Change search
Link to record
Permanent link

Direct link
Gellerstedt, Karl
Publications (10 of 647) Show all publications
Bertoli, G., Bohm, C., Carney, R. M. D., Clément, C., Gellerstedt, K., Hellman, S., . . . Wallängen, V. (2020). ATLAS data quality operations and performance for 2015-2018 data-taking. Journal of Instrumentation, 15(4), Article ID P04003.
Open this publication in new window or tab >>ATLAS data quality operations and performance for 2015-2018 data-taking
Show others...
2020 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 15, no 4, article id P04003Article in journal (Refereed) Published
Abstract [en]

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 root s = 13 TeV certified for physics analysis.

Keywords
Large detector systems for particle and astroparticle physics, Large detector-systems performance
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-183172 (URN)10.1088/1748-0221/15/04/P04003 (DOI)000534740000003 ()
Available from: 2020-07-01 Created: 2020-07-01 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., Clement, C., Gellerstedt, K., . . . Wallängen, V. (2020). Determination of jet calibration and energy resolution in proton-proton collisions at s=8 TeV using the ATLAS detector. European Physical Journal C, 80(12), Article ID 1104.
Open this publication in new window or tab >>Determination of jet calibration and energy resolution in proton-proton collisions at s=8 TeV using the ATLAS detector
Show others...
2020 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 80, no 12, article id 1104Article in journal (Refereed) Published
Abstract [en]

The jet energy scale, jet energy resolution, and their systematic uncertainties are measured for jets reconstructed with the ATLAS detector in 2012 using proton-proton data produced at a centre-of-mass energy of 8 TeV with an integrated luminosity of 20 fb-1. Jets are reconstructed from clusters of energy depositions in the ATLAS calorimeters using the anti-kt algorithm. A jet calibration scheme is applied in multiple steps, each addressing specific effects including mitigation of contributions from additional proton-proton collisions, loss of energy in dead material, calorimeter non-compensation, angular biases and other global jet effects. The final calibration step uses several in situ techniques and corrects for residual effects not captured by the initial calibration. These analyses measure both the jet energy scale and resolution by exploiting the transverse momentum balance in gamma + jet, Z + jet, dijet, and multijet events. A statistical combination of these measurements is performed. In the central detector region, the derived calibration has a precision better than 1% for jets with transverse momentum 150 GeV<pT< 1500 GeV, and the relative energy resolution is (8.4 +/- 0.6)% for pT=100 GeV and (23 +/- 2)% for pT=20 GeV. The calibration scheme for jets with radius parameter R=1.0, for which jets receive a dedicated calibration of the jet mass, is also discussed.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-190699 (URN)10.1140/epjc/s10052-020-08477-8 (DOI)000598026400006 ()
Available from: 2021-03-03 Created: 2021-03-03 Last updated: 2022-02-25Bibliographically approved
Bertoli, G., Bohm, C., Carney, R. M. D., Clément, C., Gellerstedt, K., Hellman, S., . . . Wallängen, V. (2020). Measurement of Azimuthal Anisotropy of Muons from Charm and Bottom Hadrons in pp Collisions at root s=13 TeV with the ATLAS Detector. Physical Review Letters, 124(8), Article ID 082301.
Open this publication in new window or tab >>Measurement of Azimuthal Anisotropy of Muons from Charm and Bottom Hadrons in pp Collisions at root s=13 TeV with the ATLAS Detector
Show others...
2020 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 124, no 8, article id 082301Article in journal (Refereed) Published
Abstract [en]

The elliptic flow of muons from the decay of charm and bottom hadrons is measured in pp collisions at root 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 vertical bar eta vertical bar < 2.4. A significant nonzero elliptic anisotropy coefficient nu(2) is observed for muons from charm decays, while the nu(2) value for muons from bottom decays is consistent with zero within uncertainties.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-180373 (URN)10.1103/PhysRevLett.124.082301 (DOI)000517288800010 ()32167369 (PubMedID)
Available from: 2020-04-02 Created: 2020-04-02 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bohm, C., Carney, R. M. D., Clément, C., Gellerstedt, K., Hellman, S., . . . Wallängen, V. (2020). Measurement of long-range two-particle azimuthal correlations in Z-boson tagged pp collisions at root s=8 and 13 TeV. European Physical Journal C, 80(1), Article ID 64.
Open this publication in new window or tab >>Measurement of long-range two-particle azimuthal correlations in Z-boson tagged pp collisions at root s=8 and 13 TeV
Show others...
2020 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 80, no 1, article id 64Article in journal (Refereed) Published
Abstract [en]

Results are presented from the measurement by ATLAS of long-range (|Delta eta|>2) dihadron angular correlations in root s=8 and 13 TeV pp collisions containing a Z boson. The analysis is performed using 19.4 fb-1 of root s=8 TeV data recorded during Run 1 of the LHC and 36.1 fb-1 of root s=13 TeV data recorded during Run 2. Two-particle correlation functions are measured as a function of relative azimuthal angle over the relative pseudorapidity range 2<|Delta eta|<5 for different intervals of charged-particle multiplicity and transverse momentum. The measurements are corrected for the presence of background charged particles generated by collisions that occur during one passage of two colliding proton bunches in the LHC. Contributions to the two-particle correlation functions from hard processes are removed using a template-fitting procedure. Sinusoidal modulation in the correlation functions is observed and quantified by the second Fourier coefficient of the correlation function, v2,2, which in turn is used to obtain the single-particle anisotropy coefficient v2. The v2 values in the Z-tagged events, integrated over 0.5<pT<5 GeV, are found to be independent of multiplicity and <mml:msqrt>s</mml:msqrt>, and consistent within uncertainties with previous measurements in inclusive pp collisions. As a function of charged-particle pT, the Z-tagged and inclusive v2 values are consistent within uncertainties for pT<3 GeV.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-181116 (URN)10.1140/epjc/s10052-020-7606-6 (DOI)000521222100003 ()
Available from: 2020-04-27 Created: 2020-04-27 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bohm, C., Carney, R. M. D., Clément, C., Gellerstedt, K., Hellman, S., . . . Wallängen, V. (2020). Performance of electron and photon triggers in ATLAS during LHC Run 2. European Physical Journal C, 80(1), Article ID 47.
Open this publication in new window or tab >>Performance of electron and photon triggers in ATLAS during LHC Run 2
Show others...
2020 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 80, no 1, article id 47Article in journal (Refereed) Published
Abstract [en]

Electron and photon triggers covering transverse energies from 5 GeV to several TeV are essential for the ATLAS experiment to record signals for a wide variety of physics: from StandardModel processes to searches for new phenomena in both proton-proton and heavy-ion collisions. To cope with a fourfold increase of peak LHC luminosity from 2015 to 2018 (Run 2), to 2.1 x 10(34) cm(-2) s(-1), and a similar increase in the number of interactions per beam-crossing to about 60, trigger algorithms and selections were optimised to control the rates while retaining a high efficiency for physics analyses. For proton-proton collisions, the single-electron trigger efficiency relative to a single-electron offline selection is at least 75% for an offline electron of 31 GeV, and rises to 96% at 60 GeV; the trigger efficiency of a 25GeVleg of the primary diphoton trigger relative to a tight offline photon selection is more than 96% for an offline photon of 30 GeV. For heavy-ion collisions, the primary electron and photon trigger efficiencies relative to the corresponding standard offline selections are at least 84% and 95%, respectively, at 5 GeV above the corresponding trigger threshold.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-181117 (URN)10.1140/epjc/s10052-019-7500-2 (DOI)000519817900001 ()
Available from: 2020-04-27 Created: 2020-04-27 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bohm, C., Carney, R. M. D., Clément, C., Gellerstedt, K., Hellman, S., . . . Wallängen, V. (2020). Search for electroweak production of charginos and sleptons decaying into final states with two leptons and missing transverse momentum in root s=13 TeV pp collisions using the ATLAS detector. European Physical Journal C, 80(2), Article ID 123.
Open this publication in new window or tab >>Search for electroweak production of charginos and sleptons decaying into final states with two leptons and missing transverse momentum in root s=13 TeV pp collisions using the ATLAS detector
Show others...
2020 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 80, no 2, article id 123Article in journal (Refereed) Published
Abstract [en]

A search for the electroweak production of charginos and sleptons decaying into final states with two electrons or muons is presented. The analysis is based on 139 fb(-1) of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at v s = 13 TeV. Three R-parity-conserving scenarios where the lightest neutralino is the lightest supersymmetric particle are considered: the production of chargino pairs with decays via eitherW bosons or sleptons, and the direct production of slepton pairs. The analysis is optimised for the first of these scenarios, but the results are also interpreted in the others. No significant deviations from the Standard Model expectations are observed and limits at 95% confidence level are set on the masses of relevant supersymmetric particles in each of the scenarios. For a massless lightest neutralino, masses up to 420 GeV are excluded for the production of the lightest-chargino pairs assuming W-boson-mediated decays and up to 1 TeV for slepton-mediated decays, whereas for slepton-pair production masses up to 700 GeV are excluded assuming three generations of mass-degenerate sleptons.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-180416 (URN)10.1140/epjc/s10052-019-7594-6 (DOI)000515792500002 ()
Available from: 2020-03-30 Created: 2020-03-30 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bohm, C., Carney, R., Clement, C., Gellerstedt, K., Hellman, S., . . . Wallangen, V. (2020). Search for light long-lived neutral particles produced in pp collisions at root s=13 TeV and decaying into collimated leptons or light hadrons with the ATLAS detector. European Physical Journal C, 80(5), Article ID 450.
Open this publication in new window or tab >>Search for light long-lived neutral particles produced in pp collisions at root s=13 TeV and decaying into collimated leptons or light hadrons with the ATLAS detector
Show others...
2020 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 80, no 5, article id 450Article in journal (Refereed) Published
Abstract [en]

Several models of physics beyond the Standard Model predict the existence of dark photons, light neutral particles decaying into collimated leptons or light hadrons. This paper presents a search for long-lived dark photons produced from the decay of a Higgs boson or a heavy scalar boson and decaying into displaced collimated Standard Model fermions. The search uses data corresponding to an integrated luminosity of 36.1 fb-1 collected in proton-proton collisions at <mml:msqrt>s</mml:msqrt>=13 Te recorded in 2015-2016 with the ATLAS detector at the Large Hadron Collider. The observed number of events is consistent with the expected background, and limits on the production cross section times branching fraction as a function of the proper decay length of the dark photon are reported. A cross section times branching fraction above 4 pb is excluded for a Higgs boson decaying into two dark photons for dark-photon decay lengths between 1.5 mm and 307 mm.

Keywords
Proton-Proton Collisions, Higgs-Boson Production, Vector Gauge Boson, Phi-Meson Decays, Parton Distributions, Exclusion Limits, Dark Photon, Forces, Jets, Pair
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-184610 (URN)10.1140/epjc/s10052-020-7997-4 (DOI)000546996400002 ()
Available from: 2020-08-28 Created: 2020-08-28 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., Clément, C., Gellerstedt, K., . . . Wallängen, V. (2019). A strategy for a general search for new phenomena using data-derived signal regions and its application within the ATLAS experiment. European Physical Journal C, 79(2), Article ID 120.
Open this publication in new window or tab >>A strategy for a general search for new phenomena using data-derived signal regions and its application within the ATLAS experiment
Show others...
2019 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 79, no 2, article id 120Article in journal (Refereed) Published
Abstract [en]

This paper describes a strategy for a general search used by the ATLAS Collaboration to find potential indications of new physics. Events are classified according to their final state into many event classes. For each event class an automated search algorithm tests whether the data are compatible with the Monte Carlo simulated expectation in several distributions sensitive to the effects of new physics. The significance of a deviation is quantified using pseudo-experiments. A data selection with a significant deviation defines a signal region for a dedicated follow-up analysis with an improved background expectation. The analysis of the data-derived signal regions on a new dataset allows a statistical interpretation without the large look-elsewhere effect. The sensitivity of the approach is discussed using Standard Model processes and benchmark signals of new physics. As an example, results are shown for 3.2fb-1 of proton-proton collision data at a centre-of-mass energy of 13TeV collected with the ATLAS detector at the LHC in 2015, in which more than 700 event classes and more than 105 regions have been analysed. No significant deviations are found and consequently no data-derived signal regions for a follow-up analysis have been defined.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-166542 (URN)10.1140/epjc/s10052-019-6540-y (DOI)000457998500007 ()
Available from: 2019-03-06 Created: 2019-03-06 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bohm, C., Carney, R. M. D., Clement, C., Gellerstedt, K., Hellman, S., . . . Wallängen, V. (2019). Charged-hadron suppression in Pb plus Pb and Xe plus Xe collisions measured with the ATLAS detector. Nuclear Physics A, 982, 571-574
Open this publication in new window or tab >>Charged-hadron suppression in Pb plus Pb and Xe plus Xe collisions measured with the ATLAS detector
Show others...
2019 (English)In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 571-574Article in journal (Refereed) Published
Abstract [en]

The ATLAS detector at the LHC recorded 0.49 nb(-1) of Pb+Pb collisions and 25 of pp(-1) collisions, both at the center-of-mass energy 5.02 TeV per nucleon pair. Recently, ATLAS also recorded 30 mu b(-1) of Xe+Xe collisions at the center-of-mass energy 5.44 TeV, which provides a new opportunity to study the system-size dependence of the charged-hadron production in heavy-ion collisions. The large acceptance of the ATLAS detector allows to measure the spectra of charged hadrons in a wide range of pseudorapidity and transverse momentum. The nuclear modification factors R-AA are constructed as a ratio of the spectra measured in Pb+Pb or Xe+Xe collisions to that measured in pp collisions. The R-AA obtained in the two systems are presented for different centrality intervals and the results are discussed.

Keywords
xenon-xenon collisions, lead-lead collisions, charged-hadron production, nuclear modification factor
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-166734 (URN)10.1016/j.nuclphysa.2018.10.079 (DOI)000457515500128 ()
Available from: 2019-03-18 Created: 2019-03-18 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bohm, C., Carney, R. M. D., Clément, C., Gellerstedt, K., Hellman, S., . . . Wallängen, V. (2019). Comparison of Fragmentation Functions for Jets Dominated by Light Quarks and Gluons from pp and Pb plus Pb Collisions in ATLAS. Physical Review Letters, 123(4), Article ID 042001.
Open this publication in new window or tab >>Comparison of Fragmentation Functions for Jets Dominated by Light Quarks and Gluons from pp and Pb plus Pb Collisions in ATLAS
Show others...
2019 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, no 4, article id 042001Article in journal (Refereed) Published
Abstract [en]

Charged-particle fragmentation functions for jets azimuthally balanced by a high-transverse-momentum, prompt, isolated photon are measured in 25 pb(-1) of pp and 0.49 nb(-1) of Pb + Pb collision data at 5.02 TeV per nucleon pair recorded with the ATLAS detector at the Large Hadron Collider. The measurements are compared to predictions of Monte Carlo generators and to measurements of inclusively selected jets. In pp collisions, a different jet fragmentation function in photon-tagged events from that in inclusive jet events arises from the difference in fragmentation between light quarks and gluons. The ratios of the fragmentation functions in Pb + Pb events to that in pp events are used to explore the parton color-charge dependence of jet quenching in the hot medium. In relatively peripheral collisions, fragmentation functions exhibit a similar modification pattern for photon-tagged and inclusive jets. However, photon-tagged jets are observed to have larger modifications than inclusive jets in central Pb + Pb events.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-171638 (URN)10.1103/PhysRevLett.123.042001 (DOI)000476696300004 ()
Available from: 2019-08-22 Created: 2019-08-22 Last updated: 2022-03-23Bibliographically approved
Organisations

Search in DiVA

Show all publications