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ATLAS b-jet identification performance and efficiency measurement with t-t events in p p collisions at p s = 13 TeV

- The ATLAS Collaboration

Authors: The ATLAS Collaboration
Date: 2020
Language: English
Type: Article
Identifier: http://hdl.handle.net/10210/462056 , uj:41184 , Citation: The ATLAS Collaboration. 2020. ATLAS b-jet identification performance and efficiency measurement with t-t events in p p collisions at p s = 13 TeV. , DOI: 10.1140/epjc/s10052-019-7450-8
Description: 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 t ¯t 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 GeV 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 to 2017 at a centre-of-mass energy p 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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Combination of searches for invisible Higgs boson decays with the ATLAS experiment

- The ATLAS Collaboration

Authors: The ATLAS Collaboration
Date: 2020
Language: English
Type: Article
Identifier: http://hdl.handle.net/10210/462080 , uj:41189 , Citation: The ATLAS Collaboration. 2020. Combination of searches for invisible Higgs boson decays with the ATLAS experiment. , DOI: 10.1103/PhysRevLett.122.231801
Description: Abstract: Dark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This Letter presents a statistical combination of searches for H ! invisible decays where H is produced according to the Standard Model via vector boson fusion, Z¹``ºH, and WZ¹hadºH, all performed with the ATLAS detector using 36.1 fb􀀀1 of pp collisions at a center-of-mass energy of p s = 13 TeV at the LHC. In combination with the results at p s = 7 and 8 TeV, an exclusion limit on the H ! invisible branching ratio of 0:26 ¹0:17+0:07 0:05º at 95% confidence level is observed (expected).
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Measurement of angular and momentum distributions of charged particles within and around jets in Pb+Pb and p p collisions at p sNN = 5:02 TeV with the ATLAS detector

- The ATLAS Collaboration

Authors: The ATLAS Collaboration
Date: 2020
Language: English
Type: Article
Identifier: http://hdl.handle.net/10210/461863 , uj:41153 , Citation: The ATLAS Collaboration. 2020. Measurement of angular and momentum distributions of charged particles within and around jets in Pb+Pb and p p collisions at p sNN = 5:02 TeV with the ATLAS detector. , DOI: 10.1103/PhysRevC.100.064901
Description: 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 psNN = 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 0.49 nb􀀀1 and 25 pb􀀀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 1–63 GeV range, matched to jets with transverse momenta in the 126–316 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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