606 research outputs found
Study of B c + → J / ψ D s + and B c + → J / ψ D s ∗ + decays in pp collisions at √s = 13 TeV with the ATLAS detector
No full textA study of B+
c → J/ψD+
s and B+
c → J/ψD∗+
s decays using 139 fb−1 of integrated luminosity collected with the ATLAS detector from √
s = 13 TeV pp collisions
at the LHC is presented. The ratios of the branching fractions of the two decays to the
branching fraction of the B+
c → J/ψπ+ decay are measured: B(B+
c → J/ψD+
s
)/B(B+
c →
J/ψπ+) = 2.76 ± 0.47 and B(B+
c → J/ψD∗+
s
)/B(B+
c → J/ψπ+) = 5.33 ± 0.96. The ratio
of the branching fractions of the two decays is found to be B(B+
c → J/ψD∗+
s
)/B(B+
c →
J/ψD+
s
) = 1.93 ± 0.26. For the B+
c → J/ψD∗+
s decay, the transverse polarization fraction,
Γ±±/Γ, is measured to be 0.70 ± 0.11. The reported uncertainties include both the statistical and systematic components added in quadrature. The precision of the measurements
exceeds that in all previous studies of these decays. These results supersede those obtained
in the earlier ATLAS study of the same decays with √s = 7 and 8 TeV pp collision data. A
comparison with available theoretical predictions for the measured quantities is presented
Foraminiferal stratigraphy of raised marine deposits, representing isotope stage 5, Prins Karls Forland, western Svalbard
No full textTwo raised marine sequences from Prins Karls Forland, western Svalbard, interpreted to have been deposited during part of isotope substage 5e (Eemian) and substage 5a, were studied for foraminifera content. Time constraints are given by 14C ages, infrared stimulated luminescence age estimates and amino acid ratios in subfossil marine molluscs. A diamicton (unit B) separates the two marine sequences and reflects an advancement of local glaciers sometime late in isotope stage 5. The two marine sequences contain diverse benthic foraminiferal faunas, indicating periods of a relatively warm and seasonally ice-free marine shelf environment. Compared to the lowermost sequence (unit A), the upper marine sequence (unit C) seems to reflect a more shallow environment that could have resulted from the global lowering of the sea level towards the end of isotope stage 5. Our results further emphasise the problem of biostratigraphic distinction between interglacial and interstadial deposits at high latitudes, with temperature conditions for substage 5a close to those of substage 5e and present conditions
Spatial distribution of hauled out seals.
No full text<p>Distribution and group sizes of hauled out harbour seals along the west coast of Prins Karls Forland during three aerial surveys. Shaded circles indicate haul out areas that were disturbed i.e. some animals were moving towards the water. The red arrow indicates a hauled out site that was disturbed by a polar bear. A, B and C represent the survey results from 01 August 2009, 01 August 2010 and 19 August 2010, respectively.</p
Search for flavour-changing neutral-current interactions of a top quark and a gluon in collisions at TeV with the ATLAS detector
No full textA search is presented for the production of a single top quark via
left-handed flavour-changing neutral-current (FCNC) interactions of a top
quark, a gluon and an up or charm quark. Two production processes are
considered: and . The analysis is based on
proton-proton collision data taken at a centre-of-mass energy of 13TeV with
the ATLAS detector at the LHC. The data set corresponds to an integrated
luminosity of 139 fb. Events with exactly one electron or muon, exactly
one -tagged jet and missing transverse momentum are selected, resembling the
decay products of a singly produced top quark. Neural networks based on
kinematic variables differentiate between events from the two signal processes
and events from background processes. The measured data are consistent with the
background-only hypothesis, and limits are set on the production cross-sections
of the signal processes: pb and pb at the 95% confidence
level, with being the sum of
branching ratios of all three leptonic decay modes of the boson. Based on
the framework of an effective field theory, the cross-section limits are
translated into limits on the strengths of the and couplings
occurring in the theory: TeV and
TeV. These bounds correspond to
limits on the branching ratios of FCNC-induced top-quark decays:
and
.Comment: 51 pages in total, author list starting page 35, 7 figures, 4 tables,
published by Eur. Phys. J. C, All figures including auxiliary figures are
available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2018-06
Search for single vector-like quark production and decay via in collisions at TeV with the ATLAS detector
No full textA search is presented for single production of a vector-like B quark decaying into a Standard Model b-quark and a Standard Model Higgs boson, which decays into a pair. The search is carried out in 139 fb of = 13 TeV proton-proton collision data collected by the ATLAS detector at the LHC between 2015 and 2018. No significant deviation from the Standard Model background prediction is observed, and mass-dependent exclusion limits at the 95% confidence level are set on the resonance production cross-section in several theoretical scenarios determined by the couplings c, c and c between the B quark and the Standard Model W, Z and Higgs bosons, respectively. For a vector-like B occurring as an isospin singlet, the search excludes values of c greater than 0.45 for a B resonance mass (m) between 1.0 and 1.2 TeV. For 1.2 TeV < m< 2.0 TeV, c values larger than 0.50–0.65 are excluded. If the B occurs as part of a (B, Y) doublet, the smallest excluded c coupling values range between 0.3 and 0.5 across the investigated resonance mass range 1.0 TeV < m< 2.0 TeV.[graphic not available: see fulltext]A search is presented for single production of a vector-like quark decaying into a Standard Model -quark and a Standard Model Higgs boson, which decays into a pair. The search is carried out in 139 fb of TeV proton-proton collision data collected by the ATLAS detector at the LHC between 2015 and 2018. No significant deviation from the Standard Model background prediction is observed, and mass-dependent exclusion limits at the 95% confidence level are set on the resonance production cross-section in several theoretical scenarios determined by the couplings , and between the quark and the Standard Model , and Higgs bosons, respectively. For a vector-like occurring as an isospin singlet, the search excludes values of greater than 0.45 for a resonance mass () between 1.0 and 1.2 TeV. For 1.2 TeV < < 2.0 TeV, values larger than 0.50-0.65 are excluded. If the occurs as part of a doublet, the smallest excluded coupling values range between 0.3 and 0.5 across the investigated resonance mass range 1.0 TeV < < 2.0 TeV
Configuration and performance of the ATLAS b-jet triggers in Run 2
No full textSeveral improvements to the ATLAS triggers used to identify jets containing b-hadrons (b-jets) were implemented for data-taking during Run 2 of the Large Hadron Collider from 2016 to 2018. These changes include reconfiguring the b-jet trigger software to improve primary-vertex finding and allow more stable running in conditions with high pile-up, and the implementation of the functionality needed to run sophisticated taggers used by the offline reconstruction in an online environment. These improvements yielded an order of magnitude better light-flavour jet rejection for the same b-jet identification efficiency compared to the performance in Run 1 (2011–2012). The efficiency to identify b-jets in the trigger, and the conditional efficiency for b-jets that satisfy offline b-tagging requirements to pass the trigger are also measured. Correction factors are derived to calibrate the b-tagging efficiency in simulation to match that observed in data. The associated systematic uncertainties are substantially smaller than in previous measurements. In addition, b-jet triggers were operated for the first time during heavy-ion data-taking, using dedicated triggers that were developed to identify semileptonic b-hadron decays by selecting events with geometrically overlapping muons and jets
Measurement of the nuclear modification factor of b-jets in 5.02 TeV Pb+Pb collisions with the ATLAS detector
No full textThis paper presents a measurement of b-jet production in Pb+Pb and pp collisions at TeV with the ATLAS detector at the LHC. The measurement uses 260 of pp collisions collected in 2017 and 1.4 of Pb+Pb collisions collected in 2018. In both collision systems, jets are reconstructed via the anti- algorithm. The b-jets are identified from a sample of jets containing muons from the semileptonic decay of b-quarks using template fits of the muon momentum relative to the jet axis. In pp collisions, b-jets are reconstructed for radius parameters and , and only jets are used in Pb+Pb collisions. For comparison, inclusive jets are also measured using 1.7 of Pb+Pb collisions collected in 2018 and the same pp collision data as the b-jet measurement. The nuclear modification factor, , is calculated for both b-jets and inclusive jets with over the transverse momentum range of 80–290 GeV. The nuclear modification factor for b-jets decreases from peripheral to central collisions. The ratio of the b-jet to inclusive jet is also presented and suggests that the for b-jets is larger than that for inclusive jets in central Pb+Pb collisions. The measurements are compared with theoretical calculations and suggest a role for mass and colour-charge effects in partonic energy loss in heavy-ion collisions
Measurement of the c-jet mistagging efficiency in tt ̄ events using pp collision data at √s=13 TeV collected with the ATLAS detector
No full textA technique is presented to measure the efficiency with which c-jets are mistagged as b-jets (mistagging efficiency) using tt ̄ events, where one of the W bosons decays into an electron or muon and a neutrino and the other decays into a quark–antiquark pair. The measurement utilises the relatively large and known W→ cs branching ratio, which allows a measurement to be made in an inclusive c-jet sample. The data sample used was collected by the ATLAS detector at s=13 TeV and corresponds to an integrated luminosity of 139 fb- 1. Events are reconstructed using a kinematic likelihood technique which selects the mapping between jets and tt ̄ decay products that yields the highest likelihood value. The distribution of the b-tagging discriminant for jets from the hadronic W decays in data is compared with that in simulation to extract the mistagging efficiency as a function of jet transverse momentum. The total uncertainties are in the range 3–17%. The measurements generally agree with those in simulation but there are some differences in the region corresponding to the most stringent b-jet tagging requirement
Measurement of the c-jet mistagging efficiency in tt¯ events using pp collision data at √s=13 TeV collected with the ATLAS detector
No full textA technique is presented to measure the efficiency with which c-jets are mistagged as b-jets (mistagging efficiency) using tt¯ events, where one of the W bosons decays into an electron or muon and a neutrino and the other decays into a quark–antiquark pair. The measurement utilises the relatively large and known W→ cs branching ratio, which allows a measurement to be made in an inclusive c-jet sample. The data sample used was collected by the ATLAS detector at s=13 TeV and corresponds to an integrated luminosity of 139 fb- 1. Events are reconstructed using a kinematic likelihood technique which selects the mapping between jets and tt¯ decay products that yields the highest likelihood value. The distribution of the b-tagging discriminant for jets from the hadronic W decays in data is compared with that in simulation to extract the mistagging efficiency as a function of jet transverse momentum. The total uncertainties are in the range 3–17%. The measurements generally agree with those in simulation but there are some differences in the region corresponding to the most stringent b-jet tagging requirement
A search for an unexpected asymmetry in the production of and pairs in proton-proton collisions recorded by the ATLAS detector at TeV
No full textThis search, a type not previously performed at ATLAS, uses a comparison of
the production cross sections for and pairs to
constrain physics processes beyond the Standard Model. It uses of protonproton collision data recorded at
TeV at the LHC. Targeting sources of new physics which prefer final states
containing to , the search contains two broad
signal regions which are used to provide model-independent constraints on the
ratio of cross sections at the 2% level. The search also has two special
selections targeting supersymmetric models and leptoquark signatures.
Observations using one of these selections are able to exclude, at 95%
confidence level, singly produced smuons with masses up to 640 GeV in a model
in which the only other light sparticle is a neutralino when the
-parity-violating coupling is close to unity. Observations
using the other selection exclude scalar leptoquarks with masses below 1880 GeV
when , at 95% confidence level. The
limit on the coupling reduces to for a mass of 1420 GeV.Comment: 38 pages in total, author list starting page 22, 8 figures, 1 table,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2018-29
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