-
D Buskulic,
D Casper,
I De Bonis,
D Decamp,
P Ghez,
C Goy,
J.-P Lees,
M.-N Minard,
P Odier,
B Pietrzyk, [......],
I.J Scott,
V Sharma,
J.D Turk,
A.M Walsh,
F.V Weber,
Sau Lan Wu,
X Wu,
J.M Yamartino,
M Zheng,
G Zobernig
[show abstract]
[hide abstract]
ABSTRACT: From a sample of 152,000 τ decays collected by the ALEPH detector at LEP an upper limit of 24 MeV at 95% CL on the τ neutrino mass has been determined. The limit is obtained using a two dimensional likelihood fit of the visible energy and the invariant mass distribution of 25 τ → 5π(π0)ντ events.
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: 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
-
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
-
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
-
S Chatrchyan,
V Khachatryan,
A M Sirunyan,
A Tumasyan,
W Adam,
E Aguilo,
T Bergauer,
M Dragicevic,
J Erö,
C Fabjan, [......],
R Loveless,
A Mohapatra,
M U Mozer,
I Ojalvo,
F Palmonari,
G A Pierro,
I Ross,
A Savin,
W H Smith,
J Swanson
[show abstract]
[hide abstract]
ABSTRACT: A study is presented of the mass and spin-parity of the new boson recently observed at the LHC at a mass near 125 GeV. An integrated luminosity of 17.3 fb^{-1}, collected by the CMS experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, is used. The measured mass in the ZZ channel, where both Z bosons decay to e or μ pairs, is 126.2±0.6(stat)±0.2(syst) GeV. The angular distributions of the lepton pairs in this channel are sensitive to the spin-parity of the boson. Under the assumption of spin 0, the present data are consistent with the pure scalar hypothesis, while disfavoring the pure pseudoscalar hypothesis.
Physical Review Letters 02/2013; 110(8):081803. · 7.37 Impact Factor
-
S Chatrchyan,
V Khachatryan,
A M Sirunyan,
A Tumasyan,
W Adam,
E Aguilo,
T Bergauer,
M Dragicevic,
J Erö,
C Fabjan, [......],
J Leonard,
R Loveless,
A Mohapatra,
I Ojalvo,
F Palmonari,
G A Pierro,
I Ross,
A Savin,
W H Smith,
J Swanson
[show abstract]
[hide abstract]
ABSTRACT: Results are presented from a search for the pair production of third-generation scalar and vector leptoquarks, as well as for top squarks in R-parity-violating supersymmetric models. In either scenario, the new, heavy particle decays into a τ lepton and a b quark. The search is based on a data sample of pp collisions at sqrt[s]=7 TeV, which is collected by the CMS detector at the LHC and corresponds to an integrated luminosity of 4.8 fb^{-1}. The number of observed events is found to be in agreement with the standard model prediction, and exclusion limits on mass parameters are obtained at the 95% confidence level. Vector leptoquarks with masses below 760 GeV are excluded and, if the branching fraction of the scalar leptoquark decay to a τ lepton and a b quark is assumed to be unity, third-generation scalar leptoquarks with masses below 525 GeV are ruled out. Top squarks with masses below 453 GeV are excluded for a typical benchmark scenario, and limits on the coupling between the top squark, τ lepton, and b quark, λ_{333}^{'} are obtained. These results are the most stringent for these scenarios to date.
Physical Review Letters 02/2013; 110(8):081801. · 7.37 Impact Factor
-
S Chatrchyan,
V Khachatryan,
A M Sirunyan,
A Tumasyan,
W Adam,
E Aguilo,
T Bergauer,
M Dragicevic,
J Erö,
C Fabjan, [......],
C Lazaridis,
R Loveless,
A Mohapatra,
I Ojalvo,
F Palmonari,
G A Pierro,
I Ross,
A Savin,
W H Smith,
J Swanson
[show abstract]
[hide abstract]
ABSTRACT: The polarizations of the Υ(1S), Υ(2S), and Υ(3S) mesons are measured in proton-proton collisions at sqrt[s]=7 TeV, using a data sample of Υ(nS)→μ^{+}μ^{-} decays collected by the CMS experiment, corresponding to an integrated luminosity of 4.9 fb^{-1}. The dimuon decay angular distributions are analyzed in three different polarization frames. The polarization parameters λ_{ϑ}, λ_{φ}, and λ_{ϑφ}, as well as the frame-invariant quantity λ[over ˜], are presented as a function of the Υ(nS) transverse momentum between 10 and 50 GeV, in the rapidity ranges |y|<0.6 and 0.6<|y|<1.2. No evidence of large transverse or longitudinal polarizations is seen in the explored kinematic region.
Physical Review Letters 02/2013; 110(8):081802. · 7.37 Impact Factor
-
S Chatrchyan,
V Khachatryan,
A M Sirunyan,
A Tumasyan,
W Adam,
E Aguilo,
T Bergauer,
M Dragicevic,
J Erö,
C Fabjan, [......],
J Leonard,
R Loveless,
A Mohapatra,
I Ojalvo,
F Palmonari,
G A Pierro,
I Ross,
A Savin,
W H Smith,
J Swanson
[show abstract]
[hide abstract]
ABSTRACT: Evidence is presented for the associated production of a single top quark and W boson in pp collisions at sqrt[s]=7 TeV with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 4.9 fb^{-1}. The measurement is performed using events with two leptons and a jet originated from a b quark. A multivariate analysis based on kinematic properties is utilized to separate the tt[over ¯] background from the signal. The observed signal has a significance of 4.0σ and corresponds to a cross section of 16_{-4}^{+5} pb, in agreement with the standard model expectation of 15.6±0.4_{-1.2}^{+1.0} pb.
Physical Review Letters 01/2013; 110(2):022003. · 7.37 Impact Factor
-
S Chatrchyan,
V Khachatryan,
A M Sirunyan,
A Tumasyan,
W Adam,
E Aguilo,
T Bergauer,
M Dragicevic,
J Erö,
C Fabjan, [......],
C Lazaridis,
R Loveless,
A Mohapatra,
I Ojalvo,
F Palmonari,
G A Pierro,
I Ross,
A Savin,
W H Smith,
J Swanson
[show abstract]
[hide abstract]
ABSTRACT: Results are presented from a search for heavy, right-handed muon neutrinos, N_{μ}, and right-handed W_{R} bosons, which arise in the left-right symmetric extensions of the standard model. The analysis is based on a 5.0 fb^{-1} sample of proton-proton collisions at a center-of-mass energy of 7 TeV, collected by the CMS detector at the Large Hadron Collider. No evidence is observed for an excess of events over the standard model expectation. For models with exact left-right symmetry, heavy right-handed neutrinos are excluded at 95% confidence level for a range of neutrino masses below the W_{R} mass, dependent on the value of M_{W_{R}}. The excluded region in the two-dimensional (M_{W_{R}}, M_{N_{μ}}) mass plane extends to M_{W_{R}}=2.5 TeV.
Physical Review Letters 12/2012; 109(26):261802. · 7.37 Impact Factor
-
S Chatrchyan,
V Khachatryan,
A M Sirunyan,
A Tumasyan,
W Adam,
E Aguilo,
T Bergauer,
M Dragicevic,
J Erö,
C Fabjan, [......],
J Leonard,
R Loveless,
A Mohapatra,
I Ojalvo,
F Palmonari,
G A Pierro,
I Ross,
A Savin,
W H Smith,
J Swanson
[show abstract]
[hide abstract]
ABSTRACT: We report an investigation of the invariant mass spectrum of the two jets with highest transverse momentum in pp→W+2-jet and W+3-jet events to look for resonant enhancement. The data sample corresponds to an integrated luminosity of 5.0 fb^{-1} collected with the CMS detector at sqrt[s]=7 TeV. We find no evidence for the anomalous structure reported by the CDF Collaboration, and establish an upper limit of 5.0 pb at 95% confidence level on the production cross section for a generic Gaussian signal with mass near 150 GeV. Additionally, we exclude two theoretical models that predict a CDF-like dijet resonance near 150 GeV.
Physical Review Letters 12/2012; 109(25):251801. · 7.37 Impact Factor
-
D Buskulic,
D Casper,
I De Bonis,
D Decamp,
P Ghez,
C Goy,
J.-P Lees,
A Lucotte,
M.-N Minard,
P Odier, [......],
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: 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 (stat) −0.14+0.13 (syst) %.
Physics Letters B 12/2012; · 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: 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
-
Damir Buskulic,
I De Bonis,
D Décamp,
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,
Wu Sau Lan,
X Wu,
J M Yamartino,
M Zheng,
G Zobernig
[show abstract]
[hide abstract]
ABSTRACT: Using data obtained with the ALEPH detector at the Z resonance, a measure based on transverse momentum is shown to exhibit a correlation between the two halves of a hadronic event which cannot be explained by energy-momentum conservation, flavour conservation, the imposition of an event axis or imperfect event reconstruction. Two possible explanations based on Monte Carlo models are examined: a) ARIADNE, with the correlation forming early in the parton shower and with the transition from partons to hadrons playing only a minor part; b) JETSET, with the correlation forming at the fragmentation stage. A correlation technique based on a jet cluster analysis is used to make a comparison of the models with the data. It is concluded that both non-perturbative and perturbative effects make important contributions to the observed correlation.
Zeitschrift für Physik C 12/2012; 73(3):421.
-
D. Abbaneo,
G. Abbiendi,
M. Abbrescia,
S. Abdullin,
A. Abdulsalam,
B.S. Acharya,
D. Acosta,
J.G. Acosta,
A. Adair,
W. Adam, [......],
M.H. Zoeller,
O. Zorba,
P. Zotto,
W. Zou,
G. Zumerle,
M. Zupan,
A. Zuranski,
R. Zuyeuski,
M. Zvada,
P. Zych
[show abstract]
[hide abstract]
ABSTRACT: The Higgs boson was postulated nearly five decades ago within the framework of the standard model of particle physics and
has been the subject of numerous searches at accelerators around the world. Its discovery would verify the existence of a
complex scalar field thought to give mass to three of the carriers of the electroweak force—the W+, W–, and Z0 bosons—as well as to the fundamental quarks and leptons. The CMS Collaboration has observed, with a statistical significance
of five standard deviations, a new particle produced in proton-proton collisions at the Large Hadron Collider at CERN. The
evidence is strongest in the diphoton and four-lepton (electrons and/or muons) final states, which provide the best mass resolution
in the CMS detector. The probability of the observed signal being due to a random fluctuation of the background is about 1
in 3 × 106. The new particle is a boson with spin not equal to 1 and has a mass of about 1.25 giga–electron volts. Although its measured
properties are, within the uncertainties of the present data, consistent with those expected of the Higgs boson, more data
are needed to elucidate the precise nature of the new particle.
Science 12/2012; 338(6114):1569-1575. · 31.20 Impact Factor
-
S Chatrchyan,
V Khachatryan,
A M Sirunyan,
A Tumasyan,
W Adam,
E Aguilo,
T Bergauer,
M Dragicevic,
J Erö,
C Fabjan, [......],
J Leonard,
R Loveless,
A Mohapatra,
I Ojalvo,
F Palmonari,
G A Pierro,
I Ross,
A Savin,
W H Smith,
J Swanson
[show abstract]
[hide abstract]
ABSTRACT: The suppression of the individual Υ(nS) states in PbPb collisions with respect to their yields in pp data has been measured. The PbPb and pp data sets used in the analysis correspond to integrated luminosities of 150 μb^{-1} and 230 nb^{-1}, respectively, collected in 2011 by the CMS experiment at the LHC, at a center-of-mass energy per nucleon pair of 2.76 TeV. The Υ(nS) yields are measured from the dimuon invariant mass spectra. The suppression of the Υ(nS) yields in PbPb relative to the yields in pp, scaled by the number of nucleon-nucleon collisions, R_{AA}, is measured as a function of the collision centrality. Integrated over centrality, the R_{AA} values are 0.56±0.08(stat)±0.07(syst), 0.12±0.04(stat)±0.02(syst), and lower than 0.10 (at 95% confidence level), for the Υ(1S), Υ(2S), and Υ(3S) states, respectively. The results demonstrate the sequential suppression of the Υ(nS) states in PbPb collisions at LHC energies.
Physical Review Letters 11/2012; 109(22):222301. · 7.37 Impact Factor
-
S Chatrchyan,
V Khachatryan,
A M Sirunyan,
A Tumasyan,
W Adam,
T Bergauer,
M Dragicevic,
J Erö,
C Fabjan,
M Friedl, [......],
J Leonard,
R Loveless,
A Mohapatra,
I Ojalvo,
F Palmonari,
G A Pierro,
I Ross,
A Savin,
W H Smith,
J Swanson
[show abstract]
[hide abstract]
ABSTRACT: A search for physics beyond the standard model is performed in events with at least three jets and large missing transverse momentum produced in proton-proton collisions at a center-of-mass energy of sqrt[s]=7 TeV. No significant excess of events above the expected backgrounds is observed in 4.98 fb^{-1} of data collected with the CMS detector at the Large Hadron Collider. The results are presented in the context of the constrained minimal supersymmetric extension of the standard model and more generically for simplified models. For the simplified models of gluino-gluino and squark-squark production, gluino masses below 1.0 TeV and squark masses below 0.76 TeV are excluded in case the lightest supersymmetric particle mass is below 200 GeV. These results significantly extend previous searches.
Physical Review Letters 10/2012; 109(17):171803. · 7.37 Impact Factor
-
S Chatrchyan,
V Khachatryan,
A M Sirunyan,
A Tumasyan,
W Adam,
T Bergauer,
M Dragicevic,
J Erö,
C Fabjan,
M Friedl, [......],
J Leonard,
R Loveless,
A Mohapatra,
I Ojalvo,
F Palmonari,
G A Pierro,
I Ross,
A Savin,
W H Smith,
J Swanson
[show abstract]
[hide abstract]
ABSTRACT: The transverse energy (E_{T}) in Pb-Pb collisions at 2.76 TeV nucleon-nucleon center-of-mass energy (sqrt[s_{NN}]) has been measured over a broad range of pseudorapidity (η) and collision centrality by using the CMS detector at the LHC. The transverse energy density per unit pseudorapidity (dE_{T}/dη) increases faster with collision energy than the charged particle multiplicity. This implies that the mean energy per particle is increasing with collision energy. At all pseudorapidities, the transverse energy per participating nucleon increases with the centrality of the collision. The ratio of transverse energy per unit pseudorapidity in peripheral to central collisions varies significantly as the pseudorapidity increases from η=0 to |η|=5.0. For the 5% most central collisions, the energy density per unit volume is estimated to be about 14 GeV/fm^{3} at a time of 1 fm/c after the collision. This is about 100 times larger than normal nuclear matter density and a factor of 2.6 times higher than the energy density reported at sqrt[s_{NN}]=200 GeV at the Relativistic Heavy Ion Collider.
Physical Review Letters 10/2012; 109(15):152303. · 7.37 Impact Factor
