scholarly journals Combination of the W boson polarization measurements in top quark decays using ATLAS and CMS data at $$ \sqrt{s} $$ = 8 TeV

2020 ◽  
Vol 2020 (8) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Standard Model ◽  
Top Quark ◽  
W Boson ◽  
W Bosons ◽  
Proton Collision ◽  
Final State ◽  
Proton Proton ◽  
Perturbative Quantum Chromodynamics ◽  
Quark Decays ◽  
8 Tev

Abstract The combination of measurements of the W boson polarization in top quark decays performed by the ATLAS and CMS collaborations is presented. The measurements are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of about 20 fb−1 for each experiment. The measurements used events containing one lepton and having different jet multiplicities in the final state. The results are quoted as fractions of W bosons with longitudinal (F0), left-handed (FL), or right-handed (FR) polarizations. The resulting combined measurements of the polarization fractions are F0 = 0.693 ± 0.014 and FL = 0.315 ± 0.011. The fraction FR is calculated from the unitarity constraint to be FR = −0.008 ± 0.007. These results are in agreement with the standard model predictions at next-to-next-to-leading order in perturbative quantum chromodynamics and represent an improvement in precision of 25 (29)% for F0 (FL) with respect to the most precise single measurement. A limit on anomalous right-handed vector (VR), and left- and right-handed tensor (gL, gR) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [−0.11, 0.16] for VR, [−0.08, 0.05] for gL, and [−0.04, 0.02] for gR, at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived.

scholarly journals MUSiC: a model-unspecific search for new physics in proton–proton collisions at $$\sqrt{s} = 13\,\text {TeV} $$

2021 ◽  
Vol 81 (7) ◽  
Author(s):  
◽  
A. M. Sirunyan ◽  
A. Tumasyan ◽  
W. Adam ◽  
F. Ambrogi ◽  
...  
Keyword(s):  
Standard Model ◽  
Model Simulation ◽  
Standard Model Prediction ◽  
Proton Collision ◽  
Final States ◽  
Final State ◽  
Data Set ◽  
Proton Proton ◽  
Wide Range ◽  
The Standard Model

AbstractResults of the Model Unspecific Search in CMS (MUSiC), using proton–proton collision data recorded at the LHC at a centre-of-mass energy of 13$$\,\text {TeV}$$ TeV , corresponding to an integrated luminosity of 35.9$$\,\text {fb}^{-1}$$ fb - 1 , are presented. The MUSiC analysis searches for anomalies that could be signatures of physics beyond the standard model. The analysis is based on the comparison of observed data with the standard model prediction, as determined from simulation, in several hundred final states and multiple kinematic distributions. Events containing at least one electron or muon are classified based on their final state topology, and an automated search algorithm surveys the observed data for deviations from the prediction. The sensitivity of the search is validated using multiple methods. No significant deviations from the predictions have been observed. For a wide range of final state topologies, agreement is found between the data and the standard model simulation. This analysis complements dedicated search analyses by significantly expanding the range of final states covered using a model independent approach with the largest data set to date to probe phase space regions beyond the reach of previous general searches.

scholarly journals Measurement of the top quark mass using events with a single reconstructed top quark in pp collisions at $$ \sqrt{s} $$ = 13 TeV

2021 ◽  
Vol 2021 (12) ◽  
Author(s):  
◽  
A. Tumasyan ◽  
W. Adam ◽  
J. W. Andrejkovic ◽  
T. Bergauer ◽  
...  
Keyword(s):  
Top Quark ◽  
Quark Mass ◽  
High Signal ◽  
Proton Collision ◽  
Top Quark Mass ◽  
Final State ◽  
Proton Proton ◽  
Single Top ◽  
Lepton Charge ◽  
The Masses

Abstract A measurement of the top quark mass is performed using a data sample enriched with single top quark events produced in the t channel. The study is based on proton- proton collision data, corresponding to an integrated luminosity of 35.9 fb−1, recorded at $$ \sqrt{s} $$ s = 13 TeV by the CMS experiment at the LHC in 2016. Candidate events are selected by requiring an isolated high-momentum lepton (muon or electron) and exactly two jets, of which one is identified as originating from a bottom quark. Multivariate discriminants are designed to separate the signal from the background. Optimized thresholds are placed on the discriminant outputs to obtain an event sample with high signal purity. The top quark mass is found to be $$ {172.13}_{-0.77}^{+0.76} $$ 172.13 − 0.77 + 0.76 GeV, where the uncertainty includes both the statistical and systematic components, reaching sub-GeV precision for the first time in this event topology. The masses of the top quark and antiquark are also determined separately using the lepton charge in the final state, from which the mass ratio and difference are determined to be $$ {0.9952}_{-0.0104}^{+0.0079} $$ 0.9952 − 0.0104 + 0.0079 and $$ {0.83}_{-1.35}^{+1.79} $$ 0.83 − 1.35 + 1.79 GeV, respectively. The results are consistent with CPT invariance.

scholarly journals Measurement of the inclusive and differential Higgs boson production cross sections in the leptonic WW decay mode at $$ \sqrt{s} $$ = 13 TeV

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
A. M. Sirunyan ◽  
◽  
A. Tumasyan ◽  
W. Adam ◽  
F. Ambrogi ◽  
...  
Keyword(s):  
Higgs Boson ◽  
Standard Model ◽  
Cross Sections ◽  
Production Cross ◽  
W Bosons ◽  
Final State ◽  
Proton Proton ◽  
Proton Collisions ◽  
The Standard Model ◽  
Proton Proton Collisions

Abstract Measurements of the fiducial inclusive and differential production cross sections of the Higgs boson in proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV are performed using events where the Higgs boson decays into a pair of W bosons that subsequently decay into a final state with an electron, a muon, and a pair of neutrinos. The analysis is based on data collected with the CMS detector at the LHC during 2016–2018, corresponding to an integrated luminosity of 137 fb−1. Production cross sections are measured as a function of the transverse momentum of the Higgs boson and the associated jet multiplicity. The Higgs boson signal is extracted and simultaneously unfolded to correct for selection efficiency and resolution effects using maximum-likelihood fits to the observed distributions in data. The integrated fiducial cross section is measured to be 86.5 ± 9.5 fb, consistent with the Standard Model expectation of 82.5 ± 4.2 fb. No significant deviation from the Standard Model expectations is observed in the differential measurements.

scholarly journals Search for a heavy resonance decaying to a top quark and a W boson at $$ \sqrt{s} $$ = 13 TeV in the fully hadronic final state

2021 ◽  
Vol 2021 (12) ◽  
Author(s):  
◽  
A. M. Sirunyan ◽  
A. Tumasyan ◽  
W. Adam ◽  
T. Bergauer ◽  
...  
Keyword(s):  
Top Quark ◽  
W Boson ◽  
Center Of Mass ◽  
Large Radius ◽  
Hadronic Final State ◽  
Final State ◽  
Proton Proton ◽  
Center Of Mass Energy ◽  
Heavy Resonances ◽  
Using Data

Abstract A search for a heavy resonance decaying to a top quark and a W boson in the fully hadronic final state is presented. The analysis is performed using data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb−1 recorded by the CMS experiment at the LHC. The search is focused on heavy resonances, where the decay products of each top quark or W boson are expected to be reconstructed as a single, large-radius jet with a distinct substructure. The production of an excited bottom quark, b*, is used as a benchmark when setting limits on the cross section for a heavy resonance decaying to a top quark and a W boson. The hypotheses of b* quarks with left-handed, right-handed, and vector-like chiralities are excluded at 95% confidence level for masses below 2.6, 2.8, and 3.1 TeV, respectively. These are the most stringent limits on the b* quark mass to date, extending the previous best limits by almost a factor of two.

scholarly journals Evidence for $$t\bar{t}t\bar{t}$$ production in the multilepton final state in proton–proton collisions at $$\sqrt{s}=13$$ $$\text {TeV}$$ with the ATLAS detector

2020 ◽  
Vol 80 (11) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Top Quark ◽  
Production Cross ◽  
Atlas Detector ◽  
Proton Collision ◽  
Final State ◽  
Proton Proton ◽  
Top Quark Production ◽  
Quark Production ◽  
Proton Proton Collision ◽  
Multivariate Discriminant

AbstractA search is presented for four-top-quark production using an integrated luminosity of 139 fb$$^{-1}$$ - 1 of proton–proton collision data at a centre-of-mass energy of $$13~\text {TeV}$$ 13 TeV collected by the ATLAS detector at the LHC. Events are selected if they contain a same-sign lepton pair or at least three leptons (electrons or muons). Jet multiplicity, jet flavour and event kinematics are used to separate signal from the background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The four-top-quark production cross section is measured to be $$24^{+7}_{-6}$$ 24 - 6 + 7  fb. This corresponds to an observed (expected) significance with respect to the background-only hypothesis of 4.3 (2.4) standard deviations and provides evidence for this process.

scholarly journals Evidence for Higgs boson decay to a pair of muons

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
A. M. Sirunyan ◽  
◽  
A. Tumasyan ◽  
W. Adam ◽  
T. Bergauer ◽  
...  
Keyword(s):  
Higgs Boson ◽  
Top Quark ◽  
Vector Boson ◽  
Gluon Fusion ◽  
Measured Signal ◽  
Proton Collision ◽  
Proton Proton ◽  
Back Ground ◽  
Proton Proton Collision ◽  
8 Tev

Abstract Evidence for Higgs boson decay to a pair of muons is presented. This result combines searches in four exclusive categories targeting the production of the Higgs boson via gluon fusion, via vector boson fusion, in association with a vector boson, and in association with a top quark-antiquark pair. The analysis is performed using proton-proton collision data at $$ \sqrt{s} $$ s = 13 TeV, corresponding to an integrated luminosity of 137 fb−1, recorded by the CMS experiment at the CERN LHC. An excess of events over the back- ground expectation is observed in data with a significance of 3.0 standard deviations, where the expectation for the standard model (SM) Higgs boson with mass of 125.38 GeV is 2.5. The combination of this result with that from data recorded at $$ \sqrt{s} $$ s = 7 and 8 TeV, corresponding to integrated luminosities of 5.1 and 19.7 fb−1, respectively, increases both the expected and observed significances by 1%. The measured signal strength, relative to the SM prediction, is $$ {1.19}_{-0.39}^{+0.40}{\left(\mathrm{stat}\right)}_{-0.14}^{+0.15}\left(\mathrm{syst}\right) $$ 1.19 − 0.39 + 0.40 stat − 0.14 + 0.15 syst . This result constitutes the first evidence for the decay of the Higgs boson to second generation fermions and is the most precise measurement of the Higgs boson coupling to muons reported to date.

scholarly journals Does SUSY have friends? A new approach for LHC event analysis

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Anna Mullin ◽  
Stuart Nicholls ◽  
Holly Pacey ◽  
Michael Parker ◽  
Martin White ◽  
...  
Keyword(s):  
Hadron Collider ◽  
Local Network ◽  
Proton Collision ◽  
Event Analysis ◽  
Final State ◽  
Proton Proton ◽  
Kinematic Space ◽  
Boosted Decision Tree ◽  
The Individual ◽  
Particle Search

Abstract We present a novel technique for the analysis of proton-proton collision events from the ATLAS and CMS experiments at the Large Hadron Collider. For a given final state and choice of kinematic variables, we build a graph network in which the individual events appear as weighted nodes, with edges between events defined by their distance in kinematic space. We then show that it is possible to calculate local metrics of the network that serve as event-by-event variables for separating signal and background processes, and we evaluate these for a number of different networks that are derived from different distance metrics. Using a supersymmetric electroweakino and stop production as examples, we construct prototype analyses that take account of the fact that the number of simulated Monte Carlo events used in an LHC analysis may differ from the number of events expected in the LHC dataset, allowing an accurate background estimate for a particle search at the LHC to be derived. For the electroweakino example, we show that the use of network variables outperforms both cut-and-count analyses that use the original variables and a boosted decision tree trained on the original variables. The stop example, deliberately chosen to be difficult to exclude due its kinematic similarity with the top background, demonstrates that network variables are not automatically sensitive to BSM physics. Nevertheless, we identify local network metrics that show promise if their robustness under certain assumptions of node-weighted networks can be confirmed.

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