Top quark in theory

Top quark spin and $Htb$ interaction in charged Higgs and top quark associated production at LHC

We study the charged Higgs production at LHC via its associated production with top quark. The kinematic cuts are optimized to suppress the background processes so that the reconstruction of the charged Higgs and top quark is possible. The angular distributions with respect to top quark spin are explored to study the $Htb$ interaction at LHC.

Production of heavy Higgs bosons and decay into top quarks at the LHC. II: Top-quark polarization and spin correlation effects

We analyze, within several parameter scenarios of type-II two-Higgs doublet extensions of the standard model, the impact of heavy neutral Higgs-boson resonances on top-quark pair production and their subsequent decay to dileptonic final states at the LHC (13 TeV). In particular, we investigate the effects of heavy Higgs bosons on top-spin observables, that is, the longitudinal top-quark polarization and top-quark spin correlations. We take into account NLO QCD as well as weak interaction corrections and show that top-spin observables, if evaluated in judiciously chosen top-quark pair invariant…

Spin Correlations in Top Quark Production and the Top Quark Mass

Top-antitop quark pairs produced at the Tevatron have a sizeable spin correlation. That correlation feeds into the angular distribution of the decay products, particularly in the dilepton channel. Including the expected correlation in an overall analysis of a handful of actual dilepton events continues to favor a lower top mass (centered on 155 GeV) than the single lepton events.

Top Quark Physics at the ILC: Methods and Meanings

The physics case for studying top-quark physics at the International Linear Collider is well established. This summary places in context the top-quark physics goals, examines the current state-of-the art in understanding of the top-quark mass, and identifies some areas in which the study of the top-quark mass enhances our understanding of new techniques.

Top quark physics at the LHC

The physics perspectives of the production and decay of single top quarks and top quark pairs at the CERN Large Hadron Collider (LHC) are reviewed from a phenomenological point of view.

Topics in Top Quark Physics

The status of top quark searches will be briefly reviewed. Theoretical predictions for the top quark decay rate are presented including QCD and electroweak radiative corrections. The possibilities for quarkonium searches at an hadron collider will be discussed. The perspectives for top production at an electron positron collider will be described in detail with emphasis on the behavior of the cross section and decay distribution in the threshold region.

Search for top quark flavour changing neutral currents in same-sign top quark production

The presence of the anomalous top quark flavour changing neutral current (FCNC) interactions leads to the production of same-sign top quarks in proton-proton collisions. The results of a search for events with same-sign dileptons and b-jets conducted by CMS collaboration with 10.5 $fb^{-1}$ of data collected in pp colisions at $\sqrt{s}=8$ TeV are used to obtain the constraints on the strength of top quark FCNC interactions. The 95$%$ confidence level upper limits on the branching ratios of top quark decays to a light quark $q=u,c$ and a gauge or a Higgs boson are set to be ${\cal B}R(t\righta…

Probing top quark electromagnetic dipole moments in single-top-plus-photon production

The production of a single top quark in association with an isolated photon probes the electromagnetic coupling structure of the top quark. We investigate the sensitivity of kinematical distributions at the LHC in single-top-plus-photon production in view of a detection of anomalous electric and magnetic dipole moments of the top quark.

Implications of the anomalous top quark couplings in $B_s-\bar{B}_s$ mixing, $B \to X_s γ$ and top quark decays

Combined analysis of recent measured $\bs$ mixing and $B \to X_s γ$ decays provides constraints on the anomalous $\bar{t}sW$ couplings. We discuss the perspectives to examine the anomalous $\bar{t}sW$ couplings through CKM-suppressed $ t \to s W$ decays at the LHC.

Top quark physics in hadron collisions

The top quark is the heaviest elementary particle observed to date. Its large mass makes the top quark an ideal laboratory to test predictions of perturbation theory concerning heavy quark production at hadron colliders. The top quark is also a powerful probe for new phenomena beyond the Standard Model of particle physics. In addition, the top quark mass is a crucial parameter for scrutinizing the Standard Model in electroweak precision tests and for predicting the mass of the yet unobserved Higgs boson. Ten years after the discovery of the top quark at the Fermilab Tevatron top quark physics …

Top Quark Physics at Hadron Colliders

I briefly report on what we can learn about the top quark at hadron colliders.

Polarization of top quark in vector-like quark decay

Vector-like quarks (VLQs) are attractive extensions to the Standard Model. They mix with the SM quarks and can lead to rich phenomenology. Determination of VLQ's interaction structure with the SM is then an important issue, which can be inferred from the decay products of VLQs, such as top quark. We calculate the spin-analyzing powers for charged leptons from top quark in VLQ decay for various VLQ scenarios. We find that the top polarization effect will be helpful to distinguish different natures of the VLQ couplings with the SM.

Top quark production near threshold and the top quark mass

We consider top-anti-top production near threshold in $e^+ e^-$ collisions, resumming Coulomb-enhanced corrections at next-to-next-to-leading order (NNLO). We also sum potentially large logarithms of the small top quark velocity at the next-to-leading logarithmic level using the renormalization group. The NNLO correction to the cross section is large, and it leads to a significant modification of the peak position and normalization. We demonstrate that an accurate top quark mass determination is feasible if one abandons the conventional pole mass scheme and if one uses a subtracted potential a…

顶夸克过程中对撞机对单圈阶SMEFT重夸克算符的敏感度

Collider sensitivity to SMEFT heavy-quark operators at one-loop in top-quark processes

本研究在SMEFT框架下首次计算单圈四顶夸克算符对LHC顶夸克对产生的贡献，验证相关模拟工具，给出两类过程的算符限制并比较其敏感度，同时给出HL-LHC的预期灵敏度。

Heavy quark dynamics for charm and bottom flavor on Fermi surface at zero temperature

We discuss the dynamics in finite density medium including a heavy impurity particle (hadron or quark) with a heavy flavor, charm and bottom, at zero temperature. As a system, we consider a $\bar{D}$ ($B$) meson embedded in nuclear matter as a heavy impurity boson with SU(2) isospin symmetry. As another system, we also consider a charm (bottom) quark embedded in quark matter as a heavy impurity fermion with SU(3) color symmetry. We suppose a vector current interaction with SU($n$) symmetry ($n \ge 2$) for the fermion composing the Fermi surface and the embedded heavy impurity particle, and cal…

Improving the Top Quark Forward-Backward Asymmetry Measurement at the LHC

At the LHC, top quark pairs are dominantly produced from gluons, making it difficult to measure the top quark forward-backward asymmetry. To improve the asymmetry measurement, we study variables that can distinguish between top quarks produced from quarks and those from gluons: the invariant mass of the top pair, the rapidity of the top-antitop system in the lab frame, the rapidity of the top quark in the top-antitop rest frame, the top quark polarization and the top-antitop spin correlation. We combine all the variables in a likelihood discriminant method to separate quark-initiated events fr…

Electroweak corrections to top-quark pair production in quark--antiquark annihilation

Top-quark physics plays an important role at hadron colliders such as the Tevatron at Fermilab or the LHC at CERN. Given the planned precision at these colliders, precise theoretical predictions are required. In this paper we present the complete electroweak corrections to QCD-induced top-quark pair production in quark--antiquark annihilation. In particular we provide compact analytic expressions for the differential partonic cross section, which will be useful for further theoretical investigations.

Top Quark Analysis in the Light Gluino Scenario

The Fermilab top quark analysis is heavily dependent on the assumption of standard model backgrounds only. In the light gluino scenario, the stop quarks lie near the top in mass and their decays can influence the resulting top quark mass by an amount that is not small relative to the currently quoted errors. Several slight anomalies in the top quark analysis find a natural explanation in the light gluino case.

Spin Correlation in Top-Quark Production at Hadron Colliders

We propose techniques to observe the correlation of the spins of top quarks and antiquarks at the Tevatron and the LHC. Observation of the spin correlation would confirm that the top quark decays before its spin flips, and would place a lower bound on the top-quark width and V_tb. The spin correlation may also be a useful tool to study the weak decay amplitude of the top quark.

Top-quark pole mass

The top quark decays more quickly than the strong-interaction time scale, $\lqcd^{-1}$, and might be expected to escape the effects of nonperturbative QCD. Nevertheless, the top-quark pole mass, like the mass of a stable heavy quark, is ambiguous by an amount proportional to $\lqcd$.

Top Quark Mass

The influence of the top quark mass on mixing processes and precise electroweak measurements is described. Experimental observation of the top quark in proton-antiproton collisions is discussed, and some brief remarks are made about electron-positron production. Some speculations are noted about the possible significance of the large top quark mass.

The Single Top Quark Physics

The single top quark production has an electroweak nature and provides an additional to the top pair production source of the top quarks. The processes involving single top have unique properties, they are very interesting from both theoretical and experimental view points. Short review of the single top quark production processes is given in the paper.

Singlet quarks beyond the top at the Tevatron?

The first evidence for the top quark at the Tevatron may indicate a cross section higher than the QCD expectation. We consider the possibility that isosinglet heavy quarks may be contributing to the signal and discuss ways of testing this possibility. For example, a charge $\case2/3$ singlet quark, approximately degenerate and mixing with the top quark, would effectively double the standard top signals. A charge $-\case1/3$ singlet quark mixing with the bottom quark would not affect top signals but would generate excess $Z+{}$multijet events with a $b$-tag.

Some Phenomenology of the top quark with non-standard couplings

In this talk I will use effective lagrangian and discuss possible new physics associated with top quark.

Spin Correlations in Top Quark Production at e^+ e^- Linear Colliders

The object of this thesis is to study the spin-spin correlations for top quark productions and their decay at polarized e^+e^- linear colliders. For the analyses of the spin-spin correlations in top quark production, we introduce a generic spin basis and show which spin basis is the most optimal. We discuss the spin-angular correlations for the top quark decay, and demonstrate that the directions of electro-weak decay products of polarized top quarks are strongly correlated to the top quark spin. We also explain how to measure the top quark spin using decay products. The spin correlations usin…

Gluon Radiation and Top Quark Physics

Radiation of gluons gives rise to extra jets in top quark events that can lead to complications in event reconstruction and mass measurement. I review recent results for gluon radiation in top quark production and decay, and discuss their implications for top quark physics.

NLO QCD corrections to single vector-like top partner production in association with top quark at the LHC

The single vector-like top partner hadroproduction in association with top quark in the five and the six-flavour schemes at the LHC is investigated. The inclusive cross section and the differential distributions are evaluated for many benchmark scenarios at leading and next-to-leading orders, both for fixed-order and fixed-order matched to parton shower. The associated Higgs production with a top quark pair, where the final state arises from the decay of the vector-like top partner into a Higgs boson and a top quark, is examined.

Determination of the top-quark mass from hadro-production of single top-quarks

We present a new determination of the top-quark mass $m_t$ based on the experimental data from the Tevatron and the LHC for single-top hadro-production. We use the inclusive cross sections of $s$- and $t$-channel top-quark production to extract $m_t$ and to minimize the dependence on the strong coupling constant and the gluon distribution in the proton compared to the hadro-production of top-quark pairs. As part of our analysis we compute the next-to-next-to-leading order approximation for the $s$-channel cross section in perturbative QCD based on the known soft-gluon corrections and implement…

Photon initiated single top quark production via flavor-changing neutral currents at the LHC

Single top quark production is a powerful process to search for new physics signs. In this work we propose and investigate a search for top quark flavor changing neutral currents (FCNC) via a photon using direct single top quark production events in proton-proton collisions at the LHC at CERN. We show that the direct single top quark final state can provide constraints on the strengths of tq$γ$ (top-quark-$γ$) and tqg (top-quark-gluon) FCNC couplings simultaneously. Results of a search for direct single top quark production at the LHC at a center-of-mass energy of 8 TeV performed by the ATLAS …

Gluon Radiation in Top Quark Production and Decay at $e^+e^-$ Colliders

We study gluon radiation in top quark production above threshold at high energy $e^+e^-$ colliders. We allow for the top quarks to be off-shell, considering radiation in both the top production and decay processes simultaneously. Our calculation includes all top width effects, spin correlations, and $b$ quark mass effects. We study the effects of gluon radiation on top mass reconstuction and examine the interference between production- and decay-stage radiation, which can be sensitive to the value of the top quark decay width.

Top Quark As A Topological Color Soliton

In this paper I propose an scenario for the top quark as a topological color soliton. I illustrate some features of the top quark as a soliton in a toy model based on nonlinear realization of the $SU(3)_L \times SU(3)_R / SU(3)_{L+R}$, with $SU(3)_{L+R}$ being the color gauge group.

Gauge created top quark condensate and heavy top

The scalar interaction term of the top mode standard model can be generated by a gauge theory. It is emphasized that in this approach generalization to family space directly yields a heavy top quark while leaving all other quarks massless. By generating the new interaction from gauge extension to custodial $SU(2)$, the standard model bound $m_{top} \stackrel{<}{\sim} 200 GeV$ is pushed to $m_{top} \stackrel{<}{\sim} 270 GeV$, thereby significantly reducing the amount of finetuning required to match this number.

Top Quark and Electroweak Symmetry Breaking Mechanism

After a brief comment on the role of top quark in models of electroweak symmetry breaking (EWSB), I shall discuss what we know about top quark interaction and how to improve that knowledge. Since bottom quark is the weak isospin partner of the top quark, its interaction with a scalar boson may also distinguish models of EWSB. We show that Tevatron can provide useful information through the associated production of a scalar with a bottom quark pair.

The Top Quark, QCD, and New Physics

The role of the top quark in completing the Standard Model quark sector is reviewed, along with a discussion of production, decay, and theoretical restrictions on the top quark properties. Particular attention is paid to the top quark as a laboratory for perturbative QCD. As examples of the relevance of QCD corrections in the top quark sector, the calculation of $e^+e^-\to t {\bar t}$ at next-to-leading-order QCD using the phase space slicing algorithm and the implications of a precision measurement of the top quark mass are discussed in detail. The associated production of a $t {\bar t}$ pair…

Effective Field Theory for Nonstandard Top Quark Couplings

We present an effective-field-theory calculation of the effect of a dimension-six operator involving the top quark on precision electroweak data via a top-quark loop. We demonstrate the renormalizability, in the modern sense, of the effective field theory. We use the oblique parameter U to bound the coefficient of the operator, and compare with the bound derived from top-quark decay.

Total and differential cross sections for Higgs and top-quark production

I present theoretical calculations for Higgs-boson and top-quark production, including high-order soft-gluon corrections. I discuss charged-Higgs production in association with a top quark or a $W$ boson, as well as single-top and top-antitop production. Total cross sections as well as transverse-momentum and rapidity distributions of the top quark or the Higgs boson are presented for various LHC energies.

Constraining top-quark couplings combining top-quark and $\boldsymbol{B}$ decay observables

We present a first, consistent combination of measurements from top-quark and $B$ physics to constrain top-quark properties within the Standard Model Effective Field Theory (SMEFT). We demonstrate the feasibility and benefits of this approach and detail the ingredients required for a proper combination of observables from different energy scales. Specifically, we employ measurements of the $t\bar tγ$ cross section together with measurements of the $\bar B\rightarrow X_sγ$ branching fraction to test the Standard Model and look for new physics contributions to the couplings of the top quark to t…

Top Quark Decays into Heavy Quark Mesons

For top quark decays into heavy quark mesons $Υ$ and $\bar{B}_c^*$ , a complete calculation to the leading order both in QCD coupling constant $α_s$ and in $v$, the typical velocity of the heavy quarks inside the mesons, is performed. Relatons between the top quark mass and the decay branching ratios are studied. Comparion with the results which are obtained by using the quark frangmentation functions is also discussed. The branching ratios are consistent (within a factor of $2\sim 3 $) with that obtained using fragmentation functions at $m_t\sim 150$ GeV.

Physics of Top Quark at the Tevatron

We discuss the physics of the top quark at the Fermilab Tevatron. By the year 2000, many properties of the top quark can be measured at the Tevatron.

Sudakov Expansions and Top Quark Physics at LHC

We review some peculiar features of Sudakov expansions in the calculation of electroweak radiative corrections in the MSSM at high energy. We give specific examples and consider in particular the process b g -> t W of single top quark production relevant for the top quark physics programme at LHC.

Top Quark Physics for Beautiful and Charming Physicists

I discuss two aspects of top-quark physics: V_tb and the top-quark mass. The similarities and differences with bottom and charm physics are emphasized.

The top quark mass and flavor mixing in a Seesaw model of Quark Masses

The top quark mass and the flavor mixing are studied in the context of a Seesaw model of Quark Masses based on the gauge group $SU(2)_L \times SU(2)_R \times U(1)$. Six isosinglet quarks are introduced to give rise to the mass hierarchy of ordinary quarks. In this scheme, we reexamine a mechanism for the generation of the top quark mass. It is shown that, in order to prevent the Seesaw mechanism to act for the top quark, the mass parameter of its isosinglet partner must be much smaller than the breaking scale of $SU(2)_R$. As a result the fourth lightest up quark must have a mass of the order …

Top Quark production dynamics

I discuss various aspects of the dynamics of top quark production both via the strong interaction (pair production) and via the charged current weak interaction (single top production).

Event generators for top quark production and decays

This contribution provides brief descriptions the current status of the basic Monte Carlo event generators for top-quark production and decays.

Improved Spin Basis for Angular Correlation Studies in Single Top Quark Production at the Tevatron

We show in single top quark production that the spin of the top quark is correlated with the direction of the d-type quark in the event. For single top production in the W* channel, the d-type quark comes dominantly from the antiproton at the Tevatron, whereas for the W-gluon fusion channel the spectator jet is the d-type quark the majority of the time at this machine. Our results are that 98% of the top quarks from the W* process have their spins in the antiproton direction, and 96% of the top quarks in the W-gluon fusion process have their spins in the spectator jet direction. We also compar…

Effective-Field-Theory Approach to Top-Quark Production and Decay

We discuss new physics in top-quark interactions, using an effective field theory approach. We consider top-quark decay, single top production, and top-quark pair production. We identify 15 dimension-six operators that contribute to these processes, and we compute the deviation from the Standard Model induced by these operators. The results provide a systematic way of searching for (or obtaining bounds on) physics beyond the Standard Model.

Master Integrals for the two-loop, non-planar QCD corrections to top-quark pair production in the quark-annihilation channel

We present the analytic calculation of the Master Integrals for the two-loop, non-planar topologies that enter the calculation of the amplitude for top-quark pair hadroproduction in the quark-annihilation channel. Using the method of differential equations, we expand the integrals in powers of the dimensional regulator $ε$ and determine the expansion coefficients in terms of generalized harmonic polylogarithms of two dimensionless variables through to weight four.

Top Quark Mass and Supersymmetry

We summarize the expectations for the top quark mass in supersymmetric models and discuss the potential implications of its value measured by the CDF group in Fermilab.

Electrical conductivity of quark matter in magnetic field

Fermion currents in dense quark matter embedded into magnetic field are under intense discussions motivated by Chiral Magnetic Effect. We argue that conductivity of quark matter may be independent of the magnetic field direction and not proportional to the magnetic field strength.

Does the quark-gluon plasma contain stable hadronic bubbles?

We calculate the thermodynamic potential of bubbles of hadrons embedded in quark-gluon plasma, and of droplets of quark-gluon plasma embedded in hadron phase. This is a generalization of our previous results to the case of non-zero chemical potentials. As in the zero chemical potential case, we find that a quark-gluon plasma in thermodynamic equilibrium may contain stable bubbles of hadrons of radius $R \simeq 1$ fm. The calculations are performed within the MIT Bag model, using an improved multiple reflection expansion. The results are of relevance for neutron star phenomenology and for ultra…

EMBEDDED DEFECTS AND SYMMETRY BREAKING IN FLIPPED $SU(5)$

We explicitly show the analogy between the symmetry breaking scheme for the GUT flipped $SU(5)$ with that of the Weinberg-Salam theory of electroweak interactions. This allows us to construct the embedded defect spectrum of the theory flipped $SU(5)$. We find that the spectrum consists of twelve gauge-equivalent unstable Lepto-quark strings, which are analogous to W-strings in electroweak theory, and another string that is gauge inequivalent to the Lepto-quark strings, which we call the `V-string'. The V-string is analogous to the Z-string of electroweak theory, correspondingly admitting a sta…

Recent results on top quark mass and properties and rare/anomalous top quarks interactions in CMS

The amount of data collected by the CMS experiment at the CERN LHC in the second data taking period provides the possibility to study absolute and differential cross sections of top quark interaction processes with high precision. Utilizing these results, fundamental standard model parameters such as the top quark mass are extracted. Moreover, given standard model measurements are interpreted in the context of Beyond the standard model theories. Recent results on top quark properties and rare or anomalous top quark interactions by CMS are presented in these proceedings. Furthermore, the implic…

Dependence of the top-quark mass measured in top-quark pair production on the parton distribution functions at the LHC and future colliders

The dependence of the top-quark mass measurement in top-quark production on the parton distribution functions is explored through the differential distribution of the invariant mass of the top-antitop system in top-quark pair production at hadron colliders. Several different proton-proton collider options are considered: 8 TeV, 13 TeV, 13.6 TeV, 14 TeV, and 100 TeV. The top-quark mass is obtained from a chi-squared fit to the invariant mass of the top-antitop-quark pair. The parton distribution function uncertainties are used in the chi-square evaluation. The uncertainties are reduced through …

Measuring Top Quark Polarization in Top Pair plus Missing Energy Events

The polarization of a top quark can be sensitive to new physics beyond the standard model. Since the charged lepton from top quark decay is maximally correlated with the top quark spin, it is common to measure the polarization from the distribution in the angle between the charged lepton and the top quark directions. We propose a novel method based on the charged lepton energy fraction and illustrate the method with a detailed simulation of top quark pairs produced in supersymmetric top squark pair production. We show that the lepton energy ratio distribution that we define is very sensitive t…