Studies of Quantum Chromodynamics with the ALEPH Detector

1998

Previously published and as vet unpublished QCD results obtained with the ALEPH detector at LEP1 are presented. The unprecedented statistics allows detailed studies of both perturbative and non-perturbative aspects of strong interactions to be carried out using hadronic Z and tau decays. The studies presented include precise determinations of the strong coupling constant. tests of its flavour independence, tests of the SU(3) gauge structure of QCD, study of coherence effects, and measurements of single-particle inclusive distributions and two-particle correlations for many identified baryons and mesons. (C) 1998 Elsevier Science B.V.

Four-jet final state production in e+e- collisions at centre-of-mass energies of 130 and 136 GeV

1996

The four-jet final state is analyzed to search for hadronic decays of pair-produced heavy particles. The analysis uses the ALEPH data collected at LEP in November 1995 at centre-of-mass energies of 130 and 136 GeV, corresponding to a total integrated luminosity of 5.7 pb(-1). An excess of four-jet events is observed with respect to the standard model predictions. In addition, these events exhibit an enhancement in the sum of the two di-jet masses around 105 GeV/c(2). The properties of these events are studied and compared to the expectations from standard processes and to pair production hypotheses. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-…

Search for contact interactions in the reactionse + e −→l + l − ande + e −→γγ

1993

Contact interactions are searched for using the differential cross sections for the reactions e + e -→ e + e -, e + e -→ µ + µ -, e + e -→ τ + τ - and e + e -→γγ measured at 12 energies around the Z peak and corresponding to about 20 pb-1 of cumulated luminosity. Four-fermion contact term models assuming various chiralities of lepton currents are fitted to the lepton data and lower limits on the energy scale Λ of such terms are set at 95% c.l. The limits vary in the range 0.9 4.7 TeV, depending on the model and on the lepton flavour. The eeγγ contact terms are searched for assuming various chiralities. Limits on the energy scale Λ between 79 and 130 GeV are extracted from the data. The resu…

Transverse momentum correlations in hadronic Z decays

1997

Using data obtained with the ALEPH detector at the Z resonance, a measure based on transverse momentum is shown to exhibit a correlation between the two halves of a hadronic event which cannot be explained by energy-momentum conservation, flavour conservation, the imposition of an event axis or imperfect event reconstruction. Two possible interpretations based on existing Monte Carlo models are examined: a) ARIADNE, with the correlation forming early in the parton shower and with the transition from partons to hadrons playing only a minor part; b) JETSET, with the correlation forming at the fragmentation stage. A correlation technique based on a jet cluster analysis is used to make a compar…

Measurement of trilinear gauge couplings in e(+)e(-) collisions at 161 GeV and 172 GeV

1998

Trilinear gauge boson couplings are measured using data taken by DELPHI at 161 GeV and 172 GeV, Values for WWV couplings (V = Z,gamma) are determined from a study of the reactions e(+)e(-) --> W+W- and e(+)e(-) --> We nu, 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 ZV gamma couplings from an analysis of the reaction e(+)e(-) --> gamma + invisible particles. (C) 1998 Elsevier Science B.V.

Search for charginos and neutralinos with R-parity violation at =130 136

1996

Searches for charginos and neutralinos produced in e+e− collisions at centre-of-mass energies of 130 and 136 GeV have been performed under the assumptions that R-parity is not conserved, that the dominant R-parity violating coupling involves only leptonic fields, and that the lifetime of the lightest supersymmetric particle can be neglected. In the 5.7 pb−1 data sample collected by ALEPH, no candidate events were found. As a result, chargino and neutralino masses and couplings are constrained and the domains previously excluded at LEP1 are extended.

Measurement of the b → τ-ν̄τX branching ratio

1993

The definitions of “anthropology” found in various dictionaries cover a whole range of terms and in this section we provide an overview of all its connotations. In this way a variety of reflections about the essence of man become possible, for instance as : summit of creation; source of his own values; specific biological reality; intelligence (but what is this, really?); knowing subject or object of knowledge; social being and product of a culture. Following these lines of thought one realises that all these preoccupations have already been taken up, or at least touched upon, by communication theory.

Search for high mass photon pairs in (f= e, μ, τ, v, q) at LEP

1993

Abstract The result of a search for high mass photon pairs from the processes e + e − → f f γγ (f = e, μ, τ, v and q) with the ALEPH detector is reported. The result for f = e , μ and τ is to be compared with the observation of 4 events by the L3 Collaboration with invariant masses, M γγ , of the two photons near 60 GeV. From a data sample approximately twice as large taken from 1990 to 1992, 6 events are found with M γγ distributed between 50 GeV and 72 GeV, while 4.9 events are expected from a QED calculation. There is no evidence for a mass peak; only one event ( μ + μ − γγ ) at M γγ = 59.4 ± 0.2 GeV is compatible with the L3 observation. In addition, for M γγ > 50 GeV, no event is found…

Study of muon-pair production at centre-of-mass energies from 20 to 136 GeV with the ALEPH detector

1997

The total cross section and the forward-backward asymmetry for the process e(+)e --> mu(+)mu(-)(n gamma) are measured in the energy range 20-136 GeV by reconstructing the effective centre-of-mass energy after initial state radiation. The analysis is based on the data recorded with the ALEPH detector at LEP between 1990 and 1995, corresponding to a total integrated luminosity of 143.5 pb(-1). Two different approaches are used: in the first one an exclusive selection of events with hard initial state radiation in the energy range 20-88 GeV is directly compared with the Standard Model predictions showing good agreement. In the second one, all events are used to obtain a precise measurement of …

Studies of QCD in ${\rm e^+ e^-}\to $ hadrons at $E_{\rm cm} = 130$ and 136 GeV

1997

Studies of QCD in $\mbox{e}^+\mbox{e}^- \rightarrow$ Hadrons at $E_{cm} = $} 130 and 136 GeV The ALEPH Collaboration An analysis of the properties of hadronic final states produced in electron-positron annihilation at centre-of-mass energies of 130 and 136 GeV is presented. The measurements are based on a data sample of 5.7 $\mbox{pb}^{-1}$ collected in November 1995 with the \Aleph detector at LEP. Inclusive charged particle distributions, jet rates and event-shape distributions are measured and the results are compared with the predictions of QCD-based models. From the measured distributions quantities are determined for which the dependence on the centre-of-mass energy can be predicted b…

Search for a new weakly interacting particle

1991

Abstract A search for events of the type e + e − →l + l − X 0 , where X 0 can be any weakly interacting particle which couples to the Z, has been performed with the ALEPH detector at LEP, by searching for acollinear lepton pairs. Such particles can be excluded up to a mass of 7.0 GeV/c 2 for a value of the ratio of branching fractions, Br( Z →X 0 l + l − )/Br(Z→ l + l − ), greater than 2.5 × 10 −3 if the X 0 has third component of isospin, I 3 greater than 1 2 and decays to a pair of virtual gauge bosons. When this analysis is combined with the previous results of the Higgs particle searches from ALEPH, this limit can be extended to an X 0 mass of 60 GeV/c 2 .

Inclusive production of neutral vector mesons in hadronic Z decays

1996

Data on the inclusive production of the neutral vector mesons rho(0)(770), omega(782), K*(0)(892), and phi (1020) in hadronic Z decays recorded with the ALEPH detector at LEP are presented and compared to Monte Carlo model predictions. Bose-Einstein effects are found to be important in extracting a reliable value for the p(0) production rate. An average p(0) multiplicity of 1.45 +/- 0.21 per event is obtained. The omega is detected via its three pion decay mode omega --> pi(+)pi(-)pi(0) and has a total rate of 1.07 +/- 0.14 per event. The multiplicity of the K*(0) is 0.83 +/- 0.09, whilst that of the phi is 0.122 +/- 0.009, both measured using their charged decay modes. The measurements pro…

Four-fermion production in $e^+e^-$ collisions at centre-of-mass energies of 130 and 136 GeV

1996

Four-fermion events have been selected in a data sample of 5.8 pb(-1) collected with the ALEPH detector at centre-of-mass energies of 130 and 136 GeV. The final states l(+)l(-), l(+)l(-)l(+)l(-), , and <l(+)l(-) have been examined Five events are observed in the data, in agreement with the Standard Model predictions of 6.67 +/- 0.38 events from four-fermion processes and 0.14(-0.05)(+0.19) from background processes. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; Sanchez, Federico/F-5809-2012; Ferrante, Isidoro/F-1017-2012

Measurements of the charged particle multiplicity distribution in restricted rapidity intervals

1995

Charged particle multiplicity distributions have been measured with the ALFPH detector in restricted rapidity intervals \Y\ less than or equal to 0.5, 1.0, 1.5, 2.0 along the thrust axis and also without restriction on rapidity. The distribution for the full range can be parametrized by a log-normal distribution. For smaller windows one finds a more complicated structure, which is understood to arise from perturbative effects. The negative-binomial distribution fails to describe the data both with and without the restriction on rapidity. The JETSET model is found to describe all aspects of the data while the width predicted by HERWIG is in significant disagreement.

Measurement of the ratio using event shape variables

1993

Abstract The branching fraction of Z → b b relative to all hadronic decays of the Z has been measured using event shape variables to preferentially select Z → b b events. The method chosen applies a combination of shape discriminators and the selection of high transverse momentum leptons to event hemispheres. From a sample of 440 000 hadronic Z decays collected with the ALEPH detector at LEP, the ration Γ b b Γ had = 0.228±0.005( stat. )±0.005( syst. ) is measured.

Measurement of the inclusive charmless and double-charm B branching ratios

1998

The DELPHI experiment at LEP has measured the inclusive charmless B hadron decay branching ratio, the B branching ratio into two charmed particles, and the total number of charmed particles per B decay, using the hadronic Z data taken between 1992 and 1995. The results are extracted from a fit to the b-tagging probability distribution based on the precise impact parameter measurements made using the microvertex detector. The inclusive charmless B branching ratio, including B decays into hidden charm (c (c) over bar), is measured to be 0.033 +/- 0.021. The B branching ratio into two open charmed particles is 0.136 +/- 0.042. The mean number of charmed particles per B decay (including hidden …

First evidence for a charm radial excitation, D

1998

Using D*+ mesons exclusively reconstructed in the DELPHI detector at LEP, an excess of 66 +/- 14(stat.) events is observed in the D(*+)pi(+)pi(-) final state with a mass of 2637 +/- 2(stat.) +/- 6(syst.) MeV/c(2) and a full width smaller than 15 MeV/c(2) (95% C.L.). This signal is compatible with the expected decay of a radially excited D*' (J(P) = 1(-))meson. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

PHP39 Explaning Differences in EU5 Market Penetration Levels and Rates of Biosimilars: The Case of Epoetine, Granulocyte-Colony Stimulating Factor, a…

2012

Charm counting in b decays

1996

??? The inclusive production of charmed particles in Z--> decays has been measured from the yield of D-0, D+, D-s(+) and Lambda(c)(+) decays in a sample of events with high b purity collected with the ALEPH detector from 1992 to 1995. From these measurements, adding the charmonia production rate and an estimate of the charmed strange baryon contribution, the average number of charm quarks per b decay is determined to be n(c)=1.230+/-0.036+/-0.038+/-0.053, where the uncertainties are due to statistics, systematic effects and branching ratios, respectively.

Energy dependence of inclusive spectra in e+ e- annihilation

1999

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, xi(p), 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. (C) 1999 Elsevier Science B.V. All rights reserved.

Search for the sgoldstino at √s = 189 to 202 GeV.

2000

A search for the supersymmetric partner of the goldstino, the sgoldstino S, at LEP2 is presented. The production Sgamma followed by S decay into two gluons or into two photons was studied at 189 - 202 GeV LEP centre-of-mass energies. No evidence for the S production was found and limits on the S mass corresponding to different theory parameters are given.

Test of the flavour independence of αs

1995

Abstract 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.

Search for a non-minimal Higgs boson produced in the reaction →

1993

Abstract A data sample corresponding to 1.23 million hadronic Z decays collected by the ALEPH detector at LEP has been searched for signals of the production of a non-minimal CP-even Higgs boson h in the reaction e + e − → hZ ∗ . The h decay modes considered were: those of the minimal standard model Higgs boson, with modified branching ratios; decays into a pair of CP-odd Higgs bosons A; and decays into invisible final states. Only one event was found, a very acoplanar e+e− pair which could originate from the standard model background process e + e − → e + e − v v . Upper limits for the cross-section of the reaction e + e − → hZ ∗ have been derived as a function of mh, the mass of the Higgs…

First measurement of the quark-to-photon fragmentation function

1996

Earlier measurements at LEP of isolated hard photons in hadronic Z decays, attributed to radiation from primary quark pairs, have been extended in the ALEPH experiment to include hard photon production inside hadron jets. Events are selected where all particles combine democratically to form hadron jets, one of which contains a photon with a fractional energy z greater than or equal to 0.7. After statistical subtraction of non-prompt photons, the quark-to-photon fragmentation function, D(z), is extracted directly from the measured 2-jet rate. By taking into account the perturbative contributions to D(z) obtained from an O(alpha alpha(s)) QCD calculation, the unknown non-perturbative compone…

Production of orbitally excited charm mesons in semileptonic B decays

1997

A sample of 3.6 million hadronic Z decays recorded between 1991 and 1995 with the ALEPH detector at LEP is used to investigate semileptonic decays of B mesons into final states involving orbitally excited charm mesons. Topological vertex criteria are used to search for decays involving narrow D** states as well as wide D** resonances and non-resonant D(*)pi final states. The sum of the branching ratios for these processes is measured to be Br((B) over bar --> D pi l(-)(v) over bar) + Br((B) over bar --> D*pi l(-)(v) over bar) = (2.26 +/-t 0.29(stat) +/- 0.33(syst))%, which accounts for a significant fraction of the deficit between inclusive measurements and the sum of exclusive semileptonic…

A search for invisible Higgs bosons produced in e+e- interactions at LEP 2 energies

1999

Searches for HZ production with the Higgs boson decaying into an invisible final state have been performed with the data collected by the DELPHI experiment up to the centre-of-mass energy of 183 GeV. The hadronic and muon pair final states of the Z boson were analysed. From the absence of signal, upper limits on the cross-section and the corresponding Higgs boson mass limits were set at 95% confidence level. The results are interpreted as excluded parameter regions in the framework of the minimal supersymmetric standard model and in the simplest Majoron model with one Higgs doublet and one Higgs singlet field. (C) 1999 Elsevier Science B.V. All rights reserved.

Search for chargino pair production in scenarios with gravitino LSP and stau NLSP at GeV at LEP

1999

Promptly decaying lightest charginos were searched for in the context of scenarios with gravitino LSP. It was assumed that the stau is the next to lightest supersymmetric particle (NLSP). Data collected with the DELPHI detector at a centre-of-mass energy near 183~{~mbox{${mathrm{GeV}}$}}\nwere analysed combining the methods developed in previous searches. No evidence for the production of these particles was found. Hence, limits were derived at 95% confidence level. The mass of charginos was found to be greater than 85.5~GeV/$c^2$ for $m_{ ilde{chi}^+_1}-m_{ ilde{ au}_1}geq 0.3 {mathrm{GeV}}/c^2$, independently of the mass of the gravitino.

Improved measurement of theB 0 andB + meson lifetimes

1996

The lifetimes of the B 0 and B + mesons have been measured with the Aleph detector at LEP, using approximately 3 million hadronic Z decays collected in the period 1991 1994. In the first of three methods, semileptonic decays of B 0 and B + mesons were partially reconstructed by identifying events containing a lepton with an associated D*- orbar D^0 meson. The second method used fully reconstructed B 0 and B + mesons. The third method, used to measure the B 0 lifetime, employed a partial reconstruction technique to identify B 0→ D*- π + X decays. The combined results are begin{gathered} tau _0 = 1.55 ± 0.06 ± 0.03 ps, \ tau _ + = 1.58 ± 0.09 ± 0.03 ps, \ tfrac{{tau _ + }}{{tau _0 }} = 1.03 ±…

Production of excited beauty states in Z decays

1996

A data sample of about 3.0 million hadronicZ decays collected by the ALEPH experiment at LEP in the years 1991 through 1994 is used to make an inclusive selection of B hadron events. In this event sample 4227±140±252B* mesons in the decayB*→Bγ and 1944±108±161B** u,d mesons decaying into a B meson and a charged pion are reconstructed. Here and in the followingB** u,d denotes the eightL=1(bū) and (bd) states and their charge conjugate. For the well establishedB* meson the following quantities are obtained:ΔM=M B*−MB=(45.30±0.35±0.87) MeV/c2 andN B*/(N B+N B*)=(77.1±2.6±7.0)%. The angular distribution of the photons in theB* rest frame is used to measure the relative contribution of longitudi…

Measurement of the and B− meson lifetimes

1993

Abstract The lifetimes of the B 0 and B − mesons have been measured with the ALEPH detector at LEP. Semileptonic decays of B 0 and B − mesons were partially reconstructed by identifying events containing a lepton with an associated D ∗+ or D 0 meson. The proper time of the B meson was estimated from the measured decay length and the momentum and mass of the D -lepton system. A fit to the proper time of 77 D ∗+ l − and 77 D 0 l − candidates, combined with a constraint on the lifetime ratio ( τ − τ 0 ) arising from the relative rates of observed D ∗+ l − and D 0 l − events, yielded the following lifetimes: τ 0 =1.52 −0.18 +0.20 ( stat. ) −0.13 +0.07 ( syst. ) ps , τ − = 1.47 −0.19 +0.22 ( sta…

The topology dependence of charged particle multiplicities in three-jet events

1997

A study of individual jet and whole-event charged particle multiplicities in three-jet events measured in e(+)e(-) annihilation at the Z reveals a significant topology dependence. Mean jet multiplicities are inadequately described by jet energies; interjet angles must also be specified. Quantitative tests suggest that it is necessary to use transverse-momentum-like scales to describe the data. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; St.Denis, Richard/C-8997-2012; Sanchez, Federico/F-5809-2012; Forti, Francesco/H-3035-2011; Ferrante, Isidoro/F-1017-2012

Determination of sin^2(theta(eff)(w)) using jet charge measurements in hadronic Z decays

1996

The electroweak mixing angle is determined with high precision from measurements of the mean difference between forward and backward hemisphere charges in hadronic decays of the Z. A data sample of 2.5 million hadronic Z decays recorded over the period 1990 to 1994 in the ALEPH detector at LEP is used. The mean charge separation between event hemispheres containing the original quark and antiquark is measured for b (b) over bar and c (c) over bar events in subsamples selected by their long lifetimes or using fast D*'s. The corresponding average charge separation for light quarks is measured in an inclusive sample from the anticorrelation between charges of opposite hemispheres and agrees wi…

Energy dependence of event shapes and of $\alpha_s$ at LEP 2

1999

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 M-Z with the DELPHI detector at LEP. From the event shapes, the strong coupling alpha(s) is extracted in O(alpha(s)(2)), 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 M-Z, the energy dependence (running) of alpha(s) is accessible. The logarithmic energy slope of the inverse strong coupling is measured to be d alpha(s)(-1)/d log(E-cm) = 1.39 +/- 0.34 (stat) +/- 0.17(syst), in good ag…

Measurement of the branching ratio and an upper limit on

1995

Abstract Using 1.45 million hadronic Z decays collected by the ALEPH experiment at LEP, the b → τ − ν - τ X branching ratio is measured to be 2.75 ± 0.30 ± 0.37%. In addition an upper limit of 1.8 × 10 −3 at 90% confidence level is placed upon the exclusive branching ratio of B − → τ − ν - τ . These measurements are consistent with SM expectations, and put the constraint tan β M h ± GeV −1 at 90% confidence level on all Type II two Higgs doublet models (such as the MSSM).

Inclusive production of neutral pions in hadronic Z decays

1997

A measurement of the inclusive production of pi(0) mesons in hadronic Z decays is presented and compared to Monte Carlo model predictions. The analysis is based on approximately 2 million hadronic events recorded with the ALEPH detector at LEP at a centre-of-mass energy of root s = 91.2 GeV. Neutral pions are reconstructed using photons measured in the electromagnetic calorimeter and photons from conversion pairs. The inclusive pi(0) momentum spectrum is measured in the range 0.025 < x(p) = p/p(beam) < 1. In this range the number of pi(0) per hadronic Z is found to be 4.80 +/- 0.07(stat) +/- 0.31(sys). The differential inclusive pi(0) cross section is also measured as a function of transver…

Observation of charmless hadronic B decays

1996

Four candidates for charmless hadronic B decay are observed in a data sample of four million hadronic Z decays recorded by the ALEPH detector at LEP. The probability that these events come from background sources is estimated to be less than 10(-6). The average branching of weakly decaying B hadrons (a mixture of B-d(0), B-s(0) and Lambda(b) weighted by their production The average branching ratio of weakly decaying B hadrons (a mixture of B-d(0) cross sections and lifetimes, here denoted B) into two long-lived charged hadrons (pions, kaons or protons) is measured to be Br(B-->h(+)h(-))=(1.7(-0.7)(+1.0)+/-0.2)x10(-5). The relative branching fraction Br(B-d(s)(0)-->pi(+)pi(-)(K-))/Br(B-d(s)(…

Measurement of the strong coupling constant using τ decays

1993

The strong coupling constant is determined from the leptonic branching ratios, the lifetime, and the invariant mass distribution of the hadronic final state of the tau lepton, using data accumulated at LEP with the ALEPH detector. The strong coupling constant measurement, alpha(s), (m(tau)2) = 0.330 +/-0.046, evolved to the Z mass, yields alpha(s)(M(Z)2) = 0. 1 18 +/- 0.005. The error includes experimental and theoretical uncertainties, the latter evaluated in the framework of the Shifman, Vainshtein and Zakharov (SVZ) approach. The method allows the non-perturbative contribution to the hadronic decay rate to be determined to be 0.3 +/- 0.5% . RI Perrier, Frederic/A-5953-2011; ANTONELLI, AN…

Tau hadronic branching ratios

1996

From 64492 selected tau-pair events, produced at the Zeta(o) resonance, the measurement of the tau decays into hadrons from a global analysis using 1991, 1992 and 1993 ALEPH data is presented. Special emphasis is given to the reconstruction of photons and pi(o)'s, and the removal of fake photons. A detailed study of the systematics entering the pi(o) reconstruction is also given. A complete and consistent set of tau hadronic branching ratios is presented for 18 exclusive modes. Most measurements are more precise than the present world average. The new level of precision reached allows a stringent test of tau - mu universality in hadronic decays, g(tau)/g(mu) = 1.0013 +/- 0.0095, and the fir…

Two-particle angular correlations in e(+)e(-) interactions compared with QCD predictions

1998

Two-particle angular correlations in jet cones have been measured in e(+)e(-) annihilation into hadrons at LEP energies (root s = 91 and 183 GeV) and are compared with QCD predictions using the LPHD hypothesis. Two different functions have been tested. While the differentially normalized correlation function shows substantial deviations from the predictions, a globally normalized correlation function agrees well. The size of alpha(s)(eff) land other QCD parameters) and its running with the relevant angular scale, the validity of LPHD, and problems due to non-perturbative effects are discussed critically. (C) 1998 Elsevier Science B.V. All rights reserved.

Production and decay of charmed mesons at the Z resonance

1991

Abstract In a sample of 190 000 hadronic Z decays, three signals of charm production are observed: two from the exclusive decays D ° → K − π + and D ∗+ → D °π + → K − π + π + and one in the transverse-momentum distribution of soft hadrons relative to the nearest jet. The features of these signals are in good agreement with expectations based on the standard model and previous measurements of the branching fractions. The number of D ∗± → K ± π ± π ± per hadronic decay of the Z is measured to be (5.11±0.34) × 10 −3 , and the branching ratio B(D 0 → K − π + ) is (3.62 ± 0.34 ± 0.44)%. Charm hadronization has been studied. The average fraction of the beam energy carried by the D ∗ meson is foun…

Measurement of the D∗± cross section in two photon collisions at LEP

1995

Abstract 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 co…

Measurement ofD s + meson production inZ decays and of theB s 0 lifetime

1995

D + mesons produced inZ 0→bb events were separated from theZ 0→cc component using a lifetime tag. Using a sample of 1.5 million hadronicZ decays collected with theAleph detector theB 0 andD s + yields have been measured: $$\begin{gathered} \hfill B(b \to \bar B_s^0 )B(\bar B_s^0 \to D_s^ + ) = 0.088 \pm 0.020(stat.) \\ \hfill \pm 0.020(stat.) \\ \hfill B(c \to D_s^ + ) = 0.088 \pm 0.020(stat.)_{ - 0.016}^{ + 0.019} (syst.) \\ \end{gathered} $$ TheB 0 lifetime was measured in aB 0 enriched sample reconstructing the decay length from the vertex of theD + with a hadron from theB 0 decay. The result obtained is: $$\tau _{B_s } = 1.61_{ - 0.29}^{ + 0.30} (stat.)_{ - 0.016}^{ + 0.018} (syst.)$$ p…

Determination of |Vub|/|Vcb| with DELPHI at LEP

2001

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 -&gt; X_u lepton anti-nu transitions are characterised by hadronic masses below those of the D mesons produced in B -&gt; 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 -&gt; u enriched and depleted samples with M_X above and…

Measurement of the

1997

A new method is presented for the measurement of the mean $\tau$ lepton lifetime using events in which $\tau$'s are pair-produced and both $\tau$'s decay to hadrons and $\nu_\tau$. Based on the correlation between the two $\tau$'s produced at a symmetric $e^+ e^-$ collider, the 3DIP method relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the $\tau$ decay angles. Using the data collected from 1992 to 1994 with the ALEPH detector at LEP, a $\tau$ lifetime of $288.0 \pm 3.1 \pm 1.3 $\fs is obtained from the sample in which both $\tau$'s decay to one charged track, and $292.8 \pm 5.6 \pm 3.0 $\fs from the…

Measurements of |Vcb|, form factors and branching fractions in the decays → ℓ and → ℓ

1997

Two samples of exclusive semileptonic decays, 579 B0 -> D*+l-νl events and 261 B0 -> D+l-νl events, are selected from approximately 3.9 million hadronic Z decays collected by the ALEPH detector at LEP. From the reconstructed differential decay rate of each sample, the product of the hadronic form factor F(ω) at zero recoil of the D(*)+ meson and the CKM matrix element Vcb are measured to be FD*+ (1) Vcb = (31.9 +/- 1.8stat +/- 1.9syst) × 10-3,FD+ (1) Vcb = (27.8 +/- 6.8stat +/- 6.5syst) × 10-3. The ratio of the form factorsFD+ (1) and FD*+ (1) is measured to beFD+ (1)/FD*+ (1) = 0.87 +/- 0.22stat +/- 0.21syst. A value of Vcb is extracted from the two samples, using theoretical constraints o…

Study of the four-jet anomaly observed at LEP centre-of-mass energies of 130 and 136 GeV

1999

The four-jet events collected by DELPHI during the special LEP run at centre-of-mass energies of 130 and 136 GeV in 1997 with an integrated luminosity of 5.9 pb(-1) are analysed. Their rate and the distributions of their di-jet masses, their smallest jet charges, and their di-jet charge separations all agree well with Standard Model predictions. Thus the hypothesis of pair production of a new particle with a sum of di-jet masses around 105 GeV/c(2) is not supported. The combined result of the four LEP collaborations refuting this hypothesis at over 99% confidence level is also given. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

A measurement of the QCD colour factors and a limit on the light gluino

1997

Using data collected from 1992 to 1995 with the ALEPH detector at LEP, a measurement of the colour factor ratios C-A/C-F and T-F/C-F and the strong coupling constant = C-F alpha(s), (M-Z)/(2 pi) has been performed by fitting theoretical predictions simultaneously to the measured differential two-jet rate and angular distributions in four-jet events. The result is found to be in excellent agreement with QCD. C-A/C-F = 2.20 +/- 0.09 (stat) +/- 0.13 (syst), T-F/C-F = 0.29 +/- 0.05 (stat) +/- 0.06 (syst). Fixing C-A/C-F and T-F/C-F to the QCD values permits a determination of alpha(s) (M-Z) and n(f), the number of active flavours. With this measurement the existence of a gluino with mass below …

Correlation measurements in Z→τ+τ− and the τ neutrino helicity

1994

Using data collected with the ALEPH detector at LEP correlations between the decay products of the τ+ and τ- produced in the decay of the Z have been measured. The measurements performed in the decays τ-->πν and τ-->ϱν place limits on deviations from the Standard Model. These are given by the parameter ζ with ζ = -1 for the Standard Model. The measured values are ζπ = -0.95 +/- 0.11 +/- 0.05 and ζϱ = -1.03 +/- 0.11 +/- 0.05. For models which predict ζπ = ζϱ = ζ - interpreted as the average τ neutrino helicity - the measurement is ζ = -0.99 +/- 0.07 +/- 0.04.

Measurement of inclusive ρ0, f0(980), f2(1270), K and f′2(1525) production in Z0 decays

1999

DELPHI results are presented on the inclusive production of the neutral mesons ρ0, f0(980), f2(1270), KView the MathML source and f′2(1525) in hadronic Z0 decays. They are based on about 2 million multihadronic events collected in 1994 and 1995, using the particle identification capabilities of the DELPHI Ring Imaging Cherenkov detectors and measured ionization losses in the Time Projection Chamber. The total production rates per hadronic Z0 decay have been determined to be: 1.19±0.10 for ρ0; 0.164±0.021 for f0(980); 0.214±0.038 for f2(1270); 0.073±0.023 for KView the MathML source; and 0.012±0.006 for f′2(1525). The total production rates for all mesons and differential cross-sections for …

Search for charged Higgs bosons in e^{+}e^{-}$ collisions at √s=172 GeV

1998

This paper presents results on charged Higgs boson production, based on LEP data collected at √s = 172 GeV, that complement the previous DELPHI results obtained at centre of mass energies up to 161 GeV. The charged Higgs bosons are assumed to be pair produced and to decay either into a quark pair or into τVτ. The three different possible final states are included in the analysis. Data from ring imaging Cherenkov and microvertex detectors are used to identify the quarks as a cs pair. The number of candidates found is compatible with the background expected from standard processes. Combining the results of the present analysis with those of the previous analysis at lower energies, a new lower…

Measurement of the B hadron lifetime

1991

The average lifetime of B hadrons has been measured by the ALEPH experiment at LEP. Events containing B hadrons are selected by the identification of leptons with high transverse momentum in hadronic Z decays, and the lifetime is extracted from a fit to the impact parameter distribution of the lepton tracks. From a sample of 1.7×105 hadronic Z decays a lifetime of 1.29±0.06±0.10 ps is measured.

Measurement of B- mixing at the Z

1991

Abstract From more than 175 000 hadronic Z decays observed with the ALEPH detector at LEP, we select 823 events with pairs of leptons in the final state. From these we measure χ , the probability thata b hadron which is observed to decay originated as a b hadron. We find χ =0.132 −0.026 +0.027 .

Measurements of the trilinear gauge boson couplings WWV (V = $\gamma$ Z) in e$^+$e$^-$ collisions at 183 GeV

1999

Measurements of the trilinear gauge boson couplings WWγ and WWZ are presented from data taken by DELPHI in 1997 at an energy of 183 GeV. From a study of the reactions e + e − → W + W − , e + e − → Weν and e + e − → ννγ , values are obtained for Δg 1 Z and Δκ γ , the differences of the WWZ charge coupling and of the WWγ dipole couplings from their Standard Model values, and for λ γ , the WWγ quadrupole coupling. The observations are consistent with the predictions of the Standard Model. (Elsevier)

Search for composite and exotic fermions at LEP 2

1999

A search for unstable heavy fermions with the DELPHI detector at LEP is reported. Sequential and non-canonical leptons, as well as excited leptons and quarks, are considered. The data analysed correspond to an integrated luminosity of about 48~pb$^{-1}$ at an $e^+e^-$ centre-of-mass energy of 183~GeV and about 20~pb$^{-1}$ equally shared between the centre-of-mass energies of 172~GeV and 161~GeV. The search for pair-produced new leptons establishes 95\% confidence level mass limits in the region between 70~GeV/$c^2$ and 90~GeV/$c^2$, depending on the channel. The search for singly produced excited leptons and quarks establishes upper limits on the ratio of the coupling of the excited fermio…

Improved tau polarisation measurement

1996

Using 22 pb−1 of data collected at LEP in 1992 on the peak of the Z resonance, the ALEPH collaboration has measured the polarisation of the tau leptons decaying into $$ev\bar v, \mu v\bar v$$ ,πν, ρν and a1 ν from their individual decay product distributions. The measurement of the tau polarisation as a function of the production polar angle yields the two parametersN τ andN e, where, in terms of the axial and vector couplingsg Al andg Vl,N l=2g Vl gAl/(g Vl 2 +g 2 ). This analysis follows to a large extent the methods devised for the 1990 and 1991 data but with improvements which bring a better understanding of the systematic uncertainties. Combining the 1992 measurements with our previous…

Search for neutralino pair production at root s = 189 GeV

2001

A search for pair-production of neutralinos at a LEP centre-of-mass energy of 189 GeV gave no evidence for a signal. This limits the neutralino production cross-section and excludes regions in the parameter space of the Minimal Supersymmetric Standard Model (MSSM).

Tau leptonic branching ratios

1996

A sample of 62249 tau-pair events is selected from data taken with the ALEPH detector in 1991, 1992 and 1993. The measurement of the branching fractions for tau decays into electrons and muons is presented with emphasis on the study of systematic effects from selection, particle identification and decay classification. The results obtained are: B-e=17.79+/-0.12(stat)+/-0.06(syst)(%) and B-mu=17.31+/-0.11(stat)+/-0.05(syst)(%). Combined with the most recent ALEPH determination of the tau lifetime, these results provide a relative measurement of the leptonic couplings in the weak charged current for transverse W bosons: g(mu)/g(e)=1.0002+/-0.0051 and g(tau)/g(mu)=0.9943+/-0.0065. RI ANTONELLI…

Determination of sin2 θeff w using jet charge measurements in hadronic Z decays

2011

The electroweak mixing angle is determined with high precision from measurements of the mean difference between forward and backward hemisphere charges in hadronic decays of the Z. A data sample of 2.5 million hadronic Z decays recorded over the period 1990 to 1994 in the ALEPH detector at LEP is used. The mean charge separation between event hemispheres containing the original quark and antiquark is measured for bb̄ and cc̄ events in subsamples selected by their long lifetimes or using fast D*'s. The corresponding average charge separation for light quarks is measured in an inclusive sample from the anticorrelation between charges of opposite hemispheres and agrees with predictions of hadr…

A measurement of the Tau topological branching ratios

2001

Using data collected in the DELPHI detector at LEP-1, measurements of the inclusive tau branching ratios for decay modes containing one, three, or five charged particles have been performed, giving the following results: B_1 = B(\tau^- -> (particle)^- \geq 0pi^0 \geq 0K^0 \nu_\tau(\bar{\nu})) = (85.316 +/- 0.093 +/- 0.049)%; B_3 = B(\tau^- -> 2h^-h^+ \geq 0pi^0 \geq 0K^0 \nu_\tau) = (14.569 +/- 0.093 +/- 0.048)%; B_5 = B(\tau^- -> 3h^-2h^+ \geq 0pi^0 \geq 0K^0 \nu_\tau) = (0.115 +/- 0.013 +/- 0.006)%, where h is either a charged pi or K meson. The first quoted uncertainties are statistical and the second systematic.

Measurement of Prompt Photon Production In Hadronic-z Decays

1993

The production of isolated photons in hadronic Z decays is measured with the ALEPH detector at LEP using a sample of 450 000 hadronic events. The corrected rate is given for several values of the minimum invariant mass squared cut between the photon and the jets. This measurement of final state radiation from the quarks is compared with the predictions of parton shower models JETSET, ARIADNE and HERWIG as well as with the predictions of QCD matrix element calculations. RI Perrier, Frederic/A-5953-2011; ANTONELLI, ANTONELLA/C-6238-2011; Buttar, Craig/D-3706-2011; Stahl, Achim/E-8846-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; St.Denis, Richard/C-8997-2012; Forti, Franc…

A search for $\eta'_c$ production in photon-photon fusion at LEP

1998

A search for the production of the $\eta'_c$ meson, the first radial excitation of the ground state of charmonium $\eta_c$(2980), in the photon-photon fusion reaction at LEP has been performed using the data collected by the DELPHI detector during 1992-1996. No evidence of $\eta'_c$ production is found in the mass region 3520--3800 MeV/c^2. An upper limit for the ratio of the two-photon widths of the $\eta'_c$ and $\eta_c$ is obtained.

A Precise Measurement of the $\tau$ Polarisation at LEP-1

2000

The $\tau$ polarisation has been studied with the ${\rm e^+e^-}\to \tau^+\tau^-$ data collected by the DELPHI detector at LEP in 1993, 1994 and 1995 around the Z resonance firstly through the exclusive decay channels ${\rm e}\nu\bar{\nu}$ , $\mu\nu\bar{\nu}$ , $\pi\nu$ , $\rho\nu$ and ${\rm a}_1\nu$ and secondly with an inclusive hadronic analysis which benefits from a higher efficiency and a better systematic precision. The results have been combined with those previously published on 1990 to 1992 DELPHI data, to produce results which reflect the full LEP-1 statistics. The fit of the $\tau$ polarisation dependence on the production angle yielded the polarisation parameters ${\cal A}_{_{\sc…

Identified charged particles in quark and gluon jets

2000

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.

Update of the search for charginos nearly mass-degenerate with the lightest neutralino

2000

The data collected by DELPHI in 1998 at the centre-of-mass energy of 189 GeV have been used to update the search for charginos nearly mass-degenerate with the lightest supersymmetric particle, which is assumed to be the lightest neutralino. Mass differences below \Delta M = 3 GeV/c^2 are considered. No excess of events with respect to the Standard Model expectation has been observed, and exclusions in the plane of \Delta M versus chargino mass are given. The new \Delta M independent lower limit on the mass of the chargino is 62.4 GeV/c^2 in the higgsino scenario (which includes the gaugino mass unification scenario), if all sfermions are heavier than the lightest chargino. In the approximat…

An experimental study of γγ → hadrons at LEP

1993

An analysis of γγ interactions has been performed using untagged hadronic data obtained by the ALEPH detector at LEP. The data show at low transverse momentum (pt) are well reproduced by a model based on the vector meson dominance mechinism (VDM). At high pt thrust the presence of hard scattering processes is demonstrated. This component is well described in shape and normalization by a QCD calculation.

Measurement of trilinear gauge boson couplings WWV, (V Z,gamma) in e(+)e(-) collisions at 189 GeV

2001

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 identifie…

A precise measurement of ΓZ→bb/ΓZ→hadrons

1993

A measurement of the partial width ratio Γbb/Γhad using a method which tags the Z --> bb decays through the lif etime of the produced heavy hadrons is presented. This method relies on the tracking precision afforded by a double-sided silicon vertex detector. The tag algorithm makes a probabilistic interpretation of three-dimensional track impact parameters, using the data to measure the resolution. By tagging the two b hadrons separately, both Γbb/Γhad and the tag efficiency can be determined from the data. For a 26% efficiency of tagging a single b hadron within the vertex detector solid angle coverage, a purity of 96% is achieved. A value of Γbb/Γhad = 0.2192+/-0.0026(stat.)+/-0.0016(Γcc/…

Inclusive π±, K± and(p,p¯) differential cross-sections at the Z resonance

1995

Inclusive π±, K± and $$(p,\bar p)$$ differential cross-sections in hadronic decays of the Z have been measured as a function ofz=P hadron/P beam, the scaled momentum. The results are based on approximately 520 000 events measured by the ALEPH detector at LEP during 1992. Charged particles are identified by their rate of ionization energy loss in the ALEPH Time Projection Chamber. The position, ξ*, of the peak in the ln(1/z) distribution is determined, and the evolution of the peak position with centre-of-mass energy is compared with the prediction of QCD.

Search for supersymmetric particles in scenarios with a gravitino LSP and stau NLSP

2000

Sleptons, neutralinos and charginos were searched for in the context of scenarios where the lightest supersymmetric particle is the gravitino. It was assumed that the stau is the next-to-lightest supersymmetric particle. Data collected with the DELPHI detector at a centre-of-mass energy near 189 GeV were analysed combining the methods developed in previous searches at lower energies. No evidence for the production of these supersymmetric particles was found. Hence, limits were derived at 95% confidence level.

Study of dimuon production in photon-photon collisions and measurement of QED photon structure functions at LEP

2001

Muon pair production in the process e+e- -> e+e-mu+mu- is studied using the data taken at LEP1 (sqrt(s) \simeq m_Z) with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb^{-1}. The QED predictions have been tested over the whole Q^2 range accessible at LEP1 (from several GeV^2/c^4 to several hundred GeV^2/c^4) by comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators. Selected events are used to extract the leptonic photon structure function F_2^\gamma. Azimuthal correlations are used to obtain information on additional structure functions, F_A^\gamma and F_B^\gamma, which orig…

Single intermediate vector boson production in e(+)e(-) collisions at root s=183 and 189 GeV

2001

The cross sections for the production of single charged and neutral intermediate vector bosons were measured using integrated luminosities of 52 pb-1 and 154 pb-1 collected by the experiment at centre-of-mass energies of 182.6 GeV and 188.6 GeV, respectively. The cross sections for the reactions were determined in limited kinematic regions. The results found are in agreement with the Standard Model predictions for these channels. © 2001 Elsevier Science B.V.

A study of the Lorentz structure in tau decays

2000

This paper describes a measurement of the Michel parameters, \eta, \rho, \xi, \xi\delta, and the average \nu_{\tau} helicity, h_{\nu_{\tau}}, in tau lepton decays together with the first measurement of the tensor coupling in the weak charged current. The tau+tau- pairs were produced at the LEP e+e- collider at CERN from 1992 through 1995 in the DELPHI detector. Assuming lepton universality in the decays of the tau the measured values of the parameters were: \eta = -0.005 +/- 0.036 +/- 0.037, \rho = 0.775 +/- 0.023 +/- 0.020, \xi = 0.929 +/- 0.070 +/- 0.030, \xi\delta = 0.779 +/- 0.070 +/- 0.028, h_{\nu_{\tau}} = -0.997 +/- 0.027 +/- 0.011. The strength of the tensor coupling was measured to…

Search for a fermiophobic Higgs at LEP 2

2001

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.

A Search for Heavy Stable and Long-Lived Squarks and Sleptons in $e^+ e^-$ Collisions at Energies from 130 to 183 GeV

1998

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/c$^2$. Upper limits are given on the production cross-section and masses of sleptons, free squarks with a charge of $q = \pm 2/3e$ and hadronizing squarks. 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 io…

Measurement of the mass of the W boson using direct reconstruction at √s = 183 GeV

1999

From data corresponding to an integrated luminosity of 53.5 pb(-1) taken during the 183 GeV run in 1997, DELPHI has measured the W mass from direct reconstruction of WW --> lq (q) over bar and WW --> q (q) over bar q (q) over bar events. Combining these channels, a value of m(w) = 80.238 +/- 0.154(stat) +/- 0.035(syst) +/- 0.035(fsi) +/- 0.021 (LEP) GeV/c(2) is obtained, where fsi denotes final state interaction. Combined with the W mass obtained by DELPHI from the WW production cross-section and with the direct measurement at 172 GeV this leads to a measured value of m(w) = 80.270 +/- 0.137(stat) +/- 0.031(syst) +/- 0.030(fsi) +/- 0.021(LEP)GeV/c(2), in good agreement with the Standard Mod…

Search for the standard model Higgs boson

1993

Using a data sample corresponding to about 1 233 000 hadronic Z decays collected by the ALEPH experiment at LEP, the reaction e+e- --> HZ* has been used to search for the standard model Higgs boson, in association with missing energy when Z* --> nunuBAR, or with a pair of energetic leptons when Z* --> e+e- or mu+mu-. No signal was found and, at the 95% confidence level, m(H) exceeds 58.4 GeV/c2. RI ANTONELLI, ANTONELLA/C-6238-2011; Buttar, Craig/D-3706-2011; Stahl, Achim/E-8846-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; St.Denis, Richard/C-8997-2012; Forti, Francesco/H-3035-2011; Ferrante, Isidoro/F-1017-2012

Consistent measurements of alpha(s) from precise oriented event shape distributions

2000

An updated analysis using about 1.5 million events recorded at $\sqrt{s} = M_Z$ with the DELPHI detector in 1994 is presented. Eighteen infrared and collinear safe event shape observables are measured as a function of the polar angle of the thrust axis. The data are compared to theoretical calculations in ${\cal O} (\alpha_s^2)$ including the event orientation. A combined fit of $\alpha_s$ and of the renormalization scale $x_{\mu}$ in $\cal O(\alpha_s^2$) yields an excellent description of the high statistics data. The weighted average from 18 observables including quark mass effects and correlations is $\alpha_s(M_Z^2) = 0.1174 \pm 0.0026$. The final result, derived from the jet cone energ…

Cross-sections and leptonic forward-backward asymmetries from the Z(0) running of LEP

2000

During 1993 and 1995 LEP was run at 3 energies near the Z $^0$ peak in order to give improved measurements of the mass and width of the resonance. During 1994, LEP operated only at the Z $^0$ peak. In total DELPHI accumulated data corresponding to an integrated luminosity of approximately 116 pb $^{-1}$ . Analyses of the hadronic cross-sections and of the cross-sections and forward-backward asymmetries in the leptonic channels used the most precise evaluations of the LEP energies. In the dimuon channel, events with a photon radiated from the initial state have been used to probe the cross-sections and asymmetries down to PETRA energies. Model independent fits to all DELPHI lineshape and asy…