| 1. |
- Aad, G., et al.
(author)
-
Commissioning of the ATLAS Muon Spectrometer with cosmic rays
- 2010
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 70:3, s. 875-916
-
Journal article (peer-reviewed)abstract
- The ATLAS detector at the Large Hadron Collider has collected several hundred million cosmic ray events during 2008 and 2009. These data were used to commission the Muon Spectrometer and to study the performance of the trigger and tracking chambers, their alignment, the detector control system, the data acquisition and the analysis programs. We present the performance in the relevant parameters that determine the quality of the muon measurement. We discuss the single element efficiency, resolution and noise rates, the calibration method of the detector response and of the alignment system, the track reconstruction efficiency and the momentum measurement. The results show that the detector is close to the design performance and that the Muon Spectrometer is ready to detect muons produced in high energy proton-proton collisions.
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| 2. |
- Aad, G, et al.
(author)
-
Determination of spin and parity of the Higgs boson in the [Formula: see text] decay channel with the ATLAS detector.
- 2015
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:5
-
Journal article (peer-reviewed)abstract
- Studies of the spin and parity quantum numbers of the Higgs boson in the [Formula: see text] final state are presented, based on proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb[Formula: see text] at a centre-of-mass energy of [Formula: see text] TeV. The Standard Model spin-parity [Formula: see text] hypothesis is compared with alternative hypotheses for both spin and CP. The case where the observed resonance is a mixture of the Standard-Model-like Higgs boson and CP-even ([Formula: see text]) or CP-odd ([Formula: see text]) Higgs boson in scenarios beyond the Standard Model is also studied. The data are found to be consistent with the Standard Model prediction and limits are placed on alternative spin and CP hypotheses, including CP mixing in different scenarios.
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| 3. |
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| 4. |
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| 5. |
- Aad, G, et al.
(author)
-
Measurements of fiducial cross-sections for [Formula: see text] production with one or two additional b-jets in pp collisions at [Formula: see text]=8 TeV using the ATLAS detector.
- 2016
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 76
-
Journal article (peer-reviewed)abstract
- Fiducial cross-sections for [Formula: see text] production with one or two additional b-jets are reported, using an integrated luminosity of 20.3 fb[Formula: see text] of proton-proton collisions at a centre-of-mass energy of 8 TeV at the Large Hadron Collider, collected with the ATLAS detector. The cross-section times branching ratio for [Formula: see text] events with at least one additional b-jet is measured to be 950 [Formula: see text] 70 (stat.) [Formula: see text] (syst.) fb in the lepton-plus-jets channel and 50 [Formula: see text] 10 (stat.) [Formula: see text] (syst.) fb in the [Formula: see text] channel. The cross-section times branching ratio for events with at least two additional b-jets is measured to be 19.3 [Formula: see text] 3.5 (stat.) [Formula: see text] 5.7 (syst.) fb in the dilepton channel ([Formula: see text], [Formula: see text], and ee) using a method based on tight selection criteria, and 13.5 [Formula: see text] 3.3 (stat.) [Formula: see text] 3.6 (syst.) fb using a looser selection that allows the background normalisation to be extracted from data. The latter method also measures a value of 1.30 [Formula: see text] 0.33 (stat.) [Formula: see text] 0.28 (syst.)% for the ratio of [Formula: see text] production with two additional b-jets to [Formula: see text] production with any two additional jets. All measurements are in good agreement with recent theory predictions.
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| 6. |
- Aad, G, et al.
(author)
-
Measurements of the Higgs boson production and decay rates and coupling strengths using pp collision data at [Formula: see text] and 8 TeV in the ATLAS experiment.
- 2016
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 76
-
Journal article (peer-reviewed)abstract
- Combined analyses of the Higgs boson production and decay rates as well as its coupling strengths to vector bosons and fermions are presented. The combinations include the results of the analyses of the [Formula: see text] and [Formula: see text] decay modes, and the constraints on the associated production with a pair of top quarks and on the off-shell coupling strengths of the Higgs boson. The results are based on the LHC proton-proton collision datasets, with integrated luminosities of up to 4.7 [Formula: see text] at [Formula: see text] TeV and 20.3 [Formula: see text] at [Formula: see text] TeV, recorded by the ATLAS detector in 2011 and 2012. Combining all production modes and decay channels, the measured signal yield, normalised to the Standard Model expectation, is [Formula: see text]. The observed Higgs boson production and decay rates are interpreted in a leading-order coupling framework, exploring a wide range of benchmark coupling models both with and without assumptions on the Higgs boson width and on the Standard Model particle content in loop processes. The data are found to be compatible with the Standard Model expectations for a Higgs boson at a mass of 125.36 GeV for all models considered.
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| 7. |
- Aad, G, et al.
(author)
-
Observation and measurements of the production of prompt and non-prompt [Formula: see text] mesons in association with a [Formula: see text] boson in [Formula: see text] collisions at [Formula: see text] with the ATLAS detector.
- 2015
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:5
-
Journal article (peer-reviewed)abstract
- The production of a [Formula: see text] boson in association with a [Formula: see text] meson in proton-proton collisions probes the production mechanisms of quarkonium and heavy flavour in association with vector bosons, and allows studies of multiple parton scattering. Using [Formula: see text] of data collected with the ATLAS experiment at the LHC in [Formula: see text] collisions at [Formula: see text], the first measurement of associated [Formula: see text] production is presented for both prompt and non-prompt [Formula: see text] production, with both signatures having a significance in excess of [Formula: see text]. The inclusive production cross-sections for [Formula: see text] boson production (analysed in [Formula: see text] or [Formula: see text] decay modes) in association with prompt and non-prompt [Formula: see text] are measured relative to the inclusive production rate of [Formula: see text] bosons in the same fiducial volume to be [Formula: see text] and [Formula: see text] respectively. Normalised differential production cross-section ratios are also determined as a function of the [Formula: see text] transverse momentum. The fraction of signal events arising from single and double parton scattering is estimated, and a lower limit of [Formula: see text] at [Formula: see text] confidence level is placed on the effective cross-section regulating double parton interactions.
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| 8. |
- Aad, G, et al.
(author)
-
Search for a new resonance decaying to a W or Z boson and a Higgs boson in the [Formula: see text] final states with the ATLAS detector.
- 2015
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:6
-
Journal article (peer-reviewed)abstract
- A search for a new resonance decaying to a W or Z boson and a Higgs boson in the [Formula: see text] final states is performed using 20.3 fb[Formula: see text] of pp collision data recorded at [Formula: see text] 8 TeV with the ATLAS detector at the Large Hadron Collider. The search is conducted by examining the WH / ZH invariant mass distribution for a localized excess. No significant deviation from the Standard Model background prediction is observed. The results are interpreted in terms of constraints on the Minimal Walking Technicolor model and on a simplified approach based on a phenomenological Lagrangian of Heavy Vector Triplets.
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| 9. |
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| 10. |
- Aad, G, et al.
(author)
-
Search for direct pair production of a chargino and a neutralino decaying to the 125 GeV Higgs boson in [Formula: see text] TeV [Formula: see text] collisions with the ATLAS detector.
- 2015
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:5
-
Journal article (peer-reviewed)abstract
- A search is presented for the direct pair production of a chargino and a neutralino [Formula: see text], where the chargino decays to the lightest neutralino and the [Formula: see text] boson, [Formula: see text], while the neutralino decays to the lightest neutralino and the 125 GeV Higgs boson, [Formula: see text]. The final states considered for the search have large missing transverse momentum, an isolated electron or muon, and one of the following: either two jets identified as originating from bottom quarks, or two photons, or a second electron or muon with the same electric charge. The analysis is based on 20.3 [Formula: see text] of [Formula: see text] proton-proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with the Standard Model expectations, and limits are set in the context of a simplified supersymmetric model.
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| 11. |
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| 12. |
- Aad, G, et al.
(author)
-
Search for heavy long-lived multi-charged particles in pp collisions at [Formula: see text] TeV using the ATLAS detector.
- 2015
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:8
-
Journal article (peer-reviewed)abstract
- A search for heavy long-lived multi-charged particles is performed using the ATLAS detector at the LHC. Data collected in 2012 at [Formula: see text] TeV from pp collisions corresponding to an integrated luminosity of 20.3 fb[Formula: see text]are examined. Particles producing anomalously high ionisation, consistent with long-lived massive particles with electric charges from [Formula: see text] to [Formula: see text] are searched for. No signal candidate events are observed, and 95 % confidence level cross-section upper limits are interpreted as lower mass limits for a Drell-Yan production model. The mass limits range between 660 and 785 GeV.
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| 13. |
- Aad, G, et al.
(author)
-
Search for Higgs boson pair production in the [Formula: see text] final state from pp collisions at [Formula: see text] TeVwith the ATLAS detector.
- 2015
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:9
-
Journal article (peer-reviewed)abstract
- A search for Higgs boson pair production [Formula: see text] is performed with 19.5 fb[Formula: see text] of proton-proton collision data at [Formula: see text] TeV, which were recorded by the ATLAS detector at the Large Hadron Collider in 2012. The decay products of each Higgs boson are reconstructed as a high-momentum [Formula: see text] system with either a pair of small-radius jets or a single large-radius jet, the latter exploiting jet substructure techniques and associated b-tagged track-jets. No evidence for resonant or non-resonant Higgs boson pair production is observed. The data are interpreted in the context of the Randall-Sundrum model with a warped extra dimension as well as the two-Higgs-doublet model. An upper limit on the cross-section for [Formula: see text] of 3.2 (2.3) fb is set for a Kaluza-Klein graviton [Formula: see text] mass of 1.0 (1.5) TeV, at the 95 % confidence level. The search for non-resonant Standard Model hh production sets an observed 95 % confidence level upper limit on the production cross-section [Formula: see text] of 202 fb, compared to a Standard Model prediction of [Formula: see text] fb.
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| 14. |
- Aad, G, et al.
(author)
-
Search for Higgs Boson Pair Production in the γγbb[over ¯] Final State Using pp Collision Data at sqrt[s]=8 TeV from the ATLAS Detector.
- 2015
-
In: Physical Review Letters. - 1079-7114. ; 114:8
-
Journal article (peer-reviewed)abstract
- Searches are performed for resonant and nonresonant Higgs boson pair production in the γγbb[over ¯] final state using 20 fb^{-1} of proton-proton collisions at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the CERN Large Hadron Collider. A 95% confidence level upper limit on the cross section times branching ratio of nonresonant production is set at 2.2 pb, while the expected limit is 1.0 pb. The difference derives from a modest excess of events, corresponding to 2.4 standard deviations from the background-only hypothesis. The limit observed in the search for a narrow X→hh resonance ranges between 0.7 and 3.5 pb as a function of the resonance mass.
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| 15. |
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| 16. |
- Aad, G, et al.
(author)
-
Search for production of [Formula: see text] resonances decaying to a lepton, neutrino and jets in [Formula: see text] collisions at [Formula: see text] TeV with the ATLAS detector.
- 2015
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:5
-
Journal article (peer-reviewed)abstract
- A search is presented for narrow diboson resonances decaying to [Formula: see text] or [Formula: see text] in the final state where one [Formula: see text] boson decays leptonically (to an electron or a muon plus a neutrino) and the other [Formula: see text] boson decays hadronically. The analysis is performed using an integrated luminosity of 20.3 fb[Formula: see text] of [Formula: see text] collisions at [Formula: see text] TeV collected by the ATLAS detector at the large hadron collider. No evidence for resonant diboson production is observed, and resonance masses below 700 and 1490 GeV are excluded at 95 % confidence level for the spin-2 Randall-Sundrum bulk graviton [Formula: see text] with coupling constant of 1.0 and the extended gauge model [Formula: see text] boson respectively.
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| 17. |
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| 18. |
- Aad, G, et al.
(author)
-
Searches for scalar leptoquarks in pp collisions at [Formula: see text] = 8 TeV with the ATLAS detector.
- 2016
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 76
-
Journal article (peer-reviewed)abstract
- Searches for pair-produced scalar leptoquarks are performed using 20 fb[Formula: see text] of proton-proton collision data provided by the LHC and recorded by the ATLAS detector at [Formula: see text] TeV. Events with two electrons (muons) and two or more jets in the final state are used to search for first (second)-generation leptoquarks. The results from two previously published ATLAS analyses are interpreted in terms of third-generation leptoquarks decaying to [Formula: see text] and [Formula: see text] final states. No statistically significant excess above the Standard Model expectation is observed in any channel and scalar leptoquarks are excluded at 95 % CL with masses up to [Formula: see text] 1050 GeV for first-generation leptoquarks, [Formula: see text] 1000 GeV for second-generation leptoquarks, [Formula: see text] 625 GeV for third-generation leptoquarks in the [Formula: see text] channel, and 200 [Formula: see text] 640 GeV in the [Formula: see text] channel.
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| 19. |
- Aad, G., et al.
(author)
-
Studies of the performance of the ATLAS detector using cosmic-ray muons
- 2011
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 71:3
-
Journal article (peer-reviewed)abstract
- Muons from cosmic-ray interactions in the atmosphere provide a high-statistics source of particles that can be used to study the performance and calibration of the ATLAS detector. Cosmic-ray muons can penetrate to the cavern and deposit energy in all detector subsystems. Such events have played an important role in the commissioning of the detector since the start of the installation phase in 2005 and were particularly important for understanding the detector performance in the time prior to the arrival of the first LHC beams. Global cosmic-ray runs were undertaken in both 2008 and 2009 and these data have been used through to the early phases of collision data-taking as a tool for calibration, alignment and detector monitoring. These large datasets have also been used for detector performance studies, including investigations that rely on the combined performance of different subsystems. This paper presents the results of performance studies related to combined tracking, lepton identification and the reconstruction of jets and missing transverse energy. Results are compared to expectations based on a cosmic-ray event generator and a full simulation of the detector response.
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| 20. |
- Aad, G, et al.
(author)
-
Study of the [Formula: see text] and [Formula: see text] decays with the ATLAS detector.
- 2016
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 76
-
Journal article (peer-reviewed)abstract
- 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, a sample of [Formula: see text] decays is used to derive the ratios of branching fractions [Formula: see text] and [Formula: see text], where the third error corresponds to the uncertainty of the branching fraction of [Formula: see text] decay. The available theoretical predictions are generally consistent with the measurement.
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| 21. |
- Aad, G., et al.
(author)
-
The ATLAS Inner Detector commissioning and calibration
- 2010
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 70:3, s. 787-821
-
Journal article (peer-reviewed)abstract
- The ATLAS Inner Detector is a composite tracking system consisting of silicon pixels, silicon strips and straw tubes in a 2 T magnetic field. Its installation was completed in August 2008 and the detector took part in data-taking with single LHC beams and cosmic rays. The initial detector operation, hardware commissioning and in-situ calibrations are described. Tracking performance has been measured with 7.6 million cosmic-ray events, collected using a tracking trigger and reconstructed with modular pattern-recognition and fitting software. The intrinsic hit efficiency and tracking trigger efficiencies are close to 100%. Lorentz angle measurements for both electrons and holes, specific energy-loss calibration and transition radiation turn-on measurements have been performed. Different alignment techniques have been used to reconstruct the detector geometry. After the initial alignment, a transverse impact parameter resolution of 22.1 +/- 0.9 mu m and a relative momentum resolution sigma (p) /p=(4.83 +/- 0.16)x10(-4) GeV(-1)xp (T) have been measured for high momentum tracks.
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| 22. |
- Aad, G., et al.
(author)
-
The ATLAS Simulation Infrastructure
- 2010
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 70:3, s. 823-874
-
Journal article (peer-reviewed)abstract
- The simulation software for the ATLAS Experiment at the Large Hadron Collider is being used for large-scale production of events on the LHC Computing Grid. This simulation requires many components, from the generators that simulate particle collisions, through packages simulating the response of the various detectors and triggers. All of these components come together under the ATLAS simulation infrastructure. In this paper, that infrastructure is discussed, including that supporting the detector description, interfacing the event generation, and combining the GEANT4 simulation of the response of the individual detectors. Also described are the tools allowing the software validation, performance testing, and the validation of the simulated output against known physics processes.
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| 23. |
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| 24. |
- Abat, E., et al.
(author)
-
A layer correlation technique for pion energy calibration at the 2004 ATLAS Combined Beam Test
- 2011
-
In: Journal of Instrumentation. - : Institute of Physics (IOP). - 1748-0221. ; 6
-
Journal article (peer-reviewed)abstract
- A new method for calibrating the hadron response of a segmented calorimeter is developed and successfully applied to beam test data. It is based on a principal component analysis of energy deposits in the calorimeter layers, exploiting longitudinal shower development information to improve the measured energy resolution. Corrections for invisible hadronic energy and energy lost in dead material in front of and between the calorimeters of the ATLAS experiment were calculated with simulated Geant4 Monte Carlo events and used to reconstruct the energy of pions impinging on the calorimeters during the 2004 Barrel Combined Beam Test at the CERN H8 area. For pion beams with energies between 20 GeV and 180 GeV, the particle energy is reconstructed within 3% and the energy resolution is improved by between 11% and 25% compared to the resolution at the electromagnetic scale.
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| 25. |
- Abat, E., et al.
(author)
-
Combined performance studies for electrons at the 2004 ATLAS combined test-beam
- 2010
-
In: Journal of Instrumentation. - : Institute of Physics (IOP). - 1748-0221. ; 5, s. P11006-
-
Journal article (peer-reviewed)abstract
- In 2004 at the ATLAS (A Toroidal LHC ApparatuS) combined test beam, one slice of the ATLAS barrel detector (including an Inner Detector set-up and the Liquid Argon calorimeter) was exposed to particles from the H8 SPS beam line at CERN. It was the first occasion to test the combined electron performance of ATLAS. This paper presents results obtained for the momentum measurement p with the Inner Detector and for the performance of the electron measurement with the LAr calorimeter (energy E linearity and resolution) in the presence of a magnetic field in the Inner Detector for momenta ranging from 20 GeV/c to 100 GeV/c. Furthermore the particle identification capabilities of the Transition Radiation Tracker, Bremsstrahlungs-recovery algorithms relying on the LAr calorimeter and results obtained for the E/p ratio and a way how to extract scale parameters will be discussed.
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| 26. |
- Abat, E., et al.
(author)
-
Photon reconstruction in the ATLAS Inner Detector and Liquid Argon Barrel Calorimeter at the 2004 Combined Test Beam
- 2011
-
In: Journal of Instrumentation. - 1748-0221. ; 6
-
Journal article (peer-reviewed)abstract
- The reconstruction of photons in the ATLAS detector is studied with data taken during the 2004 Combined Test Beam, where a full slice of the ATLAS detector was exposed to beams of particles of known energy at the CERN SPS. The results presented show significant differences in the longitudinal development of the electromagnetic shower between converted and unconverted photons as well as in the total measured energy. The potential to use the reconstructed converted photons as a means to precisely map the material of the tracker in front of the electromagnetic calorimeter is also considered. All results obtained are compared with a detailed Monte-Carlo simulation of the test-beam setup which is based on the same simulation and reconstruction tools as those used for the ATLAS detector itself.
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| 27. |
- Abata, E., et al.
(author)
-
Study of energy response and resolution of the ATLAS barrel calorimeter to hadrons of energies from 20 to 350 GeV
- 2010
-
In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576 .- 0167-5087. ; 621:1-3, s. 134-150
-
Journal article (peer-reviewed)abstract
- A fully instrumented slice of the ATLAS detector was exposed to test beams from the SPS (Super Proton Synchrotron) at CERN in 2004. In this paper, the results of the measurements of the response of the barrel calorimeter to hadrons with energies in the range 20-350 GeV and beam impact points and angles corresponding to pseudo-rapidity values in the range 0.2-0.65 are reported. The results are compared to the predictions of a simulation program using the Geant 4 toolkit. (C) 2010 Published by Elsevier B.V.
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| 28. |
- Banerjee, Ambar, 1985-, et al.
(author)
-
Accessing metal-specific orbital interactions in C–H activation with resonant inelastic X-ray scattering
- 2024
-
In: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 15:7, s. 2398-2409
-
Journal article (peer-reviewed)abstract
- Photochemically prepared transition-metal complexes are known to be effective at cleaving the strong C–H bonds of organic molecules in room temperature solutions. There is also ample theoretical evidence that the two-way, metal to ligand (MLCT) and ligand to metal (LMCT), charge-transfer between an incoming alkane C–H group and the transition metal is the decisive interaction in the C–H activation reaction. What is missing, however, are experimental methods to directly probe these interactions in order to reveal what determines reactivity of intermediates and the rate of the reaction. Here, using quantum chemical simulations we predict and propose future time-resolved valence-to-core resonant inelastic X-ray scattering (VtC-RIXS) experiments at the transition metal L-edge as a method to provide a full account of the evolution of metal–alkane interactions during transition-metal mediated C–H activation reactions. For the model system cyclopentadienyl rhodium dicarbonyl (CpRh(CO)2), we demonstrate, by simulating the VtC-RIXS signatures of key intermediates in the C–H activation pathway, how the Rh-centered valence-excited states accessible through VtC-RIXS directly reflect changes in donation and back-donation between the alkane C–H group and the transition metal as the reaction proceeds via those intermediates. We benchmark and validate our quantum chemical simulations against experimental steady-state measurements of CpRh(CO)2 and Rh(acac)(CO)2 (where acac is acetylacetonate). Our study constitutes the first step towards establishing VtC-RIXS as a new experimental observable for probing reactivity of C–H activation reactions. More generally, the study further motivates the use of time-resolved VtC-RIXS to follow the valence electronic structure evolution along photochemical, photoinitiated and photocatalytic reactions with transition metal complexes.
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| 29. |
- Born, Artur, et al.
(author)
-
Quantification of Ni L-2,L-3 core-hole relaxation pathways utilizing Auger photoelectron coincidence spectroscopy
- 2021
-
In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:11
-
Journal article (peer-reviewed)abstract
- Ni LVV Auger spectra, in coincidence with the corresponding 2p(1/2), 2p(3/2), and 6 eV satellite photoelectrons, have been used to examine electron correlation and itinerance effects in Ni. In coincidence with the 2p(3/2) core level, the Auger spectral shape is represented by localized 3d(8) and itinerant valence final states with an additional 3d(7) Auger shake-up contribution. The spectra in coincidence with the 6 eV satellite probe the decay of localized 2p(5)3d(9) double hole states, leading to 3d(7) final states. It is found that a fraction of the double hole states delocalize before the Auger decay. A similar delocalization is observed for the double hole states produced by the L2L3M45 Coster-Kronig process, and the delocalization rates have been determined.
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| 30. |
- Born, Artur, et al.
(author)
-
Separation of surface oxide from bulk Ni by selective Ni 3p photoelectron spectroscopy for chemical analysis in coincidence with Ni M-edge Auger electrons
- 2021
-
In: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11:1
-
Journal article (peer-reviewed)abstract
- The chemical shift of core level binding energies makes electron spectroscopy for chemical analysis (ESCA) a workhorse analytical tool for science and industry. For some elements, close lying and overlapping spectral features within the natural life time broadening restrict applications. We establish how the core level binding energy chemical shift can be picked up experimentally by the additional selectivity through Auger electron photoelectron coincidence spectroscopy (APECS). Coincident measurement of Ni 3p photoemission with different MVV Auger regions from specific decay channels, narrows the 3p core-levels to a width of 1.2 eV, resolves the spin-orbit splitting of 1.6 eV and determines the chemical shift of Ni 3p levels of a Ni(111) single crystal and its oxidized surface layer to 0.6 eV.
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| 31. |
- Cappel, Ute B, et al.
(author)
-
Electronic structure dynamics in a low bandgap polymer studied by time-resolved photoelectron spectroscopy.
- 2016
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 18:31, s. 21921-9
-
Journal article (peer-reviewed)abstract
- Means to measure the temporal evolution following a photo-excitation in conjugated polymers are a key for the understanding and optimization of their function in applications such as organic solar cells. In this paper we study the electronic structure dynamics by direct pump-probe measurements of the excited electrons in such materials. Specifically, we carried out a time-resolved photoelectron spectroscopy (TRPES) study of the polymer PCPDTBT by combining an extreme ultraviolet (XUV) high harmonic generation source with a time-of-flight spectrometer. After excitation to either the 1st excited state or to a higher excited state, we follow how the electronic structure develops and relaxes on the electron binding energy scale. Specifically, we follow a less than 50 fs relaxation of the higher exited state and a 10 times slower relaxation of the 1st excited state. We corroborate the results using DFT calculations. Our study demonstrates the power of TRPES for studying photo-excited electron energetics and dynamics of solar cell materials.
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| 32. |
- Cappel, Ute B, et al.
(author)
-
Partially Reversible Photoinduced Chemical Changes in a Mixed-Ion Perovskite Material for Solar Cells.
- 2017
-
In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9:40, s. 34970-34978
-
Journal article (peer-reviewed)abstract
- ) with the element specificity and chemical sensitivity of core-level photoelectron spectroscopy. By carrying out measurements at a synchrotron beamline optimized for low X-ray fluxes, we are able to avoid sample changes due to X-ray illumination and are therefore able to monitor what sample changes are induced by visible illumination only. We find that laser illumination causes partially reversible chemistry in the surface region, including enrichment of bromide at the surface, which could be related to a phase separation into bromide- and iodide-rich phases. We also observe a partially reversible formation of metallic lead in the perovskite structure. These processes occur on the time scale of minutes during illumination. The presented methodology has a large potential for understanding light-induced chemistry in photoactive materials and could specifically be extended to systematically study the impact of morphology and composition on the photostability of metal halide perovskites.
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| 33. |
- Giangrisostomi, Erika, et al.
(author)
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Low Dose Photoelectron Spectroscopy at BESSY II : Electronic structure of matter in its native state
- 2018
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier. - 0368-2048 .- 1873-2526. ; 224:SI, s. 68-78
-
Journal article (peer-reviewed)abstract
- The implementation of a high-transmission, angular-resolved time-of-Right electron spectrometer with a 1.25 MHz pulse selector at the PM4 soft X-ray dipole beamline of the synchrotron BESSY II creates unique capabilities to inquire electronic structure via photoelectron spectroscopy with a minimum of radiation dose. Solid-state samples can be prepared and characterized with standard UHV techniques and rapidly transferred from various preparation chambers to a 4-axis temperature-controlled measurement stage. A synchronized MHz laser system enables excited-state characterization and dynamical studies starting from the picosecond timescale. This article introduces the principal characteristics of the PM4 beamline and LowDosePES end-station. Recent results from graphene, an organic hole transport material for solar cells and the transition metal dichalcogenide MoS2 are presented to demonstrate the instrument performances. (C) 2017 The Authors. Published by Elsevier B.V.
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| 34. |
- Holldack, K., et al.
(author)
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Single bunch X-ray pulses on demand from a multi-bunch synchrotron radiation source
- 2014
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5
-
Journal article (peer-reviewed)abstract
- Synchrotron radiation facilities routinely operate in a multi-bunch regime, but applications relying on time-of-flight schemes require single bunch operation. Here we show that pulse picking by resonant excitation in a storage ring creates in addition to the multi-bunch operation a distinct and separable single bunch soft X-ray source. It has variable polarization, a photon flux of up to 10(7)-10(9) ph s(-1)/0.1%BW at purity values of 10(4)-10(2) and a repetition rate of 1.25 MHz. The quasi-resonant excitation of incoherent betatron oscillations of electrons allows horizontal pulse separation at variable (also circular) polarization accessible for both, regular 30 ps pulses and ultrashort pulses of 2-3 ps duration. Combined with a new generation of angularly resolving electron spectrometers this creates unique opportunities for time-resolved photoemission studies as confirmed by time-of-flight spectra. Our pulse picking scheme is particularly suited for surface physics at diffraction-limited light sources promising ultimate spectral resolution.
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| 35. |
- Ibek, Mateusz, et al.
(author)
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Monochromatizing and focussing femtosecond high-order harmonic radiation with one optical element
- 2013
-
In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 84:10, s. 103102-
-
Journal article (peer-reviewed)abstract
- A novel approach for monochromatizing and focussing the Vacuum-Ultraviolet and soft x-ray radiation from high-order harmonic generation of a femtosecond optical laser with only one optical element is presented. We demonstrate that off-axis reflection zone plates applied as focussing monochromators allow for efficiently optimizing the trade-off between energy resolution and temporal dispersion of the femtosecond pulses. In the current experimental realization, we show how the temporal dispersion can be varied between 2 fs and 16 fs with a correlating variation of the energy resolution E/Delta E between 20 and 90 for an off-axis reflection zone plate optimized for harmonic 13 at 20.41 eV. We also show how the focal spot size varies correspondingly between 80 x 90 mu m(2) and 290 x 140 mu m(2) as determined with a computational fitting approach based on a 3D Gaussian model. The diffraction efficiency for the tested zone plates amounts to up to 10%. We furthermore evaluate the influence of pointing stability on the performance of the zone plates. Based on our results we propose an optimized realization of a dedicated beam line for femtosecond pulses from high-order harmonic generation with an off-axis reflection zone plate.
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| 36. |
- Jay, Raphael, et al.
(author)
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Tracking C–H activation with orbital resolution
- 2023
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 380:6648, s. 955-960
-
Journal article (peer-reviewed)abstract
- Transition metal reactivity toward carbon-hydrogen (C-H) bonds hinges on the interplay of electron donation and withdrawal at the metal center. Manipulating this reactivity in a controlled way is difficult because the hypothesized metal-alkane charge-transfer interactions are challenging to access experimentally. Using time-resolved x-ray spectroscopy, we track the charge-transfer interactions during C-H activation of octane by a cyclopentadienyl rhodium carbonyl complex. Changes in oxidation state as well as valence-orbital energies and character emerge in the data on a femtosecond to nanosecond timescale. The x-ray spectroscopic signatures reflect how alkane-to-metal donation determines metal-alkane complex stability and how metal-to-alkane back-donation facilitates C-H bond cleavage by oxidative addition. The ability to dissect charge-transfer interactions on an orbital level provides opportunities for manipulating C-H reactivity at transition metals.
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| 37. |
- Johansson, Fredrik, et al.
(author)
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Auger- and Photoelectron Coincidences of Molecular O2 Adsorbed on Ag(111)
- 2022
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier. - 0368-2048 .- 1873-2526. ; 256
-
Journal article (peer-reviewed)abstract
- The oxygen on Ag(111) system has been investigated with Auger electron–photoelectron coincidence spectroscopy (APECS). The coincidence spectra between O 1s core level photoelectrons and O KLL Auger electrons have been studied together with Ag3d/AgM4,5NN coincidences. We also describe the electron–electron coincidence spectrometer setup, CoESCA, consisting of two angle resolved time-of-flight spectrometers at a synchrotron light source. Contributions from molecular oxygen and chemisorbed oxygen are assigned using the coincidence data, conclusions are drawn primarily from the O 1s/O KLL data. The data acquisition and treatment procedure are also outlined. The chemisorbed oxygen species observed are relevant for the catalytic ethylene oxidation.
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| 38. |
- Leitner, Torsten, 1979-, et al.
(author)
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Coherent wave packet dynamics in photo-excited Nal
- 2013
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In: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. - 9782759809561 ; 41, s. 02027-
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Journal article (other academic/artistic)abstract
- Time and energy resolved photoelectron distributions of photo-excited Nal are presented. A splitting in the photo-excited state suggested by calculations of the intramolecular potential energy surfaces could be confirmed experimentally for the first time.
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| 39. |
- Leitner, Torsten, et al.
(author)
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Probing photoelectron angular distributions in molecules with polarization-controlled two-color above-threshold ionization
- 2015
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 91:6
-
Journal article (peer-reviewed)abstract
- We present polarization-controlled multiphoton two-color above-threshold ionization (TCATI) of molecules. The intensity modulations of valence photoelectron intensities of molecules arising from varying the relative orientation of the linear polarization vectors of femtosecond infrared (IR) and vacuum-ultraviolet (VUV) radiation in TCATI of the highest occupied molecular orbitals of H2O, O-2, and N-2 are reported. The results on the molecular systems are compared to the 3p photoionization of atomic Ar, which serves as a reference system. Modeling the large differences of the modulation amplitudes within the soft-photon approximation enables us to extract the one-photon-ionization anisotropy parameter beta(2). Accounting only for the first sideband due to two-photon TCATI by one VUV and one IR photon we find satisfactory agreement between experiment and simulation for H2O and O2. However, the model fails for N2 and possible reasons are discussed. We discuss that the described approach may represent an alternative way of determining photoelectron angular distributions from valence shells of molecules and indicate future directions for modeling TCATI of molecules.
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| 40. |
- Leitner, Torsten, 1979-, et al.
(author)
-
The CoESCA station at BESSY: Auger electron–photoelectron coincidences from surfaces demonstrated for Ag MNN
- 2021
-
In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 250
-
Journal article (peer-reviewed)abstract
- In this work, we present the CoESCA station for electron–electron coincidence spectroscopy from surfaces, built in a close collaboration between Uppsala University and Helmholtz-Zentrum Berlin at the BESSY II synchrotron facility in Berlin, Germany. We start with a detailed overview of previous work in the field of electron–electron coincidences, before we describe the CoESCA setup and its design parameters. The system is capable of recording shot-to-shot resolved 6D coincidence datasets, i.e. the kinetic energy and the two take off angles for both coincident electrons. The mathematics behind extracting and analysing these multi-dimensional coincidence datasets is introduced, with a focus on coincidence statistics, resulting in fundamental limits of the signal-to-noise ratio and its implications for acquisition times and the size of the raw data stream. The functionality of the CoESCA station is demonstrated for the example of Auger electron–photoelectron coincidences from silver surfaces for photoelectrons from the Ag 3d core levels and their corresponding MNN Auger electrons. The Auger spectra originating from the different core levels, 3d and 3d could be separated and further, the two-hole state energy distributions were determined for these Auger decay channels.
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| 41. |
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| 42. |
- Stegmayr, Bernd, 1949-, et al.
(author)
-
Using the World Apheresis Association Registry Helps to Improve the Treatment Quality of Therapeutic Apheresis
- 2021
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In: Transfusion Medicine and Hemotherapy. - : S. Karger. - 1660-3796 .- 1660-3818. ; 48:4, s. 234-239
-
Research review (peer-reviewed)abstract
- Therapeutic apheresis (TA) is prescribed to patients that suffer from a severe progressive disease that is not sufficiently treated by conventional medications. A way to gain more knowledge about this treatment is usually by the local analysis of data. However, the use of large quality assessment registries enables analyses of even rare findings. Here, we report some of the recent data from the World Apheresis Association (WAA) registry. Data from >104,000 procedures were documented, and TA was performed on >15,000 patients. The main indication for TA was the collection of autologous stem cells (45% of patients) as part of therapy for therapy. Collection of stem cells from donors for allogeneic transplantation was performed in 11% of patients. Patients with indications such as neurological diseases underwent plasma exchange (28%). Extracorporeal photochemotherapy, lipid apheresis, and antibody removal were other indications. Side effects recorded in the registry have decreased significantly over the years, with approximately only 10/10,000 procedures being interrupted for medical reasons. Conclusion: Collection of data from TA procedures within a multinational and multicenter concept facilitates the improvement of treatment by enabling the analysis of and feedback on indications, procedures, effects, and side effects. (c) 2021 S. Karger AG, Basel
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| 43. |
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| 44. |
- Svanström, Sebastian, et al.
(author)
-
The Complex Degradation Mechanism of Copper Electrodes on Lead Halide Perovskites
- 2022
-
In: ACS Materials Science Au. - : American Chemical Society (ACS). - 2694-2461. ; 2:3, s. 301-312
-
Journal article (peer-reviewed)abstract
- Lead halide perovskitesolar cells have reached power conversionefficiencies during the past few years that rival those of crystallinesilicon solar cells, and there is a concentrated effort to commercializethem. The use of gold electrodes, the current standard, is prohibitivelycostly for commercial application. Copper is a promising low-costelectrode material that has shown good stability in perovskite solarcells with selective contacts. Furthermore, it has the potential tobe self-passivating through the formation of CuI, a copper salt whichis also used as a hole selective material. Based on these opportunities,we investigated the interface reactions between lead halide perovskitesand copper in this work. Specifically, copper was deposited on theperovskite surface, and the reactions were followed in detail usingsynchrotron-based and in-house photoelectron spectroscopy. The resultsshow a rich interfacial chemistry with reactions starting upon depositionand, with the exposure to oxygen and moisture, progress over manyweeks, resulting in significant degradation of both the copper andthe perovskite. The degradation results not only in the formationof CuI, as expected, but also in the formation of two previously unreporteddegradation products. The hope is that a deeper understanding of theseprocesses will aid in the design of corrosion-resistant copper-basedelectrodes.
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| 45. |
- Wernet, Ph., et al.
(author)
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Communication : Direct evidence for sequential dissociation of gas-phase Fe(CO)(5) via a singlet pathway upon excitation at 266 nm
- 2017
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 146:21
-
Journal article (peer-reviewed)abstract
- We prove the hitherto hypothesized sequential dissociation of Fe(CO)(5) in the gas phase upon photoexcitation at 266 nm via a singlet pathway with time-resolved valence and core-level photoelectron spectroscopy with an x-ray free-electron laser. Valence photoelectron spectra are used to identify free CO molecules and to determine the time constants of stepwise dissociation to Fe(CO)(4) within the temporal resolution of the experiment and further to Fe(CO)(3) within 3 ps. Fe 3p core-level photoelectron spectra directly reflect the singlet spin state of the Fe center in Fe(CO)(5), Fe(CO)(4), and Fe(CO)(3) showing that the dissociation exclusively occurs along a singlet pathway without triplet-state contribution. Our results are important for assessing intra- and intermolecular relaxation processes in the photodissociation dynamics of the prototypical Fe(CO)(5) complex in the gas phase and in solution, and they establish time-resolved core-level photoelectron spectroscopy as a powerful tool for determining the multiplicity of transition metals in photochemical reactions of coordination complexes.
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| 46. |
- Wernet, Philippe, et al.
(author)
-
Mapping chemical bonding of reaction intermediates with femtosecond X-ray laser spectroscopy
- 2013
-
In: XVIIIth International Conference on Ultrafast Phenomena. - : EDP Sciences. - 9782759809561 ; , s. 05025-
-
Conference paper (other academic/artistic)abstract
- We determine the pathways in the photo-dissociation reactions of Fe(CO)5 both in the gas phase and in solution by mapping the valence electronic structure of the reaction intermediates with femtosecond X-ray laser spectroscopy.
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