arXiv subjects

D. Keller

Publications and source records attributed to D. Keller.

At least 19 recordsLinked to original sources

arXiv2026

Deep-neural-network extraction of unpolarized transverse-momentum-dependent parton distributions in $b_T$ space from Drell-Yan data

We present a physics-informed deep-neural-network extraction of unpolarized transverse-momentum-dependent parton distribution functions (TMDPDFs) in impact-parameter space from Drell--Yan data. The perturbative contribution is computed with a resummed $W$ term using $\mathrm{N}^{3}\mathrm{LL}$ evolution, strict-NLO hard and operator-product-expansion matching, and smooth profile scales at small and large $b_T$. A compact feature-wise linear modulation network learns only a shared nonperturbative factor $F_{NP}(x,b_T)$; the collinear PDFs, hard factor, evolution kernel, matching coefficients, and Fourier--Bessel transform remain fixed. The primary result is a smooth light-flavor $b_T$-space TMD ensemble and its cross-section-level validation. The reported $k_T$ distributions are regularized finite-$b_T$ Hankel transforms, not independent momentum-space fits. As a separate robustness test, a smooth finite-$Y$ transition is applied to 24 additional Tevatron points extending to $q_T/Q\simeq0.30$. The nominal 329-point fit is unchanged, and the results remain stable when $F_{\rm NP}$ is held fixed while the transition profile is varied. An independent 122-bin Tevatron $\mathrm{N}^{3}\mathrm{LL}+\mathrm{NNLO}$ $W+Y$ grid provides a direct perturbative benchmark. A separate $W+Y$ candidate using the specified non-LHCb finite-$Y$ inputs is retained as an identifiability study.

hep-ph↗

arXiv2026

First measurement of polarized spin-density matrix elements and differential cross sections d$\sigma$/d$t$ in $\omega$~photoproduction off the proton for $2.7 < E_\gamma < 5.2$ GeV using CLAS at Jefferson Lab

We report on the differential cross sections d$\sigma$/d$t$, the unpolarized spin-density matrix elements $\rho^0_{00}$, $\rho^0_{1-1}$, Re\,$\rho^0_{10}$, and the first extraction of the polarized elements Im\,$\rho^3_{10}$, Im\,$\rho^3_{1-1}$ for the reaction $\gamma p\to p\omega$ using the CLAS spectrometer at Jefferson Laboratory. The $\omega$~mesons were detected in their dominant charged decay mode, $\omega \to \pi^+\pi^-\pi^0$, and all $t$-dependent results are presented in a fine binning for incident photon energies between 2.73 and 5.16~GeV (corresponding to the center-of-mass energy range $W \in [\,2.45,3.25\,]$~GeV). All matrix elements are first measurements for $-t > 0.6$~GeV$^2$. Moreover, differential cross sections d$\sigma$/d(cos\,$\Theta_{\rm \,c.m.}^{\,\omega}$) and the corresponding angle-dependent unpolarized spin-density matrix elements in the Adair frame are presented for the incident photon energy range 1.56--3.80~GeV (corresponding to $W \in [\,1.95,2.83\,]$~GeV). These new $\omega$~photoproduction data are consistent with earlier CLAS results but extend the energy range well beyond the nucleon resonance region into the Regge regime. The comparison with Regge-theory-based model predictions shows that the new data impose more stringent constraints on our understanding of $\omega$~photoproduction.

nucl-ex↗

arXiv2026

A New Low $Q^2$ Measurement of the Proton's $g_1$ Spin Structure Function from Longitudinal & Transverse Polarized Data

The proton's spin structure has proven to be far more complicated than was originally believed, and has been the subject of a number of experimental investigations. %Early measurements of the proton's spin structure function $g_1$ showed that the proton does not solely derive its spin from the spins of its quarks, starting the `proton spin crisis'. Of particular interest are the spin structure functions $g_1$ and $g_2$, which can be used to generate moments to directly compare experimental results to Chiral Perturbation Theory and other theories of Quantum Chromodynamics (QCD). The proton's $g_1$ structure function has been the subject of two other recent low momentum transfer experiments, but there are currently no published low momentum transfer measurements which collected data on the proton structure functions using both a longitudinally-polarized and a transversely-polarized target at the same kinematics. In this paper, we present the longitudinally polarized results of the Jefferson Lab E08-027 experiment, along with linked moments which combine this new result with the previously published transversely-polarized data from the same experiment. These results provide a proton $g_1$ extraction measured with very high precision across the resonance region, and provide new information on the value of $g_1$ dependent sum rules and moments.

nucl-ex↗

arXiv2026

Evidence for Q-Dependent Nuclear Transverse-Momentum Redistribution Beyond Broadening from AI-driven analysis of p-Cu Drell-Yan

We extract a target-side Cu transverse-momentum profile from fixed-target $p$--Cu Drell--Yan data by holding a momentum-space proton reference fixed and training only an asymmetric Cu kernel in the small-$q_T$ region. In the supported window, $0.15 \le x_{Cu} \le 0.46$ and $7.5 \le Q_M \le 15.75$ GeV, the nuclear modification is not a universal width increase. It appears as $Q$-dependent redistribution: an $\mathcal{O}(1~{\rm GeV})$ shoulder and compensating probability flow between shoulder and resolved-tail regions, beyond one-parameter broadening.

hep-ph↗

arXiv2026

Toward selective quantum advantage in hadronic tomography:explicit cases from Compton form factors, GPDs, TMDs, and GTMDs

We recast the case for quantum advantage in hadronic physics as an observable-by-observable question rather than a blanket claim about Quantum Chromo-Dynamics (QCD). Focusing on hadronic tomography, we analyze why Compton form factors (CFF), generalized parton distributions (GPDs), Transverse Momentum-dependent Distributions (TMDs), and Generalized Transverse Momentum-dependent Distributions (GTMDs) are natural quantum targets: they are defined by light-front, off-forward, or real-time correlation functions whose extraction from Euclidean calculations or sparse experimental data is often an ill-posed inverse problem. We separate three notions of advantage -- algorithmic, computational, and representational -- and connect each to explicit formal objects. At the algorithmic level, Hamiltonian simulation, linear-response algorithms, and amplitude-estimation primitives motivate gains for real-time and sign-problematic observables. At the computational level, direct quantum evaluation of matrix elements and correlators becomes plausible for PDFs, GPDs, timelike response, and high-energy evolution. At the inference level, recent Quantum Deep Neural Network (QDNN) studies of CFF extraction indicate improved performance in noisy and sparse regimes and motivate hybrid fits in which a quantum simulator supplies a physics prior while a classical network models detector and nuisance effects. We discuss why real-device execution is scientifically necessary, summarize current hardware milestones, and propose benchmark criteria for credible claims of quantum advantage in hadronic tomography.

hep-ph↗

arXiv2026

Adiabatic Fast Passage Spin Manipulation Measurements in Solid Polarized Targets

Adiabatic fast passage (AFP) is a rapid method for reversing nuclear polarization and manipulating spin populations in polarized solid targets, avoiding the long repolarization times associated with dynamic nuclear polarization (DNP). We report AFP measurements in a 5~T, 1~K polarized-target system for irradiated $^{15}$NH$_3$, irradiated $^{14}$ND$_3$, and butanol-based materials prepared either with TEMPO doping or by irradiation. We also present a joint manipulated-lineshape analysis for spin-1 targets and demonstrate that vector and tensor polarizations can be extracted from AFP-manipulated deuteron NMR spectra even when the populations are not described by a single Boltzmann spin temperature. Finally, we report a reproducible polarization- and direction-dependent AFP response in a large irradiated $^{15}$NH$_3$ sample. These ammonia results are presented as empirical observations under the specific sample-coil conditions of the experiment, with possible circuit-mediated mechanisms such as radiation damping or superradiant behavior discussed but not assigned as a definitive cause.

physics.atom-ph↗

arXiv2026

Measurements of Beam Spin Asymmetries of $\pi^\pm\pi^0$ dihadrons at CLAS12

A first measurement of beam spin asymmetries for $\pi^+\pi^0$ and $\pi^-\pi^0$ pairs in semi-inclusive deep inelastic scattering is reported. The asymmetries in the dihadron angular distributions were measured from the scattering of a 10.6 GeV longitudinally polarized electron beam off a proton target, using the CLAS12 detector at Jefferson Lab. A photon classifier using a Gradient Boosted Trees (GBTs) architecture was trained with Monte Carlo simulations to reduce the amount of false combinatorial background $\pi^0$s, increasing statistics by up to five-fold compared to previous CLAS12 $\pi^0$ analyses. A nonzero $\sin\phi_{R_\perp}$ asymmetry is observed. This measurement is sensitive to the underexplored collinear twist-3 PDF $e(x)$, which encodes quark-gluon correlations in the proton, and presents a new avenue for its point-by-point extraction. The asymmetries also provide the first experimental evidence for the isospin-dependence of the helicity-dependent dihadron fragmentation function $G_1^\perp$, revealed by a sign-difference between the $\pi^+\pi^0$ and $\pi^-\pi^0$ channels in the $\sin(\phi_h-\phi_{R_\perp})$ modulation. In contrast, a large, same-sign enhancement near the $\rho$ mass for the $\sin(2\phi_h-2\phi_{R_\perp})$ modulation is observed, matching spectator model predictions in $\pi^+\pi^-$ pairs.

hep-ex↗

arXiv2026

Quantum Qualifiers for Neural Network Model Selection in Hadronic Physics

As quantum machine-learning architectures mature, a central challenge is no longer their construction, but identifying the regimes in which they offer practical advantages over classical approaches. In this work, we introduce a framework for addressing this question in data-driven hadronic physics problems by developing diagnostic tools - centered on a quantitative quantum qualifier - that guide model selection between classical and quantum deep neural networks based on intrinsic properties of the data. Using controlled classification and regression studies, we show how relative model performance follows systematic trends in complexity, noise, and dimensionality, and how these trends can be distilled into a predictive criterion. We then demonstrate the utility of this approach through an application to Compton form factor extraction from deeply virtual Compton scattering, where the quantum qualifier identifies kinematic regimes favorable to quantum models. Together, these results establish a principled framework for deploying quantum machine-learning tools in precision hadronic physics.

cs.LG↗

arXiv2025

First Study of the Nuclear Response to Fast Hadrons via Angular Correlations between Pions and Slow Protons in Electron-Nucleus Scattering

We report on the first measurement of angular correlations between high-energy pions and slow protons in electron-nucleus ($eA$) scattering, providing a new probe of how a nucleus responds to a fast-moving quark. The experiment employed the CLAS detector with a 5-GeV electron beam incident on deuterium, carbon, iron, and lead targets. For heavier nuclei, the pion-proton correlation function is more spread-out in azimuth than for lighter ones, and this effect is more pronounced in the $\pi p$ channel than in earlier $\pi\pi$ studies. The proton-to-pion yield ratio likewise rises with nuclear mass, although the increase appears to saturate for the heaviest targets. These trends are qualitatively reproduced by state-of-the-art $eA$ event generators, including BeAGLE, eHIJING, and GiBUU, indicating that current descriptions of target fragmentation rest on sound theoretical footing. At the same time, the precision of our data exposes model-dependent discrepancies, delineating a clear path for future improvements in the treatment of cold-nuclear matter effects in $eA$ scattering.

nucl-ex↗

arXiv2025

Deep Neural Network extraction of Unpolarized Transverse Momentum Distributions

Building on the first-ever application of neural networks in TMD phenomenology: "Extraction of the Sivers function with deep neural networks", we now present a momentum space, physics-informed deep learning framework for the direct extraction of unpolarized transverse momentum dependent parton distributions (TMDs) from fixed target Drell-Yan data (E288, E605). Rather than transforming to impact-parameter space, we remain in k and embed a normalized integrand s(x, k; Q) whose auto-convolution produces the observed qT spectra. The extraction proceeds in two steps. Stage I learns the structure kernel S(qT , x1, x2; QM ) by regressing the cross-section with known kinematic prefactors and charge-weighted PDF combinations factored out; experimental and PDF uncertainties are propagated with Monte Carlo replicas. Stage II reconstructs s(x, k; Q) with an end-to-end differentiable k quadrature layer. Applied to Fermilab cross-section data from experiments E288 and E605, the method reproduces the measured qT spectra across Q and yields x and Q dependent TMDs that broaden with Q, with uncertainty bands that consistently propagate experimental, PDF, algorithmic and methodological components. The approach is minimally biased (no factorized Ansatze and no bT transform) and provides a transferable template for polarized TMDs and related QCD inverse problems.

hep-ph↗

arXiv2025

Global Deep Neural Network Modeling of Compton Form Factors Constrained from Local $\chi^2$ Maps Fits

Over the past two decades, intense experimental efforts have focused on measuring observables that contribute to a three-dimensional description of the nucleon. Generalized Parton Distributions provide complementary insights into the internal structure and dynamics of hadrons, including information about the orbital angular momentum carried by quarks. The most direct process to access these distributions is Deeply Virtual Compton Scattering, in which the cross section can be expressed in terms of Compton Form Factors. These quantities are defined as convolutions of the Generalized Parton Distributions with coefficient functions derived in perturbative Quantum Chromodynamics. We extract the Compton Form Factors from Deeply Virtual Compton Scattering data collected at Jefferson Lab, including the most recent measurements in Hall A, using a novel local fitting technique based on $\chi^2$ mapping to constrain the real parts of the Compton Form Factors $\mathcal{H}, \mathcal{E}$ and $\widetilde{\mathcal{H}}$. They are determined independently in each kinematic bin for the unpolarized beam-target configuration under the twist-2 approximation, following the formalism developed by Belitsky, M\"uller, and Kirchner. The extracted Compton Form Factors are then used to train and regularize a deep neural network, enabling a global determination of their behavior with minimal model dependence. This procedure is validated and systematically studied using pseudodata generated with kinematics matching those of the experimental measurements.

nucl-ex↗

arXiv2025

Measurement of single- and double-polarization observables in the photoproduction of $\pi^+\pi^-$~meson pairs off the proton using CLAS at Jefferson Laboratory

The photoproduction of $\pi^+\pi^-$ meson pairs off the proton has been studied in the reaction $\gamma p\to p\,\pi^+\pi^-$ using the CEBAF Large Acceptance Spectrometer (CLAS) and the frozen-spin target (FROST) in Hall B at the Thomas Jefferson National Accelerator Facility. For the first time, the beam and target asymmetries, $I^{s,c}$ and $P_{x,y}$, have been measured along with the beam-target double-polarization observables, $P^{s,c}_{x,y}$, using a transversely polarized target with center-of-mass energies ranging from 1.51 GeV up to 2.04 GeV. These data and additional $\pi\pi$ photoproduction observables from CLAS and experiments elsewhere were included in a partial-wave analysis within the Bonn-Gatchina framework. Significant contributions from $s$-channel resonance production are observed in addition to $t$-channel exchange processes. The data indicate significant contributions from $N^\ast$ and $\Delta^\ast$ resonances in the third and fourth resonance regions.

nucl-ex↗

arXiv2025

LHCspin: a Polarized Gas Target for LHC

The goal of the LHCspin project is to develop innovative solutions for measuring the 3D structure of nucleons in high-energy polarized fixed-target collisions at LHC, exploring new processes and exploiting new probes in a unique, previously unexplored, kinematic regime. A precise multi-dimensional description of the hadron structure has, in fact, the potential to deepen our understanding of the strong interactions and to provide a much more precise framework for measuring both Standard Model and Beyond Standard Model observables. This ambitious task poses its basis on the recent experience with the successful installation and operation of the SMOG2 unpolarized gas target in front of the LHCb spectrometer. Besides allowing for interesting physics studies ranging from astrophysics to heavy-ion physics, SMOG2 provides an ideal benchmark for studying beam-target dynamics at the LHC and demonstrates the feasibility of simultaneous operation with beam-beam collisions. With the installation of the proposed polarized target system, LHCb will become the first experiment to simultaneously collect data from unpolarized beam-beam collisions at $\sqrt{s}$=14 TeV and polarized and unpolarized beam-target collisions at $\sqrt{s_{NN}}\sim$100 GeV. LHCspin has the potential to open new frontiers in physics by exploiting the capabilities of the world's most powerful collider and one of the most advanced spectrometers. This document also highlights the need to perform an R\&D campaign and the commissioning of the apparatus at the LHC Interaction Region 4 during the Run 4, before its final installation in LHCb. This opportunity could also allow to undertake preliminary physics measurements with unprecedented conditions.

hep-ex↗

arXiv2025

Inclusive Electron Scattering in the Resonance Region off a Hydrogen Target with CLAS12

Inclusive electron scattering cross sections off a hydrogen target at a beam energy of 10.6 GeV have been measured with data collected from the CLAS12 spectrometer at Jefferson Laboratory. These first absolute cross sections from CLAS12 cover a wide kinematic area in invariant mass W of the final state hadrons from the pion threshold up to 2.5 GeV for each bin in virtual photon four-momentum transfer squared $Q^2$ from 2.55 to 10.4~GeV$^2$ owing to the large scattering angle acceptance of the CLAS12 detector. Comparison of the cross sections with the resonant contributions computed from the CLAS results on the nucleon resonance electroexcitation amplitudes has demonstrated a promising opportunity to extend the information on their $Q^2$ evolution up to 10 GeV$^2$. Together these results from CLAS and CLAS12 offer good prospects for probing the nucleon parton distributions at large fractional parton momenta $x$ for $W$ < 2.5 GeV, while covering the range of distances where the transition from the strongly coupled to the perturbative regimes is expected.

hep-ex↗

arXiv2024

Comparing fingers and gestures for bci control using an optimized classical machine learning decoder

Severe impairment of the central motor network can result in loss of motor function, clinically recognized as Locked-in Syndrome. Advances in Brain-Computer Interfaces offer a promising avenue for partially restoring compromised communicative abilities by decoding different types of hand movements from the sensorimotor cortex. In this study, we collected ECoG recordings from 8 epilepsy patients and compared the decodability of individual finger flexion and hand gestures with the resting state, as a proxy for a one-dimensional brain-click. The results show that all individual finger flexion and hand gestures are equally decodable across multiple models and subjects (>98.0\%). In particular, hand movements, involving index finger flexion, emerged as promising candidates for brain-clicks. When decoding among multiple hand movements, finger flexion appears to outperform hand gestures (96.2\% and 92.5\% respectively) and exhibit greater robustness against misclassification errors when all hand movements are included. These findings highlight that optimized classical machine learning models with feature engineering are viable decoder designs for communication-assistive systems.

q-bio.NC↗

arXiv2023

A Direct Measurement of Hard Two-Photon Exchange with Electrons and Positrons at CLAS12

One of the most surprising discoveries made at Jefferson Lab has been the discrepancy in the determinations of the proton's form factor ratio $μ_p G_E^p/G_M^p$ between unpolarized cross section measurements and the polarization transfer technique. Over two decades later, the discrepancy not only persists but has been confirmed at higher momentum transfers now accessible in the 12-GeV era. The leading hypothesis for the cause of this discrepancy, a non-negligible contribution from hard two-photon exchange, has neither been conclusively proven or disproven. This state of uncertainty not only clouds our knowledge of one-dimensional nucleon structure but also poses a major concern for our field's efforts to map out the three-dimensional nuclear structure. A better understanding of multi-photon exchange over a wide phase space is needed. We propose making comprehensive measurements of two-photon exchange over a wide range in momentum transfer and scattering angle using the CLAS12 detector. Specifically, we will measure the ratio of positron-proton to electron-proton elastic scattering cross sections, using the proposed positron beam upgrade for CEBAF. The experiment will use 2.2, 4.4, and 6.6 GeV lepton beams incident on the standard CLAS12 unpolarized hydrogen target. Data will be collected by the CLAS12 detector in its standard configuration, except for a modified trigger to allow the recording of events with beam leptons scattered into the CLAS12 central detector. The sign of the beam charge, as well as the polarity of the CLAS12 solenoid and toroid, will be reversed several times in order to suppress systematics associated with local detector efficiency and time-dependent detector performance. The proposed high-precision determination of two-photon effects will be...

nucl-ex↗

arXiv2023

Extraction of the Sivers function with deep neural networks

Deep Neural Networks (DNNs) are a powerful and flexible tool for information extraction and modeling. In this study, we use DNNs to extract the Sivers functions by globally fitting Semi- Inclusive Deep Inelastic Scattering (SIDIS) and Drell-Yan (DY) data. To make predictions of this Transverse Momentum-dependent Distribution (TMD), we construct a minimally biased model using data from COMPASS and HERMES. The resulting Sivers function model, constructed using SIDIS data, is also used to make predictions for DY kinematics specific to the valence and sea quarks, with careful consideration given to experimental errors, data sparsity, and complexity of phase space.

hep-ph↗

arXiv2023

First measurement of hard exclusive $π^- Δ^{++}$ electroproduction beam-spin asymmetries off the proton

The polarized cross section ratio $σ_{LT'}/σ_{0}$ from hard exclusive $π^{-} Δ^{++}$ electroproduction off an unpolarized hydrogen target has been extracted based on beam-spin asymmetry measurements using a 10.2 GeV / 10.6 GeV incident electron beam and the CLAS12 spectrometer at Jefferson Lab. The study, which provides the first observation of this channel in the deep-inelastic regime, focuses on very forward-pion kinematics in the valence regime, and photon virtualities ranging from 1.5 GeV$^{2}$ up to 7 GeV$^{2}$. The reaction provides a novel access to the $d$-quark content of the nucleon and to $p \rightarrow Δ^{++}$ transition generalized parton distributions. A comparison to existing results for hard exclusive $π^{+} n$ and $π^{0} p$ electroproduction is provided, which shows a clear impact of the excitation mechanism, encoded in transition generalized parton distributions, on the asymmetry.

hep-ex↗