Search

Approximate knowledge of the renormalon structure of the Bjorken polarised sum rule (BSR) Γ‾1p−n(Q2) leads to the corresponding BSR characteristic function that allows us to evaluate the leading-twist part of BSR. In our previous work [1], this evaluation (resummation) was performed using perturbative QCD (pQCD) coupling a(Q2)≡αs(Q2)/π in specific renormalisation schemes. In the present paper, we continue this work, by using instead holomorphic couplings [a(Q2)↦A(Q2)] that have no Landau singularities and thus require, in contrast to the pQCD case, no regularisation of the resummation formula. The D=2 and D=4 terms are included in the Operator Product Expansion (OPE) of inelastic BSR, and fits are performed to the available experimental data in a specific interval (Qmin2,Qmax2) where Qmax2=4.74GeV2. We needed relatively high Qmin2≈1.7GeV2 in the pQCD case since the pQCD coupling a(Q2) has Landau singularities at Q2≲1GeV2. Now, when holomorphic (AQCD) couplings A(Q2) are used, no such problems occur: for the 3δAQCD and 2δAQCD variants the preferred values are Qmin2≈0.6GeV2. The preferred values of αs in general cannot be unambiguously extracted, due to large uncertainties of the experimental BSR data. At a fixed value of αsMS‾(MZ2), the values of the D=2 and D=4 residue parameters are determined in all cases, with the corresponding uncertainties.

The discovery of collective effects in small collision systems has spurred a renewed interest in hadronization models, and is also a source for collective effects all the way to large collision systems, where they are usually ascribed to the creation of a Quark–Gluon Plasma. In this topical mini-review, the microscopic model for string interactions, based on the Lund string hadronization model, developed with exactly this aim in mind is reviewed, and some prospects for the future are presented. [ABSTRACT FROM AUTHOR]

We use the known renormalon structure of Bjorken polarised sum rule (BSR) Γ‾1p−n(Q2) to evaluate the leading-twist part of that quantity. In addition, we include D=2 and D=4 Operator Product Expansion (OPE) terms and fit this expression to available experimental data for inelastic BSR. Since we use perturbative QCD (pQCD) coupling, which fails at low squared spacelike momenta Q2≲1GeV2 due to Landau singularities, the fit is performed for Q2≥Qmin2 where Qmin2≈(1.7±0.3)GeV2. Due to large BSR experimental uncertainties, the extracted value of the pQCD coupling has very large uncertainties, especially when Qmin2 is varied. However, when we fix the pQCD coupling to the known world average values, the D=2 and D=4 residue parameters can be determined within large but reasonable uncertainties.

We study the jet energy drop, which is the relative difference between the groomed and ungroomed jet energy or transverse momentum. It is one of the fundamental quantities that characterizes the impact of grooming on jets produced in high energy collisions. We consider three different grooming algorithms i) soft drop, ii) iterated soft drop, and iii) trimming. We carry out the resummation of large logarithms of the jet energy drop, the jet radius as well as relevant grooming parameters at next-to-leading logarithmic (NLL′) accuracy. In addition, we account for non-global and clustering logarithms, and determine the next-to-leading order corrections. For soft drop we perform a joint resummation of the jet energy drop and the groomed jet radius, which is necessary to achieve the correct all-order structure of the cross section, in particular for the Sudakov-safe case of soft drop with β = 0. We present numerical results for LHC energies and compare to Pythia simulations as well as CMS data. Our factorization framework predicts the onset of nonperturbative effects in the jet energy distribution, in line with what we find in Pythia. The jet energy drop observables stand out because they only probe soft radiation, making them ideal candidates for the tuning of parton shower Monte Carlo event generators and for probing medium effects in heavy-ion collisions.

We analyze the behavior of cumulants of conserved charges in a subvolume of a thermal system with exact global conservation laws by extending a recently developed subensemble acceptance method (SAM) [1] to multiple conserved charges. Explicit expressions for all diagonal and off-diagonal cumulants up to sixth order that relate them to the grand canonical susceptibilities are obtained. The derivation is presented for an arbitrary equation of state with an arbitrary number of different conserved charges. The global conservation effects cancel out in any ratio of two second order cumulants, in any ratio of two third order cumulants, as well as in a ratio of strongly intensive measures Σ and ∆ involving any two conserved charges, making all these quantities particularly suitable for theory-to-experiment comparisons in heavy-ion collisions. We also show that the same cancellation occurs in correlators of a conserved charge, like the electric charge, with any non-conserved quantity such as net proton or net kaon number. The main results of the SAM are illustrated in the framework of the hadron resonance gas model. We also elucidate how net-proton and net-Λ fluctuations are affected by conservation of electric charge and strangeness in addition to baryon number.

We consider the longitudinal momentum distribution of hadrons inside jets in proton-proton collisions. At partonic threshold large double logarithmic corrections arise which need to be resummed to all orders. We develop a factorization formalism within SCET that allows for the joint resummation of threshold and jet radius logarithms. We achieve next-to-leading logarithmic NLL′ accuracy by including non-global logarithms in the leading-color approximation. Overall, we find that the threshold resummation leads to a sizable enhancement of the cross section and a reduced QCD scale dependence, suggesting that the all-order resummation can be important for the reliable extraction of fragmentation functions in global analyses when jet substructure data is included.

We present results for the soft drop groomed jet radius Rg at next-to-leading logarithmic accuracy. The radius of a groomed jet which corresponds to the angle between the two branches passing the soft drop criterion is one of the characteristic observables relevant for the precise understanding of groomed jet substructure. We establish a factorization formalism that allows for the resummation of all relevant large logarithms, which is based on demonstrating the all order equivalence to a jet veto in the region between the boundaries of the groomed and ungroomed jet. Non-global logarithms including clustering effects due to the Cambridge/Aachen algorithm are resummed to all orders using a suitable Monte Carlo algorithm. We perform numerical calculations and find a very good agreement with Pythia 8 simulations. We provide theoretical predictions for the LHC and RHIC.

The coordinate and momentum space configurations of the net baryon number in heavy ion collisions that undergo spinodal decomposition, due to a first-order phase transition, are investigated using state-of-the-art machine-learning methods. Coordinate space clumping, which appears in the spinodal decomposition, leaves strong characteristic imprints on the spatial net density distribution in nearly every event which can be detected by modern machine learning techniques. On the other hand, the corresponding features in the momentum distributions cannot clearly be detected, by the same machine learning methods, in individual events. Only a small subset of events can be systematically differ- entiated if only the momentum space information is available. This is due to the strong similarity of the two event classes, with and without spinodal decomposition. In such sce- narios, conventional event-averaged observables like the baryon number cumulants signal a spinodal non-equilibrium phase transition. Indeed the third-order cumulant, the skewness, does exhibit a peak at the beam energy (Elab = 3–4 A GeV), where the transient hot and dense system created in the heavy ion collision reaches the first-order phase transition.

Abstract In this paper, we give comprehensive analyses for event shape observables in electron-positron annihilation by using the Principle of Maximum Conformality (PMC) which is a rigorous scale-setting method to eliminate the renormalization scheme and scale ambiguities in perturbative QCD predictions. Conventionally the renormalization scale and theoretical uncertainties in event shape observables are often evaluated by setting the scale to the center-of-mass energy s $$ \sqrt{s} $$ . The event shape distributions using this conventional scale setting are plagued by the large renormalization scale uncertainty and underestimate the experimental data. Moreover, since the renormalization scale is simply fixed to the center-of-mass energy s $$ \sqrt{s} $$ , only one value of the coupling α s at the single scale s $$ \sqrt{s} $$ can be extracted. In contrast, the PMC renormalization scales are determined by absorbing the nonconformal β contributions that govern the behavior of the running coupling via the Renormalization Group Equation (RGE). The resulting PMC scales change with event shape kinematics, reflecting the virtuality of the underlying quark and gluon subprocess. The PMC scales thus yield the correct physical behavior of the scale and the PMC predictions agree with precise event shape distributions measured at the LEP experiment. More importantly, we can precisely determine the running of the QCD coupling constant α s (Q 2) over a wide range of Q 2 in perturbative domain from event shape distributions measured at a single center-of-mass energy s $$ \sqrt{s} $$ .

The discovery of collective effects in small collision systems has spurred a renewed interest in hadronization models, and is also a source for collective effects all the way to large collision systems, where they are usually ascribed to the creation of a Quark–Gluon Plasma. In this topical mini-review, the microscopic model for string interactions, based on the Lund string hadronization model, developed with exactly this aim in mind is reviewed, and some prospects for the future are presented.

Abstract Due to the inclination for forward gauge radiation, lepton colliders beyond a few TeV are effectively electroweak (EW) boson colliders, suggesting the treatment of EW bosons as constituents of high-energy leptons. In the context of a muon collider, we revisit the validity of W and Z parton distribution functions (PDFs) at leading order in 2 → n process. We systematically investigate universal and quasi-universal power-law and logarithmic corrections that arise when deriving (polarized) weak boson PDFs in the collinear limit. We go on to survey a multitude of 2 → n processes at s $$ \sqrt{s} $$ = 2–30 TeV via polarized and unpolarized EW boson fusion/scattering. To conduct this study, we report a public implementation of the Effective W/Z and Weizsäcker-Williams Approximations, which we collectively call the Effective Vector Boson Approximation, into the Monte Carlo event generator MadGraph5_aMC@NLO. This implementation lays the groundwork for developing matrix-element matching prescriptions involving EW parton showers and renormalized EW PDFs. To further with this agenda, we give recommendations on using W/Z PDFs.

Abstract We consider the production of a pair of Z bosons at the LHC and study the inclusion of EW corrections in theoretical predictions at fixed order and based on multijet-merged parton-shower simulations. To this end we present exact NLO EW results for pp → e + e − μ + μ − , and, for the first time, for pp → e + e − μ + μ − j, and compare them to the EW virtual and NLL Sudakov approximation. We then match the exact NLO EW result to the resummed Sudakov logarithms to achieve an improved NLO EW + NLL EW sud exp $$ \mathrm{NLO}\ \mathrm{EW}+\mathrm{NLL}\ {\mathrm{EW}}_{\mathrm{sud}}^{\mathrm{exp}} $$ result. Further, we discuss the inclusion of the above EW corrections in MePs@Nlo event simulations in the framework of the Sherpa event generator. We present detailed phenomenological predictions for inclusive ZZ and ZZj production taking into account the dominant EW corrections through the EW virtual approximation, as well as through (exponentiated) EW Sudakov logarithms.

A triangular quark diagram describes the vertex 𝐾1𝐾𝜔 with axial-vector, vector, and pseudoscalar mesons is considered in the leading order of 1𝑁𝐶. The application of the obtained vertex to the hadronic decays of the 𝜏-lepton with the production of 𝐾𝜔, 𝐾𝜙 meson pairs in the final state is discussed. Calculation of quark diagrams are considered within the 𝑆𝑈(3) symmetric chiral Lagrangians, which describe the interactions of four meson nonets: scalar, pseudoscalar, vector, and axial-vector in the ground and in the first radially excited states. The calculated integral decay widths of 𝐾1(1270) → 𝐾 [𝜔, 𝜌] are in the agreement with the experimental data of the BES-III and Belle collaborations obtained at the BEPC II and KEK colliders. It is shown that the axial-vector channel with the intermediate meson 𝐾1𝐴 with quantum numbers 𝐽𝑃𝐶 = 1++ plays a dominant role in describing the decay widths of 𝜏 → 𝐾[𝜔, 𝜙]𝜈𝜏. In 𝜏 lepton decays, the contact channel and the channel with the axial vector meson 𝐾1𝐴 are taken into account. The first of them is related with the intermediate 𝑊 boson, which products a meson pair. The second channel is related with the intermediate 𝑊 boson, which transits into the axial vector state 𝐾1𝐴 and also products meson pairs. Consideration of these two channels independently of each other allows us to study the processes in more detail. The splitting of the strange axial vector state 𝐾1𝐴 into two physical mesons 𝐾1(1270) and 𝐾1(1400) due to the mixing of axial vector mesons from nonets 3𝑃1 and 1𝑃1 is also taken into account. The negative interference of the contact channel with the axial vector channel is established. The dependences of the integral decay widths of 𝜏 → 𝐾[𝜔, 𝜙]𝜈𝜏 on the value of the mixing angle of axial-vector mesons 𝐾1𝐴 and 𝐾1𝐵 are studied. A comparative analysis of the results with experimental data and theoretical estimates of other authors is carried out. The obtained theoretical predictions are in satisfactory agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Abstract In the paper, we calculate the fragmentation functions for g → B c and g → B c ∗ $$ {B}_c^{\ast } $$ . The ultraviolet divergences in the calculation are removed through the renormalization of the operator definition of the fragmentation functions under the modified minimal subtrac- tion scheme. We then obtain the fragmentation functions D g → B c $$ {D}_{g\to {B}_c} $$ (z, μ F ) and D g → B c ∗ $$ {D}_{g\to {B}_c^{\ast }} $$ (z, μ F ), which are presented as figures and fitting functions. The obtained fragmentation functions are complementary to the previous work on the next-to-leading order fragmentation functions for b ¯ $$ \overline{b} $$ → B c ( B c ∗ $$ {B}_c^{\ast } $$ ) and c → B c ( B c ∗ $$ {B}_c^{\ast } $$ ).

Abstract We investigate the subleading-power corrections to the exclusive B → Dℓν ℓ form factors at O $$ \mathcal{O} $$ ( α s 0 $$ {\alpha}_s^0 $$ ) in the light-cone sum rules (LCSR) framework by including the two- and three-particle higher-twist contributions from the B-meson light-cone distribution amplitudes up to the twist-six accuracy, by taking into account the subleading terms in expanding the hard-collinear charm-quark propagator, and by evaluating the hadronic matrix element of the subleading effective current . Employing further the available leading-power results for the semileptonic B → D form factors at the next-to- leading-logarithmic level and combining our improved LCSR predictions with the recent lattice determinations, we then carry out a comprehensive phenomenological analysis on the semi-leptonic B → Dℓν ℓ decay. We extract V cb = 40.2 − 0.5 + 0.6 th − 1.4 + 1.4 exp × 10 − 3 V cb = 40.9 − 0.5 + 0.6 th − 1.0 + 1.0 exp × 10 − 3 $$ \left|{V}_{cb}\right|=\left({40.2}_{-0.5}^{+0.6}{\left|{{}_{\mathrm{th}}}_{-1.4}^{+1.4}\right|}_{\mathrm{exp}}\right)\times {10}^{-3}\left(\left|{V}_{cb}\right|=\left({40.9}_{-0.5}^{+0.6}{\left|{{}_{\mathrm{th}}}_{-1.0}^{+1.0}\right|}_{\mathrm{exp}}\right)\times {10}^{-3}\right) $$ using the BaBar (Belle) experimental data, and particularly obtain for the gold-plated ratio R(D) = 0.302 ± 0.003.

Abstract The hadroproduction of a W boson in association with a charm quark at the Large Hadron Collider is at the centre of current investigations due to its potential to probe the strangeness content of the proton. In this paper we present an implementation of the W + c production process in the PowHel event generator matched to the PYTHIA8 parton shower approach, allowing to obtain predictions for differential cross-sections with NLO QCD accuracy matched to the accuracy of the Shower Monte Carlo event generator. Effects of non-diagonal CKM matrix elements, finite charm quark mass and off-shell W decays including spin correlations are taken into account. We investigate the production of a leptonically decaying W boson in association with either a charmed meson (W ± + D ∗∓) or a charmed jet (W ± + j c ) and compare our predictions with particle-level measurements by the ATLAS and CMS collaborations at s $$ \sqrt{s} $$ = 7 and 13 TeV. The role of the so-called “opposite sign” and “same sign” contributions to the theoretical cross-sections is presented and discussed, pointing out the importance of including parton shower effects for a reliable estimate of the latter and a faithful comparison with experimental data.

Abstract We discuss the necessary steps for implementing an angularly ordered (AO) electroweak (EW) parton shower in Herwig 7 multi-purpose event generator. This includes calculating the helicity-dependent quasi-collinear EW branching functions that correspond to the full range of final-state EW parton shower, in addition to the initial-state EW gauge vector boson radiations. The results are successfully embedded in the AO Herwig 7 shower algorithm and have undergone a set of comprehensive and conclusive performance tests. Furthermore, we have used this EW parton shower algorithm, alongside the existing QCD + QED AO shower, to predict the angular distributions of W ± bosons in LHC events with high transverse momentum jets. These results are compared against the explicitly generated underlying events as well as the existing ATLAS data to show the effectiveness of the newly implemented QCD + QED + EW AO parton shower scheme.

Abstract We present precise predictions for the hadronic production of an on-shell Higgs boson in association with a leptonically decaying gauge boson and a jet up to order α s 3 $$ {\alpha}_{\mathrm{s}}^3 $$ . We include the complete set of NNLO QCD corrections to both charged- and neutral-current Drell-Yan type contributions, as well as the previously known leading heavy quark loop induced contributions which involve a direct Higgs-quark coupling. As an application, we study a range of differential observables in proton-proton collisions at s $$ \sqrt{s} $$ = 13 TeV for both the charged- and neutral-current production modes. For each Higgs production process, we assess the improvement in the theoretical uncertainty for both the exclusive (n jet = 1) and inclusive (n jet ≥ 1) jet categories. We find that the inclusion of the NNLO corrections to the Drell-Yan type contributions is essential in stabilising the predictions and in reducing the theoretical uncertainty for both inclusive and exclusive jet production for all three modes. This is particularly true in the kinematical regimes associated with low to medium values of the transverse momentum of the produced vector boson and where the differential cross sections are the largest. For the neutral-current process, we find that the heavy quark loop induced contributions have their largest phenomenological impact (an increase in the size of the NNLO corrections, a distortion of the distribution shape and an enlargement of the left over remaining uncertainties) in kinematical regions associated to large values of p T,Z (typically above 150 GeV) where the cross sections are smaller.

Abstract We discuss the measurement of gluon transverse momentum distribution (TMD) in dijet and heavy hadron pair (HHP) production in semi-inclusive deep inelastic scattering. The factorization of these processes in position space shows the appearance of a specific new soft factor matrix element on top of angular and complex valued anomalous dimensions. We show in detail how these features can be treated consistently and we discuss a scale prescription for the evolution kernel of the dijet soft function. As a result we obtain phenomenological predictions for unpolarized and angular modulated cross-sections for the electron-ion collider (EIC) using current available information on unpolarized TMD.

Abstract We study the polar and azimuthal decay angular distributions of J/ψ mesons produced in semi-inclusive, deep-inelastic electron-proton scattering. For the description of the quarkonium formation mechanism, we adopt the framework of nonrelativistic QCD, with the inclusion of the intermediate color-octet channels that are suppressed at most by a factor v 4 in the velocity parameter v relative to the leading color-singlet channel. We put forward factorized expressions for the helicity structure functions in terms of transverse momentum dependent gluon distributions and shape functions, which are valid when the J/ψ transverse momentum is small with respect to the hard scale of the process. By requiring that such expressions correctly match with the collinear factorization results at high transverse momentum, we determine the perturbative tails of the shape functions and find them to be independent of the J/ψ polarization. In particular, we focus on the cos 2ϕ azimuthal decay asymmetry, which originates from the distribution of linearly polarized gluons inside an unpolarized proton. We therefore suggest a novel experiment for the extraction of this so-far unknown parton density that could be performed, in principle, at the future Electron-Ion Collider.

Abstract We present calculations of Higgs boson production via gluon-gluon fusion in association with one or two additional jets at next-to-leading order in QCD. The calculation of H+jet is exact in the treatment of the top-quark mass, whereas for the H+2 jets calculation the two-loop virtual amplitudes are approximated via a reweighting with leading-order mass effects, while keeping all top-quark mass effects in the real radiation contributions. For H+jet production, this study extends a previous calculation, revealing an error in the previous results. For total and differential cross sections, we present new results and compare the QCD corrections with the infinite top-mass limit, for which we find a strikingly good agreement if all amplitudes are rescaled by the leading-order mass dependence.

Abstract We compute for the first time the complete corrections at N3LO in the strong coupling constant to the inclusive neutral-current Drell-Yan process including contributions from both photon and Z-boson exchange. Our main result is the computation of the QCD corrections to the inclusive production cross section of an axial-vector boson to third order in the strong coupling in a variant of QCD with five massless quark flavours. Since the axial anomaly does not cancel for an odd number of flavours, we also consistently include non-decoupling effects in the top-quark mass through three loops. We perform a phenomenological study of our results, and we present for the first time predictions for the inclusive Drell-Yan process at the LHC at this order in QCD perturbation theory.

Abstract Non-global QCD observables are characterised by a sensitivity to the full angular distribution of soft radiation emitted coherently in hard scattering processes. This complexity poses a challenge to their all-order resummation, that was formulated at the leading-logarithmic order about two decades ago. In this article we present a solution to the long-standing problem of their resummation beyond this order, and carry out the first complete next-to-leading logarithmic calculation for non-global observables. This is achieved by solving numerically the recently derived set of non-linear differential equations which describe the evolution of soft radiation in the planar, large-N c limit. As a case study we address the calculation of the transverse energy distribution in the interjet rapidity region in e + e − → dijet production. The calculation is performed by means of an algorithm that we formulate in the language of jet-calculus generating functionals, which also makes the resummation technique applicable to more general non-global problems, such as those that arise in hadronic collisions. We find that NLL corrections are substantial and their inclusion leads to a significant reduction of the perturbative scale uncertainties for these observables. The computer code used in the calculations is made publicly available.

Abstract We introduce a simple procedure that resolves the long-standing question of how to account for single-logarithmic spin-correlation effects in parton showers not just in the collinear limit, but also in the soft wide-angle limit, at leading colour. We discuss its implementation in the context of the PanScales family of parton showers, where it complements our earlier treatment of the purely collinear spin correlations. Comparisons to fixed-order matrix elements help validate our approach up to third order in the strong coupling, and an appendix demonstrates the small size of residual subleading-colour effects. To help probe wide-angle soft spin correlation effects, we introduce a new declustering-based non-global spin-sensitive observable, the first of its kind. Our showers provide a reference for its single-logarithmic resummation. The work in this paper represents the last step required for final-state massless showers to satisfy the broad PanScales next-to-leading logarithmic accuracy goals.

Approximate knowledge of the renormalon structure of the Bjorken polarised sum rule (BSR) Γ ‾ 1 p − n (Q 2) leads to the corresponding BSR characteristic function that allows us to evaluate the leading-twist part of BSR. In our previous work [1] , this evaluation (resummation) was performed using perturbative QCD (pQCD) coupling a (Q 2) ≡ α s (Q 2) / π in specific renormalisation schemes. In the present paper, we continue this work, by using instead holomorphic couplings [ a (Q 2) ↦ A (Q 2) ] that have no Landau singularities and thus require, in contrast to the pQCD case, no regularisation of the resummation formula. The D = 2 and D = 4 terms are included in the Operator Product Expansion (OPE) of inelastic BSR, and fits are performed to the available experimental data in a specific interval (Q min 2 , Q max 2) where Q max 2 = 4.74 GeV 2. We needed relatively high Q min 2 ≈ 1.7 GeV 2 in the pQCD case since the pQCD coupling a (Q 2) has Landau singularities at Q 2 ≲ 1 GeV 2. Now, when holomorphic (AQCD) couplings A (Q 2) are used, no such problems occur: for the 3 δ AQCD and 2 δ AQCD variants the preferred values are Q min 2 ≈ 0.6 GeV 2. The preferred values of α s in general cannot be unambiguously extracted, due to large uncertainties of the experimental BSR data. At a fixed value of α s MS ‾ (M Z 2) , the values of the D = 2 and D = 4 residue parameters are determined in all cases, with the corresponding uncertainties. [ABSTRACT FROM AUTHOR]

Abstract We discuss peculiarities that arise in the computation of real-emission contributions to observables that contain Heaviside functions. A prominent example of such a case is the zero-jettiness soft function in SCET, whose calculation at next-to-next-to-next-to-leading order in perturbative QCD is an interesting problem. Since the zero-jettiness soft function distinguishes between emissions into different hemispheres, its definition involves θ-functions of light-cone components of emitted soft partons. This prevents a direct use of multi-loop methods, based on reverse unitarity, for computing the zero-jettiness soft function in high orders of perturbation theory. We propose a way to bypass this problem and illustrate its effectiveness by computing various non-trivial contributions to the zero-jettiness soft function at NNLO and N3LO in perturbative QCD.

Abstract Hadronic signals of new-physics origin at the Large Hadron Collider can remain hidden within the copiously produced hadronic jets. Unveiling such signatures require highly performant deep-learning algorithms. We construct a class of Graph Neural Networks (GNN) in the message-passing formalism that makes the network output infra-red and collinear (IRC) safe, an important criterion satisfied within perturbative QCD calculations. Including IRC safety of the network output as a requirement in the construction of the GNN improves its explainability and robustness against theoretical uncertainties in the data. We generalise Energy Flow Networks (EFN), an IRC safe deep-learning algorithm on a point cloud, defining energy weighted local and global readouts on GNNs. Applying the simplest of such networks to identify top quarks, W bosons and quark/gluon jets, we find that it outperforms state-of-the-art EFNs. Additionally, we obtain a general class of graph construction algorithms that give structurally invariant graphs in the IRC limit, a necessary criterion for the IRC safety of the GNN output.

Abstract We compute the next-to-next-to-leading order QCD corrections to Higgs boson production in weak boson fusion followed by its decay to a b b ¯ $$ \overline{b} $$ pair or to a pair of leptonically-decaying W bosons. Our calculation allows us to compute realistic fiducial cross sections and assess the impact of fiducial cuts applied to the Higgs boson decay products on the magnitude of QCD radiative corrections in weak boson fusion.

Abstract Sudakov form factors appear ubiquitously in factorized cross sections where they allow one to resum large logarithms to all orders in perturbation theory. Their exact evaluation requires numerical integrals over anomalous dimensions, which in practice can hamper efficiency. Alternatively, one can use approximate analytic solutions, which provide fast evaluation at the cost of numerical precision and loss of properties such as renormalization group invariance. We provide an exact analytic expression of the QCD Sudakov form factor which allows one to obtain fast and numerically exact results.

Abstract In scenarios beyond the Standard Model (BSM) characterised by charged (W′) or neutral (Z′) massive gauge bosons with large width, resonant mass searches are not very effective, so that one has to exploit the tails of the mass distributions measured at the Large Hadron Collider (LHC). In this case, the LHC sensitivity to new physics signals is influenced significantly by systematic uncertainties associated with the Parton Distribution Functions (PDF), particularly in the valence quark sector relevant for the multi-TeV mass region. As a BSM framework featuring such conditions, we consider the 4-Dimensional Composite Higgs Model (4DCHM), in which multiple W′ and Z′ broad resonances are present, with strongly correlated properties. By using the QCD tool xFitter, we study the implications on W′ and Z′ searches in Drell-Yan (DY) lepton decay channels that follow from the reduction of PDF uncertainties obtained through combining high-statistics precision measurements of DY lepton-charge and forward-backward asymmetries. We find that the sensitivity to the BSM states is greatly increased with respect to the case of base PDF sets, thereby enabling one to set more stringent limits on (or indeed discover) such new particles, both independently and in correlated searches.

Abstract We formulate the basic points of the pseudo-PDF approach to the lattice calculation of polarized gluon PDFs. We present the results of our calculations of the one-loop corrections for the bilocal G μα (z) G ~ $$ \overset{\sim }{G} $$ λβ (0) correlator of gluonic fields. Expressions are given for a general situation when all four indices are arbitrary, and also for specific combinations of indices corresponding to three matrix elements that contain the twist-2 invariant amplitude related to the polarized PDF. We study the evolution properties of these matrix elements, and derive matching relations between Euclidean and light-cone Ioffe-time distributions. These relations are necessary for extraction of the polarized gluon distributions from the lattice data.

Abstract We study polarisation of W-bosons produced in association with one jet at the LHC. In particular, we provide all necessary theoretical ingredients for the precise extraction of polarisation fractions. To that end, we present new polarised predictions up to NNLO QCD accuracy employing the narrow-width approximation, in two phase spaces: inclusive and fiducial. We compare results in the fiducial phase space to a full off-shell computation as well as experimental data. Finally, we fit the polarisation fractions using shape templates and show that NNLO corrections significantly improve their determination.

Abstract We report on the calculation of the next-lo-leading order QCD corrections to Higgs boson production and decay in association with top quarks. We consider leptonic decays of top quarks leading to the hadronic process pp → e + ν e μ − ν ¯ $$ \overline{\nu} $$ μ b b ¯ $$ \overline{b} $$ H(H → X) at the LHC with s $$ \sqrt{s} $$ = 13 TeV. All resonant as well as non-resonant Feynman diagrams, interferences and off-shell effects are included for the top quark and W gauge boson. Decays of the Higgs boson, on the other hand, are included in the narrow-width approximation. Specifically, we consider Higgs boson decays into b b ¯ $$ \overline{b} $$ , τ + τ − , γγ and e + e − e + e − . Numerical results are given at the integrated and differential fiducial level for various factorisation and renormalisation scale choices and different PDF sets. We study the main theoretical uncertainties that are associated with neglected higher order terms in the perturbative expansion and with different parametrisations of the PDFs. Furthermore, we examine the size of the off-shell effects by an explicit comparison to the calculation in the full narrow-width approximation. Finally, the impact of the contributions induced by the bottom-quark parton density is investigated.

Abstract We present a new approach to jet definition alternative to clustering methods, such as the anti-kT scheme, that exploit kinematic data directly. Instead the new method uses kinematic information to represent the particles in a multidimensional space, as in spectral clustering. After confirming its Infra-Red (IR) safety, we compare its performance in analysing gg → H 125 GeV → H 40 GeV H 40 GeV → b b ¯ b b ¯ $$ b\overline{b}b\overline{b} $$ , gg → H 500 GeV → H 125 GeV H 125 GeV → b b ¯ b b ¯ $$ b\overline{b}b\overline{b} $$ and gg, q q ¯ $$ q\overline{q} $$ → t t ¯ $$ t\overline{t} $$ → b b ¯ W + W − $$ b\overline{b}{W}^{+}{W}^{-} $$ → b b ¯ jj ℓ v ℓ $$ b\overline{b} jj\mathrm{\ell}{v}_{\mathrm{\ell}} $$ events from Monte Carlo (MC) samples, specifically, in reconstructing the relevant final states, to that of the anti-k T algorithm. Finally, we show that the results for spectral clustering are obtained without any change in the parameter settings of the algorithm, unlike the anti-k T case, which requires the cone size to be adjusted to the physics process under study.

Abstract We present a calculation of the helicity amplitudes for the process gg → γγ in three-loop massless QCD. We employ a recently proposed method to calculate scattering amplitudes in the ’t Hooft-Veltman scheme that reduces the amount of spurious non-physical information needed at intermediate stages of the computation. Our analytic results for the three-loop helicity amplitudes are remarkably compact, and can be efficiently evaluated numerically. This calculation provides the last missing building block for the computation of NNLO QCD corrections to diphoton production in gluon fusion.

Abstract We study the simulation of initial-state radiation in angular-ordered parton showers in order to investigate how different interpretations of the ordering variable affect the logarithmic accuracy of such showers. This also enables us to implement a recoil scheme which is consistent between final-state and initial-state radiation. We present optimal values of the strong coupling and intrinsic transverse momentum to be used in each version of the parton shower, tuned using Z 0-boson production at the LHC at 7 TeV. With these tuned showers, we perform a phenomenological study of the Drell-Yan process at several centre-of-mass energies.

Abstract In this paper we consider the next-to-next-to-leading order total cross section of Higgs boson pair production in the large top quark mass limit and compute four expansion terms in 1/ m t 2 $$ {m}_t^2 $$ . To this end, we analytically compute the real-virtual and double-real contributions to the total cross section and combine them with the existing virtual contribution. Good convergence is observed below the top quark threshold, which makes our results a valuable input for approximation methods which aim for next-to-next-to-leading order corrections over the whole kinematic range. We present details on various steps of our calculation; in particular, we provide results for three- and four-particle phase-space master integrals and describe in detail the evaluation of the collinear counterterms.

Abstract The rare three-body decay of a Higgs boson to a lepton-antilepton pair and a photon is starting to become experimentally accessible at the LHC. We investigate how higher-order QCD corrections to the dominant gluon-fusion production process impact on the fiducial cross sections in this specific Higgs decay mode for electrons and muons. Corrections up to NNLO QCD are found to be sizeable. They are generally uniform in kinematical variables related to the Higgs boson, but display several distinctive features in the kinematics of its individual decay products.

Abstract We use rational approximants to study missing higher orders in the massless scalar-current quark correlator. We predict the yet unknown six-loop coefficient of its imaginary part, related to Γ(H → b b ¯ $$ \overline{b} $$ ), to be c 5 = −6900 ± 1400. With this result, the perturbative series becomes almost insensitive to renormalization scale variations and the intrinsic QCD truncation uncertainty is tiny. This confirms the expectation that higher-order loop computations for this quantity will not be required in the foreseeable future, as the uncertainty in Γ(H → b b ¯ $$ \overline{b} $$ ) will remain largely dominated by the Standard Model parameters.

Abstract We propose a new approach for combining next-to-leading order (NLO) and parton shower (PS) calculations so as to obtain three core features: (a) applicability to general showers, as with the MC@NLO and POWHEG methods; (b) positive-weight events, as with the KrkNLO and POWHEG methods; and (c) all showering attributed to the parton shower code, as with the MC@NLO and KrkNLO methods. This is achieved by using multiplicative matching in phase space regions where the shower overestimates the matrix element and accumulative (additive) matching in regions where the shower underestimates the matrix element, an approach that can be viewed as a combination of the MC@NLO and KrkNLO methods.

Abstract We consider ZZ production in hadronic collisions and present state-of-the-art predictions in QCD perturbation theory matched to parton showers. Next-to-next-to-leading order corrections to the quark-initiated channel are combined with parton showers using the MiNNLOPS method, while next-to-leading order corrections to the loop-induced gluon fusion channel are matched using the Powheg method. Their combination, dubbed nNNLO+PS, constitutes the best theoretical description of ZZ events to date. Spin correlations, interferences and off-shell effects are included by calculating the full process pp → ℓ + ℓ − ℓ (′)+ ℓ (′)− . We show the crucial impact of higher-order corrections for both quark- and gluon-initiated processes as well as the relevance of the parton shower in certain kinematical regimes. Our predictions are in very good agreement with recent LHC data.

Abstract We study the resummation of the 0-jettiness resolution variable T $$ \mathcal{T} $$ 0 for the top-quark pair production process in hadronic collisions. Starting from an effective theory framework we derive a factorisation formula for this observable which allows its resummation at any logarithmic order in the T $$ \mathcal{T} $$ 0 → 0 limit. We then calculate the O $$ \mathcal{O} $$ (α s ) corrections to the soft function matrices and, by employing renormalisation group equation methods, we obtain the ingredients for the resummation formula up to next-to-next-to-leading logarithmic (NNLL) accuracy. We study the impact of these corrections to the 0-jettiness distribution by comparing predictions at different accuracy orders: NLL, NLL′, NNLL and approximate NNLL′ ( NNLL a ′ $$ {\mathrm{NNLL}}_{\mathrm{a}}^{\prime } $$ ). We match these results to the corresponding fixed order calculations both at leading order and next-to-leading order for the t t ¯ $$ \overline{t} $$ +jet production process, obtaining the most accurate prediction of the 0-jettiness distribution for the top-quark pair production process at NNLL a ′ $$ {\mathrm{NNLL}}_{\mathrm{a}}^{\prime } $$ +NLO accuracy.

Abstract We study linear power corrections O $$ \mathcal{O} $$ (ΛQCD /Q) to certain collider observables. We present arguments that prove that such corrections cannot appear in observables that are inclusive with respect to QCD radiation, such as total cross sections as well as rapidity and transverse momentum distributions of color-neutral particles. Although our calculations are carried out in a simplified framework, our arguments and conclusions are applicable, with some reservations, to processes both at lepton and hadron colliders. We also show how an improved understanding of the origin of linear power corrections allows us to simplify their calculation. As an application, we compute the leading non-perturbative corrections to the C-parameter and the thrust in e + e − annihilation in a generic three-jet configuration.

Abstract Hadron production in proton-nucleus (pA) collisions was previously shown to be suppressed by medium-induced fully coherent energy loss (FCEL). We show that the quenching of D and B mesons in pPb collisions at the LHC due solely to FCEL is, at least, on par with other nuclear effects such as gluon shadowing or saturation. This is consistent with previous findings for both quarkonium and light hadron production in pA collisions, emphasising that FCEL effects need to be included for a reliable understanding of hadron production measurements in pA collisions.

Abstract Through this article, we present the two-loop massless QCD corrections to the production of di-Higgs and di-pseudo-Higgs boson through quark annihilation in the large top quark mass limit. Within dimensional regularisation, we employ the non-anticommuting γ 5 and treat it under the Larin prescription. We discover the absence of any additional renormalisation, so-called contact renormalisation, that could arise from the short distance behaviour of two local operators. This finding is in corroboration with the operator product expansion. By examining the results, we discover the lack of similarity in the highest transcendentality weight terms between these finite remainders and that of a pair of half-BPS primary operators in maximally supersymmetric Yang-Mills theory. We need these newly computed finite remainders to calculate observables involving di-Higgs or di-pseudo- Higgs at the next-to-next-to-leading order. We implement the results to a numerical code for further phenomenological studies.

Abstract We provide the renormalization constants of the axial current operators, both singlet and non-singlet, in dimensional regularization up to four-loop order in (QCD), determined using the off-shell Ward-Takahashi identity for an axial current with a non-anticommuting γ 5. A possible application of the result for the singlet axial current operator is the extraction of the non-decoupling mass logarithms in the axial quark form factors.

We study jet mass distributions measured in the single inclusive jet production in proton-proton collisions pp → jet+X at the LHC. We consider both standard ungroomed jets as well as soft drop groomed jets. Within the Soft Collinear Effective Theory (SCET), we establish QCD factorization theorems for both cases and we study their relation. The developed framework allows for the joint resummation of several classes of logarithmic corrections to all orders in the strong coupling constant. For the ungroomed case, we resum logarithms in the jet radius parameter and in the small jet mass. For the groomed case, we resum in addition the logarithms in the soft threshold parameter zcut which is introduced by the soft drop grooming algorithm. In this way, we are able to reliably determine the absolute normalization of the groomed jet mass distribution in proton-proton collisions. All logarithmic corrections are resummed to the next-to-leading logarithmic accuracy. We present numerical results and compare with the available data from the LHC. For both the groomed and ungroomed jet mass distributions we find very good agreement after including non-perturbative corrections.

Abstract : A number of recent applications of jet substructure, in particular searches for light new particles, require substructure observables that are decorrelated with the jet mass. In this paper we introduce the Convolved SubStructure (CSS) approach, which uses a theoretical understanding of the observable to decorrelate the complete shape of its distribution. This decorrelation is performed by convolution with a shape function whose parameters and mass dependence are derived analytically. We consider in detail the case of the D 2 observable and perform an illustrative case study using a search for a light hadronically decaying Z′. We find that the CSS approach completely decorrelates the D 2 observable over a wide range of masses. Our approach highlights the importance of improving the theoretical understanding of jet substructure observables to exploit increasingly subtle features for performance.