scispace - formally typeset
Search or ask a question

Showing papers by "D. M. Strom published in 1993"


Journal ArticleDOI
P. D. Acton1, Gideon Alexander2, John Allison3, Phillip Allport4  +323 moreInstitutions (29)
TL;DR: In this paper, the authors used reconstructed secondary vertices from heavy quark decay in conjunction with energy ordering of the jets to anti-tag the gluon jets and found that the mean particle multiplicity is larger for gluons than for quark jets.
Abstract: 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 ordering of the jets to anti-tag the gluon jets. Selection of jets from a symmetric event topology allows their properties to be compared in a simple and direct manner. The jets under study have an energy of about 24 GeV. It is observed that gluon jets have a larger angular width than quark jets and yield a softer particle energy spectrum. Correspondingly, the mean particle multiplicity is found to be larger for gluon than for quark jets. Correcting the distributions for residual misidentification of the quark and gluon jets, the ratio of mean particle multiplicty of gluon relative to quark jets is measured to be $$\frac{{\left\langle n \right\rangle _{gluon} }}{{\left\langle n \right\rangle _{quark} }} = 1.27 \pm 0.04(stat.) \pm 0.06(syst.),$$ where the jets are defined using thek⊥ jet finder. The numerical value of this ratio is found to be sensitive to the choice of the jet algorithm. The experimental results are compared to Monte Carlo calculations which incorporate perturbative QCD along with different assumptions about the hadronization process.

66 citations


Journal ArticleDOI
P. D. Acton1, P. D. Acton2, Gideon Alexander3, J. Allison4  +311 moreInstitutions (29)
TL;DR: In this article, the strong coupling constant, αs, has been determined in hadronic decays of the Z0 resonance, using measurements of seven observables relating to global event shapes, energy correlations and jet rates.
Abstract: The strong coupling constant, αs, has been determined in hadronic decays of theZ0 resonance, using measurements of seven observables relating to global event shapes, energy correlations and jet rates. The data have been compared with resummed QCD calculations, which are combined with theO(s2) theory. The seven measurements agree to about 10% and the final results, based on a weighted average, is: $$\alpha _s (M_{Z^0 } ) = 0.120 \pm 0.006,$$ where the error includes both experimental and theoretical uncertainties. This value corresponds to renormalization scale\(\mu = M_{Z^0 } \) and the error includes the uncertainty in this choice of scale. The present measurement complements previous determinations using theO(s2) QCD matrix elements alone, and yields a compatible result, with comparable errors.

66 citations



Journal ArticleDOI
TL;DR: This paper presents national plans on referencing and archiving doctoral theses coordinated by the government as well as some initiatives for creating full text archives.

43 citations


Journal ArticleDOI
P. D. Acton1, P. D. Acton2, G. Alexander3, G. Alexander2  +583 moreInstitutions (28)
TL;DR: In this paper, the production dynamics of baryon-antibaryon pairs are investigated using hadronic Z0 decays, recorded with the OPAL detector, which contain at least two identified baryons.

40 citations


Journal ArticleDOI
R.J. Akers1, Gideon Alexander2, J. Allison1, K. J. Anderson3  +327 moreInstitutions (30)
TL;DR: In this article, the average semileptonic branching ratio of Z0 bosons into hadrons containing bottom quarks, and the mean scaled energy of these hadrons were obtained using a simultaneous fit to single-lepton and dilepton events collected with the OPAL detector at LEP, including both electrons and muons.
Abstract: From a sample of about 450 000 hadronicZ0 decays, measurements of the average\(B^0 - \bar B^0 \) mixing parameter, χ, the branching fraction ofZ0 bosons into hadrons containing bottom quarks,\({{\Gamma (Z^0 \to b\bar b)} \mathord{\left/ {\vphantom {{\Gamma (Z^0 \to b\bar b)} {\Gamma (Z^0 \to hadrons)}}} \right. \kern- ulldelimiterspace} {\Gamma (Z^0 \to hadrons)}}\), the average semileptonic branching ratios for such hadrons,B(b→l) andB(b→c→l), and the mean scaled energy of these hadrons, 〈xE〉, are presented. The measurements were obtained using a simultaneous fit to single-lepton and dilepton events collected with the OPAL detector at LEP, including both electrons and muons. The results are where the errors are statistical and systematic, respectively, in each case. The result forB)b→c→l) excludes decays of the typeb→→l.

34 citations


Journal ArticleDOI
P. D. Acton1, P. D. Acton2, R.J. Akers3, R.J. Akers2  +600 moreInstitutions (29)
TL;DR: In this article, a search for events with photon pairs of large invariant mass is described based on a data sample of 43 pb−1 collected with the OPAL detector, and an upper limit is set on any anomalous production of l+l−γγ (l = e, μ, τ) events, where the l−l− pair comes from a virtual Z0 and mγγ is near 60 GeV, of B( Z 0 → Z ∗0 γγ → l + l − γ) −7 at the 95% CL.

28 citations


Journal ArticleDOI
P. D. Acton1, P. D. Acton2, G. Alexander3, G. Alexander1  +586 moreInstitutions (28)
TL;DR: In this paper, the authors measured the K ∗ (892) ± production in hadronic decays of the Z0 using a sample of about half a million events recorded with the OPAL experiment at LEP.

25 citations


Journal ArticleDOI
P. D. Acton1, Gideon Alexander2, J. Allison, P. P. Allport  +314 moreInstitutions (27)
TL;DR: In this article, the authors measured the fraction of hadronicZ 0 decays from the yield of leptons in the data samples collected by OPAL in 1990 and 1991.
Abstract: The fraction of $$b\bar b$$ events in hadronicZ 0 decays has been measured from the yield of leptons in the data samples collected by OPAL in 1990 and 1991. A sample enriched in events containing $${\rm Z}^0 \to b\bar b$$ decays was obtained by requiring the presence of an electron or muon with high momentum and high momentum component transverse to the associated hadronic jet. After accounting for backgrounds and acceptances, a value of $$\frac{{\Gamma ({\rm Z}^0 \to b\bar b)}}{{\Gamma ({\rm Z}^0 \to hadrons)}} = 0.220 \pm 0.002 \pm 0.0006 \pm 0.011$$ was obtained. The first two errors reflect the data statistics and the systematic uncertainties arising from detector modelling uncertainties, respectively. The third error includes systematic effects fromb andc fragmentation and decay uncertainties.

24 citations



Journal ArticleDOI
P. D. Acton1, R.J. Akers2, Gideon Alexander3, John Allison2  +313 moreInstitutions (30)
TL;DR: In this article, the authors measured the lifetime of the Bs0 in a data sample of 8890000 hadronic events recorded with the ALEPH detector at LEP, and attributed these events to the semileptonic decay of the bs0 to a Ds− and an opposite-sign lepton.

Journal ArticleDOI
P. D. Acton1, Gideon Alexander2, John Allison3, Phillip Allport4  +309 moreInstitutions (27)
TL;DR: In this paper, Bose-Einstein correlations in K0SK0S pairs have been studied for the first time in e+e− annihilations, and the correlation was measured through the quantity Q, the four momentum difference of the pair.

Journal ArticleDOI
P. D. Acton1, Gideon Alexander2, John Allison3, Phillip Allport4  +323 moreInstitutions (29)
TL;DR: In this paper, 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.
Abstract: 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.

Journal ArticleDOI
P. D. Acton1, R.J. Akers2, Gideon Alexander3, John Allison2  +326 moreInstitutions (30)
TL;DR: In this article, a sample of 2610 electron candidates and 2762 muon candidates identified in hadronicZ0 decays has been used to measure the averageb hadron lifetime.
Abstract: A sample of 2610 electron candidates and 2762 muon candidates identified in hadronicZ0 decays has been used to measure the averageb hadron lifetime. These data were recorded with the OPAL detector during 1990 and 1991. Maximum likelihood fits to the distributions of the lepton impact parameters yield an averageb hadron lifetime of $$\tau _b = 1523 \pm 34 \pm 38fs$$ , where the first error is statistical and the second systematic. This result is a weighted average over the semileptonic branching fractions and production rates of theb hadrons produced inZ0 decays.

Journal ArticleDOI
R.J. Akers1, Gideon Alexander2, John Allison1, K. J. Anderson3  +321 moreInstitutions (30)
TL;DR: In this article, the properties of single-tagged events were studied and the QED structure function was extracted from a sample of 1462γγ→μ�+μπππφ+φφ− events in which one photon is off the mass shell (singletagged).
Abstract: We have studied the reactionsγγ→μ + μ − andγγ→τ + τ − by measuring the properties of events of the typese + e −→e + e − μ + μ − ande + e −→e + e − τ + τ − ate + e − centre-of-mass energies between 88 and 94 GeV. The data sample corresponds to an integratede + e − luminosity of 40.4 pb−1 collected by the OPAL detector at LEP. The QED structure functionF 2 is extracted from a sample of 1462γγ→μ + μ − events in which one photon is off the mass shell (single-tagged). TheQ 2 range for these massive photons is 4–400 GeV2, with an averageQ 2 of 8 GeV2. We have observed 48e + e −→e + e − μ + μ − events in which both final state electrons are detected. In the sample of single-tag events we have identified 34.9±6.7 events as due to the reactionγ;→τ + τ −, on an estimated background of 5.1±2.7 events. In all cases the measured event distributions agree with QED calculations.

Journal ArticleDOI
R.J. Akers1, Gideon Alexander2, J. Allison1, K. J. Anderson3  +325 moreInstitutions (32)
TL;DR: In this article, a measurement of the forwardbackward asymmetry of the processes is presented at the center of mass energies near 91 GeV Decays of the Z0 into charm and bottom quarks are identified using 6507 charged D* mesons, reconstructed in the decays.
Abstract: A measurement is presented of the forwardbackward asymmetry of the processes\(e^ + e^ + \to c\bar c\) and\(e^ + e^ + \to b\bar b\) at centre of mass energies near 91 GeV Decays of theZ0 into charm and bottom quarks are identified using 6507 chargedD* mesons, reconstructed in the decaysD*±→D0π±→(K∓π±)π±,D*±→D0π±→(K∓π±π0)π± andD*±→D0π±→(K∓π±π∓π±)π± Thec quark asymmetry on theZ0 peak is measured to be $$A_{FB}^c = 0052 \pm 0028(stat) \pm 0012(sys)$$ The energy dependence of the asymmetry has been investigated at energies close to theZ0 peak Consistency with the predictions of the Standard Model is found

Journal ArticleDOI
R.J. Akers1, Gideon Alexander2, John Allison1, K. J. Anderson3  +312 moreInstitutions (30)
TL;DR: The average lifetime of baryons containing a b quark has been measured with the OPAL detector using data collected between 1990 and 1992 as mentioned in this paper, where the decay point of the baryon is estimated by the λ-lepton vertex, and the observed distribution of decay lengths is fitted to determine the average lifetime.

Journal ArticleDOI
P. D. Acton1, Gideon Alexander2, John Allison3, Phillip Allport4  +323 moreInstitutions (29)
TL;DR: In this paper, the cross section and jet rates of Z0 decays into photons and quarks are compared with matrix element Monte Carlos ofO(ααs) and good agreement is found between data and theoretical predictions.
Abstract: The cross section and jet rates ofZ0 decays into photons and quarks are compared with matrix element Monte Carlos ofO(ααs). Good agreement is found between data and theoretical predictions. From the ratio of events with three jets plus a photon to those with two jets plus a photon, αs in first order is determined to be 0.176±0.010. Combining the cross section of final state photon events with the LEP average hadronic partial decay width of theZ0, the widths of theZ0 into up and down type quarks can be calculated. The results $$\begin{gathered} \Gamma _{u - type} = 242 \pm 46MeV; \hfill \\ \Gamma _{d - type} = 419 \pm 30MeV \hfill \\ \end{gathered} $$ are in good agreement with the standard model expectation. A comparison of the measured cross section as a function ofycut with predictions of QCD shower models shows that, at the current level of accuracy ARIADNE and, to a lesser extent, HERWIG and JETSET can reproduce the measurement.

Journal ArticleDOI
P. D. Acton1, R.J. Akers2, Gideon Alexander3, John Allison2  +318 moreInstitutions (30)
TL;DR: The forward-backward asymmetries of hadronic events have been measured by the OPAL Collaboration using samples of electron or muon candidates from different sources as mentioned in this paper, where the distributions of the track momentum and transverse momentum component with respect to the associated jet were measured simultaneously in a two parameter fit.
Abstract: The forward-backward asymmetries of $$e^ + e^ - \to Z^0 \to b\bar b and e^ + e^ - \to Z^0 \to c\bar c$$ have been measured by the OPAL Collaboration using samples of hadronicZ 0 decays in which electron or muon candidates were observed. The asymmetries were measured simultaneously in a two parameter fit, which used the distributions of the track momentum and transverse momentum component with respect to the associated jet to distinguish lepton candidates from different sources. From a sample of 360 000 hadronic events with centre-of-mass energies within ±0.5 GeV of theZ 0 mass and mean energy 91.24. GeV, the values obtained for the $$b\bar b$$ asymmetry before and after correcting, for the effect of $$B^0 \overline {B^0 } $$ mixing, and for the $$c\bar c$$ asymmetry are, respectively: $$\begin{gathered} A_{FB}^{b,mix} = 0.070 \pm 0.014(stat) \pm 0.005(sys), \hfill \\ A_{FB}^b = 0.092 \pm 0.018(stat) \pm 0.007(sys) \hfill \\ \pm 0.003(mix), \hfill \\ A_{FB}^c = 0.014 \pm 0.030(stat) \pm 0.020(sys). \hfill \\ \end{gathered} $$ The measurement of the $$b\bar b$$ asymmetry is confirmed by a measurement using only leptons with high transverse momentum. This sample is highly enriched in semileptonic decays ofb hadrons. Measurements using high transverse momentum leptons were also performed using samples of events with centre-of-mass energies further from theZ 0 mass. After correcting for the effect of $$B^0 \overline {B^0 } $$ mixing, the results are: $$\begin{gathered} A_{FB}^b (\langle \sqrt s \rangle = 89.66GeV) \hfill \\ = 0.071 \pm 0.054(stat) \pm 0.007(sys) \pm 0.002(mix), \hfill \\ A_{FB}^b (\langle \sqrt s \rangle = 92.75GeV) \hfill \\ = 0.131 \pm 0.047(stat) \pm 0.012(sys) \pm 0.004(mix). \hfill \\ \end{gathered} $$

Journal ArticleDOI
P. D. Acton1, R.J. Akers2, Gideon Alexander3, John Allison2  +324 moreInstitutions (30)
TL;DR: In this paper, the fractional partial width of the Z0-trees and quarks was measured by OPAL using an impact parameter technique, and the measurement assumes the relative rates of theZ0 touds andc quarks given by the Standard Model.
Abstract: The fractional partial width of theZ0 tob quarks,\(\Gamma _{b\bar b} /\Gamma _{had} \), has been measured by OPAL using an impact parameter technique. The method has been developed using 130 000 hadronic events collected by OPAL in 1990. We find: $$\frac{{\Gamma _{b\bar b} }}{{\Gamma _{had} }} = 0.222 \pm 0.007(stat) \pm 0.008(sys).$$ The measurement assumes the relative rates of theZ0 touds andc quarks given by the Standard Model. Varying the charm fraction from the Standard Model value of\(\Gamma _{c\bar c} /\Gamma _{had} = 0.171\) changes the result by an additional\(\Delta \Gamma _{b\bar b} /\Gamma _{b\bar b} = - 0.135 \times \Delta \Gamma _{c\bar c} /\Gamma _{c\bar c} \).

Journal ArticleDOI
P. D. Acton1, R.J. Akers2, Gideon Alexander3, John Allison2  +326 moreInstitutions (30)
TL;DR: In this paper, a search for unstable, massive photinos pair produced in e + e − collisions has been performed using the OPAL detector at LEP, where the unstable photino is assumed to decay into τ ± / gn l ( l = e or μ ) final states, thereby violating individual lepton numbers and R parity.

Journal ArticleDOI
R.J. Akers1, Gideon Alexander2, John Allison1, K. J. Anderson3  +321 moreInstitutions (30)
TL;DR: In this paper, a measurement of the ratio of the strong coupling constants for various data samples with different quark flavour compositions obtained frome+e− annihilation at LEP is reported. But no evidence for a dependence of αs on any of these quark properties is observed.
Abstract: We report on a measurement of the ratio of the strong coupling constants\(\alpha _s (M_{Z^0 } )\) for various data samples with different quark flavour compositions obtained frome+e− annihilation at LEP. We select events with muons, electrons, andD*± mesons from charm and bottom decays, events with highly energeticKs0 mesons originating predominantly from strange quarks, and events with highly energetic stable charged particles from a combination of up, down and strange quarks. From the jet production rates in these events we obtain from these samples the relative value of αs for the individual quark flavours as $$\begin{gathered} \frac{{\alpha _s^b }}{{\alpha _s^{udsc} }} = 1.017 \pm 0.036,\frac{{\alpha _s^c }}{{\alpha _s^{udsb} }} = 0.918 \pm 0.115, \hfill \\ \frac{{\alpha _s^s }}{{\alpha _s^{udcb} }} = 1.158 \pm 0.164,\frac{{\alpha _s^{uds} }}{{\alpha _s^{cb} }} = 1.038 \pm 0.221, \hfill \\ \end{gathered}$$ with quadratically combined statistical and systematic errors. We also compare the αs values for quarks of diffrent weak isospin, charge and generation. No evidence for a dependence of αs on any of these quark properties is observed. Finally, combining all samples and determining the αsf/αsincl ratio for each flavour, we do not find any dependence of the strong coupling constant on flavour.

Journal ArticleDOI
P. D. Acton1, P. D. Acton2, G. Alexander1, G. Alexander3  +589 moreInstitutions (26)
TL;DR: In this paper, a sample of three-jet events containing a lepton with high momentum and transverse momentum was selected from hadronic decays of the Z0. The presence of the lepton indicates the semi-leptonic decay of a bottom quark and allows us, in combination with energy ordering of the jets, to distinguish between quarks and gluon jets.

Journal ArticleDOI
P. D. Acton1, Gideon Alexander2, John Allison, Phillip Allport  +320 moreInstitutions (29)
TL;DR: In this article, the azimuthal correlations of particles in hadronic events are studied and compared to QCD Monte Carlo models which include and do not include interference effects, and it is found that the distributions of these correlations are not reproduced by the parton shower models they have tested unless interference effects are included.
Abstract: From a sample of 146900 hadronicZ 0 decays recorded by the OPAL detector at LEP, we have studied the azimuthal correlations of particles in hadronic events. It is expected that these correlations are sensitive to interference effects in QCD. We have compared the data to QCD Monte Carlo models which include and which do not include interference effects. We find that the distributions of azimuthal correlations are not reproduced by the parton shower models we have tested unless interference effects are included, no matter which hadronisation scheme is used.