→Jψℓ±νℓ) < (5.8 to 5.0) × 10−5, where the ranges quoted correspond to the range of predicted Bc± lifetimes from 0.4 to 1.4 ps, and Br(Z0→ Bc±X) × Br(Bc±→Jψπ+π−π±) < 1.75 × 10−4, constant over the range of predicted Bc± lifetimes.

The hadronic structure of the decay of the τ lepton to three charged particles, τ→3πντ, is studied using data collected by the DELPHI detector at LEP between 1992 and 1995. The invariant mass of the 3π system, m3π, is fitted using the models of Kühn and Santamaria, Isgur, Morningstar and Reader, and Feindt. The 3π and π+π− mass spectra are compared with each model. Below m3π2=2.3GeV2, all are in good qualitative agreement. Above m3π2=2.3GeV2, anomalous behaviour is observed, consistent with the existence of a hitherto unseen decay mode of the τ through a radial excitation of the a1 meson.

Measurements of the trilinear gauge boson couplings WWgamma and WWZ are presented using the data taken by DELPHI in 1998 at a centre-of-mass energy of 189 GeV and combined with DELPHI data at 183 GeV. Values are determined for Delta(g_1^Z) and Delta(kappa_gamma), the differences of the WWZ charge coupling and of the WWgamma dipole coupling from their Standard Model values, and for lambda_gamma, the WWgamma quadrupole coupling. A measurement of the magnetic dipole and electric quadrupole moment of the W is extracted from the results for Delta(kappa_gamma) and lambda_gamma. The study uses data from the final states jjlv, jjjj, lX, jjX and gammaX, where j represents a quark jet, l an identified lepton and X missing four-momentum. The observations are consistent with the predictions of the Standard Model.

Trilinear gauge boson couplings are measured using data taken by DELPHI at 161 GeV and 172 GeV. Values for WWV couplings (V=Z,γ) are determined from a study of the reactions e+e−→W+W− and e+e−→Weν, using differential distributions from the WW final state in which one W decays hadronically and the other leptonically, and total cross-section data from other channels. Limits are also derived on neutral ZVγ couplings from an analysis of the reaction e+e−→γ+invisibleparticles.

Inclusive charged hadron distributions as obtained from the DELPHI measurements at 130, 136, 161, 172 and 183 GeV are presented as a function of the variables rapidity, ξp, p and transversal momenta. Data are compared with event generators and with MLLA calculations, in order to examine the hypothesis of local parton hadron duality. The differential momentum spectra show an indication for coherence effects in the production of soft particles. The relation between the energy dependence of the charged multiplicity and the rapidity distribution is examined.

A study of the production of strange octet and decuplet baryons in hadronic decays of the Z recorded by the DELPHI detector at LEP is presented. This includes the first measurement of the∑ ± average multiplicity. The total and differential cross sections, the event topology and the baryon-antibaryon correlations are compared with current hadronization models.

The total and the differential cross sections for the reaction e+e− → γγ(γ) have been measured with the DELPHI detector at LEP using an integrated luminosity of 36.9 pb−1. The results agree with the QED predictions and consequently there is no evidence for non-standard channels with the same experimental signature. The lower limits obtained on the QED cutoff parameters are Λ+ > 143 GeV and Λ− > 120 GeV, and the lower bound on the mass of an excited electron with an effective coupling constant λγ = 1 is 132 GeV/c2. Upper limits on the branching ratios for the decays Z0 → γγ, Z0 → π0γ, Z0 → ηγ and Z0 → γγγ have been determined to be 5.5 × 10−5, 5.5 × 10−5, 8.0 × 10−5, and 1.7 × 10−5 respectively. All the limits are at the 95% confidence level.

Measurements are presented of short range three-particle correlations in e+e− annihilations at LEP using data collected by the DELPHI detector. At small values of the four-momentum difference, strong three-particle correlations are observed for like-sign (+++ and −−−) and for unlike-sign (++− and +−−) pion combinations which are not a consequence of two-particle correlations. A possible explanation of the observed effects in like-sign combinations is the existence of higher order Bose-Einstein interference, which significantly changes the particle distributions in jets.

A study of the fragmentation properties of charm and bottom quarks intoD mesons is presented. From 263 700Z 0 hadronic decays collected in 1991 with the DELPHI detector at the LEP collider,D 0,D + andD *+ are reconstructed in the modesK − π +,K − π + K + andD 0 π + followed byD 0→K − π +, respectively. The fractional decay widths $$\Gamma {{(Z^0 \to {D \mathord{\left/ {\vphantom {D {\bar D}}} \right. \kern-\nulldelimiterspace} {\bar D}}X)} \mathord{\left/ {\vphantom {{(Z^0 \to {D \mathord{\left/ {\vphantom {D {\bar D}}} \right. \kern-\nulldelimiterspace} {\bar D}}X)} {\Gamma _h }}} \right. \kern-\nulldelimiterspace} {\Gamma _h }}$$ are determined, and first results are presented for the production ofD mesons from $$c\bar c$$ and $$b\bar b$$ events separately. The average energy fraction ofD *± in charm quark fragmentation is found to be 〈X E (D *)〉 c =0.487±0.015 (stat)±0.005 (sys.). Assuming that the fraction ofD s and charm-baryons produced at LEP is similar to that around 10 GeV, theZ 0 partial width into charm quark pairs is determined to beΓ c /Γ h =0.187±0.031 (stat)±0.023 (sys). The probability for ab quark to fragment into $$\bar B_s $$ orb-baryons is inferred to be 0.268±0.094 (stat)±0.100 (sys) from the measured probability that it fragments into a $$\bar B^0 $$ orB −.

The 40 MHz bunched muon beam set up at CERN was used in May 2003 to make a full test of the drift tubes local muon trigger. The main goal of the test was to prove that the integration of the various devices located on a muon chamber was adequately done both on the hardware and software side of the system. Furthermore the test provided complete information about the general performance of the trigger algorithms in terms of efficiency and noise. Data were collected with the default configuration of the trigger devices and with several alternative configurations at various angles of incidence of the beam. Tests on noise suppression and di-muon trigger capability were performed.

A search has been made for pairs oade for pairs of scalar quarks (squarks) produced in e+e− annihilations at LEP (s≅Mz0), and decaying into a standard quark and a neutral, non-interacting, stable, massive particle (the lightest supersymmetric particle, LSP). The search has been conducted for differences in the mass of the squark and LSP of 2 GeV/c2 and above. Up squarks with masses below 42 GeV/c2 and down squarks below 43 GeV/c2 were excluded. Six squark flavours degenerate in mass were excluded below 45 GeV/c2.

A search for stable and long-lived heavy charged particles used the data taken by the DELPHI experiment at energies from 130 to 183 GeV. The Cherenkov light detected in the Ring Imaging Cherenkov Detector and the ionization loss measured in the Time Projection Chamber identify heavy particles from masses of 2 to nearly 89 GeV/c2. Upper limits are given on the production cross-section and masses of sleptons, free squarks with a charge of q=±23e and hadronizing squarks.

Higgs bosons predicted by the fermiophobic scenario within Two Higgs Doublets Models were searched for in the data collected by the DELPHI detector at centre-of-mass energies between 189 GeV and 202 GeV, corresponding to a total integrated luminosity of 380 pb−1. No signal was found and confidence limits were derived in the framework of possible extensions of the Standard Model Higgs sector.

The ratio of the CKM quark-mixing matrix elements |Vub|/|Vcb| has been measured using B hadron semileptonic decays. The analysis uses the reconstructed mass M_X of the secondary hadronic system produced in association with an identified lepton. Since B -> X_u lepton anti-nu transitions are characterised by hadronic masses below those of the D mesons produced in B -> X_c lepton anti-nu transitions, events with a reconstructed value of M_X significantly below the D mass are selected. Further signal enrichments are obtained using the topology of reconstructed decays and hadron identification. A fit to the numbers of decays in the b -> u enriched and depleted samples with M_X above and below 1.6 GeV/c^2 and to the shapes of the lepton energy distribution in the B rest frame gives |Vub|/|Vcb|= 0.103^{+0.011}_{-0.012} (stat.) +/- 0.016 (syst.) +/- 0.010 (model) and, correspondingly, a charmless semileptonic B decay branching fraction of BR(B -> X_u lepton anti-nu) = (1.57 +/- 0.35 (stat.) +/- 0.48 (syst.) +/- 0.27 (model)) x 10^{-3}.

The weak mixing angle has been measured from the charge asymmetry of hadronic events with two different approaches using the DELPHI detector at LEP. Both methods are based on a momentum-weighted charge sum to determine the jet charge in both event hemispheres. In a data sample of 247 300 multihadronic Z0 decays a charge asymmetry of 〈QF〉 − 〈QB〉 = −0.0076±0.0012(stat.)±0.0005(exp. syst.)±0.0014(frag.) and a raw forward-backward asymmetry of ArawFB = −0.0109±0.0020(stat.)±0.0010(exp. syst.)±0.0017(frag.) have been measured. This result corresponds to a value of sinθeff=0.2345±0.0030(exp.)±0.0027(frag.), sin2θMS=0.2341±0.0030(exp.)±0.0027(frag.) and to sin2θW=1−m2W/m2Z=0.2299± 0.0030(exp.)±0.0027(frag.)±0.0028(theor.). The experimental error is the quadratic sum of the statistical and the experimental systematic error and the theoretical error originates from a value of mt=130±40 GeV/c2 and a range of mH from 45 GeV/c2 to 1000 GeV/c2.

A search for fully reconstructed Λb0 beauty baryons is performed using about 3 million Z decays collected with the DELPHI detector at LEP. The analysis relies on the combined use of the accurate tracking and of the hadron identification capabilities of DELPHI. A total of four events has been found, three in the Λc+π− channel and one in the Λc+a1− channel over a small background. The Λb0 beauty baryon mass is measured to be (5668 ± 16 (stat.) ± 8 (syst.)) MeV/c2.

Rare decays of beauty particles were studied in several charmless modes using the data collected with the DELPHI detector at LEP from 1991 to 1994. These decays are mediated by both tree levelb→u and one-loop penguinb→s, d transitions. Evidence for charmlessB decays was obtained in two body hadronic modes. The branching ratios ofB 0 toπ + π − orK + π − andB − toρ 0 π − orK*0 π − were found to be (2.8 −1.0 +1.5 ±0.2)×10−5 and (1.7 −0.8 +1.2 ±0.2)×10−4 respectively. The fraction of these decays with a charged kaon in the final state that is not from the spectators quark, was measured to be 0.58±0.18. Upper limits were set at 90% confidence level on the branching ratios for three and four body charmless hadronic decays in the range of (1–3)×10−4, for inclusive radiativeb→sγ decays at 5.4×10−4, for the exclusive radiative decaysB 0 →K*(892)0 γ andB 0 →φ(1020)γ at 2.1×10−4 and 7.0×10−4 respectively, and for dineutrino decays $$b \to s\nu \bar \nu $$ , in the exclusive channels $$B_d^0 \to K^* (892)^0 \nu \bar \nu $$ and $$B_s^0 \to \phi (1020)\nu \bar \nu $$ at 1.0×10−3 and 5.4×10−3 respectively. The limits on dineutrino decays constrain theories with a newU(1) gauge boson coupling predominantly to the third family of fermions.

Evidence for the production of b-flavoured baryons in Z0 decays is reported from the analysis of 365 000 hadronic events collected by the DELPHI detector. Assuming that most of the weakly decaying b flavoured baryons produced by the Z0 are Λb, the observed signal of (Λ−+Λl+) pairs, where l is a high transverse momentum lepton in the same jet as the Λ, leads to a production rate: f(b→Λb)×Br(Λb→Λlν X) = (0.41±0.13±0.09)%. Using a sample of 18 reconstructed Λb decay vertices, the lifetime is determined to be τ(Λb) = (1.04+0.48−0.38±0.10) ps.

Measurements of on-shell ZZ production are described, using data from the DELPHI experiment at LEP in e+e- collisions at centre-of-mass energies between 183 and 209 GeV, corresponding to an integrated luminosity of about 665 pb^{-1}. Results obtained in each of the final states q anti-q q anti-q, nu anti-nu q anti-q, mu+ mu- q anti-q, e+ e- q anti-q, tau+ tau- q anti-q, l+ l- l+ l-, and nu anti-nu l+ l- (with l=e,mu) are presented. The measured production cross-sections are consistent with the Standard Model expectations. These results update and supersede those already published at 183 and 189 GeV.

In the reaction e+e-→WW→(q1q̄2)(q3q̄4) the usual hadronization models treat the colour singlets q1q̄2 and q3q̄4 coming from two W bosons independently. However, since the final state partons may coexist in space and time, cross-talk between the two evolving hadronic systems may be possible during fragmentation through soft gluon exchange. This effect is known as colour reconnection. In this article the results of the investigation of colour reconnection effects in fully hadronic decays of W pairs in DELPHI at LEP are presented. Two complementary analyses were performed, studying the particle flow between jets and W mass estimators, with negligible correlation between them, and the results were combined and compared to models. In the framework of the SK-I model, the value for its κ parameter most compatible with the data was found to be: κSK-I=2.2+2.5 -1.3 corresponding to the probability of reconnection $\mathcal{P}_{\text{reco}}$ to be in the range $0.31 <\mathcal{P}_{{\text{reco}}} < 0.68$ at 68% confidence level with its best value at 0.52.

Muon bremsstrahlung photons converted in front of the DELPHI main tracker (TPC) in dimuon events at LEP1 were studied in two photon kinematic ranges: 0.2<E γ ≤1 GeV and transverse momentum with respect to the parent muon p T <40 MeV/c, and 1<E γ ≤10 GeV and p T <80 MeV/c. A good agreement of the observed photon rate with predictions from QED for the muon inner bremsstrahlung was found, contrary to the anomalous soft photon excess that has been observed recently in hadronic Z 0 decays. The obtained ratios of the observed signal to the predicted level of the muon bremsstrahlung are 1.06±0.12±0.07 in the photon energy range 0.2<E γ ≤1 GeV and 1.04±0.09±0.12 in the photon energy range 1<E γ ≤10 GeV. The bremsstrahlung dead cone is observed for the first time in the direct photon production at LEP.

The effect of the heavy b-quark mass on the two, three and four-jet rates is studied using LEP data collected by the DELPHI experiment at the Z peak in 1994 and 1995. The rates of b-quark jets and light quark jets (ℓ=uds) in events with n=2, 3, and 4 jets, together with the ratio of two and four-jet rates of b-quarks with respect to light-quarks, Rn bℓ, have been measured with a double-tag technique using the CAMBRIDGE jet-clustering algorithm. A comparison between experimental results and theory (matrix element or Monte Carlo event generators such as PYTHIA, HERWIG and ARIADNE) is done after the hadronisation phase. Using the four-jet observable R4 bℓ, a measurement of the b-quark mass using massive leading-order calculations gives: $m_b(M_Z) = 3.76 \pm0.32 ({\text{stat}}) \pm0.17 ({\text{syst}}) \pm0.22 ({\text{had}}) \pm0.90 ({\text{theo}})\,\text{GeV}/c^2\,.$ This result is compatible with previous three-jet determinations at the MZ energy scale and with low energy mass measurements evolved to the MZ scale using QCD renormalisation group equations.