The Schwinger effect, a non-perturbative mechanism for particle production in strong fields, plays a crucial role in understanding quantum vacuum decay and high-energy phenomena, including heavy-ion collisions (HIC). Although holographic quantum chromodynamics (QCD) models have been widely used to study this effect, most treatments assume isotropy or consider only a single type of anisotropy, neglecting the interplay between spatial and magnetic anisotropies that arise in realistic HIC scenarios. A unified framework accounting for both anisotropies is needed to accurately model particle production. We investigate the Schwinger effect in a twice anisotropic holographic QCD model incorporating both spatial and magnetic anisotropies. Using the anti-de Sitter/conformal field theory correspondence, we compute the total potential of a particle-antiparticle pair to quantify how these anisotropies influence pair production. Our results show that the magnetic field (parameterized by $c_B$ and $q_3$ ) enhances the Schwinger effect by lowering and narrowing the potential barrier, while increasing spatial anisotropy (controlled by $\nu$ ) suppresses the process by raising and widening the barrier. These findings demonstrate that magnetic and spatial anisotropies exert competing effects on particle production, emphasizing the necessity of treating both concurrently in holographic models. This work advances the theoretical description of the Schwinger effect in anisotropic environments, with implications for understanding non-equilibrium dynamics in HIC and other strongly coupled systems.

China

Wen-Bin Chang

Defu Hou

Schwinger effect in a twice anisotropic holographic model * Defu Hou's research is supported in part by the National Key Research and Development Program of China (2022YFA1604900). Additionally, Defu Hou receives partial support from the National Natural Science Foundation of China (NSFC) (12435009, 12275104). Wen-Bin Chang is supported by the Ph.D. Research Startup Project at Hubei Minzu University (RZ2500000857)

<p>Parton distribution functions (PDFs) form an essential part of particle physics calculations. Currently, the most precise predictions for these nonperturbative functions are generated through fits to global data. A problem that several PDF fitting groups encounter is the presence of tension in datasets that appear to pull the fits in different directions. In other words, the best fit depends on the choice of dataset. Several methods to capture the uncertainty in PDFs in presence of seemingly inconsistent fits have been proposed and are currently in use. These methods are important to ensure that uncertainty in PDFs are not underestimated. Here we propose a novel method for estimating the uncertainty by introducing a generalized statistical model based on Bayesian hierarchical models, which is implemented via the Gaussian Mixture Model (GMM). The methodology is inspired by unsupervised machine learning techniques and is closely related to the statistical methods of ensemble learning and Bayesian model averaging. Using a toy model of PDFs, we demonstrate how the GMM can be used to faithfully reconstruct the likelihood associated with PDF fits, which can in turn be used to accurately determine the uncertainty on PDFs, especially in the presence of tension in the fitted datasets. We further show how this statistical model reduces to the usual <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>χ</mi><mn>2</mn></msup></math> likelihood function for a consistent dataset and provide measures to optimize the number of Gaussians in the GMM.</p>

Mengshi Yan

Tie-Jiun Hou

Zhao Li

United States

Kirtimaan Mohan

C.P. Yuan

Generalized statistical model for fits to parton distributions

<p>In this study, we investigate the impact of new Large Hadron Collider (LHC) inclusive jet and dijet measurements on parton distribution functions (PDFs) that describe the proton structure, with a particular focus on the gluon distribution at large momentum fraction, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>x</mi></math>, and the corresponding partonic luminosities. We assess constraints from these datasets using next-to-next-to-leading-order (NNLO) theoretical predictions, accounting for a range of uncertainties from scale dependence and numerical integration. From the scale choices available for the calculations, our analysis shows that the central predictions for inclusive jet production show a smaller scale dependence than dijet production. We examine the relative constraints on the gluon distribution provided by the inclusive jet and dijet distributions, and also explore the phenomenological implications for inclusive <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover><mi>H</mi></math> production at the LHC at 14 TeV.</p>

Alim Ablat

Sayipjamal Dulat

Joey Huston

Pavel Nadolsky

Ibrahim Sitiwaldi

Keping Xie

Impact of LHC precision measurements of inclusive jet and dijet production on the CTEQ-TEA global PDF fit

The impact of recent LHC top-quark pair production single differential cross section measurements at 13 TeV collision energy on the structure of the proton is explored. In particular, the impact of these high-precision data on the gluon and other parton distribution functions (PDFs) of the proton at intermediate and large partonic momentum fraction <math><mi>x</mi></math> is analyzed. This study extends the CT18 global analysis framework to include these new data. The interplay between top-quark pair and inclusive jet production as well as other processes at the LHC, is studied. In addition, a study of the impact of scale choice on the theory description of the new 13 TeV <math><mi>t</mi><mover><mi>t</mi><mo>¯</mo></mover></math> measurements is performed.

Marco Guzzi

Exploring the impact of high-precision top-quark pair production data on the structure of the proton at the LHC

In this study, we examine closely the impact of the post-CT18 LHC Drell-Yan data on parton distribution functions (PDFs) in the general CTEQ-TEA global analysis framework. We compare the two main theoretical predictions, the MCFM fixed order calculations at next-to-next-to-leading order (NNLO) and the ResBos2 NNLO matched to <math><msub><mi>q</mi><mi>T</mi></msub></math> resummation up to next-to-next-to-next-to-leading logarithmic (N3LL) level. We find that the overall inclusive cross sections agree well but the fiducial distributions can differ at a percent level. We mainly discuss the result of the ResBos2 resummation calculation which yields a smaller Monte Carlo uncertainty, and a better description to the post-CT18 LHC Drell-Yan data. We find that the majority of post-CT18 LHC Drell-Yan data are consistent with the ATLAS 7 TeV <math><mrow><mi>W</mi></mrow></math>, <math><mrow><mi>Z</mi></mrow></math> data, which were included in the CT18A, but not CT18, fit and increases the strange-quark distribution at the small <math><mi>x</mi></math> region. The noticeable exception is that the ATLAS and LHCb 8 TeV <math><mi>W</mi></math> data pull <math><mi>d</mi><mo>(</mo><mover><mi>d</mi><mo>¯</mo></mover><mo>)</mo></math> quark PDFs to the opposite direction with respect to the ATLAS 7 TeV <math><mrow><mi>W</mi></mrow></math>, <math><mrow><mi>Z</mi></mrow></math> data. The inclusion of these post-CT18 LHC Drell-Yan datasets in the CTEQ-TEA global analysis is to update the CT18 PDFs following similar trends as CT18Z PDFs. The parton luminosities and a few phenomenological implications with the fiducial <math><msup><mi>W</mi><mo>±</mo></msup><mo>,</mo><mi>Z</mi></math> and inclusive <math><mi>H</mi><mo>,</mo><mi>t</mi><mover><mi>t</mi><mo>¯</mo></mover><mo>,</mo><mi>t</mi><mover><mi>t</mi><mo>¯</mo></mover><mi>H</mi></math> productions at the 14 TeV LHC, as examples, are presented.

Precision studies of the post-CT18 LHC Drell-Yan data in the CTEQ-TEA global analysis

In this paper, we present a CT18 PDF global QCD analysis at leading order in QCD perturbation theory. The CT18 LO PDFs is obtained within the general CT18 framework, along with two additional procedures imposed to improve the quality of the fit. We take the <math><mi>W</mi></math>-boson charge asymmetry and inclusive single-top production at LHC as examples to illustrate implications of the CT18 LO PDFs.

CT18 global PDF fit at leading order in QCD

We study the impact of lattice data on the determination of the strangeness asymmetry distribution <math><mrow><msub><mrow><mi>s</mi></mrow><mrow><mo>−</mo></mrow></msub><mo>(</mo><mi>x</mi><mo>)</mo><mo>≡</mo><mi>s</mi><mo>(</mo><mi>x</mi><mo>)</mo><mo>−</mo><mover><mrow><mi>s</mi></mrow><mrow><mo>¯</mo></mrow></mover><mo>(</mo><mi>x</mi><mo>)</mo></mrow></math> in the general CTEQ-TEA global analysis of parton distribution functions (PDFs) of the proton. Firstly, we find that allowing a nonvanishing <math><msub><mi>s</mi><mo>−</mo></msub><mo>(</mo><mi>x</mi><mo>)</mo></math>, at the initial <math><msub><mi>Q</mi><mn>0</mn></msub><mo>=</mo><mn>1.3</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> scale, in a global PDF analysis leads to a CT18As fit with similar quality to CT18A. Secondly, including the lattice data in the CT18As_Lat fit greatly reduces the <math><mrow><msub><mrow><mi>s</mi></mrow><mrow><mo>−</mo></mrow></msub></mrow></math>-PDF error band size in the large-<math><mi>x</mi></math> region. To further reduce its error would require more precise lattice data, extended to smaller <math><mi>x</mi></math> values. We take ATLAS 7 TeV <math><mi>W</mi></math> and <math><mi>Z</mi></math> production data, SIDIS dimuon production data, <math><msub><mi>F</mi><mn>3</mn></msub></math> structure function data, E866 NuSea data, and E906 SeaQuest data as examples to illustrate the implication of CT18As and CT18As_Lat fits. The parametrization dependence for PDF ratio <math><mrow><mo>(</mo><mi>s</mi><mo>+</mo><mover><mrow><mi>s</mi></mrow><mrow><mo>¯</mo></mrow></mover><mo>)</mo><mo>/</mo><mo>(</mo><mover><mrow><mi>u</mi></mrow><mrow><mo>¯</mo></mrow></mover><mo>+</mo><mover><mrow><mi>d</mi></mrow><mrow><mo>¯</mo></mrow></mover><mo>)</mo><mo>(</mo><mi>x</mi><mo>)</mo></mrow></math> is analyzed with CT18As2 and CT18As2_Lat fits as results.

Huey-Wen Lin

Impact of lattice strangeness asymmetry data in the CTEQ-TEA global analysis

The forward-backward asymmetry (<math><msub><mi>A</mi><mrow><mi>F</mi><mi>B</mi></mrow></msub></math>) in the Drell-Yan process <math><mi>p</mi><mi>p</mi><mo>/</mo><mi>p</mi><mover><mi>p</mi><mo>¯</mo></mover><mo>→</mo><mi>Z</mi><msup><mi>γ</mi><mo>*</mo></msup><mo>→</mo><msup><mo>ℓ</mo><mo>+</mo></msup><msup><mo>ℓ</mo><mo>−</mo></msup></math> is sensitive to the proton structure information. Such information has been factorized into well-defined proton structure parameters which can be regarded as experimental observables. In this paper, we extract the structure parameters from the <math><msub><mi>A</mi><mrow><mi>F</mi><mi>B</mi></mrow></msub></math> distributions reported by the CMS Collaboration in <math><mi>p</mi><mi>p</mi></math> collisions at <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>8</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>, and by the D0 Collaboration in <math><mi>p</mi><mover><mi>p</mi><mo>¯</mo></mover></math> collisions at <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>1.96</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>. It is the first time that the unique parton information in the <math><msub><mi>A</mi><mrow><mi>F</mi><mi>B</mi></mrow></msub></math> spectrum can be decoupled from the electroweak calculation and measured as standalone observables, which can be used as new data constraints in the global quantum chromodynamics analysis of the parton distribution functions. Although the parton information in the <math><mi>p</mi><mi>p</mi></math> and <math><mi>p</mi><mover><mi>p</mi><mo>¯</mo></mover></math> collisions are different, and the precisions are statistically limited, the results from both the hadron colliders indicate that the down quark contribution might be higher in the data than their theoretical predictions.

Mingzhe Xie

Siqi Yang

Yao Fu

Minghui Liu

Liang Han

Measurement of the proton structure parameters in the forward-backward charge asymmetry

The separation of the connected and disconnected sea partons, which were uncovered in the Euclidean path-integral formulation of the hadronic tensor, is accommodated with an extended parametrization of the nonperturbative parton distribution functions in the CT18 global analysis. This is achieved with the help of the distinct small <math><mi>x</mi></math> behaviors of these two sea partons and the constraint from the lattice calculation of the ratio of the strange momentum fraction to that of the <math><mover><mi>u</mi><mo>¯</mo></mover></math> or <math><mover><mi>d</mi><mo>¯</mo></mover></math> in the disconnected insertion. The whole dataset of CT18 is used in this CT18CS fit. The impact of the recent SeaQuest data on the <math><mover><mi>d</mi><mo>¯</mo></mover><mo>(</mo><mi>x</mi><mo>)</mo><mo>−</mo><mover><mi>u</mi><mo>¯</mo></mover><mo>(</mo><mi>x</mi><mo>)</mo></math> distribution of CT18CS is also discussed. The separate momentum fractions for the valence, the connected sea and disconnected sea of <math><mi>u</mi></math> and <math><mi>d</mi></math>, the strange and the gluon partons are presented at the input scale <math><mi>μ</mi><mo>=</mo><mn>1.3</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> for the first time. They can be compared term-by-term with systematic error controlled lattice calculations.

Jian Liang

Keh-Fei Liu

Connected and disconnected sea partons from the CT18 parametrization of PDFs

We propose the boost asymmetry of the diboson productions <math><msub><mi>q</mi><mi>i</mi></msub><msub><mover><mi>q</mi><mo>¯</mo></mover><mi>j</mi></msub><mo>→</mo><mi>V</mi><msup><mi>V</mi><mo>′</mo></msup></math> in <math><mi>p</mi><mi>p</mi></math> collisions (<math><mi>V</mi><msup><mi>V</mi><mo>′</mo></msup><mo>=</mo><mi>W</mi><mi>γ</mi></math>, <math><msup><mi>W</mi><mo>+</mo></msup><msup><mi>W</mi><mo>−</mo></msup></math>, and <math><mi>W</mi><mi>Z</mi></math>) as a new experimental observable, which can provide unique information on the proton structure. The boost asymmetry rises as the difference in the kinematics of the two bosons, that are coupled to the two different quark and antiquark initial states, respectively, and thus reflects different features of the <math><msub><mi>q</mi><mi>i</mi></msub></math> and <math><msub><mover><mi>q</mi><mo>¯</mo></mover><mi>j</mi></msub></math> parton densities. By comparing the kinematics of the two bosons, such as the boson energy or rapidity, the diboson events with <math><msub><mover><mi>q</mi><mo>¯</mo></mover><mi>j</mi></msub></math> having higher energy than <math><msub><mi>q</mi><mi>i</mi></msub></math> can be distinguished from those with <math><msub><mi>q</mi><mi>i</mi></msub></math> having higher energy than <math><msub><mover><mi>q</mi><mo>¯</mo></mover><mi>j</mi></msub></math>. This would provide unique information in some special parton momentum fraction regions, which cannot be directly proved by current <math><mi>W</mi></math> and <math><mi>Z</mi></math> measurements at the Large Hadron Collider or other deep inelastic scattering experiments.