0000000000069230
AUTHOR
O Deschamps
Analysis of transverse momentum correlations in hadronic Z decays
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.
Limits on neutral Higgs boson production in the forward region in $pp$ collisions at $\sqrt{s} = 7$ TeV
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…
Search for an invisibly decaying Higgs boson in e+e-collisions at 189 GeV
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
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…
Search for CP violation in D (+/-) -> (KSK +/-)-K-0 and D-s(+/-) -> K-S(0)pi(+/-) decays
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
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
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…
Search for invisible Higgs boson decays in e+e- collisions at centre-of-mass energies up to 184 GeV
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.
Four-jet final state production in $e^+ e^-$ collisions at centre-of-mass energies ranging from 130 to 184 GeV
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
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…
Measurement of the B-0 -> K*(0) e(+) e(-) branching fraction at low dilepton mass
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.