The electroweak production and subsequent decay of single top quarks is determined by the propert... more The electroweak production and subsequent decay of single top quarks is determined by the properties of the Wtb vertex. This vertex can be described by the complex parameters of an effective Lagrangian. An analysis of angular distributions of the decay products of single top quarks produced in the t-channel constrains these parameters simultaneously. The analysis described in this paper uses 4.6 fb −1 of proton-proton collision data at √ s = 7 TeV collected with the ATLAS detector at the LHC. Two parameters are measured simultaneously in this analysis. The fraction f 1 of decays containing transversely polarised W bosons is measured to be 0.37 ± 0.07 (stat.⊕syst.). The phase δ − between amplitudes for transversely and longitudinally polarised W bosons recoiling against lefthanded b-quarks is measured to be −0.014π ± 0.036π (stat.⊕syst.). The correlation in the measurement of these parameters is 0.15. These values result in two-dimensional limits at the 95% confidence level on the ratio of the complex coupling parameters g R and V L , yielding Re[g R /V L ] ∈ [−0.36, 0.10] and Im[g R /V L ] ∈ [−0.17, 0.23] with a correlation of 0.11. The results are in good agreement with the predictions of the Standard Model.
The European physical journal. C, Particles and fields
The decays [Formula: see text] and [Formula: see text] are studied with the ATLAS detector at the... more The decays [Formula: see text] and [Formula: see text] are studied with the ATLAS detector at the LHC using a dataset corresponding to integrated luminosities of 4.9 and 20.6 fb[Formula: see text] of pp collisions collected at centre-of-mass energies [Formula: see text] TeV and 8 TeV, respectively. Signal candidates are identified through [Formula: see text] and [Formula: see text] decays. With a two-dimensional likelihood fit involving the [Formula: see text] reconstructed invariant mass and an angle between the [Formula: see text] and [Formula: see text] candidate momenta in the muon pair rest frame, the yields of [Formula: see text] and [Formula: see text], and the transverse polarisation fraction in [Formula: see text] decay are measured. The transverse polarisation fraction is determined to be [Formula: see text], and the derived ratio of the branching fractions of the two modes is [Formula: see text], where the first error is statistical and the second is systematic. Finally, ...
ABSTRACT The new high energy high luminosity experiments require an improvement in both the count... more ABSTRACT The new high energy high luminosity experiments require an improvement in both the counting rate and the space resolution for the detectors. This improvement can be achieved by reducing the charge per count, however this implies a need for a better signal to noise ratio in the signal processing. In this article we will show the performances of diamond detectors and RPCs using a new preamplifier with low noise (500-1000 electrons RMS), fast shaping (about 10 ns) and large input capacitance.
A search for events with large missing transverse momentum, jets, and at least two tau leptons ha... more A search for events with large missing transverse momentum, jets, and at least two tau leptons has been performed using 2 fb −1 of proton-proton collision data at √ s = 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. No excess above the Standard Model background expectation is observed and a 95% CL upper limit on the visible cross section for new phenomena is set, where the visible cross section is defined by the product of cross section, branching fraction, detector acceptance and event selection efficiency. A 95% CL lower limit of 32 TeV is set on the gauge-mediated supersymmetry breaking scale Λ independent of tan β. These limits provide the most stringent tests to date in a large part of the considered parameter space.
Recent studies have highlighted the potential of jet substructure techniques to identify the hadr... more Recent studies have highlighted the potential of jet substructure techniques to identify the hadronic decays of boosted heavy particles. These studies all rely upon the assumption that the internal substructure of jets generated by QCD radiation is well understood. In this article, this assumption is tested on an inclusive sample of jets recorded with the ATLAS detector in 2010, which corresponds to 35 pb −1 of pp collisions delivered by the LHC at √ s = 7 TeV. In a subsample of events with single pp collisions, measurements corrected for detector efficiency and resolution are presented with full systematic uncertainties. Jet invariant mass, k t splitting scales and N-subjettiness variables are presented for anti-k t R = 1.0 jets and Cambridge-Aachen R = 1.2 jets. Jet invariant-mass spectra for Cambridge-Aachen R = 1.2 jets after a splitting and filtering procedure are also presented. Leading-order parton-shower Monte Carlo predictions for these variables are found to be broadly in agreement with data. The dependence of mean jet mass on additional pp interactions is also explored.
In order to study further the long-range correlations ("ridge") observed recently in p+Pb collisi... more In order to study further the long-range correlations ("ridge") observed recently in p+Pb collisions at √ s NN = 5.02 TeV, the second-order azimuthal anisotropy parameter of charged particles, v 2 , has been measured with the cumulant method using the ATLAS detector at the LHC. In a data sample corresponding to an integrated luminosity of approximately 1 µb −1 , the parameter v 2 has been obtained using two-and four-particle cumulants over the pseudorapidity range |η| < 2.5. The results are presented as a function of transverse momentum and the event activity, defined in terms of the transverse energy summed over 3.1 < η < 4.9 in the direction of the Pb beam. They show features characteristic of collective anisotropic flow, similar to that observed in Pb+Pb collisions. A comparison is made to results obtained using two-particle correlation methods, and to predictions from hydrodynamic models of p+Pb collisions. Despite the small transverse spatial extent of the p+Pb collision system, the large magnitude of v 2 and its similarity to hydrodynamic predictions provide additional evidence for the importance of final-state effects in p+Pb reactions.
This paper presents a measurement of the top quark pair (tt) production charge asymmetry A C usin... more This paper presents a measurement of the top quark pair (tt) production charge asymmetry A C using 4.7 fb −1 of proton-proton collisions at a centre-of-mass energy √ s = 7 TeV collected by the ATLAS detector at the LHC. A tt-enriched sample of events with a single lepton (electron or muon), missing transverse momentum and at least four high transverse momentum jets, of which at least one is tagged as coming from a b-quark, is selected. A likelihood fit is used to reconstruct the tt event kinematics. A Bayesian unfolding procedure is employed to estimate A C at the parton-level. The measured value of the tt production charge asymmetry is A C = 0.006 ± 0.010, where the uncertainty includes both the statistical and the systematic components. Differential A C measurements as a function of the invariant mass, the rapidity and the transverse momentum of the ttsystem are also presented. In addition, A C is measured for a subset of events with large tt velocity, where physics beyond the Standard Model could contribute. All measurements are consistent with the Standard Model predictions.
Using inelastic proton-proton interactions at $ \sqrt {s} = 900 $ GeV and 7 TeV, recorded by the ... more Using inelastic proton-proton interactions at $ \sqrt {s} = 900 $ GeV and 7 TeV, recorded by the ATLAS detector at the LHC, measurements have been made of the correlations between forward and backward charged-particle multiplicities and, for the first time, between forward and backward charged-particle summed transverse momentum. In addition, jet-like structure in the events is studied by means of azimuthal distributions of charged particles relative to the charged particle with highest transverse momentum in a selected kinematic region of the event. The results are compared with predictions from tunes of the pythia and herwig++ Monte Carlo generators, which in most cases are found to provide a reasonable description of the data.
It has been found that the squark mass isolines overlaid on figure 13 are misplaced. The figure h... more It has been found that the squark mass isolines overlaid on figure 13 are misplaced. The figure has been replaced to fix this part whilst none of the results or exclusion lines have been changed.
The extended gamma-ray source MGRO J1908+06, discovered by the Milagro air shower detector in 200... more The extended gamma-ray source MGRO J1908+06, discovered by the Milagro air shower detector in 2007, has been observed for ∼4 years by the ARGO-YBJ experiment at TeV energies, with a statistical significance of 6.2 standard deviations. The peak of the signal is found at a position consistent with the pulsar PSR J1907+0602. Parameterizing the source shape with a two-dimensional Gauss function, we estimate an extension of σ ext = 0. • 49 ± 0. • 22, which is consistent with a previous measurement by the Cherenkov Array H.E.S.S. The observed energy spectrum is dN/dE = 6.1 ± 1.4 × 10 −13 (E/4 TeV) −2.54±0.36 photons cm −2 s −1 TeV −1 , in the energy range of ∼1-20 TeV. The measured gamma-ray flux is consistent with the results of the Milagro detector, but is ∼2-3 times larger than the flux previously derived by H.E.S.S. at energies of a few TeV. The continuity of the Milagro and ARGO-YBJ observations and the stable excess rate observed by ARGO-YBJ and recorded in four years of data support the identification of MGRO J1908+06 as the steady powerful TeV pulsar wind nebula of PSR J1907+0602, with an integrated luminosity over 1 TeV ∼ 1.8 times the luminosity of the Crab Nebula.
A search for microscopic black holes has been performed in a same-sign dimuon final state using 1... more A search for microscopic black holes has been performed in a same-sign dimuon final state using 1.3 fb −1 of proton-proton collision data collected with the ATLAS detector at a centre of mass energy of 7 TeV at the CERN Large Hadron Collider. The data are found to be consistent with the expectation from the Standard Model and the results are used to derive exclusion contours in the context of a low scale gravity model.
A search for a heavy Standard Model Higgs boson decaying via H → Z Z → + − qq, where = e, μ, is p... more A search for a heavy Standard Model Higgs boson decaying via H → Z Z → + − qq, where = e, μ, is presented. The search is performed using a data set of pp collisions at √ s = 7 TeV, corresponding to an integrated luminosity of 1.04 fb −1 collected in 2011 by the ATLAS detector at the CERN LHC collider. No significant excess of events above the estimated background is found. Upper limits at 95% confidence level on the production cross section (relative to that expected from the Standard Model) of a Higgs boson with a mass in the range between 200 and 600 GeV are derived. Within this mass range, there is at present insufficient sensitivity to exclude a Standard Model Higgs boson. For a Higgs boson with a mass of 360 GeV, where the sensitivity is maximal, the observed and expected cross section upper limits are factors of 1.7 and 2.7, respectively, larger than the Standard Model prediction.
This Letter presents measurements of the differential cross-sections for inclusive electron and m... more This Letter presents measurements of the differential cross-sections for inclusive electron and muon production in proton-proton collisions at a centre-of-mass energy of âs = 7 TeV, using data collected by the ATLAS detector at the LHC. The muon cross-section is measured as a function of pT in the range 4 &amp;amp;amp;lt; pT &amp;amp;amp;lt; 100 GeV and within pseudorapidity |η| &amp;amp;amp;lt;
This paper presents a search for a new heavy particle produced in association with a top or antit... more This paper presents a search for a new heavy particle produced in association with a top or antitop quark. Two models in which the new heavy particle is a color singlet or a color triplet are considered, decaying, respectively, to " tq or tq, leading to a resonance within the t " t þ jets signature. The full 2011 ATLAS pp collision data set from the LHC (4:7 fb À1) is used to search for t " t events produced in association with jets, in which one of the W bosons from the top quarks decays leptonically and the other decays hadronically. The data are consistent with the Standard Model expectation, and a new particle with mass below 430 Gev for both W 0 boson and color triplet models is excluded at 95% confidence level, assuming unit right-handed coupling.
The ARGO-YBJ experiment has been designed to study the Extensive Air Showers with an energy thres... more The ARGO-YBJ experiment has been designed to study the Extensive Air Showers with an energy threshold lower than that of the existing arrays by exploiting the high altitude location (4300 m a.s.l. in Tibet, P.R. China) and the full ground plane coverage. The lower energy limit of the detector (E ∼ 1 GeV) is reached by the scaler mode technique, i.e. recording the counting rate at fixed time intervals. At these energies, transient signals due to local (e.g. Forbush Decreases) and cosmological (e.g. Gamma Ray Bursts) phenomena are expected as a significant variation of the counting rate compared to the background. In this paper the performance of the ARGO-YBJ detector operating in scaler mode is described and discussed.
Measurements are presented of the properties of high transverse momentum jets, produced in proton... more Measurements are presented of the properties of high transverse momentum jets, produced in protonproton collisions at a center-of-mass energy of ffiffi ffi s p ¼ 7 TeV. The data correspond to an integrated luminosity of 35 pb À1 and were collected with the ATLAS detector in 2010. Jet mass, width, eccentricity, planar flow and angularity are measured for jets reconstructed using the anti-k t algorithm with distance parameters R ¼ 0:6 and 1.0, with transverse momentum p T > 300 GeV and pseudorapidity jj < 2. The measurements are compared to the expectations of Monte Carlo generators that match leading-logarithmic parton showers to leading-order, or next-to-leading-order, matrix elements. The generators describe the general features of the jets, although discrepancies are observed in some distributions.
The European physical journal. C, Particles and fields
Studies of the spin, parity and tensor couplings of the Higgs boson in the [Formula: see text], [... more Studies of the spin, parity and tensor couplings of the Higgs boson in the [Formula: see text], [Formula: see text] and [Formula: see text] decay processes at the LHC are presented. The investigations are based on [Formula: see text] of pp collision data collected by the ATLAS experiment at [Formula: see text] TeV and [Formula: see text] TeV. The Standard Model (SM) Higgs boson hypothesis, corresponding to the quantum numbers [Formula: see text], is tested against several alternative spin scenarios, including non-SM spin-0 and spin-2 models with universal and non-universal couplings to fermions and vector bosons. All tested alternative models are excluded in favour of the SM Higgs boson hypothesis at more than 99.9 % confidence level. Using the [Formula: see text] and [Formula: see text] decays, the tensor structure of the interaction between the spin-0 boson and the SM vector bosons is also investigated. The observed distributions of variables sensitive to the non-SM tensor couplin...
The electroweak production and subsequent decay of single top quarks is determined by the propert... more The electroweak production and subsequent decay of single top quarks is determined by the properties of the Wtb vertex. This vertex can be described by the complex parameters of an effective Lagrangian. An analysis of angular distributions of the decay products of single top quarks produced in the t-channel constrains these parameters simultaneously. The analysis described in this paper uses 4.6 fb −1 of proton-proton collision data at √ s = 7 TeV collected with the ATLAS detector at the LHC. Two parameters are measured simultaneously in this analysis. The fraction f 1 of decays containing transversely polarised W bosons is measured to be 0.37 ± 0.07 (stat.⊕syst.). The phase δ − between amplitudes for transversely and longitudinally polarised W bosons recoiling against lefthanded b-quarks is measured to be −0.014π ± 0.036π (stat.⊕syst.). The correlation in the measurement of these parameters is 0.15. These values result in two-dimensional limits at the 95% confidence level on the ratio of the complex coupling parameters g R and V L , yielding Re[g R /V L ] ∈ [−0.36, 0.10] and Im[g R /V L ] ∈ [−0.17, 0.23] with a correlation of 0.11. The results are in good agreement with the predictions of the Standard Model.
The European physical journal. C, Particles and fields
The decays [Formula: see text] and [Formula: see text] are studied with the ATLAS detector at the... more The decays [Formula: see text] and [Formula: see text] are studied with the ATLAS detector at the LHC using a dataset corresponding to integrated luminosities of 4.9 and 20.6 fb[Formula: see text] of pp collisions collected at centre-of-mass energies [Formula: see text] TeV and 8 TeV, respectively. Signal candidates are identified through [Formula: see text] and [Formula: see text] decays. With a two-dimensional likelihood fit involving the [Formula: see text] reconstructed invariant mass and an angle between the [Formula: see text] and [Formula: see text] candidate momenta in the muon pair rest frame, the yields of [Formula: see text] and [Formula: see text], and the transverse polarisation fraction in [Formula: see text] decay are measured. The transverse polarisation fraction is determined to be [Formula: see text], and the derived ratio of the branching fractions of the two modes is [Formula: see text], where the first error is statistical and the second is systematic. Finally, ...
ABSTRACT The new high energy high luminosity experiments require an improvement in both the count... more ABSTRACT The new high energy high luminosity experiments require an improvement in both the counting rate and the space resolution for the detectors. This improvement can be achieved by reducing the charge per count, however this implies a need for a better signal to noise ratio in the signal processing. In this article we will show the performances of diamond detectors and RPCs using a new preamplifier with low noise (500-1000 electrons RMS), fast shaping (about 10 ns) and large input capacitance.
A search for events with large missing transverse momentum, jets, and at least two tau leptons ha... more A search for events with large missing transverse momentum, jets, and at least two tau leptons has been performed using 2 fb −1 of proton-proton collision data at √ s = 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. No excess above the Standard Model background expectation is observed and a 95% CL upper limit on the visible cross section for new phenomena is set, where the visible cross section is defined by the product of cross section, branching fraction, detector acceptance and event selection efficiency. A 95% CL lower limit of 32 TeV is set on the gauge-mediated supersymmetry breaking scale Λ independent of tan β. These limits provide the most stringent tests to date in a large part of the considered parameter space.
Recent studies have highlighted the potential of jet substructure techniques to identify the hadr... more Recent studies have highlighted the potential of jet substructure techniques to identify the hadronic decays of boosted heavy particles. These studies all rely upon the assumption that the internal substructure of jets generated by QCD radiation is well understood. In this article, this assumption is tested on an inclusive sample of jets recorded with the ATLAS detector in 2010, which corresponds to 35 pb −1 of pp collisions delivered by the LHC at √ s = 7 TeV. In a subsample of events with single pp collisions, measurements corrected for detector efficiency and resolution are presented with full systematic uncertainties. Jet invariant mass, k t splitting scales and N-subjettiness variables are presented for anti-k t R = 1.0 jets and Cambridge-Aachen R = 1.2 jets. Jet invariant-mass spectra for Cambridge-Aachen R = 1.2 jets after a splitting and filtering procedure are also presented. Leading-order parton-shower Monte Carlo predictions for these variables are found to be broadly in agreement with data. The dependence of mean jet mass on additional pp interactions is also explored.
In order to study further the long-range correlations ("ridge") observed recently in p+Pb collisi... more In order to study further the long-range correlations ("ridge") observed recently in p+Pb collisions at √ s NN = 5.02 TeV, the second-order azimuthal anisotropy parameter of charged particles, v 2 , has been measured with the cumulant method using the ATLAS detector at the LHC. In a data sample corresponding to an integrated luminosity of approximately 1 µb −1 , the parameter v 2 has been obtained using two-and four-particle cumulants over the pseudorapidity range |η| < 2.5. The results are presented as a function of transverse momentum and the event activity, defined in terms of the transverse energy summed over 3.1 < η < 4.9 in the direction of the Pb beam. They show features characteristic of collective anisotropic flow, similar to that observed in Pb+Pb collisions. A comparison is made to results obtained using two-particle correlation methods, and to predictions from hydrodynamic models of p+Pb collisions. Despite the small transverse spatial extent of the p+Pb collision system, the large magnitude of v 2 and its similarity to hydrodynamic predictions provide additional evidence for the importance of final-state effects in p+Pb reactions.
This paper presents a measurement of the top quark pair (tt) production charge asymmetry A C usin... more This paper presents a measurement of the top quark pair (tt) production charge asymmetry A C using 4.7 fb −1 of proton-proton collisions at a centre-of-mass energy √ s = 7 TeV collected by the ATLAS detector at the LHC. A tt-enriched sample of events with a single lepton (electron or muon), missing transverse momentum and at least four high transverse momentum jets, of which at least one is tagged as coming from a b-quark, is selected. A likelihood fit is used to reconstruct the tt event kinematics. A Bayesian unfolding procedure is employed to estimate A C at the parton-level. The measured value of the tt production charge asymmetry is A C = 0.006 ± 0.010, where the uncertainty includes both the statistical and the systematic components. Differential A C measurements as a function of the invariant mass, the rapidity and the transverse momentum of the ttsystem are also presented. In addition, A C is measured for a subset of events with large tt velocity, where physics beyond the Standard Model could contribute. All measurements are consistent with the Standard Model predictions.
Using inelastic proton-proton interactions at $ \sqrt {s} = 900 $ GeV and 7 TeV, recorded by the ... more Using inelastic proton-proton interactions at $ \sqrt {s} = 900 $ GeV and 7 TeV, recorded by the ATLAS detector at the LHC, measurements have been made of the correlations between forward and backward charged-particle multiplicities and, for the first time, between forward and backward charged-particle summed transverse momentum. In addition, jet-like structure in the events is studied by means of azimuthal distributions of charged particles relative to the charged particle with highest transverse momentum in a selected kinematic region of the event. The results are compared with predictions from tunes of the pythia and herwig++ Monte Carlo generators, which in most cases are found to provide a reasonable description of the data.
It has been found that the squark mass isolines overlaid on figure 13 are misplaced. The figure h... more It has been found that the squark mass isolines overlaid on figure 13 are misplaced. The figure has been replaced to fix this part whilst none of the results or exclusion lines have been changed.
The extended gamma-ray source MGRO J1908+06, discovered by the Milagro air shower detector in 200... more The extended gamma-ray source MGRO J1908+06, discovered by the Milagro air shower detector in 2007, has been observed for ∼4 years by the ARGO-YBJ experiment at TeV energies, with a statistical significance of 6.2 standard deviations. The peak of the signal is found at a position consistent with the pulsar PSR J1907+0602. Parameterizing the source shape with a two-dimensional Gauss function, we estimate an extension of σ ext = 0. • 49 ± 0. • 22, which is consistent with a previous measurement by the Cherenkov Array H.E.S.S. The observed energy spectrum is dN/dE = 6.1 ± 1.4 × 10 −13 (E/4 TeV) −2.54±0.36 photons cm −2 s −1 TeV −1 , in the energy range of ∼1-20 TeV. The measured gamma-ray flux is consistent with the results of the Milagro detector, but is ∼2-3 times larger than the flux previously derived by H.E.S.S. at energies of a few TeV. The continuity of the Milagro and ARGO-YBJ observations and the stable excess rate observed by ARGO-YBJ and recorded in four years of data support the identification of MGRO J1908+06 as the steady powerful TeV pulsar wind nebula of PSR J1907+0602, with an integrated luminosity over 1 TeV ∼ 1.8 times the luminosity of the Crab Nebula.
A search for microscopic black holes has been performed in a same-sign dimuon final state using 1... more A search for microscopic black holes has been performed in a same-sign dimuon final state using 1.3 fb −1 of proton-proton collision data collected with the ATLAS detector at a centre of mass energy of 7 TeV at the CERN Large Hadron Collider. The data are found to be consistent with the expectation from the Standard Model and the results are used to derive exclusion contours in the context of a low scale gravity model.
A search for a heavy Standard Model Higgs boson decaying via H → Z Z → + − qq, where = e, μ, is p... more A search for a heavy Standard Model Higgs boson decaying via H → Z Z → + − qq, where = e, μ, is presented. The search is performed using a data set of pp collisions at √ s = 7 TeV, corresponding to an integrated luminosity of 1.04 fb −1 collected in 2011 by the ATLAS detector at the CERN LHC collider. No significant excess of events above the estimated background is found. Upper limits at 95% confidence level on the production cross section (relative to that expected from the Standard Model) of a Higgs boson with a mass in the range between 200 and 600 GeV are derived. Within this mass range, there is at present insufficient sensitivity to exclude a Standard Model Higgs boson. For a Higgs boson with a mass of 360 GeV, where the sensitivity is maximal, the observed and expected cross section upper limits are factors of 1.7 and 2.7, respectively, larger than the Standard Model prediction.
This Letter presents measurements of the differential cross-sections for inclusive electron and m... more This Letter presents measurements of the differential cross-sections for inclusive electron and muon production in proton-proton collisions at a centre-of-mass energy of âs = 7 TeV, using data collected by the ATLAS detector at the LHC. The muon cross-section is measured as a function of pT in the range 4 &amp;amp;amp;lt; pT &amp;amp;amp;lt; 100 GeV and within pseudorapidity |η| &amp;amp;amp;lt;
This paper presents a search for a new heavy particle produced in association with a top or antit... more This paper presents a search for a new heavy particle produced in association with a top or antitop quark. Two models in which the new heavy particle is a color singlet or a color triplet are considered, decaying, respectively, to " tq or tq, leading to a resonance within the t " t þ jets signature. The full 2011 ATLAS pp collision data set from the LHC (4:7 fb À1) is used to search for t " t events produced in association with jets, in which one of the W bosons from the top quarks decays leptonically and the other decays hadronically. The data are consistent with the Standard Model expectation, and a new particle with mass below 430 Gev for both W 0 boson and color triplet models is excluded at 95% confidence level, assuming unit right-handed coupling.
The ARGO-YBJ experiment has been designed to study the Extensive Air Showers with an energy thres... more The ARGO-YBJ experiment has been designed to study the Extensive Air Showers with an energy threshold lower than that of the existing arrays by exploiting the high altitude location (4300 m a.s.l. in Tibet, P.R. China) and the full ground plane coverage. The lower energy limit of the detector (E ∼ 1 GeV) is reached by the scaler mode technique, i.e. recording the counting rate at fixed time intervals. At these energies, transient signals due to local (e.g. Forbush Decreases) and cosmological (e.g. Gamma Ray Bursts) phenomena are expected as a significant variation of the counting rate compared to the background. In this paper the performance of the ARGO-YBJ detector operating in scaler mode is described and discussed.
Measurements are presented of the properties of high transverse momentum jets, produced in proton... more Measurements are presented of the properties of high transverse momentum jets, produced in protonproton collisions at a center-of-mass energy of ffiffi ffi s p ¼ 7 TeV. The data correspond to an integrated luminosity of 35 pb À1 and were collected with the ATLAS detector in 2010. Jet mass, width, eccentricity, planar flow and angularity are measured for jets reconstructed using the anti-k t algorithm with distance parameters R ¼ 0:6 and 1.0, with transverse momentum p T > 300 GeV and pseudorapidity jj < 2. The measurements are compared to the expectations of Monte Carlo generators that match leading-logarithmic parton showers to leading-order, or next-to-leading-order, matrix elements. The generators describe the general features of the jets, although discrepancies are observed in some distributions.
The European physical journal. C, Particles and fields
Studies of the spin, parity and tensor couplings of the Higgs boson in the [Formula: see text], [... more Studies of the spin, parity and tensor couplings of the Higgs boson in the [Formula: see text], [Formula: see text] and [Formula: see text] decay processes at the LHC are presented. The investigations are based on [Formula: see text] of pp collision data collected by the ATLAS experiment at [Formula: see text] TeV and [Formula: see text] TeV. The Standard Model (SM) Higgs boson hypothesis, corresponding to the quantum numbers [Formula: see text], is tested against several alternative spin scenarios, including non-SM spin-0 and spin-2 models with universal and non-universal couplings to fermions and vector bosons. All tested alternative models are excluded in favour of the SM Higgs boson hypothesis at more than 99.9 % confidence level. Using the [Formula: see text] and [Formula: see text] decays, the tensor structure of the interaction between the spin-0 boson and the SM vector bosons is also investigated. The observed distributions of variables sensitive to the non-SM tensor couplin...
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Papers by P. Camarri