| 1. |
- Aad, G., et al.
(författare)
-
Measurement of the W(+/-)Z production cross section and limits on anomalous triple gauge couplings in proton-proton collisions at root s=7 TeV with the ATLAS detector
- 2012
-
Ingår i: Physics Letters B. - Elsevier Science Bv. - 0370-2693. ; 709:4-5, s. 341-357
-
Tidskriftsartikel (refereegranskat)abstract
- This Letter presents a measurement of W(+/-)Z production in 1.02 fb(-1) of pp collision data at root s = 7 TeV collected by the ATLAS experiment in 2011. Doubly leptonic decay events are selected with electrons, muons and missing transverse momentum in the final state. In total 71 candidates are observed, with a background expectation of 12.1 +/- 1.4(stat.)(-2.0)(+4.1)(syst.) events. The total cross section for W(+/-)Z production for Z/gamma* masses within the range 66 GeV to 116 GeV is determined to be sigma(tot)(WZ) = 20.5(-2.8)(+3.1)(stat.)(-1.3)(+1.4)(syst)(-0.8)(+0.9)(lumi.) pb, which is consistent with the Standard Model expectation of 17.3(0.8)(+1.3) pb. Limits on anomalous triple gauge boson couplings are extracted. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
|
|
| 2. |
- Aad, G., et al.
(författare)
-
Search for pair production of heavy top-like quarks decaying to a high-p(T) W boson and a b quark in the lepton plus jets final state at root s=7 TeV with the ATLAS detector
- 2013
-
Ingår i: Physics Letters B. - Elsevier. - 0370-2693. ; 718:4-5, s. 1284-1302
-
Tidskriftsartikel (refereegranskat)abstract
- A search is presented for production of a heavy up-type quark (t') together with its antiparticle, assuming a significant branching ratio for subsequent decay into a W boson and a b quark. The search is based on 4.7 fb(-1) of pp collisions root s = 7 TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton + jets final state, characterized by a high-transverse-momentum isolated electron or muon, large missing transverse momentum and at least three jets. The analysis strategy relies on the substantial boost of the W bosons in the t'(t') over bar signal when m(t') greater than or similar to 400 GeV. No significant excess of events above the Standard Model expectation is observed and the result of the search is interpreted in the context of fourth-generation and vector-like quark models. Under the assumption of a branching ratio BR(t' -> W b) = I, a fourth-generation t' quark with mass lower than 656 GeV is excluded at 95% confidence level. In addition, in light of the recent discovery of a new boson of mass similar to 126 GeV at the LHC, upper limits are derived in the two-dimensional plane of BR(t' -> Wb) versus BR(t' -> Ht), where H is the Standard Model Higgs boson, for vector-like quarks of various masses. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
|
|
| 3. |
- Aad, G., et al.
(författare)
-
Measurement of angular correlations in Drell-Yan lepton pairs to probe Z/gamma* boson transverse momentum at root s=7 TeV with the ATLAS detector
- 2013
-
Ingår i: Physics Letters B. - Elsevier. - 0370-2693. ; 720:1-3, s. 32-51
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of angular correlations in Drell-Yan lepton pairs via the phi(eta)* observable is presented. This variable probes the same physics as the Z/gamma* boson transverse momentum with a better experimental resolution. The Z/gamma* -> e(+)e(-) and Z/gamma* -> mu(+)mu(-) decays produced in proton-proton collisions at a centre-of-mass energy of root s = 7 TeV are used. The data were collected with the ATLAS detector at the LHC and correspond to an integrated luminosity of 4.6 fb(-1). Normalised differential cross sections as a function of phi(eta)* are measured separately for electron and muon decay channels. These channels are then combined for improved accuracy. The cross section is also measured double differentially as a function of phi(eta)* for three independent bins of the Z boson rapidity. The results are compared to QCD calculations and to predictions from different Monte Carlo event generators. The data are reasonably well described, in all measured Z boson rapidity regions, by resummed QCD predictions combined with fixed-order perturbative QCD calculations or by some Monte Carlo event generators. The measurement precision is typically better by one order of magnitude than present theoretical uncertainties. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.
|
|
| 4. |
- Aad, G., et al.
(författare)
-
Measurements of the electron and muon inclusive cross-sections in proton-proton collisions at root s=7 TeV with the ATLAS detector
- 2012
-
Ingår i: Physics Letters B. - Elsevier Science BV. - 0370-2693. ; 707:5, s. 438-458
-
Tidskriftsartikel (refereegranskat)abstract
- 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 root s = 7 TeV, using data collected by the ATLAS detector at the LHC. The muon cross-section is measured as a function of p(T) in the range 4 < p(T) < 100 GeV and within pseudorapidity vertical bar eta vertical bar < 2.5. In addition the electron and muon cross-sections are measured in the range 7 < p(T) < 26 GeV and within vertical bar eta vertical bar < 2.0, excluding 1.37 < vertical bar eta vertical bar < 1.52. Integrated luminosities of 1.3 pb(-1) and 1.4 pb(-1) are used for the electron and muon measurements, respectively. After subtraction of the W/Z/gamma* contribution, the differential cross-sections are found to be in good agreement with theoretical predictions for heavy-flavour production obtained from Fixed Order NLO calculations with NLL high-p(T) resummation, and to be sensitive to the effects of NLL resummation. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.
|
|
| 5. |
- Aad, G., et al.
(författare)
-
Search for anomalous production of prompt like-sign muon pairs and constraints on physics beyond the standard model with the ATLAS detector
- 2012
-
Ingår i: Physical Review D. - American Physical Society. - 1550-7998. ; 85:3, s. 032004
-
Tidskriftsartikel (refereegranskat)abstract
- An inclusive search for anomalous production of two prompt, isolated muons with the same electric charge is presented. The search is performed in a data sample corresponding to 1.6 fb(-1) of integrated luminosity collected in 2011 at root s = 7 TeV with the ATLAS detector at the LHC. Muon pairs are selected by requiring two isolated muons of the same electric charge with p(T) > 20 GeV and vertical bar eta vertical bar < 2.5. Minimal requirements are placed on the rest of the event activity. The distribution of the invariant mass of the muon pair m(mu mu) is found to agree well with the background expectation. Upper limits on the cross section for anomalous production of two muons with the same electric charge are placed as a function of m(mu mu) within a fiducial region defined by the event selection. The fiducial cross-section limit constrains the like-sign top-quark pair-production cross section to be below 3.7 pb at 95% confidence level. The data are also analyzed to search for a narrow like-sign dimuon resonance as predicted for e. g. doubly charged Higgs bosons (H-+/-+/-). Assuming pair production of H-+/-+/- bosons and a branching ratio to muons of 100% (33%), this analysis excludes masses below 355 (244) GeV and 251 (209) GeV for H-+/-+/- bosons coupling to left-handed and right-handed fermions, respectively.
|
|
| 6. |
- Aad, G., et al.
(författare)
-
Search for anomaly-mediated supersymmetry breaking with the ATLAS detector based on a disappearing-track signature in pp collisions at root s=7 TeV
- 2012
-
Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 72:4
-
Tidskriftsartikel (refereegranskat)abstract
- In models of anomaly-mediated supersymmetry breaking (AMSB), the lightest chargino is predicted to have a lifetime long enough to be detected in collider experiments. This letter explores AMSB scenarios in pp collisions at root s = 7 TeV by attempting to identify decaying charginos which result in tracks that appear to have few associated hits in the outer region of the tracking system. The search was based on data corresponding to an integrated luminosity of 1.02 fb(-1) collected with the ATLAS detector in 2011. The p(T) spectrum of candidate tracks is found to be consistent with the expectation from Standard Model background processes and constraints on the lifetime and the production cross section were obtained. In the minimal AMSB framework with m(3/2) < 32 TeV, m(0) < 1.5 TeV, tan beta = 5 and mu > 0, a chargino having mass below 92 GeV and a lifetime between 0.5 ns and 2 ns is excluded at 95 % confidence level.
|
|
| 7. |
- Aad, G., et al.
(författare)
-
Search for first generation scalar leptoquarks in pp collisions at root s=7 TeV with the ATLAS detector
- 2012
-
Ingår i: Physics Letters B. - Elsevier. - 0370-2693. ; 709:3, s. 158-176
-
Tidskriftsartikel (refereegranskat)abstract
- We report a search for first generation scalar leptoquarks using 1.03 fb(-1) of proton-proton collisions data produced by the Large Hadron Collider at root s = 7 TeV and recorded by the ATLAS experiment. Leptoquarks are sought via their decay into an electron or neutrino and a quark, producing events with two oppositely charged electrons and at least two jets, or events with an electron, missing transverse momentum and at least two jets. Control data samples are used to validate background predictions from Monte Carlo simulation. In the signal region, the observed event yields are consistent with the background expectations. We exclude at 95% confidence level the production of first generation scalar leptoquark with masses m(LQ) < 660 (607) GeV when assuming the branching fraction of a leptoquark to a charged lepton is equal to 1.0 (0.5). (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
|
|
| 8. |
- Aad, G., et al.
(författare)
-
Search for long-lived, heavy particles in final states with a muon and multi-track displaced vertex in proton-proton collisions at root s=7 TeV with the ATLAS detector
- 2013
-
Ingår i: Physics Letters B. - Elsevier Science BV. - 0370-2693. ; 719:4-5, s. 280-298
-
Tidskriftsartikel (refereegranskat)abstract
- Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. In this Letter, results are presented of a search for events containing one or more such particles, which decay at a significant distance from their production point, using a final state containing charged hadrons and an associated muon. This analysis uses a data sample of proton-proton collisions at root s = 7 TeV corresponding to an integrated luminosity of 4.4 fb(-1) collected in 2011 by the ATLAS detector operating at the Large Hadron Collider. Results are interpreted in the context of R-parity violating supersymmetric scenarios. No events in the signal region are observed and limits are set on the production cross section for pair production of supersymmetric particles, multiplied by the square of the branching fraction for a neutralino to decay to charged hadrons and a muon, based on the scenario where both of the produced supersymmetric particles give rise to neutralinos that decay in this way. However, since the search strategy is based on triggering on and reconstructing the decay products of individual long-lived particles, irrespective of the rest of the event, these limits can easily be reinterpreted in scenarios with different numbers of long-lived particles per event. The limits are presented as a function of neutralino lifetime, and for a range of squark and neutralino masses. (c) 2013 CERN. Published by Elsevier B.V. All rights reserved.
|
|
| 9. |
- Aad, G., et al.
(författare)
-
Searches for heavy long-lived sleptons and R-hadrons with the ATLAS detector in pp collisions at root s=7 TeV
- 2013
-
Ingår i: Physics Letters B. - Elsevier. - 0370-2693. ; 720:4-5, s. 277-308
-
Tidskriftsartikel (refereegranskat)abstract
- A search for long-lived particles is performed using a data sample of 4.7 fb(-1) from proton-proton collisions at a centre-of-mass energy. root s = 7 TeV collected by the ATLAS detector at the LHC. No excess is observed above the estimated background and lower limits, at 95% confidence level, are set on the mass of the long-lived particles in different scenarios, based on their possible interactions in the inner detector, the calorimeters and the muon spectrometer. Long-lived staus in gauge-mediated SUSY-breaking models are excluded up to a mass of 300 GeV for tan beta = 5-20. Directly produced long-lived sleptons are excluded up to a mass of 278 GeV. R-hadrons, composites of gluino (stop, sbottom) and light quarks, are excluded up to a mass of 985 GeV (683 GeV, 612 GeV) when using a generic interaction model. Additionally two sets of limits on R-hadrons are obtained that are less sensitive to the interaction model for R-hadrons. One set of limits is obtained using only the inner detector and calorimeter observables, and a second set of limits is obtained based on the inner detector alone. (c) 2013 CERN. Published by Elsevier B.V. All rights reserved.
|
|
| 10. |
- Aad, G., et al.
(författare)
-
Further search for supersymmetry at root s=7 TeV in final states with jets, missing transverse momentum, and isolated leptons with the ATLAS detector
- 2012
-
Ingår i: Physical Review D. - American Physical Society. - 1550-7998. ; 86:9, s. 092002
-
Tidskriftsartikel (refereegranskat)abstract
- This work presents a new inclusive search for supersymmetry (SUSY) by the ATLAS experiment at the LHC in proton-proton collisions at a center-of-mass energy root s = 7 TeV in final states with jets, missing transverse momentum and one or more isolated electrons and/or muons. The search is based on data from the full 2011 data-taking period, corresponding to an integrated luminosity of 4.7 fb(-1). Single-lepton and multilepton channels are treated together in one analysis. An increase in sensitivity is obtained by simultaneously fitting the number of events in statistically independent signal regions, and the shapes of distributions within those regions. A dedicated signal region is introduced to be sensitive to decay cascades of SUSY particles with small mass differences ("compressed SUSY"). Background uncertainties are constrained by fitting to the jet-multiplicity distribution in background control regions. Observations are consistent with Standard Model expectations, and limits are set or extended on a number of SUSY models.
|
|
