-
R. Barate,
D. Buskulic,
D. Decamp,
P. Ghez,
C. Goy,
J.-P. Lees,
A. Lucotte,
E. Merle,
M.-N. Minard,
J.-Y. Nief, [......],
J.M. Nachtman,
J. Nielsen,
W. Orejudos,
Y.B. Pan,
Y. Saadi,
I.J. Scott,
J. Walsh,
Sau Lan Wu,
X. Wu,
G. Zobernig
[show abstract]
[hide abstract]
ABSTRACT: An improved measurement of the forward-backward asymmetry in decays is presented, based on a sample of 4.1 million hadronic Z decays collected by ALEPH between 1991 and 1995. Data are analysed as a function of polar angle of the event axis and b purity. The event tagging efficiency and mean b-jet hemisphere charge are measured directly from data. From the measured forward-backward jet charge asymmetry, the b quark asymmetry at is determined to be: AbFB=0.1017±0.0038(stat.)±0.0032(syst.). In the context of the Standard Model this corresponds to a value of the effective weak mixing angle of sin2θWeff=0.23109±0.00096.
Physics Letters B 03/2013; · 3.95 Impact Factor
-
R. Barate,
D. Buskulic,
D. Decamp,
P. Ghez,
C. Goy,
J.-P. Lees,
A. Lucotte,
E. Merle,
M.-N. Minard,
J.-Y. Nief, [......],
J.M. Nachtman,
J. Nielsen,
W. Orejudos,
Y.B. Pan,
Y. Saadi,
I.J. Scott,
J. Walsh,
Sau Lan Wu,
X. Wu,
G. Zobernig
[show abstract]
[hide abstract]
ABSTRACT: The flavour changing neutral current decay b→sγ has been detected in hadronic Z decays collected by ALEPH at LEP. The signal is isolated in lifetime-tagged events by the presence of a hard photon associated with a system of high momentum and high rapidity hadrons. The background processes are normalised from the data themselves. The inclusive branching ratio is measured to beconsistent with the Standard Model expectation via penguin processes.
Physics Letters B 03/2013; · 3.95 Impact Factor
-
A. Heister,
S. Schael,
R. Barate,
I. De Bonis,
D. Decamp,
C. Goy,
J.-P. Lees,
E. Merle,
M.-N. Minard,
B. Pietrzyk, [......],
S. Jin,
J. Kile,
P.A. McNamara,
J. Nielsen,
Y.B. Pan,
J. Wu,
Sau Lan Wu,
X. Wu,
G. Zobernig,
G. Dissertori
[show abstract]
[hide abstract]
ABSTRACT: The 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.
Physics Letters B 03/2013; · 3.95 Impact Factor
-
R. Barate,
D. Buskulic,
D. Decamp,
P. Ghez,
C. Goy,
J.-P. Lees,
A. Lucotte,
E. Merle,
M.-N. Minard,
J.-Y. Nief, [......],
J.M. Nachtman,
J. Nielsen,
W. Orejudos,
Y.B. Pan,
Y. Saadi,
I.J. Scott,
J. Walsh,
Sau Lan Wu,
X. Wu,
G. Zobernig
[show abstract]
[hide abstract]
ABSTRACT: Starting from a sample of four million hadronic Z decays collected with the ALEPH detector at LEP, 404 charged and neutral B mesons are fully reconstructed and used to look for resonant structure in the Bπ system. An excess of events is observed above the expected background in the Bπ mass spectrum at a mass ≈5.7 GeV/c2, consistent with the production and decay to B(∗)π of the B∗∗ states predicted by Heavy Quark Symmetry (HQS). In the framework of HQS, it is found that the mass of the state is MeV/c2 and the relative production rate of the B∗∗ system is . In the same sample of B mesons, significant Bπ± charge-flavour correlations are observed, which may prove important for tagging the initial B state in future CP violation studies.
Physics Letters B 03/2013; · 3.95 Impact Factor
-
R. Barate,
D. Decamp,
P. Ghez,
C. Goy,
S. Jezequel,
J.-P. Lees,
F. Martin,
E. Merle,
M.-N. Minard,
B. Pietrzyk, [......],
J. Nielsen,
W. Orejudos,
Y.B. Pan,
Y. Saadi,
I.J. Scott,
J. Walsh,
J. Wu,
Sau Lan Wu,
X. Wu,
G. Zobernig
[show abstract]
[hide abstract]
ABSTRACT: 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 , and 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 and of the mass mH±, 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.
Physics Letters B 03/2013; · 3.95 Impact Factor
-
R. Barate,
D. Buskulic,
D. Decamp,
P. Ghez,
C. Goy,
S. Jezequel,
J.-P. Lees,
A. Lucotte,
M.-N. Minard,
J.-Y. Nief, [......],
J. Nielsen,
W. Orejudos,
Y.B. Pan,
Y. Saadi,
I.J. Scott,
J. Walsh,
Sau Lan Wu,
X. Wu,
J.M. Yamartino,
G. Zobernig
[show abstract]
[hide abstract]
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 10.65 pb−1 collected with the ALEPH detector at a mean centre-of-mass energy of 172.09 GeV. The invariant mass distribution of simulated events are fitted to the experimental distributions and the following W masses are obtained:The statistical errors are the expected errors for Monte Carlo samples of the same integrated luminosity as the data. The combination of these three measurements gives:
Physics Letters B 03/2013; · 3.95 Impact Factor
-
R. Barate,
D. Decamp,
P. Ghez,
C. Goy,
S. Jezequel,
J.-P. Lees,
F. Martin,
E. Merle,
M.-N. Minard,
B. Pietrzyk, [......],
J. Nielsen,
W. Orejudos,
Y.B. Pan,
Y. Saadi,
I.J. Scott,
J. Walsh,
J. Wu,
Sau Lan Wu,
X. Wu,
G. Zobernig
[show abstract]
[hide abstract]
ABSTRACT: A search for γγ decays of a 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 at 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 , with or . Twenty-two events are selected in the data, while 28 events are expected from standard model processes. An upper limit is derived, as a function of the Higgs boson mass, on the product of the cross section and the H→γγ branching fraction. In particular, a fermiophobic Higgs boson produced with the standard model cross section is excluded at 95% confidence level for all masses below .
Physics Letters B 03/2013; · 3.95 Impact Factor
-
D. Buskulic,
I. De Bonis,
D. Decamp,
P. Ghez,
C. Goy,
J.-P. Lees,
A. Lucotte,
M.-N. Minard,
P. Odier,
B. Pietrzyk, [......],
M. Schmitt,
I.J. Scott,
V. Sharma,
J.D. Turk,
A.M. Walsh,
Sau Lan Wu,
X. Wu,
J.M. Yamartino,
M. Zheng,
G. Zobernig
[show abstract]
[hide abstract]
ABSTRACT: Searches for supersymmetric particles produced in e+e− collisions at centre-of-mass energies of 130 and 136 GeV have been performed in a data sample of 5.7 pb−1 collected in the autumn of 1995 by the ALEPH detector at LEP. No candidate events were found, allowing limits to be set on the masses and production cross-sections of scalar leptons, scalar tops, charginos and neutralinos. The domains previously excluded at LEP1 are substantially extended. For instance, masses of gaugino-like charginos smaller than 67.8 GeV/c2 are excluded at the 95% C.L. for scalar neutrino masses larger than 200 GeV/c2.
Physics Letters B 03/2013; · 3.95 Impact Factor
-
D. Buskulic,
I. De Bonis,
D. Decamp,
P. Ghez,
C. Goy,
J.-P. Lees,
A. Lucotte,
M.-N. Minard,
J.-Y. Nief,
P. Odier, [......],
W. Orejudos,
Y.B. Pan,
Y. Saadi,
I.J. Scott,
A.M. Walsh,
Sau Lan Wu,
X. Wu,
J.M. Yamartino,
M. Zheng,
G. Zobernig
[show abstract]
[hide abstract]
ABSTRACT: A search for pair production of new heavy leptons has been performed assuming different scenarios for the mixing of the new particles with Standard Model leptons. No candidate events were found in a data sample corresponding to an integrated luminosity of 5.6 pb−1 collected by the ALEPH detector at centre-of-mass energies of 130 and 136 GeV. New limits on production cross-sections and on masses of sequential leptons were obtained which significantly extend the mass regions excluded at LEP1. For instance, charged heavy leptons with masses below 63.5 GeV/c2 are excluded at 95% C.L. for mass differences to the associated neutral lepton of more than 7 GeV/c2.
Physics Letters B 03/2013; · 3.95 Impact Factor
-
D. Buskulic,
I. De Bonis,
D. Decamp,
P. Ghez,
C. Goy,
J.-P. Lees,
A. Lucotte,
M.-N. Minard,
P. Odier,
B. Pietrzyk, [......],
Y. Saadi,
M. Schmitt,
I.J. Scott,
V. Sharma,
A.M. Walsh,
Sau Lan Wu,
X. Wu,
J.M. Yamartino,
M. Zheng,
G. Zobernig
[show abstract]
[hide abstract]
ABSTRACT: Searches for charginos and neutralinos produced in e+e− collisions at centre-of-mass energies of 130 and 136 GeV 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 the 5.7 pb−1 data sample collected by ALEPH, no candidate events were found. As a result, chargino and neutralino masses and couplings are constrained and the domains previously excluded at LEP1 are extended.
Physics Letters B 03/2013; · 3.95 Impact Factor
-
R. Barate,
D. Buskulic,
D. Decamp,
P. Ghez,
C. Goy,
S. Jezequel,
J.-P. Lees,
A. Lucotte,
F. Martin,
E. Merle, [......],
J.M. Nachtman,
J. Nielsen,
W. Orejudos,
Y.B. Pan,
Y. Saadi,
I.J. Scott,
J. Walsh,
Sau Lan Wu,
X. Wu,
G. Zobernig
[show abstract]
[hide abstract]
ABSTRACT: 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 WWγ gauge coupling parameters Δκγ and λγ. The results from the fit to the cross sections and to the energy and angular distributions of the photons are: Δκγ=0.05+1.15−1.10(stat)±0.25(syst), λγ=−0.05+1.55−1.45(stat)±0.30(syst).
Physics Letters B 03/2013; · 3.95 Impact Factor
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A. Heister,
S. Schael,
R. Barate,
R. Brunelière,
I. De Bonis,
D. Decamp,
C. Goy,
S. Jezequel,
J.-P. Lees,
F. Martin, [......],
P.A. McNamara,
J. Nielsen,
Y.B. Pan, J.H. von Wimmersperg-Toeller,
W. Wiedenmann,
J. Wu,
Sau Lan Wu,
X. Wu,
G. Zobernig,
G. Dissertori
[show abstract]
[hide abstract]
ABSTRACT: 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 for the chargino mass in the case of heavy sfermions, irrespective of the chargino-neutralino mass difference.
Physics Letters B 03/2013; · 3.95 Impact Factor
-
R. Barate,
D. Decamp,
P. Ghez,
C. Goy,
S. Jezequel,
J.-P. Lees,
F. Martin,
E. Merle,
M.-N. Minard,
B. Pietrzyk, [......],
J.M. Nachtman,
J. Nielsen,
W. Orejudos,
Y.B. Pan,
Y. Saadi,
I.J. Scott,
J. Walsh,
Sau Lan Wu,
X. Wu,
G. Zobernig
[show abstract]
[hide abstract]
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 and all channels to give the following W masses:where the theory error represents the possible effects of final state interactions. The combination of these two measurements, including the LEP energy calibration uncertainty, gives
Physics Letters B 03/2013; · 3.95 Impact Factor
-
R. Barate,
D. Buskulic,
D. Decamp,
P. Ghez,
C. Goy,
S. Jezequel,
J.-P. Lees,
A. Lucotte,
M.-N. Minard,
J.-Y. Nief, [......],
J. Nielsen,
W. Orejudos,
Y.B. Pan,
Y. Saadi,
I.J. Scott,
J. Walsh,
Sau Lan Wu,
X. Wu,
J.M. Yamartino,
G. Zobernig
[show abstract]
[hide abstract]
ABSTRACT: The triple gauge-boson couplings, αWΦ, αW and αBΦ, have been measured using 34 semileptonically and 54 hadronically decaying W+W− candidate events. The events were selected in the data recorded during 1996 with the ALEPH detector at 172 GeV, corresponding to an integrated luminosity of 10.65 pb−1. The triple gauge-boson couplings have been measured using optimal observables constructed from kinematic information of W+W− events. The results are in agreement with the Standard Model expectation.
Physics Letters B 03/2013; · 3.95 Impact Factor
-
R. Barate,
D. Decamp,
P. Ghez,
C. Goy,
S. Jezequel,
J.-P. Lees,
F. Martin,
E. Merle,
M.-N. Minard,
B. Pietrzyk, [......],
J. Nielsen,
W. Orejudos,
Y.B. Pan,
Y. Saadi,
I.J. Scott,
J. Walsh,
J. Wu,
Sau Lan Wu,
X. Wu,
G. Zobernig
[show abstract]
[hide abstract]
ABSTRACT: 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 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/c2 is set for the stop mass, independent of the stop to neutralino mass difference and of the stop lifetime.
Physics Letters B 03/2013; · 3.95 Impact Factor
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B. Aubert,
D. Boutigny,
J.-M. Gaillard,
A. Hicheur,
Y. Karyotakis,
J. P. Lees,
P. Robbe,
V. Tisserand,
A. Palano,
A. Pompili, [......],
F. Di Lodovico,
Y. Pan,
R. Prepost,
I. J. Scott,
S. J. Sekula, J. H. von Wimmersperg-Toeller,
S. L. Wu,
Z. Yu,
T. M. B. Kordich,
H. Neal
[show abstract]
[hide abstract]
ABSTRACT: We present a measurement of time-dependent CP-violating asymmetries in neutral B meson decays collected with the BABAR detector at the PEP-II asymmetric-energy e+e- collider at the Stanford Linear Accelerator Center. The data sample consists of 29.7 fb-1 recorded at the Υ(4S) resonance and 3.9 fb-1 off resonance. One of the neutral B mesons, which are produced in pairs at the Υ(4S), is fully reconstructed in the CP decay modes J/ψKS0, ψ(2S)KS0, χc1KS0, J/ψK*0 (K*0→KS0π0) and J/ψKL0, or in flavor-eigenstate modes involving D(*)π/ρ/a1 and J/ψK*0 (K*0→K+π-). The flavor of the other neutral B meson is tagged at the time of its decay, mainly with the charge of identified leptons and kaons. A neural network tagging algorithm is used to recover events without a clear lepton or kaon tag. The proper time elapsed between the decays is determined by measuring the distance between the decay vertices. Wrong-tag probabilities, the time-difference resolution function, and the B0-B0 oscillation frequency Δmd are measured with a sample of about 6350 fully-reconstructed B0 decays in hadronic flavor-eigenstate modes. A maximum-likelihood fit to this flavor eigenstate sample finds Δmd=0.516±0.016(stat)±0.010(syst)ps-1. The value of the asymmetry amplitude sin2β is determined from a simultaneous maximum-likelihood fit to the time-difference distribution of the flavor-eigenstate sample and about 642 tagged B0 decays in the CP-eigenstate modes. We find sin2β=0.59±0.14(stat)±0.05(syst), demonstrating that CP violation exists in the neutral B meson system. We also determine the value of the CP violation parameter |λ|=0.93±0.09(stat)±0.03(syst), which is consistent with the expectation of |λ|=1 for no direct CP violation.
Physical Review D 02/2013; 66(3). · 4.56 Impact Factor
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D. Buskulic,
I. De Bonis,
D. Decamp,
P. Ghez,
C. Goy,
J.-P. Lees,
A. Lucotte,
M.-N. Minard,
P. Odier,
B. Pietrzyk, [......],
Y. Saadi,
M. Schmitt,
I.J. Scott,
V. Sharma,
A.M. Walsh,
Sau Lan Wu,
X. Wu,
J.M. Yamartino,
M. Zheng,
G. Zobernig
[show abstract]
[hide abstract]
ABSTRACT: The B0 - B̄0 average mixing parameter and b forward-backward asymmetry AFB0(b) are measured from a sample of about 4 200 000 Z → qq̄ events recorded with the ALEPH detector at LEP in the years 1990–1995. High transverse momentum electrons and muons produced in b semileptonic decays provide the tag of the quark flavour and of its charge.The average mixing parameter and the pole b asymmetry are measured to be = 0.1246 ± 0.0051stat ± 0.0052syst, AFB0(b) = 0.1008 ± 0.0043stat ± 0.0028syst. The value of sin2θweff = 0.23198 ± 0.00092 is extracted from the asymmetry measurement.
Physics Letters B 12/2012; · 3.95 Impact Factor
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S. Schael,
R. Barate,
R. Brunelière,
I. De Bonis,
D. Decamp,
C. Goy,
S. Jézéquel,
J.-P. Lees,
F. Martin,
E. Merle, [......],
J. Nielsen,
Y.B. Pan, J.H. von Wimmersperg-Toeller,
W. Wiedenmann,
J. Wu,
Sau Lan Wu,
X. Wu,
G. Zobernig,
G. Dissertori,
The ALEPH Collaboration
[show abstract]
[hide abstract]
ABSTRACT: A search for Higgs bosons produced in association with a fermion pair, and decaying to WW, is performed with the data collected
by the ALEPH detector at centre-of-mass energies ranging from 191 to 209GeV. The data correspond to an integrated luminosity
of 453.2pb-1. Thirteen exclusive selections are developed according to the different final state topologies. No statistically significant
evidence for a Higgs boson decaying into a WW pair has been found. An upper limit is derived, as a function of the Higgs boson
mass, on the product of the e+e-→Hff̄ cross section and the H→WW branching ratio. The data on the search for H→WW are combined with previously published ALEPH
results on the search for H→γγ, to significantly extend the limits on the mass of a fermiophobic Higgs boson.
European Physical Journal C 04/2012; 49(2):439-455. · 3.63 Impact Factor
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S. Schael,
R. Barate,
R. Brunelière,
I. De Bonis,
D. Decamp,
C. Goy,
S. Jézéquel,
J.-P. Lees,
F. Martin,
E. Merle, [......],
J. Nielsen,
Y.B. Pan, J.H. von Wimmersperg-Toeller,
W. Wiedenmann,
J. Wu,
S.L. Wu,
X. Wu,
G. Zobernig,
G. Dissertori,
The ALEPH Collaboration
[show abstract]
[hide abstract]
ABSTRACT: Hadronic Z decays into three jets are used to test QCD models of colour reconnection (CR). A sensitive quantity is the rate
of gluon jets with a gap in the particle rapidity distribution and zero jet charge. Gluon jets are identified by either energy-ordering
or by tagging two b-jets. The rates predicted by two string-based tunable CR models, one implemented in JETSET (the GAL model),
the other in ARIADNE, are too high and disfavoured by the data, whereas the rates from the corresponding non-CR standard versions
of these generators are too low. The data can be described by the GAL model assuming a small value for the R0 parameter in the range 0.01-0.02.
European Physical Journal C 04/2012; 48(3):685-698. · 3.63 Impact Factor
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S. Schael,
R. Barate,
R. Brunelière,
I. De Bonis,
D. Decamp,
C. Goy,
S. Jézéquel,
J.-P. Lees,
F. Martin,
E. Merle, [......],
G.W. Wilson,
J.A. Wilson,
T.R. Wyatt,
S. Yamashita,
D. Zer-Zion,
L. Zivkovic,
S. Heinemeyer,
A. Pilaftsis,
G. Weiglein,
The LEP Working Group for Higgs Boson Searches
[show abstract]
[hide abstract]
ABSTRACT: The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by
the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined
for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no
significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper
bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number
of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large
exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses
of neutral Higgs bosons.
European Physical Journal C 04/2012; 47(3):547-587. · 3.63 Impact Factor
