arXiv subjects

Bernard Pire

Publications and source records attributed to Bernard Pire.

At least 19 recordsLinked to original sources

arXiv2026

Next-to-next-to-leading order QCD corrections to pion (kaon)-induced exclusive Drell-Yan process

The high-energy pion and kaon beams proposed for future experiments at J-PARC offer a unique opportunity to investigate exclusive Drell-Yan processes induced by pions or kaons, which correspond to inverse deeply virtual meson production with $M=\pi,K$. To facilitate precise comparisons between theoretical predictions and forthcoming experimental data, we calculate the next-to-next-to-leading order (NNLO) QCD corrections to the processes $\pi^- p\to \gamma^*(\to l^+l^-) + n$ and $K^- p\to \gamma^*(\to l^+l^-) + \Lambda$. Our calculations are performed within the generalized parton distribution (GPD) factorization framework, accurate to leading twist in the generalized Bjorken limit ($Q^2\gg |t|,\,\Lambda_{\rm QCD}^2$). We find that the NNLO QCD corrections are substantial and positive; therefore, their inclusion is imperative for reliable theoretical predictions in confrontation with future experiments.

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arXiv2025

Hard exclusive photoproduction of photon-meson pairs: pseudoscalar channels $\pi$, $\eta$ and $\eta'$

We investigate the hard exclusive photoproduction of photon-meson pairs at leading-twist and leading-order in perturbative QCD, and focus on pseudoscalar mesons $\text{M} \in \{\pi^\pm, \pi^0, \eta, \eta'\}$. Compact analytical expressions are obtained for the amplitudes involving quark generalized parton distributions, with the two-gluon components of the $\eta$ and $\eta'$ distribution amplitudes included. The numerical analysis is performed in the moderate-$\xi$ region, where valence-quark GPDs are expected to be important. In this region, we find a strong impact of the pion-pole term in $\gamma\pi^\pm$ production, and a non-negligible effect for neutral mesons. We also observe a marked dependence of $\gamma\eta'$ photoproduction on two-gluon contributions. This process offers enhanced sensitivity to the shape of the GPDs already at leading-order, while the tested dependence on the meson distribution amplitude and the renormalization scale introduces further theoretical uncertainties, the latter emphasizing the need for next-to-leading-order corrections. Our results provide a concise analytical framework and a numerical baseline for future studies.

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arXiv2025

Accessing baryon-antibaryon generalized distribution amplitudes in $e^{\pm} \gamma \to e^{\pm} B \bar{B} $

$\gamma^* \gamma \to B \bar{B}$ is the golden process to access chiral-even di-baryon generalized distribution amplitudes (GDAs) as deeply virtual Compton scattering has proven to be for the generalized parton distributions. In the framework of colinear QCD factorization where the leading twist amplitude is the convolution of GDAs and a perturbatively calculable coefficient function, we study the scattering amplitude for the baryonic channels where $B$ is a spin $1/2$ baryon such as the nucleon or hyperon $\Lambda, \Sigma$. Taking into account the interfering QED amplitude, we calculate the cross section of the $e^\pm \gamma \to e^\pm B \bar B$ process that can be experimentally studied in $e^- e^+$ as well as in electron-ion facilities. We explore both the final state polarization summed case and the polarization dependent effects. Numerical estimates are presented for $e^- \gamma \to e^- p \bar{p}$, using motivated models for GDAs. Our results show that a first extraction of baryon-antibaryon GDAs from experimental measurements is feasible at Belle II.

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arXiv2025

Improved phenomenology of $\pi N$ transition distribution amplitudes

To study cross sections and polarization asymmetries for the processes $e p \to e n \pi^+$ and $e p \to e p \pi^0$ in the backward region, we develop a flexible phenomenological model for nucleon-to-pion transition distribution amplitudes ($\pi N$ TDAs), which are used in the QCD collinear factorization description of the scattering amplitudes. Our model is based on the two-component factorized Ansatz for the corresponding spectral densities, quadruple distribution. It takes into account the constraints for $\pi N$ TDAs arising from the threshold pion production theorem and also includes a forward limit contribution that can be fitted to experimental data. We examine the sensitivity of observable predictions to various modelling assumptions.

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arXiv2025

Revealing chiral-odd two-meson generalized distribution amplitudes in $e^- e^+ \to (\pi \pi) (\pi \pi)$ reactions

We demonstrate that chiral-odd dimeson generalized distribution amplitudes (CO-GDAs) -- nonperturbative objects encoding the transition of a quark-antiquark pair into two mesons -- can be accessed in high-energy $e^- e^+$ annihilation into two meson pairs, each with a relatively low invariant mass. While chiral-even GDAs contribute to the leading one-photon amplitude, the chiral-odd sector enters via two-photon exchange. We show that the interference between these amplitudes leads to specific effects which may be measurable at BES III or future tau-charm factories. This work opens a direct path to experimentally probing the long-missing chiral-odd sector of meson structure-specifically, the spin-orbit correlation in a spin-zero meson, in some contexts referred to as anomalous tensorial magnetic moment.

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arXiv2025

Baryon-antibaryon generalized distribution amplitudes and $e^+ e^- \to B \bar{B} \gamma$

Baryon-antibaryon generalized distribution amplitudes (GDAs) give an access to timelike gravitational form factors (GFFs) which are complementary to the spacelike ones which can be deduced from the hadronic generalized parton distributions (GPDs) measured in deep exclusive electroproduction processes. They allow to probe the GFFs of unstable baryons in the baryon octet, since the second moments of hadronic generalized distribution amplitudes (GDAs) lead to the timelike GFFs. These GDAs can be measured in the process $e^+ e^- \to B \bar{B} \gamma$, in the generalized Bjorken regime where the invariant mass of the $B \bar{B}$ pair is near threshold at high energy facilities, such as BESIII, Belle II, and the proposed Super Tau-Charm Facility. In this work, we investigate this process using the QCD collinear factorization framework, where the scattering amplitudes are expressed in terms of the baryon timelike electromagnetic (EM) FFs and Compton FFs. We also provide a numerical estimate of the cross sections with a model for baryon-antibaryon GDAs. Our work provides us a possibility to extract the timelike baryon GFFs from near future experimental measurements, and these GFFs may be further used to study longstanding questions in hadronic physics such as the baryon spin decomposition and D-term.

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arXiv2025

Backward DVCS in a Sullivan process

Mesons' internal structure and dynamics may be accessed through hard exclusive electroproduction processes such as deeply virtual Compton scattering in both near forward and near backward kinematics. With the help of the Sullivan process which allows us to use a nucleon target as a quasi-real $\pi$ meson emitter, we study backward scattering in the framework of collinear QCD factorization where pion-to-photon transition distribution amplitudes describe the photon content of the $\pi$ meson. We present a model of these TDAs based on the overlap of lightfront wave functions primarily developed for generalized parton distributions, using a previously developed pion lightfront wave function and deriving a new model for the lightfront wave functions of the photon. This leads us to an estimate of the cross-sections for JLab energies. We conclude that deeply virtual $ep\rightarrow e\gamma M n$ processes, in backward kinematics, may be experimentally discovered in the near future.

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arXiv2024

Prospective report of the French QCD community to the ESPPU 2025 with respect to the program of the LHC Run 5 and beyond and future colliders at CERN

This document summarizes the prospective physics plans of the French QCD and Heavy-Ion community, including the experimental programs at the LHC Run 5 and beyond and future colliders at CERN, within the context of the French contribution to the update of the European Strategy in Particle Physics (ESPPU 2025), as discussed in the workshop on European Strategy for Particle Physics Update 2025 organised by the QCD GdR in Oct. 2024.

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arXiv2024

Accessing Generalized Parton Distributions through $2 \to 3$ exclusive processes

We review our results on a new class of $2 \to 3$ exclusive processes, as a probe of both chiral-even and chiral-odd quark GPDs. We consider the exclusive photoproduction of a photon-meson pair, in the kinematics where the pair has a large invariant mass, described in the collinear factorization framework. We cover the whole kinematical range from medium energies in fixed target experiments to very large energies of colliders, by considering the experimental conditions of JLab 12-GeV, COMPASS, future EIC and LHC (in ultra-peripheral collisions) cases. Our analysis covers neutral and charged rho-mesons, as well as charged pions. The case of the rho-meson, depending on its polarization, provides access to either chiral-even or chiral-odd GPDs, at leading twist. We find that the order of magnitude of the obtained cross sections are sufficiently large for a dedicated experimental analysis to be performed, especially at JLab. Furthermore, we compute the linear photon beam polarization asymmetry, which we find to be sizeable, in the case of a longitudinally polarized $\rho$-meson or of a charged pion. These predictions are obtained for both asymptotic distribution amplitude (DA) and holographic DA.

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arXiv2024

Backward DVCS on the pion in Sullivan processes

The purpose of this work is to do a systematic feasibility study of measuring in backward region deeply virtual Compton scattering on the pion in Sullivan processes in the framework of collinear QCD factorization where pion to photon transition distribution amplitudes (TDAs) describe the photon content of the $\pi$ meson. Our approach employs TDAs based on the overlap of light front wave functions, using a previously developed pion light-front wave function and deriving a consistent model for the light front wave functions of the photon. This work is expected to lead us to an estimate of the cross-sections that could be measured in the future U.S. and China's electron-ion colliders. It will also provide a comparison with the forward Sullivan DVCS case, which gives access to pion GPDs and for which a strong signal is expected.

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arXiv2024

Kinematical higher-twist corrections in $γ^* \to M_1 M_2 γ$: Charged meson production

Generalized distribution amplitudes (GDAs) of mesons can be probed by the reactions $e^- e^+ \to M_1 M_2 γ$, which are accessible at electron-positron colliders such as BESIII and Belle II. After discussing the neutral meson production case in the first paper of this series \cite{Pire:2023kng}, we discuss here the complementary case of the charged meson ($M^+ M^-$) production, where one can extract the complete information on GDAs from the interference of the amplitudes of the two competing processes where the photon is emitted either in the initial or in the final state. Considering the importance of the charged meson production, we present a complete expression for the interference term of the cross section which is experimentally accessible thanks to its charge conjugation specific property. We adopt two types of models for leading twist $ππ$ GDAs to estimate the size of the interference term in the process $e^- e^+ \to π^+ π^- γ$ numerically, namely a model extracted from previous experimental results on $γ^* γ\to π^0 π^0$ at Belle and the asymptotic form predicted by QCD evolution equations. We include in the calculation the kinematical power suppressed (sometimes called kinematical higher-twist) corrections up to $1/Q^2$ for the helicity amplitudes. Both models of GDAs indicate that the kinematical corrections are not negligible for the interference term of the cross section measured at BESIII, thus it is necessary to include them if we try to extract the GDAs precisely. On the other side, the kinematical corrections are very tiny for the measurements at Belle II, and the leading twist-2 formula of the interference term will be good enough to describe the charge conjugation odd part of the differential cross section.

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arXiv2024

Exclusive photoproduction of a photon-meson pair: A new class of observables to probe GPDs

We discuss the exclusive photoproduction of a photon-meson pair with large $ p_{T} $ as a channel to probe generalised parton distributions (GPDs). Like other $ 2\to3 $ exclusive processes, this channel allows us to better study the $ x $-dependence of GPDs, in contrast to $ 2\to2 $ processes such as Deeply Virtual Compton Scattering (DVCS) which give only "moment-type" information. Moreover, it also gives the possibility to access, at leading twist, the chiral-odd GPDs, which are still completely unknown experimentally. In the first part of these proceedings, we present the computation of the amplitude at leading order and leading twist, for charged pions, and rho mesons of any charge and polarisation. These processes are sensitive to quark GPDs only. We also discuss the possibility of measuring such processes at various experiments, namely JLab, COMPASS, future EIC and LHC in ultra-peripheral collisions. In particular, in collider experiments, the dependence of GPDs at small skewness $ (<10^{-3}) $ can be extracted. For the second part, we report on our recent work on the exclusive photoproduction of $ π^{0}γ$ pair, which, in addition to a quark GPD channel, also has a contribution from gluon GPDs. In the latter case, we demonstrate that a collinear factorisation of the process fails, due to the presence of a Glauber pinch. Our findings also imply that other similar processes, like $ π^{0} N \to γγN $ also suffer from the same issue. On the other hand, we stress that the processes discussed earlier, which are sensitive to the quark GPD channels only, are safe from these factorisation breaking effects.

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arXiv2023

Kinematical higher-twist corrections in $γ^* \to M_1 M_2 γ$: Neutral meson production

We carry out the calculation of kinematical higher-twist corrections to the cross section of $γ^* \to M_1 M_2 γ$ up to twist 4, where $M_i$ is a scalar or pseudoscalar neutral meson. The three independant helicity amplitudes are presented in terms of the twist-2 generalized distribution amplitudes (GDAs), which are important non-perturbative quantities for understanding the 3D structure of hadrons. Since this process can be measured by BESIII in $e^+ e^-$ collisions, we perform the numerical estimate of the kinematical higher-twist corrections by using the kinematics of BESIII. We adopt the $ππ$ GDA extracted from Belle measurements and the asymptotic $ππ$ GDA to study the size of the kinematical corrections in the case of pion meson pair, and a model $ηη$ GDA is used to see the impact of target mass corrections $\mathcal O(m^2/s)$ for $γ^* \to ηηγ$. Our results show that the kinematical higher-twist corrections account for $\sim 20\%$ of the cross sections at BESIII on the average, and it is necessary to include them if one tries to extract GDAs from experimental measurements precisely. We also comment the case of $π^0 η$ production which is important for the search of hybrid mesons.

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arXiv2023

Pion and photon beam initiated backward charmonium or lepton pair production

Hard exclusive reactions initiated by pion or photon beams within the near-backward kinematical regime specified by the small Mandelstam variable $-u$ can be studied to access pion-to-nucleon and photon-to-nucleon Transition Distribution Amplitudes (TDAs). Checking the validity of collinear factorized description of pion and photon induced reactions in terms of TDAs allows to test the universality of TDAs between the space-like and time-like regimes that is the indispensable feature of the QCD collinear factorization approach. In this short review we consider the exclusive pion- and photo-production off nucleon of a highly virtual lepton pair (or heavy quarkonium) in the near-backward region. We first employ a simplistic cross channel nucleon exchange model of pion-to-nucleon TDAs to estimate the magnitude of the corresponding cross sections for the kinematical conditions of J-PARC. We then illustrate the flexibility of our approach by building a two parameter model for the photon-to-nucleon TDAs based on preliminary results for near threshold $J/ψ$ photoproduction at JLab and provide our estimates for near-backward $J/ψ$ photoproduction and Timelike Compton Scattering cross sections for the kinematical conditions of JLab and of future EIC and EicC.

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arXiv2023

Probing chiral-even and chiral-odd leading twist quark generalised parton distributions through the exclusive photoproduction of a $ γρ$ pair

We extend our studies of a new class of $2 \to 3$ exclusive processes using the collinear factorisation framework by considering the exclusive photoproduction of a $γ\,ρ$ pair, in the kinematics where the pair has a large invariant mass, {and the outgoing $ ρ$-meson has a sufficiently large transverse momentum to not resonate with the nucleon}. We cover the whole kinematical range from medium energies in fixed target experiments to very large energies of colliders, by considering the experimental conditions of JLab~12-GeV, COMPASS, future EIC and LHC (in ultra-peripheral collisions) cases. One of the main interest in studying the present process is that it provides access to both chiral-even and chiral-odd GPDs, depending on the polarisation of the outgoing $ρ$-meson, both at leading twist. Our analysis covers both neutral and charged $ ρ$-mesons. We find that the order of magnitude of the obtained cross sections are sufficiently large for a dedicated experimental analysis to be performed, especially at JLab, for both longitudinally and transversely polarised $ρ$. Furthermore, we compute the linear photon beam polarisation asymmetry {which is} sizeable for a longitudinally polarised meson. These predictions are obtained for both asymptotic distribution amplitude (DA) and the \textit{holographic} DA.

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arXiv2022

Accessing GPDs through the exclusive photoproduction of a photon-meson pair with a large invariant mass

We study the exclusive photoproduction of a photon-meson pair with a large invariant mass, working in the QCD factorisation framework. Explicitly, we consider a $ ρ$-meson or a charged $ π$ in the final state. This process gives access to chiral-even GPDs as well as chiral-odd GPDs. We focus here on the chiral-even sector. The computation is performed at leading order and leading twist. We discuss the prospects of measuring them in various experiments such as JLab 12-GeV, COMPASS, future EIC and LHC (in ultraperipheral collisions). In particular, the high centre of mass energies available at collider experiments can be used to probe GPDs at small skewness $ ξ$. We also compute the polarisation asymmetries with respect to the incoming photon. The results for an alternative distribution amplitude (`holographic' form) are also compared with the predictions obtained with an asymptotic distribution amplitude.

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arXiv2022

Accessing chiral-even quark generalised parton distributions in the exclusive photoproduction of a $ γπ^{\pm} $ pair with large invariant mass in both fixed-target and collider experiments

We compute the exclusive photoproduction of a $γ\,π^\pm$ pair using the collinear factorisation framework, in the kinematic regime where the pair has a large invariant mass. This exclusive channel presents a new avenue for the investigation of GPDs. It is particularly interesting as the high centre of mass energies available at future experiments will allow the study of GPDs at small skewness $ ξ$. We compute the scattering amplitude of the process, at leading twist and leading order in $α_s$, which is used to estimate its cross-section and linear polarisation asymmetries with respect to the incoming photon, for JLab~12-GeV, COMPASS, future EIC and LHC (in ultra-peripheral collisions) kinematics. We find that the order of magnitude of estimates are sufficiently large for a dedicated experimental analysis to be performed, especially at JLab. We also compare the results from an asymptotic distribution amplitude (DA) to those using a recently proposed \textit{holographic} DA.

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arXiv2022

Kinematical higher-twist corrections in $γ^* γ\to M \bar M $

We estimate kinematical higher-twist (up to twist 4) corrections to the $γ^*(q_1) γ(q_2) \to M(p_1) \bar{M}(p_2)$ amplitudes at large $Q^2=-q_1^2$ and small $s=(q_1+q_2)^2$, where $M$ is a scalar or pseudoscalar meson. This process is known to factorize at leading twist into a perturbatively calculable coefficient function and generalized distribution amplitudes (GDAs). The kinematical higher-twist contributions of order $s/Q^2$ and $m^2/Q^2$ turn out to be important in the cross section, considering the kinematics accessible at Belle and Belle II. We present numerical estimates for the cross section for $γ^* γ\to π^0 π^0$ with the $ππ$ GDA extracted from Belle measurements and with the asymptotic $ππ$ GDA as inputs to study the magnitude of the kinematical corrections. To see how the target mass corrections of order $m^2/Q^2$ affect the cross section, we also perform the calculation for $γ^* γ\to ηη$ by using a model $ηη$ GDA.In the range $s> 1$ GeV$^2$, the kinematical higher-twist corrections account for $\sim 15 \%$ of the total cross section, an effect which is not negligible. Since $ππ$ GDAs are the best way to access the pion energy-momentum tensor (EMT), our study demonstrates that an accurate evaluation of EMT form factors requires the inclusion of kinematical higher-twist contributions.

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