0000000000085891
AUTHOR
Perez P
showing 23 related works from this author
Three-prong τ decays with charged kaons
1998
Final states with charged kaons in three-prong τ decays are studied by exploiting the particle identification from the dE/dx measurement. The results are based on a sample of about 1.6 × 105 detected τ pairs collected with the ALEPH detector between 1991 and 1995 around the Z peak. The following branching ratios have been measured: B(τ- → K−K+π−ντ) = (1.63 ± 0.21 ± 0.17) × 10−3, B(τ− → K−π+π−ντ) = (2.14 ± 0.37 ± 0.29) × 10−3, B(τ− → K−K+π−π0ντ) = (0.75 ± 0.29 ± 0.15) × 10−3, and B(τ− → K−π+π−π0ντ) = (0.61 ± 0.39 ± 0.18) × 10−3. The first two measurements are more precise than the current world averages, while the last two channels are investigated for the first time. The 95% C.L. upper limi…
Improved measurements of electroweak parameters from Z decays into fermion pairs
1992
The properties of the Z resonance are measured on the basis of 190000 Z decays into fermion pairs collected with the ALEPH detector at LEP. Assuming lepton universality, M(Z) = (91.182 +/- 0.009exp +/- 0.020L;P) GeV, GAMMA(Z) = (2484 +/- 17) MeV, sigma(had)0 = (41.44 +/- 0.36) nb, and GAMMA(had)/GAMMA(ll) = 21.00 +/- 0.20. The corresponding number of light neutrino species is 2.97 +/- 0.07. The forward-backward asymmetry in leptonic decays is used to determine the ratio of vector to axial-vector coupling constants of leptons: g(V)2(M(Z)2)/g(A)2(M(Z)2) = 0.0072 +/- 0.0027. Combining these results with ALEPH results on quark charge and bbBAR asymmetries, and tau-polarization, sin2 theta(W)(M(…
Production of Charmed Mesons In Z Decays
1994
The production of charmed mesons $$\mathop {D^0 }\limits^{( - )} $$ ,D ± , andD *± is studied in a sample of 478,000 hadronicZ decays. The production rates are measured to be $$\begin{gathered} \frac{{\Gamma ({\rm Z} \to D^{* \pm } X)}}{{\Gamma _{had} }} = 0.187 \pm 0.015(\exp .) \pm 0.013(BR), \hfill \\ \frac{{\Gamma ({\rm Z} \to D^ \pm X)}}{{\Gamma _{had} }} = 0.251 \pm 0.026(\exp .) \pm 0.025(BR), \hfill \\ \frac{{\Gamma ({\rm Z} \to \mathop {D^0 }\limits^{( - )} X)}}{{\Gamma _{had} }} = 0.518 \pm 0.052(\exp .) \pm 0.035(BR), \hfill \\ \end{gathered} $$ where the errors from this analysis are separated from those coming from theD branching ratios (BR). TheD *± momentum distribution is ex…
Study of the fragmentation of b quarks into B mesons at the Z peak
2001
The fragmentation of b quarks into B mesons is studied with four million hadronic Z decays collected by the ALEPH experiment during the years 1991-1995. A semi-exclusive reconstruction of B->l nu D(*) decays is performed, by combining lepton candidates with fully reconstructed D(*) mesons while the neutrino energy is estimated from the missing energy of the event. The mean value of xewd, the energy of the weakly-decaying B meson normalised to the beam energy, is found to be mxewd = 0.716 +- 0.006 (stat) +- 0.006 (syst) using a model-independent method; the corresponding value for the energy of the leading B meson is mxel = 0.736 +- 0.006 (stat) +- 0.006 (syst). The reconstructed spectra …
Measurements of mean lifetime and branching fractions of b hadrons decaying to J/ψ
1992
From a data sample of 450 000 hadronic events recorded with the ALEPH detector at LEP, 92 +/- 10 events are observed containing a J/psi meson decaying to mu+mu- or e+e-. From these data the measured inclusive branching fraction for a b flavoured hadron to decay to a J/psi is BR(b --> J/psiX) = (1.21 +/- 0.13 (stat.) +/- 0.08 (syst.))%, and the average b hadron lifetime in the events tagged with a J/psi is tau(b) = 1.35(-0.17)+0.19 +/- 0.05 ps. Five events are observed consistent with the exclusive decay B+/- --> J/psiK+/- and from these events the exclusive branching fraction is measured to be BR(B+/- --> J/psiK+/-) = (0.22 +/- 0.10 +/- 0.02)%. Upper limits for other exclusive branching rat…
Search for CP violation in the decay Z → τ+τ−
1995
Data collected by ALEPH in the years 1990, 1991 and 1992 have been used to update a previous search for CP violation in the decay of the Z into tau(+)tau(-). The measurement of the weak dipole form factor of the tau lepton has been performed by studying correlations between the tau leptons. No signal of CP violation was found. The weak dipole form factor is found to be ($) over tilde d(tau) = (+0.15 +/- 0.58(stat) +/- 0.38(sys)) 10(-17)e . cm, obtained with 19628 identified tau(+)tau(-) events. This gives an upper limit on the weak dipole form factor of j\($) over tilde d(tau)\ < 1.5 . 10(-17)e . cm at the 95% confidence level.
Production ofK 0 and Λ in hadronic Z decays
1994
Measurements of the inclusive cross-sections forK 0 and Λ production in hadronic decays of the Z are presented together with measurements of two-particle correlations within pairs of Λ andK 0. The results are compared with predictions from the hadronization models Jetset, based on string fragmentation, and Herwig, based on cluster decays. TheK 0 spectrum is found to be harder than predicted by both models, while the Λ spectrum is softer than predicted. The correlation measurements are all reproduced well by Jetset, while Herwig misses some of the qualitative features and overestimates the size of the $$\Lambda \bar \Lambda $$ correlation. Finally, the possibility of Bose-Einstein correlatio…
The forward-backward asymmetry for charm quarks at the Z pole
1995
From 1.4 million hadronic Z decays collected by the ALEPH detector at LEP, an enriched sample of Z --> c $$($) over bar c events is extracted by requiring the presence of a high momentum D*(+/-). The charm quark forward-backward charge asymmetry at the Z pole is measured to be A(FB)(0,c) = (8.0 +/- 2.4)% corresponding to an effective electroweak mixing angle of sin(2) theta(W)(eff) = 0.2302 +/- 0.0054.
Properties of Hadronic Z-decays and Test of QCD Generators
1992
Distributions are presented of event shape variables, jet roduction rates and charged particle momenta obtained from 53 000 hadronic Z decays. They are compared to the predictions of the QCD + hadronization models JETSET, ARIADNE and HERWIG, and are used to optimize several model parameters. The JETSET and ARIADNE coherent parton shower (PS) models with running alpha(s) and string fragmentation yield the best description of the data. The HERWIG parton shower model with cluster fragmentation fits the data less well. The data are in better agreement with JETSET PS than with JETSET O(alpha(s)2) matrix elements (ME) even when the renormalization scale is optimized.
A study of tau decays involving eta and omega mesons
1997
The 132 pb(-1) of data collected by ALEPH from 1991 to 1994 have been used to analyze eta and omega production in 7 decays. The following branching fractions have been measured: B(tau(-) --> nu(tau)omega h(-)) = (1.91 +/- 0.07 +/- 0.06) x 10(-2), B(tau(-) --> nu(tau)omega h(-)pi(0)) = (4.3 +/- 0.6 +/- 0.5) x 10(-3), B(tau(-) --> nu(tau)eta K-) = (2.9(-1.2)(+1.3) +/- 0.7) x 10(-4), B(tau(-) --> nu(tau)eta(h)(-)pi(0)) = (1.8 +/- 0.4 +/- 0.2) x 10(-3) and the 95% C.L. limit B(tau(-) --> nu(tau)eta pi(-)) < 6.2 x 10(-4) has been obtained. The omega pi(-) and eta pi(-)pi(0) rates and dynamics are found in agreement with the predictions made from e(+)e(-) annihilation data with the help of isospi…
Observation of monojet events and tentative interpretation
1994
Abstract A data sample corresponding to almost two million hadronic Z decays collected by the ALEPH detector at LEP has been searched for monojet events. Three events were found, in agreement with the expectation from the process e + e − → γ * v v ¯ , with γ * → f f ¯ . Two events are hadronic, the third one being an e + e − pair. All monojet masses are in excess of 3 GeV/ c 2 , and two of the event have large transverse momenta: 18.5 and 20.3 GeV/ c . These kinematic characteristics are quite unlikely in the process e + e − → γ * v v ¯ . The probability of their occurence increases substantially when processes involving further Z or W exchanges are taken into account, but still remains at …
A measurement of the b baryon lifetime
1992
In 451 000 hadronic Z0 decays, recorded with the ALEPH detector at LEP, the yields of lambdal- and lambdal+ combinations are measured. Semileptonic decays of b baryons result in a signal of 122 +/- 18(stat.)+22/-23(syst.) lambdal- combinations. From a fit to the impact parameter distribution of the leptons in the lambdal- sample, the lifetime of b baryons is measured to be 1.12+0.32/-0.29(stat.) +/- 0.16(syst.) ps.
Heavy Flavor Production and Decay With Prompt Leptons In the Aleph Detector
1994
In 431 000 hadronicZ decays recorded with the ALEPH detector at LEP, the yields of electrons and muons in events with one or more prompt leptons have been analysed to give information on the production and decay of heavy quarks. The fractions of $$b\bar b$$ and $$c\bar c$$ events are measured to be 0.219±0.006±0.005 and 0.165±0.005±0.020, and the corresponding forward-backward asymmetries at theZ mass are measured to be 0.090±0.013±0.003 and 0.111±0.021±0.018, after QED and QCD corrections. Measurements for the semileptonic branching ratios BR $$(b \to \ell ^ - \bar vX)$$ and BR (b→cl+ vX) yield 0.114±0.003±0.004 and 0.082±0.003±0.012, respectively. The dilepton events enable measurement of…
Evidence for b baryons in Z decays
1992
Abstract In 160 000 hadronic Z decays recorded with the ALEPH detector at LEP, the yields of Λl− and Λl+ combinations have been measured. The observed excess of Λl− over Λl+ of 53±13 is interpreted as evidence for b baryons and their semileptonic decay. Assuming that three body decay processes such as Λ b →Λ c + l − v dominate the semileptonic decay of b baryons, this ex cess corresponds to a product branching ratio BR ( b →Λ b )· BR (Λ b →Λ c + l − v )· BR (Λ c + →ΛX) = (0.95±0.22 ( stat. )±0.21( syst. ))% , where Λb and Λc+ denote the bottom and charm baryons respectively.
Search for CP violation in ZmF ττ
1992
Abstract 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 dτ(mZ) = (1.3 ± 1.4 ± 0.1) × 10−17 e·cm which results in an upper limit on the weak dipole moment of |dτ(mZ)| ⩽ 3.7 × 10−17 e·cm with 95% confidence level.
Measurement of the Effective b quark Fragmentation Function At the Z resonance
1995
Using a sample of about 1.46 million hadronic Z decays collected between 1991 and 1993 with the ALEPH detector at LEP, the energy distribution of the B-0 and B-+/- mesons produced at the Z resonance is measured by reconstructing semileptonic decays B --> l nu(l)D(X) or B --> l nu(l)D*(+)(X). The charmed mesons are reconstructed through the decay modes D-0 --> K(-)pi(+), D-0, --> K(-)pi(+)pi(-)pi(+),D+ --> K(-)pi(+)pi(+), and D*(+) --> D-0 pi(+). The neutrino energy is estimated from the missing energy in the lepton hemisphere. Accounting for B* and B** production, the shape of the scaled energy distribution x(E)((b)) for mesons containing a b quark is compared to the predictions of differen…
MEASUREMENT OF THE PRODUCTION-RATES OF ETA AND ETA' IN HADRONIC-Z DECAYS
1992
The decays eta --> gammagamma and eta' --> etapi+pi- have been observed in hadronic decays of the Z produced at LEP. The fragmentation functions of both the eta and eta' have been measured. The measured multiplicities for x > 0.1 are 0.298 +/- 0.023 +/- 0.021 and 0.068 +/- 0.018 +/- 0.016 for eta and eta' respectively. While the fragmentation function for the eta is fairly well described by the JETSET Monte Carlo, it is found that the production rate of the eta' is a factor of four less than the corresponding prediction.
Measurement of triple gauge WWγ couplings at LEP2 using photonic events
1998
A study of events with photons and missing energy has been performed with the data sample obtained with the ALEPH detector at centre-of-mass energies from 161 to 184 GeV,corresponding to a total integrated luminosity of about 80 pb**-1.The measured distributions are in agreement with Standard Model predictions, leading to constraints on W W gamma gauge coupling parameters Delta(kappa_gamma) and lambda_gamma. The results from the fit to the cross sectionsand to the energy and angular distributions of the photons are: Delta(kappa_gamma) = 0.05 +1.15/-1.10 (stat) +/- 0.25 (syst) lambda_gamma = 0.05 +1.55/-1.45 (stat) +/- 0.30 (syst) A study of events with photons and missing energy has been pe…
Study of the subjet structure of quark and gluon jets
1995
Measurements of the subjet structure of quark and gluon jets in hadronic Z decays are presented. The analysis is based on one million hadronic events recorded by the ALEPH detector. Roughly symmetric three-jet events are selected with a coarse jet-resolution cut-off, y(1). Gluon jets are identified with a purity of 94.6% in those events where evidence of long-lived heavy-flavour hadrons in the other two jets is found. The jets are then analyzed using a smaller cut-off y(0) (< y(1)) so that subjets are resolved. The properties of the jets (subjet multiplicities [N-q], [N-g] and rates R(n)(g(q)) for n = 1,2,3,4) are determined and are found to be in good agreement with the expectations of per…
Michel Parameters and tau neutrino Helicity From Decay Correlations In Z->tau+tau-
1995
The Michel parameters and the average tau-neutrino helicity are measured using correlations between the decays of the tau(+) and tau(-) produced on the Z resonance and observed in the ALEPH detector at LEP. The Michel parameters, rho(e), eta(e), xi(e), (delta xi)(e), are determined from tau --> e ($) over bar upsilon(e) upsilon(tau) with e = (e, mu), and the average tau neutrino helicity, (h(upsilon(tau))), from tau --> h tau with h = (pi, rho, a(1)). The results obtained with e-mu universality are: rho(e) = 0.751 +/- 0.039 +/- 0.022, eta(e) = -0.04 +/- 0.15 +/- 0.11, xi(e) = 1.18 +/- 0.15 +/- 0.06, (delta xi)(e) = 0.88 +/- 0.11 +/- 0.07, and the average tau neutrino helicity (h(upsilon(tau…
Search for Single Top Production in $e^{+} e^{-}$ Collisions at $\sqrt{s}$ up to 209 GeV
2002
Single top production via the flavour changing neutral current reactions e+e- -> \bar{t}c, \bar{t}u is searched for within the 214 pb-1 of data collected by ALEPH at centre-of-mass energies between 204 and 209 GeV. No deviation from the Standard Model expectation is observed and upper limits on the single top production cross sections are derived. The combination with data collected at lower centre-of-mass energies yields an upper limit on the branching ratio BR(t -> Zc)+BR(t -> Zu) 14%, for BR(t -> ��c)+BR(t -> ��u)= 0 and mt=174 GeV/c2.
Measurements of the b baryon lifetime
1995
Using about 1.5 million hadronic Z decays recorded with the ALEPH detector, the lifetime of the b baryons has been measured using two independent data samples. From a maximum likelihood fit to the impact parameter distribution of leptons in 519 Lambda l(-) combinations containing a b baryon sample of 290 decays, the measured b baryon lifetime is tau(b-baryon) = 1.05(-0.11)(+0.12)(stat) +/-0.09(syst) ps. The lifetime of the Lambda(b)(0) baryon from a maximum likelihood fit to the proper time distribution of 58 Lambda(c)(+)l(-) candidates containing a Lambda(b)(0) sample of 44 decays, is tau(Lambda b0) = 1.02(-0.18)(+0.23)(stat) +/- 0.06(syst) ps.
AN INVESTIGATION INTO INTERMITTENCY
1992
The results of an investigation based on ALEPH data, e+ e- --> hadrons at square-root s = 91 GeV, into fluctuations in rapidity space are presented. It is found that the behaviour of the factorial moments is well represented by the Lund parton shower model. An estimate is made of the scale of fluctuations needed to describe the data. Differential moments are introduced and are used to demonstrate that within the average represented by the traditional factorial moments the pattern of fluctu10.1007/BF01483869ations is itself a strong function of rapidity. This pattern is shown to be primarily associated with the emission of hard gluons. The implied structure between the hadron clusters and pa…