| 1. |
- Aad, G, et al.
(författare)
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Determination of spin and parity of the Higgs boson in the [Formula: see text] decay channel with the ATLAS detector.
- 2015
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:5
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Tidskriftsartikel (refereegranskat)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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| 2. |
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| 3. |
- Aad, G, et al.
(författare)
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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
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 76
-
Tidskriftsartikel (refereegranskat)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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| 4. |
- Aad, G, et al.
(författare)
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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
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 76
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Aad, G, et al.
(författare)
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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
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:6
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Aad, G, et al.
(författare)
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Search for heavy long-lived multi-charged particles in pp collisions at [Formula: see text] TeV using the ATLAS detector.
- 2015
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:8
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Aad, G, et al.
(författare)
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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
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:9
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Aad, G, et al.
(författare)
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Searches for scalar leptoquarks in pp collisions at [Formula: see text] = 8 TeV with the ATLAS detector.
- 2016
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 76
-
Tidskriftsartikel (refereegranskat)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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| 9. |
- Aad, G, et al.
(författare)
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Study of the [Formula: see text] and [Formula: see text] decays with the ATLAS detector.
- 2016
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 76
-
Tidskriftsartikel (refereegranskat)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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| 10. |
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| 11. |
- Aad, G, et al.
(författare)
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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
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:5
-
Tidskriftsartikel (refereegranskat)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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| 12. |
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| 13. |
- Aad, G, et al.
(författare)
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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
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:5
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Tidskriftsartikel (refereegranskat)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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| 14. |
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| 15. |
- Aad, G, et al.
(författare)
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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
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Ingår i: Physical Review Letters. - 1079-7114. ; 114:8
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Tidskriftsartikel (refereegranskat)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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| 16. |
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| 17. |
- Aad, G, et al.
(författare)
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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
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:5
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Tidskriftsartikel (refereegranskat)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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| 18. |
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| 19. |
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| 20. |
- Pillai, Rajath S, et al.
(författare)
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Assessment of Somatosensory and Psychosocial Function of Patients With Trigeminal Nerve Damage
- 2020
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Ingår i: Clinical Journal of Pain. - : Lippincott Williams & Wilkins. - 1536-5409 .- 0749-8047. ; 36:5, s. 321-335
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: The present study assessed somatosensory changes related to trigeminal nerve damage using extensive evaluation tools and assessed the effect of such damage on the patients' psychosocial status and quality of life compared with healthy participants.METHODS: In 37 patients with intraorally or extraorally presenting trigeminal nerve damage diagnosed as painful or nonpainful posttraumatic trigeminal neuropathy, psychophysical tests like quantitative sensory testing (QST) and qualitative sensory testing and the electrophysiological "nociceptive-specific" blink reflex were performed. The patients and 20 healthy participants completed a set of questionnaires assessing their psychosocial status and quality of life.RESULTS: A loss or gain of somatosensory function was seen in at least 1 QST parameter in >88.9% of the patients. Patients in whom extraoral QST was performed showed an overall loss of somatosensory function, whereas intraoral QST showed a general gain of somatosensory function. Qualitative sensory testing identified a side-to-side difference in the tactile and pinprick stimulation in >77% of the patients. An abnormal "nociceptive-specific" blink reflex response was seen in 42.1% to 71.4% of patients dependent on the trigeminal branch stimulated, though comparisons with healthy reference values showed ambiguous results. Compared with the healthy participants, patients showed higher scores for pain catastrophizing, symptoms of depression and anxiety, limited jaw function, more somatic symptoms, and significantly impaired oral health-related quality of life (all P<0.038).DISCUSSION: The results from the present study showed presence of varied somatosensory abnormalities when assessed using psychophysical and electrophysiological investigations and a significantly impaired psychosocial status.
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| 21. |
- Taneja, Pankaj, et al.
(författare)
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Assessment of experimental orofacial pain, pleasantness and unpleasantness via standardized psychophysical testing
- 2019
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Ingår i: European Journal of Pain. - : WILEY. - 1090-3801 .- 1532-2149. ; 23:7, s. 1297-1308
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Tidskriftsartikel (refereegranskat)abstract
- Background Somatosensory assessment within the orofacial region may be performed using highly standardized quantitative sensory testing (QST). However, the function of the C-tactile (CT) afferent, a nerve fibre linked to the perception of pleasant touch, is usually not evaluated. Furthermore, the perception of unpleasantness is also rarely assessed, a dimension not only limited to a painful experience. Therefore, the primary aim was to apply standardized QST stimuli as well as standardized pleasant stimuli and evaluate their potential capacity for evocation of perceived pain, pleasant and unpleasant sensations in the facial region. Methods Twenty-one female participants underwent QST as per the protocol derived from the German Research Network on Neuropathic Pain. For the first time, two modified protocols were used to investigate stimuli for perceived pleasantness and unpleasantness. Results Thermal stimuli provided separate thresholds for each sensation. From certain mechanical stimuli (e.g., vibration), overlap between the perceived sensations of pleasantness and unpleasantness was identified. It was not possible to evoke only an unpleasant sensation without a painful contribution, and both these sensations increased significantly when utilizing an increasing pinprick force (p amp;lt; 0.011). Between dynamic stimuli, the brush was rated as significantly more pleasant than the cotton wool tip (p = 0.015). A quadratic model provided the best fit for velocity against mean pleasantness ratings (R-2 = 0.62 +/- 0.08), supporting previous CT afferent literature to some extent. Conclusion Stimuli were generally not isolated to one sensation, highlighting the multidimensional construct of stimulus perception and the need for scales to capture this. Significance The battery of QST tests from the DFNS protocol has been modified to investigate pleasant and unpleasant sensations. This allows the evaluation of psychophysical properties across standardized dimensions to provide a thorough view of somatosensory function and to better understand the affective spectrum of somatosensory function.
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| 22. |
- Vase, Lene, et al.
(författare)
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How May Placebo Mechanisms Influence Orofacial Neuropathic Pain?
- 2019
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Ingår i: Journal of Dental Research. - : Sage Publications. - 0022-0345 .- 1544-0591. ; 98:8, s. 861-869
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Forskningsöversikt (refereegranskat)abstract
- The conceptualization of placebo has changed from inactive pills to a detailed understanding of how patients' perception of receiving a treatment influences pain processing and overall treatment outcome. Large placebo effects were recently demonstrated in chronic neuropathic pain, thereby opening the question of whether placebo effects also apply to orofacial neuropathic pain. In this article, we review the new definitions, magnitude, and social, psychological, neurobiologic, and genetic mechanisms of placebo effects in pain, especially neuropathic pain, to illustrate that placebo effects are not simply response bias but psychoneurobiological phenomena that can be measured at many levels of the neuroaxis. We use this knowledge to carefully illustrate how patients' perceptions of the treatment, the relationship with the health care provider, and the expectations and emotions toward a treatment can influence test and treatment outcome and potentially skew the results if they are not taken into consideration. Orofacial neuropathic pain is a new research area, and we review the status on definition, diagnosis, mechanisms, and pharmacologic treatment of neuropathic pain after trigeminal nerve injury, as this condition may be especially influenced by placebo factors. Finally, we have a detailed discussion of how knowledge of placebo mechanisms may help improve the understanding, diagnosis, and treatment of orofacial neuropathic pain, and we illustrate pitfalls and opportunities of applying this knowledge to the test of dental treatments.
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| 23. |
- Watanabe, Takeshi, et al.
(författare)
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Nocebo response in dentistry : A systematic review and meta-analysis of adverse events in analgesic trials of third molar removal
- 2023
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Ingår i: Journal of Oral Rehabilitation. - : John Wiley & Sons. - 1365-2842 .- 0305-182X. ; 50:4, s. 332-342
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Forskningsöversikt (refereegranskat)abstract
- BackgroundThe nocebo response refers to the phenomenon where non-specific factors, including negative verbal suggestion and treatment expectations, cause adverse events (AE) following a placebo treatment. Non-specific factors are also likely to influence AE occurrence following administration of active pharmacological treatments. ObjectiveThis meta-analysis aimed to estimate the nocebo response in dentistry by assessing the AEs prevalence in placebo- and active arms of randomised controlled trials (RCTs) assessing analgesic treatment following third molar (M3) surgery. MethodsA systematic search was performed in PubMed, Embase, Scopus, Web of Science and the Cochrane Central Register of Controlled Trials. Eligible studies had to report the number of patients experiencing at least one drug-related AE (patients with AE >= 1) separately for the active and placebo arms. The proportion of patients with AE >= 1 and drug-related dropouts were pooled, and risk differences (RDs) between patients in the placebo- and active arm were calculated. ResultsIn 50 independent RCTs of 47 identified articles, the pooled rates of patients with AE >= 1 were 22.8% in the placebo arm and 20.6% in the active arm. The pooled rates of drug-related dropout were 0.24% in the placebo arm and 0.08% in the active arm. There were no significant RDs in patients with AE >= 1 and drug-related dropouts. ConclusionThese results show that patients in the placebo arm reported AEs to the same extent as patients receiving active treatment, suggesting that most AEs in analgesic medication following M3 surgery may be attributed to the nocebo phenomenon.
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| 24. |
- Watanabe, Takeshi, et al.
(författare)
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What is the nocebo effect and does it apply to dentistry? : A narrative review
- 2022
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Ingår i: Journal of Oral Rehabilitation. - : John Wiley & Sons. - 1365-2842 .- 0305-182X. ; 49:5, s. 586-591
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Forskningsöversikt (refereegranskat)abstract
- Evidence for the nocebo effect, a phenomenon characterised by suboptimal treatment efficacy, worsening of symptoms, or the occurrence of adverse events caused by an individual's negative treatment expectations, is growing across a multitude of medical fields. Within dentistry, little attention has been paid to patients' negative expectations, despite a number of studies supporting the influence of related factors, such as dental fear and anxiety, on the severity of peri- and post-operative dental pain. Only recently, a small number of commentaries and letters have emerged, urging dentists to recognise the possible existence of nocebo effects in dentistry and its implications for patient care. The present review summarises essential evidence of the nocebo phenomenon especially in relation to pain and drug administration. Subsequently, an overview of the current evidence of the nocebo phenomenon in the dental field is presented. Finally, based on the general knowledge of the nocebo effect, the review indicates fruitful arrays of research into the nocebo effect in dentistry.
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| 25. |
- Aaboud, M, et al.
(författare)
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Combinations of single-top-quark production cross-section measurements and |f LV Vtb| determinations at √s = 7 and 8 TeV with the ATLAS and CMS experiments
- 2019
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2019:5
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the combinations of single-top-quark production cross-section measurements by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at s = 7 and 8 TeV corresponding to integrated luminosities of 1.17 to 5.1 fb−1 at s = 7 TeV and 12.2 to 20.3 fb−1 at s = 8 TeV. These combinations are performed per centre-of-mass energy and for each production mode: t-channel, tW, and s-channel. The combined t-channel cross-sections are 67.5 ± 5.7 pb and 87.7 ± 5.8 pb at s = 7 and 8 TeV respectively. The combined tW cross-sections are 16.3 ± 4.1 pb and 23.1 ± 3.6 pb at s = 7 and 8 TeV respectively. For the s-channel cross-section, the combination yields 4.9 ± 1.4 pb at s = 8 TeV. The square of the magnitude of the CKM matrix element Vtb multiplied by a form factor fLV is determined for each production mode and centre-of-mass energy, using the ratio of the measured cross-section to its theoretical prediction. It is assumed that the top-quark-related CKM matrix elements obey the relation |Vtd|, |Vts| ≪ |Vtb|. All the |fLVVtb|2 determinations, extracted from individual ratios at s = 7 and 8 TeV, are combined, resulting in |fLVVtb| = 1.02 ± 0.04 (meas.) ± 0.02 (theo.). All combined measurements are consistent with their corresponding Standard Model predictions.[Figure not available: see fulltext.]. © 2019, The Author(s).
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| 26. |
- Aaboud, M, et al.
(författare)
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Constraints on mediator-based dark matter and scalar dark energy models using √s = 13 TeV pp collision data collected by the ATLAS detector
- 2019
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2019:5
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Tidskriftsartikel (refereegranskat)abstract
- Constraints on selected mediator-based dark matter models and a scalar dark energy model using up to 37 fb−1s = 13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015-2016 are summarised in this paper. The results of experimental searches in a variety of final states are interpreted in terms of a set of spin-1 and spin-0 single-mediator dark matter simplified models and a second set of models involving an extended Higgs sector plus an additional vector or pseudo-scalar mediator. The searches considered in this paper constrain spin-1 leptophobic and leptophilic mediators, spin-0 colour-neutral and colour-charged mediators and vector or pseudo-scalar mediators embedded in extended Higgs sector models. In this case, also s = 8 TeV pp collision data are used for the interpretation of the results. The results are also interpreted for the first time in terms of light scalar particles that could contribute to the accelerating expansion of the universe (dark energy).[Figure not available: see fulltext.]. © 2019, The Author(s).
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| 27. |
- Aaboud, M, et al.
(författare)
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Fluctuations of anisotropic flow in Pb+Pb collisions at √sNN = 5.02 TeV with the ATLAS detector
- 2020
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2020:1
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Tidskriftsartikel (refereegranskat)abstract
- Multi-particle azimuthal cumulants are measured as a function of centrality and transverse momentum using 470 μb−1 of Pb+Pb collisions at sNN = 5.02 TeV with the ATLAS detector at the LHC. These cumulants provide information on the event-by-event fluctuations of harmonic flow coefficients vn and correlated fluctuations between two harmonics vn and vm. For the first time, a non-zero four-particle cumulant is observed for dipolar flow, v1. The four-particle cumulants for elliptic flow, v2, and triangular flow, v3, exhibit a strong centrality dependence and change sign in ultra-central collisions. This sign change is consistent with significant non-Gaussian fluctuations in v2 and v3. The four-particle cumulant for quadrangular flow, v4, is found to change sign in mid-central collisions. Correlations between two harmonics are studied with three- and four-particle mixed-harmonic cumulants, which indicate an anti-correlation between v2 and v3, and a positive correlation between v2 and v4. These correlations decrease in strength towards central collisions and either approach zero or change sign in ultra-central collisions. To investigate the possible flow fluctuations arising from intrinsic centrality or volume fluctuations, the results are compared between two different event classes used for centrality definitions. In peripheral and mid-central collisions where the cumulant signals are large, only small differences are observed. In ultra-central collisions, the differences are much larger and transverse momentum dependent. These results provide new information to disentangle flow fluctuations from the initial and final states, as well as new insights on the influence of centrality fluctuations. [Figure not available: see fulltext.]. © 2020, The Author(s).
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| 28. |
- Aaboud, M, et al.
(författare)
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Measurement of fiducial and differential W+W- production cross-sections at √s=13 TeV with the ATLAS detector
- 2019
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:10
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Tidskriftsartikel (refereegranskat)abstract
- A measurement of fiducial and differential cross-sections for W+W- production in proton–proton collisions at s=13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 36.1 fb - 1 is presented. Events with one electron and one muon are selected, corresponding to the decay of the diboson system as WW→ e±νμ∓ν. To suppress top-quark background, events containing jets with a transverse momentum exceeding 35 GeV are not included in the measurement phase space. The fiducial cross-section, six differential distributions and the cross-section as a function of the jet-veto transverse momentum threshold are measured and compared with several theoretical predictions. Constraints on anomalous electroweak gauge boson self-interactions are also presented in the framework of a dimension-six effective field theory. © 2019, CERN for the benefit of the ATLAS collaboration.
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| 29. |
- Aaboud, M, et al.
(författare)
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Measurement of prompt photon production in sNN=8.16 TeV p + Pb collisions with ATLAS
- 2019
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 796, s. 230-252
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Tidskriftsartikel (refereegranskat)abstract
- The inclusive production rates of isolated, prompt photons in p+Pb collisions at sNN=8.16 TeV are studied with the ATLAS detector at the Large Hadron Collider using a dataset with an integrated luminosity of 165 nb−1 recorded in 2016. The cross-section and nuclear modification factor RpPb are measured as a function of photon transverse energy from 20 GeV to 550 GeV and in three nucleon–nucleon centre-of-mass pseudorapidity regions, (−2.83,−2.02), (−1.84,0.91), and (1.09,1.90). The cross-section and RpPb values are compared with the results of a next-to-leading-order perturbative QCD calculation, with and without nuclear parton distribution function modifications, and with expectations based on a model of the energy loss of partons prior to the hard scattering. The data disfavour a large amount of energy loss and provide new constraints on the parton densities in nuclei. © 2019 The Author
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| 30. |
- Aaboud, M, et al.
(författare)
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Measurement of ZZ production in the ℓℓνν final state with the ATLAS detector in pp collisions at √s = 13 TeV
- 2019
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2019:10
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a measurement of ZZ production with the ATLAS detector at the Large Hadron Collider. The measurement is carried out in the final state with two charged leptons and two neutrinos, using data collected during 2015 and 2016 in pp collisions at s = 13 TeV, corresponding to an integrated luminosity of 36.1 fb−1. The integrated cross-sections in the total and fiducial phase spaces are measured with an uncertainty of 7% and compared with Standard Model predictions, and differential measurements in the fiducial phase space are reported. No significant deviations from the Standard Model predictions are observed, and stringent constraints are placed on anomalous couplings corresponding to neutral triple gauge-boson interactions. [Figure not available: see fulltext.]. © 2019, The Author(s).
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| 31. |
- Aaboud, M, et al.
(författare)
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Measurements of inclusive and differential fiducial cross-sections of tt¯ γ production in leptonic final states at √s=13TeV in ATLAS
- 2019
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:5
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Tidskriftsartikel (refereegranskat)abstract
- Inclusive and differential cross-sections for the production of a top-quark pair in association with a photon are measured with proton-proton collision data corresponding to an integrated luminosity of 36.1 fb-1, collected by the ATLAS detector at the LHC in 2015 and 2016 at a centre-of-mass energy of 13 TeV. The measurements are performed in single-lepton and dilepton final states in a fiducial volume. Events with exactly one photon, one or two leptons, a channel-dependent minimum number of jets, and at least one b-jet are selected. Neural network algorithms are used to separate the signal from the backgrounds. The fiducial cross-sections are measured to be 521±9(stat.)±41(sys.)fb and 69±3(stat.)±4(sys.)fb for the single-lepton and dilepton channels, respectively. The differential cross-sections are measured as a function of photon transverse momentum, photon absolute pseudorapidity, and angular distance between the photon and its closest lepton in both channels, as well as azimuthal opening angle and absolute pseudorapidity difference between the two leptons in the dilepton channel. All measurements are in agreement with the theoretical predictions. © 2019, CERN for the benefit of the ATLAS collaboration.
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| 32. |
- Aaboud, M, et al.
(författare)
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Observation of H→bb¯ decays and VH production with the ATLAS detector
- 2018
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 786, s. 59-86
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Tidskriftsartikel (refereegranskat)abstract
- A search for the decay of the Standard Model Higgs boson into a bb¯ pair when produced in association with a W or Z boson is performed with the ATLAS detector. The data, corresponding to an integrated luminosity of 79.8fb−1 were collected in proton–proton collisions during Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13TeV. For a Higgs boson mass of 125GeV, an excess of events over the expected background from other Standard Model processes is found with an observed (expected) significance of 4.9 (4.3) standard deviations. A combination with the results from other searches in Run 1 and in Run 2 for the Higgs boson in the bb¯ decay mode is performed, which yields an observed (expected) significance of 5.4 (5.5) standard deviations, thus providing direct observation of the Higgs boson decay into b-quarks. The ratio of the measured event yield for a Higgs boson decaying into bb¯ to the Standard Model expectation is 1.01±0.12(stat.)−0.15 +0.16(syst.). Additionally, a combination of Run 2 results searching for the Higgs boson produced in association with a vector boson yields an observed (expected) significance of 5.3 (4.8) standard deviations. © 2018 The Author(s)
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| 33. |
- Aaboud, M, et al.
(författare)
-
Search for Higgs boson pair production in the bb¯ WW * decay mode at √s = 13 TeV with the ATLAS detector
- 2019
-
Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2019:4
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Tidskriftsartikel (refereegranskat)abstract
- A search for Higgs boson pair production in the bb¯ WW * decay mode is performed in the bb¯ ℓνqq final state using 36.1 fb −1 of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. No evidence of events beyond the background expectation is found. Upper limits on the non-resonant pp → HH production cross section of 10 pb and on the resonant production cross section as a function of the HH invariant mass are obtained. Resonant production limits are set for scalar and spin-2 graviton hypotheses in the mass range 500 to 3000 GeV.[Figure not available: see fulltext.] © 2019, The Author(s).
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| 34. |
- Aad, G., et al.
(författare)
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ATLAS b-jet identification performance and efficiency measurement with tt¯ events in pp collisions at √s=13 TeV
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:11
-
Tidskriftsartikel (refereegranskat)abstract
- The algorithms used by the ATLAS Collaboration during Run 2 of the Large Hadron Collider to identify jets containing b-hadrons are presented. The performance of the algorithms is evaluated in the simulation and the efficiency with which these algorithms identify jets containing b-hadrons is measured in collision data. The measurement uses a likelihood-based method in a sample highly enriched in tt¯ events. The topology of the t→ Wb decays is exploited to simultaneously measure both the jet flavour composition of the sample and the efficiency in a transverse momentum range from 20 to 600 GeV. The efficiency measurement is subsequently compared with that predicted by the simulation. The data used in this measurement, corresponding to a total integrated luminosity of 80.5 fb - 1, were collected in proton–proton collisions during the years 2015–2017 at a centre-of-mass energy s= 13 TeV. By simultaneously extracting both the efficiency and jet flavour composition, this measurement significantly improves the precision compared to previous results, with uncertainties ranging from 1 to 8% depending on the jet transverse momentum.
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| 35. |
- Aad, G, et al.
(författare)
-
ATLAS data quality operations and performance for 2015-2018 data-taking
- 2020
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Ingår i: Journal of Instrumentation. - : Institute of Physics Publishing (IOPP). - 1748-0221. ; 15:4
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Tidskriftsartikel (refereegranskat)abstract
- The ATLAS detector at the Large Hadron Collider reads out particle collision data from over 100 million electronic channels at a rate of approximately 100 kHz, with a recording rate for physics events of approximately 1 kHz. Before being certified for physics analysis at computer centres worldwide, the data must be scrutinised to ensure they are clean from any hardware or software related issues that may compromise their integrity. Prompt identification of these issues permits fast action to investigate, correct and potentially prevent future such problems that could render the data unusable. This is achieved through the monitoring of detector-level quantities and reconstructed collision event characteristics at key stages of the data processing chain. This paper presents the monitoring and assessment procedures in place at ATLAS during 2015-2018 data-taking. Through the continuous improvement of operational procedures, ATLAS achieved a high data quality efficiency, with 95.6% of the recorded proton-proton collision data collected at s=13 TeV certified for physics analysis.
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| 36. |
- Aad, G, et al.
(författare)
-
Combination of searches for Higgs boson pairs in pp collisions at s=13TeV with the ATLAS detector
- 2020
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 800
-
Tidskriftsartikel (refereegranskat)abstract
- This letter presents a combination of searches for Higgs boson pair production using up to 36.1 fb−1 of proton–proton collision data at a centre-of-mass energy s=13 TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the bb¯bb¯, bb¯W+W−, bb¯τ+τ−, W+W−W+W−, bb¯γγ and W+W−γγ final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. No statistically significant excess in data above the Standard Model predictions is found. The combined observed (expected) limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 (10) times the predicted Standard Model cross-section. Limits are also set on the ratio (κλ) of the Higgs boson self-coupling to its Standard Model value. This ratio is constrained at 95% confidence level in observation (expectation) to −5.0
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| 37. |
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| 38. |
- Aad, G, et al.
(författare)
-
Combined measurements of Higgs boson production and decay using up to 80 fb-1 of proton-proton collision data at s =13 TeV collected with the ATLAS experiment
- 2020
-
Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 1550-2368. ; 101:1
-
Tidskriftsartikel (refereegranskat)abstract
- Combined measurements of Higgs boson production cross sections and branching fractions are presented. The combination is based on the analyses of the Higgs boson decay modes H→γγ, ZZ∗, WW∗, ττ, bb, μμ, searches for decays into invisible final states, and on measurements of off-shell Higgs boson production. Up to 79.8 fb-1 of proton-proton collision data collected at s=13 TeV with the ATLAS detector are used. Results are presented for the gluon-gluon fusion and vector-boson fusion processes, and for associated production with vector bosons or top-quarks. The global signal strength is determined to be μ=1.11-0.08+0.09. The combined measurement yields an observed (expected) significance for the vector-boson fusion production process of 6.5σ (5.3σ). Measurements in kinematic regions defined within the simplified template cross section framework are also shown. The results are interpreted in terms of modifiers applied to the Standard Model couplings of the Higgs boson to other particles, and are used to set exclusion limits on parameters in two-Higgs-doublet models and in the simplified minimal supersymmetric Standard Model. No significant deviations from Standard Model predictions are observed. © 2020 CERN. © 2020 CERN, for the ATLAS Collaboration. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/" Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.
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| 39. |
- Aad, G, et al.
(författare)
-
Evidence for the production of three massive vector bosons with the ATLAS detector
- 2019
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 798
-
Tidskriftsartikel (refereegranskat)abstract
- A search for the production of three massive vector bosons in proton–proton collisions is performed using data at s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider in the years 2015–2017, corresponding to an integrated luminosity of 79.8 fb−1. Events with two same-sign leptons ℓ (electrons or muons) and at least two reconstructed jets are selected to search for WWW→ℓνℓνqq. Events with three leptons without any same-flavour opposite-sign lepton pairs are used to search for WWW→ℓνℓνℓν, while events with three leptons and at least one same-flavour opposite-sign lepton pair and one or more reconstructed jets are used to search for WWZ→ℓνqqℓℓ. Finally, events with four leptons are analysed to search for WWZ→ℓνℓνℓℓ and WZZ→qqℓℓℓℓ. Evidence for the joint production of three massive vector bosons is observed with a significance of 4.1 standard deviations, where the expectation is 3.1 standard deviations. © 2019 The Author(s)
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| 40. |
- Aad, G, et al.
(författare)
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Identification of boosted Higgs bosons decaying into b-quark pairs with the ATLAS detector at 13 TeV
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:10
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes a study of techniques for identifying Higgs bosons at high transverse momenta decaying into bottom-quark pairs, H→ bb¯ , for proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy s=13 TeV. These decays are reconstructed from calorimeter jets found with the anti-ktR= 1.0 jet algorithm. To tag Higgs bosons, a combination of requirements is used: b-tagging of R= 0.2 track-jets matched to the large-R calorimeter jet, and requirements on the jet mass and other jet substructure variables. The Higgs boson tagging efficiency and corresponding multijet and hadronic top-quark background rejections are evaluated using Monte Carlo simulation. Several benchmark tagging selections are defined for different signal efficiency targets. The modelling of the relevant input distributions used to tag Higgs bosons is studied in 36 fb- 1 of data collected in 2015 and 2016 using g→ bb¯ and Z(→ bb¯) γ event selections in data. Both processes are found to be well modelled within the statistical and systematic uncertainties. © 2019, CERN for the benefit of the ATLAS collaboration.
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| 41. |
- Aad, G, et al.
(författare)
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Longitudinal Flow Decorrelations in Xe+Xe Collisions at sNN =5.44 TeV with the ATLAS Detector
- 2021
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Ingår i: Physical Review Letters. - 1079-7114. ; 126:12
-
Tidskriftsartikel (refereegranskat)abstract
- The first measurement of longitudinal decorrelations of harmonic flow amplitudes vn for n=2-4 in Xe+Xe collisions at sNN=5.44 TeV is obtained using 3 μb-1 of data with the ATLAS detector at the LHC. The decorrelation signal for v3 and v4 is found to be nearly independent of collision centrality and transverse momentum (pT) requirements on final-state particles, but for v2 a strong centrality and pT dependence is seen. When compared with the results from Pb+Pb collisions at sNN=5.02 TeV, the longitudinal decorrelation signal in midcentral Xe+Xe collisions is found to be larger for v2, but smaller for v3. Current hydrodynamic models reproduce the ratios of the vn measured in Xe+Xe collisions to those in Pb+Pb collisions but fail to describe the magnitudes and trends of the ratios of longitudinal flow decorrelations between Xe+Xe and Pb+Pb. The results on the system-size dependence provide new insights and an important lever arm to separate effects of the longitudinal structure of the initial state from other early and late time effects in heavy-ion collisions. © 2021 CERN.
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| 42. |
- Aad, G, et al.
(författare)
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Measurement of angular and momentum distributions of charged particles within and around jets in Pb+Pb and pp collisions at sNN =5.02 TeV with the ATLAS detector
- 2019
-
Ingår i: Physical Review C. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 100:6
-
Tidskriftsartikel (refereegranskat)abstract
- Studies of the fragmentation of jets into charged particles in heavy-ion collisions can provide information about the mechanism of jet quenching by the hot and dense QCD matter created in such collisions, the quark-gluon plasma. This paper presents a measurement of the angular distribution of charged particles around the jet axis in sNN=5.02 TeV Pb+Pb and pp collisions, using the ATLAS detector at the LHC. The Pb+Pb and pp data sets have integrated luminosities of 0.49nb-1 and 25pb-1, respectively. The measurement is performed for jets reconstructed with the anti-kt algorithm with radius parameter R=0.4 and is extended to an angular distance of r=0.8 from the jet axis. Results are presented as a function of Pb+Pb collision centrality and distance from the jet axis for charged particles with transverse momenta in the 1- to 63-GeV range, matched to jets with transverse momenta in the 126- to 316-GeV range and an absolute value of jet rapidity of less than 1.7. Modifications to the measured distributions are quantified by taking a ratio to the measurements in pp collisions. Yields of charged particles with transverse momenta below 4 GeV are observed to be increasingly enhanced as a function of angular distance from the jet axis, reaching a maximum at r=0.6. Charged particles with transverse momenta above 4 GeV have an enhanced yield in Pb+Pb collisions in the jet core for angular distances up to r=0.05 from the jet axis, with a suppression at larger distances.
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| 43. |
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| 44. |
- Aad, G, et al.
(författare)
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Measurement of Azimuthal Anisotropy of Muons from Charm and Bottom Hadrons in pp Collisions at s =13 TeV with the ATLAS Detector
- 2020
-
Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 1079-7114 .- 0031-9007. ; 124:8
-
Tidskriftsartikel (refereegranskat)abstract
- The elliptic flow of muons from the decay of charm and bottom hadrons is measured in pp collisions at √s=13 TeV using a data sample with an integrated luminosity of 150 pb-1 recorded by the ATLAS detector at the LHC. The muons from heavy-flavor decay are separated from light-hadron decay muons using momentum imbalance between the tracking and muon spectrometers. The heavy-flavor decay muons are further separated into those from charm decay and those from bottom decay using the distance-of-closest-approach to the collision vertex. The measurement is performed for muons in the transverse momentum range 4-7 GeV and pseudorapidity range |η| < 2.4. A significant nonzero elliptic anisotropy coefficient v2 is observed for muons from charm decays, while the v2 value for muons from bottom decays is consistent with zero within uncertainties.
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| 45. |
- Aad, G, et al.
(författare)
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Measurement of differential cross sections for single diffractive dissociation in √s = 8 TeV pp collisions using the ATLAS ALFA spectrometer
- 2020
-
Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2020:2
-
Tidskriftsartikel (refereegranskat)abstract
- A dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy s = 8 TeV is used to study inclusive single diffractive dissociation, pp → X p. The intact final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system X are measured in the central detector components. The fiducial range of the measurement is −4.0 < log10ξ < −1.6 and 0.016 < |t| < 0.43 GeV2, where ξ is the proton fractional energy loss and t is the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1.59 ± 0.13 mb. Cross sections are also measured differentially as functions of ξ, t, and ∆η, a variable that characterises the rapidity gap separating the proton and the system X. The data are consistent with an exponential t dependence, dσ/dt ∝ eBt with slope parameter B = 7.65 ± 0.34 GeV−2. Interpreted in the framework of triple Regge phenomenology, the ξ dependence leads to a pomeron intercept of α(0) = 1.07 ± 0.09. [Figure not available: see fulltext.] © 2020, The Author(s).
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| 46. |
- Aad, G, et al.
(författare)
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Measurement of distributions sensitive to the underlying event in inclusive Z boson production in pp collisions at √s = 13 TeV with the ATLAS detector
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:8
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents measurements of charged-particle distributions sensitive to the properties of the underlying event in events containing a Z boson decaying into a muon pair. The data were obtained using the ATLAS detector at the LHC in proton–proton collisions at a centre-of-mass energy of 13 Te with an integrated luminosity of 3.2fb-1. Distributions of the charged-particle multiplicity and of the charged-particle transverse momentum are measured in regions of the azimuth defined relative to the Z boson direction. The measured distributions are compared with the predictions of various Monte Carlo generators which implement different underyling event models. The Monte Carlo model predictions qualitatively describe the data well, but with some significant discrepancies. © 2019, CERN for the benefit of the ATLAS collaboration.
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| 47. |
- Aad, G, et al.
(författare)
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Measurement of flow harmonics correlations with mean transverse momentum in lead–lead and proton–lead collisions at √sNN=5.02TeV with the ATLAS detector
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:12
-
Tidskriftsartikel (refereegranskat)abstract
- To assess the properties of the quark–gluon plasma formed in ultrarelativistic ion collisions, the ATLAS experiment at the LHC measures a correlation between the mean transverse momentum and the flow harmonics. The analysis uses data samples of lead–lead and proton–lead collisions obtained at the centre-of-mass energy per nucleon pair of 5.02 TeV, corresponding to total integrated luminosities of 22μb-1 and 28nb-1, respectively. The measurement is performed using a modified Pearson correlation coefficient with the charged-particle tracks on an event-by-event basis. The modified Pearson correlation coefficients for the 2nd-, 3rd-, and 4th-order flow harmonics are measured in the lead–lead collisions as a function of event centrality quantified as the number of charged particles or the number of nucleons participating in the collision. The measurements are performed for several intervals of the charged-particle transverse momentum. The correlation coefficients for all studied harmonics exhibit a strong centrality evolution, which only weakly depends on the charged-particle momentum range. In the proton–lead collisions, the modified Pearson correlation coefficient measured for the 2nd-order flow harmonics shows only weak centrality dependence. The lead-lead data is qualitatively described by the predictions based on the hydrodynamical model.
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| 48. |
- Aad, G, et al.
(författare)
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Measurement of isolated-photon plus two-jet production in pp collisions at √s = 13 TeV with the ATLAS detector
- 2020
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Ingår i: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; 2020:3
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics of isolated-photon plus two-jet production in pp collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset corresponding to an integrated luminosity of 36.1 fb−1. Cross sections are measured as functions of a variety of observables, including angular correlations and invariant masses of the objects in the final state, γ + jet + jet. Measurements are also performed in phase-space regions enriched in each of the two underlying physical mechanisms, namely direct and fragmentation processes. The measurements cover the range of photon (jet) transverse momenta from 150 GeV (100 GeV) to 2 TeV. The tree-level plus parton-shower predictions from Sherpa and Pythia as well as the next-to-leading-order QCD predictions from Sherpa are compared with the measurements. The next-to-leading-order QCD predictions describe the data adequately in shape and normalisation except for regions of phase space such as those with high values of the invariant mass or rapidity separation of the two jets, where the predictions overestimate the data. [Figure not available: see fulltext.] © 2020, The Author(s).
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| 49. |
- Aad, G, et al.
(författare)
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Measurement of KS0 and Λ production in tt¯ dileptonic events in pp collisions at √s= 7 TeV with the ATLAS detector
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:12
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of KS0 and Λ production in tt¯ final states have been performed. They are based on a data sample with integrated luminosity of 4.6 fb - 1 from proton–proton collisions at a centre-of-mass energy of 7 TeV, collected in 2011 with the ATLAS detector at the Large Hadron Collider. Neutral strange particles are separated into three classes, depending on whether they are contained in a jet, with or without a b-tag, or not associated with a selected jet. The aim is to look for differences in their main kinematic distributions. A comparison of data with several Monte Carlo simulations using different hadronisation and fragmentation schemes, colour reconnection models and different tunes for the underlying event has been made. The production of neutral strange particles in tt¯ dileptonic events is found to be well described by current Monte Carlo models for KS0 and Λ production within jets, but not for those produced outside jets. © 2019, CERN for the benefit of the ATLAS collaboration.
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| 50. |
- Aad, G, et al.
(författare)
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Measurement of single top-quark production in association with a W boson in the single-lepton channel at √s=8TeV with the ATLAS detector
- 2021
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 81:8
-
Tidskriftsartikel (refereegranskat)abstract
- The production cross-section of a top quark in association with a W boson is measured using proton–proton collisions at s√=8TeV. The dataset corresponds to an integrated luminosity of 20.2fb−1, and was collected in 2012 by the ATLAS detector at the Large Hadron Collider at CERN. The analysis is performed in the single-lepton channel. Events are selected by requiring one isolated lepton (electron or muon) and at least three jets. A neural network is trained to separate the tW signal from the dominant tt¯ background. The cross-section is extracted from a binned profile maximum-likelihood fit to a two-dimensional discriminant built from the neural-network output and the invariant mass of the hadronically decaying W boson. The measured cross-section is σtW=26±7pb, in good agreement with the Standard Model expectation.
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