Flavor Scheme Research Articles

Measurements of the production cross-section for a Z boson in association with b- or c-jets in proton–proton collisions at s=13\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s} = 13$$\\end{document} TeV with the ATLAS detector

This paper presents a measurement of the production cross-section of a Z boson in association with b- or c-jets, in proton–proton collisions at s=13\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s} = 13$$\\end{document} TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 140 fb-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {fb}^{-1}$$\\end{document}. Inclusive and differential cross-sections are measured for events containing a Z boson decaying into electrons or muons and produced in association with at least one b-jet, at least one c-jet, or at least two b-jets with transverse momentum pT>20\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$p_\ ext {T} > 20$$\\end{document} GeV and rapidity |y|<2.5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$|y| < 2.5$$\\end{document}. Predictions from several Monte Carlo generators based on next-to-leading-order matrix elements interfaced with a parton-shower simulation, with different choices of flavour schemes for initial-state partons, are compared with the measured cross-sections. The results are also compared with novel predictions, based on infrared and collinear safe jet flavour dressing algorithms. Selected Z+≥1c\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z + \\ge 1~c$$\\end{document}-jet observables, optimized for sensitivity to intrinsic-charm, are compared with benchmark models with different intrinsic-charm fractions.

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

The flavor puzzle: Textures and symmetries

We discuss aspects of a promising top-down origin of flavor symmetries in particle physics. Modular transformations originating from string theory dualities are shown to play a crucial role. We introduce the notion of an “eclectic” flavor scheme that unifies traditional flavor symmetries, modular symmetries and [Formula: see text]-transformations. It exhibits the phenomenon of “Local Flavor Unification” with enhanced flavor symmetries at fixed points or lines in moduli space. Successful fits of masses and mixing angles of quarks and leptons are found in the vicinity of these points and lines.

On lowest-lying 1/2− octet baryons * *Supported in part by National Nature Science Foundations of China (11975028, 10925522)

The recently proposed baryon is studied in a flavor scheme with K-matrix unitarization, by fitting to low-energy cross section and phase shift data. It is found that co-exists with low-lying poles in other channels, which have been extensively discussed in the literature, though they belong to different octets in the limit. Hence, the existence of is further verified.

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.

Top-down anatomy of flavor symmetry breakdown

A top-down approach to the flavor puzzle leads to eclectic flavor groups which include modular and traditional flavor symmetries. Based on examples of semirealistic T2/Z3 orbifold compactifications of heterotic string theory, we discuss the breakdown patterns of the eclectic flavor group via the interplay of vacuum expectation values (vevs) of moduli and flavon fields. This leads to an attractive flavor scheme with various possibilities to obtain "flavor hierarchies" through the alignment of these vevs. Despite the fact that the top-down approach gives strong restrictions for bottom-up flavor model building, it seems to be well suited to provide a realistic flavor pattern for quarks and leptons.

Two-loop leading-colour QCD helicity amplitudes for Higgs boson production in association with a bottom-quark pair at the LHC

We compute the two-loop QCD helicity amplitudes for the production of a Higgs boson in association with a bottom quark pair at a hadron collider. We take the approximations of leading colour and work in the five flavour scheme, where the bottom quarks are massless while the Yukawa coupling is non-zero. We extract analytic expressions from multiple numerical evaluations over finite fields and present the results in terms of an independent set of special functions that can be reliably evaluated over the full phase space.

Completing the eclectic flavor scheme of the \u21242 orbifold

We present a detailed analysis of the eclectic flavor structure of the two-dimensional ℤ2 orbifold with its two unconstrained moduli T and U as well as SL(2, ℤ)T× SL(2, ℤ)U modular symmetry. This provides a thorough understanding of mirror symmetry as well as the R-symmetries that appear as a consequence of the automorphy factors of modular transformations. It leads to a complete picture of local flavor unification in the (T, U) modulus landscape. In view of applications towards the flavor structure of particle physics models, we are led to top-down constructions with high predictive power. The first reason is the very limited availability of flavor representations of twisted matter fields as well as their (fixed) modular weights. This is followed by severe restrictions from traditional and (finite) modular flavor symmetries, mirror symmetry, mathcal{CP} and R-symmetries on the superpotential and Kähler potential of the theory.

Eclectic flavor scheme from ten-dimensional string theory - II detailed technical analysis

String theory leads to a flavor scheme where modular symmetries play a crucial role. Together with the traditional flavor symmetries they combine to an eclectic flavor group, which we determine via outer automorphisms of the Narain space group. Unbroken flavor symmetries are subgroups of this eclectic group and their size depends on the location in moduli space. This mechanism of local flavor unification allows a different flavor structure for different sectors of the theory (such as quarks and leptons) and also explains the spontaneous breakdown of flavor- and CP-symmetries (via a motion in moduli space). We derive the modular groups, including CP and R-symmetries, for different sub-sectors of six-dimensional string compactifications and determine the general properties of the allowed flavor groups from this top-down perspective. It leads to a very predictive flavor scheme that should be confronted with the variety of existing bottom-up constructions of flavor symmetry in order to clarify which of them could have a consistent top-down completion.

Single production of vectorlike T quark decaying into Wb at the LHC and the future pp colliders

In a simplified model including a singlet vectorlike top partner $T$ with charge $2/3$, we investigate the single production of $T$ decaying into $Wb$ in the four flavor scheme at the 14 TeV LHC, high luminosity LHC, and future high energy $pp$ colliders, such as high energy (HE)-LHC with $\sqrt{s}=27\text{ }\text{ }\mathrm{TeV}$ and FCC-hh with $\sqrt{s}=100\text{ }\text{ }\mathrm{TeV}$. By performing a detailed detector simulation and the background analysis, we display the excluding capability on the top partner $T$ at different colliders with a different integrated luminosity at 95% confidence level. We find that the excluding capability is enhanced obviously with the increase of the collision energy and the HE-LHC and FCC-hh have a greater advantage in high ${m}_{T}$ regions. If the colliders reach their high integrated luminosity, (1) the high luminosity LHC can exclude the region ${g}^{*}\ensuremath{\in}[0.19,0.50]$ with ${m}_{T}\ensuremath{\in}[1300\text{ }\text{ }\mathrm{GeV},2420\text{ }\text{ }\mathrm{GeV}]$ with $3\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$, (2) the HE-LHC can exclude the regions ${g}^{*}\ensuremath{\in}[0.07,0.50]$ with ${m}_{T}\ensuremath{\in}[1300\text{ }\text{ }\mathrm{GeV},4500\text{ }\text{ }\mathrm{GeV}]$ with $15\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$, and (3)the FCC-hh can exclude the regions ${g}^{*}\ensuremath{\in}[0.02,0.50]$ with ${m}_{T}\ensuremath{\in}[1300\text{ }\text{ }\mathrm{GeV},11250\text{ }\text{ }\mathrm{GeV}]$ with $30\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$. For these typical integrated luminosities, we also display the discovering capability on the top partner $T$ at different colliders. Besides, if the narrow width approximation limit is considered, we find that the excluding and discovering parameter space will be reduced.

NLO QCD+EW predictions for tHj and tZj production at the LHC

In this work we calculate the cross sections for the hadroproduction of a single top quark or antiquark in association with a Higgs (tHj) or Z boson (tZj) at NLO QCD+EW accuracy. In the case of tZj production we consider both the case of the Z boson undecayed and the complete final state tℓ+ℓ−j, including off-shell and non-resonant effects. We perform our calculation in the five-flavour-scheme (5FS), without selecting any specific production channel (s-, t- or tW associated). Moreover, we provide a more realistic estimate of the theory uncertainty by carefully including the differences between the four-flavour-scheme (4FS) and 5FS predictions. The difficulties underlying this procedure in the presence of EW corrections are discussed in detail. We find that NLO EW corrections are in general within the NLO QCD theory uncertainties only if the flavour scheme uncertainty (4FS vs. 5FS) is taken into account. For the case of tℓ+ℓ−j production we also investigate differences between NLO QCD+EW predictions and NLO QCD predictions matched with a parton shower simulation including multiple photon emissions.

Eclectic flavor scheme from ten-dimensional string theory – I. Basic results

In a consistent top-down approach based on orbifold compactifications, modular and traditional flavor symmetries combine nontrivially to the so-called eclectic flavor symmetry. We extend this scheme from two extra dimensions, discussed previously, to the six extra dimensions of string theory. By doing so, new insights on the nature of CP and its spontaneous breaking emerge. Moreover, we identify a new interpretation of R-symmetries as unbroken remnants from modular symmetries that are associated with geometrically stabilized complex structure moduli. Hence, all symmetries (i.e. modular, traditional flavor, CP and R) share a common origin in string theory: on a technical level, they are given by outer automorphisms of the Narain space group. The eclectic top-down approach leads to a very restrictive scheme with high predictive power. It remains a challenge to connect this with existing bottom-up constructions of modular flavor symmetry.

Measurements of the production cross-section for a Z boson in association with b-jets in proton-proton collisions at sqrt{s} = 13 TeV with the ATLAS detector

This paper presents a measurement of the production cross-section of a Z boson in association with b-jets, in proton-proton collisions at sqrt{s} = 13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 35.6 fb−1. Inclusive and differential cross-sections are measured for events containing a Z boson decaying into electrons or muons and produced in association with at least one or at least two b-jets with transverse momentum pT> 20 GeV and rapidity |y| < 2.5. Predictions from several Monte Carlo generators based on leading-order (LO) or next-to-leading-order (NLO) matrix elements interfaced with a parton-shower simulation and testing different flavour schemes for the choice of initial-state partons are compared with measured cross-sections. The 5-flavour number scheme predictions at NLO accuracy agree better with data than 4-flavour number scheme ones. The 4-flavour number scheme predictions underestimate data in events with at least one b-jet.

Single top production in PDF fits

We study the impact of recent LHC t-channel single top-quark and top-antiquark measurements at centre-of-mass energies of 7, 8 and 13 TeV on the parton distribution functions (PDFs) of the proton. We consider, namely, total cross sections, top-antitop cross section ratios, and differential distributions. We present a critical appraisal of the data, studying in particular how their description is affected by the theoretical details that enter the computation of the corresponding observables: QCD and electroweak higher-order corrections, the flavour scheme, and the value of the bottom-quark threshold. We perform a series of fits to the data within the NNPDF3.1 framework, whereby next-to-next-to-leading order QCD corrections are applied to single top measurements in a systematic way. We find that there exists an optimal combination of data that maximises consistency with the rest of the dataset, and efficiency in constraining the up, down and, partially, gluon PDFs.

NNLO QCD⊕QED corrections to Higgs production in bottom quark annihilation

We present next-to-next-to leading order (NNLO) quantum electrodynamics (QED) corrections to the production of the Higgs boson in bottom quark annihilation at the Large Hadron Collider (LHC) in the five flavor scheme. We have systematically included the NNLO corrections resulting from the interference of quantum chromodynamics (QCD) and QED interactions. We have investigated the infrared (IR) structure of the bottom quark form factor up to two loop level in QED and in QCD$\times$QED using K+G equation. We find that the IR poles in the form factor are controlled by the universal cusp, collinear and soft anomalous dimensions. In addition, we derive the QED as well as QCD$\times$QED contributions to soft distribution function as well as to the ultraviolet renormalization constant of the bottom Yukawa coupling up to second order in strong coupling and fine structure constant. Finally, we report our findings on the numerical impact of the NNLO results from QED and QCD$\times$QED at the LHC energies taking into account the dominant NNLO QCD corrections.

Higgs pair production from bottom quark annihilation to NNLO in QCD

We present the first results on the two-loop massless QCD corrections to the four-point amplitude b+overline{b}to H+H in the five flavor scheme, treating bottom quarks as massless. This amplitude is sensitive to the trilinear Higgs boson coupling. Our two-loop result for this amplitude constitutes of purely virtual contributions to the next-to-next-to-leading order QCD predictions for the production of a pair of Higgs bosons at the Large Hadron Collider. Using these two loop amplitudes and exploiting the universality of the soft contributions in perturbative QCD, we obtain the NNLO QCD effects in the soft plus virtual approximation. We find that the inclusion of higher order terms reduce the uncertainties resulting from the unphysical renormalisation and factorisation scales.

Electroweak and QCD corrections to Z -boson production with one b jet in a massive five-flavor scheme

We compute the $O(\alpha_s \alpha^2)$ and $O(\alpha_s^2 \alpha)$ contributions to the production cross section of a $Z$ boson with one $b$ jet at the Large Hadron Collider (LHC), and study their phenomenological relevance for LHC physics. The accurate prediction of hadronic $Z+b$-jet production is needed to control a background that greatly affects both the measurement of Higgs-boson properties and searches of new physics at the LHC. At the same time it could enable the first precise measurement of the $b$-quark parton distribution function. In this context $b$-quark mass effects become relevant and need to be studied with care, both at the level of the hard process and at the level of the initial- and final-state parton evolution. It is the aim of this paper to explore some of these issues in the framework of a massive 5 Flavor Scheme and to assess the need for both the inclusion of electroweak corrections, in addition to QCD corrections, and $b$-quark mass effects in the prediction of total and differential cross sections for hadronic $Z+b$-jet production.

Probing anomalous Wtb couplings at the LHC in single t -channel top quark production

We study the sensitivity of certain observables to the anomalous right tensorial coupling in single top production at the LHC at $\sqrt{s}=13 \text{ TeV}$. The observables consist of asymmetries constructed from the energy and angles of the decay products of the top quark produced in single top production through $t$-channel. The computation is done at Leading Order (LO) and Next-to-Leading Order (NLO) in the strong coupling in the $5$ flavor scheme. We have estimated projected limits on the anomalous coupling, both at the parton level without cuts and at the particle level with cuts. We find that the asymmetries are robust with respect to the higher order QCD corrections and are indeed a very good probe of this anomalous coupling of the top. Hence they can be used as experimental probes of the same.

Measurements of the vector boson production with the ATLAS detector

Measurements of the Drell-Yan production of W and Z bosons at the LHC provide a benchmark of our understanding of perturbative QCD and probe the proton structure in a unique way. The ATLAS collaboration has performed new high precision measurements at a center-of-mass energy of 7 TeV. The measurements are performed for W+, W- and Z bosons integrated and as a function of the boson or lepton rapidity and the Z mass. Unprecedented precision is reached and strong constraints on Parton Distribution Functions, in particular the strange density are found. Z boson cross sections are also measured at center-of-mass energies of 8 TeV and 13 TeV, and cross-section ratios to the top-quark pair production have been derived. This ratio measurement leads to a cancellation of systematic effects and allows for a high precision comparison to the theory predictions. The production of jets in association with vector bosons is a further important process to study perturbative QCD in a multi-scale environment. The ATLAS collaboration has performed new measurements of Z boson plus jets cross sections, differential in several kinematic variables, in proton-proton collision data taken at a center-of-mass energy of 13 TeV. The measurements are compared to state-of-the art theory predictions. They are sensitive to higher-order pQCD effects, probe flavour and mass schemes and can be used to constrain the proton structure. In addition, a new measurement of the splitting scales of the kt jet-clustering algorithm for final states containing a Z boson candidate at a center-of-mass energy of 8 TeV is presented.

Measurements of the associated production of a Z boson and b jets in pp collisions at {sqrt{s}} = 8,text {TeV}

Measurements of the associated production of a mathrm{Z} boson with at least one jet originating from a b quark in proton–proton collisions at sqrt{s} = 8,text {TeV} are presented. Differential cross sections are measured with data collected by the CMS experiment corresponding to an integrated luminosity of 19.8,text {fb}^{-1}. mathrm{Z} bosons are reconstructed through their decays to electrons and muons. Cross sections are measured as a function of observables characterizing the kinematics of the mathrm{b} jet and the mathrm{Z} boson. Ratios of differential cross sections for the associated production with at least one mathrm{b} jet to the associated production with any jet are also presented. The production of a mathrm{Z} boson with at least two mathrm{b} jets is investigated, and differential cross sections are measured for the dijet system. Results are compared to theoretical predictions, testing two different flavour schemes for the choice of initial-state partons.