High Energy LHC Research Articles

Search potential of the high energy-large hadron collider for spin-1/2 excited quarks in di-jet final state

Composite models, which suggest a possible substructure of fundamental particles, can be directly proven by the discovery of the excited quark. Higher energy and higher-luminosity particle colliders are needed to discover the composite structure predicted in the proposed models. The High Energy Large Hadron Collider (HE-LHC) has the potential to be a possible discovery machine for composite models. In this collider, with a center-of-mass energy of 27 TeV and integrated luminosity between 750 and 15000 fb\textsuperscript{-1}, we calculated the exclusion, observation, and discovery limits for the mass of spin-1/2 excited quark in the \textit{di-jet} final state, as well as the attainable compositeness scale values. In addition to these calculations, we scanned free parameters from 0.06 to 1 to determine the HE-LHC potential to reveal spin-1/2 excited quark.

Single production of an exotic vectorlike Y quark at future high energy pp colliders

Vectorlike quarks have been predicted in various new physics scenarios beyond the Standard Model. In a simplified modelling of a (B,Y) doublet including a vectorlike quark Y, with charge −43e, there are only two free parameters: the Y coupling κY and mass mY. In the five flavor scheme, we investigate the single production of the Y state decaying into Wb at the Large Hadron Collider (LHC) run-III and High-Luminosity LHC (HL-LHC) operating at s=14 TeV, the possible High-Energy LHC (HE-LHC) with s=27 TeV as well as the Future Circular Collider in hadron-hadron mode (FCC-hh) with s=100 TeV. Through detailed signal-to-background analyses and detector simulations, we assess the exclusion capabilities of the Y state at the different colliders. We find that this can be improved significantly with increasing collision energy, especially at the HE-LHC and FCC-hh, both demonstrating an obvious advantage with respect to the HL-LHC in the case of high mY. Assuming a 10% systematic uncertainty on the background event rate, the exclusion capabilities are summarized as follows: (1) the LHC run-III can exclude the correlated regions of κY∈[0.06,0.5] and mY∈[1500 GeV,3800 GeV] with integrated luminosity L=300 fb−1; (2) the HL-LHC can exclude the correlated regions of κY∈[0.05,0.5] and mY∈[1500 GeV,3970 GeV] with L=3 ab−1; (3) the HE-LHC can exclude the correlated regions of κY∈[0.06,0.5] and mY∈[1500 GeV,6090 GeV] with L=3 ab−1; (4) the FCC-hh can exclude the correlated regions of κY∈[0.08,0.5] and mY∈[1500 GeV,10080 GeV] with L=3 ab−1. Published by the American Physical Society 2024

Improving sensitivity of trilinear R-parity violating SUSY searches using machine learning at the LHC

In this work, we have explored the sensitivity of multilepton final states in probing the gaugino sector of a R-parity violating supersymmetric scenario with specific lepton number violating trilinear couplings (λijk) being nonzero. The gaugino spectrum is such that the charged leptons in the final state can arise from the R-parity violating decays of the lightest supersymmetric particle (LSP) as well as R-parity conserving decays of the next-to-LSP (NLSP). Apart from a detailed cut-based analysis, we have also performed a machine learning-based analysis using a boosted decision tree algorithm, which provides much better sensitivity. In the scenarios with nonzero λ121 and/or λ122 couplings, the LSP pair in the final states decays to 4l (l=e,μ)+ET final states with a 100% branching ratio. We have shown that under this circumstance, a final state with ≥4l has the highest sensitivity while probing for gaugino masses. We also discuss how the sensitivity can change in the presence of τ lepton(s) in the final state due to other choices of trilinear couplings. We present our results through the estimation of the discovery and exclusion contours in the gaugino mass plane for both the high luminosity LHC (HL-LHC with s=14 TeV and L=3000 fb−1) and high energy LHC (HE-LHC with s=27 TeV and L=3000 fb−1). For the λ121 and/or λ122 nonzero scenario, the projected 2σ exclusion limit on NLSP masses reaches upto 2.37 TeV and 4 TeV for the HL-LHC and the HE-LHC, respectively, by using a machine learning based algorithm. We observe an enhancement of ∼380 (190) GeV in the projected 2σ exclusion limit on the NLSP masses at the 27 (14) TeV LHC. Considering the same final state (Nl≥4) for the λ133 and/or λ233 nonzero scenario, we find that the corresponding 2σ projected limits are ∼1.97 TeV and ∼3.25 TeV for the HL-LHC and HE-LHC, respectively. Published by the American Physical Society 2024

A simulated search for the singlet vector-like bottom quark decaying into tW at high energy pp colliders

In a framework of simplified model, we perform a simulated search for the singlet vector-like bottom quark B decaying into tW with t hadronic decay and W leptonic decay at the 14 TeV high-luminosity LHC (HL-LHC), 27 TeV high energy LHC (HE-LHC) and 100 TeV Future Circular Hadron Collider (FCC-hh). In this work, we focus on the case that the B only couples with the third generation quarks of the Standard Model. We make a detailed detector simulations of the signal and backgrounds and obtain the 2sigma exclusion limit and 5sigma discovery prospects. Our results show that the upcoming HL-LHC can exclude (discover) the m_B to 2100 (1900) GeV for a typical coupling strength g^{*}=0.2. For the HE-LHC (FCC-hh), this exclusion capability on the B quark mass can be expanded to more than 3000 (5000) GeV.

On the coupling of axion-like particles to the top quark

In this paper we explore the coupling of a light axion-like particle (ALP) to top quarks. We use high-energy LHC probes, and examine both the direct probe to this coupling in associated production of a top-pair with an ALP, and the indirect probe through loop-induced gluon fusion to an ALP leading to top pairs. Using the latest LHC Run II data, we provide the best limit on this coupling. We also compare these limits with those obtained from loop-induced couplings in diboson final states, finding that the tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ t\\overline{t} $$\\end{document}+MET channel is the best current handle on this coupling.

Collider probe of heavy additional Higgs bosons solving the muon g−2 and dark matter problems

We study the Large Hadron Collider (LHC) search potential of a $\mathbb{Z}_4$-based two Higgs doublet model which can simultaneously explain the muon $g-2$ anomaly and the observed dark matter. The neutral scalars in the second Higgs doublet couple to $\mu$ and $\tau$ and largely contribute to the muon anomalous magnetic moment through the one-loop diagram involving $\tau$ and scalars. An additional singlet scalar which is charged under the discrete symmetry can be a dark matter candidate. An upper limit on the scalar mass originates from the unitarity constraint, and the $\mu\tau$ flavor-violating nature of the scalars predicts non-standard signatures at the LHC. However, the previously proposed $\mu^\pm\mu^\pm\tau^\mp\tau^\mp$ signal via the electroweak heavy neutral scalar pair production at the LHC loses sensitivity for increasing scalar mass. We revisit this model and investigate the LHC prospects for the single production of the $\mu\tau$ flavor-violating neutral scalar. It is shown that the single scalar process helps to extend the LHC reach to the 1$\,$TeV mass regime of the scenario. The search potential at the high energy LHC is also discussed.

Single vector-like quark X production in the tW channel at high energy pp colliders

Vector-like quarks (VLQs) are color-triplet spin-1/2 fermions whose left- and right-handed chiral components have the same transformation properties under the weak-isospin SU(2) gauge group. The X vector-like particle with a charge of |Q|=+5/3 exists in the (X,T) doublet or (X,T,B) triplet states. Based on a simplified model, we investigate the prospect of discovering the doublet right-handed X via the single production of X followed by X→tW at the 14 TeV High Luminosity LHC (HL-LHC), 27 TeV High Energy LHC (HE-LHC), and 100 TeV hadron-hadron Future Circular Hadron Collider (FCC-hh). We perform a detailed detector simulation, and find that the excluding and discovering capabilities on the X quark are enhanced obviously with the increase of collision energy. Assuming the system uncertainty is 30% of the number of the background events, the excluding capabilities are given as follows: (1) the HL-LHC can exclude the correlated regions of the mixing constant sin⁡θR∈[0.082,0.2] and the X quark mass mX ∈ [1000 GeV, 1680 GeV] with L=3 ab−1; (2) the HE-LHC can exclude the correlated regions of sin⁡θR∈[0.067,0.2] and mX ∈ [1000 GeV, 2230 GeV] with L=15 ab−1; (3) the FCC-hh can exclude the correlated regions of sin⁡θR∈[0.078,0.2] and mX ∈ [1000 GeV, 2560 GeV] with L=30 ab−1.

A comparative study of Z′ mediated charged lepton flavor violation at future lepton colliders

Charged lepton flavor violation (CLFV) represents a transition between charged leptons of different generations that violates lepton flavor conservation, which is a clear signature of possible new physics beyond the standard model. By exploiting a typical example model of extra Z′ gauge boson, we perform a detailed comparative study on CLFV searches at several future lepton colliders, including a 240 GeV electron-positron collider and a TeV scale muon collider. Based on detailed signal and background Monte-Carlo studies with fast detector simulations, we derive the potentials in searching for Z′ mediated CLFV couplings with eμ, eτ and μτ of different future colliders. The results are compared with the current and prospect limits set by either low-energy experiments or the high-energy LHC experiments. The sensitivity of the τ related CLFV coupling strength at future lepton colliders will be significantly improved in comparison to the current best constraints and the prospect constraints for the μτ channel.

Observability of triple top quark signal at future hadron colliders

Abstract The Standard Model (SM) cross-sections for the production of single top quarks, top-quark pairs, triple top quarks, and four top quarks at three different center-of-mass energies, i.e. $\sqrt{s}=$ 7, 10, and 14 TeV, at existing particle colliders as well as at future hadron colliders, are studied. A fully kinematic analysis with the optimized preselection cuts along with invariant mass reconstruction of top quarks is performed for triple-top production processes pp→tttW, tttd, and tttb in the presence of the SM background. All three signal processes are forced to decay in fully hadronic mode. The studies are performed for the High-Luminosity Large Hadron Collider (HL−LHC) at $\sqrt{s}=$ 14 TeV and for the High-Energy LHC (HE−LHC) at $\sqrt{s}=$ 27 TeV. The signal to background ratio and signal significance of all signal and background processes are estimated for both the scenarios. It is found that the chances of signal observability at the HE−LHC are higher than those at the HL−LHC. PACS numbers: 12.60.Fr, 14.80.Fd

Constraining 3-3-1 models at the LHC and future hadron colliders

In this work, we derive lower mass bounds on the Z' gauge boson based on the dilepton data from LHC with 13 TeV of center-of-mass energy, and forecast the sensitivity of the High-Luminosity-LHC with $L=3000 fb^{-1}$, the High-Energy LHC with $\sqrt{s}=27$ TeV, and also at the Future Circular Collider with $\sqrt{s}=100$ TeV. We take into account the presence of exotic and invisible decays of the Z' gauge boson to find a more conservative and robust limit, different from previous studies. We investigate the impact of these new decays channels for several benchmark models in the scope of two different 3-3-1 models. We found that in the most constraining cases, LHC with $139fb^{-1}$ can impose $m_{Z^{\prime}}>4$ TeV. Moreover, we forecast HL-LHC, HE-LHC, and FCC bounds that yield $m_{Z^{\prime}}>5.8$ TeV, $m_{Z^{\prime}}>9.9$ TeV, and $m_{Z^{\prime}}> 27$ TeV, respectively. Lastly, put our findings into perspective with dark matter searches to show the region of parameter space where a dark matter candidate with the right relic density is possible.

The anomalous Wtb vertex and top-pair production at the LHC

We perform an exclusive study of the anomalous Wtb interaction in the context of LHC. The limits on Wtb anomalous couplings have been estimated via the measurements of the top-quark decay width and cross-section as well as production asymmetries in case the CP is violated. Our investigations reveal that the upper bounds on (|CL|,|CR|) would be of about (1.82, 0.03) ×10−4 at 2.5σ C.L., for the already collected data at the LHC with S=13 TeV for an integrated luminosity of 139 fb−1. The corresponding limits for future hadron colliders, namely, High Luminosity LHC (HL-LHC), High Energy LHC (HE-LHC) and Future Circular Collider (FCC-hh) for the projected luminosities of 3 ab−1, 12 ab−1 and 30 ab−1 are found to be to (0.81,0.006)×10−4, (0.44,0.0017)×10−4 and (0.21,0.0004)×10−4 respectively at 2.5σ C.L.

Sensitivity of anomalous quartic gauge couplings via Zγγ production at future hadron-hadron colliders

Triple gauge boson production provides a promising opportunity to probe the anomalous quartic gauge couplings in understanding the details of electroweak symmetry breaking at future hadron-hadron collider facilities with increasing center of mass energy and luminosity. In this paper, we investigate the sensitivities of dimension-8 anomalous couplings related to the ZZγγ and Zγγγ quartic vertices, defined in the effective field theory framework, via pp→Zγγ signal process with Z-boson decaying to charged leptons at the high luminosity phase of LHC (HL-LHC) and future facilities, namely the High Energy LHC (HE-LHC) and Future Circular hadron-hadron collider (FCC-hh). We analyzed the signal and relevant backgrounds via a cut based method with Monte Carlo event sampling where the detector responses of three hadron collider facilities, the center-of-mass energies of 14, 27 and 100 TeV with integrated luminosities of 3, 15 and 30ab−1 are considered for the HL-LHC, HE-LHC and FCC-hh, respectively. The reconstructed 4-body invariant mass of l+l−γγ system is used to constrain the anomalous quartic gauge coupling parameters under the hypothesis of absence of anomalies in triple gauge couplings. Our results indicate that the sensitivity on anomalous quartic couplings fT8/Λ4 and fT9/Λ4 (fT0/Λ4, fT1/Λ4 and fT2/Λ4) at 95% C.L. for FCC-hh with Lint=30ab−1 without systematic errors is two (one) order better than the current experimental limits. Considering a realistic systematic uncertainty such as 10% from possible experimental sources, the sensitivity of all anomalous quartic couplings gets worsen by about 1.2%, 1.7% and 1.5% compared to those without systematic uncertainty for HL-LHC, HE-LHC and FCC-hh, respectively.

Single vectorlike top quark production in the tZ channel at high energy pp colliders

In a simplified model including a singlet vectorlike top quark $T$ with charge $|\mathrm{Q}|=2/3$, we investigate the single production of $T$ decaying into $tZ$ at the 14 TeV LHC, 27 TeV high energy LHC (HE-LHC), and 100 TeV hadron-hadron Future Circular Hadron Collider (FCC-hh). In the four flavor scheme, we make detailed detector simulations and the background analysis. We find that the excluding and discovering capability is enhanced obviously with the increase of the collision energy. The model includes only two free parameters, the coupling constant ${g}^{*}$, and top quark partner mass ${m}_{T}$. For the highest integrated luminosity designed, the excluding capability can be given as follows: (1) the LHC can exclude the correlated regions ${g}^{*}\ensuremath{\in}[0.085,0.50]$ with ${m}_{T}\ensuremath{\in}[1000\text{ }\text{ }\mathrm{GeV},1840\text{ }\text{ }\mathrm{GeV}]$ for $\mathcal{L}=3000\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$; (2) the HE-LHC can exclude the correlated regions ${g}^{*}\ensuremath{\in}[0.035,0.50]$ with ${m}_{T}\ensuremath{\in}[1000\text{ }\text{ }\mathrm{GeV},2610\text{ }\text{ }\mathrm{GeV}]$ for $\mathcal{L}=15\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$; (3) the FCC-hh can exclude the correlated regions ${g}^{*}\ensuremath{\in}[0.005,0.50]$ with ${m}_{T}\ensuremath{\in}[1000\text{ }\text{ }\mathrm{GeV},4270\text{ }\text{ }\mathrm{GeV}]$ for $\mathcal{L}=30\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$. Besides, we find that the excluding and discovering regions will be reduced if the narrow width approximation limit is considered.

SpaceMath version 1.0 A Mathematica package for beyond the standard model parameter space searches

We present a pedagogical Mathematica package, so-called SpaceMath, for Beyond the Standard Model parameter space searches. This software is directed mainly for the training of human resources related to elementary particle physics phenomenology, however, it is sophisticated enough to be used in researches. In this first version, SpaceMath v1.0 works with Higgs Boson Data whose results are the most up-to-date experimental measurements made at the Large Hadron Collider. In addition, we also include the expected results at future colliders, namely, High Luminosity LHC and High Energy LHC. SpaceMath v1.0 is able to find allowed regions for free parameters of extension models using the Higgs Boson Data within a friendly interface and an intuitive environment in which the user enters the couplings symbolically, sets parameters and execute Mathematica in the traditional way. As result, both tables as plots with values and areas agree with experimental data are generated. We present examples using SpaceMath v1.0 to analyze the free Two-Higgs Doublet Model and the Simplest Little Higgs Model parameter spaces, step by step, in order to start new users in a fast and efficient way. Finally, to validate SpaceMath v1.0, widely known results are reproduced.

Neutrino up-scattering via the dipole portal at forward LHC detectors

The significant neutrino flux at high rapidity at the LHC motivates dedicated forward detectors to study the properties of neutrinos at TeV energies. We investigate magnetic dipole interactions between the active neutrinos and new sterile states at emulsion and liquid argon experiments that could be located in a future Forward Physics Facility (FPF) downstream of the ATLAS interaction point. The up-scattering of neutrinos off electrons produces an electron recoil signature that can probe new regions of parameter space at the High Luminosity LHC (HL-LHC), particularly for liquid argon detectors due to low momentum thresholds. We also consider the decay of the sterile neutrino through the dipole operator, which leads to a photon that could be displaced from the production vertex. FPF detectors can test sterile neutrino states as heavy as 1 GeV produced through the dipole portal, highlighting the use of high energy LHC neutrinos as probes of new physics.

Renaissance of Nuclear Physics at the LHC

High-energy Large Hadron Collider (LHC) experiments provide a unique laboratory for nuclear and hadron physics studies that have a wide breadth of possible applications to astrophysics. This articl...

Forward experiment sensitivity estimator for the LHC and future hadron colliders

We introduce a numerical package FORward Experiment SEnsitivity Estimator, or $\mathtt{FORESEE}$, that can be used to simulate the expected sensitivity reach of experiments placed in the far-forward direction from the proton-proton interaction point. The simulations can be performed for 14 TeV collision energy characteristic for the LHC, as well as for larger energies; 27 and 100 TeV. In the package, a comprehensive list of validated forward spectra of various SM species is also provided. The capabilities of $\mathtt{FORESEE}$ are illustrated for the popular dark photon and dark Higgs boson models, as well as for the search for light up-philic scalars. For the dark photon portal, we also comment on the complementarity between such searches and dark matter direct detection bounds. Additionally, for the first time, we discuss the prospects for the LLP searches in the proposed future hadron colliders: High-Energy LHC (HE-LHC), Super proton-proton Collider (SppC), and Future Circular Collider (FCC-hh).

Phenomenological investigation of the parton distribution functions (PDFs) and the partonic luminosities in high energy LHC physics

Phenomenological investigation of the parton distribution functions (PDFs) and the partonic luminosities in high energy LHC physics

Search for single production of vectorlike top partners through th channel at the HE-LHC and FCC-hh

The vectorlike top partners are potential signature of some new physics beyond the Standard Model at the TeV scale. In this paper, we propose to search for the vectorlike T quark with charge 2/3 in the framework of a simplified model where the top partners only couples with the third generation of Standard Model quarks. We investigate the observability for electroweak production of a vectorlike T quark in association with a standard model bottom quark through the process pp rightarrow Tbar{b}j with the subsequent decay mode of Trightarrow t(rightarrow b W^+rightarrow b ell ^{+} nu _{ell })h( rightarrow gamma gamma ), at the proposed High Energy Large Hadron Collider (HE-LHC) and Future Circular Collider in hadron-hadron mode (FCC-hh) including the realistic detector effects. The 95% confidence level excluded regions and the 5sigma discovery reach in the parameter plane of kappa _{T}-m_T, are respectively obtained at the HE-LHC with the integrated luminosity of 15 ab^{-1} and the FCC-hh with the integrated luminosity of 30 ab^{-1}. We also analyze the projected sensitivity in terms of the production cross section times branching fraction at the HE-LHC and FCC-hh.

Flavor changing top decays to charm and a Higgs boson with ττ at the LHC

We investigate the prospects of discovering the top quark decay into a charm quark and a Higgs boson ($t \to c h^0$) in top quark pair production at the CERN Large Hadron Collider (LHC). A general two Higgs doublet model is adopted to study flavor changing neutral Higgs (FCNH) interactions. We perform a parton level analysis as well as Monte Carlo simulations using \textsc{Pythia}~8 and \textsc{Delphes} to study the flavor changing top quark decay $t \to c h^0$, followed by the Higgs decaying into $\tau^+ \tau^-$, with the other top quark decaying to a bottom quark ($b$) and two light jets ($t\to bW\to bjj$). To reduce the physics background to the Higgs signal, only the leptonic decays of tau leptons are used, $\tau^+\tau^- \to e^\pm\mu^\mp +\slashed{E}_T$, where $\slashed{E}_T$ represents the missing transverse energy from the neutrinos. In order to reconstruct the Higgs boson and top quark masses as well as to effectively remove the physics background, the collinear approximation for the highly boosted tau decays is employed. Our analysis suggests that a high energy LHC at $\sqrt{s} = 27$ TeV will be able to discover this FCNH signal with an integrated luminosity $\mathcal{L} = 3$ ab$^{-1}$ for a branching fraction ${\cal B}(t \to ch^0) \agt 1.4 \times 10^{-4}$ that corresponds to a FCNH coupling $|\lambda_{tch}| \agt 0.023$. This FCNH coupling is significantly below the current ATLAS combined upper limit of $|\lambda_{tch}| = 0.064$.