Search for pair production of heavy top-like quarks decaying to a high-p(T) W boson and a b quark in the lepton plus jets final state at root s=7 TeV with the ATLAS detector
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Search for a right-handed W boson and a heavy neutrino in proton-proton collisions at $\sqrt{s}$ = 13 TeV
A search is presented for a right-handed W boson (W R ) and a heavy neutrino (N), in a final state consisting of two same-flavor leptons (ee or μμ) and two quarks. The search is performed with the CMS experiment at the CERN LHC using a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 138 fb -1 . The search covers two regions of phase space, one where the decay products of the heavy neutrino are merged into a single large-area jet, and one where the decay products are well separated. The expected signal is characterized by an excess in the invariant mass distribution of the final-state objects. No significant excess over the standard model background expectations is observed. The observations are interpreted as upper limits on the product of W R production cross sections and branching fractions assuming that couplings are identical to those of the standard model W boson. For N masses m N equal to half the W R mass m W R (m N = 0.2 TeV), m W R is excluded at 95% confidence level up to 4.7 (4.8) and 5.0 (5.4) TeV for the electron and muon channels, respectively. This analysis provides the most stringent limits on the W R mass to date.
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High-precision measurement of the W boson mass with the CDF II detector
The mass of the W boson, a mediator of the weak force between elementary particles, is tightly constrained by the symmetries of the standard model of particle physics. The Higgs boson was the last missing component of the model. After observation of the Higgs boson, a measurement of the W boson mass provides a stringent test of the model. We measure the W boson mass, M W , using data corresponding to 8.8 inverse femtobarns of integrated luminosity collected in proton-antiproton collisions at a 1.96 tera–electron volt center-of-mass energy with the CDF II detector at the Fermilab Tevatron collider. A sample of approximately 4 million W boson candidates is used to obtain M W = 80,433.5 ± 6.4 stat ± 6.9 syst = 80,433.5 ± 9.4 MeV/c 2 , the precision of which exceeds that of all previous measurements combined (stat, statistical uncertainty; syst, systematic uncertainty; MeV, mega–electron volts; c, speed of light in a vacuum). This measurement is in significant tension with the standard model expectation.
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Measurements of properties of the Higgs boson decaying to a W boson pair in pp collisions at s = 13 Te V
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Searches for W′ bosons decaying to a top quark and a bottom quark in proton-proton collisions at 13 TeV
Searches are presented for heavy gauge bosons decaying into a top and a bottom quark in data collected by the CMS experiment at $ \sqrt{s}=13 $ TeV that correspond to an integrated luminosity of 2.2 and 2.6 fb$^{−1}$ in the leptonic and hadronic analyses, respectively. Two final states are analyzed, one containing a single electron, or muon, and missing transverse momentum, and the other containing multiple jets and no electrons or muons. No evidence is found for a right-handed W′ boson (W′$_{R}$) and the combined analyses exclude at 95% confidence level W′$_{R}$ with masses below 2.4 TeV if $ {M}_{\mathrm{W}{\prime}_{\mathrm{R}}}\gg {M}_{\nu_{\mathrm{R}}} $ (mass of the right-handed neutrino), and below 2.6 TeV if $ {M}_{\mathrm{W}{\prime}_{\mathrm{R}}}<{M}_{\nu_{\mathrm{R}}} $ . The results provide the most stringent limits for right-handed W′ bosons in the top and bottom quark decay channel.
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Measurement of the W boson polarisation in $t\bar{t}$ events from pp collisions at $\sqrt{s} = 8$ TeV in the lepton + jets channel with ATLAS
This paper presents a measurement of the polarisation of $W$ bosons from $t\bar{t}$ decays, reconstructed in events with one high-$p_{\mbox{T}}$ lepton and at least four jets. Data from $pp$ collisions at the LHC were collected at $\sqrt{s}$ = 8 TeV and correspond to an integrated luminosity of 20.2 fb$^{-1}$. The angle $\theta^{*}$ between the $b$-quark from the top quark decay and a direct $W$ boson decay product in the $W$ boson rest frame is sensitive to the $W$ boson polarisation. Two different $W$ decay products are used as polarisation analysers: the charged lepton and the down-type quark for the leptonically and hadronically decaying $W$ boson, respectively. The most precise measurement of the $W$ boson polarisation via the distribution of $\cos{\theta^{*}}$ is obtained using the leptonic analyser and events in which at least two of the jets are tagged as $b$-quark jets. The fitted fractions of longitudinal, left- and right-handed polarisation states are $F_{\mathrm{0}}= 0.709 \pm {0.019}$, $F_{\mathrm{L}}= 0.299 \pm {0.015}$ and $F_{\mathrm{R}}= -0.008 \pm {0.014}$, and are the most precisely measured $W$ boson polarisation fractions to date. Limits on anomalous couplings of the $Wtb$ vertex are set.
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Nonperturbative Uncertainties on the Transverse Momentum Distribution of Electroweak Bosons and on the Determination of the W Boson Mass at the LHC
In this work we present an overview of recent results concerning the impact of a possible flavour dependence of the intrinsic quark transverse momentum on electroweak observables. In particular, we focus on the q T spectrum of electroweak gauge bosons produced in proton-proton collisions at the LHC and on the direct determination of the W boson mass. We reveal that these effects are comparable in size to other nonperturbative effects commonly included in phenomenological analyses and should thus be included in precise theoretical predictions for present and future hadron colliders.
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Model-independent measurement of the Higgs boson associated production with two jets and decaying to a pair of W bosons in proton-proton collisions at $\sqrt{s}=13$ TeV
A model-independent measurement of the differential production cross section of the Higgs boson decaying into a pair of W bosons, with a final state including two jets produced in association, is presented. In the analysis, events are selected in which the decay products of the two W bosons consist of an electron, a muon, and missing transverse momentum. The model independence of the measurement is maximized by employing a discriminating variable, developed through machine learning, that is agnostic to the signal hypothesis. The analysis is based on proton-proton collision data at $\sqrt{s}=13$ TeV collected with the CMS detector from 2016–2018, corresponding to an integrated luminosity of 138 fb −1 . The production cross section is measured as a function of the difference in azimuthal angle between the two jets. The differential cross section measurements are used to constrain Higgs boson couplings within the standard model effective field theory framework.
Hadron-Hadron Scattering↗
Search for a heavy right-handed W boson and a heavy neutrino in events with two same-flavor leptons and two jets at $\sqrt{s}=$ 13 TeV
A search for a heavy right-handed W boson (W$_{R}$) decaying to a heavy right-handed neutrino and a charged lepton in events with two same-flavor leptons (e or μ) and two jets, is presented. The analysis is based on proton-proton collision data, collected by the CMS Collaboration at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb$^{−1}$. No significant excess above the standard model expectation is seen in the invariant mass distribution of the dilepton plus dijet system. Assuming that couplings are identical to those of the standard model, and that only one heavy neutrino flavor N$_{R}$ contributes significantly to the W$_{R}$ decay width, the region in the two-dimensional $ \left({m}_{{\mathrm{W}}_{\mathrm{R}}},{m}_{{\mathrm{N}}_{\mathrm{R}}}\right) $ mass plane excluded at 95% confidence level extends to approximately $ {m}_{{\mathrm{W}}_{\mathrm{R}}}=4.4 $ TeV and covers a large range of right-handed neutrino masses below the W$_{R}$ boson mass. This analysis provides the most stringent limits on the W$_{R}$ mass to date.
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Prospects for a measurement of the W boson mass in the all-jets final state at hadron colliders
Precise measurements of the mass of the W boson are important to test the overall consistency of the Standard Model of particle physics. The current best measurements of the W boson mass come from single production measurements at hadron colliders in its decay mode to a lepton (electron or muon) and a neutrino and pair production of W bosons at lepton colliders, where both the leptonic and hadronic decay modes of the W boson have been considered. In this study, prospects for a measurement of the W boson mass in the all-jet final state at hadron colliders are presented. The feasibility of this measurement takes advantage of numerous recent developments in the field of jet substructure. Compared to other methods for measuring the W mass, a measurement in the all-jets final state would be complementary in methodology and have systematic uncertainties orthogonal to previous measurements. We have estimated the main experimental and theoretical uncertainties affecting a measurement in the all-jet final state. With new trigger strategies, a statistical uncertainty for the measurement of the mass difference between the Z and W bosons of 30 MeV could be reached with HL-LHC data corresponding to 3000 fb$^{-1}$ of integrated luminosity. However, in order to reach that precision, the current understanding of non-perturbative contributions to the invariant mass of W → $ q\overline{q}^{\prime } $ and Z → $ b\overline{b} $ jets will need to be refined. Similar strategies will also allow the reach for generic boosted resonances searches in hadronic channels to be extended.
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An Improved W Boson Mass Measurement Using the Collider Detector at Fermilab
The mass of the W boson is one of the most important parameters in the Standard Model. A precise measurement of the W boson mass, together with a precise measurement of the top quark mass, can constrain the mass of the undiscovered Higgs boson within the Standard Model framework or give a hint for physics beyond the Standard Model. This dissertation describes a measurement of the W boson mass through its decay into a muon and a neutrino using ~ 2.2 fb -1 of √ s = 1.96 TeV p$\bar{p}$ data taken with the CDF II detector at Fermilab. We measure the W boson mass to be (80.374 ± 0.015 stat . ± 0.016 syst. ) GeV/c 2 . This result, when combined with the W mass measurement in the electron channel, leads to the single most precise mW value and greatly constrains the possible mass range of the undiscovered Higgs boson. iv
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Precision measurement of the W boson mass using the full CDF Run II data set
The mass of the W boson, a mediator of the weak force between elementary particles, is tightly constrained by the symmetries of the standard model of particle physics. After the observation of the Higgs boson, the last missing component of the model, the measurement of the W boson mass provides a stringent test of the model. A measurement of the W boson mass is presented, which used data corresponding to 8.8 fb$^{-1}$ of integrated luminosity, collected in proton-antiproton collisions at a 1.96 TeV center-of-mass energy with the CDF II detector at the Fermilab Tevatron collider. A sample of approximately 4 million W boson candidates was used to obtain a Wboson mass of 80433.5±6.4$_{stat}$ ±6.9$_{syst}$ = 80433.5±9.4 MeV, the precision of which exceeds that of all previous measurements combined. This measurement is in significant tension with the standard model expectation.
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The s-Channel Single Top Quark Production as a Constraint for W ' Boson Contribution
An analysis is performed to constrain the W' boson production using the measurement of the s‑channel single top quark production cross section. Both phenomenological and statistical approaches are examined and results are presented. In the best case, W' bosons that interact only to the right-handed fermions are excluded below 1390 GeV. To our knowledge, it is the first time that the measured cross section of the s-channel single top quark production from the colliders is used to rule out a part of the phase space of the W' boson.
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Search for W′ bosons decaying to a top and a bottom quark in leptonic final states in proton-proton collisions at $ \sqrt{s} $ = 13 TeV
A search for W′ bosons decaying to a top and a bottom quark in final states including an electron or a muon is performed with the CMS detector at the LHC. The analyzed data correspond to an integrated luminosity of 138 fb$^{−1}$ of proton-proton collisions at a center-of-mass energy of 13 TeV. Good agreement with the standard model expectation is observed and no evidence for the existence of the W′ boson is found over the mass range examined. The largest observed deviation from the standard model expectation is found for a W′ boson mass ($ {m}_{{\textrm{W}}^{\prime }} $) hypothesis of 3.8 TeV with a relative decay width of 1%, with a local (global) significance of 2.6 (2.0) standard deviations. Upper limits on the production cross sections of W′ bosons decaying to a top and a bottom quark are set. Left- and right-handed W′ bosons with $ {m}_{{\textrm{W}}^{\prime }} $ below 3.9 and 4.3 TeV, respectively, are excluded at the 95% confidence level, under the assumption that the new particle has a narrow decay width. Limits are also set for relative decay widths up to 30%.[graphic not available: see fulltext]
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Measurements of the $W$ Boson Mass with the D0 Detector
In the first part, we describe what is the W boson mass in the context of the Standard Model. We discuss the prominent role this physical observable plays in the determination of the internal self consistency of the Electroweak Sector. We review measurements and calculation of the W boson mass done in past and argue about the importance and feasibility of improving the experimental determination. We give a description of the Fermilab Tevatron Collider and the D0 detector, highlighting the relevant parts for the measurement described in this Dissertation. In the second part, we give a detailed description of a measurement of the W boson mass using the D0 Central Calorimeter. The measurement uses 1.68 x 10 6 candidates from W → en decays, corresponding to 4.3 fb -1 of integrated luminosity collected from 2006 to 2009. We measure the mass using the transverse mass, electron transverse momentum, and missing transverse energy distributions. The transverse mass and electron transverse momentum measurements are the most precise and are combined to give MW = 80.367 ± 0.013(stat) ± 0.023 (syst) GeV = 80.367 ± 0.026 GeV. This is combined with an earlier D0 result determined using an independent 1 fb -1 data sample, also with central electrons only, to give M W = 80.375± 0.023 GeV. The uncertainty in the measurement is dominated by the determination of the calorimeter electron energy scale, the W sample size, the knowledge of the parton distribution function. In the third part, we discuss methods of reducing the dominant uncertainties in the W boson mass measurements. We show that introducing electrons detected in the End Calorimeters greatly reduce the measurement systematic uncertainty, especially the on related to the parton distribution functions. We describe a precise calibration of the End Calorimeter using Z → ee events corresponding to 4.3 fb -1 of integrated luminosity. The calibration is an important milestone in a measurement that explores a larger part of the D0 Calorimeter. We present parametrized models that describe the response of the End Calorimeters to electron showers and soft hadronic particles, giving special attention to the specific challenges of a measurement in the forward region: the inhomogeneity of the uninstrumented materials, the large hadronic energy flow in the calorimeter and the jet misidentification probability.
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Search for W' bosons decaying to a top and a bottom quark at s=13TeV in the hadronic final state
A search is performed for W' bosons decaying to a top and a bottom quark in the all-hadronic final state, in proton-proton collisions at a center-of-mass energy of 13 TeV. The analyzed data were collected by the CMS experiment between 2016 and 2018 and correspond to an integrated luminosity of 137 fb -1 . Deep neural network algorithms are used to identify the jet initiated by the bottom quark and the jet containing the decay products of the top quark when the W' boson from the top quark decays hadronically. No excess above the estimated standard model background is observed. Upper limits on the production cross sections of W' bosons decaying to a top and a bottom quark are set. Both left- and right-handed W' bosons with masses below 3.4 TeV are excluded at 95% confidence level, and the most stringent limits to date on W bosons decaying to a top and a bottom quark in the all-hadronic final state are obtained.
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Measurements of the $W$ boson rapidity, helicity, double-differential cross sections, and charge asymmetry in $pp$ collisions at $\sqrt {s}$ = 13 TeV
The differential cross section and charge asymmetry for inclusive W boson production at s=13 TeV is measured for the two transverse polarization states as a function of the W boson absolute rapidity. The measurement uses events in which a W boson decays to a neutrino and either a muon or an electron. The data sample of proton-proton collisions recorded with the CMS detector at the LHC in 2016 corresponds to an integrated luminosity of 35.9 fb-1. The differential cross section and its value normalized to the total inclusive W boson production cross section are measured over the rapidity range |yW|<2.5. In addition to the total fiducial cross section, the W boson double-differential cross section, d2σ/dpTℓd|ηℓ|, and the charge asymmetry are measured as functions of the charged lepton transverse momentum and pseudorapidity. The precision of these measurements is used to constrain the parton distribution functions of the proton using the next-to-leading order NNPDF3.0 set.
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Measurement of the W-boson mass in pp collisions at $\sqrt{s}=7 TeV$ with the ATLAS detector
A measurement of the mass of the W boson is presented based on proton–proton collision data recorded in 2011 at a centre-of-mass energy of 7 TeV with the ATLAS detector at the LHC, and corresponding to 4.6 fb -1 of integrated luminosity. The selected data sample consists of 7.8 × 10 6 candidates in the W→μν channel and 5.9×10 6 candidates in the W→eν channel. The W-boson mass is obtained from template fits to the reconstructed distributions of the charged lepton transverse momentum and of the W boson transverse mass in the electron and muon decay channels, yielding m W =80370 ± 7 (stat.) ± 11 (exp.syst.) ±14 (mod.syst.) MeV = 80370 ± 19 MeV where the first uncertainty is statistical, the second corresponds to the experimental systematic uncertainty, and the third to the physics-modelling systematic uncertainty. Finally, a measurement of the mass difference between the W + and W - bosons yields m W + -m W = -29 ± 28 MeV.
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