The top quark is the heaviest elementary particle in the Standard Model (SM). For this reason, a precise determination of its mass $m_t$ is part of the LHC physics program. The most accurate determinations of $m_t$ rely on the kinematic reconstruction of the top decay products and on the use of Monte Carlo event generators. In these proceedings I discuss the impact of different theoretical descriptions for the process of top pair production at the LHC on the extraction of $m_t$.
The High-Luminosity LHC is expected to provide $3 ab^{-1}$ of integrated luminosity. As a result billions of events containing top quarks will be detected at the CMS and ATLAS experiments, allowing for precise measurements of the top quark properties. The experimental challenges that will be faced in a high luminosity environment, with a special focus on top quark related observables are examined. We discuss prospects for measuring top quark anomalous couplings at the HL-LHC. Projections for detecting flavor changing neutral currents involving top quarks are also reviewed.
We study the hadronic production of four-quark states with double heavy quarks and double light antiquarks at LHC. The production mechanism is that a color anti-triplet diquark cluster consisting of double heavy quarks is formed first from the produced double heavy quark-antiquark pairs via $gg$ fusion hard process, followed by the fragmentation of the diquark cluster into a four-quark (tetraquark) state. Predictions for the production cross sections and their differential distributions are presented. Our results show that it is quite promising to discover these tetraquark states in LHC experi…
We study the precision with which the t-channel single top quark production cross section is expected to be measured in future LHC runs at 14 TeV. The single top final state has a lepton and neutrino from the top quark decay plus two jets, one of which is required to be b-tagged. This measurement is done in the context of the Snowmass 2013 study for the low-luminosity 14 TeV and the high-luminosity 14 TeV LHC as well as for high-luminosity 33 TeV LHC.
The LHCb collaboration has recently performed a first measurement of the angular production asymmetry in the distribution of beauty quarks and anti-quarks at a hadron collider. We calculate the corresponding standard model prediction for this asymmetry at fixed-order in perturbation theory. Our results show good agreement with the data, which is provided differentially for three bins in the invariant mass of the $b \bar b$ system. We also present similar predictions for both beauty-quark and charm-quark final states within the LHCb acceptance for a collision energy of $\sqrt{s} = 13 \, {\rm Te…
We update the theoretical precision of the total cross section for direct top quark production at the LHC by extending the threshold resummation to the next-to-next-to-leading logarithmic accuracy.
Theoretical predictions for standard model (SM) processes involving top quarks, such as top quark-antiquark pair or single top production, depend on fundamental SM parameters like the strong coupling constant or the top quark mass. By confronting predictions with measurements performed at the ATLAS and CMS Collaboration using data collected at the CERN LHC in the second data taking period, these parameters can be determined precisely. In these proceedings, recent results measuring SM and top quark properties are presented.
Selected topics of the top-quark mass measurements in well-defined schemes are presented. The measurements have been performed using data recorded with the ATLAS and CMS detectors at the LHC at proton-proton centre-of-mass energies of 7 and 8 TeV. Precision theoretical QCD calculations for both inclusive top-antitop quark pair production and top-antitop quark pair production with an additional jet to extract the top quark mass in the pole-mass scheme have been used.
Alternative top quark mass determinations can provide inputs to the world average with orthogonal systematic uncertainties and may help to refine the interpretation of the standard method. Among a number of recent results I focus on the extractions by ATLAS and CMS of the top quark pole mass from the top quark pair and tt + 1 jet production cross-section, which have now reached a precision of 1%.
Resonant production of fourth chiral family up quark at the LHC via anomalous interactions have been analyzed. It is shown that search for resonances in W^{+}b final states could lead to discovery of the fourth chiral family and simultaneously determine scale of the new physics, presumabely related to the quark and lepton compositeness. Obtained results emphasize an importance of W-leading jet invariant mass analysis in search for W+jets final states at the LHC, both with and without b-tagging.
I present the latest calculations of total and differential cross sections for top-antitop pair production and single top quark production via all main partonic channels. Higher-order corrections from the resummation of soft gluons are added through NNLL accuracy. Detailed numerical results are presented for approximate NNLO cross sections and top quark transverse momentum distributions at the Tevatron and LHC colliders.
We illustrate the utility of jet mass distributions as probes of new physics at the LHC, focusing on a heavy vector-quark doublet that mixes with the top as a concrete example. For 1 TeV vector-quark masses, we find that signals with greater than 5 sigma significance can be achieved after 100 fb^-1. More generally, jet mass distributions have the potential to provide signals for heavy states that produce highly boosted weak gauge bosons and/or top quarks.
We report on the current status of knowledge on inclusive quarkonium production in high-energy photon-photon collisions. As a perspective for the LHC, we compute various production cross sections via direct photon-photon fusion in ultra-peripheral pp, pA and AA collisions at the LHC using the tree-level quarkonium amplitude generator MadOnia.
The recently reported effect of long-range near-side angular correlations at LHC occurs for large multiplicities of particles with $1\,GeV\,<p_T\,<\,3\,GeV$. To understand the effect several possibilities have been discussed. In the letter we propose a simple qualitative mechanism which corresponds to gluon bremstralung of quarks moving with acceleration appropriate to the quark--anti-quark string. The smallness of azimuthal angle difference $Δϕ$ along with large $Δη$ at large multiplicities in this interval of $p_T$ are natural in the mechanism. The mechanism predicts also bremstralung photon…
We analyze the collider signatures of models with a vector-like top-prime quark and a massive color-octet boson. The top-prime quark mixes with the top quark in the Standard Model, leading to richer final states than ones that are investigated by experimental collaborations. We discuss the multi-lepton final states, and show that they can provide increased sensitivity to models with a top-prime quark and gluon-prime. Searches for new physics in high multiplicity events are an important component of the LHC program and complementary to analyses that have been performed.
Almost two decades after its discovery at Fermilab's Tevatron collider experiments, the top quark is still under the spotlight due to its connections to some of the most interesting puzzles in the Standard Model. The Tevatron has been shut down two years ago, yet some interesting results are coming out of the CDF and D0 collaborations. The LHC collider at CERN produced two orders of magnitude more top quarks than Tevatron's, thus giving birth to a new era for top quark physics. While the LHC is also down at the time of this writing, many top quark physics results are being extracted out of the…
Quark partners with non-chiral couplings appear in several extensions of the Standard Model. They may have non-trivial generational structure to their couplings, and may be produced either in pairs via the strong and EM interactions, or singly via the new couplings of the model. Their decays often produce heavy quarks and gauge bosons, which will contribute to a variety of already-measured "Standard Model" cross-sections at the LHC. We present a study of the sensitivity of such published LHC measurements to vector-like quarks, first comparing to limits already obtained from dedicated searches,…
I briefly discuss some theoretical aspects of top mass measurements at the LHC. In particular, I illustrate a recent theoretical study performed using next-to-leading order (NLO) calculations interfaced to shower generators (NLO+PS) of increasing accuracy, interfaced to both Pythia8 and Herwig7 Monte Carlo generators.
New vector-like quarks can have sizable couplings to first generation quarks without conflicting with current experimental constraints. The coupling with valence quarks and unique kinematics make single production the optimal discovery process. We perform a model-independent analysis of the discovery reach at the Large Hadron Collider for new vector-like quarks considering single production and subsequent decays via electroweak interactions. An early LHC run with 7 TeV center of mass energy and 1 fb-1 of integrated luminosity can probe heavy quark masses up to 1 TeV and can be competitive with…
We investigate collider signatures of a top-philic W' model, in which the W' boson couples only to the third-generation quarks of the standard model. The main discovery channel for this W' is through associated production of the W' and top quark, yielding a top-quark pair plus an extra bottom quark jet as a signal. We do a full simulation of the signal and relevant backgrounds. We develop a method of analysis that allows us to conclude that discovery of the W' is promising at the LHC despite large standard model backgrounds. Bottom quark tagging of the extra jet is key to suppressing the backg…
The asymmetry in the forward region production cross section of D^\pm is calculated using the heavy-quark recombination mechanism for pp collisions at 7 TeV. By suitable choices of four non-perturbative parameters, our calculated results can reproduce those obtained at LHCb. We find A_p ~ -1% when integrated over 2.0 GeV < p_T < 18 GeV and 2.2< eta <4.75, which agrees with A_p=-0.96\pm0.26\pm0.18% as measured by LHCb. Furthermore, the calculated distributions in eta and p_T agree reasonably well with those obtained at LHCb.
We quantify the constraints on the flavour separation between the quarks and antiquarks in the proton provided by the recent forward weak gauge boson production data from the LHCb experiment at $\sqrt{s}=7$ and 8 TeV. Performed in the framework of the NNPDF3.1 global analysis, this study highlights the key role that the LHCb W and Z data have in achieving a robust quark flavour separation in the large-x region, including the strange and charm quarks. We demonstrate how the LHCb measurements lead to improved determinations of the the up and down quark PDFs in the region $x\ge 0.1$, with an unce…
The production of four top quarks is a rare process in the Standard Model that provides unique opportunities and sensitivity to Standard Model observables including potential enhancement from many popular new physics extensions. This article summarises the latest experimental measurements of the four-top quark production cross section at the LHC. An overview of the interpretations of the experimental results in terms of the top quark Yukawa coupling and limits on physics beyond the Standard Model is also given as well as prospects for future measurements and opportunities offered by this chall…
In this paper, the soft gluon resummation effect in double heavy quarkonium production at the LHC is studied. By applying the transverse momentum dependent factorization formalism, the large logarithms introduced by the small total transverse momentum of heavy quarkonium pair final state system, are resummed to all orders in the expansion of the strong interaction coupling at the Next-to-Leading Logarithm accuracy. We also compare our result with the LHC data. We find that the distribution shape predicted by resummation calculation is consistent with experimental data very well. Since this pro…
This review summarizes the highlights in the area of top quark physics obtained with the two general purpose detectors ATLAS and CMS during the first two years of operation of the Large Hadron Collider LHC. It covers the 2010 and 2011 data taking periods, where the LHC provided pp collisions at a center-of-mass energy of sqrt(s)=7 TeV. Measurements are presented of the total and differential top quark pair production cross section in many different channels, the top quark mass and various other properties of the top quark and its interactions, for instance the charge asymmetry. Measurements of…
In this paper, we examine the sensitivity of the three-top quark production at the LHC to the top quark flavor-changing neutral currents (FCNC) as well as the sensitivity of the four-top production to the strong and weak dipole moments of the top quark. Upper limits at $95\%$ CL on the branching fractions of $\mathcal{B}(t\rightarrow qX)$, where $X = g, Z, γ, H$ and $q=u,c$, are set by performing an analysis on three-top events in the same-sign dilepton channel. We consider the main sources of the background processes and a realistic detector simulation is performed at the center-of-mass energ…
The forward LHCb acceptance offers the possibility of measuring the top-quark pair asymmetry in a kinematic region that does not receive overwhelming dilution from the symmetric gluon-fusion channel. To investigate this possibility, two leptonic final states are identified, and analysis strategies are proposed for each channel with 14~TeV data. Leading fixed-order predictions are then provided for the relevant leptonic asymmetry variables in each channel. If backgrounds can be experimentally constrained, statistically, a non-zero asymmetry is estimated to be observable beyond 5$σ$ confidence l…
We investigate the discovery potential of light color-octet bosons in the mass range of 100 - 400 GeV in exclusive top-pair plus jet production at the LHC. We study the impact of such bosons on the incline, the energy and the rapidity asymmetries. We show that light axigluons with large couplings to quarks can be discovered at the LHC with a luminosity of a few inverse fb. Almost all of the considered axigluon parameter space can be probed using the already available 2011/2012 LHC data. In a small-coupling scenario, axigluons could be discovered using the charge asymmetry with 65 inverse fb at…
We consider transverse-momentum resummation for top-quark pair production in hadron collisions. At small transverse momenta of the top-quark pair, the logarithmically-enhanced QCD contributions are resummed to all orders up to next-to-leading logarithmic accuracy. At intermediate and large values of transverse momenta, the resummation is consistently combined with the complete result at fixed perturbative order. We present numerical results for the transverse-momentum distribution of top-quark pairs at LHC energies. We perform a detailed study of the scale dependence of the results to estimate…
Focusing attention on top-quark pair production and its decay processes at the LHC, non-standard top-quark couplings are studied based on the effective Lagrangian constructed with SU(3)X SU(2)X U(1) invariant dimension-6 operators. The optimal-observable analysis is carried out for the charged-lepton distributions in pp -> t t-bar X -> l^+ X' (l=e or mu) in order to estimate the expected statistical uncertainties in measurements of those non-standard t t-bar g and tbW couplings that contribute to this process in the leading order.
Higgs production in association with a photon at hadron colliders is a rare process, not yet observed at the LHC. We show that this process is sensitive to significant deviations of Higgs couplings to first and second generation SM quarks (particularly the up-type) from their SM values, and use a multivariate neural network analysis to derive the prospects of the High Luminosity LHC to probe deviations in the up and charm Higgs Yukawa couplings through $h + γ$ production.
We calculate the finite part of the heavy quark impact factor at next-to-leading logarithmic accuracy in a form suitable for phenomenological studies such as the calculation of the cross-section for single bottom quark production 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.
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.
We present hadron-level predictions from the Monte-Carlo generator CASCADE and numerical calculations of beauty quark and quarkonium production in the framework of the kt-factorization approach for LHC energies. Our predictions are compared with the CMS experimental data.
LHC is expected to be a top quark factory. If the fundamental Planck scale is near a TeV, then we also expect the top quarks to be produced from black holes via Hawking radiation. In this paper we calculate the cross sections for top quark production from black holes at the LHC and compare it with the direct top quark cross section via parton fusion processes at next-to-next-to-leading order (NNLO). We find that the top quark production from black holes can be larger or smaller than the pQCD predictions at NNLO depending upon the Planck mass and black hole mass. Hence the observation of very h…
We discuss the discovery potential of the bound states of singlet quarks at LHC. We find that it is possible to discover bound states of singlet quarks at LHC with singlet quark masses up to 300 Gev for $e_{Q} = \frac{2}{3}$ and up to 200 Gev for $e_{Q} = -\frac{1}{3}$.
The determination of the electromagnetic dipole moments of the top quark is one of the most important goals of the top quark physics program in the collider experiments. For this reason, the top quark pair production to investigate the sensitivity on the electric and magnetic dipole moments of the top quark via the process $pp\rightarrow p γp \rightarrow p t \bar{t} X$ at the Large Hadron Collider (LHC), the High-Luminosity Large Hadron Collider (HL-LHC) and High-Energy Large Hadron Collider (HE-LHC) is discussed. We apply pure leptonic and semileptonic decays for top quark pair production in …
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.
The average charged hadron multiplicities induced by top quark decays are calculated in pQCD at LHC energies. Different modes of top production are considered. Proposed measurements can be used as an additional test of pQCD calculations independent on a fragmentation model.
The ratios of particle densities in lead-lead and proton-lead collisions to particle density in proton-proton collision in the central rapidity region at the LHC energy are predicted on the basis of wounded quark-diquark model.
Soft multiparticle production processes in hadronic collisions are considered in the framework of the Quark-Gluon Strings Model and the model predictions are compared with data from SppS and Tevatron. Predictions for LHC energies are given.
We study the radiative correction to $p_\perp$-broadening of a fast quark in a quark-gluon plasma beyond the soft gluon approximation. We find that the radiative contribution to quark $\langle p_\perp^2\rangle$ for RHIC and LHC conditions is negative.
We propose to extract the electric and weak dipole moments of the top quark via $t\bar tγ$ and $t\bar t Z$ productions at the CERN LHC. With the large numbers of events available at the LHC, these dipole moments can be measured to the accuracy of $10^{-18}e cm$.
We comment on the calculation of the finite part of the heavy quark impact factor at next-to-leading logarithmic (NLx) accuracy. The result is presented in a form suitable for phenomenological studies such as the calculation of the cross-section for single heavy quark production at the LHC within the kT-factorization scheme.
A new version of the $k_T$ factorization approach is formulated for the high energy heavy quark production. The results are in reasonable agreement with the experimental data at LHC energies.
Top like vector quarks arising from underlying strong sectors are expected to have large decay widths pushing them beyond the narrow width approximation. In this paper we consider a broad colored vector quark that strongly couples to an exotic pseudoscalar. We use the full 1PI resummed propagator for the exotic quark to recast the present LHC constraints ruling out masses below $\sim1.2~(1.1)$ TeV for width to mass ratio of $0.1~(0.6)$. We utilize machine learning techniques that are demonstratively more efficient than traditional cut based searches to present the reach of HL-LHC on the parame…
Elastic $pp$ scattering at LHC energies is treated in Additive Quark Model together with Pomeron exchange theory. The obtained results are compared with the new experimental data on the ratio of real to imaginary part of the scattering amplitude at the small transverse momenta
Vector-like quark is a common feature in many new physics models. We study the vector-like quark production as an s-channel resonance at the Large Hadron Collider for the vector-like quarks mainly mixing with the top- and bottom-quark in the Standard Model. We emphasize that the leptonic angular distribution can be used to discriminate various vector-like quark models.
I briefly overview the methods employed at the LHC to extract the top-quark mass, taking particular care about the theory uncertainty and the dependence on the Monte Carlo hadronization parameters.
Although Tevatron has discovered top quark and LHC (pp collisions) has discovered Higgs boson but the RHIC and LHC heavy-ion colliders have not discovered thermalized quark-gluon plasma (QGP). This is because the experimental data of top quark at Tevatron and the experimental data of Higgs boson at LHC are compared with the exact first principle calculation but the experimental data at RHIC and LHC are compared with simplistic models and assumptions which are not exact first principle calculation. In this paper we show that the exact first principle method to study quark-gluon plasma at RHIC a…
Electroweak production of single top quarks is an as-yet-unverified prediction of the Standard model, potentially sensitive to new physics. Two of the single top quark productions channels have significant charge asymmetries at the LHC, while the much larger background from $t\bar{t}$ is nearly charge-symmetric. This can be used to reduce systematic uncertainties and make precision measurements of single top quark production.
The $αm_t^2/m_W^2$ order supersymmetric electroweak corrections arising from loops of chargino, neutralino, and squark to top quark pair production by $gg$ fusion at LHC are calculated in the minimal supersymmetric model. We found that the corrections amount about a few percent.
We study the combined effects of both strong and electroweak dimension six effective operators on flavour changing top quark physics at the LHC. Analytic expressions for the cross sections and decay widths of several flavour changing processes will be presented, as well as an analysis of the feasibility of their observation at the LHC.
Recent results on production of $J/ψ$ pairs in LHCb initiated discussion on double parton scattering (DPS) contribution to this process, which is not yet elaborated well. In this short report $J/ψχ_c$ and $J/ψΥ$ modes are proposed for DPS studies. Estimations for $ΥΥ$ and $J/ψΥ$ production in LHCb are presented.
