0000000000102940
AUTHOR
O Schneider
showing 25 related works from this author
Analysis of transverse momentum correlations in hadronic Z decays
1999
In a recent paper, evidence was presented for a significant, positive correlation between the total transverse momenta of particles on opposite hemispheres of hadronic events. A new, model independent analysis of the data has been made. Two components can be distinguished in the correlation, and quantitative estimates of each are given. The results form a significant test of Monte Carlo models and some of the physics behind them. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Search for pair-production of long-lived heavy charged particles in e+e− annihilation
1997
A search for pair-production of long-lived, heavy, singly-charged particles has been performed with data collected by the ALEPH detector at a centre-of-mass energy of 172 GeV. Data at \sqrt{s} = 161, 136, and 130 GeV are also included to improve the sensitivity to lower masses. No candidate is found in the data. A model-independent 95% confidence level upper limit on the production cross section at 172 GeV of 0.2-0.4pb is derived for masses between 45 and 86 GeV/c^2. This cross section limit implies, assuming the MSSM, a lower limit of 67 (69) GeV/c^2 on the mass of right- (left-) handed long-lived scalar taus or scalar muons and of 86 GeV/c^2 on the mass of long-lived charginos.
Search for charged Higgs bosons in $e^+ e^-$ collisions at centre-of-mass energies from 130 to 172 GeV
1998
Abstract The data collected at centre-of-mass energies ranging from 130 to 172 GeV by ALEPH at LEP, corresponding to an integrated luminosity of 27.5 pb−1, are analysed in a search for pair-produced charged Higgs bosons H±. Three analyses are employed to select the τ + ν τ τ − ν τ , c s τ − ν τ and c s s c final states. No evidence for a signal is found. Mass limits are set as a function of the branching fraction B (τν) for H±→τν. Charged Higgs bosons with masses below 52 GeV/c2 are excluded at 95% C.L. independently of B (τν) , thus significantly improving on existing limits.
Limits on neutral Higgs boson production in the forward region in $pp$ collisions at $\sqrt{s} = 7$ TeV
2013
Limits on the cross-section times branching fraction for neutral Higgs bosons, produced in p p collisions at root s = 7 TeV, and decaying to two tau leptons with pseudorapidities between 2.0 and 4.5, are presented. The result is based on a dataset, corresponding to an integrated luminosity of 1.0 fb(-1), collected with the LHCb detector. Candidates are identified by reconstructing final states with two muons, a muon and an electron, a muon and a hadron, or an electron and a hadron. A model independent upper limit at the 95% confidence level is set on a neutral Higgs boson cross-section times branching fraction. It varies from 8.6 pb for a Higgs boson mass of 90 GeV to 0.7 pb for a Higgs bos…
MEASUREMENT OF ALPHA(S) FROM SCALING VIOLATIONS IN FRAGMENTATION FUNCTIONS IN E(+)E(-) ANNIHILATION
1995
A study of scaling violations in fragmentation functions performed by the ALEPH collaboration at LEP is presented. Data samples enriched in uds, c, b and gluon jets, respectively, together with measurements of the longitudinal and transverse inclusive cross sections are used to extract the fragmentation function for the gluon and for each flavour. The measurements are compared to data from experiments at energies between 22 GeV and 91 GeV and scaling violations consistent with QCD predictions are observed. From this, a measurement of the strong coupling constant alpha(s) (M(z)) = 0.126 +/- 0.009 is obtained.
Measurement of Ab_FB using inclusive b-hadron decays
2001
Based on a sample of four million events collected by ALEPH from 1991 to 1995, a measurement of the forward-backward asymmetry in Z -> b-barb decays using inclusive final states is presented. High-performance tagging of b-barb events in a wide angular range is achieved using neural network techniques. An optimal hemisphere charge estimator is built by merging primary and secondary vertex information, leading kaon identification and jet charge in a neural network. The average charge asymmetry, the flavour tagging efficiencies and mean b-hemisphere charges are measured from data and used to extract the pole b asymmetry in the Standard Model A^{0,b}_{FB} = 0.1009 +- 0.0027 (stat) +- 0.0015 …
A measurement of |Vcb| from
1995
Abstract From approximately 3 million hadronic decays of Z bosons recorded with the aleph detector at lep , a sample of 410 ± 32 B 0 → D ∗+ l − ν l candidates is selected, where l is either an electron or a muon. The differential decay rate dΓ ( B 0 → D ∗+ l − ν l ) dω from this sample is fitted, yielding a value for the product of the CKM matrix element |Vcb| and the normalisation of the decay form factor at the point of zero recoil of the D∗+ meson F (ω = 1)|Vcb| = (31.4 ± 2.3stat ± 2.5syst) × 10−3. A value for |Vcb| is extracted using theoretical calculations of the form factor normalisation, with the result |Vcb| = (34.5 ± 2.5stat ± 2.7syst ± 1.5theory) × 10−3. From the integrated s the…
Searches for Supersymmetry in the photon(s) plus missing energy channels at $\sqrt{s}$ = 161 GeV and 172 GeV
1997
Searches for supersymmetric particles in channels with one or more photons and missing energy have been performed with data collected by the ALEPH detector at LEP. The data consist of 11.1 pb-1 at $\sqrt{s} = 161 GeV$, 1.1 pb-1 at 170 GeV and 9.5 pb-1 at 172 GeV. The e+e- -> nunu+photon cross section is measured. The data are in good agreement with predictions based on the Standard Model, and are used to set upper limits on the cross sections for anomalous photon production. These limits are compared to two different SUSY models and used to set limits on the neutralino mass. A limit of 71 GeV/c^2 at 95% C.L. is set on the mass of the lightest neutralino ($\tau_{\chi_{1}^{0}} \leq $ 3 ns) fo…
Measurement of the Bs0 lifetime and production rate with Ds−ℓ+ combinations in Z decays
1995
Abstract The lifetime of the Bs0 meson is measured in approximately 3 million hadronic Z decays accumulated using the ALEPH detector at LEP from 1991 to 1994. Seven different Ds− decay modes were reconstructed and combined with an opposite sign lepton as evidence of semileptonic Bs0 decays. Two hundred and eight Ds−l+ candidates satisfy selection criteria designed to ensure precise proper time reconstruction and yield a measured Bs0 lifetime of τ(Bs0) = 1.59−0.15+0.17 (stat) ±0.03 (syst) ps. Using a larger, less constrained sample of events, the product branching ratio is measured to be Br ( b → B s 0 ) · Br(B s 0 → D s − l + νX) = 0.82 ± 0.09 (stat) −0.14+0.13 (syst) %.
The topology dependence of charged particle multiplicities in three-jet events
1997
A study of individual jet and whole-event charged particle multiplicities in three-jet events measured in e(+)e(-) annihilation at the Z reveals a significant topology dependence. Mean jet multiplicities are inadequately described by jet energies; interjet angles must also be specified. Quantitative tests suggest that it is necessary to use transverse-momentum-like scales to describe the data. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; St.Denis, Richard/C-8997-2012; Sanchez, Federico/F-5809-2012; Forti, Francesco/H-3035-2011; Ferrante, Isidoro/F-1017-2012
Search for an invisibly decaying Higgs boson in e+e-collisions at 189 GeV
1999
The data collected in 1998 by ALEPH at LEP at a centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 176.2 pb(-1), are analysed to search for invisible decays of a Higgs boson produced in the reaction e(+) e(-) --> hZ. The number of events found in the data and their properties art: in agreement with the Standard Model expectation. This search results in an improved 95% C.L. lower limit on the Higgs boson mass of 95.4 GeV/c(2), assuming it decays totally invisibly and for a production cross section equal to that of the Standard Model. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Measurement of the W mass in e+e− collisions at 183 GeV
1999
Abstract The mass of the W boson is obtained from reconstructed invariant mass distributions in W-pair events. The sample of W pairs is selected from 57 pb−1 collected with the ALEPH detector in 1997 at a centre-of-mass energy of 183 GeV. The invariant mass distributions of reweighted Monte Carlo events are fitted separately to the experimental distributions in the q q q q and all lν q q channels to give the following W masses: m W hadronic =80.461±0.177 (stat.) ±0.045 (syst.) ±0.056 (theory) GeV /c 2 , m W semileptonic =80.326±0.184 (stat.) ±0.040 (syst.) GeV /c 2 , where the theory error represents the possible effects of final state interactions. The combination of these two measurements…
Measurement of the W-pair cross section in $e^+ e^-$ collisions at 172 GeV
1997
The e(+)e(-) --> W+W- cross section is measured in a data sample collected by ALEPH at a mean centre-of-mass energy of 172.09 GeV, corresponding to an integrated luminosity of 10.65 pb(-1). Cross sections are given for the three topologies, fully leptonic, semi-leptonic and hadronic of a W-pair decay. Under the assumption that no other decay modes are present, the W-pair cross section is measured to be 11.7 +/- 1.2(stat.) +/- 0.3(syst.) pb. The existence of the triple gauge boson vertex of the Standard Model is clearly preferred by the data. The decay branching ratio of the W boson into hadrons is measured to be B(W --> hadrons) = 67.7 +/- 3.1(stat.) +/- 0.7(syst.) %, allowing a determinati…
Search for CP violation in D (+/-) -> (KSK +/-)-K-0 and D-s(+/-) -> K-S(0)pi(+/-) decays
2014
A search for \CP violation in Cabibbo-suppressed $D^{\pm}\rightarrow K^0_{\mathrm{S}} K^{\pm}$ and $D^{\pm}_{s}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}$ decays is performed using $pp$ collision data, corresponding to an integrated luminosity of 3~fb$^{-1}$, recorded by the LHCb experiment. The individual $CP$-violating asymmetries are measured to be \begin{eqnarray*} \mathcal{A}_{CP}^{D^{\pm}\rightarrow K^0_{\mathrm{S}} K^{\pm}} & = & (+0.03 \pm 0.17 \pm 0.14) \% \mathcal{A}_{CP}^{D^{\pm}_{s}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}} & = & (+0.38 \pm 0.46 \pm 0.17) \%, \end{eqnarray*} assuming that $CP$ violation in the Cabibbo-favoured decays is negligible. A combination of the measured asymmet…
Single- and multi-photon production in e+e− collisions at a centre-of-mass energy of 183 GeV
1998
The production of final states involving one or more energetic photons from e(+)e(-) collisions is studied in a sample of 58.5 pb(-1) of data recorded at a centre-of-mass energy of 183 GeV by the ALEPH detector at LEP. The e(+)e(-) --> v (v) over bar gamma(gamma) and e(+)e(-) --> gamma gamma(gamma) cross sections are measured. The data are in good agreement with predictions based on the Standard Model and are used to set upper limits on the cross sections for anomalous photon production in the context of two supersymmetric models and for various extensions to QED. In particular, in the context of a super-light gravitino model a cross section upper limit of 0.38 pb is placed on the process e…
Measurement of polarization amplitudes and CP asymmetries in B 0 → Φk *(892)0
2014
An angular analysis of the decay $B^0 \to \phi K^*(892)^0$ is reported based on a $pp$ collision data sample, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected at a centre-of-mass energy of $\sqrt{s} = 7$ TeV with the LHCb detector. The P-wave amplitudes and phases are measured with a greater precision than by previous experiments, and confirm about equal amounts of longitudinal and transverse polarization. The S-wave $K^+ \pi^-$ and $K^+K^-$ contributions are taken into account and found to be significant. A comparison of the $B^0 \to \phi K^*(892)^0$ and $\bar{B}^0 \to \phi \bar{K}^*(892)^0$ results shows no evidence for direct CP violation in the rate asymmetry, in th…
Measurement of the Michel parameters and the nu(tau) helicity in tau lepton decays
2001
A measurement of the Michel parameters and the average $\nu_\tau$ helicity in $\tau$ lepton decays is described. The data was collected with the ALEPH detector at LEP during the years 1991 to 1995. A total integrated luminosity of 155\,$\text{pb}^{-1}$ is analysed. The Michel parameters $\rho_l$, $\xi_l$, $(\xi\delta)_l$ ($l=e,\mu$), and $\eta_\mu$ are determined for the leptonic deca ys, and the chirality parameters $\xi_\pi$, $\xi_\rho$, and $\xi_{a_1}$ for the hadronic final states. Under the assumptions of $e$\bis $\mu$ universality and $\xi_\pi=\xi_\rho=\xi_{a_1}$, the values $\rho_l=0.742\pm 0.016, \eta_l=0.01 2\pm 0.026,\break (\xi\delta)_l=0.776\pm 0.051, \xi_l=0.986\pm 0.074$, and …
A measurement of Rb using mutually exclusive tags
1997
A measurement of R-b using five mutually exclusive hemisphere tags has been performed by ALEPH using the full LEP1 statistics. Three tags are designed to select the decay of the Z(0) to b quarks, while the remaining two select Z(0) decays to c and light quarks, and are used to measure the tagging efficiencies. The result, R-b = 0.2159 +/- 0.0009(stat) +/-0.0011(syst), is in agreement with the electroweak theory prediction of 0.2158 +/- 0.0003. (C) 1997 Published by Elsevier Science B.V. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; St.Denis, Richard/C-8997-2012; Forti, Francesco/H-3035-2011; Ferrante, Isidoro/F-1017-2012
Search for invisible Higgs boson decays in e+e- collisions at centre-of-mass energies up to 184 GeV
1999
In a data sample of 78.3 pb(-1) collected in 1996 and 1997 by the ALEPH detector at centre-of-mass energies from 161 to 184 GeV, invisible decays of a Higgs boson have been searched for in the reaction e(+)e(-) --> hZ, where the Z can decay into e(+)e(-), mu(+) mu(-) or . No evidence for a signal is found and limits on the production cross section are derived as a function of the Higgs boson mass. These results are combined with those obtained in an update of the analyses of the ALEPH data taken at LEP 1. For a production cross section equal to that of the minimal standard model Higgs boson, masses below 80 GeV/c(2) are excluded at 95% C.L. (C) 1999 Elsevier Science B.V. All rights reserved.
A measurement of the QCD colour factors and a limit on the light gluino
1997
Using data collected from 1992 to 1995 with the ALEPH detector at LEP, a measurement of the colour factor ratios C-A/C-F and T-F/C-F and the strong coupling constant = C-F alpha(s), (M-Z)/(2 pi) has been performed by fitting theoretical predictions simultaneously to the measured differential two-jet rate and angular distributions in four-jet events. The result is found to be in excellent agreement with QCD. C-A/C-F = 2.20 +/- 0.09 (stat) +/- 0.13 (syst), T-F/C-F = 0.29 +/- 0.05 (stat) +/- 0.06 (syst). Fixing C-A/C-F and T-F/C-F to the QCD values permits a determination of alpha(s) (M-Z) and n(f), the number of active flavours. With this measurement the existence of a gluino with mass below …
Four-jet final state production in $e^+ e^-$ collisions at centre-of-mass energies ranging from 130 to 184 GeV
1998
The four jet topology is analysed in the ALEPH data taken between November 1995 and November 1997, at centre-of-mass energies ranging from 130 to 184 GeV. While an unexpected accumulation of events with a dijet mas sum around 105 GeV/c**2 had been observed during the first run in 1995 at 130/136 GeV, corresponding to an integrated luminosity of 5.7 pb-1, no significant differences between data and standard model prediction is noticed, either in the high energy runs (81.1 pb-1 taken at centre-of-mass energies from 161 to 184 GeV) or in the 7.1 pb-1 recorded during a new short run at 130/136 GeV in 1997. We have found no other explanation for the earlier reported ``four jet anomaly'' than a s…
Angular analysis of charged and neutral B → Kμ + μ − decays
2014
The angular distributions of the rare decays B → K+µ+µ- and B0 → K0 <inf>a</inf>Sμ+μ- are studied with data corresponding to 3 fb-1 of integrated luminosity, collected in proton-proton collisions at 7 and 8TeV centre-of-mass energies with the LHCb detector. The angular distribution is described by two parameters, FH and the forward-backward asymmetry of the dimuon system AFB, which are determined in bins of the dimuon mass squared. The parameter F<inf>H</inf> is a measure of the contribution from (pseudo)scalar and tensor amplitudes to the decay width. The measurements of A<inf>FB</inf> and F<inf>H</inf> reported here are the most precise to d…
Search for supersymmetric particles with R-parity violation in Z decays
1995
Searches for supersymmetric particles produced in e(+)e(-) interactions at the Z peak have been performed under the assumptions that R-parity is not conserved, that the dominant R-parity violating coupling involves only leptonic fields, and that the lifetime of the lightest supersymmetric particle can be neglected. In a data sample collected by the ALEPH detector at LEP up to 1993, and corresponding to almost two million hadronic Z decays, no signal was observed. As a result, supersymmetric particle masses and couplings are at least as well constrained as under the usual assumption of R-parity conservation.
Measurement of the transverse spin correlations in the decay Z → τ+τ-
1997
For tau leptons produced in e(+)e(-) --> tau(+)tau(-) interactions there are, in addition to the longitudinal spin correlations, two independent transverse spin correlations associated with the transverse (within the production plane) and normal (to the production plane) polarization components. A measurement of the transverse-transverse and transverse-normal tau spin correlations in the decay Z --> tau(+)tau(-), C-TT and C-TN, is presented based on the aplanarity angle of the decay products of both tau leptons. Using 80 pb(-1) of data collected by ALEPH on the peak of the Z resonance, the results are C-TT = 1.06 +/- 0.13(stat) +/- 0.05(syst), and C-TN = 0.08 +/- 0.13(stat) +/- 0.04(syst). …
Measurement of the B-0 -> K*(0) e(+) e(-) branching fraction at low dilepton mass
2013
The branching fraction of the rare decay B-0 -> K*(0) e(+) e(-) in the dilepton mass region from 30 to 1000 MeV/c(2) has been measured by the LHCb experiment, using pp collision data, corresponding to an integrated luminosity of 1.0 fb(-1), at a centre-of-mass energy of 7 TeV. The decay mode B-0 -> J/psi (e(+) e(-)) K*(0) is utilized as a normalization channel. The branching fraction B(B-0 -> K*(0) e(+) e(-)) is measured to be B(B-0 -> K*(0) e(+) e(-))(30-1000 MeV/c2) = (3.1(-0.8)(-0.3)(+0.9)(+0.2) +/- 0.2) x 10(-7) where the fi rst error is statistical, the second is systematic, and the third comes from the uncertainties on the B-0 -> J/K*(0) and J/psi -> e(+) e(-) branching fractions.