| 1. |
- Aad, G., et al.
(författare)
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Determination of the strong coupling constant from transverse energy-energy correlations in multijet events at √ s=13 TeV with the ATLAS detector
- 2023
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of transverse energy-energy correlations and their associated azimuthal asymmetries in multijet events are presented. The analysis is performed using a data sample corresponding to 139 fb-1 of proton-proton collisions at a centre-of-mass energy of root s = 13TeV, collected with the ATLAS detector at the Large Hadron Collider. The measurements are presented in bins of the scalar sum of the transverse momenta of the two leading jets and unfolded to particle level. They are then compared to next-to-next-to-leading-order perturbative QCD calculations for the first time, which feature a significant reduction in the theoretical uncertainties estimated using variations of the renormalisation and factorisation scales. The agreement between data and theory is good, thus providing a precision test of QCD at large momentum transfers Q. The strong coupling constant alpha(s) is extracted as a function of Q, showing a good agreement with the renormalisation group equation and with previous analyses. A simultaneous fit to all transverse energy-energy correlation distributions across different kinematic regions yields a value of alpha(s)( mZ) = 0.1175 +/- 0.0006 (exp.)(+0.0034) (-0.0017) (theo.), while the global fit to the asymmetry distributions yields alpha(s)(m(Z)) = 0.1185 +/- 0.0009 (exp.)(+0.0025)(-0.0012)(theo.).
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| 2. |
- Chartkunchand, Kiattichart C., et al.
(författare)
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Radiative lifetimes of the bound excited states of Pt-
- 2016
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Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 94:3
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 American Physical Society.The intrinsic radiative lifetimes of the 5d106sS1/22 and 5d96s2 D3/22 bound excited states in the platinum anion Pt- have been studied at cryogenic temperatures at the Double ElectroStatic Ion Ring Experiment (DESIREE) facility at Stockholm University. The intrinsic lifetime of the higher-lying 5d106s S1/22 state was measured to be 2.54±0.10s, while only a lifetime in the range of 50-200 ms could be estimated for the 5d96s2 D3/22 fine-structure level. The storage lifetime of the Pt- ion beam was measured to be a little over 15 min at a ring temperature of 13K. The present study reports the lifetime of an atomic negative ion in an excited bound state with an electron configuration different from that of the ground state.
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| 3. |
- Eklund, Gustav, 1990-, et al.
(författare)
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Experimental lifetime of the a1Δ electronically excited state of CH−
- 2022
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Ingår i: Physical Review Research. - : American Physical Society (APS). - 2643-1564. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- By repeatedly probing the a1Δ excited state and the X3Σ− ground-state populations in a beam of CH− ions stored in a cryogenic ion-beam storage ring for 100 s, we extract an intrinsic lifetime of 14.9±0.5 s for this excited state. This is far longer than all earlier experimental and theoretical results, exposing large difficulties in measuring and calculating slow decays and the need for benchmark quality experiments.
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| 4. |
- Kristiansson, Moa K., 1989-, et al.
(författare)
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High-precision electron affinity of oxygen
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Negative ions are important in many areas of science and technology, e.g., in interstellar chemistry, for accelerator-based radionuclide dating, and in anti-matter research. They are unique quantum systems where electron-correlation effects govern their properties. Atomic anions are loosely bound systems, which with very few exceptions lack optically allowed transitions. This limits prospects for high-resolution spectroscopy, and related negative-ion detection methods. Here, we present a method to measure negative ion binding energies with an order of magnitude higher precision than what has been possible before. By laser-manipulation of quantum-state populations, we are able to strongly reduce the background from photodetachment of excited states using a cryogenic electrostatic ion-beam storage ring where keV ion beams can circulate for up to hours. The method is applicable to negative ions in general and here we report an electron affinity of 1.461 112 972(87) eV for O-16. High-precision measurements are useful to find isotopic shifts and electron correlation. Here the authors measure electron affinity and hyperfine splitting of atomic oxygen with higher precision than previous studies.
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| 5. |
- Kristiansson, Moa, 1989-
(författare)
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Negative ion experiments at DESIREE : Photodetatchment studies of transitions and lifetimes of excited states of Ir-
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis I present measurements using laser photodetachment to investigate negative ions of iridium produced in a cesium sputter ion source and stored in the cryogenic storage ring, DESIREE. The ions are photodetached by either a tunable OPO laser system or a tunable narrow bandwidth Titanium Sapphire laser. The vacuum conditions of DESIREE allowed us to store the ions for several thousand seconds and investigate the lifetimes of longlived excited states. Iridium has an electron affinity of 1.56436(15) eV and the ground state electron configuration is [Xe]4f14 5d8 6s2 3F4 , where the term scheme is determined by the partly filled 5d shell. Predicted bound excited states are metastable as they are of the same configuration and therefore the same parity as the ground state. The 3F3 level can decay to the ground state by a magnetic- dipole transition while the 3P2 level can only decay by an electric-quadrupole transition. The higher lying fine structure components, 3F2 and 3P1 , have been assumed to be unbound. We performed systematic studies of the photodetachment signal as function of photon energy and time after ion injection (milliseconds to 2000 seconds). We locate the threshold for detachment from the 3P2 level and find that this level is bound by 1.00 ± 0.03 eV. The lifetime of this state could only be estimated with a lower bound since it does not decay within the timeframe of the experiment. A lower limit of the lifetime is 1000 s. The previously observed 3F3 state was not observed in this experiment most likely due to a short lifetime of < 100 ms. A third excited state was observed with a lifetime of 146 ± 20 ms. This is most likely the lifetime of one of the two states 3F2 or 3P1 , that was previously predicted to be unbound.
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| 6. |
- Kristiansson, Moa, 1989-
(författare)
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Precision measurements on negative ions
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, experiments with negative ions performed at the DESIREE facility are presented. DESIREE consists of two electrostatic storage rings operated at 13 K. The low temperature in combination with a low pressure allows for storage times of the negative ion beams to be up to several hours. This unique feature is to advantage in the development of a new method for high-precision measurements of electron affinities and binding energies of excited states of negative ions. In this method, ions are stored in the one of the two storage rings of DESIREE, and a high-power laser is applied to photodetach ions in the excited state. These excited states are often very long-lived for negative ions and the photodetachment signal from these states are a major source of background, which dominates the uncertainties, in threshold spectroscopy experiments. By removing the ions in the excited state, threshold photodetachment spectroscopy can be performed with almost no background below the photodetachment threshold. This allows the threshold energy to be determined with a very high precision.The new method is demonstrated by performing measurements of the electron affinities of 16O and 18O. The obtained uncertainty in the electron affinity of 16O is a tenfold improvement in accuracy compared to previous measurements and the resulting electron affinity is the most accurately measured electron affinity of any element to date. In addition to the electron affinity, the fine-structure splitting of the ground state is also measured for both isotopes. From the measured electron affinities, the isotope shift in the 18O and 16O electron affinity is determined with a high accuracy. This shift is a quantity not only relevant in atomic physics but also of great interest in nuclear physics.In addition to the high-precision electron affinity measurements, the possibility to store ions for a long time is utilized to perform measurements of lifetimes of excited states in negative ions. Measurements are presented where excited states in Ir-, Bi-, and CH- are studied. Lifetimes ranging from 100 ms up to 5000 s are observed.
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| 7. |
- Najeeb, P. K., 1986-, et al.
(författare)
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Stability and Cooling of the C72- Dianion
- 2023
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 131:11
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the stability of the smallest long-lived all carbon molecular dianion (C72-) in new time domains and with a single ion at a time using a cryogenic electrostatic ion-beam storage ring. We observe spontaneous electron emission from internally excited dianions on millisecond timescales and monitor the survival of single colder C72- molecules on much longer timescales. We find that their intrinsic lifetime exceeds several minutes - 6 orders of magnitude longer than established from earlier experiments on C72-. This is consistent with our calculations of vertical electron detachment energies predicting one inherently stable isomer and one isomer which is stable or effectively stable behind a large Coulomb barrier for C72-→C7-+e- separation.
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| 8. |
- Najeeb, P. K., 1986-, et al.
(författare)
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Stability and Cooling of the C2−7 Dianion
- 2023
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 131:11
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the stability of the smallest long-lived all carbon molecular dianion () in new time domains and with a single ion at a time using a cryogenic electrostatic ion-beam storage ring. We observe spontaneous electron emission from internally excited dianions on millisecond timescales and monitor the survival of single colder molecules on much longer timescales. We find that their intrinsic lifetime exceeds several minutes—6 orders of magnitude longer than established from earlier experiments on . This is consistent with our calculations of vertical electron detachment energies predicting one inherently stable isomer and one isomer which is stable or effectively stable behind a large Coulomb barrier for →+e− separation.
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| 9. |
- Navarro-Navarrete, José E., 1988-, et al.
(författare)
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High-resolution measurement of the electron affinity of cesium
- 2024
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Ingår i: PHYSICAL REVIEW A. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 109:2
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Tidskriftsartikel (refereegranskat)abstract
- Negative ions are unique quantum systems where electron correlation plays a decisive role in determining their properties. The lack of optically allowed transitions prevents traditional optical spectroscopy and the electron affinity is, therefore, for most elements, the only atomic quantity that can be determined with high accuracy. In this work, we present a high-precision experimental determination of the electron affinity of cesium. A collinear laser-ion beam apparatus was used to investigate the partial photodetachment cross section for the cesium anion, leaving the neutral atom in the 6p 2P3/2 excited state. A resonance ionization scheme was used to obtain final-state selectivity, which enabled the investigation of a sharp onset of the cross section associated with a Wigner s-wave threshold behavior. The electron affinity was determined to be 0.471 598 3(38) eV.
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