A study of QCD coherence is presented based on a sample of about 397000 $e^+e^-$ hadronic annihilation events collected at $\sqrt{s}=91$ GeV with the OPAL detector at LEP. The study is based on four recently proposed observables that are sensitive to coherence effects in the perturbative regime. The measurement of these observables is presented, along with a comparison with the predictions of different parton shower models. The models include both conventional parton shower models and dipole antenna models. Different ordering variables are used to investigate their influence on the predictions.
The normalized corrected data at the hadron level for the emission angle $\theta_{14}$.
The correlation matrix of the normalized corrected data at the hadron level for the emission angle $\theta_{14}$.
The normalized corrected data at the hadron level for the mass ratio $\rho=M_L^2/M_H^2$.
The production of $J/\psi$ mesons in continuum $e^+e^-$ annihilations has been studied with the BABAR detector at energies near the $\Upsilon(4S)$ resonance, approximately 10.6 GeV. The mesons are distinguished from $J/\psi$ production in B decays through their center-of-mass momentum and energy. We measure the cross section $e^+e^-\to J/\psi X$ to be $2.52\pm 0.21\pm 0.21$ pb: for momentum above 2 GeV/c, it is $1.87\pm 0.10\pm 0.15$ pb. We set a 90% confidence level upper limit on the branching fraction for direct $\Upsilon(4S)$\to J/\psi X$ decays at $4.7\times 10^{-4}$.
Cross section measurement.
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 o
Hadronic cross section measured with the 1993 data. Additional systematic error of 0.10 PCT (efficiencies and backgrounds) and 0.29 PCT (absolute luminosity).
Hadronic cross section measured with the 1994 data. Additional systematic error of 0.11 PCT (efficiencies and backgrounds) and 0.11 PCT (absolute luminosity).
Hadronic cross section measured with the 1995 data. Additional systematic error of 0.10 PCT (efficiencies and backgrounds) and 0.11 PCT (absolute luminosity).
The DELPHI experiment at LEP uses Ring Imaging Cherenkov detectors for particle identification. The good understanding of the RICH detectors allows the identification of charged pions, kaons and proto
Mean particle multiplicities for Z0-->Q-QBAR events. The second systematic (DSYS) error is due to the extrapolation of the differential distributions to the full kinematic range.
Mean particle multiplicities for Z0-->B-BBAR events. The second systematic (DSYS) error is due to the extrapolation of the differential distributions to the full kinematic range.
Mean particle multiplicities for Z0-->(U-UBAR,D-DBAR,S-SBAR) events. The second systematic (DSYS) error is due to the extrapolation of the differential distributions to the full kinematic range.
The total and the differential cross-sections for the reaction e + e − → γγ ( γ ) have been measured with the DELPHI detector at LEP at centre-of-mass energies from 130 to 183 GeV for an integrated luminosity of 78.19 pb −1 . The results agree with the QED predictions. The lower limits (obtained including previously published results at the Z 0 energies) on the QED cutoff parameters are Λ + >253 GeV and Λ − >225 GeV and the lower bound on the mass of an excited electron with an effective coupling constant λ γ =1 is 231 GeV/ c 2 . All the limits are at the 95% confidence level.
The cross section of the previously published data (sqrt(s)=91.25 GeV, see PL 327B, 386) is given at the mean of the CM energies weighted by the luminosityat each point.
Statistical errors only. Additional overall systematic uncertainty is givenabove.
Statistical errors only. Additional overall systematic uncertainty is givenabove.
The production of K^0_S mesons and Lambda baryons in quark and gluon jets has been investigated using two complementary techniques. In the first approach, which provides high statistical accuracy, jets were selected using different jet finding algorithms and ordered according to their energy. Production rates were determined taking into account the dependences of quark and gluon compositions as a function of jet energy as predicted by Monte Carlo models. Selecting three-jet events with the k_perp (Durham) jet finder (y_cut = 0.005), the ratios of K^0_S and Lambda production rates in gluon and quark jets relative to the mean charged particle multiplicity were found to be 1.10 +/- 0.02 +/- 0.02 and 1.41 +/- 0.04 +/- 0.04, respectively, where the first uncertainty is statistical and the second is systematic. In the second approach, a new method of identifying quark jets based on the collimation of energy flow around the jet axis is introduced and was used to anti-tag gluon jets in symmetric (Y-shaped) three-jet events. Using the cone jet finding algorithm with a cone size of 30 degrees, the ratios of relative production rates in gluon and quark jets were determined to be 0.94 +/- 0.07 +/- 0.07 for K^0_S and 1.18 +/- 0.10 +/- 0.17 for Lambda. The results of both analyses are compared to the predictions of Monte Carlo models.
Ratios of relative yields.
Ratios of absolute rates.
The splitting processes in identified quark and gluon jets are investigated using longitudinal and transverse observables. The jets are selected from symmetric three-jet events measured in Z decays with the Delphi detector in 1991-1994. Gluon jets are identified using heavy quark anti-tagging. Scaling violations in identified gluon jets are observed for the first time. The scale energy dependence of the gluon fragmentation function is found to be about two times larger than for the corresponding quark jets, consistent with the QCD expectation CA/CF. The primary splitting of gluons and quarks into subjets agrees with fragmentation models and, for specific regions of the jet resolution y, with NLLA calculations. The maximum of the ratio of the primary subjet splittings in quark and gluon jets is 2.77±0.11±0.10. Due to non-perturbative effects, the data are below the expectation at small y. The transition from the perturbative to the non-perturbative domain appears at smaller y for quark jets than for gluon jets. Combined with the observed behaviour of the higher rank splittings, this explains the relatively small multiplicity ratio between gluon and quark jets.
Scaled energy distribution of charged hadrons produced in Quark jets in 'Y'topology 3-JET events.
Scaled energy distribution of charged hadrons produced in Gluon jets in 'Y'topology 3-JET events.
Scaled energy distribution of charged hadrons produced in Quark jets in 'Mercedes' topology 3-JET events.
The transverse, longitudinal and asymmetric components of the fragmentation function are measured from the inclusive charged particles produced in$e^+e^-$collisi
Transverse component of the differential cross section.
Longitudinal component of the differential cross section.
Asymmetric component of the differential cross section.
The production rates of D^*+/- mesons in charm and bottom events at centre-of-mass energies of about 91 GeV and the partial width of primary cc(bar) pairs in hadronic Z^0 decays have been measured at LEP using almost 4.4 million hadronic Z^0 decays collected with the OPAL detector between 1990 and 1995. Using a combination of several charm quark tagging methods based on fully and partially reconstructed D^*+/- mesons, and a bottom tag based on identified muons and electrons, the hadronisation fractions of charm and bottom quarks into D^*+/- mesons have been found to be: f(b -> D^*+ X) = 0.173 +/- 0.016 +/- 0.012 and f(c -> D^*+ X) = 0.222 +/- 0.014 +/- 0.014 The fraction of cc(bar) events in hadronic Z^0 decays, Gamma_cc(bar)/Gamma_had = Gamma(Z^0 -> cc(bar))/Gamma(Z^0 -> hadrons), is determined to be Gamma_cc(bar)/Gamma_had = 0.180 +/- 0.011 +/- 0.012 +/- 0.006 In all cases the first error is statistical, and the second one systematic. The last error quoted for Gamma_cc(bar)/Gamma_had is due to external branching ratios.
No description provided.
No description provided.
The second syst. errors results due to extranal branching ratios. Charge conjugated states are implied. FD is considered as a quark fragmentation fraction. Sqrt(s(E+ E-)) = 91.2 GeV.
The spin density matrix elements for the ϱ 0 , K ∗0 (892) and F produced in hadronic Z 0 decays are measured in the DELPHI detector. There is no evidence for spin alignment of the K ∗0 (892) and F in the region x p ≤ 0.3 ( x p = p p beam ), where ϱ 00 = 0.33 ± 0.05 and ϱ 00 = 0.30 ± 0.04, respectively. In the fragmentation region, x p ≥ 0.4, there is some indication for spin alignment of the ϱ 0 and K ∗0 (892), since ϱ 00 = 0.43 ± 0.05 and ϱ 00 = 0.46 ± 0.08, respectively. These values are compared with those found in meson-induced hadronic reactions. For the F, ϱ 00 = 0.30 ± 0.04 for x p ≥ 0.4 and 0.55 ± 0.10 for x p ≥ 0.7. The off-diagonal spin density matrix element ϱ 1-1 is consistent with zero in all cases.
Helicity density matrices elements. The statistical and systematic errors are combined quadratically.
Helicity density matrices elements. The statistical and systematic errors are combined quadratically.
Helicity density matrices elements. The statistical and systematic errors are combined quadratically.
An inclusive measurement of the average multiplicity of b b pairs from gluons, g b b , in hadronic Z 0 events collected by the DELPHI experiment at LEP, is presented. A counting technique, based on jet b -tagging in 4-jet events, has been used. Looking for secondary bottom production in events with production of any primary flavour, by requiring two b -tagged jets in well defined topological configurations, gave g b b = (0.21 ± 0.11 ( stat ) ± 0.09 ( syst ))% . This result was checked with a different method designed to select events with four b quarks in the final state. Agreement within the errors was found.
No description provided.
Measurements of helicity density matrix elements have been made for the φ(1020), D*± and B* vector mesons in multihadronic Z0 decays in the OPAL experiment at LEP. Results for inclusive φ produced with high energy show evidence for production preferentially in the helicity zero state, with ρ00 = 0.54 ± 0.08, compared to the value of 1/3 expected for no spin alignment. The corresponding element for the D*± has a value of 0.40 ± 0.02, also suggesting a deviation from 1/3. The B* result, with ρ00 = 0.36 ± 0.09, is consistent with no spin alignment. Off-diagonal elements have been measured for the f and D* mesons; for the D* the element Re ρ1−1 is non-zero, indicating non-independent fragmentation of the primary quarks.
Helicity density matrices elements. Helicity beam frame is used.
Charge conjugated states are understood.
Helicity density matrices elements. Charge conjugated states are understood.
In a sample of 3.02 million hadronic Z 0 decays collected by the DELPHI detector, 270 J ψ → ℓ + ℓ − candidates have been selected. A search for fully reconstructed B c ± mesons has yielded one B c ± → J ψ π ± candidate, no B c ± → J ψ ℓ ± ν ℓ candidates, and one B c ± → J ψ , π + π − π ± candidate, consistent with expected background in each channel. The following 90% confidence level upper limits are determined: Br(Z 0 → B c ± X) × Br(B c ± → J ψ π ± ) < (1.05 to 0.84) × 10 −4 and Br(Z 0 → B c ± X) × Br(B c ± → J ψ ℓ ± ν ℓ ) < (5.8 to 5.0) × 10 −5 , where the ranges quoted correspond to the range of predicted B c ± lifetimes from 0.4 to 1.4 ps, and Br(Z 0 → B c ± X) × Br(B c ± → J ψ π + π − π ± ) < 1.75 × 10 −4 , constant over the range of predicted B c ± lifetimes.
B/C life-time equals (0.4 to 1.4) ps.
The hadronic fragmentation functions of the various quark flavours and of gluons are measured in a study of the inclusive hadron production from Z 0 decays with the DELPHI detector and are compared with the fragmentation functions measured elsewhere at energies between 14 GeV and 91 GeV. A large scaling violation is observed, which is used to extract the strong coupling constant from a fit using a numerical integration of the second order DGLAP evolution equations. The result is α s ( M Z ) = 0.124 −0.007 +0.006 (exp) ± 0.009(theory) where the first error represents the experimental uncertainty and the second error is due to the factorization and renormalization scale dependence.
SIG(Q=BQ, Q=CQ, Q=UDS) corresponds to BQ, CQ, and U,D,S quarks fragmentation into charged hadron.
alpha_s was evaluated from the scaling violation of the fragmentation func tions. The data from other experiments are used for the fitting procedure.
A sample of about 1.4 million hadronic Z decays, selected among the data recorded by the DELPHI detector at LEP during 1994, was used to measure for the first time the momentum spectra of K + , K 0 , p , Λ and their antiparticles in gluon and quark jets. As observed for inclusive charged particles, the production spectra of identified particles were found to be softer in gluon jets than in quark jets, with a higher total multiplicity.
Y events.
Mercedes events.
This paper describes an update of the double tagging measurement of the fraction, Rb, of Z0 → bb̅ events in hadronic Z0 decays, with statistics improved by including the data collected in 1994. The presence of electrons or muons from semileptonic decays of bottom hadrons and the detection of bottom hadron decay vertices were used together to obtain an event sample enriched in Z0 → bb̅ decays. The efficiency of the bb̅ event tagging was obtained from the data by comparing the numbers of events having a bottom signature in either one or both thrust hemispheres. Efficiency correlations between opposite event hemispheres are small (< 0.5%) and well understood through comparisons between the real and simulated data samples. A value of Rb= 0.2175 ± 0.0014 ± 0.0017 was obtained, where the first error is statistical and the second systematic. The uncertainty on the decay width Γ(Z0 → cc̅) is not included in these errors. The result depends on Rc as follows: $${⩼ Delta R_{⤪ b}⩈er R_{⤪ b}}=-0.084{⩼ Delta R_{⤪ c}⩈er R_{⤪ c}},$$ where ΔRc is the deviation of Rc from the value 0.172 predicted by the Standard Model.
No description provided.
We have studied azimuthal correlations in singly-tagged e+e− → e+e−μ+μ− events at an average Q2 of 5.2 GeV2. The data were taken with the OPAL detector at LEP at e+e− centre-of-mass energies close to the Z0 mass, with an integrated luminosity of approximately 100 pb−1. The azimuthal correlations are used to extract the ratio $F_{B}^{αmma}/F_{2}^{αmma}$ of the QED structure functions $F_{B}^{αmma}(x,Q^{2})$ and $F_{2}^{αmma}(x,Q^{2})$ of the photon. In leading order and neglecting the muon mass $F_{B}^{αmma}$ is expected to be identical to the longitudinal structure function $F_{L}^{αmma}$. The measurement of $F_{B}^{αmma}/F_{2}^{αmma}$ is found to be significantly different from zero and to be consistent with the QED prediction.
No description provided.
Inclusive charged particle and event shape distributions are measured using 321 hadronic events collected with the DELPHI experiment at LEP at effective centre of mass energies of 130 to 136 GeV. These distributions are presented and compared to data at lower energies, in particular to the precise Z data. Fragmentation models describe the observed changes of the distributions well. The energy dependence of the means of the event shape variables can also be described using second order QCD plus power terms. A method independent of fragmentation model corrections is used to determine αs from the energy dependence of the mean thrust and heavy jet mass. It is measured to be: $$←pha _s(133 {⤪ GeV})={0.116}pm {0.007}_{exp-0.004theo}^{+0.005}$$ from the high energy data.
mean values for event shape variables.
Integral of event shape distribution over the specified interval.
Integral of event shape distribution over the specified interval.
Gluon jets with about 39 GeV energy are identified in hadronic Z 0 decays by tagging two jets in the same hemisphere of an event as quark jets. Identifying the gluon jet to be all the particles observed in the hemisphere opposite to that containing the two tagged jets yields an inclusive gluon jet definition corresponding to that used in analytic calculations, allowing the first direct test of those calculations. In particular, this jet definition yields results which are only weakly dependent on a jet finding algorithm. We find r ch. =1.552±0.0041 ( stat ) ±0.061 ( syst. ) for the ratio of the mean charged particle multiplicity in gluon jets to that in light quark uds jets, where the uds jets are identified using an inclusive jet definition similar to that used for the gluon jets. Our result is in general agreement with the prediction of a recent analytic calculation which incorporates energy conservation into the parton shower branching processes, but is considerably smaller than analytic predictions which do not incorporate energy conservation.
Mean charged particle multiplicity in gluon jets.
Mean charged particle multiplicity in single hemisphere light quark jets.
A measurement of the charm and bottom forward-backward asymmetry in e+e− annihilations is presented at energies on and around the peak of the Z0 resonance. Decays of the Z0 into charm and bottom quarks are tagged using D mesons identified in about 4 million hadronic decays of the Z0 boson recorded with the OPAL detector at LEP between 1990 and 1995. Approximately 33000 D mesons are tagged in seven different decay modes. From these the charm and bottom asymmetries are measured in three energy ranges around the Z0 peak: \(\matrix {A_{\rm FB}^{\rm c}=0.039\pm 0.051\pm 0.009\cr A_{\rm FB}^{\rm c}=0.063\pm 0.012\pm 0.006\cr A_{\rm FB}^{\rm c}=0.158\pm 0.041\pm 0.011}\)\(\matrix {A_{\rm FB}^{\rm b}=0.086\pm 0.108\pm 0.029\cr A_{\rm FB}^{\rm b}=0.094\pm 0.027\pm 0.022\cr A_{\rm FB}^{\rm b}=0.021\pm 0.090\pm 0.026}\)\(\matrix{\langle E_{cm}\rangle =89.45\ {\rm GeV}\cr \langle E_{cm}\rangle =91.22\ {\rm GeV}\cr \langle E_{cm}\rangle =93.00\ {\rm GeV}}\) The results are in agreement with the predictions of the standard model and other measurements at LEP.
Forward-backward asymmetry.
No description provided.
The production rates of the $J_{P}={1⩈er 2}^{+}$ octet Σ baryons in hadronic Z0 decays have been measured using the OPAL detector at LEP. The inclusive production rates per hadronic Z0 decay of the three isospin states (including the respective antiparticle) have been separately measured for the first time: $άtrix {n_{Sigma^{+}}=0.099pm 0.008pm 0.013ŗ n_{Sigma^{0}}=0.071pm 0.012pm 0.013ŗ n_{Sigma^{-}}=0.083pm 0.006pm 0.009ŗ}$ where the first error is statistical and the second is systematic. Differential cross-sections are also presented for the Σ+ and Σ− and compared with JETSET and HERWIG predictions. Assuming full isospin symmetry, the average inclusive rate is: ${1⩈er 3}[n_{Sigma^{+}+Sigma^{0}+Sigma^{-}}]=0.084pm 0.005 ({⤪ stat.}) pm 0.008 ({⤪ syst.})$.
Differential cross section for SIGMA+ production.
Differential cross section for SIGMA- production.
No description provided.
A measurement of theτ lepton polarization and its forward-backward asymmetry at the Z0 resonance using the OPAL detector is described. The measurement is based on analyses of τ→ρντ, ττπ(K)ντ,\(\tau\to e\bar \nu _e \nu _\tau\),\(\tau\to \mu \bar \nu _\mu\nu _\tau\) andτ→a1ντ decays from a sample of 89075 e+e−→τ+τ− candidates corresponding to an integrated luminosity of 117 pb−1. Assuming that theτ lepton decays according to V-A theory, we measure the averageτ polarization at √s=MZ to be 〈P〉=(−13.0±0.9±0.9)% and theτ polarization forward-backward asymmetry to be ApolFB=(−9.4±1.0±0.4)%, where the first error is statistical and the second systematic. These results are consistent with the hypothesis of lepton universality and, when combined, can be expressed as a measurement of sin2θefflept=0.2334±0.0012 within the context of the Standard Model.
No description provided.
The inclusive production of the neutral vector mesons K*0(892) and ϕ(1020), and of the tensor meson ${⤪ K}_{2}^{⇒t 0}(1430)$, in hadronic decays of the Z has been measured by the DELPHI detector at LEP. The average production rates per hadronic Z decay have been determined to be 0.77 ± 0.08 K*0(892), 0.104 ± 0.008 ϕ(1020) and ${⤪ K}_{2}^{⇒t 0}(1430)$. The ratio of the tensor-to-vector meson production yields, $«ngle {⤪ K}_{2}^{⇒t 0}(1430)»ngle$, is smaller than the 〈f2(1270)〉/〈ρ0(770)〉 and $«ngle f_{2}^{⌕ime}(1525)»ngle$ ratios measured by DELPHI. The production rates and differential cross sections are compared with the predictions of JETSET 7.4 tuned to the DELPHI data and of HERWIG 5.8. The K*0(892) and ϕ(1020) data are compatible with model predictions, but a large disagreement is observed for the ${⤪ K}_{2}^{⇒t 0}(1430)$.
SIG in (1/SIG) is the total hadronic cross section. The statistical and systematic errors are combined quadratically.
SIG in (1/SIG) is the total hadronic cross section. The erros are statistical ones. The cross sections SIG(C=A), SIG(C=B), and SIG(C=C) obtained with A) both kaons identified, B) at least one kaon identified, and C) without requiring kaon identification.
SIG in (1/SIG) is the total hadronic cross section. The statistical and systematic erros are combined quadratically. For 0.05<X<0.2 the resulting cross s ection was taken by averaging the results with both identified kaons and with at least one identified kaon, for 0.2<X<1 the results obtained without particle id entification.
The inclusive production of the f ′ 2 (1525) in hadronic Z 0 decays has been studied in data collected by the DELPHI detector at LEP. The Ring Imaging Cherenkov detectors were important tools in the identification of the decay f ′ 2 (1525) → K + K − . The average number of f ′ 2 (1525) produced per hadronic Z decay, 〈f′ 2 〉 = 0.020 ± 0.005 (stat) ± 0.006 (syst), and the momentum distribution of the f ′ 2 (1525) have both been measured. The mass and width of the f ′ 2 (1525) are found to be 〈M f′ 2 〉 = 1535 ± 5 (stat) ± 4 (syst) MeV/c 2 , (T f′ 2 ;) = 60 ± 20 (stat) ± 19 (syst) MeV/c 2
SIG in (1/SIG) is the total hadronic cross section.
No description provided.
Data are presented on the reaction e+e− → γ + no other detected particle at centre-of-mass energies of 89.48, 91.26 and 93.08 GeV. The cross-section for this reaction is related directly to the number of light neutrino generations which couple to the Z° boson, and to several other possible phenomena such as the production of excited neutrinos, the production of any invisible ‘X’ particle, and the magnetic moment of the tau neutrino. Based on the observed number of single photon events, the number of light neutrinos that couple to the Z° is measured to be Nv = 2.89 ± 0.38. No evidence is found for anomalous production of energetic single photons, and upper limits at 95% confidence level are determined for excited neutrino production (BR < 4 − 8 × 10−6 depending on its mass), production of an invisible ‘X’ particle (σ, < 0.1 pb for masses below 60 GeV), and the magnetic moment of the tau neutrino (< 5.1 × 10-6 μB).
No description provided.
Limit on an anomalous magnetic moment for tau-neutrino from '1GAMMA + nothing' events. Magnetic moment in Bohr magnetons.
Here UNSPEC is invisible particle.
Statistical error only.
No description provided.
No description provided.
None
No description provided.
No description provided.
A search is described to detect charged Higgs bosons via the process Z 0 → H + H − , using data collected by the OPAL detector at LEP which correspond to an integrated luminosity of approximately 110 pb −1 . It is assumed that the H + boson decays only to τ + ν τ and c s final states. From the negative outcome of this search a lower bound of 44.1 GeV (95% CL) is derived for the mass of the charged Higgs boson.
No description provided.
Three jet events arising from decays of the Z boson, collected by the DELPHI detector, were used to measure differences in quark and gluon fragmentation. Gluon jets were anti-tagged by identifying b quark jets. Unbiased quark jets came from events with two jets plus one photon. Quark and gluon jet properties in different energy ranges were compared for the first time within the same detector. Quark and gluon jets of nearly the same energy in symmetric three jet event topologies were also compared. Using three independent methods, the average value of the ratio of the mean charged multiplicities of gluon and quark jets is $$< r >=1.241 pm 0.015 (stat.)pm 0.025 (syst.).$$ Gluon jets are broader and produce fragments with a softer energy spectrum than quark jets of equivalent energy. The string effect has been observed in fully symmetric three jet events. The measured ratio Rγ of the charged particle flow in the qq̅ inter-jet region of the qq̅g and qq̅γ samples agrees with the perturbative QCD expectation. The dependence of the mean charged multiplicity on the hadronic center-of-mass energy was analysed in photon plus n-jet events. The value for αs(MZ) determined from these data using a QCD prediction with corrections at leading and next-to-leading order is $$←pha_s(M_Z)=0.116pm 0.003 (stat.)pm 03009 (syst.).$$
No description provided.
Durham and JADE algoritms were used.
An analysis is presented of inclusive π0 production in Z0 decays measured with the DELPHI detector. At low energies, π0 decays are reconstructed by using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to $x_p={2cdot p≪/{sqrt s}=0.75}$) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy for qq̅ and bb̅ events. The number of π0’s per hadronic Z0 event is $N(≪^0)/Z_{had} ^0=9.2pm 0.2({⤪ stat})pm 1.0 ({⤪ syst})$ and for bb̅ events the number of π0’s is ${⤪ N}(≪^0)/{⤪ b⋏r b}=10.1pm 0.4({⤪ stat})pm 1.1 ({⤪ syst})$. The ratio of the number of π0’s in bb̅ events to hadronic Z0 events is less affected by the systematic errors and is found to be 1.09 ±0.05 ±0.01. The measured π0 cross sections are compared with the predictions of different parton shower models. For hadronic events, the peak position in the $xi_{⤪ p}={⤪ ln}(1/{⤪ x_p})$ distribution is $xi_p^{⋆ar}=3.90_{-0.14}^{+0.24}.$ The average number of π0’s from the decay of primary B hadrons is found to be N(B → π0X)/B hadron = 2.78 ± 0.15(stat) ± 0.60(syst).
Differential cross section for all events.
Mean PI0 multiplicity extrapolated below 0.011 with JETSET 7.3.
Differential cross section for the enriched (b bbar) data set.
A study of b quark fragmentation at LEP is presented using a sample of semileptonic B decays containing a fully reconstructed charm meson. The data are compared to several theoretical models for heavy quark fragmentation; the free parameters in these models are fitted and the sensitivity of the model parameters to the rate of P-wave B meson production is studied. The mean scaled energy fraction of B 0 and B + mesons has been determined to be < x E > = 0.695 ± 0.006 ± 0.003 ± 0.007, where the errors are statistical, systematic and model dependence respectively. This result is consistent with previous, less direct measurements from inclusive leptonic B decays. Also presented is a model independent fit to the shape of the energy distribution of weakly decaying B mesons at LEP.
No description provided.
A measurement of the Δ ++ (1232) inclusive production in hadronic decays of the Z at LEP is presented, based on 1.3 million hadronic events collected by the DELPHI detector in the 1994 LEP running period. The DELPHI ring imaging Cherenkov counters are used for identifying hadrons. The average Δ ++ (1232) multiplicity per hadronic event is 0.079 ± 0.015 which is more than a factor of two below the JETSET, HERWIG and UCLA model predictions. It agrees with a recently proposed universal mass dependence of particle production rates in e + e − annihilations.
Differential DELTA(1232)++ cross section. Errors are combined statistics and systematics.
Mean multiplicities. Extrapolation to full x range using a combination of JETSET, HERWIG and UCLA models. The second systematic error comes from the uncertainty in the extrapolation.
Rates for gamma + 1 jet.
Rates for gamma + 2 jet.
Rates for gamma + 3 jet.
A sample of 25000 Z 0 → τ + τ − events collected by the DELPHI experiment at LEP in 1991 and 1992 is used to measure the leptonic branching fractions of the τ lepton. The results are B(τ → eν ν ) = (17.51 ± 0.39) % and B(τ → μν ν ) = (17.02 ± 0.31) %. The ratio of the muon and electron couplings to the weak charged current is measured to be g μ g e = 1.000 ± 0.013 , satisfying e-μ universality. The leptonic branching fraction corrected to the value for a massless lepton, assuming e-μ universality, is found to be B(τ → lν ν ) = (17.50 ± 0.25) %.
Axis error includes +- 0.23/0.23 contribution (Data statistics).
Axis error includes +- 0.19/0.19 contribution (Data statistics).
Combined from the two branching fractions above. E-MU universality assumed.
The fragmentation function for the process e+e−→h+X, whereh represents a hadron, may be decomposed into transverse, longitudinal and asymmetric contributions by analysis of the distribution of polar production angles. A number of new tests of QCD have been proposed using these fragmentation functions, but so far no data have been published on the separate components. We have performed such a separation using data on charged particles from hadronic Z0 decays atOpal, and have compared the results with the predictions of QCD. By integrating the fragmentation functions, we determine the average charged particle multiplicity to be\(\overline {n_{ch} }= 21.05 \pm 0.20\). The longitudinal to total cross-section ratio is determined to be σL/σtot=0.057±0.005. From the longitudinal fragmentation function we are able to extract the gluon fragmentation function. The connection between the asymmetry fragmentation function and electroweak asymmetrics is discussed.
Transverse component of the fragmentation function.
Longitudinal component of the fragmentation function.
Asymmetry component of the fragmentation function.
We have measured the multiplicity of charm quark pairs arising from gluon splitting in a sample of about 3.5 million hadronic Z 0 decays. By selecting a 3-jet event topology and tagging charmed hadrons in the lowest energy jet using leptons, we established a signature of heavy quark pair production from gluons. The average number of gluons splitting into a c c pair per hadronic event was measured to be n g→c c =(2.27±0.28±0.41) × 10 −2 .
Axis error includes +- 8.4/8.4 contribution (Total generator error for the electron channel due to the uncertainties in parameters of Peterson model of fragmentation, LAMBDA_QCD, ALPHA_S, Lund fragmentation parameters and lepton decay model).
We have used data from the OPAL detector at LEP to reconstruct D ∗ mesons and secondary vertices in jets. We have studied the hemispheres of the events opposite these jets and obtain values of the hemisphere charged particle multiplicity in Z 0 → u u , d d , s s , Z 0 → c c and Z 0 → b b events of n uds = 10.41 ± 0.06 ± 0.09 ± 0.19 ; n c = 10.76 ± 0.20 ± 0.14 ± 0.19 ; n b = 11.81 ± 0.01 ± 0.12 ± 0.21 where the first errors are statistical, the second systmatic and the third a common scale uncertainty. We find the difference in total charged particle multiplicity between c and b quark events and light (u, d, s) quark events to be δ cl = 0.69 ± 0.51 ± 0.35; δ bl = 2.79 ± 0.12 ± 0.27. These results are compared to the predictions of various models and QCD based calculations.
Second systematic error is a common scale uncertainty.
Difference in the TOTAL charged particle multiplicity.
The production of neutral kaons in e+e− annihilation at centre-of-mass energies in the region of the Z0 mass and their Bose-Einstein correlations are investigated with the OPAL detector at LEP. A total of about 1.26×106 Z0 hadronic decay events are used in the analysis. The production rate of K0 mesons is found to be 1.99±0.01±0.04 per hadronic event, where the first error is statistical and the second systematic. Both the rate and the differential cross section for K0 production are compared to the predictions of Monte Carlo generators. This comparison indicates that the fragmentation is too soft in bothJetset andHerwig. Bose-Einstein correlations in Ks0Ks0 pairs are measured through the quantityQ, the four momentum difference of the pair. A threshold enhancement is observed in Ks0Ks0 pairs originating from a mixed sample of\(K^0 \bar K^0\) and K0K0 (\(\bar K^0 \bar K^0\)) pairs. For the strength of the effect and for the radius of the emitting source we find values of λ=1.14±0.23±0.32 andR0=(0.76±0.10±0.11) fm respectively. The first error is statistical and the second systematic.
No description provided.
The mean x is computed using the method of Lafferty and Wyatt NIM A355(1995)541.
The mean x is computed using the method of Lafferty and Wyatt NIM A355(1995)541.
Measurements have been made in the OPAL experiment at LEP of the inclusive production of strange vector φ(1020) and K*(892)0 mesons, and the tensor meson K2*(1430)0. The overall production rates per hadronic Z0 decay have been determined to be 0.100±0.004stat.±0.007syst. φ(1020) mesons, 0.74±0.03stat.±0.03syst. K*(892)0 mesons and (forxE<0.3) 0.19±0.04stat.±0.06syst. K2*(1430)0 mesons. The measurements for the vector states update previously published results based on lower statistics, while the K2*(1430)0 rate represents the first direct measurement of a strange tensor state in Z0 decay. For the vector states, both the overall production rates and normalised differential cross sections, with respect to the scaled energy variablexE, have been compared to JETSET and HERWIG predictions. The peak positions in the ζ=ln(1/xp) distributions have been measured and compared to measurements of other hadron states.
No description provided.
No description provided.
Extrapolated to full x region.
We have studied the production of D*± mesons in a sample of 1.25 million multihadronic decays of the Z0, in which 1969 candidates have been identified. We have determined the total multiplicity of charged D* mesons in multihadronic Z0 decays to be
No description provided.
Multiplicity data uncorrected for decay branching ratios.
No description provided.
We describe a cone-based jet finding algorithm (similar to that used in\(\bar p\)p experiments), which we have applied to hadronic events recorded using the OPAL detector at LEP. Comparisons are made between jets defined with the cone algorithm and jets found by the “JADE” and “Durham” jet finders usually used ine+e− experiments. Measured jet rates, as a function of the cone size and as a function of the minimum jet energy, have been compared with O(αs2) calculations, from which two complementary measurements\(\alpha _s \left( {M_{Z^0 } } \right)\) have been made. The results are\(\alpha _s \left( {M_{Z^0 } } \right)\)=0.116±0.008 and\(\alpha _s \left( {M_{Z^0 } } \right)\)=0.119±0.008 respectively, where the errors include both experimental and theoretical uncertainties. Measurements are presented of the energy flow inside jets defined using the cone algorithm, and compared with equivalent data from\(\bar p\)p interactions, reported by the CDF collaboration. We find that the jets ine+e− are significantly narrower than those observed in\(\bar p\)p. The main contribution to this effect appears to arise from differences between quark- and gluon-induced jets.
Measured 2 jet production rate as a function of EPSILON, the minimum energy of a jet for a fixed cone radius R = 0.7 radians.
Measured 2 jet production rate as a function of R, the jet cone radius, for a fixed value of the minimum jet energy, EPSILON, of 7 GeV.
Measured 3 jet production rate as a function of EPSILON, the minimum energy of a jet for a fixed cone radius R = 0.7 radians.
The forward-backward asymmetries of$$e^ + e^ - \to Z^0 \to b\bar b and e^ + e^ - \to Z^0 \to c\bar c$$
Measurement of the asymmetry in b-quark production on the Z0 peak using a two parameter fit, neglecting the effects of B0-BBAR0 mixing.
Measurement of the asymmetry in b-quark production on the Z0 peak using a two parameter fit and correcting for B0-BBAR0 mixing. The second systematic error is due to the uncertainty of the mixing factor.
Measurement of the asymmetry in c-quark production on the Z0 peak using a two parameter fit.
The production dynamics of baryon-antibaryon pairs are investigated using hadronic Z 0 decays, recorded with the OPAL detector, which contain at least two identified Λ baryons. The rapidly difference for Λ Λ pairs shows the correlations expected from models with a chain-like production of baryon-antibaryon pairs. If the baryon number of a Λ is compensated by a Λ , the Λ is found with a probability of 53% in an interval of ±0.6 around the Λ rapidity. This correlation strength is weaker than predicted by the Herwig Monte Carlo and the Jetset Monte Carlo with a production chain of baryon-antibaryon, and stronger than predicted by the UCLA model. The observed rapidity correlations can be described by the Jetset Monte Carlo with a dominant production chain of baryon-meson-antibaryon, the popcorn mechanism. In addition to the short range correlations, one finds an indication of a correlation of Λ Λ pairs in opposite hemispheres if both the Λ and the Λ have large rapidities. Such long range correlations are expected if the primary quark flavours are compensated in opposite hemispheres and if these quarks are found in energetic baryons. Rates for simultaneous baryon and strangeness number compensation for Λ Λ , Ξ − Ξ + and Ξ − Λ ( Λ + Λ ) are measured and compared with different Monte Carlo models.
No description provided.
Opposite and same baryon number invariant PI P mass distribuition for additional LAMBDA(LAMBDABAR) candidates in events with one identified LAMBDA(LAMBDABAR). CT.= Data read from plot.
Opposite and same baryon number invariant PI P mass distribuition for additional LAMBDA(LAMBDABAR) candidates in events with one identified XI-(XIBAR+). CT.= Data read from plot.
New measurements of the hadronic and leptonic cross sections and of the leptonic forward-backward asymmetries ine+e− collisions are presented. The analysis includes data recorded up to the end of 1991 by the OPAL experiment at LEP, with centre-of-mass energies within ±3 GeV of the Z0 mass. The results are based on a recorded total of 454 000 hadronic and 58 000 leptonic events. A model independent analysis of Z0 parameters based on an extension of the improved Born approximation is presented leading to test of lepton universality and an interpretation of the results within the Standard Model framework. The determination of the mass and width of the Z0 benefit from an improved understanding of the LEP energy calibration.
Statistical and systematic point-to-point errors included. There is an additional 0.2 pct overall systematic uncertainty.
Systematic error of 0.45 pct not included.
Systematic error of 0.25 pct not included.
Quark and gluon jets with equal energies are identified in three-jet hadronicZ0 events, using reconstructed secondary vertices from heavy quark decay in conjunction with energy orderi
No description provided.
Measurements are presented of the inclusive cross section for K ∗ (892) ± production in hadronic decays of the Z 0 using a sample of about half a million events recorded with the OPAL experiment at LEP. Charged K ∗ mesons are reconstructed in the decay channel K 0 S π ± . A mean rate of 0.72±0.02±0.08 K ∗ mesons per hadronic event is found. Comparison of the results with predictions of the JETSET and HERWIG models shows that JETSET overestimates the K ∗± production cross section while HERWIG is consistent with the data.
No description provided.
No description provided.
Using the 18.8 pb −1 of data accumulated at LEP in 1990 and 1991 with the ALEPH detector, a direct test of neutral current CP -invariance is performed by a search for CP -odd correlations in Z decays to τ pairs where both τ decay modes are identified. No evidence for CP -violation is observed. The weak dipole moment of the τ has been measured to be d τ ( m Z ) = (1.3 ± 1.4 ± 0.1) × 10 −17 e ·cm which results in an upper limit on the weak dipole moment of | d τ ( m Z )| ⩽ 3.7 × 10 −17 e ·cm with 95% confidence level.
No description provided.
We present a measurement of the forward-backward charge asymmetry in hadronic decays of the Z 0 using data collected with the OPAL detector at LEP. The forward-backward charge asymmetry was measured using a weight function method which gave the number of forward events on a statistical basis. In a data sample of 448 942 hadronic Z 0 decays, we have observed a charge asymmetry of A h = 0.040±0.004 (stat.)±0.006 (syst.)±0.002 (B 0 B 0 mix.), taking into account the effect of B 0 B 0 mixing. In the framework of the standard model, this asymmetry corresponds to an effective weak mixing angle averaged over five quark flavours of sin 2 θ W = 0.2321 ± 0.0017 ( stat. ) ± 0.0027 ( syst. ) ± 0.0009 (B 0 B 0 mix.). The result agrees with the value obtained from the Z 0 line shape and lepton pair forward-backward asymmetry.
No description provided.
The second systematic error is due to the uncertainty in the correction for B.BBAR mixing which had been applied to the data.
The second systematic error is due to the uncertainty in the correction for B.BBAR mixing which had been applied to the data.
The production of the octet and decuplet baryons Λ, Ξ − , Σ (1385) ± , Ξ(1530) 0 and Ω − and the corresponding antibaryons has been measured in a sample of 485 000 hadronic Z 0 decays. Results on differential and integrated cross sections are presented. The differential cross section of Λ baryons is found to be softer than the one predicted by the Jetset and Herwig Monte Carlo generators. The measured decuplet yields are found to disagree with the simple diquark picture where only one tuning parameter for spin 1 diquarks is used. Comparisons of the momentum spectra for Λ and Ξ − with the predictions of an analytical QCD formula are also presented.
No description provided.
No description provided.
No description provided.
Results are reported of a study of neutral vector meson production in multihadronicZ0 decays in the OPAL experiment at LEP. Pions and kaons have been identified by specific ionisation energy loss andK±π∓ andK+K− mass spectra have been fitted, in bins of the scaled momentum variablexp, to combinations of resonance signals and non-resonant backgrounds. Rates are given forK*(892)° and ø(1020), and production cross sections are compared to the predictions of Monte Carlo models. Overall multiplicities have been determined as 0.76±0.07±0.06K*(892)° and 0.086±0.015±0.010 ø(1020) per hadronicZ0 decay (the quoted errors are respectively statistical and systematic). Momentum dependent distortions of the ππ mass spectra, possibly associated indirectly with Bose-Einstein effects, have prevented reliable measurement of the ρ(770)° cross section in this study.
No description provided.
No description provided.
No description provided.
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