-
H. Anderhub,
M. Backes,
A. Biland,
V. Boccone,
I. Braun,
T. Bretz,
J. Buß,
F. Cadoux,
V. Commichau,
L. Djambazov, [......],
T. Steinbring,
F. Temme,
J. Thaele,
S. Tobler,
G. Viertel,
P. Vogler,
R. Walter,
K. Warda,
Q. Weitzel,
M. Z"anglein
[show abstract]
[hide abstract]
ABSTRACT: The First G-APD Cherenkov Telescope (FACT) is designed to detect cosmic
gamma-rays with energies from several hundred GeV up to about 10 TeV using the
Imaging Atmospheric Cherenkov Technique. In contrast to former or existing
telescopes, the camera of the FACT telescope is comprised of solid-state
Geiger-mode Avalanche Photodiodes (G-APD) instead of photomultiplier tubes for
photo detection. It is the first full-scale device of its kind employing this
new technology. The telescope is operated at the Observatorio del Roque de los
Muchachos (La Palma, Canary Islands, Spain) since fall 2011. This paper
describes in detail the design, construction and operation of the system,
including hardware and software aspects. Technical experiences gained after one
year of operation are discussed and conclusions with regard to future projects
are drawn.
04/2013;
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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
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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
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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: 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
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S Chatrchyan,
V Khachatryan,
AM Sirunyan,
A Tumasyan,
W Adam,
E Aguilo,
T Bergauer,
M Dragicevic,
J Erö,
C Fabjan, [......],
R Loveless,
A Mohapatra,
MU Mozer,
I Ojalvo,
F Palmonari,
GA Pierro,
I Ross,
A Savin,
WH Smith,
J Swanson
[show abstract]
[hide abstract]
ABSTRACT: The first measurement of vector-boson production associated with a top quark-antiquark pair in proton-proton collisions at √s=7 TeV is presented. The results are based on a data set corresponding to an integrated luminosity of 5.0 fb1, recorded by the CMS detector at the LHC in 2011. The measurement is performed in two independent channels through a trilepton analysis of tt̄Z events and a same-sign dilepton analysis of tt̄V (V=W or Z) events. In the trilepton channel a direct measurement of the tt̄Z cross section σ=0.28-0.11+0.14 (stat)-0.03+0.06 (syst) pb is obtained. In the dilepton channel a measurement of the tt̄V cross section yields σ=0.43-0.15+0.17 (stat)-0.07+0.09 (syst) pb. These measurements have a significance, respectively, of 3.3 and 3.0 standard deviations from the background hypotheses and are compatible, within uncertainties, with the corresponding next-to-leading order predictions of 0.137-0.016+0.012 and 0.306-0.053+0.031 pb. © 2013 CERN. Published by the American Physical Society.
Physical Review Letters 01/2013; 110(17). · 7.37 Impact Factor
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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
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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
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J. Albert,
E. Aliu,
H. Anderhub,
P. Antoranz,
C. Baixeras,
J. A. Barrio,
H. Bartko,
D. Bastieri,
J. K. Becker,
W. Bednarek, [......],
P. Temnikov,
D. Tescaro,
M. Teshima,
D. F. Torres,
N. Turini,
H. Vankov,
A. Venturini,
V. Vitale,
R. M. Wagner,
W. Wittek
-
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
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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
-
[show abstract]
[hide abstract]
ABSTRACT: Scintillating ceramics are a promising, new development for various
applications in science and industry. Their application in calorimetry for
particle physics experiments is expected to involve an exposure to high levels
of ionizing radiation. In this paper, changes in performance have been measured
for scintillating ceramic samples of different composition after exposure to
penetrating ionizing radiation up to a dose of 38 kGy.
11/2012;
-
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
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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
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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: A search is performed in pp collisions at sqrt[s]=7 TeV for exotic particles decaying via WZ to final states with electrons and muons. The data sample corresponds to an integrated luminosity of approximately 5 fb^{-1}. No significant excess is observed in the data above the expected standard model background. Upper bounds at 95% confidence level are set on the production cross section of the W^{'} boson described by the sequential standard model and on the W^{'} WZ coupling. W^{'} bosons with masses below 1143 GeV are excluded. Limits are also set in the context of low-scale technicolor models, under a range of assumptions concerning the model parameters.
Physical Review Letters 10/2012; 109(14):141801. · 7.37 Impact Factor
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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 dimuon invariant mass spectrum is searched in the range between 5.5 and 14 GeV for a light pseudoscalar Higgs boson a, predicted in a number of new physics models, including the next-to-minimal supersymmetric standard model. The data sample used in the search corresponds to an integrated luminosity of 1.3 fb^{-1} collected in pp collisions at sqrt[s]=7 TeV with the CMS detector at the LHC. No excess is observed above the background predictions and upper limits are set on the cross section times branching fraction σ×B(pp→a→μ^{+}μ^{-}) in the range of 1.5-7.5 pb. These results improve on existing bounds on the abb[over ¯] coupling for m_{a}<m_{Υ(1S)} and are the first significant limits for m_{a}>m_{Υ(3S)}. Constraints on the supersymmetric parameter space are presented in the context of the next-to-minimal model.
Physical Review Letters 09/2012; 109(12):121801. · 7.37 Impact Factor
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S Chatrchyan,
V Khachatryan,
A M Sirunyan,
A Tumasyan,
W Adam,
T Bergauer,
M Dragicevic,
J Erö,
C Fabjan,
M Friedl, [......],
C Lazaridis,
J Leonard,
R Loveless,
A Mohapatra,
I Ojalvo,
G A Pierro,
I Ross,
A Savin,
W H Smith,
J Swanson
[show abstract]
[hide abstract]
ABSTRACT: The azimuthal anisotropy of charged particles in Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV is measured with the CMS detector at the LHC over an extended transverse momentum (p_{T}) range up to approximately 60 GeV/c. The data cover both the low-p_{T} region associated with hydrodynamic flow phenomena and the high-p_{T} region where the anisotropies may reflect the path-length dependence of parton energy loss in the created medium. The anisotropy parameter (v_{2}) of the particles is extracted by correlating charged tracks with respect to the event-plane reconstructed by using the energy deposited in forward-angle calorimeters. For the six bins of collision centrality studied, spanning the range of 0-60% most-central events, the observed v_{2} values are found to first increase with p_{T}, reaching a maximum around p_{T}=3 GeV/c, and then to gradually decrease to almost zero, with the decline persisting up to at least p_{T}=40 GeV/c over the full centrality range measured.
Physical Review Letters 07/2012; 109(2):022301. · 7.37 Impact Factor
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MAGIC Collaboration,
J. Aleksić,
E. A. Alvarez,
L. A. Antonelli,
P. Antoranz,
M. Asensio,
M. Backes,
J. A. Barrio,
D. Bastieri,
J. Becerra González, [......],
A. Treves,
M. Uellenbeck,
H. Vankov,
P. Vogler,
R. M. Wagner,
Q. Weitzel,
V. Zabalza,
F. Zandanel,
R. Zanin,
G. Ghisellini
[show abstract]
[hide abstract]
ABSTRACT: We present the results of a long M87 monitoring campaign in very high energy
$\gamma$-rays with the MAGIC-I Cherenkov telescope. We aim to model the
persistent non-thermal jet emission by monitoring and characterizing the very
high energy $\gamma$-ray emission of M87 during a low state. A total of 150\,h
of data were taken between 2005 and 2007 with the single MAGIC-I telescope, out
of which 128.6\,h survived the data quality selection. We also collected data
in the X-ray and \textit{Fermi}--LAT bands from the literature (partially
contemporaneous). No flaring activity was found during the campaign. The source
was found to be in a persistent low-emission state, which was at a confidence
level of $7\sigma$. We present the spectrum between 100\,GeV and 2\,TeV, which
is consistent with a simple power law with a photon index $\Gamma=2.21\pm0.21$
and a flux normalization at 300\,GeV of $(7.7\pm1.3) \times 10^{-8}$ TeV$^{-1}$
s$^{-1}$ m$^{-2}$. The extrapolation of the MAGIC spectrum into the GeV energy
range matches the previously published \textit{Fermi}--LAT spectrum well,
covering a combined energy range of four orders of magnitude with the same
spectral index. We model the broad band energy spectrum with a spine layer
model, which can satisfactorily describe our data.
07/2012;
-
S. CMS Collaboration Chatrchyan,
V. Khachatryan,
A. M. Sirunyan,
A. Tumasyan,
W. Adam,
T. Bergauer,
M. Dragicevic,
J. Erö,
C. Fabjan,
M. Friedl, [......],
C. Lazaridis,
J. Leonard,
R. Loveless,
A. Mohapatra,
I. Ojalvo,
G. A. Pierro,
I. Ross,
A. Savin,
W. H. Smith,
J. Swanson
[show abstract]
[hide abstract]
ABSTRACT: A search for neutral Higgs bosons decaying to tau pairs at a
center-of-mass energy of 7 TeV is performed using a dataset
corresponding to an integrated luminosity of 4.6 fb-1
recorded by the CMS experiment at the LHC. The search is sensitive to
both the standard model Higgs boson and to the neutral Higgs bosons
predicted by the minimal supersymmetric extension of the standard model
(MSSM). No excess of events is observed in the tau-pair invariant-mass
spectrum. For a standard model Higgs boson in the mass range of
110-145 GeV upper limits at 95% confidence level (CL) on the
production cross section are determined. We exclude a Higgs boson with
mH=115 GeV with a production cross section 3.2 times of
that predicted by the standard model. In the MSSM, upper limits on the
neutral Higgs boson production cross section times branching fraction to
tau pairs, as a function of the pseudoscalar Higgs boson mass,
mA, sets stringent new bounds in the parameter space,
excluding at 95% CL values of tan β as low as 7.1 at
mA=160 GeV in the mhmax benchmark scenario.
Physics Letters B 05/2012; 713:68-90. · 3.95 Impact Factor
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The CMS Collaboration,
S. Chatrchyan,
V. Khachatryan,
A. M. Sirunyan,
A. Tumasyan,
W. Adam,
T. Bergauer,
M. Dragicevic,
J. Erö,
C. Fabjan, [......],
J. Leonard,
R. Loveless,
A. Mohapatra,
F. Palmonari,
D. Reeder,
I. Ross,
A. Savin,
W. H. Smith,
J. Swanson,
M. Weinberg
[show abstract]
[hide abstract]
ABSTRACT: A measurement of the t[`(t)]\mathrm{t{\bar{t}}} production cross section in proton-proton collisions at a centre-of-mass energy of 7TeV has been performed at the LHC with
the CMS detector. The analysis uses a data sample corresponding to an integrated luminosity of 36pb−1 and is based on the reconstruction of the final state with one isolated, high transverse-momentum electron or muon and three
or more hadronic jets. The kinematic properties of the events are used to separate the t[`(t)]\mathrm{t{\bar{t}}} signal from W+jets and QCD multijet background events. The measured cross section is 173+39-32(stat. + syst.)173^{+39}_{-32}~(\mathrm{stat}. + \mathrm{syst}.)pb, consistent with standard model expectations.
European Physical Journal C 05/2012; 71(9):1-27. · 3.63 Impact Factor
