Measurement of the mass and width of the W boson in e+e- collisions at ?s\sqrt{s} = 161–209 GeV

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^-→ℓν̄_ℓqq̄’ and W⁺W^-→qq̄’q̄q’ channels. The W mass result for the combined data set is 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 These results supersede all values previously published by the DELPHI collaboration. This paper is dedicated to the memory of Carlo Caso.     

Measurements of charged kaon semileptonic decay branching fractions K±→π0μ±ν and K±→π0e±ν and their ratio

Measured ratios of decay rates for , and are presented. These measurements are based on K^± decays collected in a dedicated run in 2003 by the NA48/2 experiment at CERN. The results obtained are and . Using the PDG average for the K^±→π^±π⁰ normalisation mode, both values are found to be larger than the current values given by the particle data book and lead to a larger magnitude of the |V_us| CKM element than previously accepted. When combined with the latest particle data book value of |V_ud|, the result is in agreement with unitarity of the CKM matrix. In addition, a new measured value of is compared to the semi-empirical predictions based on the latest form factor measurements. An erratum to this article can be found at     

Measurements of charged kaon semileptonic decay branching fractions K±→π0μ±ν and K±→π0e±ν and their ratio

In an earlier paper [1], the background for K_e3 was over estimated due to an erroneous calculation of the electron identification efficiency. The correct ratios of the partial widths involving this channel are and . Assuming the PDG value [2] for the K_2π branching ratio, the measured branching fraction of Br (K_e3) continues to exceed the current PDG value [2]. The extracted value of |V_us|f₊(0) is in agreement with the CKM unitary prediction; thus, our conclusions in [1] do not change. The online version of the original article can be found at     

Measurement of the strong coupling αS from the four-jet rate in e+e- annihilation using JADE data

Data from e⁺e^- annihilation into hadrons collected by the JADE experiment at centre-of-mass energies between 14 GeV and 44 GeV are used to study the four-jet event production rate as a function of the Durham jet algorithm’s resolution parameter y_cut. The four-jet rate is compared to QCD next-to-leading order calculations including resummation of large logarithms in the next-to-leading logarithmic approximation. The strong coupling measured from the four-jet rate is in agreement with the world average.     

Measurement of the strong coupling αS from four-jet observables in e+e- annihilation

Data from e⁺e^- annihilation into hadrons at centre-of-mass energies between 91 GeV and 209 GeV collected with the OPAL detector at LEP, are used to study the four-jet rate as a function of the Durham algorithm resolution parameter y_cut. The four-jet rate is compared to next-to-leading order calculations that include the resummation of large logarithms. The strong coupling measured from the four-jet rate is in agreement with the world average. Next-to-leading order fits to the D-parameter and thrust minor event-shape observables are also performed for the first time. We find consistent results, but with significantly larger theoretical uncertainties.     

Study of W-boson polarisations and triple gauge boson couplings in the reaction e+e-→W+W- at LEP 2

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, ρ_ττ’ ^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, Λ_ττ’, 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: at a mean energy of 198 GeV. The SDM elements are also used to determine the triple gauge couplings Δg₁ ^Z,Δκ_γ,λ_γ and g₄ ^Z, and . For the CP-violating couplings the results of single parameter fits are: The errors are a combination of statistical and systematic errors. All results are consistent with the Standard Model.     

Measurement of the e+e-→W+W- cross section and W decay branching fractions at LEP

From a total data sample of 701.1 pb^-1 recorded with e⁺e^- centre-of-mass energies of 161–209 GeV with the OPAL detector at LEP, 11693 W-pair candidate events are selected. These data are used to obtain measurements of the W-pair production cross sections at 10 different centre-of-mass energies. The ratio of the measured cross sections to the standard model expectation is found to be: , where the uncertainties are statistical, experimental systematics and theory systematics respectively. The data are used to determine the W boson branching fractions, which are found to be consistent with lepton universality of the charged current interaction. Assuming lepton universality, the branching ratio to hadrons is determined to be 67.41±0.37(stat.)±0.23(syst.)%, from which the CKM matrix element |V_cs| is determined to be 0.969±0.017(stat.)±0.012(syst.). The differential cross section as a function of the W^- production angle is measured for the qqeν and qqμν final states. The results described in this paper are consistent with the expectations from the standard model. This paper is dedicated to the memory of Ben Shen.     

Measurement of the W boson mass and width in e+e- collisions at LEP

The mass of the W boson is determined from the direct reconstruction of W decays in WW→qq̄qq̄ and WW→ℓνqq̄ events in e⁺e^- collisions at LEP. The data sample corresponds to an integrated luminosity of 683 pb^-1 collected with the ALEPH detector at centre-of-mass energies up to 209 GeV. To minimise any effect from colour reconnection a new procedure is adopted in which low energy particles are not considered in the mass determination from the qq̄qq̄ channel. The combined result from all channels is where FSI represents the possible effects of final state interactions in the qq̄qq̄ channel and LEP indicates the uncertainty in the beam energy. From two-parameter fits to the W mass and width, the W width is found to be      

Editorial

The production of charmed mesons ,D ^± , andD ^*± is studied in a sample of 478,000 hadronicZ decays. The production rates are measured to be

Determination of the b quark mass at the MZ scale with the DELPHI detector at LEP

An experimental study of the normalized three-jet rate of b quark events with respect to light quarks events (light=ℓ≡u,d,s) has been performed using the CAMBRIDGE and DURHAM jet algorithms. The data used were collected by the DELPHI experiment at LEP on the Z peak from 1994 to 2000. The results are found to agree with theoretical predictions treating mass corrections at next-to-leading order. Measurements of the b quark mass have also been performed for both the b pole mass: M_b and the b running mass: m_b(M_Z). Data are found to be better described when using the running mass. The measurement yields: for the CAMBRIDGE algorithm. This result is the most precise measurement of the b mass derived from a high energy process. When compared to other b mass determinations by experiments at lower energy scales, this value agrees with the prediction of quantum chromodynamics for the energy evolution of the running mass. The mass measurement is equivalent to a test of the flavour independence of the strong coupling constant with an accuracy of 7 ‰.     

Measurement of the mass and width of the W boson

The mass and width of the W boson are measured using e⁺e^– → W⁺W^– events from the data sample collected by the OPAL experiment at LEP at centre-of-mass energies between 170 GeV and 209 GeV. The mass (m_W) and width (Γ_W) are determined using direct reconstruction of the kinematics of W⁺W^– → and W⁺W^– → events. When combined with previous OPAL measurements using W⁺W^– → events and the dependence on of the WW production cross-section at threshold, the results are determined to be

Λ<Subscript>b</Subscript>→Λℓ<Superscript>+</Superscript>ℓ<Superscript>-</Superscript> decay in universal extra dimensions

We study the exclusive Λ_b→Λℓ⁺ℓ^- decay in the Appelquist, Chang, Dobrescu model with a single universal extra dimension. We investigate the sensitivity of the branching ratio, lepton polarization and forward–backward asymmetry to the compactification parameter 1/R. We obtain the result that the branching ratio for the Λ_b→Λℓ⁺ℓ^- (ℓ=μ,τ) decay changes about 25% compared to the SM value when 1/R=250 GeV, and the zero position of the forward–backward asymmetry is shifted to the left compared to the SM result. Therefore, measurement of the branching ratio of Λ_b→Λℓ⁺ℓ^- decay and determination of the zero position of are very useful in looking for new physics in the framework of the UED models. PACS 12.60.-i; 13.30.-a; 14.20.Mr     

Determination of heavy quark non-perturbative parametersfrom spectral moments in semileptonic B decays

Moments of the hadronic invariant mass and of the lepton energy spectra in semileptonic B decays have been determined with the data recorded by the DELPHI detector at LEP. From measurements of the inclusive b-hadron semileptonic decays, and imposing constraints from other measurements on b- and c-quark masses, the first three moments of the lepton energy distribution and of the hadronic mass distribution, have been used to determine parameters which enter into the extraction of |V_cb| from the measurement of the inclusive b-hadron semileptonic decay width. The values obtained in the kinetic scheme are: and include corrections at order 1/m_b³. Using these results, and present measurements of the inclusive semileptonic decay partial width of b-hadrons at LEP, an accurate determination of |V_cb| is obtained: Received: 26 April 2005, Revised: 16 September 2005, Published online: 16 November 2005     

Measurement of the mass and the width of the W boson at LEP

The mass and the total decay width of the W boson are measured with the L3 detector at the LEP e⁺e^– collider using W-boson pairs produced in 0.7 fb^–1 of data collected at centre-of-mass energies between 161 and 209 GeV. Combining semi-leptonic and fully-hadronic final states, the mass and the width of the W boson are determined to be

A comparison of b and uds quark jets to gluon jets

Symmetric three-jet events are selected from hadronic Z⁰ decays such that the two lower energy jets are each produced at an angle of about 150° with respect to the highest energy jet. In some cases, a displaced secondary vertex is reconstructed in one of the two lower energy jets, which permits the other lower energy jet to be identified as a gluon jet through anti-tagging. In other cases, the highest energy jet is tagged as a b jet or as a light quark (uds) jet using secondary vertex or track impact parameter and momentum information. Comparing the two lower energy jets of the events with a tag in the highest energy jet to the anti-tagged gluon jets yields a direct comparison of b, uds and gluon jets, which are produced with the same energy of about 24 GeV and under the same conditions. We observe b jets and gluon jets to have similar properties as measured by the angular distribution of particle energy around the jet directions and by the fragmentation functions. In contrast, gluon jets are found to be significantly broader and to have a markedly softer fragmentation function than uds jets. For thek _⊥ jet finder withy _cut=0.02, we find as the ratios of the mean charged particle multiplicity in the gluon jets compared to the b and uds jets. Results are also reported using the cone jet finder.     

Probing little Higgs model in e<Superscript>+</Superscript>e<Superscript>-</Superscript>→νν̄γ process

We study the process e⁺e^-→νν̄γ to search for its sensitivity to the extra gauge bosons Z₂, Z₃ and W₂ ^±, which are suggested by the little Higgs models. We find that the ILC with and CLIC with cover different regions of the LHM parameters. We show that this channel can provide a determination of the parameters, complementary to measurements of the extra gauge bosons obtainable at the upcoming LHC experiments. PACS 14.80.Cp; 12.60.Fr; 12.60.Cn     

Combinatorial Point for Fused Loop Models

Integrable loop models associated with higher representations (spin ℓ/2) of are investigated at the point . The ground state eigenvalue and eigenvectors are described. Introducing inhomogeneities into the models allows to derive a sum rule for the ground state entries. Supported by ANR program “GIMP” ANR-05-BLAN-0029-01, European networks “ENIGMA” MRT-CT-2004-5652, “ENRAGE” MRTN-CT-2004-005616, and ESF program “MISGAM”.     

Search for a fourth generation b’-quark at LEP-II at ?s= \sqrt{s}=\,196–209?GeV

A search for the pair production of fourth generation b’-quarks was performed using data taken by the DELPHI detector at LEP-II. The analysed data were collected at centre-of-mass energies ranging from 196 to 209 GeV, corresponding to an integrated luminosity of 420 pb^-1. No evidence for a signal was found. Upper limits on BR(b’→bZ) and BR(b’→cW) were obtained for b’ masses ranging from 96 to 103 GeV/c ². These limits, together with the theoretical branching ratios predicted by a sequential four generations model, were used to constrain the value of , where V_cb′, V_tb′ and V_tb are elements of the extended CKM matrix.     

A study of the nuclear-medium influence on neutral-strange-particle production in deep-inelastic neutrino scattering

The influence of nuclear effects on the production of neutral strange particles (V ⁰) is investigated using the data obtained with SKAT propane-freon bubble chamber irradiated in the neutrino beam (with E _v =3−30 GeV) at the Serpukhov accelerator. The mean multiplicity of V ⁰ particles in nuclear interactions, , is found to exceed significantly that in “quasideuteron” interactions, . The ratio of is larger than that for π⁻ mesons, . It is shown that the multiplicity gain of V ⁰ particles can be explained by intranuclear interactions of produced pions. The text was submitted by the authors in English.