A resonance peak in the invariant mass spectrum has been the main feature of a particle at collider experiments. However, broad resonances not exhibiting such a sharp peak are generically predicted in new physics models beyond the Standard Model. Without a peak, how do we discover a broad resonance at colliders? We use machine learning technique to explore answers beyond common knowledge. We learn that, by applying deep neural network to the case of a $t\bar{t}$ resonance, the invariant mass $M_{t\bar{t}}$ is still useful, but additional information from off-resonance region, angular correlations, $p_T$, and top jet mass are also significantly important. As a result, the improved LHC sensitivities do not depend strongly on the width. The results may also imply that the additional information can be used to improve narrow-resonance searches too. Further, we also detail how we assess machine-learned information.
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 $10^{-18}e cm$.
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…
We study the case of a di-bottomonium $bb\bar b\bar b$ particle at the LHC. Its mass and decay width are obtained within a new model of diquark-antidiquark interactions in tetraquarks. The same model solves several open problems on the phenomenology of the experimentally better known $X,Z$ states. We show that the $bb\bar b\bar b$ tetraquark is expected approximately 100 MeV below threshold, and compare to a recent analysis by LHCb seeking it in the $Υμμ$ final state.
We perform a quantitative analysis of the $bb\bar{b}\bar{b}$ tetraquark decays into hidden- and open-bottom mesons and calculate, for the first time, the $bb\bar{b}\bar{b}$ tetraquark total decay width. On the basis of our results, we propose the $bb\bar{b}\bar{b} \to B^{+} B^{-} (B^0 \bar{B}^0) (B_s^0 \bar{B}_s^0) \to l^{+} l^{-}+\text{X}$ decays as the most suitable channels to observe the $bb\bar{b}\bar{b}$ tetraquark states, since the calculated two-lepton cross section upper limit, $\simeq 39 $ fb, is so large as to be potentially detectable with the 2018 LHCb sensitivity, paving the way …
We observe that the flavour symmetries of the Standard Model gauge sector, broken as they are in the Standard Model Yukawa Lagrangian, naturally suppress baryon and lepton number violation at low energies and, simultaneously, make it accessible at the LHC through resonant processes involving at least six fermions from all three generations. We establish a model independent classification of such transitions and identify two classes that give rise to particularly clean LHC signatures, namely $\bar t μ^+ e^+$ and $\bar t \bar t$ + jets.
The hadronic production of $D$-wave states of $\bar b c$ is studied. The relative yield of such states is estimated for kinematic conditions of LHC experiments.
A sizable rate of events, with several pairs of $b$-quarks produced contemporarily by multiple parton interactions, may be expected at very high energies as a consequence of the large parton luminosities. The production rates are further enhanced in hadron-nucleus reactions, which may represent a convenient tool to study the phenomenon. We compare the different contributions to $b{\bar b}b{\bar b}$ production, due to single and double parton scatterings, in collisions of protons with nuclei at the CERN-LHC.
We discuss charm production at LHC. The production of single $c \bar c$ pairs is calculated in the $k_t$-factorization approach. We use several unintegrated gluon distributions from the literature. Differential distributions for several charmed mesons are presented and compared to recent results of the ALICE and LHCb collaborations. Some missing strength can be observed. Furthermore we discuss production of two $c \bar c$ pairs within a simple formalism of double-parton scattering (DPS). Surprisingly large cross sections, comparable to single-parton scattering (SPS) contribution to $c \bar c$ …
We perform a quantitative analysis of the decays of $cc\bar c\bar c$ tetraquarks with $J^{PC}=0^{++}, 2^{++}$ into 4 muons and into hidden- and open-charm mesons and estimate, for the first time, the fully charmed tetraquark decay width. The calculated cross section upper limit is $\sim 40$ fb for the 4 muons channel, and $\sim 28$ nb for the $D^{(*)} \bar D^{(*)} \to eμ$ channel. On the basis of our results, with the present sensitivity LHCb should detect both signals, for $0^{++}$ and $2^{++}$ fully-charmed tetraquarks.
We study the possible production of the $ρ$-resonance from the Strong Electroweak Symmetry Breaking sector at LHC. Due to possibly enhanced couplings of $ρ$ to the top and bottom quarks we focus on the process pp -> b \bar{b} t \bar{t} where either b \bar{b} or t \bar{t} are the products of the $ρ$ decay.
In this paper, we study the sensitivity of the fraction of $t\bar{t}$ events arising from gluon-gluon fusion to the chromoelectric and chromomagnetic dipole moments (CEDM and CMDM) as well as the total and differential $t\bar{t}$ cross sections at the LHC and Tevatron. The sensitivity of measured charged asymmetry at the LHC to CEDM and CMDM is also studied. We find that at the Tevatron and the LHC, non-zero values of CMDM could suppress the $t\bar{t}$ production rate. It is shown that the ratio of $σ(gg\rightarrow t\bar{t})/σ(p\bar{p}\rightarrow t\bar{t})$ at the Tevatron is more sensitive to…
We consider the production of the new gauge boson $Z^{}_{μτ}$ predicted by the ${U(1)}_{L^{}_μ - L^{}_τ}$ model via SM-like Higgs boson $h^{}_{1}$ decaying in the ${t}\bar{t}h^{}_{1}$ production at LHC. Considering the current constraints on the relevant free parameters, we calculate its production cross section and further investigate the possibility of detecting $Z^{}_{μτ}$ through the process $pp\to{t(\to{bjj})}\bar{t}(\to{\bar{b}l^{-}\barν_{l}})h_{1}(\to{Z_{μτ}Z_{μτ}})\to{b\bar{b}jjl^{-}\barν_{l}}+/\!\!\!\!E_{T}$ at LHC. We find that $Z^{}_{μτ}$ might be detected via this process at LHC wi…
We calculate the amplitude of gg->bb(bar) production for the colour singlet, J_z=0 di-gluon state at O(α_S^2) order. We consider the cancellation, and a realistic cutoff, of the infrared divergent terms. We show that the one-loop radiative QCD contributions effectively reduce the Born level result for the central exclusive bb(bar) cross section at the LHC. This process is essentially the only irreducible QCD background to the exclusive H->bb(bar) signal.
The production of $c\bar{c}c\bar{c}$, $b\bar{b}b\bar{b}$ and $c\bar{c}b\bar{b}$ pairs considering double parton scattering at LHC energies is investigated. We estimate the contribution of saturation effects to the different final states and predict the energy dependence of the cross sections. Moreover, we estimate the ratio between the double and single parton scattering cross sections for the full rapidity range of the LHC and for the rapidity range of the LHCb experiment. For the full rapidity range we confirm a previous prediction, namely that for charm production the double parton scatteri…
In this paper, we investigate the effects of dimension six operators in the framework of the standard model (SM) effective field theory on using $t\bar{t}b\bar{b}$ channel at the LHC with the center-of-mass energy of 13 TeV. In this analysis, we only assume leptonic top-quarks. Once the events were simulated, the CMS-measured cross-section was used to constrain the corresponding effective Wilson coefficients at $95\%$ confidence level. Considering the SM effective Lagrangian, the $t\bar{t}b\bar{b}$ events in proton-proton collision were very sensitive to the effective Wilson coefficients $ \ba…
With an eye toward the precision physics of the LHC, FCC-ee and possible high energy muon colliders, we present the extension of the CEEX (coherent exclusive exponentiation) realization of the YFS approach to resummation in our KK MC to include the processes f\bar{f}\rightarrow f'\bar{f'}, f=μ,τ, q,ν_\ell, f'=e, μ,τ, q, ν_\ell, q=u,d,s,c,b,t, \ell =e,μ,τwith f \ne f'. After giving a brief summary of the CEEX theory with reference to the older EEX (exclusive exponentiation) theory, we illustrate theoretical results relevant to the LHC, FCC-ee, and possible muon collider physics programs.
We present the upgrade of the coherent exclusive (CEEX) exponentiation realization of the Yennie-Frautschi-Suura (YFS) theory used in our Monte Carlo ({\cal KK} MC) to the processes f\bar{f}\rightarrow f'\bar{f'}, f=μ,τ,q,ν_\ell, f'=e,μ,τ,q,ν_\ell, q=u,d,s,c,b,t, \ell=e,μ,τwith f\ne f', with an eye toward the precision physics of the LHC and possible high energy muon colliders. We give a brief summary of the CEEX theory in comparison to the older (EEX) exclusive exponentiation theory and illustrate theoretical results relevant to the LHC and possible muon collider physics programs.
We compute Gamma(H+ -> t \bar{b}) at one-loop in the MSSM and show how future data at the Tevatron and/or at the LHC could be used to unravel the potential SUSY nature of the charged Higgs.
Resonance searches generally focus on narrow states that would produce a sharp peak rising over background. Early LHC running will, however, be sensitive primarily to broad resonances. In this paper we demonstrate that statistical methods should suffice to find broad resonances and distinguish them from both background and contact interactions over a large range of previously unexplored parameter space. We furthermore introduce an angular measure we call ellipticity, which measures how forward (or backward) the muon is in eta, and allows for discrimination between models with different parity …
A feasibility study for an experimental analysis searching for $t\bar{t}H(H\rightarrow b\bar{b})$ production at the LHC and its high luminosity phase is presented in this note. Unlike search strategies currently being used in experimental collaborations, the present analysis exploits jet substructure techniques and focuses on the reconstruction of boosted Higgs bosons, to obtain sensitivity to the signal in a simple cut-based analysis. The $t\bar{t} +$ jets background may be constrained in the proposed analysis through a control region with very small signal contamination. Using this analysis …
One of the future goals of the LHC is to precisely measure the properties of Higgs boson. The associated production of Higgs boson and the top quark pair is a promising process to investigate the related Yukawa interaction and the properties of Higgs. Compared with the pure scalar sector in the Standard Model, the Higgs sector contains both scalar and pseudoscalar in many new physics models, which makes the $t\bar t H$ interaction more complex and provides a variety of phenomena. To investigate the $t\bar t H$ interaction and the properties of Higgs, we study the top quark spin correlation obs…
In the light of the 125 GeV Higgs ($h$) discovery at the Large Hadron Collider (LHC), one of the primary goals of the LHC and possible future colliders is to understand its interactions more precisely. Here we have studied the $h$-$b$-$\bar b$-$γ$ effective interaction terms arising out of gauge invariant dimension six operators in a model independent setting, as a potential source of new physics. Their role in some detectable final states have been compared with those coming from anomalous $h$-$b$-$\bar b$ interactions. We have considered the bounds coming from the existing collider and other…
We study the ratio of the cross sections for $t\bar{t}γ$ and $t\bar{t}$ production at the LHC. The presence of correlations between theoretical uncertainties of the two processes makes possible a precise determination of this observable. This can help to evidentiate effects of new physics that might reveal themselves only when sufficiently precise theoretical predictions are available. Our analysis is based on fully realistic simulations of $t\bar{t}γ$ and $t\bar{t}$ production in the dilepton decay channel, including complete off-shell and non-resonant effects at NLO QCD accuracy. We discuss …
We present state-of-the-art predictions for off-shell $t\bar{t}b\bar{b}$ production with di-lepton decays at the LHC with $\sqrt{s}=13$ TeV. Results are accurate at NLO in QCD and include all resonant and non-resonant diagrams, interferences and finite-width effects for top quarks and $W$ bosons. We discuss the impact of QCD corrections and assess theoretical uncertainties from scale and PDF dependence at the integrated and differential level. Additionally we investigate the size of contributions induced by initial-state $b$ quarks to the NLO cross section.
We report on state-of-the-art theoretical predictions for $pp\to t\bar{t}b\bar{b}$ including full off-shell effects in the di-lepton decay channel at NLO QCD accuracy. We briefly discuss the impact of NLO QCD corrections on differential distributions and also asses theoretical uncertainties from scale and PDF dependence. Furthermore, we propose a simple kinematic reconstruction in order to distinguish $b$ jets originating from top-quark decays from arising from gluon splittings.
We present a detailed discussion on the doubly charmed baryon $Ξ_{cc}$ production at the RHIC and LHC via the proton-nucleus ($p$-N) and nucleus-nucleus (N-N) collision modes. The extrinsic charm mechanism via the subprocesses $g+c\to (cc)[n]+\bar{c}$ and $c+c\to (cc)[n]+g$ together with the gluon-gluon fusion mechanism via the subprocess $g+g\to(cc)[n]+\bar{c}+\bar{c}$ have been taken into consideration, where the intermediate diquark is in $[n]=[^1S_0]_{\bf 6}$-state or $[^3S_1]_{\bar{\bf 3}}$-state, respectively. Total and differential cross sections have been discussed under various collis…
In this paper, we investigate the anomalous chromoelectric and chromomagnetic dipole moments of the top quark through top pair production in association with two photons at the LHC. We first present the strategy to reconstruct this process assuming a different source for background processes. Then, we focus on the existing constraints from inclusive top-pair production from the Tevatron and LHC, adding the new LHC measurement. Afterwards, we introduce the new cross section ratio $R_{2γ/γ}=σ_{t\bar{t}γγ}/σ_{t\bar{t}γ}$ and show the usefulness of this ratio in canceling most of the systematic un…
We have investigated non-standard $ν\bar νγ$ and $ν\bar νγγ$ couplings via $ν\bar ν$ production in a $γp$ collision at the LHC. We obtain 95\% confidence level bounds on $ν\bar νγ$ and $ν\bar νγγ$ couplings by considering three different forward detector acceptances; $0.0015 <ξ< 0.15$, $0.0015 <ξ< 0.5$ and $0.1 <ξ< 0.5$. We show that the reaction $p p\to pγp\to p ν\bar νq X$ provides more than eight orders of magnitude improvement in neutrino-two photon couplings compared to LEP limits.
We study the Standard Model Higgs and vector boson associated production with large transvese momentum at the 13 TeV LHC, followed by Higgs decay to bottom quark pair. Using mass-drop tagging and filtering techiques, we obtained the cross section of signal and background. The background mainly come from $Vb\bar{b}$, $t\bar{t}$ and single top production. In order to suppress them further, we combined the mass-drop tagging and filtering analysis with $N$-subjettiness jet shape. After performing $N$-subjettiness identification, the significance can be enhanced to 3.52$σ$ with current integrated l…
NNLO QCD corrections to the production and decay of top-quark pairs allow performing precision phenomenology in inclusive and fiducial phase spaces. State-of-the-art predictions for top-quark pair production and their comparison to recent collider data are discussed.
Torsion models constitute a well known class of extended quantum gravity models. In this work, one investigates the phenomenological consequences of a torsion field interacting with top quarks at the LHC. A torsion field could appear as a new heavy state characterized by its mass and couplings to fermions. This new state would form a resonance decaying into a top anti-top pair. The latest ATLAS $t\bar t$ production results from LHC 13 TeV data are used to set limits on torsion parameters. The integrated luminosity needed to observe torsion resonance at the next LHC upgrades are also evaluated,…
We investigate the hadronic production of the doubly heavy baryon $Ξ_{bc}$ at the large hadron collider (LHC), where contributions from the four $(bc)$-diquark states $(bc)_{\bf\bar{3},6}[^1S_0]$ and $(bc)_{\bf\bar{3},6}[^3S_1]$ have been taken into consideration. Numerical results show that under the condition of $p_T>4$ GeV and $|y|<1.5$, sizable $Ξ_{bc}$ events about $ 1.7\times 10^7$ and $3.5\times10^9$ per year can be produced for the center-of-mass energy $\sqrt{S}=7$ TeV and $\sqrt{S}=14$ TeV respectively. For experimental usage, the total and the interested differential cross-sections …
The Higgs boson $H$ has the largest coupling to the top quark $t$ among the standard model (SM) fermions. This is one of the ideal places to investigate new physics beyond SM. In this work, we study the potential of determining Higgs boson $CP$ properties at the LHC and future 33 TeV and 100 TeV $pp$ colliders by analysing various operators formed from final states variables in $t\bar{t}H$ production. The discrimination power from SM coupling is obtained with Higgs boson reconstructed from $ H\to γγ$ and $ H\to b \bar{b}$. We find that $t\bar{t}b\bar{b}$ process can provide more than 3$σ$ disc…
We calculate $c\bar{c}c\bar{c}$ and $b\bar{b}b\bar{b}$ production cross section in Double Parton Scattering (DPS) processes at the energies of LHC. In our calculation we include saturation effects in the gluon distribution. For charm production, our results confirm the prediction of a previous work in which saturation effects were neglected, namely that at the energies of LHC charm production in DPS processes becomes comparable with charm production in SPS. We also estimate the production of $c\bar{c}b\bar{b}$ in DPS. Our results indicate that at $\sqrt{s}=14$ TeV half of the total amount of b…
We investigate the possibility to detect the scalar Higgs boson decay $H\to b\bar b$ in the associated $Z$ and $b\bar b$ production at the LHC using the $k_T$-factorization QCD approach. Our consideration is based on the off-shell (i.e. depending on the transverse momenta of initial quarks and gluons) production amplitudes of $q^* \bar q^* \to Z H \to Z q^\prime \bar q^\prime$, $q^* \bar q^* \to Z q^\prime \bar q^\prime$ and $g^* g^* \to Z q^\prime \bar q^\prime$ partonic subprocesses supplemented with the Catani-Ciafoloni-Fiorani-Marchesini (CCFM) dynamics of parton densities in a proton. We …
Precision studies of the properties of the top quark represent a cornerstone of the LHC physics program. In this contribution we focus on the production of $t\bar{t}$ pairs in association with one hard jet and in particular on its connection with precision measurements of the top quark mass at the LHC. We report a summary of a full calculation of the process $pp \to e^+ν_eμ^-\barν_μb \bar{b}j$ at NLO QCD accuracy, which describes $t\bar{t}j$ production with leptonic decays beyond the Narrow Width Approximation (NWA), and discuss the impact of the off-shell effects through comparisons with NWA.…
In the following we present our recent results on the resummation of soft gluon corrections to the $pp\rightarrow t\bar{t}H$ cross section at the LHC. The resummation was carried out at next-to-next-to-leading-logarithmic (NNLL) accuracy using the Mellin space technique. Obtained results were matched to the NLO cross section. We show that the resummation leads to reduction of scale-variation uncertainty of the total $pp\rightarrow t\bar{t}H$ cross section.
In Randall-Sundrum models, the Kaluza-Klein (KK) excitations of the gluon, g_{KK} have enhanced couplings to the right-handed quarks. In the absence of a gg g_{KK} coupling in these models, the single production of a g_{KK} from an initial gg state is not possible. The search for other production mechanisms at the LHC, therefore, becomes important. We suggest that the associated production of a g_{KK} with a t t(bar) pair is such a mechanism. Our study shows that through this process the LHC can probe KK gluon masses in the range of 2.8 -- 2.9 TeV.
In the following we present our results on resummation of invariant mass threshold corrections for the $2 \to 3$ type hadronic production processes in the Mellin moment space formalism. This method is applied to the associated Higgs boson production process $pp \to t \bar{t} H$ at the LHC. The results for the total cross section, the differential distribution with respect to the invariant mass and their uncertainties are presented.
We perform resummation of soft gluon corrections to the total cross section for the process $pp \to t\bar{t}H$. The resummation is carried out at next-to-leading-logarithmic (NLL) accuracy using the Mellin space technique, extending its application to the class of $2 \to 3$ processes. We present an analytical result for the soft anomalous dimension for a hadronic production of two coloured massive particles in association with a colour singlet. We discuss the impact of resummation on the numerical prediction for the associated Higgs boson production with top quarks at the LHC.
We present state-of-the-art predictions for $t\bar{t}γ$ and $t\bar{t}Z(Z \to ν_\ell\barν_\ell)$ production in the fully leptonic channel at the LHC. The first process can provide key information on the strength and structure of the top-quark coupling to the photon. The invisible-decay channel $t\bar{t}Z(Z \to ν_\ell\barν_\ell)$ is an important SM background for Dark Matter searches in $t\bar{t}+E_{T}^{miss}$ final states. Our results are accurate to NLO in QCD and include all resonant and non-resonant diagrams, interferences and off-shell effects for top quarks and $W/Z$ bosons. As such, they …
We study the collider phenomenology of the electroweak phase transition and electroweak baryogenesis in the framework of the effective field theory. Our study shows that the effective theory using the dimension-6 operators can enforce strong first order phase transition and provide sizable CP violation to realize a successful electroweak baryogenesis. Such dimension-6 operators can induce interesting Higgs phenomenology that can be verified at colliders such as the LHC and the planning CEPC. We then demonstrate that this effective theory can originate from vector-like quarks and the triplet Hi…
Understanding the pattern of gluon radiation in $t \bar t$ production and decay processes is important for making an accurate determination of the top mass from the momenta of its decay products. The larger energy of the LHC $pp$ collider boosts the top cross section by a factor of 100 compared to that at the Tevatron, but it also increases the amount of additional gluon radiation. We calculate the cross section for gluon radiation in top production and decay at the LHC. The distributions of this radiation are presented and the exact matrix-element results are compared with results from the HE…
The production of two b-quark pairs is a prominent background for Higgs and New Physics searches in various extensions of the Standard Model. We present here the next-to-leading order QCD corrections to the quark induced subprocess using the GOLEM approach for the virtual corrections. We show that our result considerably improves the prediction and conclude that the inclusion of next-to-leading order effects is indispensable for reliable studies of four b-quark observables in hadronic collisions.
In the framework of the topcolor-assisted technicolor $(TC2)$ model, we study production of the neutral top-pion $π_{t}^{0}$ in association with a high-$p_{T}$ jet at the $LHC$, which proceeds via the partonic processes $gg\longrightarrow π_{t}^{0}g$, $gq\longrightarrow π_{t}^{0}q$, $q\bar{q}\longrightarrow π_{t}^{0}g$, $gb(\bar{b})\longrightarrow π_{t}^{0}b(\bar{b})$, and $b\bar{b}\longrightarrow π_{t}^{0}g$. We find that it is very challenging to detect the neutral top-pion $π_{t}^{0}$ via the process $pp\longrightarrow π_{t}^{0}+jet+X\to t\bar{t}+jet+X$, while the possible signatures of $π_…
We study open b\bar{b} production at large rapidity at the LHC in an attempt to pin down the gluon distribution at very low x. For the LHC energy of 7 TeV, at next-to-leading order (NLO), there is a large factorization scale uncertainty. We show that the uncertainty can be greatly reduced if events are selected in which the transverse momenta of the two B-mesons balance each other to some accuracy, that is |\vec p_{1T}+\vec p_{2T}| < k_0. This will fix the scale μ_F \simeq k_0, and will allow the LHCb experiment, in particular, to study the x-behaviour of gluon distribution down to x ~ 10^{-5}…
Sizable amount of heavy-quarkonium events can be produced through $W$-boson decays at the LHC. Such channels will provide a suitable platform to study the heavy-quarkonium properties. The "improved trace technology", which disposes the amplitude ${\cal M}$ at the amplitude-level, is helpful for deriving compact analytical results for complex processes. As an important new application, in addition to the production of the lower-level Fock states $|(Q\bar{Q'})[1S]>$ and $|(Q\bar{Q'})[1P]>$, we make a further study on the production of higher-excited $|(Q\bar{Q'})>$-quarkonium Fock states $|(Q\ba…
In this paper, a combined resummation of soft and Coulomb corrections is performed for the associated production of the Higgs boson with a top quark pair at the LHC. We illustrate the similarities and critical differences between this process and the $t\bar{t}$ production process. We show that up to the next-to-leading power, the total cross section for $t\bar{t}h$ production admits a similar factorization formula in the threshold limit as that for $t\bar{t}$ production. This fact, however, is not expected to hold at higher powers. Based on the factorization formula, we perform the resummation…
We propose a new search for Dark Matter at the LHC, characteristic of scenarios beyond the Standard Model with a pseudoscalar portal between the visible and dark sectors. This search, leading to a $\bar{b} b Z( \rightarrow \ell\ell) + E_{T} \hspace{-4mm}/\hspace{2mm}$ final state, reaches large regions of parameter space not probed by Dark Matter searches via multi-jet $+ E_{T} \hspace{-4mm}/\hspace{2mm}$, searches for new scalars and flavour bounds. We show that this search could be used to test the Dark Matter origin of the gamma ray Galactic Centre excess with LHC Run 2 data.
We consider the top quark charge asymmetry in the process $pp \to t\bar{t}+γ$ at the 13 TeV LHC. The genuine tree level asymmetry in the $q\bar{q}$ channel is large with about -12%. However, the symmetric $gg$ channel, photon radiation off top quark decay products, and higher order corrections wash out the asymmetry and obscure its observability. In this work, we investigate these effects at next-to-leading order QCD and check the robustness of theoretical predictions. We find a sizable perturbative correction and discuss its origins and implications. We also study dedicated cuts for enhancing…
The associated production of a Higgs boson and a top-quark pair, $t{\bar t} H$, in proton-proton collisions is addressed in this paper for a center of mass energy of 13TeV at the LHC. Dileptonic final states of $t{\bar t}H$ events with two oppositely charged leptons and four jets from the decays $t\rightarrow bW^+ \rightarrow b \ell^+ν_\ell$, $\bar{t}\rightarrow \bar{b}W^- \rightarrow \bar{b} \ell^-\barν_\ell$ and $h\rightarrow b\bar{b}$, are used. Signal events, generated with MadGraph5_aMC@NLO, are fully reconstructed by applying a kinematic fit. New angular distributions of the decay produc…
A method using jets is investigated for detecting the Higgs boson at LHC in the mass range about 114 \GeVc2, suggested by LEP experiments. Higgs bosons are produced in association with a $t \bar{t}$ pair, and both t and $\bar{t}$ decay semileptonically to reduce the QCD background. After appropriate cuts, the signal is compared with the main background, $t \bar{t} + 2$ jets. This estimate, using a reasonable approximation for the dominant background $t\bar {t}gg$, suggests a $5.1σ$ effect. This method is seen to be complimentary to the two gamma signal. The $t\bar{t}Z$ channel, with Z decaying…
We study the charge asymmetry between the $t$ and $\bar t$ quark at the LHC, when they are produced in association with a $W$ boson. Though sizably reducing the cross section with respect to the inclusive production, requiring a $W$ boson in the final state has two important implications. First, at leading order in QCD, $t \bar t W^{\pm}$ production can only occur via $q \bar q$ annihilation. As a result, the asymmetry between the $t$ and $\bar t$ generated at NLO in QCD is significantly larger than that of inclusive $t \bar t$ production, which is dominated by gluon fusion. Second, the top qu…
In this paper we consider the production of proton-antiproton pairs in two-photon interactions in electron-positron and heavy-ion collisions. We try to understand the dependence of the total cross section on the photon-photon c.m. energy as well as corresponding angular distributions measured by the Belle Collaboration for the $γγ\to p \bar{p}$ process. To understand the Belle data we include the proton-exchange, the $f_2(1270)$ and $f_2(1950)$ $s$-channel exchanges, as well as the hand-bag mechanism. The helicity amplitudes for the $γγ\to f_{2} \to p \bar{p}$ process are written explicitly ba…
We discuss our recent progress on improving the theoretical description of the $pp \to t\bar{t}W^\pm$ process with particular focus on fiducial signatures that include top-quark decays. We employ a wide range of techniques from parton shower matching, narrow width approximation to full off-shell computations to assess the importance of the different modeling approaches.
We report on the calculation of the next-to-leading order QCD corrections to the production of a $t\bar{t}$ pair in association with two heavy-flavour jets. We concentrate on the di-lepton $t\bar{t}$ decay channel at the LHC with $\sqrt{s}=13$ TeV. The computation is based on $pp \to e^+ ν_e\, μ^-\barν_μ\, b\bar{b} \,b\bar{b}$ matrix elements and includes all resonant and non-resonant diagrams, interferences and off-shell effects of the top quark and the $W$ gauge boson. As it is customary for such studies, results are presented in the form of inclusive and differential fiducial cross sections…
Baryon triality (B3) is a Z3 discrete symmetry that can protect the proton from decay. Although its realization does not require supersymmetry, it is particularly appealing in the supersymmetry as an alternative to the popular R-parity. We discuss the issues in gauging B3, and present the minimal supersymmetric model with B3 as the remnant discrete symmetry of a TeV scale U(1) gauge symmetry. A flavor-dependent U(1) charge is necessary to achieve this, and it results in very distinguishable and flavorful predictions for the LHC experiments. We find a complementarity between a 2-lepton sneutrin…
Having a mass comparable to the weak scale, the top quark may have a sizable flavor changing couplings to Higgs bosons. We show that such couplings can be probed at the LHC through the parton subprocess $c(\bar c)g \to t (\bar t)A^0$, where the pseudoscalar $A^0$ subsequently decays into $t \bar c$ or ${\bar t} c$, giving rise to the intriguing final state of like sign top quark pairs. We also discuss major backgrounds to the above signal, in particular the QCD-Weak process $q\bar q' \to W^+(W^-) t \bar t$. The issue of background reduction is briefly discussed.
We investigate the impact of the fourth generation quarks on production and decays of the charged Higgs boson at CERN Large Hadron Collider (LHC) with triple $b$-tagging. The signal is the process $gg\to \bar{u_4}u_4$, followed by $\bar{u_4}\to W^{-} \bar{b}$ and $u_4\to h^{+} b$ decays with subsequent $h^{+}\to t \bar{b}$ and corresponding hermitic conjugates. It is shown that, if $m_{u_{4}}= 400$ GeV, considered process will provide unique opportunity to discover charged Higgs boson with mass range of 200 to 350 GeV at the first years of the LHC run.
We calculate α^{2}α_{s}^{2} order QED contribution to J/ψproduction in pp(\bar{p})\to J/ψ+c\bar{c} color-singlet process at the Tevatron and LHC in the framework of non-relativistic QCD. The contribution of the interference between the α^{2}α_{s}^{2} QED and α_{s}^{4} QCD is also taken into account. The J/ψproduction associated with a charm quark pair could be a measurable signal at hadron collider experiment. Our calculations show that by including the QED contribution, the p_{t} distribution is enhanced by a factor of 1.5 (1.9) at the Tevatron (LHC) at p_{t}=50 (100) GeV. In addition, the po…
