<p>We present a study of the central exclusive production (CEP) of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>η</mi></mrow><mrow><mo>′</mo></mrow></msup><mo stretchy="false">(</mo><mn>958</mn><mo stretchy="false">)</mo></mrow></math> mesons in diffractive proton-proton collisions at high energies. The amplitudes, including pomeron and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mrow><mn>2</mn><mi mathvariant="double-struck">R</mi></mrow></msub></math> reggeon exchanges, are calculated within the tensor-pomeron model. Absorption effects are also taken into account at the amplitude level. We fit some undetermined model parameters (coupling constants and cutoff parameters in form factors) to the WA102 experimental data and then make predictions for the LHC energy <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math>. Both total cross sections and several differential distributions are presented. For <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi><mo stretchy="false">→</mo><mi>p</mi><mi>p</mi><mi>η</mi></math>, we find an upper limit for the total cross section of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>2.5</mn><mtext> </mtext><mtext> </mtext><mi mathvariant="normal">μ</mi><mi mathvariant="normal">b</mi></mrow></math> for pseudorapidity of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi></math> meson <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">|</mo><msub><mrow><mi>η</mi></mrow><mrow><mi>M</mi></mrow></msub><mo stretchy="false">|</mo><mo>&lt;</mo><mn>1</mn></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>5.6</mn><mtext> </mtext><mtext> </mtext><mi mathvariant="normal">μ</mi><mi mathvariant="normal">b</mi></mrow></math> for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>2</mn><mo>&lt;</mo><msub><mrow><mi>η</mi></mrow><mrow><mi>M</mi></mrow></msub><mo>&lt;</mo><mn>5</mn></mrow></math>. For <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi><mo stretchy="false">→</mo><mi>p</mi><mi>p</mi><msup><mi>η</mi><mo>′</mo></msup></math>, we predict the cross section to be in the range of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>0.3</mn><mi>–</mi><mn>0.7</mn><mtext> </mtext><mtext> </mtext><mi mathvariant="normal">μ</mi><mi mathvariant="normal">b</mi></mrow></math> for pseudorapidity of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>η</mi><mo>′</mo></msup></math> meson <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">|</mo><msub><mi>η</mi><mi>M</mi></msub><mo stretchy="false">|</mo><mo>&lt;</mo><mn>1</mn></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>0.9</mn><mi>–</mi><mn>2.1</mn><mtext> </mtext><mtext> </mtext><mi mathvariant="normal">μ</mi><mi mathvariant="normal">b</mi></mrow></math> for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2</mn><mo>&lt;</mo><msub><mi>η</mi><mi>M</mi></msub><mo>&lt;</mo><mn>5</mn></math>. This opens the possibility to study diffractive production of pseudoscalar mesons in experiments at the LHC. We discuss if there are arguments from SU(3)-flavor symmetry which would forbid pomeron-pomeron fusion giving an <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi></math> meson. In our opinion such arguments do not exist. We also consider CEP of the pseudoscalars <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>η</mi><mo>′</mo></msup><mo stretchy="false">(</mo><mn>958</mn><mo stretchy="false">)</mo></math> and the pseudovector meson <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>1</mn></msub><mo stretchy="false">(</mo><mn>1285</mn><mo stretchy="false">)</mo></math> in diffractive proton-proton collisions in a theory with a scalar pomeron. We show that none of these particles can be produced in this way in the scalar-pomeron theory. Thus, experimental observation of any of these particles in the above CEP processes at the LHC would give striking evidence against a scalar character of the pomeron.</p>

Poland

Piotr Lebiedowicz

Germany

Otto Nachtmann

Antoni Szczurek

Central exclusive production of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>η</mi><mo>′</mo></msup></math> mesons in diffractive proton-proton collisions at the LHC within the tensor-pomeron approach

<p>We discuss prompt production of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo>/</mo><mi>ψ</mi></math> mesons in proton-proton collisions at the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mrow><mn>68.5</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math> energy within the nonrelativistic quantum chromodynamics <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>k</mi><mi>t</mi></msub></math>-factorization approach using different unintegrated gluon distribution functions (UGDFs). We include both direct color-singlet production (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>g</mi><mi>g</mi><mo stretchy="false">→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><mi>g</mi></math>) as well as a feed-down from <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mi>c</mi></msub><mo stretchy="false">→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><mi>γ</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>ψ</mi><mo>′</mo></msup><mo stretchy="false">→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><mi>X</mi></math> decays. The production of the decaying mesons <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mi>c</mi></msub></math> or <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>ψ</mi><mo>′</mo></msup></math> is also calculated within the nonrelativistic quantum chromodynamics <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>k</mi><mi>t</mi></msub></math>-factorization approach. Differential distributions in the rapidity and transverse momentum of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo>/</mo><mi>ψ</mi></math> are calculated and compared with experimental data of LHCb collaboration. The LHCb fixed target data allow us to test UGDFs in a new range of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>x</mi></math>.</p>

Anna Cisek

Prompt inclusive production of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo>/</mo><mi>ψ</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>ψ</mi><mo>′</mo></msup></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mi>c</mi></msub></math> mesons at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>68.5</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> energy within the NRQCD <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>k</mi><mi>t</mi></msub></math>-factorization approach

The current state-of-the-art theoretical estimations lead to cross-sections for <math altimg='si1.svg'><mi>A</mi><mi>A</mi><mo stretchy='false'>&#8594;</mo><mi>&#947;</mi><mi>&#947;</mi><mi>A</mi><mi>A</mi></math> which are somewhat smaller than the measured ones by the ATLAS and CMS Collaborations, which motivates the searching and calculation of subleading corrections disregarded in these previous studies. In this paper, we estimate for the first time the contribution of inelastic channels to the Light-by-Light (LbL) scattering in ultraperipheral collisions of heavy ions (UPHICs), in which one or both of the incident nuclei dissociate ( <math altimg='si2.svg'><mi>A</mi><mi>A</mi><mo stretchy='false'>&#8594;</mo><mi>&#947;</mi><mi>&#947;</mi><mi>X</mi><mi>Y</mi></math> where <math altimg='si3.svg'><mi>X</mi><mo>,</mo><mi>Y</mi><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mi>A</mi><mo>,</mo><msup><mrow><mi>A</mi></mrow><mrow><mo>&#8242;</mo></mrow></msup></math>) due to the photon emission. These new mechanisms are related to extra emissions that are rather difficult to identify at the LHC and may be misinterpreted as enhanced <math altimg='si4.svg'><mi>&#947;</mi><mi>&#947;</mi><mo stretchy='false'>&#8594;</mo><mi>&#947;</mi><mi>&#947;</mi></math> scattering compared to the Standard Model result. We include processes of coupling of photons to individual nucleons (protons and neutrons) in addition to coherent coupling to the whole nuclei (called standard approach here). Both elastic (nucleon in the ground state) and inelastic (nucleon in an excited state) in the couplings of photons to nucleons are taken into account. The inelastic nucleon fluxes are calculated using CT18qed photon distribution in nucleon PDFs. The inelastic photon fluxes are shown and compared to standard photon fluxes in the nucleus. In addition, we show the ratio of the inelastic corrections to the standard contribution as a function of diphoton invariant mass and photon rapidity difference. We find that for the ATLAS acceptance region the inelastic corrections grow with <math altimg='si36.svg'><msub><mrow><mi>M</mi></mrow><mrow><mi>&#947;</mi><mi>&#947;</mi></mrow></msub></math> and rapidity difference. Our results indicate that the inelastic contributions can be of the order of 20-40% of the traditional (no nuclear excitation) predictions. Uncertainties due to factorization scale choice are quantified.

Mariola Klusek-Gawenda

Brazil

Victor P. Gonçalves

Light-by-Light scattering in ultraperipheral heavy ion collisions: Estimating inelastic contributions

We discuss the reactions <math><mi>π</mi><mi>p</mi><mo>→</mo><mi>π</mi><mi>p</mi></math> and <math><mi>π</mi><mi>p</mi><mo>→</mo><mi>π</mi><mi>p</mi><mi>γ</mi></math> from a general quantum field theory (QFT) point of view, describing these reactions in QCD and lowest relevant order of electromagnetism. We consider the pion-proton elastic scattering both off shell and on shell. The on-shell amplitudes for <math><msup><mi>π</mi><mo>±</mo></msup><mi>p</mi><mo>→</mo><msup><mi>π</mi><mo>±</mo></msup><mi>p</mi></math> scattering are described by two invariant amplitudes, while the off-shell amplitudes contain eight invariant amplitudes. We study the photon emission amplitudes in the soft-photon limit where the center-of-mass photon energy <math><mi>ω</mi><mo>→</mo><mn>0</mn></math>. The Laurent expansion in <math><mi>ω</mi></math> of the <math><msup><mi>π</mi><mo>±</mo></msup><mi>p</mi><mo>→</mo><msup><mi>π</mi><mo>±</mo></msup><mi>p</mi><mi>γ</mi></math> amplitudes is considered and the terms of the orders <math><msup><mi>ω</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> and <math><msup><mi>ω</mi><mn>0</mn></msup></math> are derived. These terms can be expressed by the on-shell invariant amplitudes and their partial derivatives with respect to <math><mi>s</mi></math> and <math><mi>t</mi></math>. The pole term <math><mo>∝</mo><msup><mi>ω</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> in the amplitudes corresponds to Weinberg’s soft-photon theorem and is well known from the literature. We derive the next-to-leading term <math><mo>∝</mo><msup><mi>ω</mi><mn>0</mn></msup></math> using only rigorous methods of QFT. We give the relation of the Laurent series for <math><msup><mi>π</mi><mn>0</mn></msup><mi>p</mi><mo>→</mo><msup><mi>π</mi><mn>0</mn></msup><mi>p</mi><mi>γ</mi></math> and Low’s soft-photon theorem. Our formulas for the amplitudes in the limit <math><mi>ω</mi><mo>→</mo><mn>0</mn></math> are valid for photon momentum <math><mi>k</mi></math> satisfying <math><msup><mi>k</mi><mn>2</mn></msup><mo>≥</mo><mn>0</mn></math>, <math><msup><mi>k</mi><mn>0</mn></msup><mo>=</mo><mi>ω</mi><mo>≥</mo><mn>0</mn></math>, that is, for both real and virtual photons. Here we consider a limit where with <math><mi>ω</mi><mo>→</mo><mn>0</mn></math> we have also <math><msup><mi>k</mi><mn>2</mn></msup><mo>→</mo><mn>0</mn></math>. We discuss the behavior of the corresponding cross sections for <math><msup><mi>π</mi><mo>−</mo></msup><mi>p</mi><mo>→</mo><msup><mi>π</mi><mo>−</mo></msup><mi>p</mi><mi>γ</mi></math> with respect to <math><mi>ω</mi></math> for <math><mi>ω</mi><mo>→</mo><mn>0</mn></math>. We consider cross sections for unpolarized as well as polarized protons in the initial and final states.

Soft-photon theorem for pion-proton elastic scattering revisited

Recent results indicate that charm quarks are intrinsic components of the proton wave function, and that the charm and anticharm distributions for a given value of the Bjorken-<math><mi>x</mi></math> variable can be different. In this paper, we will investigate the impact of this asymmetric intrinsic charm on the production of <math><msup><mi>D</mi><mn>0</mn></msup></math> and <math><msup><mover><mi>D</mi><mo>¯</mo></mover><mn>0</mn></msup></math> mesons for fixed target <math><mrow><mi>p</mi><mo>+</mo><mmultiscripts><mrow><mi>Ne</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>20</mn></mrow></mmultiscripts></mrow></math> collisions at the LHCb. In our calculations, we include the contribution of the gluon-gluon fusion, gluon-charm and recombination processes and assume distinct models for the treatment of the intrinsic charm component. We demonstrate that the presence of an intrinsic charm improves the description of the current data for the rapidity and transverse momentum distributions of <math><mi>D</mi></math> mesons. However, such models are not able to describe the LHCb data for the <math><mrow><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup><mtext>−</mtext><msup><mrow><mover><mrow><mi>D</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow><mrow><mn>0</mn></mrow></msup></mrow></math> asymmetry at large transverse momentum, which point out that the description of the intrinsic charm needs to be improved and/or new effects should be taken into account in the production of heavy mesons at forward rapidities in fixed-target collisions.

Victor P. Goncalves

Rafał Maciuła

Asymmetric intrinsic charm in the nucleon and its implications for the <math><mrow><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></math> production in the LHCb <math><mrow><mi>p</mi><mo>+</mo><mmultiscripts><mrow><mi>Ne</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>20</mn></mrow></mmultiscripts></mrow></math> fixed-target experiment

We calculate several differential distributions for diffractive dijets production in <math><mrow><mi>e</mi><mi>p</mi><mo>→</mo><msup><mrow><mi>e</mi></mrow><mrow><mo>′</mo></mrow></msup><mi>jet</mi></mrow></math> <math><mrow><mi>jet</mi><mi>p</mi></mrow></math> in the perturbative QCD dipole approach using off diagonal unintegrated gluon distributions (generalized transverse momentum dependent distributions, GTMDs). Different models from the literature are used. We concentrate on the contribution from exclusive <math><mi>q</mi><mover><mi>q</mi><mo>¯</mo></mover></math> dijets. Results of our calculations are compared to H1 and ZEUS data, including specific experimental cuts in our calculations. In general, except for one GTMD, our results are below the HERA data. The considered mechanism is expected to gives a sizeable contribution to the ZEUS data, while it is negligible in the kinematics of the H1 measurement. This is in contrast to recent results from the literature where the normalization was adjusted to some selected distributions of the H1 collaboration and no agreement with other observables was checked. The ZEUS data provide stricter limitations on the GTMDs than the H1 data. We conclude, based on comparison to different observables, that the calculated cross sections are only a small fraction of the measured ones which contain probably also processes with pomeron remnant. Alternatively one could try to explain the experimental data by inclusion of <math><mi>q</mi><mover><mi>q</mi><mo>¯</mo></mover><mi>g</mi></math> component of the photon wave function. We present also azimuthal correlations between the sum and the difference of dijet transverse momenta. The cuts on transverse momenta of jets generate corresponding azimuthal correlations that can be misidentified as due to elliptic gluon distributions.

Barbara Linek

Marta Łuszczak

Wolfgang Schäfer

Probing gluon GTMDs of the proton in deep inelastic diffractive dijet production at HERA

We continue our work on the light-front formulation of quarkonium γ ∗ γ transition form factors, extending the formalism to J  PC  = 2++ tensor meson states. We present an analysis of γ ∗ γ → χ  c2 transition amplitude and the pertinent helicity form factors. Our relativistic formalism is based on the light-front quark-antiquark wave function of the quarkonium. We calculate the two-photon decay width as well as three independent γ ∗ γ transition form factors for J  z  = 0, 1, 2 as a function of photon virtuality Q 2. We compare our results for the two-photon decay width to the recently measured ones by the Belle and BES III collaborations. Even when including relativistic corrections, a very small Γ(λ = 0)/Γ(λ = 2) ~ 10 −3 ratio is found which is beyond present experimental precision. We also present the form factors as a function of photon virtuality and compare them to the sparse experimental data on the so-called off-shell width. The formalism presented here can be used for other 2++ mesons, excited charmonia or bottomonia or even light   <math> <mi>q</mi> <mover> <mi>q</mi> <mo>¯</mo> </mover> </math>  $$ q\overline{q} $$ -mesons.

Izabela Babiarz

Sweden

Roman Pasechnik

χ  c2 tensor meson transition form factors in the light front approach

We investigate the photon emission in pion-pion and pion-proton scattering in the soft-photon limit where the photon energy <math><mi>ω</mi><mo>→</mo><mn>0</mn></math>. The expansions of the <math><msup><mi>π</mi><mo>−</mo></msup><msup><mi>π</mi><mn>0</mn></msup><mo>→</mo><msup><mi>π</mi><mo>−</mo></msup><msup><mi>π</mi><mn>0</mn></msup><mi>γ</mi></math> and the <math><msup><mi>π</mi><mo>±</mo></msup><mi>p</mi><mo>→</mo><msup><mi>π</mi><mo>±</mo></msup><mi>p</mi><mi>γ</mi></math> amplitudes, satisfying the energy-momentum relations, to the orders <math><msup><mi>ω</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> and <math><msup><mi>ω</mi><mn>0</mn></msup></math> are derived. We show that these terms can be expressed completely in terms of the on-shell amplitudes for <math><msup><mi>π</mi><mo>−</mo></msup><msup><mi>π</mi><mn>0</mn></msup><mo>→</mo><msup><mi>π</mi><mo>−</mo></msup><msup><mi>π</mi><mn>0</mn></msup></math> and <math><msup><mi>π</mi><mo>±</mo></msup><mi>p</mi><mo>→</mo><msup><mi>π</mi><mo>±</mo></msup><mi>p</mi></math>, respectively, and their partial derivatives with respect to <math><mi>s</mi></math> and <math><mi>t</mi></math>. The structure term which is nonsingular for <math><mi>ω</mi><mo>→</mo><mn>0</mn></math> is determined to the order <math><msup><mi>ω</mi><mn>0</mn></msup></math> from the gauge-invariance constraint using the generalized Ward identities for pions and the proton. For the reaction <math><msup><mi>π</mi><mo>−</mo></msup><msup><mi>π</mi><mn>0</mn></msup><mo>→</mo><msup><mi>π</mi><mo>−</mo></msup><msup><mi>π</mi><mn>0</mn></msup><mi>γ</mi></math> we discuss in detail the soft-photon theorems in the versions of both Low and Weinberg. We show that these two versions are different and must not be confounded. Weinberg’s version gives the pole term of a Laurent expansion in <math><mi>ω</mi></math> of the amplitude for <math><msup><mi>π</mi><mo>−</mo></msup><msup><mi>π</mi><mn>0</mn></msup><mo>→</mo><msup><mi>π</mi><mo>−</mo></msup><msup><mi>π</mi><mn>0</mn></msup><mi>γ</mi></math> around the phase-space point of zero radiation. Low’s version gives an approximate expression for the above amplitude at a fixed phase-space point, corresponding to nonzero radiation. Clearly, the leading and next-to-leading terms in theses two approaches must be, and are indeed, different. We show their relation. We also discuss the expansions of differential cross sections for <math><msup><mi>π</mi><mo>−</mo></msup><msup><mi>π</mi><mn>0</mn></msup><mo>→</mo><msup><mi>π</mi><mo>−</mo></msup><msup><mi>π</mi><mn>0</mn></msup><mi>γ</mi></math> with respect to <math><mi>ω</mi></math> for <math><mi>ω</mi><mo>→</mo><mn>0</mn></math>.

Different versions of soft-photon theorems exemplified at leading and next-to-leading terms for pion-pion and pion-proton scattering

We discuss possible future studies of photon-photon (light-by-light) scattering using a planned FoCal and ALICE 3 detectors. We include different mechanisms of <math><mi>γ</mi><mi>γ</mi><mo>→</mo><mi>γ</mi><mi>γ</mi></math> scattering such as double-hadronic photon fluctuations, <math><mi>t</mi><mo>/</mo><mi>u</mi></math>-channel neutral pion exchange or resonance excitations (<math><mi>γ</mi><mi>γ</mi><mo>→</mo><mi>R</mi></math>) and deexcitation (<math><mi>R</mi><mo>→</mo><mi>γ</mi><mi>γ</mi></math>). The broad range of (pseudo)rapidities and lower cuts on transverse momenta open a necessity to consider not only dominant box contributions but also other subleading contributions. Here we include low mass resonant <math><mi>R</mi><mo>=</mo><msup><mi>π</mi><mn>0</mn></msup></math>, <math><mi>η</mi></math>, <math><msup><mi>η</mi><mo>′</mo></msup></math> contributions. The resonance contributions give intermediate photon transverse momenta. However, these contributions can be eliminated by imposing windows on diphoton invariant mass. We study and quantify individual box contributions (leptonic, quarkish). The electron/positron boxes dominate at low <math><msub><mi>M</mi><mrow><mi>γ</mi><mi>γ</mi></mrow></msub><mo>&lt;</mo><mn>1</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> diphoton invariant masses. The <math><mrow><mi>Pb</mi><mrow><mi>Pb</mi><mo>→</mo></mrow><mi>PbPb</mi><mi>γ</mi><mi>γ</mi></mrow></math> cross section is calculated within equivalent photon approximation in the impact parameter space. Several differential distributions are presented and discussed. We consider four different kinematic regions. We predict a cross section in the (mb-b) range for typical ALICE 3 cuts, a few orders of magnitude larger than for the current ATLAS or CMS experiments. We also consider the two-<math><msup><mi>π</mi><mn>0</mn></msup></math> background which can, in principle, be eliminated at the new kinematical range for the ALICE 3 measurements by imposing dedicated cuts on diphoton transverse momentum and/or so-called vector asymmetry.

Paweł Jucha

Mariola Kłusek-Gawenda

Light-by-light scattering in ultraperipheral collisions of heavy ions at two future detectors

One of the main goals of future electron-ion colliders is to improve our understanding of the structure of hadrons. In this letter, we study the exclusive <math><msub><mrow><mi>η</mi></mrow><mrow><mi>c</mi></mrow></msub></math> production by <math><msup><mrow><mi>γ</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mi>γ</mi></math> interactions in eA collisions and demonstrate that future experimental analysis of this process can be used to improve the description of the <math><msub><mrow><mi>η</mi></mrow><mrow><mi>c</mi></mrow></msub></math> transition form factor. The rapidity, transverse momentum and photon virtuality distributions are estimated considering the energy and target configurations expected to be present at the EIC, EicC and LHeC and assuming different predictions for the light-front wave function of the <math><msub><mrow><mi>η</mi></mrow><mrow><mi>c</mi></mrow></msub></math> meson. Our results indicate that the electron-ion colliders can be considered an alternative to providing supplementary data to those obtained in <math><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup></math> colliders.