<p>The cross sections for the single exclusive production of (pseudo)scalar and (pseudo)tensor hadrons, as well as of even-spin QED bound states formed by pairs of opposite-charge leptons or hadrons, are estimated for photon-fusion processes in ultraperipheral collisions (UPCs) of proton-proton, proton-nucleus, and nucleus-nucleus at the Relativistic Heavy-Ion Collider, Large Hadron Collider (LHC) and Future Circular Collider, as well as in proton-air interactions at the highest energies reached by cosmic rays impinging on Earth. The UPC cross sections are computed in the equivalent photon approximation with realistic photon fluxes from the charged form factors of proton, lead, gold, and nitrogen ions. The production of four types of even-spin systems are considered: quarkonium (spin-0, 2, 4 meson bound states, from the lightest <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>π</mi><mn>0</mn></msup></math> meson up to toponium), exotic hadrons (including candidate multiquark states), leptonium (positronium, dimuonium, and ditauonium), as well as mesonium (pionium, kaonium, D-onium, and B-onium) and baryonium (notably, protonium) QED atoms. The expected yields at the different colliders are presented for about 50 such even-spin composite resonances, for which the ALICE and LHCb experiments have potential reconstruction capabilities at the LHC. The impact of the diphoton decays of such even-spin states is also discussed as resonant backgrounds in the measurement of light-by-light scattering (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi><mi>γ</mi><mo stretchy="false">→</mo><mi>γ</mi><mi>γ</mi></math>) over <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>γ</mi><mi>γ</mi></mrow></msub><mo>≈</mo><mn>0.1</mn><mi>–</mi><mn>15</mn></mrow></math>-GeV masses in Pb-Pb UPCs at the LHC.</p>

CERN

David d’Enterria

United States

Karen Kang

Exclusive photon-fusion production of even-spin resonances and exotic QED atoms in high-energy hadron collisions

Next-to-leading-order (NLO) quantum electrodynamics (QED) corrections to the production of muon and tau pairs in photon-photon collisions, $\textit{γγ}$ → $\textit{μ}$ $\textit{μ}$ , $\textit{τ}$ $\textit{τ}$ , are calculated in the equivalent photon approximation. We mostly consider $\textit{γγ}$ processes in ultraperipheral collisions of hadrons at the LHC, but the $\textit{γγ}$ → $\textit{τ}$ $\textit{τ}$ process in e e collisions at LEP is also discussed. The NLO terms are found to modify the total fiducial cross sections by up to 5%, increasing the tails of the dilepton acoplanarity and transverse momentum distributions, and depleting by up to 15% the yields at high masses, with respect to the leading-order predictions including the very small virtuality of the colliding photons. At the LHC, the calculations obtained with the charge form factor for protons and lead ions including the NLO QED corrections improve the data-theory agreement for all measured differential distributions, and prove an indispensable ingredient for the extraction of precision quantities in photon-photon processes, such as the anomalous magnetic moment of the tau lepton.

France

Hua-Sheng Shao

Switzerland

Dimuon and ditau production in photon-photon collisions at next-to-leading order in QED

Abstract Recently, lattice formulations of Abelian chiral gauge theory in two dimensions have been devised on the basis of the Abelian bosonization. A salient feature of these 2D lattice formulations is that the gauge invariance is exactly preserved for anomaly-free theories and thus is completely free from the question of the gauge mode decoupling. In the present paper, we propose yet another lattice formulation sharing this desired property. A particularly unique point in our formulation is that the vertex operator of the dual scalar field, which carries the vector charge of the fermion and the “magnetic charge” in the bosonization, is represented by a “hole” excised from the lattice; this is the excision method formulated recently by Abe et al. in a somewhat different context.

Japan

Okuto Morikawa

Soma Onoda

Hiroshi Suzuki

Yet Another Lattice Formulation of 2D (1) Chiral Gauge Theory via Bosonization David Tong: lectures on gauge theory

<p>Opportunities for searches for axionlike particles (ALPs) coupling to photons in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> collisions at the Future Circular Collider (FCC-ee) and International Linear Collider (ILC) are investigated. We perform a study of the photon-fusion production of ALPs decaying into two photons, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mover accent="true"><mrow><mo stretchy="true">→</mo></mrow><mrow><mi>γ</mi><mi>γ</mi></mrow></mover><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><mi>a</mi><mo stretchy="false">(</mo><mi>γ</mi><mi>γ</mi><mo stretchy="false">)</mo><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math>, over the light-by-light continuum background, for the planned FCC-ee and ILC center-of-mass energies and integrated luminosities. An analysis of the feasibility measurements is presented using parametrized simulations for two types of detectors. Upper limits at 95% confidence level (C.L.) on the cross section for ALP production, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi><mo stretchy="false">(</mo><mi>γ</mi><mi>γ</mi><mo stretchy="false">→</mo><mi>a</mi><mo stretchy="false">→</mo><mi>γ</mi><mi>γ</mi><mo stretchy="false">)</mo></math>, and on the ALP-photon coupling are obtained over the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>a</mi></msub><mo>≈</mo><mn>0.1</mn><mi>–</mi><mn>1000</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> ALP mass range, and compared to current and future collider searches. Production cross sections down to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi><mo stretchy="false">(</mo><mi>γ</mi><mi>γ</mi><mo stretchy="false">→</mo><mi>a</mi><mo stretchy="false">→</mo><mi>γ</mi><mi>γ</mi><mo stretchy="false">)</mo><mo>≈</mo><mn>1</mn><mtext> </mtext><mtext> </mtext><mi>fb</mi></math> (1 ab) will be probed at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>a</mi></msub><mo>≈</mo><mn>1</mn></math> (300) GeV, corresponding to constraints on the axion-photon coupling as low as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>g</mi><mrow><mi mathvariant="normal">a</mi><mi>γ</mi><mi>γ</mi></mrow></msub><mo>≈</mo><mn>2</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>3</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mrow><msup><mrow><mi>TeV</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math>.</p>

Brazil

Patricia Rebello Teles

China

Victor P. Gonçalves

Poland

Daniel E. Martins

Searches for axionlike particles via <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi><mi>γ</mi></math> fusion at future <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> colliders

We examine the properties of ditauonium, an exotic atom consisting of a pair of opposite-sign  $$\tau $$  <math> <mi>τ</mi> </math>   leptons bound together by the quantum electrodynamics (QED) interaction in a hydrogen-like state. The energy levels, decay modes and associated partial widths, as well as total widths and lifetimes of the ortho- and para-ditauonium states are calculated. Higher-order QED effects – including Lamb shifts, hyperfine splitting structure, and partial decay widths corrections – are incorporated up to approximately next-to-next-to-leading-order (NNLO) accuracy. Beyond the dominant diphoton and difermion decays, the rates of rare decay channels – including Dalitz, radiative, triple-photon, double-Dalitz, four-fermion, and neutrinos final states – are determined.

Redamy Perez-Ramos

Ditauonium spectroscopy

The automated generation of arbitrary exclusive final states produced via photon fusion in ultraperipheral high-energy collisions of protons and/or nuclei, A B   <math> <mover> <mo>→</mo> <mi>γγ</mi> </mover> </math>  $$ \overset{\upgamma \upgamma}{\to } $$  A X B, is implemented in the MadGraph5_aMC@NLO and HELAC-Onia Monte Carlo codes. Cross sections are calculated in the equivalent photon approximation using γ fluxes derived from electric dipole and charge form factors, and incorporating hadronic survival probabilities. Multiple examples of γγ cross sections computed with this setup, named gamma-UPC, are presented for proton-proton, proton- nucleus, and nucleus-nucleus ultraperipheral collisions (UPCs) at the Large Hadron Collider and Future Circular Collider. Total photon-fusion cross sections for the exclusive production of spin-0, 2 resonances (quarkonia, ditauonium, and Higgs boson; as well as axions and gravitons), and for pairs of particles (J/ψJ/ψ, WW, ZZ, Zγ,   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> </math>  $$ t\overline{t} $$ , HH) are presented. Differential cross sections for exclusive dileptons and light-by-light scattering are compared to LHC data. This development paves the way for the upcoming automatic event generation of any UPC final state with electroweak corrections at next-to-leading-order accuracy and beyond.

gamma-UPC: automated generation of exclusive photon-photon processes in ultraperipheral proton and nuclear collisions with varying form factors

The feasibility of observing true tauonium, the bound state of two tau leptons, <math><msub><mi>T</mi><mn>0</mn></msub><mo>≡</mo><mo>(</mo><msup><mi>τ</mi><mo>+</mo></msup><msup><mi>τ</mi><mo>−</mo></msup><msub><mo>)</mo><mn>0</mn></msub></math>, via photon-photon collisions at <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> colliders and at the LHC, is studied. The production cross sections of the process <math><mi>γ</mi><mi>γ</mi><mo>→</mo><msub><mi>T</mi><mn>0</mn></msub><mo>→</mo><mi>γ</mi><mi>γ</mi></math>—as well as those of all relevant backgrounds: spin-0 and 2 charmonium resonances decaying to diphotons, and light-by-light scattering—are computed in the equivalent photon approximation for <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> collisions at BES III (<math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>3.8</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>), Belle II (<math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>10.6</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>), and FCC-ee (<math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>91.2</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>), as well as for ultraperipheral p-p, p-Pb, and Pb-Pb collisions at the LHC. Despite small <math><msub><mi>T</mi><mn>0</mn></msub></math> production cross sections and a final state swamped by decays from overlapping pseudoscalar and tensor charmonium states—the <math><msub><mi>χ</mi><mrow><mi>c</mi><mn>2</mn></mrow></msub></math>, <math><msub><mi>η</mi><mi>c</mi></msub><mo>(</mo><mn>2</mn><mi>S</mi><mo>)</mo></math>, and <math><msub><mi>χ</mi><mrow><mi>c</mi><mn>0</mn></mrow></msub></math> states have masses only 2.5, 84, and 139 MeV away, respectively, from the <math><msub><mi>T</mi><mn>0</mn></msub></math> peak—evidence and observation of the ground state of the heaviest leptonium appears feasible at Belle II and FCC-ee, respectively, with in-situ high-precision measurements of the irreducible backgrounds.

Observing true tauonium via two-photon fusion at <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> and hadron colliders

Rare two-body decays of the top quark into a neutral bottom-quark meson plus an up- or charm-quark:   <math> <mi>t</mi> <mo>→</mo> <msup> <mover> <mi>B</mi> <mo>¯</mo> </mover> <mn>0</mn> </msup> <mo>+</mo> <mi>u</mi> <mo>,</mo> <mspace width="0.5em"></mspace> <mi>c</mi> <mo>;</mo> <mi>t</mi> <mo>→</mo> <msubsup> <mover> <mi>B</mi> <mo>¯</mo> </mover> <mi>s</mi> <mn>0</mn> </msubsup> <mo>+</mo> <mi>c</mi> <mo>,</mo> <mspace width="0.5em"></mspace> <mi>u</mi> </math>  $$ t\to {\overline{B}}^0+u,\kern0.5em c;t\to {\overline{B}}_s^0+c,\kern0.5em u $$ ; and t → ϒ(nS) + c, u, are studied for the first time. The corresponding partials widths are computed at leading order in the non-relativistic QCD framework. The sums of all two-body branching ratios amount to   <math> <mi>ℬ</mi> <mfenced> <mrow> <mi>t</mi> <mo>→</mo> <msup> <mover> <mi>B</mi> <mo>¯</mo> </mover> <mn>0</mn> </msup> <mo>+</mo> <mi>jet</mi> </mrow> </mfenced> <mo>≈</mo> <mi>ℬ</mi> <mfenced> <mrow> <mi>t</mi> <mo>→</mo> <msubsup> <mover> <mi>B</mi> <mo>¯</mo> </mover> <mi>s</mi> <mn>0</mn> </msubsup> <mo>+</mo> <mi>jet</mi> </mrow> </mfenced> <mo>≈</mo> <mn>4.2</mn> <mo>⋅</mo> <msup> <mn>10</mn> <mrow> <mo>−</mo> <mn>5</mn> </mrow> </msup> </math>  $$ \mathrm{\mathcal{B}}\left(t\to {\overline{B}}^0+\mathrm{jet}\right)\approx \mathrm{\mathcal{B}}\left(t\to {\overline{B}}_s^0+\mathrm{jet}\right)\approx 4.2\cdot {10}^{-5} $$  and ℬ(t → ϒ(nS) + jet) ≈ 2 ⋅ 10−9, respectively. The feasibility to observe the   <math> <mi>t</mi> <mo>→</mo> <msubsup> <mover> <mi>B</mi> <mo>¯</mo> </mover> <mfenced> <mi>s</mi> </mfenced> <mn>0</mn> </msubsup> <mo>+</mo> </math>  $$ t\to {\overline{B}}_{(s)}^0+ $$  jet decay is estimated in top- pair events produced in proton-proton collisions at   <math> <msqrt> <mi>s</mi> </msqrt> </math>  $$ \sqrt{s} $$  = 14, 100 TeV at the LHC and FCC, respectively. Combining many exclusive hadronic   <math> <msubsup> <mover> <mi>B</mi> <mo>¯</mo> </mover> <mfenced> <mi>s</mi> </mfenced> <mn>0</mn> </msubsup> </math>  $$ {\overline{B}}_{(s)}^0 $$  decays, with J/ψ or D 0,±  final states, about 50 (16 000) events are expected in 3 (20) ab −1 of integrated luminosity at the LHC (FCC), after typical selection criteria, acceptance, and efficiency losses. An observation of the two-body top-quark decay can also be achieved in the interesting t → b(jet) + c(jet) dijet final state, where the   <math> <msubsup> <mover> <mi>B</mi> <mo>¯</mo> </mover> <mfenced> <mi>s</mi> </mfenced> <mn>0</mn> </msubsup> </math>  $$ {\overline{B}}_{(s)}^0 $$  decay products are reconstructed as a jet, with 5 300 and 1.4 million signal events above backgrounds expected after selection criteria at the LHC and FCC, respectively. Such unique final states provide a new direct method to precisely measure the top-quark mass via simple 2-body invariant mass analyses.

Rare two-body decays of the top quark into a bottom meson plus an up or charm quark

The inclusive cross sections of W , W , and Z boson production from 34 different measurements performed in proton-(anti)proton collisions at center-of-mass energies $$ \sqrt{s} $$ = 1 8–13 TeV, are compared to perturbative QCD calculations at next-to-next-to-leading-order (NNLO) accuracy with four sets of parton distributions functions (CT14, HERAPDF2.0, MMHT14, and NNPDF3.0 PDFs) and varying values of the strong coupling constant at the Z mass pole, ( ). The data-theory agreement is good within the experimental and theoretical uncertainties, with the CT14 and MMHT14 parton densities providing the most overall consistent description of all cross section data. A value of ( ) = $$ {0.1188}_{-0.0013}^{+0.0019} $$ is extracted from a combined fit of the 28 experimental LHC measurements to the corresponding NNLO theoretical predictions obtained with the MMHT14 PDF set, which provides the most robust and stable QCD coupling extraction of this analysis.

Germany

Andres Poldaru

Extraction of the strong coupling

The production of the Higgs boson in photon-photon interactions with proton and nucleus beams at three planned or proposed future CERN colliders—the high-luminosity Large Hadron Collider (HL-LHC), the high-energy LHC (HE-LHC), and the Future Circular Collider (FCC)—is studied. The cross sections for the process <math><mrow><mi>AA</mi><mover><mrow><mo>→</mo></mrow><mrow><mi>γ</mi><mi>γ</mi></mrow></mover><mo>(</mo><mi>A</mi><mo>)</mo><mi>H</mi><mo>(</mo><mi>A</mi><mo>)</mo></mrow></math>, with the ions A surviving the interaction and the Higgs scalar exclusively produced, are computed with madgraph 5 modified to include the corresponding elastic <math><mi>γ</mi></math> fluxes, for Pb-Pb, Xe-Xe, Kr-Kr, Ar-Ar, O-O, p-Pb, and p-p over the nucleon-nucleon collision energy range <math><mrow><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mo>≈</mo><mn>3</mn><mi>–</mi><mn>100</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math>. Simulations of the <math><mrow><mrow><mi>γ</mi><mi>γ</mi><mo>→</mo><mi>H</mi><mo>→</mo><mi>b</mi><mover><mrow><mi>b</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow></mrow></math> decay mode—including realistic (mis)tagging and reconstruction efficiencies for the final-state b-jets, as well as appropriate kinematical selection criteria to reduce the similarly computed <math><mrow><mi>γ</mi><mi>γ</mi><mo>→</mo><mrow><mi>b</mi><mover><mrow><mi>b</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow><mo>,</mo><mrow><mi>c</mi><mover><mrow><mi>c</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow><mo>,</mo><mrow><mi>q</mi><mover><mrow><mi>q</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow></mrow></math> continuum backgrounds—have been carried out. Taking into account the expected luminosities for all systems, the yields, and significances for observing the Higgs boson in ultraperipheral collisions (UPCs) are estimated. At the HL-LHC and HE-LHC, the colliding systems with larger Higgs significance are Ar-Ar (6.3 TeV) and Kr-Kr (12.5 TeV), respectively, but <math><mn>3</mn><mi>σ</mi></math> evidence for two-photon Higgs production would require 200 and 30 times larger integrated luminosities than those planned today at both machines. Factors of 10 can be gained by running for a year, rather than the typical 1-month heavy-ion LHC operation, but the process will likely remain unobserved until a higher energy hadron collider, such as the FCC, is built. In the latter machine, the <math><mn>5</mn><mi>σ</mi></math> observation of Higgs production in UPCs is feasible in just the first nominal run of Pb-Pb and p-Pb collisions at <math><mrow><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>39</mn></mrow></math> and 63 TeV, respectively.