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1. chinaXiv:201609.00821 [pdf]

Measurement of the charge asymmetry in highly boosted top-quark pair production in $\sqrt{s} =$ 8 TeV $pp$ collision data collected by the ATLAS experiment

Aad, Georges and others
分类: 物理学 >> 核物理学

In the pp→tt¯ process the angular distributions of top and anti-top quarks are expected to present a subtle difference, which could be enhanced by processes not included in the Standard Model. This Letter presents a measurement of the charge asymmetry in events where the top-quark pair is produced with a large invariant mass. The analysis is performed on 20.3 fb−1 of pp collision data at s√= 8 TeV collected by the ATLAS experiment at the LHC, using reconstruction techniques specifically designed for the decay topology of highly boosted top quarks. The charge asymmetry in a fiducial region with large invariant mass of the top-quark pair (mtt¯> 0.75 TeV) and an absolute rapidity difference of the top and anti-top quark candidates within −2 <|yt|−|yt¯|< 2 is measured to be 4.2 ± 3.2%, in agreement with the Standard Model prediction at next-to-leading order. A differential measurement in three tt¯ mass bins is also presented.

提交时间: 2016-09-12 点击量471下载量275 评论 0

2. chinaXiv:201609.00820 [pdf]

Reconstruction of hadronic decay products of tau leptons with the ATLAS experiment

Aad, Georges and others
分类: 物理学 >> 核物理学

This paper presents a new method of reconstructing the individual charged and neutral hadrons in tau decays with the ATLAS detector. The reconstructed hadrons are used to classify the decay mode and to calculate the visible four-momentum of reconstructed tau candidates, significantly improving the resolution with respect to the calibration in the existing tau reconstruction. The performance of the reconstruction algorithm is optimised and evaluated using simulation and validated using samples of Z→ττ and Z(→μμ)+jets events selected from proton-proton collisions at a centre-of-mass energy s√=8 TeV, corresponding to an integrated luminosity of 5 fb−1.

提交时间: 2016-09-12 点击量457下载量264 评论 0

3. chinaXiv:201609.00819 [pdf]

Search for new phenomena with photon+jet events in proton-proton collisions at $ \sqrt{s}=13 $ TeV with the ATLAS detector

Aad, Georges and others
分类: 物理学 >> 核物理学

A search is performed for the production of high-mass resonances decaying into a photon and a jet in 3.2 fb−1 of proton--proton collisions at a centre-of-mass energy of s√=13 TeV collected by the ATLAS detector at the Large Hadron Collider. Selected events have an isolated photon and a jet, each with transverse momentum above 150 GeV. No significant deviation of the γ+jet invariant mass distribution from the background-only hypothesis is found. Limits are set at 95% confidence level on the cross sections of generic Gaussian-shaped signals and of a few benchmark phenomena beyond the Standard Model: excited quarks with vector-like couplings to the Standard Model particles, and non-thermal quantum black holes in two models of extra spatial dimensions. The minimum excluded visible cross sections for Gaussian-shaped resonances with width-to-mass ratios of 2% decrease from about 6 fb for a mass of 1.5 TeV to about 0.8 fb for a mass of 5 TeV. The minimum excluded visible cross sections for Gaussian-shaped resonances with width-to-mass ratios of 15% decrease from about 50 fb for a mass of 1.5 TeV to about 1.0 fb for a mass of 5 TeV. Excited quarks are excluded below masses of 4.4 TeV, and non-thermal quantum black holes are excluded below masses of 3.8 (6.2) TeV for Randall--Sundrum (Arkani-Hamed--Dimopoulous--Dvali) models with one (six) extra dimensions.

提交时间: 2016-09-12 点击量412下载量243 评论 0

4. chinaXiv:201609.00818 [pdf]

Measurement of the $ZZ$ Production Cross Section in $pp$ Collisions at $\sqrt{s} =$ 8 TeV with the ATLAS Detector

Aad, Georges and others
分类: 物理学 >> 核物理学

The ZZ production cross section in proton-proton collisions at 13 TeV center-of-mass energy is measured using 3.2 fb−1 of data recorded with the ATLAS detector at the Large Hadron Collider. The considered Z boson candidates decay to an electron or muon pair of mass 66-116 GeV. The cross section is measured in a fiducial phase space reflecting the detector acceptance. It is also extrapolated to a total phase space for Z bosons in the same mass range and of all decay modes, giving 16.7+2.2−2.0(stat.)+0.9−0.7(syst.)+1.0−0.7(lumi.) pb. The results agree with standard model predictions.

提交时间: 2016-09-12 点击量464下载量287 评论 0

5. chinaXiv:201609.00817 [pdf]

Combination of searches for $WW$, $WZ$, and $ZZ$ resonances in pp collisions at $\sqrt{s} =$ 8 TeV with the ATLAS detector

Aad, Georges and others
分类: 物理学 >> 核物理学

The ATLAS experiment at the CERN Large Hadron Collider has performed searches for new, heavy bosons decaying to WW, WZ and ZZ final states in multiple decay channels using 20.3 fb−1 of pp collision data at s√=8 TeV. In the current study, the results of these searches are combined to provide a more stringent test of models predicting heavy resonances with couplings to vector bosons. Direct searches for a charged diboson resonance decaying to WZ in the ℓνℓ′ℓ′ (ℓ=μ,e) , ℓℓqq¯, ℓνqq¯ and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the WZ bosons are compared with predictions of an extended gauge model with a heavy W′ boson. In addition, direct searches for a neutral diboson resonance decaying to WW and ZZ in the ℓℓqq¯, ℓνqq¯, and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the WW and ZZ bosons are compared with predictions for a heavy, spin-2 graviton in an extended Randall--Sundrum model where the Standard Model fields are allowed to propagate in the bulk of the extra dimension.

提交时间: 2016-09-12 点击量393下载量255 评论 0

6. chinaXiv:201609.00816 [pdf]

Search for charged Higgs bosons in the $H^\pm \rightarrow tb$ decay channel in $pp$ collisions at $\sqrt{s}=8 $ TeV using the ATLAS detector

Aad, Georges and others
分类: 物理学 >> 核物理学

Charged Higgs bosons heavier than the top quark and decaying via H±→tb are searched for in proton--proton collisions measured with the ATLAS experiment at s√=8 TeV corresponding to an integrated luminosity of 20.3 fb−1. The production of a charged Higgs boson in association with a top quark, gb→tH±, is explored in the mass range 200 to 600 GeV using multi-jet final states with one electron or muon. In order to separate the signal from the Standard Model background, analysis techniques combining several kinematic variables are employed. An excess of events above the background-only hypothesis is observed across a wide mass range, amounting to up to 2.4 standard deviations. Upper limits are set on the gb→tH± production cross section times the branching fraction BR(H±→tb). Additionally, the complementary s-channel production, qq′→H±, is investigated through a reinterpretation of W′→tb searches in ATLAS. Final states with one electron or muon are relevant for H± masses from 0.4 to 2.0 TeV, whereas the all-hadronic final state covers the range 1.5 to 3.0 TeV. In these search channels, no significant excesses from the predictions of the Standard Model are observed, and upper limits are placed on the qq′→H± production cross section times the branching fraction BR(H±→tb).

提交时间: 2016-09-12 点击量434下载量238 评论 0

7. chinaXiv:201609.00815 [pdf]

Measurement of the differential cross-sections of prompt and non-prompt production of $J/\psi $ and $\psi (2\mathrm) in pp collisions at $\sqrt{s} =$ 7 and 8 TeV with the ATLAS detector

Aad, Georges and others
分类: 物理学 >> 核物理学

The production rates of prompt and non-prompt J/ψ and ψ(2S) mesons are measured using 2.1 fb−1 and 11.4 fb−1 of data collected with the ATLAS experiment at the LHC, in proton-proton collisions at s√=7 and 8 TeV respectively. Production cross-sections for both prompt and non-prompt production sources, ratios of ψ(2S) to J/ψproduction, and fractions of non-prompt to inclusive production for J/ψ and ψ(2S) are measured double-differentially as a function of meson pT and rapidity. These measurements are made in a restricted fiducial volume and also corrected for geometrical acceptance after which they are compared to a variety of theoretical predictions.

提交时间: 2016-09-12 点击量426下载量254 评论 0

8. chinaXiv:201609.00812 [pdf]

Measurement of $D^*\pm$, $D^\pm$ and $D_s^\pm$ meson production cross sections in $pp$ collisions at $\sqrt{s}=7$ TeV with the ATLAS detector

Aad, Georges and others
分类: 物理学 >> 核物理学

The production of D∗±, D± and D±s charmed mesons has been measured with the ATLAS detector in ppcollisions at s√=7 TeV at the LHC, using data corresponding to an integrated luminosity of 280nb−1. The charmed mesons have been reconstructed in the range of transverse momentum 3.5

提交时间: 2016-09-12 点击量424下载量230 评论 0

9. chinaXiv:201609.00810 [pdf]

Search for strong gravity in multijet final states produced in pp collisions at $\sqrt{s} =$ 13 TeV using the ATLAS detector at the LHC

Aad, Georges and others
分类: 物理学 >> 核物理学

A search is conducted for new physics in multijet final states using 3.6 inverse femtobarns of data from proton-proton collisions at s√ = 13 TeV taken at the CERN Large Hadron Collider with the ATLAS detector. Events are selected containing at least three jets with scalar sum of jet transverse momenta (HT) greater than 1 TeV. No excess is seen at large HT and limits are presented on new physics: models which produce final states containing at least three jets and having cross sections larger than 1.6 fb with HT > 5.8 TeV are excluded. Limits are also given in terms of new physics models of strong gravity that hypothesize additional space-time dimensions.

提交时间: 2016-09-12 点击量415下载量246 评论 0

10. chinaXiv:201609.00809 [pdf]

Measurement of the transverse momentum and $\phi ^*_\eta $ distributions of Drell–Yan lepton pairs in proton–proton collisions at $\sqrt{s}=8$  TeV with the ATLAS detector

Aad, Georges and others
分类: 物理学 >> 核物理学

Distributions of transverse momentum pllT and the angular variable ϕ∗η of Drell--Yan lepton pairs are measured in 20.3 fb−1 of proton--proton collisions at s√=8 TeV with the ATLAS detector at the LHC. Measurements in electron-pair and muon-pair final states are corrected for detector effects and combined. Compared to previous measurements in proton--proton collisions at s√=7 TeV, these new measurements benefit from a larger data sample and improved control of systematic uncertainties. Measurements are performed in bins of lepton-pair mass above, around and below the Z-boson mass peak. The data are compared to predictions from perturbative and resummed QCD calculations. For values of ϕ∗η<1 the predictions from the Monte Carlo generator ResBos are generally consistent with the data within the theoretical uncertainties. However, at larger values of ϕ∗η this is not generally the case. Monte Carlo generators based on the parton-shower approach are unable to describe the data over the full range of pllT and the fixed-order prediction of DYNNLO falls below the data at high values of pllT. ResBos and the parton-shower Monte Carlo generators provide a much better description of the evolution of the ϕ∗η and pllT distributions as a function of lepton-pair mass and rapidity.

提交时间: 2016-09-12 点击量418下载量257 评论 0

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