Learning to increase matching efficiency in identifying additional b-jets in the $\text{t}\bar{\text{t}}\text{b}\bar{\text{b}}$ process
A.I. Institute, Hanyang University（汉阳大学人工智能研究院）；Department of Computer Science, Hanyang University（汉阳大学计算机科学系）；Department of Physics, Hanyang University（汉阳大学物理系）
The $\text{t}\bar{\text{t}}\text{H}(\text{b}\bar{\text{b}})$ process is an essential channel to reveal the Higgs properties but has an irreducible background from the $\text{t}\bar{\text{t}}\text{b}\bar{\text{b}}$ process, which produces a top quark pair in association with a b quark pair. Therefore, understanding the $\text{t}\bar{\text{t}}\text{b}\bar{\text{b}}$ process is crucial for improving the sensitivity of a search for the $\text{t}\bar{\text{t}}\text{H}(\text{b}\bar{\text{b}})$ process. To this end, when measuring the differential cross-section of the $\text{t}\bar{\text{t}}\text{b}\bar{\text{b}}$ process, we need to distinguish the b-jets originated from top quark decays, and additional b-jets originated from gluon splitting. Since there are no simple identification rules, we adopt deep learning methods to learn from data to identify the additional b-jets from the $\text{t}\bar{\text{t}}\text{b}\bar{\text{b}}$ events. Specifically, by exploiting the special structure of the $\text{t}\bar{\text{t}}\text{b}\bar{\text{b}}$ event data, we propose several loss functions that can be minimized to directly increase the matching efficiency, the accuracy of identifying additional b-jets. We discuss the difference between our method and another deep learning-based approach based on binary classification arXiv:1910.14535 using synthetic data. We then verify that additional b-jets can be identified more accurately by increasing matching efficiency directly rather than the binary classification accuracy, using simulated $\text{t}\bar{\text{t}}\text{b}\bar{\text{b}}$ event data in the lepton+jets channel from pp collision at $\sqrt{s}$ = 13 TeV.
We measure the ratio of cross sections, $σ(p\bar{p}\rightarrow Z+2~b~\text{jets})$/$σ(p\bar{p}\rightarrow Z+\text{2 jets})$, for associated production of a $Z$ boson with at least two jets with transverse momentum $p_T^{\rm jet} > 20$ GeV and pseudorapidity $|η^{\rm jet}| < 2.5$. This measurement uses data corresponding to an integrated luminosity of 9.7 fb$^{-1}$ collected by the \DO experiment in Run II of Fermilab's Tevatron \ppbar Collider at a center-of-mass energy of 1.96 TeV. The measured integrated ratio of $0.0236\pm0.0032\left(\mbox{stat}\right)\pm0.0035\left(\mbox{syst}\right)$ is i…
The cross sections for the production of tt-bar bb-bar and tt-bar jj events and their ratio sigma[tt-bar bb-bar]/sigma[tt-bar jj] are measured using data corresponding to an integrated luminosity of 2.3 inverse femtobarns collected in pp collisions at sqrt(s) = 13 TeV with the CMS detector at the LHC. Events with two leptons (e or mu) and at least four reconstructed jets, including at least two identified as b quark jets, in the final state are selected. In the full phase space, the measured ratio is 0.022 +/- 0.003 (stat) +/- 0.006 (syst), the cross section sigma[tt-bar bb-bar] is 4.0 +/- 0.6…
We present a measurement of the top pair production cross section in $p\bar{p}$ collisions at $\sqrt{s}$=1.96 TeV. We collect a data sample with an integrated luminosity of 194$\pm$11 pb$^{-1}$ with the CDF II detector at the Fermilab Tevatron. We use an artificial neural network technique to discriminate between top pair production and background processes in a sample of 519 lepton+jets events, which have one isolated energetic charged lepton, large missing transverse energy and at least three energetic jets. We measure the top pair production cross section to be $σ_{t\bar{t}}= 6.6$$\pm 1.1 \…
We present measurements of identified charged hadron production over a wide momentum range using the SLD Cherenkov Ring Imaging Detector. In addition to studying particle production in flavor-inclusive Z^0 decays, we compare the production in decays into light, c and b flavor events. We also examine particle production in gluon jets with that in light quark jets. The jet flavors are selected by using displaced vertex information.
The top quark mass was measured in the channels $t\bar{t} \to \mathrm{lepton+jets}$ and $t\bar{t} \to \mathrm{dilepton}$ (lepton=$e, μ$) based on ATLAS data recorded in 2011. The data were taken at the LHC with a proton--proton centre-of-mass energy of $\sqrt{s}=7$ TeV and correspond to an integrated luminosity of 4.6fb$^{-1}$. The $t\bar{t} \to \mathrm{lepton+jets}$ analysis uses a three-dimensional template technique which determines the top quark mass together with a global jet energy scale factor (JSF), and a relative $b$-to-light-jet energy scale factor (bJSF), where the terms $b$-jets an…
Measurements of the cross section for the production of top quark pairs in association with a pair of jets from bottom quarks ($σ_\mathrm{t\bar{t}b\bar{b}}$) and in association with a pair of jets from quarks of any flavor or gluons ($σ_\mathrm{t\bar{t}jj}$) and their ratio are presented. The data were collected in proton-proton collisions at a center-of-mass energy of 13 TeV by the CMS experiment at the LHC in 2016 and correspond to an integrated luminosity of 35.9 fb$^{-1}$. The measurements are performed in a fiducial phase space and extrapolated to the full phase space, separately in the d…
Jet multiplicity distributions in top quark pair (t t-bar) events are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC using a data set corresponding to an integrated luminosity of 19.7 inverse femtobarns. The measurement is performed in the dilepton decay channels (e+ e-, mu+ mu-, and e+/- mu-/+). The absolute and normalized differential cross sections for t t-bar production are measured as a function of the jet multiplicity in the event for different jet transverse momentum thresholds and the kinematic properties of the leading additional jets. T…
In this paper we introduce a new approach to study jet substructure in the center-of-mass frame of the jet. We demonstrate that it can be used to discriminate the boosted heavy particles from the QCD jets and the method is complimentary to the existing other jet substructure algorithms. Applications to searches for hadronically decaying W/Z+jets and heavy resonance that decays to a WW final state are also discussed.
The mass of the top quark is measured using a sample of t t-bar candidate events with at least six jets in the final state. The sample is selected from data collected with the CMS detector in pp collisions at sqrt(s) = 7 TeV in 2011 and corresponds to an integrated luminosity of 3.54 inverse femtobarns. The mass is reconstructed for each event employing a kinematic fit of the jets to a t t-bar hypothesis. The top-quark mass is measured to be 173.49 +/- 0.69 (stat.) +/- 1.21 (syst.) GeV. A combination with previously published measurements in other decay modes by CMS yields a mass of 173.54 +/-…
We present a measurement of the fraction of inclusive $W$+jets events produced with net charm quantum number $\pm1$, denoted $W$+$c$-jet, in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using approximately 1~fb$^{-1}$ of data collected by the D0 detector at the Fermilab Tevatron Collider. We identify the $W$+jets events via the leptonic $W$ boson decays. Candidate $W$+$c$-jet events are selected by requiring a jet containing a muon in association with a reconstructed $W$ boson and exploiting the charge correlation between this muon and $W$ boson decay lepton to perform a nearly model-independe…
The inclusive $t\bar{t}$ production cross-section is measured in the lepton+jets channel using 20.2 fb$^{-1}$ of proton--proton collision data at a centre-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC. Major systematic uncertainties due to the modelling of the jet energy scale and $b$-tagging efficiency are constrained by separating selected events into three disjoint regions. In order to reduce systematic uncertainties in the most important background, the W+jets process is modelled using Z+jets events in a data-based approach. The inclusive $t\bar{t}$ cross-section is m…
Measurement of $Ξ^-/\barΞ^{+}$ production in jets from $Z$ boson decays with the DELPHI open data
Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）；China Center of Advanced Science and Technology（中国科学技术协会高级研究中心）；Center for High Energy Physics, Henan Academy of Sciences（河南省科学院高能物理中心）；University of Texas at Dallas（德克萨斯大学达拉斯分校）
Measurement of differential cross-sections in $t\bar t$ and $t\bar t+$jets production in the lepton+jets final state in $pp$ collisions at $\sqrt s=13$ TeV using 140 fb$^{-1}$ of ATLAS data
A measurement of the t t-bar production cross section in pp collisions at sqrt(s) = 7 TeV is presented. The results are based on data corresponding to an integrated luminosity of 2.3 inverse femtobarns collected by the CMS detector at the LHC. Selected events are required to have one isolated, high transverse momentum electron or muon, large missing transverse energy, and hadronic jets, at least one of which must be consistent with having originated from a b quark. The measured cross section is 158.1 +/- 2.1 (stat.) +/- 10.2 (syst.) +/- 3.5 (lum.) pb, in agreement with standard model predictio…
This paper presents measurements of $t\bar{t}$ production in association with additional $b$-jets in $pp$ collisions at the LHC at a centre-of-mass energy of 13 TeV. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1 fb$^{-1}$. Fiducial cross-section measurements are performed in the dilepton and lepton-plus-jets $t\bar{t}$ decay channels. Results are presented at particle level in the form of inclusive cross-sections of $t\bar{t}$ final states with three and four $b$-jets as well as differential cross-sections as a function of global event proper…
We present measurements of single- and double-differential cross-sections in $t\bar{t}$ final states in the lepton+jets channel, unfolded to particle and parton levels with both resolved and boosted topologies considered. Fully corrected spectra are presented as functions of the top-quark as well as $t\bar{t}$ system kinematic variables and jet multiplicities in data from pp collisions at $\sqrt{s}=13$ TeV collected in 2015 and 2016 by the ATLAS detector at the LHC, corresponding to integrated luminosity of $36\,\mathrm{fb}^{-1}$ . Measurements provided detailed information on the top-quark pr…
We report the most sensitive direct search for pair production of fourth-generation bottom-like chiral quarks ($b'$) each decaying promptly to $tW$. We search for an excess of events with an electron or muon, at least five jets (one indentified as due to a $b$ or $c$ quark) and an imbalance of transverse momentum using data from $p\bar{p}$ collisions collected by the CDF II detector at Fermilab with an integrated luminosity of 4.8 fb$^{-1}$. We observe events consistent with background expectation and calculate upper limits on the $b'$ pair production cross section ($σ_{b\bar{b'}}\lesssim 30$ …
Fiducial cross-sections for $t\bar{t}$ production with one or two additional $b$-jets are reported, using an integrated luminosity of 20.3 fb$^{-1}$ of proton--proton collisions at a centre-of-mass energy of 8 TeV at the Large Hadron Collider, collected with the ATLAS detector. The cross-section times branching ratio for $t\bar{t}$ events with at least one additional $b$-jet is measured to be 950 $\pm$ 70 (stat.) $^{+240}_{-190}$ (syst.) fb in the lepton-plus-jets channel and 50 $\pm$ 10 (stat.) $^{+15}_{-10}$ (syst.) fb in the $e μ$ channel. The cross-section times branching ratio for events …
Three jet events arising from decays of the $Z^0$ boson, collected by the DELPHI detector at LEP, were used to measure differences in the properties of quark and gluon jet fragmentation. Gluon jets were anti-tagged in $b\bar{b}g$ events, by identifiying $b$ quark jets with high purities. Unbiased quark jets came from events $q\bar{q}γ$ with two jets plus one photon. A comparison of quark and gluon jet properties in different energy ranges was performed for the first time and within the same detector. The average value of the ratio of the mean charged multiplicities of gluon and quark jets was …
The first measurement of the inclusive cross section for top quark pairs ($\mathrm{t\bar{t}}$) produced in association with two additional charm jets is presented. The analysis uses the dileptonic final states of $\mathrm{t\bar{t}}$ events produced in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 41.5 fb$^{-1}$, recorded by the CMS experiment at the LHC. A new charm jet identification algorithm provides input to a neural network that is trained to distinguish among $\mathrm{t\bar{t}}$ events with two additional charm ($\mathrm…
Multivariate techniques and machine learning models have found numerous applications in High Energy Physics (HEP) research over many years. In recent times, AI models based on deep neural networks are becoming increasingly popular for many of these applications. However, neural networks are regarded as black boxes -- because of their high degree of complexity it is often quite difficult to quantitatively explain the output of a neural network by establishing a tractable input-output relationship and information propagation through the deep network layers. As explainable AI (xAI) methods are be…
We present a measurement of the mass of the top quark from proton-antiproton collisions recorded at the CDF experiment in Run II of the Fermilab Tevatron. We analyze events from the single lepton plus jets final state ($t\bar t\to W^+bW^-\bar b\to lνb q \bar q'\bar b$). The top quark mass is extracted using a direct calculation of the probability density that each event corresponds to the $t\bar t$ final state. The probability is a function of both the mass of the top quark and the energy scale of the calorimeter jets, which is constrained {\it in situ} by the hadronic $W$ boson mass. Using 16…
The mass of the top quark is measured using a sample of t t-bar candidate events with one electron or muon and at least four jets in the final state, collected by CMS in pp collisions at sqrt(s) = 7 TeV at the LHC. A total of 5174 candidate events is selected from data corresponding to an integrated luminosity of 5.0 inverse femtobarns. For each event the mass is reconstructed from a kinematic fit of the decay products to a t t-bar hypothesis. The top-quark mass is determined simultaneously with the jet energy scale (JES), constrained by the known mass of the W boson in q anti-q decays, to be …
We present a detailed examination of the heavy flavor properties of jets produced at the Fermilab Tevatron collider. The data set, collected with the Collider Detector at Fermilab, consists of events with two or more jets with transverse energy $E_T \geq 15$ GeV and pseudo-rapidity $|η| \leq 1.5$. The heavy flavor content of the data set is enriched by requiring that at least one of the jets (lepton-jet) contains a lepton with transverse momentum larger than 8 GeV/c. Jets containing hadrons with heavy flavor are selected via the identification of secondary vertices. The parton-level cross sect…
We present the first direct search for single top quark production using tau leptons. The search is based on 4.8 fb$^{-1}$ of integrated luminosity collected in $p\bar{p}$ collisions at $\sqrt{s}$=1.96 TeV with the D0 detector at the Fermilab Tevatron Collider. We select events with a final state including an isolated tau lepton, missing transverse energy, two or three jets, one or two of them $b$ tagged. We use a multivariate technique to discriminate signal from background. The number of events observed in data in this final state is consistent with the signal plus background expectation. We…
We present a study of events with Z bosons and hadronic jets produced in $\bar{p}p$ collisions at a center-of-mass energy of 1.8 TeV. The data consist of 6708 $Z \to e^+e^-$ decays from 106 pb$^{-1}$ of integrated luminosity collected using the CDF detector at the Tevatron Collider. The Z $+ \ge n$ jet cross sections and jet production properties have been measured for n = 1 to 4. The data compare well to predictions of leading order QCD matrix element calculations with added gluon radiation and simulated parton fragmentation.
We present the results of a search for new physics in the jets plus missing transverse energy data sample collected from 368 pb^{-1} of ppbar collisions at sqrt{s}=1.96 TeV recorded by the Collider Detector at Fermilab. We compare the number of events observed in the data with a data-based estimate of the Standard Model backgrounds contributing to this signature. We observe no significant excess of events, and we interpret this null result in terms of lower limits on the fundamental Planck scale for a large extra dimensions scenario.
We present a study of the dijet invariant mass distribution for the reaction $\pbp \to 2 $jets$+γ+X$, at a center of mass energy of 1.8 TeV, using data collected by the CDF experiment. We compare the data to predictions for the production of a photon with two jets, together with the resonant processes $\pbp \to W/Z+γ+X$, in which the $W$ and $Z$ bosons decay hadronically. A fit is made to the dijet invariant mass distribution combining the non-resonant background and resonant processes. We use the result to establish a limit for the inclusive production cross section of $W/Z+γ$ with hadronic d…
This Letter reports a search for non standard model topquark resonances, $Z'$, decaying to $t\bar{t} \rightarrow W^+b W^-\bar{b}$ %\rightarrow qq'b qq' \bar{b}$, where both $W$ decay to quarks. We examine the top-antitop quark invariant mass spectrum for the presence of narrow resonant states. The search uses a data sample of $\ppb$ collisions at a center of mass energy of 1.96 TeV collected by the CDF II detector at the Fermilab Tevatron, with an integrated luminosity of 2.8 fb$^{-1}$. No evidence for top-antitop quark resonant production is found. We place upper limits on the production cros…
The cross section for t t-bar production in the all-jets final state is measured in pp collisions at a centre-of-mass energy of 8 TeV at the LHC with the CMS detector, in data corresponding to an integrated luminosity of 18.4 inverse femtobarns. The inclusive cross section is found to be 275.6 +/- 6.1 (stat) +/- 37.8 (syst) +/- 7.2 (lumi) pb. The normalized differential cross sections are measured as a function of the top quark transverse momenta, pt, and compared to predictions from quantum chromodynamics. The results are reported at detector, parton, and particle levels. In all cases, the me…
The $t\bar{t}$ production cross-section is measured in the lepton+jets channel using proton$-$proton collision data at a centre-of-mass energy of $\sqrt{s}=13$ TeV collected with the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 139 fb$^{-1}$. Events with exactly one charged lepton and four or more jets in the final state, with at least one jet containing $b$-hadrons, are used to determine the $t\bar{t}$ production cross-section through a profile-likelihood fit. The inclusive cross-section is measured to be ${σ_{\text{inc}} = 830 \pm 0.4~ \text{(stat.)}\pm 3…
Results are presented for an extraction of the top quark Yukawa coupling from top quark-antiquark ($\mathrm{t\bar{t}}$) kinematic distributions in the lepton plus jets final state in proton-proton collisions, based on data collected by the CMS experiment at the LHC at $\sqrt{s} =$ 13 TeV, corresponding to an integrated luminosity of 35.8 fb$^{-1}$. Corrections from weak boson exchange, including Higgs bosons, between the top quarks can produce large distortions of differential distributions near the energy threshold of $\mathrm{t\bar{t}}$ production. Therefore, precise measurements of these di…
Some Beyond the Standard Model theories predict new particles that decay predominantly into top-antitop quark pairs. A search for top-antitop quark resonances that decay into the lepton plus jets final state is carried out with the ATLAS experiment at the LHC using 14 fb$^{-1}$ of $\sqrt{s}$ = 8 TeV proton-proton collisions. The search considers both cases where all of the final state jets are isolated and where some or all of the top quark decay products are merged into a single jet. Mass exclusion limits at a 95% credibility level are set for two benchmark models, one predicting leptophobic …
We present a measurement of the top quark pair ($t\bar{t}$) production cross section ($σ_{t\bar{t}}$) in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using 230 pb$^{-1}$ of data collected by the D0 experiment at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), missing transverse energy, and jets in the final state. We employ lifetime-based b-jet identification techniques to further enhance the $t\bar{t}$ purity of the selected sample. For a top quark mass of 175 GeV, we measure $σ_{t\bar{t}}=8.6^{+1.6}_{-1.5}(stat.+syst.)\pm 0.6(lumi.)$ pb, in agreem…
The top quark mass is measured using a template method in the $t\bar{t}\to$ lepton+jets channel (lepton is $e$ or $μ$) using ATLAS data recorded in 2012 at the LHC. The data were taken at a proton-proton centre-of-mass energy of $\sqrt{s}=8$ TeV and correspond to an integrated luminosity of 20.2 fb$^{-1}$. The $t\bar{t}\to$ lepton+jets channel is characterized by the presence of a charged lepton, a neutrino and four jets, two of which originate from bottom quarks ($b$). Exploiting a three-dimensional template technique, the top quark mass is determined together with a global jet energy scale f…
A measurement of the inclusive $pp\to t\bar{t}+X$ production cross section in the $τ+{\rm jets}$ final state using only the hadronic decays of the $τ$ lepton is presented. The measurement is performed using 20.2 fb$^{-1}$ of proton-proton collision data recorded at a center-of-mass energy of $\sqrt{s}=8$ TeV with the ATLAS detector at the Large Hadron Collider. The cross section is measured via a counting experiment by imposing a set of selection criteria on the identification and kinematic variables of the reconstructed particles and jets, and on event kinematic variables and characteristics.…
The inclusive and fiducial $t\bar{t}$ production cross-sections are measured in the lepton+jets channel using 20.2 fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC. Major systematic uncertainties due to the modelling of the jet energy scale and $b$-tagging efficiency are constrained by separating selected events into three disjoint regions. In order to reduce systematic uncertainties in the most important background, the W+jets process is modelled using Z+jets events in a data-driven approach. The inclusive $t\bar{t}$ cro…
We present a search for the pair production of scalar top quarks, $\tilde{t}$, using 995 pb$^{-1}$ of data collected in $p\bar{p}$ collisions with the D0 detector at the Fermilab Tevatron Collider at $\sqrt{s} = 1.96$ TeV. Both scalar top quarks are assumed to decay into a charm quark and a neutralino ($\tildeχ^{0}_{1}$), where $\tildeχ^{0}_{1}$ is the lightest supersymmetric particle. This leads to a final state with two acoplanar charm jets and missing transverse energy. We find the yield of such events to be consistent with the standard model expectation, and exclude sets of $\tilde{t}$ and…
A new measurement of the inclusive production cross section for pp to t t-bar is performed at a center-of-mass energy of 7 TeV using data collected by the CMS experiment at the LHC. The analysis uses a data sample corresponding to an integrated luminosity of 36 inverse picobarns, and is based on the final state with one isolated, high transverse momentum muon or electron, missing transverse energy, and hadronic jets. The ttbar content of the selected events is enhanced by requiring the presence of at least one jet consistent with b-quark hadronization. The measured cross section is 150 +/- 9 (…
We present the results of a search for new particles that lead to a \Z boson plus jets in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using the Collider Detector at Fermilab (CDF II). A data sample with a luminosity of 1.06 \ifb\ collected using \Z boson decays to $ee$ and $μμ$ is used. We describe a completely data-based method to predict the dominant background from standard-model \Z+jet events. This method can be similarly applied to other analyses requiring background predictions in multi-jet environments, as shown when validating the method by predicting the background from $W$+jets in \…
We present a search for the pair-production of a non-standard-model strongly-interacting particle that decays to a pair of quarks or gluons, leading to a final state with four hadronic jets. We consider both non-resonant production via an intermediate gluon as well as resonant production via a distinct non-standard-model intermediate strongly-interacting particle. We use data collected by the CDF experiment in proton-antiproton collisions at $\sqrt{s}=1.96$ TeV corresponding to an integrated luminosity of 6.6 fb$^{-1}$. We find the data to be consistent with standard model predictions. We repo…
We present a novel approach that is being developed at DZero for extracting information from data through a direct comparison of all measured variables in an event with a matrix element that describes the entire production process. The method is exemplified in the extraction of the mass of the top quark in top-antitop events in the lepton+jets final state. Monte Carlo studies suggest that an improvement of about a factor of two in statistical uncertainty on the mass of the top quark can be achieved relative to previously published work for the same channel. Preliminary results from the re-anal…
Inclusive and differential cross section measurements of $\text{t}\bar{\text{t}}\text{b}\bar{\text{b}}$ production in the lepton+jets channel at $\sqrt{s} = 13\text{ TeV}$
A search for the production of heavy resonances decaying into top quark-antiquark pairs is presented. The analysis is performed in the lepton+jets and fully hadronic channels using data collected in proton-proton collisions at sqrt(s) = 13 TeV using the CMS detector at the LHC, corresponding to an integrated luminosity of 2.6 inverse femtobarns. The selection is optimized for massive resonances, where the top quarks have large Lorentz boosts. No evidence for resonant t t-bar production is found in the data, and upper limits on the production cross section of heavy resonances are set. The exclu…
We present a measurement of top quark polarization in $t\bar{t}$ pair production in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using data corresponding to 9.7 fb$^{-1}$ of integrated luminosity recorded with the D0 detector at the Fermilab Tevatron Collider. We consider final states containing a lepton and at least three jets. The polarization is measured through the distribution of lepton angles along three axes: the beam axis, the helicity axis, and the transverse axis normal to the $t\bar{t}$ production plane. This is the first measurement of top quark polarization at Tevatron using lepto…
We present the first measurements of the differential cross section $dσ/dp_{T}^γ$ for the production of an isolated photon in association with at least two $b$-quark jets. The measurements consider photons with rapidities $|y^γ| < 1.0$ and transverse momenta $30 < p_{T}^γ < 200$~\GeV. The $b$-quark jets are required to have $p_T^{jet}>15$ GeV and $| y^{jet}| < 1.5$. The ratio of differential production cross sections for $γ+2~b$-jets to $γ+b$-jet as a function of $p_{T}^γ$ is also presented. The results are based on the proton-antiproton collision data at $\sqrt{s}=$1.96~\TeV collected with th…
Angular correlation of jets produced in association with a massive scalar, vector or tensor boson is crucial in the determination of their spin and CP properties. We study jet angular correlations in events with a high mass bottom quark pair or a top quark pair and two jets at the LHC, whose cross-section is dominated by the virtual gluon fusion sub-processes when appropriate kinematic selection cuts (vector-boson fusion cuts) are applied. We evaluate helicity amplitudes for sub-processes initiated by qq, qg and gg collisions in the limit where the intermediate gluons are collinear to the init…
We report on a search for the standard model Higgs boson produced in association with a $W$ or $Z$ boson in $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV recorded by the CDF II experiment at the Tevatron in a data sample corresponding to an integrated luminosity of 2.1 fb$^{-1}$. We consider events which have no identified charged leptons, an imbalance in transverse momentum, and two or three jets where at least one jet is consistent with originating from the decay of a $b$ hadron. We find good agreement between data and predictions. We place 95% confidence level upper limits on the productio…
Simultaneous efficiency measurements of $b$- and $c$-jets in $t\bar{t}$ events from $\sqrt{s}=13.6$ TeV $pp$ collision data collected with the ATLAS detector
EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH (CERN)（欧洲核子研究组织（CERN））
This document presents a search for a $W'$ boson, decaying to a top quark and a $b$ quark in an effective coupling approach, using a multivariate method based on boosted decision trees. It reports exclusion limits on the $W'\rightarrow tb$ cross-section times branching ratio and effective couplings as a function of the $W'$-boson mass. The search covers $W'$-boson masses between 0.5 and 3.0 TeV, for right-handed or left-handed $W'$-boson, with 20.3 fb$^{-1}$ of proton-proton collision data produced by the LHC in 2012, at a center-of-mass energy of 8 TeV and collected by the ATLAS detector.
The consistency of the spin correlation strength in top quark pair production with the standard model (SM) prediction is tested in the muon + jets final state. The events are selected from pp collisions, collected by the CMS detector, at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 inverse femtobarns. The data are compared with the expectation for the spin correlation predicted by the SM and with the expectation of no correlation. Using a template fit method, the fraction of events that show SM spin correlations is measured to be 0.72 +/- 0.08 (stat) +0.1…
The D0 Collaboration has studied for the first time the properties of hadron-collider jets reconstructed with a successive-combination algorithm based on relative transverse momenta ($k_{\perp}$) of energy clusters. Using the standard value D = 1.0 of the jet-separation parameter in the $k_{\perp}$ algorithm, we find that the $p_T$ of such jets is higher than the $E_T$ of matched jets reconstructed with cones of radius R = 0.7, by about 5 (8) GeV at $p_T \approx 90$ (240) GeV. To examine internal jet structure, the $k_{\perp}$ algorithm is applied within D = 0.5 jets to resolve any subjets. Th…
This paper presents a direct measurement of the decay width of the top quark using $t\bar{t}$ events in the lepton+jets final state. The data sample was collected by the ATLAS detector at the LHC in proton-proton collisions at a centre-of-mass energy of 8 TeV and corresponds to an integrated luminosity of 20.2 fb$^{-1}$. The decay width of the top quark is measured using a template fit to distributions of kinematic observables associated with the hadronically and semileptonically decaying top quarks. The result, $Γ_t = 1.76 \pm 0.33 (\rm{stat.}) ^{+0.79}_{-0.68} (\rm{syst.})\; \rm{GeV}$ for a …
Measurement of $t\bar{t}$ production in association with additional $b$-jets in the $eμ$ final state in proton-proton collisions at $\sqrt{s}$=13 TeV with the ATLAS detector
We present the first direct measurement of the top-quark mass using $\ttbar$ events decaying in the hadronic $τ$ + jets decay channel. Using data corresponding to an integrated luminosity of 2.2 fb$^{-1}$ collected by the CDF II detector in $p\bar{p}$ collisions at $\sqrt{s}=1.96 ~TeV$ at the Fermilab Tevatron, we measure the $t\bar{t}$ cross section, $σ_{t\bar{t}}$, and the top-quark mass, M$_{top}$. We extract M$_{top}$ from a likelihood based on per-event probabilities calculated with leading-order signal and background matrix elements. We measure $σ_{t\bar{t}} = 8.8 \pm 3.3 ~(\mathrm{stat}…
We have used the Collider Detector at Fermilab (CDF II) to search for the flavor-changing neutral-current (FCNC) top quark decay ${t\goes Zc}$ using a technique employing ratios of $W$ and $Z$ production, measured in \ppbar data corresponding to an integrated luminosity of 1.52 $fb^{-1}$. The analysis uses a comparison of two decay chains, ${p\bar{p}\goes t\bar{t}\goes WbWb\goes\ellνbjjb}$ and ${p\bar{p}\goes t\bar{t}\goes ZcWb\goes\ell\ell cjjb}$, to cancel systematic uncertainties in acceptance, efficiency, and luminosity. We validate the modeling of acceptance and efficiency for lepton iden…
