In this work, we study the constraining power of future lepton colliders on fragmentation functions (FFs) to light charged hadrons from quarks and gluon in the framework of QCD collinear factorization. We perform analyses of FFs at NLO by including a wide range of pseudo-data from future lepton colliders, such as measurements on hadron multiplicities in the production of two jets and boson pairs, at various center of mass energies, and from hadronic decays of the Higgs boson, including both to heavy quarks and to gluons. The high luminosity and high energies of future lepton colliders allow for quark flavor separations and ensure a precise determination of FFs based solely on data from electron-positron collisions. We find that either the CEPC, FCC- or ILC can significantly reduce the uncertainties of FFs in a wide kinematic range, compared to the NPC23 set obtained with a global analysis to current world data. We also discuss the impact of higher-order QCD corrections, and the potential constraints from measurements of three-jet production. Furthermore, we describe an update of the FMNLO program allowing for calculating hadron production cross sections at next-to-next-to-leading order in QCD, which is used in this study.

China

Bin Zhou

Jun Gao

The impact of data from future lepton colliders on light hadrons fragmentation functions

We present improved predictions of a class of event-shape distributions called angularity for a contribution from an effective operator   $ H\to gg $   in Higgs hadronic decay that suffers from large perturbative uncertainties. In the framework of the soft-collinear effective theory, logarithmic terms of the distribution are resummed at NNLL' accuracy, for which a two-loop constant of gluon-jet function for angularity is independently determined using a fit to the fixed-order distribution at the NLO corresponding to   $ H\to gg $   relative to the Born rate. Our determination has reasonable agreement with the value in a recently released thesis. In the fit, we use an asymptotic form with a fractional power conjectured from recoil corrections at one-loop order, and it improves the accuracy of determining positive values of the angularity parameter a. The resummed distribution is matched to the NLO fixed-order results to make our predictions valid at all angularity values. We also discuss the first and subtracted moments of angularity as a function of a that enable the extraction of information on leading and subleading nonperturbative corrections associated with gluons.

Jiawei Zhu

Yujin Song

South Korea

Daekyoung Kang

India

Tanmay Maji

Angularity in Higgs boson decays via → at NNLL' accuracy  

The Gao-Wald theorem says that the Penrose diagram of de Sitter spacetime reacts to a positive energy perturbation by getting “taller”. How does this change in the presence of timelike boundaries? We study this question in two-dimensional de Sitter JT gravity coupled to conformal matter. The effect of the boundaries has its roots in quantum corrections to the vacuum energy of the CFT due to Casimir-like effects. We consider two different kinds of timelike boundaries, and for each kind we compute the vacuum expectation value of the matter CFT stress tensor. The stress tensor violates the null energy condition in the first case and saturates it in the second case, with each case exhibiting a negative energy density in the vacuum state. We then compute the semiclassical backreaction of this energy density and show how it can make the spacetime “fatter” or “taller” or a combination of both, depending on the regime. The spacetime getting fatter corresponds to an increase in the value of the dilaton at the horizon and hence also in the static patch horizon area in the higher-dimensional solution. We comment on the implications of our results for the quantum theories living on the timelike boundaries.

United States

Gauri Batra

Timelike boundaries in de Sitter JT gravity and the Gao-Wald theorem

Fragmentation functions (FFs) are essential nonperturbative QCD inputs for predicting hadron production cross sections in high energy scatterings. In this study, we present a joint determination of FFs for light charged hadrons through a global analysis at next-to-leading order (NLO) in QCD. Our analysis incorporates a wide range of precision measurements from the LHC, as well as data from electron-positron collisions and semi-inclusive deep inelastic scatterings. By including measurements of jet fragmentation at the LHC in our global analysis, we are able to impose strong constraints on the gluon FFs. A careful selection of hadron kinematics is applied to ensure the validity of factorization and perturbative calculations of QCD. In addition, we introduce several methodological advances in fitting, resulting in a flexible parametrization form and the inclusion of theoretical uncertainties from perturbative calculations. Our best-fit predictions show very good agreement with the global data, with <math><msup><mi>χ</mi><mn>2</mn></msup><mo>/</mo><msub><mi>N</mi><mrow><mi>p</mi><mi>t</mi></mrow></msub><mo>∼</mo><mn>0.90</mn></math>. We also generate a large number of Hessian error sets to estimate uncertainties and correlations of the extracted FFs. FFs to charged pions (kaons and protons) are well constrained for momentum fractions down to 0.01 (0.1). Total momentum of partons carried by light charged hadrons are determined precisely. Their values for <math><mi>u</mi></math>, <math><mi>d</mi></math> quarks and gluon saturate at about 50% for a lower cut of the momentum fraction of 0.01. Comparing our determinations to results from other groups, we find significant discrepancies, particularly for the proton fragmentation functions, as well as for gluon and unfavored quarks to pions and kaons. Pulls from individual datasets and impact of various choices of the analysis are also studied in details. Our analysis raises questions concerning existing and future experimental measurements, including the need for clarifications on the definitions of various hadron final states and the necessity of further measurements on fragmentation from heavy quarks. Additionally, we present an update of the fmnlo program used for calculating hadron production cross sections. We demonstrate the broad applications of the fmnlo program combined with our new FFs, including NLO predictions on jet charges in proton collisions and reference cross sections for heavy-ion collisions, which show good agreement with LHC data. Our FFs, including the error sets (denoted as NPC23), are publicly available in the form of LHAPDF6 grids.

ChongYang Liu

Germany

XiaoMin Shen

Hongxi Xing

Yuxiang Zhao

Global analysis of fragmentation functions to charged hadrons with high-precision data from the LHC

An extension of the xFitter open-source program for QCD analyses is presented, allowing for a polynomial parameterization of the dependence of physical observables on theoretical parameters. This extension enables simultaneous determination of parton distribution functions (PDFs) and new physics parameters within the framework of the Standard Model Effective Field Theory (SMEFT). The functionalities of the code are illustrated in a sensitivity study, where a simultaneous determination of the PDFs, top quark mass and the couplings of selected dimension-6 SMEFT operators is addressed using projections for measurements of top quark-antiquark pair production at the High-Luminosity LHC. The importance of considering all the correlations of the parton distributions, top quark mass and the SMEFT parameters in a simultaneous QCD+SMEFT analysis is demonstrated. This work serves as a new platform for simultaneous extraction of the PDFs and the SM/SMEFT parameters based on xFitter.

Xiao-Min Shen

Simone Amoroso

Katerina Lipka

Oleksandr Zenaiev

A framework for simultaneous fit of QCD and BSM parameters with xFitter

We perform a simultaneous global analysis of hadron fragmentation functions (FFs) to various charged hadrons (<math><msup><mi>π</mi><mo>±</mo></msup></math>, <math><msup><mi>K</mi><mo>±</mo></msup></math>, and <math><mi>p</mi><mo>/</mo><mover><mi>p</mi><mo>¯</mo></mover></math>) at next-to-leading order in QCD. The world data include results from electron-positron single-inclusive annihilation, semi-inclusive deep inelastic scattering, as well as proton-proton collisions including jet fragmentation measurements for the first time, which lead to strong constraints on the gluon fragmentations. By carefully selecting hadron kinematics to ensure the validity of QCD factorization and the convergence of perturbative calculations, we achieve a satisfying best fit with <math><msup><mi>χ</mi><mn>2</mn></msup><mo>/</mo><mrow><mi>d</mi><mo>.</mo><mi>o</mi><mo>.</mo><mi>f</mi><mo>.</mo></mrow><mo>=</mo><mn>0.90</mn></math>. The total momentum of <math><mi>u</mi></math>, <math><mi>d</mi></math> quarks and gluon carried by light charged hadrons have been determined precisely, urging precision determinations of FFs to neutral hadrons for a test of fundamental sum rules in QCD fragmentation.

Simultaneous Determination of Fragmentation Functions and Test on Momentum Sum Rule

We present a state-of-the-art prediction for cross sections of neutrino deep inelastic scattering (DIS) from nucleon at high neutrino energies, <math><mrow><msub><mrow><mi>E</mi></mrow><mrow><mi>ν</mi></mrow></msub></mrow></math>, up to 1000 EeV (<math><msup><mn>10</mn><mn>12</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>). Our calculations are based on the latest CT18 NNLO parton distribution functions (PDFs) and their associated uncertainties. To make predictions for the highest energies, we extrapolate the PDFs to small <math><mi>x</mi></math> according to several procedures and assumptions, thus affecting the uncertainties at ultrahigh <math><msub><mi>E</mi><mi>ν</mi></msub></math>; we quantify the uncertainties corresponding to these choices. Similarly, we quantify the uncertainties introduced by the nuclear corrections that are required to evaluate neutrino-nuclear cross sections for the neutrino observatories. These results can be applied to currently running astrophysical neutrino observatories, such as IceCube and KM3NeT, as well as various future experiments that have been proposed.

Keping Xie

T. J. Hobbs

Daniel R. Stump

C.P. Yuan

High-energy neutrino deep inelastic scattering cross sections

The projected energy correlator measures the energy deposited in multiple detectors as a function of the largest angular distance x  L  = (1 − cos χ  L )/2 between detectors. The collinear limit x  L  → 0 of the projected energy correlator is particularly interesting for understanding the jet-substructures, while the large logarithms of x  L  could potentially spoil the perturbation theory and must be resummed. As a necessary ingredient for its resummation at next-to-next-to-leading logarithmic (NNLL) accuracy, we calculate the two-loop jet functions for the projected three-point energy correlator (E3C), using direct integration method and the parameter space Integration-by-Part (IBP) method. We then present the NNLL resummation for e + e  −  annihilation and an approximate NNLL resummation for pp → jj process, where the two-loop hard constant is estimated in the latter case. The convergence is improved and the hadronization effect in the collinear limit is suppressed when considering the ratio of E3C distribution to two-point energy-energy correlator (EEC). Our results show potential in precision determination of strong coupling constant using energy correlators from both e + e  −  data and pp data.

Wen Chen

Yibei Li

Zhen Xu

Xiaoyuan Zhang

Hua Zhu

NNLL resummation for projected three-point energy correlator

We present FMNLO, a framework to combine general-purpose Monte Carlo generators and fragmentation functions (FFs). It is based on a hybrid scheme of phase-space slicing method and local subtraction method, and accurate to next-to-leading order (NLO) in QCD. The new framework has been interfaced to MG5_aMC@NLO and made publicly available in this work. We demonstrate its unique ability by giving theoretical predictions of various fragmentation measurements at the LHC, followed by comparison with the data. With the help of interpolation techniques, FMNLO allows for fast calculation of fragmentation processes for a large number of different FFs, which makes it a promising tool for future fits of FFs. As an example, we perform a NLO fit of parton fragmentation functions to unidentified charged hadrons using measurements at the LHC. We find the ATLAS data from inclusive dijet production show a strong constraining power. Notable disparities are found between our gluon FF and that of BKK, DSS and NNFF, indicating the necessities of additional constraints and data for gluon fragmentation function.

Automated calculation of jet fragmentation at NLO in QCD

The charged Higgs boson plays an essential role in distinguishing between a wide variety of standard model extensions with multiple Higgs doublets, and has been searched for in various collider experiments. This paper expands our previous work to a broader Higgs mass space with discussions on subsequent issues. We study the prospect of a light charged Higgs boson, produced by top quark pairs at the Large Hadron Collider (LHC), and decaying into a <math><mi>W</mi></math> boson (can be off shell) and a pair of bottom quarks via on-shell production of an intermediate neutral Higgs boson. We reinterpret the cross sections of <math><mi>W</mi><mi>W</mi><mi>b</mi><mi>b</mi><mover><mi>b</mi><mo>¯</mo></mover><mover><mi>b</mi><mo>¯</mo></mover></math> final states measured by the ATLAS Collaboration at LHC 13 TeV in the presence of the decay chain <math><mi>t</mi><mo>→</mo><msup><mi>H</mi><mo>+</mo></msup><mi>b</mi><mo>,</mo><msup><mi>H</mi><mo>+</mo></msup><mo>→</mo><msup><mi>W</mi><mo>+</mo></msup><msub><mi>H</mi><mi>i</mi></msub><mo>,</mo><msub><mi>H</mi><mi>i</mi></msub><mo>→</mo><mi>b</mi><mover><mi>b</mi><mo>¯</mo></mover></math>, and H.c., where <math><msub><mi>H</mi><mi>i</mi></msub></math> is a neutral Higgs boson variably lighter than the charged Higgs boson. We find improved agreements with the data and obtain limits on the total branching ratio of the aforementioned decay chain. The limits impose the strongest constraints on the parameter space of type-I two-Higgs-doublet model for most Higgs masses sampled when <math><msub><mi>H</mi><mi>i</mi></msub></math> is the <math><mi>C</mi><mi>P</mi></math>-odd Higgs boson <math><mi>A</mi></math>. We also calculate potential constraints with pseudodata in high-luminosity runs of the LHC.

ChunHao Fu

Constraint for a light charged Higgs boson and its neutral partners from top quark pairs at the LHC