Composite Quarks Research Articles

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.

Measurements of Hadron Resonance Production with ALICE

Short-lived resonances have long been recognized as good probes to investigate the late-stage evolution of ultra-relativistic heavy-ion collisions. More recently, resonances with different masses and quark composition have provided valuable contributions to the understanding of strangeness production, in particular for the observed multiplicity-dependent enhancement in small systems. In this light, a comprehensive review is presented of the most recent ALICE results on [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] production in pp, p–Pb and Pb–Pb collisions at various collision energies at the LHC, including results from the latest Pb–Pb run at [Formula: see text] = 5.02 TeV.

The origin of particle masses and the naturalness problem

Electroweak symmetry breaking is the key ingredient of the standard model responsible for the generation of all elementary particle masses. The discovery of the Higgs boson is a major milestone towards understanding the mechanism of electroweak symmetry breaking but several important issues remain unexplained. Among them the key mystery is how to stabilize the electroweak symmetry scale, called the naturalness problem. To solve this problem, some new physics should be introduced to screen quantum corrections from higher energy scale. There are two classes of new physics theories: one is super symmetry model in which Higgs quadratic divergence is cancelled through the extended space-time symmetry between scalars and fermions. The other one is composite Higgs model in which the sensitivity to higher energy scale is reduced by the composite nature of Higgs. In super symmetry model, every field in standard model should have a super symmetric partner, which makes this theory very complicated. However, the composite Higgs models can address the naturalness problem in a very simple way. In this article we first review the Higgs mechanism in standard model and explain Higgs naturalness problem. Then we generally review the super symmetry model and its phenomenology. It is found that the tuning of this kind of model is worse than 1% when confronts experimental measurements. In the remaining parts we focus on discussing the composite Higgs model. We first review the structure of composite Higgs models and then discuss how to reduce Higgs mass through some symmetry collectively breaking or extra dimension mechanism. It is found that, in this kind of models, to produce a light Higgs the composite quarks canceling Higgs quadratic divergences should be relatively light, around 1 TeV. But the constraints from Large Hadron Collider (LHC) indicate that these fermions should be much heavier than 1 TeV, which results the difficulty in achieving a light Higgs. Moreover, to evade precise electroweak tests, the electroweak scale should be separated with Higgs confinement scale, called the Little Hierarchy, requiring more tuning in this model. In order to produce light Higgs while keeping composite quarks heavy, we plan to find a general principle to realize neutral naturalness mechanism in which Higgs quadratic divergences are cancelled by hidden sector. And then find the UV completion for this mechanism and fully study its phenomenology. In order to naturally solve Little Hierarchy, we plan to construct a mechanism to produce Higgs tree level or loop level self-quartic coupling, so that the big separation between electroweak and confinement scale can be achieved by adjusting properly this coupling without introducing any tuning. After solving above two problems, we combine these two mechanisms to construct the super-natural composite Higgs model which can successfully achieve electroweak symmetry breaking without any tuning.

Consistent searches for SMEFT effects in non-resonant dijet events

We investigate the bounds which can be placed on generic new-physics contributions to dijet production at the LHC using the framework of the Standard Model Effective Field Theory, deriving the first consistently-treated EFT bounds from non-resonant high-energy data. We recast an analysis searching for quark compositeness, equivalent to treating the SM with one higher-dimensional operator as a complete UV model. In order to reach consistent, model-independent EFT conclusions, it is necessary to truncate the EFT effects consistently at order 1/Λ2 and to include the possibility of multiple operators simultaneously contributing to the observables, neither of which has been done in previous searches of this nature. Furthermore, it is important to give consistent error estimates for the theoretical predictions of the signal model, particularly in the region of phase space where the probed energy is approaching the cutoff scale of the EFT. There are two linear combinations of operators which contribute to dijet production in the SMEFT with distinct angular behavior; we identify those linear combinations and determine the ability of LHC searches to constrain them simultaneously. Consistently treating the EFT generically leads to weakened bounds on new-physics parameters. These constraints will be a useful input to future global analyses in the SMEFT framework, and the techniques used here to consistently search for EFT effects are directly applicable to other off-resonance signals.

Production of exotic composite quarks at the LHC

We consider the production at the LHC of exotic composite quarks of charge $Q=+(5/3) e$ and $Q=-(4/3) e$. Such states are predicted in composite models of higher isospin multiplets ($I_W=1$ or $I_W=3/2$). Given their exotic charges (such as $5/3$), their decays proceed through the electroweak interactions. We compute decay widths and rates for resonant production of the exotic quarks at the LHC. Partly motivated by the recent observation of an excess by the CMS collaboration in the $e\not p_T jj$ final state signature we focus on $ pp \to U^+ j \to W^+ + j\, j\, \to \ell^+\not p_T jj$ and then perform a fast simulation of the detector reconstruction based on DELPHES. We then scan the parameter space of the model ($m_*=\Lambda$) and study the statistical significance of the signal against the relevant standard model background ($Wjj$ followed by leptonic decay of the $W$ gauge boson) providing the luminosity curves as function of $m_*$ for discovery at 3- and 5-$\sigma$ level.

Search strategies for TeV scale fermionic top partners with charge 2/3

Searches for fermionic top partners at the TeV scale will bring forward a new final state kinematic regime and event topologies, where Run I search strategies will inevitably fail. We propose concrete search strategies for singly produced charge 2/3 fermionic top partners ($T'$) adequate for LHC Run II. Our analysis spans over all of the $T'$ decay modes ($i.e.$ $tZ$, $th$ and $Wb$) where we present detailed discussion of the search performances, signal efficiencies and backgrounds rates. Our LHC Run II search proposals utilize signatures with large missing energy and leptons, as well as jet substructure observables for tagging of boosted heavy SM states, customized $b$-tagging tactics and forward jet tagging. We analyze the prospects for discovery and exclusion of $T'$ models within the framework of partially composite quarks at the LHC Run II. Our results show that the LHC Run II has good prospects for observing $T'$ models which predict single production cross section of $\sigma_{T'} \sim 70 -140 \, (30 -65)$ fb for $M_{T'} = 1\, (1.5)$~TeV respectively with 100 fb$^{-1}$ of integrated luminosity, depending on the branching ratios of the $T'$. Similarly, we find that cross sections of $\sigma_{T'} \sim 27 -60\, (13 - 24)$ fb for $M_{T'} = 1\, (1.5)$ TeV respectively can be excluded with the same amount of data. Our results are minimally model dependent and can be applied to most $T'$ models where $\Gamma_{T'} \ll M_{T'}$.

Quark matter at high density based on an extended confined isospin-density-dependent mass model

We investigate the effect of the inclusion of relativistic Coulomb terms in a confined-isospin-density-dependent-mass (CIDDM) model of strange quark matter (SQM). We found that if we include Coulomb term in scalar density form, SQM equation of state (EOS) at high densities is stiffer but if we include Coulomb term in vector density form is softer than that of standard CIDDM model. We also investigate systematically the role of each term of the extended CIDDM model. Compared with what was reported in Ref.~\cite {ref:isospin}, we found the stiffness of SQM EOS is controlled by the interplay among the the oscillator harmonic, isospin asymmetry and Coulomb contributions depending on the parameter's range of these terms. We have found that the absolute stable condition of SQM and the mass of 2 $M_\odot$ pulsars can constrain the parameter of oscillator harmonic $\kappa_1$ $\approx 0.53$ in the case Coulomb term excluded. If the Coulomb term is included, for the models with their parameters are consistent with SQM absolute stability condition, the $2.0~M_{\odot}$ constraint more prefer the maximum mass prediction of model with scalar Coulomb term than that of model with vector Coulomb term. On contrary, the high densities EOS predicted by model with vector Coulomb is more compatible with recent pQCD result \cite{ref:pressure} than that predicted by model with scalar Coulomb. Furthermore, we also observed the quark composition in a very high density region depends quite sensitively on the kind of Coulomb term used.

A non-abelian model SU(N) × SU(N)

A composite non-abelian model SU(N) × SU(N) is proposed as possible extension of the Yang-Mills symmetry. We obtain the corresponding gauge symmetry of the model and the most general lagrangian invariant by SU(N) × SU(N). The corresponding Feynman rules of the model are studied. Propagators and vertices are derived in the momentum space. As physical application, instead of considering the color symmetry SUc(3) for QCD, we substitute it by the combination SUc(3) × SUc(3). It yields a possibility to go beyond QCD symmetry in the sense that quarks are preserved with three colors. This extension provides composite quarks in triplets and sextets multiplets accomplished with the usual massless gluons plus massive gluons. We present a power counting analysis that satisfies the renormalization conditions as well as one studies the structure of radiative corrections to one loop approximation. Unitary condition is verified at tree level. Tachyons are avoided. For end, one extracts a BRST symmetry from lagrangian and Slavnov-Tayloridentities.

Constraints on composite quark partners from Higgs searches

In composite Higgs models, the generation of quark masses requires the standard model-like quarks to be partially or fully composite states which are accompanied by composite quark partners. The composite quark partners decay into a standard model-like quark and an electroweak gauge boson or Higgs boson, which can be searched for at the LHC. In this article, we study the phenomenological implications of composite quarks in the minimal composite Higgs model based on the coset $SO(5)/SO(4)$. We focus on light quark partners which are embedded in the $SO(4)$ singlet representation. In this case, a dominant decay mode of the partner quark is into a Higgs boson and a jet, for which no experimental bounds have been established so far. The presence of $SO(4)$ singlet partners leads to an enhancement of the di-Higgs production cross section at the LHC. This will be an interesting experimental signature in the near future, but, unfortunately, there are no direct bounds available yet from the experimental analyses. However, we find that the currently available standard model-like Higgs searches can be used in order to obtain the first constraints on partially and fully composite quark models with light quark partners in the $SO(4)$ singlet. We obtain a flavor- and composition parameter independent bound on the quark partner mass of $M_{U_h} > 310 \mbox{ GeV}$ for partially composite quark models and $M_{U_h} > 212 \mbox{ GeV}$ for fully composite quark models.

Superconducting properties of vacuum in strong magnetic field

We discuss superconducting phases of vacuum induced by strong magnetic field in the electroweak model and in Quantum Chromodynamics (QCD) at zero temperature. In these phases, the vacuum behaves as an anisotropic inhomogeneous superconductor which supports superconductivity along the axis of the magnetic field while in the transversal directions, the superconductivity does not exist. The magnetic-field-induced anisotropic superconductivity appears as a result of condensation of electrically charged spin-one particles, which are elementary W bosons in the case of the electroweak model and composite quark–antiquark pairs with quantum numbers of ρ-mesons in the case of QCD. Due to the anisotropic nature of superconductivity, the Meissner effect is absent. Intrinsic inhomogeneities of the superconducting ground state are characterized by ensembles of certain topological vortices in an analogy with a mixed Abrikosov state of a type-II superconductivity.

Radiation Damping in a Non-Abelian Strongly-Coupled Gauge Theory

We study a 'composite' or 'dressed' quark in strongly-coupled = 4 super-Yang-Mills (SYM), making use of the AdS/CFT correspondence. We show that the standard string dynamics nicely captures the physics of the quark and its surrounding non-Abelian field configuration, making it possible to derive a relativistic equation of motion that incorporates the effects of radiation damping. From this equation one can deduce a non-standard dispersion relation for the composite quark, as well as a Lorentz covariant formula for its rate of radiation.

Light top partners and precision physics

Abstract We analyze the corrections to the precision EW observables in minimal composite Higgs models by using a general effective parametrization that also includes the lightest fermionic resonances. A new, possibly large, logarithmically divergent contribution to $ \widehat{S} $ is identified, which comes purely from the strong dynamics. It can be interpreted as a running of $ \widehat{S} $ induced by the non-renormalizable Higgs interactions due to the non- linear σ-model structure. As expected, the corrections to the $ \widehat{T} $ parameter coming from fermion loops are finite and dominated by the contributions of the lightest composite states. The fit of the oblique parameters suggests a rather stringent lower bound on the σ-model scale f ≳ 750 GeV. The corrections to the Z $ \overline{b} $ L b L vertex coming from the lowest-order operators in the effective Lagrangian are finite and somewhat correlated to the corrections to $ \widehat{T} $ . Large additional contributions are generated by contact interactions with 4 composite fermions. In this case a logarithmic divergence can be generated and the correlation with $ \widehat{T} $ is removed. We also analyze the tree-level corrections to the top couplings, which are expected to be large due to the sizable degree of compositeness of the third generation quarks. We find that for a moderate amount of tuning the deviation in V tb can be of order 5% while the distortion of the Z $ \overline{t} $ L t L vertex can be 10%.

Modified Higgs physics from composite light flavors

Abstract We point out that Higgs rates into gauge bosons can be significantly modified in composite pseudo Nambu-Goldstone boson (pNGB) Higgs models if quarks belonging to the first two generation are relatively composite objects as well. Although the lightness of the latter a priori screen them from the electroweak symmetry breaking sector, we show, in an effective two-site description, that their partners can lead to order one shifts in radiative Higgs couplings to gluons and photons. Moreover, due to the pseudo-Goldstone nature of the Higgs boson, the size of these corrections is completely controlled by the degree of compositeness of the individual light quarks. The current measurements of flavor-blind Higgs decay rates at the LHC thus provide an indirect probe of the flavor structure of the framework of pNGB Higgs compositeness.

Anatomy of flavour-changing Z couplings in models with partial compositeness

In models with partially composite quarks, like composite Higgs models or models with a warped extra dimension, the couplings of quarks to the Z boson generically receive non-universal corrections that are not only constrained by electroweak precision tests but also lead to flavour-changing neutral currents at tree level. The impact of these flavour-changing couplings on rare K and B decays is studied in two-site models for three scenarios: an anarchic strong sector with two different choices of fermion representations both leading to a custodial protection of the $ Z\to b\overline{b} $ coupling, and for a strong sector invariant under a U(2)3 flavour symmetry. In the complete numerical analysis, all relevant constraints from ΔF = 2 processes are taken into account. In all scenarios, visible effects in rare K and B decays like $ K\to \pi \nu \overline{\nu} $ , B s → μ + μ − and B → K ∗ μ + μ − are possible that can be scrutinized experimentally in the near future. Characteristic correlations between observables allow to distinguish the different cases. To sample the large parameter space of the anarchic models, a new method is presented that allows larger statistics than conventional approaches.

Searches for heavy long-lived sleptons and R-hadrons with the ATLAS detector in pp collisions at [formula omitted

A search for long-lived particles is performed using a data sample of 4.7 fb−1 from proton–proton collisions at a centre-of-mass energy s=7 TeV collected by the ATLAS detector at the LHC. No excess is observed above the estimated background and lower limits, at 95% confidence level, are set on the mass of the long-lived particles in different scenarios, based on their possible interactions in the inner detector, the calorimeters and the muon spectrometer. Long-lived staus in gauge-mediated SUSY-breaking models are excluded up to a mass of 300 GeV for tanβ=5–20. Directly produced long-lived sleptons are excluded up to a mass of 278 GeV. R-hadrons, composites of gluino (stop, sbottom) and light quarks, are excluded up to a mass of 985 GeV (683 GeV, 612 GeV) when using a generic interaction model. Additionally two sets of limits on R-hadrons are obtained that are less sensitive to the interaction model for R-hadrons. One set of limits is obtained using only the inner detector and calorimeter observables, and a second set of limits is obtained based on the inner detector alone.

Top and bottom seesaw from supersymmetric strong dynamics

We propose a top and bottom seesaw model with partial composite top and bottom quarks. Such composite quarks and topcolor gauge bosons are bound states from supersymmetric strong dynamics by Seiberg duality. Supersymmetry breaking also induces the breaking of topcolor into the QCD gauge coupling. The low energy description of our model reduces to a complete non-minimal extension of the top seesaw model with bottom seesaw. The non-minimal nature is crucial for Higgs mixings and the appearance of light Higgs fields. The Higgs fields are bound states of partial composite particles with the lightest one compatible with a 125 GeV Higgs field which was discovered at the LHC.

Searches for heavy long-lived sleptons andR-hadrons with the ATLAS detector

A search for long-lived particles is performed using a data sample of 4.7 fb−1 from proton-proton collisions at a centre-of-mass energy √s = 7 TeV collected by the ATLAS detector at the LHC. No excess is observed above the estimated background and lower limits, at 95% confidence level, are set on the mass of the long-lived particles in different scenarios, based on their possible interactions in the inner detector, the calorimeters and the muon spectrometer. Long-lived staus in gauge-mediated SUSY-breaking models are excluded up to a mass of 300 GeV for tan β = 5 − 20. Directly produced long-lived sleptons are excluded up to a mass of 278 GeV. R -hadrons, composites of gluino (stop, sbottom) and light quarks, are excluded up to a mass of 985 GeV (683 GeV, 612 GeV) when using a generic interaction model. Additionally two sets of limits on R -hadrons are obtained that are less sensitive to the interaction model for R -hadrons. One set of limits is obtained using only the inner detector and calorimeter observables, and a second set of limits is obtained based on the inner detector alone. The full paper can be found in [1].

NLO QCD corrections to dijet production via quark contact interactions

We present the exact next-to-leading order (NLO) QCD corrections to dijet production at the LHC via quark contact interactions, with different color and chiral structures induced from new physics. Following the recent analysis of quark compositeness search at the LHC, we find that the NLO QCD corrections can lower the dijet cross sections by several tens percent, depending on the theory parameters and the selected kinematic regions, and reduce the dependence of the cross sections on factorization and renormalization scales. We also calculate the renormalization group (RG) improved NLO cross sections by summing over the large logarithms from the RG running of Wilson coefficients. Moreover, we investigate the NLO QCD effects on various experimental observables and exclusion limits of quark compositeness scale.

Search for quark compositeness in dijet angular distributions from pp collisions at $ \sqrt {s} = 7{ } $ TeV

Abstract A search for quark compositeness using dijet angular distributions from pp collisions at $ \sqrt {s} = 7 $ TeV is presented. The search has been carried out using a data sample corresponding to an integrated luminosity of 2.2 fb−1, recorded by the CMS experiment at the LHC. Normalized dijet angular distributions have been measured for dijet invariant masses from 0.4 TeV to above 3 TeV and compared with a variety of contact interaction models, including those which take into account the effects of next-to-leading-order QCD corrections. The data are found to be in agreement with the predictions of perturbative QCD, and lower limits are obtained on the contact interaction scale, ranging from 7.5 up to 14.5 TeV at 95 % confidence level.

MODIFICATIONS TO THE HADRONIC REGGE TRAJECTORIES

The effect of quark mass on the Regge trajectory is analyzed. Modifications in the equations of Regge trajectories are shown for mesonic as well as baryonic systems. For mesonic systems, the Regge trajectories get modified, but still remain linear. Contrary to the mesonic case, the Regge trajectories for baryonic systems indicate nonlinearity. It is shown that in low mass and angular momentum region two hadrons with different quark compositions can have same mass and angular momentum.