Parton Distribution Functions (PDFs) at large Bjorken-$x$ are mostly constrained by high-energy measurements, and thus risk to absorb the energy-growing effects of unaccounted new physics (NP) if it were present in the high-energy tails of hadron-collider observables used in global PDF fits. If undetected, such contamination biases the resulting PDFs and can potentially hide the absorbed NP signals from subsequent searches. We illustrate this effect in a Standard Model Effective Field Theory (SMEFT) risk-assessment scenario affecting high-mass Drell-Yan production at the High-Luminosity LHC, and compare two strategies to obtain robust PDFs and SMEFT bounds: conservative fits that exclude data above an energy cut, and simultaneous fits of PDFs and Wilson coefficients performed with the {\tt SIMUnet} tool. Both approaches are shown to successfully recover the injected new physics that is otherwise absorbed and hidden by the PDFs.
High-mass Drell-Yan dilepton production provides one of the most sensitive probes of semileptonic four-fermion operators in the Standard Model Effective Field Theory (SMEFT), thanks to the energy growth of the corresponding contributions. At the same time, these measurements also constrain parton distribution functions (PDFs) in the large-$x$ region, where PDF uncertainties can mimic or obscure smooth new-physics effects. In this work we study how the impact of PDF profiling on SMEFT constraints depends on the quark-flavour structure of the effective operators, by performing a joint fit of SMEFT Wilson coefficients and PDF nuisance parameters. We find that PDF profiling induces a strongly flavour-dependent degradation of the SMEFT sensitivity, both with current data and in HL-LHC projections. The largest broadenings occur for operators involving first-generation quarks, whose effects are correlated with the high-$x$ valence-quark luminosities that dominate the high-mass spectrum. Operators involving heavier quark flavours are less affected, although with non-negligible operator-dependent variations. As a byproduct of our analysis, we obtain an estimate on the changes induced in the PDF sector by profiling SMEFT effects. We also show that angular information provides an important handle to reduce degeneracies among SMEFT directions and between SMEFT effects and allowed PDF deformations. These results demonstrate that the relevance of PDF uncertainties in high-energy SMEFT fits is not uniform across flavour space, and must be assessed in a flavour-dependent way.
We present a global two-channel Flatt\'e amplitude analysis of the hidden-charm pentaquark candidates observed by the LHCb collaboration in the J/{\psi}p invariant-mass spectrum using the Run 1+2 dataset. We simultaneously fit the three pentaquark amplitudes to the full spectrum, including a polynomial background and complex coupling phases. The scattering length and effective range are extracted from the fitted amplitudes using the effective range expansion, with uncertainties determined through non-parametric bootstrap resampling. While real couplings yield scattering parameters compatible with a molecular interpretation, this conclusion becomes less robust when coupling phases are included. We further find that interference effects are important for the closely spaced Pc(4440)+ and Pc(4457)+ states, demonstrating the limitations of the incoherent-sum approximation.
A. Likéné, P. P. Hebbar, Alexis Franck Rothen et al.· 0 citations
Electroweak precision observables (EWPO) remain among the most powerful indirect probes of physics beyond the Standard Model (BSM), and future $e^+ e^-$ colliders are expected to substantially enhance their sensitivity. Within the framework of the Standard Model Effective Field Theory (SMEFT), we show how EWPO predictions can be systematically improved to next-to-leading-logarithmic (NLL) accuracy by combining fixed-order tree-level and one-loop matching with two- and one-loop renormalization-group evolution. We derive NLL expressions that encode the full dependence on all 210 independent Wilson coefficients and illustrate their impact through fits to both current and projected collider measurements. This work provides a basis for global SMEFT analyses at NLL precision, thereby maximizing the indirect reach to BSM physics through EWPO measurements. The phenomenological relevance of this framework is illustrated explicitly in both the custodial Randall-Sundrum model and a custodial composite Higgs model.
Based on the combined Deep-Inelastic Scattering (DIS) data from HERA and the exclusive $J/\psi$ and $\Upsilon$ cross sections measured at the LHC, we investigate the role of absorptive corrections on the low-$x$ behaviour of parton distribution functions (PDFs) at low and moderate scales. Using $\texttt{xFitter}$, we study the impact of these data and of non-linear evolution on PDFs at next-to-leading order (NLO) and through the NNLO$^*$ method introduced in a previous work. Finally, we determine the effective size of proton hot spots within this framework and discuss the implications of our results for future global PDF determinations.
V. Bertone, C. Flett, A. D. Martin et al.· 0 citations
We present a next-to-next-to-leading order (NNLO) QCD analysis of polarized parton distribution functions (PDFs) based on the world data set of inclusive polarized deep-inelastic scattering (DIS). The resulting PDF set, denoted as \texttt{KLS26}, includes a consistent treatment of target-mass corrections (TMCs), higher-twist (HT) contributions, and positivity constraints within a fully NNLO framework. To estimate the residual theoretical uncertainty associated with nonperturbative power corrections, both additive and multiplicative HT parametrizations are considered. Although these two approaches lead to different higher-twist coefficients, the current results yield very similar fit qualities and compatible polarized PDFs within uncertainties. The impact of NNLO corrections is assessed through a comparison with the KLSS21 polarized PDF determination at NLO, showing the most visible changes in the polarized strange-quark distribution, together with moderate modifications in the gluon sector and smaller effects in the up- and down-quark helicity distributions. Additional fits treating the nonsinglet axial charges as free parameters, together with different higher-twist implementations, induce small but flavor-dependent modifications in the PDFs, with the most noticeable effects in the polarized strange-quark distribution and moderate sensitivity in the gluon. The \texttt{KLS26} set establishes an updated determination of helicity-dependent parton distributions, enabling future precision studies of nucleon spin structure.
Javad Shahrzad, Elliot Leader, A. Khorramian· 0 citations
We present a next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) QCD analysis of the non-singlet structure function $xF_3$, utilizing a Gegenbauer-polynomial representation for the input parton distribution functions (PDFs). The main objective is to assess how this flexible parameterization improves the extraction of valence quark distributions in the presence of nuclear effects. To this end, we incorporate nuclear modification factors into the input PDFs for heavy nuclear targets and solve the DGLAP evolution equations analytically in Laplace space. The structure function in Bjorken-$x$ space is then reconstructed using a Jacobi polynomial expansion. This combined framework enables a systematic investigation of the $xF_3$ data from the CCFR, NuTeV, and CHORUS experiments at both NLO and NNLO accuracies. We further examine the sensitivity of the extracted distributions to nuclear corrections and discuss their implications for the Gross--Llewellyn Smith, Bjorken, and Adler sum rules. Our results demonstrate that the Gegenbauer-polynomial PDF formalism provides a flexible and efficient framework for describing nuclear $xF_3$ data, yielding improved phenomenological consistency across a wide kinematic range.
Shahin Atashbar Tehrani, J. Sheibani, E. Astaraki· 0 citations
