Nucl. Instrum. Meth. A

The response of a sampling tile electromagnetic calorimeter was simulated for incident electrons in the 10–500 GeV energy range. The influence of tile to tile nonuniformity on the a and b coefficients of the calorimeter energy resolution parametrisation formula was investigated in detail. An energy resolution deterioration due to nonuniformity was observed, but it was shown that by calibrating the towers individually one can reduce this undesirable effect to reasonable limits. An explicit a and b coefficients dependence on σ non , the tile response nonuniformity standard deviation, was found. Our previous results on this dependence obtained by analytical methods using the electromagnetic shower mean profile universal parametrisation and the present results obtained by Monte Carlo simulation are compared and found to be in good agreement.

Phys. Lett. B

Based on observation [L.G. Afanasyev et al., Phys. Lett. B 308 (1993) 200] of 272±49 atoms formed by π + and π − an estimation of the atom lifetime in the ground (1S) state is obtained: τ 1 = (2.9 +∞ −2.1 ) · 10 −15 s or τ 1 > 0.6·10 −15 s at 90% confidence level. Atoms were produced in inclusive p Ta interactions at 70 GeV.

Phys. Lett. B

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

Z.Phys.C

The forward-backward asymmetry of the processe+e−→Z→b

Phys.Rev.A

The method of hyperspherical "surface" functions has been applied to the calculation of eigenvalues and eigenfunctions of muonic molecular ions $~{3,4}\! H\! ed\mu $. Binding energies and nonradiative decay rates for the states of the total angular momentum $L=0,1,2$ have been obtained.

Phys. Rev. Lett.

The tensor analyzing power T20 for the reaction d↑+12C→p(0°)+X has been measured in the region of proton internal momenta k in light-cone dynamics up to 1 GeV/ c. Measurements have been carried out at Dubna Synchrophasotron with polarized deuteron beam at deuteron momenta up to 9 GeV/ c. When k increases the experimental values of T20 have a tendency to approach the value ( −0.3) obtained by the calculation based on the reduced nuclear amplitude method in which the quark degrees of freedom are taken into account.

Z.Phys.C

An analysis of inclusive production of K0 and the meson resonances K*±(892), ρ0(770),f0(975) andf2(1270) in hadronic decays of the Z0 is presented, based on about 973,000 multihadronic events collected by the DELPHI detector at LEP during 1991 and 1992. Overall multiplicities have been determined as 1.962±0.060 K0 mesons, 0.712±0.067 K*±(892) and 1.21±0.15ρ0(770) per hadronic Z0 decay. The average multiplicities off0(975) for scaled momentum,xp, in the range 0.05≤xp≤0.6 and off2(1270) for 0.05≤xp≤1.0 are 0.098±0.016 and 0.170±0.043 respectively. Thef0(975) and ρ0(770)xp-spectra have similar shapes. Thef2(1270)/ρ0(770) ratio increases withxp. The average multiplicities and the differential cross sections are compared with the JETSET Parton Shower model. The model with default parameters fails to reproduce the experimental K0 momentum spectrum at low momentum, describes the K*±(892) and ρ0(770)xp-spectrum shapes, but significantly overestimates their production rates.

Z.Phys.C

Two measurements of\(\Gamma _{b\bar b} /\Gamma _{had} \) are presented. Both measurements use 250000Z decays taken with the DELPHI detector in 1991 and rely mainly on the precision of the microvertex detector. One tagging method is as simple as possible so that background rates can be reliably predicted by simulation. The other one uses a more involved tagging technique and reduces the dependence on simulation as much as possible. Combining both results,\(\Gamma _{b\bar b} /\Gamma _{had} \) is found to be 0.2209±0.0041(stat.)±0.0042(syst.)±0.0018\(\Gamma _{c\bar c} \).

Phys. Lett. B

The time dependent mixing of B d 0 – B d 0 mesons has been observed by using the correlations between the charge of D ∗ mesons and the weighted mean charge of particles in each hemisphere. From a reconstructed D ∗± sample corresponding to about 1.7 million hadronic Z 0 decays, the mass difference between the two B d 0 mass eigenstates has been measured to be Δm = 0.50±0.12 ( stat. ) ± 0.06 ( syst. ) h ̵ / ps or, converting into eV/ c 2 : Δm = [3.29 ± 0.79 (stat) ± 0.39 (syst.)] 10 −4 eV/c 2 .

Z.Phys.C

An analysis is reported on the channele+e−→μ+μ−(nγ), n=1,2..., using data taken with the DELPHI detector at LEP from 1990 to 1992. Differential cross

Z.Phys.C

A search for charged Higgs bosons decaying into quarks is described, based on statistics of around 1.7 million hadronic Zo decays detected in DELPHI. Despite the very high background from standard hadronic decays of the Zo, masses in the range up to 43.5 GeV/c2 are excluded at the 95% confidence level. After combination with a search for leptonic decays, this mass limit is extended to cover all branching ratios. A similar analysis sets new limits on the possible production of any pair-produced heavy scalar decaying into a pair of jets, such as neutral Higgs bosons in a two doublet scheme and diquarks.

Phys.Lett.B

Kaon production in one prong tau decays has been studied using data collected with the DELPHI detector at the LEP collider. Charged kaons were identified over a large momentum range by the DELPHI barrel Ring Imaging Cherenkov detector. The following branching ratios have been determined: BR( τ → Kν τ )=(0.85±0.18)%, BR( τ → Kν τ ≥0 neutrals)=(1.54±0.24)%, BR( τ → Kν τ ≥1 neutrals)=(0.69±0.25)%. The result for the exclusive branching ratio is consistent with the Standard Model prediction based on τ - μ - e universality. In addition, tau decay into K ∗− was studied in the channel K ∗− →K − π 0 . The result BR (τ→K ∗− ν τ )× BR (K ∗− →K − π 0 )=(0.57±0.23)% was obtained.

Phys.Lett.B

J / ψ mesons have been reconstructed from their decay to μ + μ − and e + e − , using the data collected by the DELPHI experiment during 1991 and 1992 at the LEP collider. From about 1 million hadronic Z decays 153 ± 17 J / ψ were found, 5.4 ± 2.3 ψ ′ were obtained in the channel J / ψ (→ μ + μ − ) π + π − and 6.4 ± 2.7 χ c in the channel J / ψ ( → μ + μ − ) γ . As the dominant source of Jψ mesons is from b quarks, the following branching ratios: Br( b → J / ψ X ) = (1.12 ± 0.12 (stat) ± 0.10 (syst.))%, Br( b → ψ ′ X ) = (0.48 ± 0.22 (stat.± 0.10 (syst.))%, Br( b → χ c 1 X ) = (1.4 ± 0.6 (stat.) −0.2 +0.4 (syst.))% were measured. From the proper time distribution of the J / ψ sample, the average lifetime of b -hadrons decaying into J / ψ was found to be: τ B = 1.50 −0.21 +0.24 (stat.) ± 0.03 (syst.) ps. A search for completely reconstructed B meson decays to final states including a J / ψ gave a signal of 15 ± 5 events.

Phys.Rev.D

From data accumulated over 6140 h with 172 g of enriched molybdenum (1.18 mol yr of Mo100) with the NEMO 2 detector in the Fréjus Underground Laboratory, a clear ββ2ν signal (1433 events) is observed, leading to a half-life T1/2=0.95±0.04(stat)±0.09(syst) 1019 yr. The experimental two-electron energy spectrum and the two-electron angular distribution are in agreement with the expected ones. Limits for ββ0ν decays to the ground state, excited states (21+ and 01+), and also with Majoron emission are given.

Nucl.Phys.B Proc.Suppl.

Phys. Lett. B

A total of about 900 000 Z 0 → q q decays have been analyzed to measure the B 0  B 0 mixing probability. Two different b tagging techniques have been used: events with two leptons and events with one lepton and one Λ. From a combination of the two methods the average mixing parameter, χ, was determined to be (12.1±1.6(stat.)±0.4(syst.)±0.4(model)%.

Nucl.Phys.B

A search for the Standard Model Higgs boson was performed in the data sample of around 1 million hadronic Z 0 decays recorded in 1991 and 1992 with the DELPHI detector at LEP. The Higgs boson was searched for through its production in association with either neutrinos, electrons or muons. Four low mass events remain after the selections in the charged leptonic channels, that are likely to be due to background, especially four fermion processes. These results restrict the mass of the Standard Model Higgs boson to be larger than 55.7 GeV/ c 2 at the 95% confidence level.

Phys.Lett.B

Strange beauty meson B s 0 have been reconstructed through exclusive hadronic final states, using the data collected in 1992 by the DELPHI experiment at the LEP collider. The analysis relies on the combined use of accurate tracking and of the hadron identification capabilities of DELPHI. Three B s 0 decay candidates have been selected over a negligible background using theD s − π + , D s − a 1 + (1260) and J Ψ φ decay modes, with identified kaons in the final state. The B s 0 meson mass is measured to be m B s = (5374± 16± 2) MeV/ c 2 .

Z.Phys.C

The average lifetime ofB hadrons was measured using data collected with the DELPHI detector at the LEP collider during 1991 and 1992. The measurement was performed using two different anayses. The fir

Nucl. Phys. B

During the 1992 running period of the LEP e + e − collider, the DELPHI experiment accumulated approximately 24 pb − of data at the Z 0 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 Z 0 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 m t = 157 −48 +36 (expt.) −20 +19 (Higgs) GeV, and for the effective mixing angle sin 2 θ eff lept = 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.

Phys.Lett.B

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 λ γ = 1 is 132 GeV/ c 2 . Upper limits on the branching ratios for the decays Z 0 → γγ , Z 0 → π 0 γ , Z 0 → ηγ and Z 0 → 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.

Nucl.Instrum.Meth.A

A method for measuring the photomultiplier gain using a realistic photomultiplier response function is described. A precision of about 1% for the deconvoluted gain parameter can be achieved.

Z.Phys.C

Two-particle correlations in invariant mass are studied separately for like-sign and unlike-sign pions. Strong correlations are observed only at small masses. The correlations decrease very rapidly for like-sign pions and slowly for unlike-sign pions, manifesting different particle dynamics. The like-sign correlations exhibit a power-law behaviour as a function of mass, compatible with the previously observed intermittency effect. The predictions of the parton shower model (JETSET 7.3) deviate significantly from the data. However, good agreement is obtained with the mass correlations, both for the unlike-sign and for the like-sign pairs if the production of the η′ and ρ0 mesons is reduced and Bose-Einstein correlations are included in the model. The value of the Bose-Einstein correlation strength is consistent with unity for pions which are produced directly or in the decays of short-lived resonances.

Phys.Lett.B

K 0 S K 0 S correlations have been studied in a sample of 717 511 hadronic events collected by the DELPHI detector at LEP during 1992. An enhancement is found in the production of pairs of K 0 S of similar momenta, as compared with a Monte Carlo simulated reference sample. The measured values for the strength of the correlation and the radius of the emitting source of kaons are λ = 1.13 ± 0.54 (stat) ± 0.23 (syst) and r = 0.90 ± 0.19 (stat) ± 0.10 (syst) fm. This enhancement is consistent with the hypothesis that K 0 S K 0 S pairs display an enhancement, regardless of whether they come from a K 0 K̄ 0 or from a K 0 K 0 (K̄ 0 K̄ 0 ) system.

Z. Phys. C

The production of multihadronic states in γγ collisions at LEP has been studied with the DELPHI detector. The analyzed data correspond to an integrated luminosity of about 32pb−1, collected in the LEP runs of 1990–1992. Minimum bias data and a sample of events with jets at highpT have been selected under the requirement that no scattered electron or positron is observed. The two data sets have been compared to Monte Carlo predictions. The non-perturbative contribution described by the vector meson dominance Model and direct\(q\bar q\) production from pointlike photons described by the quark parton model were found to be insufficient to reproduce the data. It has been necessary to include a third interaction component, which is due to perburbative hard scattering of the partonic constituents of the photon. Several parametrisations of the quark and gluon densities of the photon have been tested. The interplay with the cut in jet transverse momentum, which is necessary for the separation of the perturbative and non-perturbative regions, is discussed. The data favour parametrisations with rather soft partonic content of the photon.