Excited Quarks 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.

Search for resonances in events with photon and jet final states in proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV

A search for resonances in events with the γ+jet final state has been performed using proton-proton collision data collected at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV by the CMS experiment at the LHC. The total data analyzed correspond to an integrated luminosity of 138 fb−1. Models of excited quarks and quantum black holes are considered. Using a wide-jet reconstruction for the candidate jet, the γ+jet invariant mass spectrum measured in data is examined for the presence of resonances over the standard model continuum background. The background is estimated by fitting this mass distribution with a functional form. The data exhibit no statistically significant deviations from the expected standard model background. Exclusion limits at 95% confidence level on the resonance mass and other parameters are set. Excited light-flavor quarks (excited bottom quarks) are excluded up to a mass of 6.0 (3.8) TeV. Quantum black hole production is excluded for masses up to 7.5 (5.2) TeV in the Arkani-Hamed-Dimopoulos-Dvali (Randall-Sundrum) model. These lower mass bounds are the most stringent to date among those obtained in the γ+jet final state.

Mass distributions of dijet resonances from excited quarks at proton-proton colliders

We study the expected experimental mass distributions of dijet resonances from excited quarks in proton-proton collisions at energies s = 13, 14, 27, 100, 300, and 500 TeV. We explore in detail the expected shapes at both the generator and experimental levels, and identify within the distributions the effects of the excited quark natural width, parton momentum distributions of the proton, radiation, and experimental resolution. We present both differential and cumulative probability distributions as a function of dijet mass, and the signal acceptance of a window in dijet mass centered on each resonance. We find that for a range of resonance masses, between 10% and 50% of s, the dijet mass distributions and window acceptance are practically universal, approximately invariant under changes in resonance mass and s. This universality is violated when the resonance mass reaches 60% of s, because the steepness of the parton momentum distributions of the proton produces a significant tail at low dijet mass. This work supports our Snowmass 2021 study on the sensitivity to dijet resonances at proton-proton colliders.

Resonance Production of the Excited Quark at High Luminosity Large Hadron Collider

Bu çalışmada etkileşim Lagranjiyen yöntemi kullanılarak, dejenere durumdaki uyarılmış kuarkların Yüksek Işınlıklı Büyük Hadron Çarpıştırıcısında (YI-BHÇ) rezonans üretimleri incelenmiştir. YI-BHÇ’de rezonans da üretilen uyarılmış kuarkların iki-jet son durumuna sahip olduğu sinyal kanalı için hesaplamalar yapılmıştır. Uyarılmış kuark sinyalini ardalandan ayırt edecek sınırlandırmaları belirlemek için sinyal ardalan analizi yapılmıştır. Bu analiz vasıtasıyla belirlenen sınırlandırmalar kullanılarak YI-BHÇ’de uyarılmış kuarkın kütlesi için keşif, gözlem ve dışarlama limitleri hesaplanmıştır. Ayrıca uyarılmış kuark için kompozitlik ölçeği taraması yapılarak, farklı kütle değerleri için ulaşabileceği en üst kompozitlik ölçeği değerleri hesaplanmıştır. Son olarak 1’den küçük serbest parametre değerlerinde dahi uyarılmış kuarkın YI-BHÇ’de keşif edilebileceği gösterilmiştir. Tüm bu hesaplamaların sonucunda, YI-BHÇ’nin uyarılmış kuarkları araştırmada çok iyi bir potansiyele sahip olacağı ortaya çıkmıştır.

Search for a heavy resonance decaying to a top quark and a W boson at sqrt{s} = 13 TeV in the fully hadronic final state

A search for a heavy resonance decaying to a top quark and a W boson in the fully hadronic final state is presented. The analysis is performed using data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb−1 recorded by the CMS experiment at the LHC. The search is focused on heavy resonances, where the decay products of each top quark or W boson are expected to be reconstructed as a single, large-radius jet with a distinct substructure. The production of an excited bottom quark, b*, is used as a benchmark when setting limits on the cross section for a heavy resonance decaying to a top quark and a W boson. The hypotheses of b* quarks with left-handed, right-handed, and vector-like chiralities are excluded at 95% confidence level for masses below 2.6, 2.8, and 3.1 TeV, respectively. These are the most stringent limits on the b* quark mass to date, extending the previous best limits by almost a factor of two.

Charm fragmentation and associated J/ψ+Z/W± production at the LHC

We consider the production of electroweak $Z$ or $W^\pm$ bosons associated with $J/\psi$ mesons at the LHC conditions. Our attention is focused on new partonic subprocesses which yet have never been considered in the literature, namely, the charmed or strange quark excitation subprocesses followed by the charmed quark fragmentation $c\to J/\psi+c$. Additionally we take into account the effects of multiple quark and gluon radiation in the initial and final states. We find that the contributions from the new mechanisms are important and significantly reduce the gap between the theoretical and experimental results on the $J/\psi + Z$ and $J/\psi + W^\pm$ production cross sections.

Search for New Resonances Coupling to Third Generation Quarks at CMS

I present an overview of searches for new physics with top and bottom quarks and top quark–antiquark pairs in the final state, using proton–proton collision data collected with the CMS detector at the CERN LHC at a center-of-mass energy of 13 TeV. The results cover non-SUSY-based extensions of the SM, including new heavy gauge bosons, like a $$W^{\prime}$$ boson replicating the features of its standard model counterpart, or excited third generation quarks. We considered both semileptonic and fully-hadronic scenarios. We explore the use of jet substructure techniques to reconstruct highly boosted objects in events, enhancing the sensitivity of these searches.

Search for high mass dijet resonances with a new background prediction method in proton-proton collisions at sqrt{s} = 13 TeV

A search for narrow and broad resonances with masses greater than 1.8 TeV decaying to a pair of jets is presented. The search uses proton-proton collision data at sqrt{s} = 13 TeV collected at the LHC, corresponding to an integrated luminosity of 137 fb−1. The background arising from standard model processes is predicted with the fit method used in previous publications and with a new method. The dijet invariant mass spectrum is well described by both data-driven methods, and no significant evidence for the production of new particles is observed. Model independent upper limits are reported on the production cross sections of narrow resonances, and broad resonances with widths up to 55% of the resonance mass. Limits are presented on the masses of narrow resonances from various models: string resonances, scalar diquarks, axigluons, colorons, excited quarks, color-octet scalars, W′ and Z′ bosons, Randall-Sundrum gravitons, and dark matter mediators. The limits on narrow resonances are improved by 200 to 800 GeV relative to those reported in previous CMS dijet resonance searches. The limits on dark matter mediators are presented as a function of the resonance mass and width, and on the associated coupling strength as a function of the mediator mass. These limits exclude at 95% confidence level a dark matter mediator with a mass of 1.8 TeV and width 1% of its mass or higher, up to one with a mass of 4.8 TeV and a width 45% of its mass or higher.

Analysis of excited quark propagator effects on neutron charge form factor

The charge form factor and charge radius of neutron are investigated in the perturbative chiral quark model (PCQM) with considering both the ground and excited states in the quark propagator. A Cornell-like potential is extracted in accordance with the predetermined ground state quark wavefunction, and the excited quark states are derived by solving the Dirac equation with the extracted PCQM potential numerically. The study reveals that the contributions of the excited quark states are considerably influential in the charge form factor and charge radius of neutron as expected, and the total results are significantly improved and increased by nearly four times by including the excited states in the quark propagator. The theoretical PCQM results are found, including the ground and excited quark propagators, in good agreement with the recent lattice QCD values at pion mass of about 130 MeV.

Excited quarks production at FCC and SppC pp colliders

Potential discovery, observation and exclusion limits of excited [Formula: see text] and [Formula: see text] quarks with gamma[Formula: see text]jet final state are researched at the multi-TeV scale colliders, FCC and S[Formula: see text]C in this paper. Both colliders, FCC and S[Formula: see text]C, show that excited [Formula: see text] and [Formula: see text] quarks could be discovered up to 42.1 TeV and 55.2 TeV for [Formula: see text], 30.3 TeV and 39.4 TeV for [Formula: see text] and 42.3 TeV and 55.5 TeV mass values for degenerate case [Formula: see text], respectively. The determination of the excited quarks compositeness scale is examined, which will be up to multi-PeV level. Besides these analyses, free parameters ([Formula: see text], [Formula: see text] and [Formula: see text]) are scanned from around 0.1 up to 1 that show excited quark could be discovered at dozens of TeV with even coupling constants under 0.1.

Looking for B→Xsℓ+ℓ− in a nonminimal universal extra dimensional model

Non-vanishing boundary localised terms significantly modify the mass spectrum and various interactions among the Kaluza-Klein excited states of 5-Dimensional Universal Extra Dimensional scenario. In this scenario we compute the contributions of Kaluza-Klein excitations of gauge bosons and third generation quarks for the decay process $B\rightarrow X_s\ell^+\ell^-$ incorporating next-to-leading order QCD corrections. We estimate branching ratio as well as Forward Backward asymmetry associated with this decay process. Considering the constraints from some other $b \to s$ observables and electroweak precision data we show that significant amount of parameter space of this scenario has been able to explain the observed experimental data for this decay process. From our analysis we put lower limit on the size of the extra dimension by comparing our theoretical prediction for branching ratio with the corresponding experimental data. Depending on the values of free parameters of the present scenario, lower limit on the inverse of the radius of compactification ($R^{-1}$) can be as high as $\geq 760$ GeV. {Even this value could slightly be higher if we project the upcoming measurement by Belle II experiment.} Unfortunately, the Forward Backward asymmetry of this decay process would not provide any significant limit on $R^{-1}$ in the present model.

Colorphilic spin-2 resonances in the LHC dijet channel

Experiments at the LHC may yet discover a dijet resonance indicative of beyond the standard model (BSM) physics. In this case, the question becomes: what BSM theories are consistent with the unexpected resonance? One possibility would be a spin-2 object called the ‘colorphilic graviton’—a spin-2 color-singlet particle which couples exclusively to the quark and gluon stress-energy tensors. We assess the possibility of this state’s discovery in the dijet channel as an s-channel resonance, and report the regions of parameter space where colorphilic gravitons have not yet been excluded by LHC-13 data but still may be discovered in the dijet channel at LHC-14 for integrated luminosities of 0.3, 1, and 3 ab−1. We then delineate which of those regions remain accessible to future collider searches, once one accounts for applicability of the narrow-width approximation, mass resolution of the detector, and self-consistency according to tree-level partial-wave unitarity. We discover that–despite the strong constraints unitarity imposes on collider searches–the colorphilic graviton remains potentially discoverable in the LHC dijet channel. A means of investigation would be to apply the color discriminant variable, a dimensionless combination of quantities (production cross-section, total decay width, and invariant mass) that can be quickly measured after the discovery of a dijet resonance. Previous publications have demonstrated the color discriminant variable’s utility when applied to theories containing vector bosons (colorons, ), excited quarks, and diquarks. We extend this analysis to the case of the colorphilic graviton by applying the color discriminant variable to the appropriate region of parameter space. We conclude that resolvable, discoverable dijet resonances consistent with colorphilic gravitons span a narrower range of masses than those consistent with leptophobic models, and can be distinguished from those originating from coloron, excited quark, and diquark models.

Search for narrow and broad dijet resonances in proton-proton collisions at sqrt{s}=13 TeV and constraints on dark matter mediators and other new particles

Searches for resonances decaying into pairs of jets are performed using proton-proton collision data collected at sqrt{s}=13 TeV corresponding to an integrated luminosity of up to 36 fb−1. A low-mass search, for resonances with masses between 0.6 and 1.6 TeV, is performed based on events with dijets reconstructed at the trigger level from calorimeter information. A high-mass search, for resonances with masses above 1.6 TeV, is performed using dijets reconstructed offline with a particle-flow algorithm. The dijet mass spectrum is well described by a smooth parameterization and no evidence for the production of new particles is observed. Upper limits at 95% confidence level are reported on the production cross section for narrow resonances with masses above 0.6 TeV. In the context of specific models, the limits exclude string resonances with masses below 7.7 TeV, scalar diquarks below 7.2 TeV, axigluons and colorons below 6.1 TeV, excited quarks below 6.0 TeV, color-octet scalars below 3.4 TeV, W′ bosons below 3.3 TeV, Z′ bosons below 2.7 TeV, Randall-Sundrum gravitons below 1.8 TeV and in the range 1.9 to 2.5 TeV, and dark matter mediators below 2.6 TeV. The limits on both vector and axial-vector mediators, in a simplified model of interactions between quarks and dark matter particles, are presented as functions of dark matter particle mass and coupling to quarks. Searches are also presented for broad resonances, including for the first time spin-1 resonances with intrinsic widths as large as 30% of the resonance mass. The broad resonance search improves and extends the exclusions of a dark matter mediator to larger values of its mass and coupling to quarks.

Search for massive resonances decaying into WW , WZ , ZZ , qW , and qZ with dijet final states at s=13 TeV

Results are presented from a search in the dijet final state for new massive narrow resonances decaying to pairs of W and Z bosons or to a W/Z boson and a quark. Results are based on data recorded in proton-proton collisions at s=13 TeV with the CMS detector at the CERN LHC. The data correspond to an integrated luminosity of 35.9 fb−1. The mass range investigated extends upwards from 1.2 TeV. No excess is observed above the estimated standard model background and limits are set at 95% confidence level on cross sections, which are interpreted in terms of various models that predict gravitons, heavy spin-1 bosons, and excited quarks. In a heavy vector triplet model, W′ and Z′ resonances, with masses below 3.2 and 2.7 TeV, respectively, and spin-1 resonances with degenerate masses below 3.8 TeV are excluded at 95% confidence level. In the case of a singlet W′ resonance masses between 3.3 and 3.6 TeV can be excluded additionally. Similarly, excited quark resonances, q*, decaying to qW and qZ with masses less than 5.0 and 4.7 TeV, respectively, are excluded. In a narrow-width bulk graviton model, upper limits are set on cross sections ranging from 0.6 fb for high resonance masses above 3.6 TeV, to 36.0 fb for low resonance masses of 1.3 TeV.1 MoreReceived 17 August 2017DOI:https://doi.org/10.1103/PhysRevD.97.072006Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.© 2018 CERN, for the CMS CollaborationPhysics Subject Headings (PhySH)Research AreasExtensions of fermion sectorExtensions of gauge sectorParticles & Fields

Search for excited quarks of light and heavy flavor in γ + jet final states in proton–proton collisions at [formula omitted

A search is presented for excited quarks of light and heavy flavor that decay to γ+jet final states. The analysis is based on data corresponding to an integrated luminosity of 35.9fb−1 collected by the CMS experiment in proton–proton collisions at s=13TeV at the LHC. A signal would appear as a resonant contribution to the invariant mass spectrum of the γ+jet system, above the background expected from standard model processes. No resonant excess is found, and upper limits are set on the product of the excited quark cross section and its branching fraction as a function of its mass. These are the most stringent limits to date in the γ+jet final state, and exclude excited light quarks with masses below 5.5 TeV and excited b quarks with masses below 1.8 TeV, assuming standard model like coupling strengths.

Search for new phenomena in high-mass final states with a photon and a jet from pp collisions at sqrt{s} = 13\xa0TeV with the ATLAS detector

A search is performed for new phenomena in events having a photon with high transverse momentum and a jet collected in 36.7~text {fb}^{-1} of proton–proton collisions at a centre-of-mass energy of sqrt{s} = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. The invariant mass distribution of the leading photon and jet is examined to look for the resonant production of new particles or the presence of new high-mass states beyond the Standard Model. No significant deviation from the background-only hypothesis is observed and cross-section limits for generic Gaussian-shaped resonances are extracted. Excited quarks hypothesized in quark compositeness models and high-mass states predicted in quantum black hole models with extra dimensions are also examined in the analysis. The observed data exclude, at 95% confidence level, the mass range below 5.3 TeV for excited quarks and 7.1 TeV (4.4 TeV) for quantum black holes in the Arkani-Hamed–Dimopoulos–Dvali (Randall–Sundrum) model with six (one) extra dimensions.

Separating dijet resonances using the color discriminant variable

Color-singlet and color-octet vector bosons predicted in theories beyond the Standard Model have the potential to be discovered as dijet resonances at the LHC. A color-singlet resonance that has leptophobic couplings needs further investigation to be distinguished from a color-octet one. In previous work, we introduced a method for discriminating between the two kinds of resonances when their couplings are flavor-universal, using measurements of the dijet resonance mass, total decay width and production cross-section. Here, we describe two extensions of that work. First, we broaden the method to the case where the vector resonances have flavor non-universal couplings, by incorporating measurements of the heavy-flavor decays of the resonance. Second, we apply the method to separating vector bosons from color-octet scalars and excited quarks.

Study of excited quark propagator contributions in perturbative chiral quark model

In this work, masses of octet baryons are evaluated in the framework of the perturbative chiral quark model (PCQM) with considering both the ground and excited states in the quark propagator, in which a Cornell-like potential is first constructed by letting the predetermined ground state quark wavefunction satisfy Dirac equation, and the excited quark states are derived by resolving Dirac equation with the extracted PCQM potential numerically employing Generalized Eigenvalue & Eigenstate Problem method. The results on the octet baryon masses are found in good agreement with the experimental data, and the study reveals that the contributions of the excited quark states are considerably influential in the octet baryon masses as expected.

Classification of Particles at Arbitrary Quantity of Generations. II. Leptons

The hypothesis on quark nature of the leptons is proposed. Leptons are compacted q3 -systems. It ensures the equality of modules for the electric charges of the proton and the electron. The classification of particles based on the U(Nf,g)×SU(3,c)×SU(4,fs)×O(3) -group is proposed at arbitrary quantity Nf of the quark generations. The U(Nf,g) -group corresponds to the quark generations, the SU(3,c) -group describes the color variables, the SU (4,fs) - group corresponds to the variables in the spin (s) and flavor (f) spaces, and the O(3) -group describes the orbital excitations of quarks. In consequence of the Pauli principle leptons consist of antiquarks from 3 different generations. Minimal quantity of leptons with definite electric charge equal 20. Excited double charged (l−−) -leptons and (l++) -antileptons with the J^p=(1/2)+ and J^p=(1/2)- are predicted, respectively. They can be resonances in e−π−, e−K−, e+π+, e+K+, μ−π−, μ−K−, μ+π+, μ+K+ -systems.

Search for dijet resonances in proton–proton collisions at [formula omitted] and constraints on dark matter and other models

A search is presented for narrow resonances decaying to dijet final states in proton–proton collisions at s=13TeV using data corresponding to an integrated luminosity of 12.9 fb−1. The dijet mass spectrum is well described by a smooth parameterization and no significant evidence for the production of new particles is observed. Upper limits at 95% confidence level are reported on the production cross section for narrow resonances with masses above 0.6 TeV. In the context of specific models, the limits exclude string resonances with masses below 7.4 TeV, scalar diquarks below 6.9 TeV, axigluons and colorons below 5.5 TeV, excited quarks below 5.4 TeV, color-octet scalars below 3.0 TeV, W′ bosons below 2.7 TeV, Z′ bosons below 2.1 TeV and between 2.3 and 2.6 TeV, and RS gravitons below 1.9 TeV. These extend previous limits in the dijet channel. Vector and axial-vector mediators in a simplified model of interactions between quarks and dark matter are excluded below 2.0 TeV. The first limits in the dijet channel on dark matter mediators are presented as functions of dark matter mass and are compared to the exclusions of dark matter in direct detection experiments.