0000000000037530
AUTHOR
K. Hüttmann
showing 38 related works from this author
Determination of the LEP centre-of-mass energy from Zγ events
1999
Radiative returns to the Z resonance (Zgamma events) are used to determine the LEP2 centre-of-mass energy from the data collected with the ALEPH detector in 1997. The average centre-of-mass energy is measured to be: E_CM = 182.50 +- 0.19(stat) +- 0.08(syst) GeV in good agreement with the precise determination by the LEP energy working group of 182.652 +- 0.050 GeV. If applied to the measurement of the W mass, its precision translates into a systematic error on M_W which is smaller than the statistical error achieved from the corresponding dataset.
Search for γγ→ηb in e+e− collisions at LEP 2
2002
A search for the pseudoscalar meson eta_b is performed in two-photon interactions at LEP~2 with an integrated luminosity of 699 pb^-1 collected at e+e- centre-of-mass energies from 181 GeV to 209 GeV. One candidate event is found in the six-charged-particle final state and none in the four-charged-particle final state, in agreement with the total expected background of about one event. Upper limits of Gamma_gammagamma(eta_b) * BR(eta_b -> 4 charged particles) 6 charged particles) < 132 eV are obtained at 95% confidence level, which correspond to 95% confidence level upper limits of 9.0% and 25% on these branching ratios.
Study of the CP asymmetry of B0 -> J/psi K0S decays in ALEPH
2000
The decay B0 -> J/psi K0_S is reconstructed with J/psi -> e+ e- or mu+ mu- and K0_S -> pi+ pi-. From the full ALEPH dataset at LEP1 of about 4 million hadronic Z decays, 23 candidates are selected with an estimated purity of 71%. They are used to measure the CP asymmetry of this decay, given by sin 2beta in the Standard Model, with the result sin 2beta = 0.84 +0.82-1.04 +-0.16. This is combined with existing measurements from other experiments, and increases the confidence level that CP violation has been observed in this channel to 98%.
Search for $\gamma\gamma$ decays of a Higgs boson produced in association with a fermion pair in $e^+ e^-$ collisions at LEP
2000
A serach for gamma gamma decays of Higgs boson is performed in the data sample collected at LEP with the ALEPH detector between 1991 and 1999. This corresponds to an integrated luminosity of 672 pb-1 centre-of-mass energies ranging from 88 to 202 GeV. The search is based on topologies arising from a Higgs boson produced in association with a fermion pair via the Higgs-strahlung process e+e- -> Hffbar, with ffbar = nunubar, e+e-, mu+mu-, tau+tau- or qqbar... (CERN)
Searches for neutral Higgs bosons in e+e− collisions at centre-of-mass energies from 192 to 202 GeV
2000
Searches for neutral Higgs bosons are performed with the 237 pb-1 of data collected in 1999 by the ALEPH detector at LEP, for centre-of-mass energies between 191.6 and 201.6 GeV. These searches apply to Higgs bosons within the context of the Standard Model and its minimal supersymmetric extension (MSSM) as well as to invisibly decaying Higgs bosons. No evidence of a signal is seen. A lower limit on the mass of the Standard Model Higgs boson of 107.7 GeV/c2 at 95% confidence level is set. In the MSSM, lower limits of 91.2 and 91.6 GeV/c2 are derived for the masses of the neutral Higgs bosons h and A, respectively. For a Higgs boson decaying invisibly and produced with the Standard Model cros…
A flavour-independent Higgs boson search in e+e- collisions at sqrt(s) up to 209GeV
2002
A search for the Higgsstrahlung process e+e- → HZ is carried out, covering decays of the Higgs boson into any quark pair, a gluon pair or a tau pair. The analysis is based on the 630 pb-1 of data collected by the ALEPH detector at LEP at centre-of-mass energies from 189 to 209 GeV. A 95% C.L. lower mass limit of 109.1 GeV/c2 is obtained for a Higgs boson cross section equal to that expected from the Standard Model if the Higgs boson decays exclusively into hadrons and/or taus, irrespective of the relative branching fractions. © 2002 Elsevier Science B.V. All rights reserved.
A study of single W production in e+e− collisions at –183 GeV
1999
Abstract Single W production is studied in the data recorded with the ALEPH detector at LEP at centre-of-mass energies between 161 and 183 GeV. The cross section is measured to be σW=0.41±0.17(stat.)±0.04(syst.) pb at 183 GeV, consistent with the Standard Model expectation. Limits on non-standard WWγ couplings are deduced as −1.6 γ (λ γ =0) and −1.6 γ (κ γ =1) at 95% C.L. A search for effectively invisible decays of the W boson in W pair production is performed, leading to an upper limit on the branching ratio of 1.3% ( Γ inv =27 MeV ) at 95% C.L.
Measurement of W-pair production in $e^+ e^-$ collisions at 189 GeV
2000
The production of W-pairs is analysed in a data sample collected by ALEPH at a mean centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 174.2 pb^-1. Cross sections are given for different topologies of W decays into leptons or hadrons. Combining all final states and assuming Standard Model branching fractions, the total W-pair cross section is measured to be 15.71 +- 0.34 (stat) +- 0.18 (syst) pb. Using also the W-pair data samples collected by ALEPH at lower centre-of-mass energies, the decay branching fraction of the W boson into hadrons is measured to be BR (W > hadrons) = 66.97 +- 0.65 (stat) +- 0.32 (syst) %, allowing a determination of the CKM matrix el…
Absolute Lower Limits on the Masses of Selectrons and Sneutrinos in the MSSM
2002
The results of searches for selectrons, charginos and neutralinos performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies up to 209 GeV are interpreted in the framework of the Minimal Supersymmetric extension of the Standard Model with R-parity conservation. Under the assumptions of gaugino and sfermion mass unification and no sfermion mixing, an absolute lower limit of 73 GeV/c2 is set on the mass of the lighter selectron at the 95% confidence level. Similarly, limits on the masses of the heavier selectron and of the sneutrino are set at 107 and 84 GeV/c2, respectively. Additional constraints are derived from the results of the searches for Higgs bosons. T…
Measurement of the hadronic photon structure function at LEP 1 for 〈Q2〉 values between 9.9 and 284 GeV2
1999
Inclusive γ*γ interactions to hadronic final states where one scattered electron or positron is detected in the electromagnetic calorimeters have been studied in the LEP 1 data taken by ALEPH from 1991 to 1995. The event sample has been used to measure the hadronic structure function of the photon F2γ in three bins with of 9.9, 20.7 and 284 GeV2.
Inclusive production of the η and ω mesons in Z decays, and the muonic branching ratio of the ω
2002
AbstractThe inclusive production of the η and ω(782) mesons is measured in the π+π−π0 decay mode in hadronic Z decays and compared to model predictions. The analysis is based on 4 million hadronic Z decays recorded by the ALEPH detector between 1991 and 1995. The η production rate for xp=pmeson/pbeam>0.10 is found to be 0.355±0.011stat±0.024sys per event, and the ω production rate for xp>0.05 is measured as 0.585±0.019stat±0.033sys per event. The branching ratio for ω→μ+μ− is investigated. A total of 18.1±5.9 events are observed, from which the muonic branching ratio is measured for the first time to be BR(ω→μ+μ−)=(9.0±2.9stat±1.1sys)×10−5.
Fermion pair production in e+e- collisions at 189-209 GeV and constraints on physics beyond the Standard Model
2006
Cross sections, angular distributions and forward-backward asymmetries are presented, of two-fermion events produced in e+e- collisions at centre-of-mass energies from 189 to 209 GeV at LEP, measured with the ALEPH detector. Results for e+e-, mu+mu-, tau+tau-, qq, bb and cc production are in agreement with the Standard Model predictions. Constraints are set on scenarios of new physics such as four-fermion contact interactions, leptoquarks, Z' bosons, TeV-scale quantum gravity and R-parity violating squarks and sneutrinos.
Improved search for $B_{s}^{0} - \overline{B}_{s}^{0}$ oscillations
2003
An improved search for Bs oscillations is performed in the ALEPH data sample collected during the first phase of LEP, and reprocessed in 1998. Three analyses based on complementary event selections are presented. First, decays of Bs mesons into hadronic flavour eigenstates are fully reconstructed. This selection yields a small sample of candidates with excellent decay length and momentum resolution and high average Bs purity. Semileptonic decays with a reconstructed Ds- meson provide a second sample with larger statistics, high average Bs purity, but a poorer momentum and decay length resolution due to the partial decay reconstruction. Finally, semileptonic b-hadron decays are inclusively s…
Search for charged Higgs bosons in $e^+ e^-$ collisions at energies up to $\sqrt{s}$ = 189 GeV
2000
The data collected at centre-of-mass energies of 188.6 GeV by ALEPH at LEP, corresponding to an integrated luminosity of 176.2 pb-1, are analysed in a search for pair-produced charged Higgs bosons H+/-. Three analyses are employed to select the taunutaunu, taunucs and cscs final states. No evidence for a signal is found. Upper limits are set on the production cross section as a function of the branching fraction BR(H+ to tau nu) and of the mass M(H+), assuming that the sum of the branching ratios is equal to one. In the framework of a two-Higgs-doublet model, charged Higgs bosons with masses below 65.4 GeV/c2 are excluded at 95% confidence level independently of the decay mode.
Search for a scalar top almost degenerate with the lightest neutralino e(+)e(-) collisions at root s up to 202 GeV
2000
Data collected at centre-of-mass energies from 189 GeV to 202 GeV by the ALEPH detector at LEP corresponding to an integrated luminosity of 411 pb(-1), are analysed in a search for the scalar top in the decay channels (t) over tilde --> c/u chi for small mass differences between the stop and the lightest neutralino. No evidence for deviations from the Standard Model expectation is found and a lower limit of 59 GeV/c(2) is set for the stop mass, independent of the stop to neutralino mass difference and of the stop lifetime. (C) 2000 Elsevier Science B.V. All rights reserved.
A direct measurement of |Vcs| in hadronic W decays using a charm tag
1999
Abstract The inclusive charm production rate in W decays is measured from a study of the properties of final state particles. The sample of W pairs is selected from 67.7 pb−1 collected by ALEPH in 1996 and 1997 at centre-of-mass energies near 172 and 183 GeV in the channels W+W−→4q and W + W − →lνq q . The branching fraction of hadronic W decays to a final state containing a c quark, RWc= Γ(W→cX)/Γ(W→hadrons), is measured to be 0.51±0.05stat±0.03syst. This allows a direct determination of the CKM matrix element |Vcs|=1.00±0.11stat±0.07syst.
Search for Supersymmetric Particles in e+e- Collisions at sqrt(s) up to 202GeV and Mass Limit for the Lightest Neutralino
2000
Searches for pair production of squarks, sleptons, charginos, and neutralinos are performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies from 188.6 to 201.6 GeV. No evidence for any such signals is observed in a total integrated luminosity of about 410pb-1. The negative results of the searches are translated into exclusion domains in the space of the relevant MSSM parameters, which improve significantly on the constraints set previously. Under the assumptions of gaugino and sfermion mass unification, these results allow a 95% C.L. lower limit of 37GeV/c2 to be set on the mass of the lightest neutralino for any tan beta and sfermion mass. Additional constra…
Final results of the searches for neutral Higgs bosons in e+e- collisions at sqrt(s) up to 209GeV
2002
The final results of the ALEPH search for the Standard Model Higgs boson at LEP, with data collected in the year 2000 at centre-of-mass energies up to 209 GeV, are presented. The changes with respect to the preceding publication are described and a complete study of systematic effects is reported. The findings of this final analysis confirm the preliminary results published in November 2000 shortly after the closing down of the LEP collider: a significant excess of events is observed, consistent with the production of a $115 \Gcs$ Standard Model Higgs boson. The final results of the searches for the neutral Higgs bosons of the MSSM are also reported, in terms of limits on $\mh$, $\mA$ and $…
Search for pentaquarks states in Z decays
2004
Exotic hadrons made of five quarks (pentaquarks) are searched for in hadronic Z decays collected by the ALEPH detector at LEP. No significant signal is observed. At 95% C.L. upper limits are set on the production rates N of such particles and their charge-conjugate state per Z decay: N Θ(1535)+·BR(Θ(1535)+→pK S0)<6.2×10-4, N Ε(1862)-·BR(Ε(1862)-→Ε -π-)<4.5×10-4, N Ε(1862)0·BR(Ε(1862)0→Ε -π+)<8.9×10-4, N Θc(3100)0·BR(Θc(3100) 0→D*-p)<6.3×10-4, N Θc(3100)0·BR(Θc(3100) 0→D-p)<31×10-4. © 2004 Elsevier B.V. All rights reserved.
Search for the glueball candidates f0(1500) and fJ(1710) in γγ collisions
2000
Abstract Data taken with the ALEPH detector at LEP1 have been used to search for γγ production of the glueball candidates f0(1500) and fJ(1710) via their decay to π+π−. No signal is observed and upper limits to the product of γγ width and π+π− branching ratio of the f0(1500) and the fJ(1710) have been measured to be Γ(γγ→f 0 (1500))· B R (f 0 (1500)→π + π − ) keV and Γ(γγ→f J (1710))· B R (f J (1710)→π + π − ) keV at 95% confidence level.
Deuteron and anti-deuteron production in e+e− collisions at the Z resonance
2006
Deuteron and anti-deuteron production in Z decays has been observed in the ALEPH experiment at LEP. The production rate of anti-deuterons is measured to be 5.9+-1.8+-0.5 10^-6 per hadronic Z decay in the anti-deuteron momentum range 0.62 to 1.03 GeV/c. The coalescence parameter B_2, which characterizes the likelihood of anti-deuteron production, is measured to be 0.0033+-0.0013 GeV^2 in Z dedays. These measurements indicate that the production of anti-deuterons is suppressed in e+e- collisions compared to pp and photoproduction collisions.
Fermi-Dirac correlations in Lambda pairs in hadronic Z decays
2000
Two-particle correlations of Lambda Lambda and pairs have been studied in multihadronic Z decays recorded with the ALEPH detector at LEP in the years from 1992 to 1995. The correlations were measured as a function of the four-momentum difference Q of the pair. A depletion of events is observed in the region Q 2 GeV the fraction of pairs with spin one is consistent with the value of 0.75 expected for a statistical spin mixture, whilst for Q pairs, where no Fermi-Dirac correlations are expected, the spin one fraction is measured to be consistent with 0.75 over the entire analysed Q range. (C) 2000 Elsevier Science B.V. All rights reserved.
Search for γγ decays of a Higgs boson in e+e- collisions at √s up to 209 GeV
2002
A search for events with a photon pair arising from the decay of a Higgs boson produced in association with a fermion pair, is performed in 893 pb-1 of data recorded by the ALEPH detector at LEP at centre-of-mass energies up to 209 GeV. No excess of such events is found over the expected background, An upper limit is derived on the product of the e+e- → HZ cross section and the H → γγ branching fraction as a function of the Higgs boson mass. A fermiophobic Higgs boson produced with the Standard Model cross section is excluded at 95% confidence level for all masses below 105.4 GeV/c2. © 2002 Elsevier Science B.V. All rights reserved.
Searches for the neutral Higgs bosons of the MSSM in e+e− collisions at centre-of-mass energies of 181–184 GeV
1998
The data collected by ALEPH at LEP at centre-of-mass energies ranging from 181 to 184 GeV, corresponding to an integrated luminosity of 57 pb(-1), are analysed to search for pair-produced neutral Higgs bosons h and A, in the b (b) over bar b (b) over bar and tau(+)tau(-)b (b) over bar final states. Two events are found in the data with 2.5 expected from standard model processes. When combined with the lower energy data collected by ALEPH and with earlier reported searches for associated hZ production, these analyses are interpreted in the context of the minimal supersymmetric extension of the standard model (MSSM). For standard choices of MSSM parameter sets, this combination results in 95%…
Searches for sleptons and squarks in e(+)e(-) collisions at 189 GeV
1999
The data collected at a centre-of-mass energy of 188.6 GeV by ALEPH at LEP, corresponding to an integrated luminosity of 173.6 pb$^{-1}$, are analysed in a search for the scalar partners of quarks and leptons predicted in supersymmetric models. No evidence for any such particles was found in the decay channels $\sle \to \ell \chi$, $\stop \rightarrow \mathrm{c}\neu$, $\stop \rightarrow \mathrm{b}\ell\snu$, $\sbot \rightarrow \mathrm{b}\neu$, and $\mathrm{\tilde{q}} \rightarrow \mathrm{q}\neu$. Improved mass lower limits have been obtained in the framework of the Minimal Supersymmetric Standard Model.
Bose-Einstein correlations in W-pair decays with an event-mixing technique
2005
Bose-Einstein correlations in W-pair decays are studied using data collected by the ALEPH detector at LEP at e(+)e(-) centre-of-mass energies from 183 to 209 GeV. The analysis is based on the comparison of WW --> q (q) over barq (q) over bar events to "mixed" events constructed with the hadronic part of WW --> q (q) over bar lv events. The data are in agreement with the hypothesis that Bose-Einstein correlations are present only for pions from the same W decay. The JETSET model with Bose-Einstein correlations between pions from different W bosons is disfavoured. (C) 2004 Elsevier B.V. All rights reserved.
Search for the standard model Higgs boson at the LEP2 collider near
1998
Abstract During 1997 the ALEPH experiment at LEP gathered 57 pb −1 of data at centre-of-mass energies near 183 GeV . These data are used to look for possible signals from the production of the Standard Model Higgs boson in the reaction e+e−→HZ. No evidence of a signal is found in the data; seven events are selected, in agreement with the expectation of 7.2 events from background processes. This observation results in an improved lower limit on the mass of the Higgs boson: m H >87.9 GeV /c 2 at 95% confidence level.
A study of the decay width difference in the B0s– system using φφ correlations
2000
In a data sample of about four million hadronic Z decays recorded with the ALEPH detector from 1991 to 1995, the decay is observed, based on tagging the final state with two φ mesons in the same hemisphere. The final state is mostly CP even and corresponds to the short-lived B0s mass eigenstate. The branching ratio of this decay is measured to be . A measurement of the lifetime of the B0s(short) gives 1.27±0.33±0.08 ps. The lifetime and branching ratio measurements provide two essentially independent methods of estimating the relative decay width difference ΔΓ/Γ in the B0s– system, corresponding to an average value ΔΓ/Γ=(25+21−14)%.
Search for single top production in e+e− collisions at –202 GeV
2000
Abstract Single top production via flavour changing neutral currents in the reactions e + e − → t c / u is searched for in approximately 411 pb −1 of data collected by ALEPH at centre-of-mass energies in the range between 189 and 202 GeV. In total, 58 events are selected in the data to be compared with 50.3 expected from Standard Model backgrounds. No deviation from the Standard Model expectation is observed. Upper limits at 95% CL on single top production cross sections at s =189 –202 GeV are derived. A model-dependent limit on the sum of branching ratios BR(t→Zc)+BR(t→Zu)
Production of Ds** mesons in hadronic Z decays
2002
The production rates of the orbitally excited Ds** mesons, Ds1 and Ds2*, are measured with the 4.1 million hadronic Z decays recorded by the ALEPH detector during 1991--1995. The Ds** mesons are reconstructed in the decay modes Ds1+ -> D*+ K0, Ds1+ -> D*0 K+ and Ds2*+ -> D0 K+. The production rate of the Ds1 is measured to be n(Z->Ds1+-)=(0.52+-0.09+-0.06)%, under the assumption that the two considered decay modes of the Ds1 saturate the branching ratio. The production rate of the Ds2* is determined to be n(Z->Ds2*+-)=(0.83+-0.29+0.07-0.13)%, assuming that the branching fraction of the decay Ds2*+ -> D0 K+ is 45%. The production rates in Z->cc and Z->bbar decays are …
Search for charginos nearly mass degenerate with the lightest neutralino in e+e− collisions at centre-of-mass energies up to 209 GeV
2002
A search for charginos nearly mass degenerate with the lightest neutralino is performed with the data collected by the ALEPH detector at LEP, at centre-of-mass energies between 189 and 209 GeV, corresponding to an integrated luminosity of 628 pb-1. The analysis is based on the detection of isolated and energetic initial state radiation photons, produced in association with chargino pairs whose decay products have little visible energy. The number of candidate events observed is in agreement with that expected from Standard Model background sources. These results are combined with those of other direct searches for charginos, and a lower limit of 88 GeV/c2 at 95 % confidence level is derived…
Measurement of the e+e- → ZZ production cross section at centre-of-mass energies of 183 and 189 GeV
1999
The ee -> ZZ cross section at sqrt(s)=182.7 and 188.6 GeV has been measured using the ALEPH detector. The analysis covers all of the visible ZZ final states and yields cross section measurements of sigma_ZZ(182.7 GeV) = 0.11 +- (0.16,0.11) (stat.) +- 0.04 (syst.) pb and sigma_ZZ(188.6 GeV) = 0.67 +- 0.13 (stat.) +- 0.04 (syst.) pb consistent with the Standard Model expectations.
Exclusive production of pion and kaon meson pairs in two photon collisions at LEP
2003
Exclusive production of pi and K meson pairs in two photon collisions is measured with ALEPH data collected between 1992 and 2000. Cross-sections are presented as a function of cos theta* and invariant mass, for \ cos theta* \ < 0.6 and invariant masses between 2.0 and 6.0 GeV/c(2) (2.25 and 4.0 GeV/c(2)) for pions (kaons). The shape of the distributions are found to be well described by QCD predictions but the data have a significantly higher normalization. (C) 2003 Published by Elsevier B.V.
Leptonic decays of the D-s meson
2002
The purely leptonic decays Ds -> tau nu and Ds -> mu nu are studied in a sample of four million hadronic Z decays collected with the ALEPH detector at the LEP e+e- collider from 1991 to 1995. The branching fractions are extracted from a combination of two analyses, one optimized to select Ds -> tau nu decays with tau -> e nu nubar or mu nu nubar, and the other optimized for Ds-> mu nu decays. The results are used to evaluate the Ds decay constant, within the Standard Model: fDs = [285 +- 19(stat) +- 40 (syst)] MeV
Inclusive semileptonic branching ratios of b hadrons produced in Z decays
2001
A measurement of the inclusive semileptonic branching ratios of b hadrons produced in Z decay is presented, using four million hadronic events collected by the ALEPH detector from 1991 to 1995. Electrons and muons are selected opposite to b-tagged hemispheres. Two different methods are explored to distinguish the contributions from direct $\bl$ and cascade $\bcl$ decays to the total lepton yield. One is based on the lepton transverse momentum spectrum, the other makes use of the correlation between the charge of the lepton and charge estimators built from tracks in the opposite hemisphere of the event. The latter method reduces the dependence on the modelling of semileptonic b decays. The r…
Observation of an excess in the search for the Standard Model Higgs boson at ALEPH
2000
A search has been performed for the Standard Model Higgs boson in the data sample collected with the ALEPH detector at LEP, at centre-of-mass energies up to 209GeV. An excess of 3sigma beyond the background expectation is found, consistent with the production of the Higgs boson with a mass near 114GeV/c2. Much of this excess is seen in the four-jet analyses, where three high purity events are selected.
Search for neutral Higgs bosons decaying into four taus at LEP2
2010
A search for the production and non-standard decay of a Higgs boson, h, into four taus through intermediate pseudoscalars, a, is conducted on 683 pb-1 of data collected by the ALEPH experiment at centre-of-mass energies from 183 to 209 GeV. No excess of events above background is observed, and exclusion limits are placed on the combined production cross section times branching ratio, β2 = σ(e+e -→Zh)/σSM(e+e-→Zh) ×B(h→aa)×B(a→τ+τ-) 2. For mh 1 is excluded at the 95% confidence level.
Measurement of Z-pair production in e(+)e(-) collisions and constraints on anomalous neutral gauge couplings
2009
The ZZ production cross section is measured from a data sample corresponding to a total integrated luminosity of 452 pb−1, collected by the ALEPH experiment at LEP at centre-of-mass energies from 192 to 209 GeV. Individual cross sections, extracted at six centre-of-mass energies, are found to be in agreement with Standard Model calculations. The results are used to set limits on anomalous neutral gauge couplings. The ZZ production cross section is measured from a data sample corresponding to a total integrated luminosity of 452 pb−1 , collected by the ALEPH experiment at LEP at centre-of-mass energies from 192 to 209 GeV. Individual cross sections, extracted at six centre-of-mass energies, …