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1. chinaXiv:201608.00182 [pdf]

Measurement of the $W^\pmZ$-boson production cross sections in $pp$ collisions at $\sqrts=13$ TeV with the ATLAS Detector

Aaboud, Morad and others
Subjects: Physics >> Nuclear Physics

The production of?W±Z?events in proton--proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC. The collected data correspond to an integrated luminosity of 3.2 fb?1. The?W±Z?candidates are reconstructed using leptonic decays of the gauge bosons into electrons or muons. The measured inclusive cross section in the detector fiducial region for leptonic decay modes is?σfid.W±Z→?′ν??=63.2±3.2?(stat.)?±2.6?(sys.)?±1.5?(lumi.) fb. In comparison, the next-to-leading-order Standard Model prediction is?53.4+3.6?2.8?fb. The extrapolation of the measurement from the fiducial to the total phase space yields?σtot.W±Z=50.6±2.6?(stat.)?±2.0?(sys.)?±0.9?(th.)?±1.2?(lumi.) pb, in agreement with a recent next-to-next-to-leading-order calculation of?48.2+1.1?1.0?pb. The cross section as a function of jet multiplicity is also measured, together with the charge-dependent?W+Z?and?W?Z?cross sections and their ratio.

submitted time 2016-08-29 Hits875Downloads478 Comment 0

2. chinaXiv:201608.00181 [pdf]

Search for new resonances in events with one lepton and missing transverse momentum in $pp$ collisions at ps = 13 TeV with the ATLAS detector

Aaboud, Morad and others
Subjects: Physics >> Nuclear Physics

A search for?W′?bosons in events with one lepton (electron or muon) and missing transverse momentum is presented. The search uses 3.2 fb?1?of?pp?collision data collected at?s√=13?TeV by the ATLAS experiment at the LHC in 2015. The transverse mass distribution is examined and no significant excess of events above the level expected from Standard Model processes is observed. Upper limits on the?W′boson cross-section times branching ratio to leptons are set as a function of the?W′?mass. Assuming a?W′?boson as predicted by the Sequential Standard Model,?W′?masses below 4.07 TeV are excluded at the 95% confidence level. This extends the limit set using LHC data at?s√=8?TeV by around 800 GeV.

submitted time 2016-08-29 Hits955Downloads530 Comment 0

3. chinaXiv:201608.00180 [pdf]

Search for top squarks in final states with one isolated lepton, jets, and missing transverse momentum in $\sqrts=13$ TeV $pp$ collisions with the ATLAS detector

Aaboud, Morad and others
Subjects: Physics >> Nuclear Physics

The results of a search for the stop, the supersymmetric partner of the top quark, in final states with one isolated electron or muon, jets, and missing transverse momentum are reported. The search uses the 2015 LHC?pp?collision data at a center-of-mass energy of?s√=13?TeV recorded by the ATLAS detector and corresponding to an integrated luminosity of 3.2 fb?1. The analysis targets two types of signal models: gluino-mediated pair production of stops with a nearly mass-degenerate stop and neutralino; and direct pair production of stops, decaying to the top quark and the lightest neutralino. The experimental signature in both signal scenarios is similar to that of a top quark pair produced in association with large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits on gluino and stop masses are set at 95% confidence level. The results extend the LHC Run-1 exclusion limit on the gluino mass up to 1460 GeV in the gluino-mediated scenario in the high gluino and low stop mass region, and add an excluded stop mass region from 745 to 780 GeV for the direct stop model with a massless lightest neutralino. The results are also reinterpreted to set exclusion limits in a model of vector-like top quarks.

submitted time 2016-08-29 Hits852Downloads507 Comment 0

4. chinaXiv:201608.00178 [pdf]

Search for resonances in diphoton events at $\sqrts$=13 TeV with the ATLAS detector

Aaboud, Morad and others
Subjects: Physics >> Nuclear Physics

Searches for new resonances decaying into two photons in the ATLAS experiment at the CERN Large Hadron Collider are described. The analysis is based on proton--proton collision data corresponding to an integrated luminosity of 3.2 fb?1?at?s√=13?TeV recorded in 2015. Two searches are performed, one targeted at a spin-2 particle of mass larger than 500 GeV, using Randall--Sundrum graviton states as a benchmark model, and one optimized for a spin-0 particle of mass larger than 200 GeV. Varying both the mass and the decay width, the most significant deviation from the background-only hypothesis is observed at a diphoton invariant mass around 750 GeV with local significances of 3.8 and 3.9 standard deviations in the searches optimized for a spin-2 and spin-0 particle, respectively. The global significances are estimated to be 2.1 standard deviations for both analyses. The consistency between the data collected at 13 TeV and 8 TeV is also evaluated. Limits on the production cross section times branching ratio to two photons for the two resonance types are reported.

submitted time 2016-08-29 Hits867Downloads503 Comment 0

5. chinaXiv:201608.00175 [pdf]

Measurement of the $t\bart$ production cross-section using $e\mu$ events with b-tagged jets in pp collisions at $\sqrts$=13 TeV with the ATLAS detector

Aaboud, Morad and others
Subjects: Physics >> Nuclear Physics

This paper describes a measurement of the inclusive top quark pair production cross-section (σtt?) with a data sample of 3.2 fb?1?of proton--proton collisions at a centre-of-mass energy of?s√=13 TeV, collected in 2015 by the ATLAS detector at the LHC. This measurement uses events with an opposite-charge electron--muon pair in the final state. Jets containing?b-quarks are tagged using an algorithm based on track impact parameters and reconstructed secondary vertices. The numbers of events with exactly one and exactly two?b-tagged jets are counted and used to determine simultaneously?σtt??and the efficiency to reconstruct and?b-tag a jet from a top quark decay, thereby minimising the associated systematic uncertainties. The cross-section is measured to be:?σtt?= 818?±?8 (stat)?±?27 (syst)?±?19 (lumi)?±?12 (beam) pb, where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, the integrated luminosity and the LHC beam energy, giving a total relative uncertainty of 4.4%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. A fiducial measurement corresponding to the experimental acceptance of the leptons is also presented.

submitted time 2016-08-29 Hits884Downloads498 Comment 0

6. chinaXiv:201608.00174 [pdf]

Measurement of the Inelastic Proton-Proton Cross Section at ps = 13 TeV with the ATLAS Detector at the LHC

Aaboud, Morad and others
Subjects: Physics >> Nuclear Physics

This Letter presents a measurement of the inelastic proton-proton cross section using 60?μb?1?of?pp?collisions at a center-of-mass energy?s√?of?13?TeV with the ATLAS detector at the LHC. Inelastic interactions are selected using plastic scintillators in the forward region of the detector. A cross section of?68.2±1.5?mb is measured in the fiducial region?ξ=M2X/s>10?6, where?MX?is the largest invariant mass of the two hadronic systems separated by the largest rapidity gap in the event. In this?ξ?range the scintillators are highly efficient. For diffractive events this corresponds to cases where at least one proton dissociates to a system with?MX>13?GeV. The measured cross section is compared with a range of theoretical predictions. When extrapolated to the full phase space, a cross-section of?79.3±2.9?mb is measured, consistent with the inelastic cross section increasing with center-of-mass energy.

submitted time 2016-08-29 Hits884Downloads516 Comment 0

7. chinaXiv:201608.00172 [pdf]

Search for TeV-scale gravity signatures in high-mass final states with leptons and jets with the ATLAS detector at $\sqrts=13$ TeV

Aaboud, Morad and others
Subjects: Physics >> Nuclear Physics

A search for physics beyond the Standard Model, in final states with at least one high transverse momentum charged lepton (electron or muon) and two additional high transverse momentum leptons or jets, is performed using 3.2 fb?1?of proton--proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015 at?s√=13?TeV. The upper end of the distribution of the scalar sum of the transverse momenta of leptons and jets is sensitive to the production of high-mass objects. No excess of events beyond Standard Model predictions is observed. Exclusion limits are set for models of microscopic black holes with two to six extra dimensions.

submitted time 2016-08-29 Hits889Downloads492 Comment 0

8. chinaXiv:201608.00171 [pdf]

Search for the Standard Model Higgs boson produced by vector-boson fusion in 8 TeV pp collisions and decaying to bottom quarks with the ATLAS detector

Aaboud, Morad and others
Subjects: Physics >> Nuclear Physics

A search with the ATLAS detector is presented for the Standard Model Higgs boson produced by vector-boson fusion and decaying to a pair of bottom quarks, using 20.2?fb?1?of LHC proton--proton collision data at?s√?= 8 TeV. The signal is searched for as a resonance in the invariant mass distribution of a pair of jets containing?b-hadrons in vector-boson-fusion candidate events. The yield is measured to be??0.8±2.3?times the Standard Model cross-section for a Higgs boson mass of 125 GeV. The upper limit on the cross-section times the branching ratio is found to be 4.4 times the Standard Model cross-section at the 95% confidence level, consistent with the expected limit value of 5.4 (5.7) in the background-only (Standard Model production) hypothesis.

submitted time 2016-08-29 Hits883Downloads502 Comment 0

9. chinaXiv:201608.00170 [pdf]

Measurement of the top quark mass in the $t\bart\to$ dilepton channel from $\sqrts=8$ TeV ATLAS data

Aaboud, Morad and others
Subjects: Physics >> Nuclear Physics

The top quark mass is measured in the?tt?→?dilepton channel (lepton?=e,μ) using ATLAS data recorded in the year 2012 at the LHC. The data were taken at a proton--proton centre-of-mass energy of?s√=?8 TeV and correspond to an integrated luminosity of about 20.2 fb?1. Exploiting the template method, and using the distribution of invariant masses of lepton--b-jet pairs, the top quark mass is measured to be?mtop=?172.99?±?0.41 (stat)?±?0.74 (syst) GeV, with a total uncertainty of 0.84 GeV. Finally, a combination with previous ATLAS?mtop?measurements from?s√=7 TeV data in the?tt?→?dilepton and?tt?→?lepton+jets channels results in?mtop=?172.84?±?0.34 (stat)?±?0.61 (syst) GeV, with a total uncertainty of 0.70 GeV.

submitted time 2016-08-29 Hits895Downloads484 Comment 0

10. chinaXiv:201608.00169 [pdf]

Measurement of the photon identification efficiencies with the ATLAS detector using LHC Run-1 data

Aaboud, Morad and others
Subjects: Physics >> Nuclear Physics

The algorithms used by the ATLAS Collaboration to reconstruct and identify prompt photons are described. Measurements of the photon identification efficiencies are reported, using 4.9 fb?1?of?pp?collision data collected at the LHC at?s√=7?TeV and 20.3 fb?1?at?s√=8?TeV. The efficiencies are measured separately for converted and unconverted photons, in four different pseudo rapidity regions, for transverse momenta between 10 GeV and 1.5 TeV. The results from the combination of three data-driven techniques are compared to the predictions from a simulation of the detector response, after correcting the electromagnetic shower momenta in the simulation for the average differences observed with respect to data. Data-to-simulation efficiency ratios used as correction factors in physics measurements are determined to account for the small residual efficiency differences. These factors are measured with uncertainties between 0.5% and 10% in 7 TeV data and between 0.5% and 3% in 8 TeV data, depending on the photon transverse momentum and pseudorapidity.

submitted time 2016-08-29 Hits703Downloads395 Comment 0

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