1.
The LUCID-2 Luminometer
Hedberg, V
International journal of modern physics. Conference series,
2018, Letnik:
46
Journal Article
The LUCID-2 detector is the main online and offline luminosity monitor of the ATLAS experiment. It provides 104 different luminosity measurements from different algorithms for each of the thousands ...
of LHC bunches. The new detector is using the quartz windows of 10 mm diameter photomultipliers and optical quartz fibers as the Cherenkov medium. A main challenge for a luminometer is to keep the efficiency constant during years of data-taking. LUCID-2 is using an innovative calibration system based on radioactive Bi-207 sources deposited on the quartz window of the readout photomultipliers.
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3.
Angular analysis of Bd 0 → K ∗ μ + μ − decays in pp collisions at √s=8 TeV with the ATLAS detector
Aaboud, M; Åkesson, Torsten; Bocchetta, Simona ...
The journal of high energy physics,
2018, Letnik:
2018, Številka:
10
Journal Article
An angular analysis of the decay Bd 0 → K∗μ+μ− is presented, based on proton-proton collision data recorded by the ATLAS experiment at the LHC. The study is using 20.3 fb−1 of integrated luminosity ...
collected during 2012 at centre-of-mass energy of s=8 TeV. Measurements of the K* longitudinal polarisation fraction and a set of angular parameters obtained for this decay are presented. The results are compatible with the Standard Model predictions.Figure not available: see fulltext.. © 2018, The Author(s).
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4.
Association with Lepton Pairs Produced via the Photon Fusion Mechanism at ATLAS
Aad, G; Åkesson, Torsten; Bocchetta, Simona ...
Physical review letters,
2020, Letnik:
125
Journal Article
The observation of forward proton scattering in association with lepton pairs (e+e−+p or μ+μ−+p) produced via photon fusion is presented. The scattered proton is detected by the ATLAS Forward Proton ...
spectrometer, while the leptons are reconstructed by the central ATLAS detector. Proton-proton collision data recorded in 2017 at a center-of-mass energy of √s=13 TeV are analyzed, corresponding to an integrated luminosity of 14.6 fb−1. A total of 57 (123) candidates in the ee+p (μμ+p) final state are selected, allowing the background-only hypothesis to be rejected with a significance exceeding 5 standard deviations in each channel. Proton-tagging techniques are introduced for cross-section measurements in the fiducial detector acceptance, corresponding to σee+p=11.0±2.6(stat)±1.2(syst)±0.3(lumi) and σμμ+p=7.2±1.6(stat)±0.9(syst)±0.2(lumi) fb in the dielectron and dimuon channel, respectively.
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5.
Measurements of photo-nuclear jet production in Pb + Pb collisions with ATLAS
Angerami, Aaron
Nuclear physics. A,
11/2017, Letnik:
967, Številka:
C
Journal Article
Ultra-peripheral heavy ion collisions provide a unique opportunity to study the parton distributions in the colliding nuclei via the measurement of photo-nuclear jet production. An analysis of jet ...
production in ultra-peripheral Pb+Pb collisions at sNN=5.02 TeV performed using data collected with the ATLAS detector in 2015 is described. The data set corresponds to a total Pb+Pb integrated luminosity of 0.38 nb−1. The ultra-peripheral collisions are selected using a combination of forward neutron and rapidity gap requirements. The cross-sections, not unfolded for detector response, are compared to results from Pythia Monte Carlo simulations re-weighted to match a photon spectrum obtained from the STARlight model. Qualitative agreement between data and these simulations is observed over a broad kinematic range suggesting that using these collisions to measure nuclear parton distributions is experimentally realisable.
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6.
Measurements of long-range azimuthal anisotropies and associated Fourier coefficients for pp collisions at s =5.02 and 13 TeV and p+Pb collisions at sNN =5.02 TeV with the ATLAS detector MEASUREMENTS of LONG-RANGE AZIMUTHAL
Aaboud, M; Aad, G; Abbott, B. ...
Physical review. C,
2017, Letnik:
96, Številka:
2
Journal Article
ATLAS measurements of two-particle correlations are presented for s=5.02 and 13 TeV pp collisions and for sNN=5.02 TeV p+Pb collisions at the LHC. The correlation functions are measured as a function ...
of relative azimuthal angle Δφ, and pseudorapidity separation Δη, using charged particles detected within the pseudorapidity interval |η|2, is studied using a template fitting procedure to remove a "back-to-back" contribution to the correlation function that primarily arises from hard-scattering processes. In addition to the elliptic, cos(2Δφ), modulation observed in a previous measurement, the pp correlation functions exhibit significant cos(3Δφ) and cos(4Δφ) modulation. The Fourier coefficients vn,n associated with the cos(nΔφ) modulation of the correlation functions for n=2-4 are measured as a function of charged-particle multiplicity and charged-particle transverse momentum. The Fourier coefficients are observed to be compatible with cos(nφ) modulation of per-event single-particle azimuthal angle distributions. The single-particle Fourier coefficients vn are measured as a function of charged-particle multiplicity, and charged-particle transverse momentum for n=2-4. The integrated luminosities used in this analysis are, 64 nb-1 for the s=13 TeV pp data, 170 nb-1 for the s=5.02 TeV pp data, and 28 nb-1 for the sNN=5.02 TeV p+Pb data. © 2017 CERN.
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7.
Combination of inclusive and differential (Formula Presented) charge asymmetry measurements using ATLAS and CMS data at (Formula Presented)= 7 and 8 TeV
Aaboud, M; Aad, G; Abbott, B. ...
The journal of high energy physics,
2018, Letnik:
2018, Številka:
4
Journal Article
This paper presents combinations of inclusive and differential measurements of the charge asymmetry (AC) in top quark pair (tt) events with a lepton+jets signature by the ATLAS and CMS ...
Collaborations, using data from LHC proton-proton collisions at centreof- mass energies of 7 and 8TeV. The data correspond to integrated luminosities of about 5 and 20 fb–1for each experiment, respectively. The resulting combined LHC measurements of the inclusive charge asymmetry are AC LHC7= 0:005±0:007 (stat) ±0:006 (syst) at 7TeV and AC LHC7= 0:0055 ± 0:0023 (stat) ± 0:0025 (syst) at 8TeV. These values, as well as the combination of AC measurements as a function of the invariant mass of the formula presented system at 8TeV, are consistent with the respective standard model predictions. © CERN, for the benefit of the ATLAS-CMS Collaboration.
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8.
Search for heavy ZZ resonances in the ℓ+ℓ-ℓ+ℓ- and ℓ+ℓ- final states using proton–proton collisions at √s=13 TeV with the ATLAS detector
Aaboud, M; Aad, G; Abbott, B. ...
The European physical journal. C, Particles and fields,
04/2018, Letnik:
78, Številka:
4
Journal Article
A search for heavy resonances decaying into a pair of Z bosons leading to ℓ+ℓ-ℓ+ℓ- and ℓ+ℓ- final states, where ℓ stands for either an electron or a muon, is presented. The search uses proton–proton ...
collision data at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 36.1 fb - 1 collected with the ATLAS detector during 2015 and 2016 at the Large Hadron Collider. Different mass ranges for the hypothetical resonances are considered, depending on the final state and model. The different ranges span between 200 and 2000 GeV. The results are interpreted as upper limits on the production cross section of a spin-0 or spin-2 resonance. The upper limits for the spin-0 resonance are translated to exclusion contours in the context of Type-I and Type-II two-Higgs-doublet models, while those for the spin-2 resonance are used to constrain the Randall–Sundrum model with an extra dimension giving rise to spin-2 graviton excitations. © 2018, CERN for the benefit of the ATLAS collaboration.
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9.
Search for heavy resonances decaying into WW in the e final state in pp collisions at √s=13TeV with the ATLAS detector
Aaboud, M; Aad, G; Abbott, B. ...
The European physical journal. C, Particles and fields,
2018, Letnik:
78, Številka:
1
Journal Article
A search for neutral heavy resonances is performed in the WW→ e decay channel using pp collision data corresponding to an integrated luminosity of 36.1fb-1, collected at a centre-of-mass energy of ...
13TeV by the ATLAS detector at the Large Hadron Collider. No evidence of such heavy resonances is found. In the search for production via the quark–antiquark annihilation or gluon–gluon fusion process, upper limits on σX× B(X→ WW) as a function of the resonance mass are obtained in the mass range between 200GeV and up to 5TeV for various benchmark models: a Higgs-like scalar in different width scenarios, a two-Higgs-doublet model, a heavy vector triplet model, and a warped extra dimensions model. In the vector-boson fusion process, constraints are also obtained on these resonances, as well as on a Higgs boson in the Georgi–Machacek model and a heavy tensor particle coupling only to gauge bosons. © 2018, CERN for the benefit of the ATLAS collaboration.
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10.
Measurement of the CP-violating phase ϕsand the Bs0meson decay width difference with Bs 0→ J/ψϕ decays in ATLAS
Aad, G; Abbott, B.; Abdallah, J ...
The journal of high energy physics,
2016, Letnik:
2016, Številka:
8
Journal Article
A measurement of the Bs0decay parameters in the Bs0→ J/ψϕ channel using an integrated luminosity of 14.3 fb−1collected by the ATLAS detector from 8 TeV pp collisions at the LHC is presented. The ...
measured parameters include the CP -violating phase ϕs, the decay width Γs and the width difference between the mass eigenstates ΔΓs. The values measured for the physical parameters are statistically combined with those from 4.9 fb−1of 7 TeV data, leading to the following: Φs = -0.090 ± 0.078 (stat.) ± (syst.) rad Δ Γs = 0.085 ± 0.011 (stat.) ± 0.007 (syst.) Ps-1 Δ Γs = 0.675 ± 0.003 (stat.) ± 0.03 (syst.) Ps-1 In the analysis the parameter ΔΓs is constrained to be positive. Results for ϕs and ΔΓs are also presented as 68% and 95% likelihood contours in the ϕs-ΔΓs plane. Also measured in this decay channel are the transversity amplitudes and corresponding strong phases. All measurements are in agreement with the Standard Model predictions.Figure not available: see fulltext. © 2016, The Author(s).
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