Light-by-light Research Articles

Searching for axionlike particles at future electron-positron colliders

We investigate the prospects for discovering axion-like particles (ALPs) via a light-by-light (LBL) scattering at two colliders, the future circular collider (FCC-ee) and circular electron-positron collider (CEPC). The promising sensitivities to the effective ALP-photon coupling $g_{a\gamma\gamma}$ are obtained. Our numerical results show that the FCC-ee and CEPC might be more sensitive to the ALPs with mass 2 GeV $\sim$ 10 GeV than the LHC and CLIC.

Polarized light-by-light scattering at the CLIC induced by axion-like particles

In this study, light-by-light (LBL) scattering with initial polarized Compton backscattered photons at the CLIC, induced by axion-like particles (ALPs), is investigated. The total cross sections are calculated assuming CP-even coupling of the pseudoscalar ALP to photons. The 95% C.L. exclusion region for the ALP mass and its coupling constant f is presented. The results are compared with CLIC bounds previously obtained for the unpolarized case. It is shown that the bounds on f for the polarized beams in the region with collision energy of 3000 GeV and integrated luminosity of 4000 fb are on average 1.5 times stronger than the bounds for the unpolarized beams. Moreover, our CLIC bounds are stronger than those for all current exclusion regions for GeV. In particular, they are more restrictive than the limits that follow from the ALP-mediated LBL scattering at the LHC.

Diffractive gamma gamma production in pp collisions at the LHC

In this letter we estimate the contribution of the double diffractive processes for the diphoton production in pp collisions at the large hadron collider (LHC). The acceptance of the central and forward LHC detectors is taken into account and predictions for the invariant mass, rapidity and, transverse momentum distributions are presented. A comparison with the predictions for the light-by-light (LbL) scattering and exclusive diphoton production is performed. We demonstrate that the events associated to double diffractive processes can be separated and its study can be used to constrain the behavior of the diffractive parton distribution functions.

Exclusive and diffractive gamma gamma production in PbPb collisions at the LHC, HE-LHC and FCC

In this paper we present a detailed analysis of the contribution of the Light-by-Light (LbL), Durham and double diffractive processes for the diphoton production in ultraperipheral PbPb collisions at the Large Hadron Collider (LHC), High-Energy LHC (HE-LHC) and Future Circular Collider (FCC). The acceptance of the central and forward LHC detectors is taken into account and predictions for the invariant mass, rapidity, transverse momentum and acoplanarity distributions are presented. Our results indicate that the contribution of the Durham process is negligible and that the double diffractive process can be strongly suppressed by the exclusivity cuts, which will allow to perform a precise analysis of the LbL scattering, as well the search of beyond Standard Model physics in this final state.

Single pseudoscalar meson pole and pion box contributions to the anomalous magnetic moment of the muon

We present results for single pseudoscalar meson pole contributions and pion box contributions to the hadronic light-by-light (LBL) correction of the muon's anomalous magnetic moment. We follow the recently developed dispersive approach to LBL, where these contributions are evaluated with intermediate mesons on-shell. However, the space-like electromagnetic and transition form factors are not determined from analytic continuation of time-like data, but directly calculated within the functional approach to QCD using Dyson-Schwinger and Bethe-Salpeter equations. This strategy allows for a systematic comparison with a strictly dispersive treatment and also with recent results from lattice QCD. Within error bars, we obtain excellent agreement for the pion electromagnetic and transition form factor and the resulting contributions to LBL. In addition, we present results for the η and η′ pole contributions and discuss the dynamical effects in the η−η′ mixing due to the strange quarks. Our result for the total pseudoscalar pole contributions is aμPS-pole=91.6(1.9)×10−11 and for the pion-box contribution we obtain aμπ−box=−16.3(2)(4)×10−11.

Evidence for light-by-light scattering in ultraperipheral PbPb collisions at [formula omitted

Evidence for light-by-light (LbL) scattering, γγ→γγ, in ultraperipheral PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV is reported. LbL scattering processes are selected in events with just two photons produced, with transverse energy ETγ>2GeV, pseudorapidity |ηγ|<2.4; and diphoton invariant mass mγγ>5GeV, transverse momentum pTγγ<1GeV, and acoplanarity (1−Δϕγγ/π)<0.01. After all selection criteria, 14 events are observed, compared to 11.1±1.1(theo) and 3.8±1.3(stat) events expected for signal and background processes respectively. The significance of the signal excess over the background-only hypothesis is 4.1σ. The measured fiducial LbL scattering cross section, σfid(γγ→γγ)=122±46(stat)±29(syst)±4(theo) nb is consistent with the standard model prediction.

Hadronic light-by-light contribution to the muon g — 2

We have computed the hadronic light-by-light (LbL) contribution to the muon anomalous magnetic moment aμ in the frame of Chiral Perturbation Theory with the inclusion of the lightest resonance multiplets as dynamical fields (RχT). It is essential to give a more accurate prediction of this hadronic contribution due to the future projects of J-Parc and FNAL on reducing the uncertainty in this observable. We, therefore, computed the pseudoscalar transition form factor and proposed the measurement of the e+ e- →μ+ μ- π0 cross section and dimuon invariant mass spectrum to determine more accurately its parameters. Then, we evaluated the pion exchange contribution to αμ, obtaining (6.66 ± 0.21) • 10-10. By comparing the pion exchange contribution and the pion-pole approximation to the corresponding transition form factor (πTFF) we recalled that the latter underestimates the complete πTFF by (15-20)%. Then, we obtained the η(') TFF, obtaining a total contribution of the lightest pseudoscalar exchanges of (10.47 ± 0.54) • 10-10, in agreement with previous results and with smaller error.

Lightest pseudoscalar exchange contribution to light-by-light scattering piece of the muon g − 2

Lightest pseudoscalar (P=π0,η,η′) exchange contribution to the light-by-light (LbL) scattering piece of the muon anomaly, aμ=(gμ−2)/2, has been evaluated using a resonance chiral Lagrangian (RχL). Best description of pion transition form-factor (TFF) data is obtained with only tiny violations of one of the relations in the minimal consistent set of short-distance constraints on the anomalous RχL couplings. η(′)TFF, predicted in terms of the πTFF and the η−η′ mixing, are in good agreement with measurements. With this input, we obtain aμP,LbL=(10.47±0.54)⋅10−10, consistent with the reference determinations in the literature, albeit with smaller error.

Some QED processes: Light-by-light and moeller scattering

We consider several applications of the simplest nonlinear QED phenomena described by the light-by-light (LBL) scattering tensor. Among the relevant processes we present the splitting of high energy photon in a Coulomb field, calculate the asymptotics of differential photon photon elastic scattering. We show that LBL mechanism of the four photon mode of neutral pion decay have a dominant role compared, for instance, with the quark loop Feynman amplitude contribution. The mechanisms of creation of two and three gluon jets at colliding electro-positron beams is analyzed. We calculate also the contribution of LBL mechanism to the ortho-positronium decay width. One Of the important application is the analytic calculation of the QED contribution to the anomalous magnetic moment of the muon arising from LBL mechanism realized through electron positron loops, which is enhanced by the logarithm of the ratio of muon to electron masses. The modification of the QED kernel, which takes into account the QED polarization operator is used to extract the pure strong interaction contribution. We consider as well the problem of the Coulomb law modification. At second part of review we consider Moeller scattering process and RC to it. We show that RC are in agreement with renormalization group approach and could be taken into account in form of Drell-Yan process cross-section.

Updated estimate of the muon magnetic momentusing revised results from e + e -annihilation

A new evaluation of the hadronic vacuum polarization contribution to the muon magnetic moment is presented. We take into account the reanalysis of the low-energy e + e -annihilation cross section into hadrons by the CMD-2 Collaboration. The agreement between e + e -and $\tau$ spectral functions in the $\pi\pi$ channel is found to be much improved. Nevertheless, significant discrepancies remain in the center-of-mass energy range between 0.85 and $1.0\;{\rm GeV}$ , so that we refrain from averaging the two data sets. The values found for the lowest-order hadronic vacuum polarization contributions are $$ a_\mu^{\rm had,LO} = \left\{ \begin{array}{@{}ll@{}} (696.3\pm6.2_{\exp}\pm3.6_{\mathrm{rad}})\,10^{-10} & \quad [e^+e^-{\rm (711.0\pm5.0_{\exp}\pm0.8_{\mathrm{rad}} \pm2.8_{\rm SU(2)})\,10^{-10} & \quad [\tau {\rm -based}], \\ \end{array} \right. $$ where the errors have been separated according to their sources: experimental, missing radiative corrections in e + e -data, and isospin breaking. The corresponding Standard Model predictions for the muon magnetic anomaly read $$ a_\mu = \left\{ \begin{array}{@{}ll@{}} (11\,659\,180.9\pm7.2_{\rm had} \pm3.5_{\rm LBL}\pm0.4_{\rm QED+EW})\,10^{-10} & \quad [e^+e^-{\rm -based}], \\ (11\,659\,195.6\pm5.8_{\rm had} \pm3.5_{\rm LBL}\pm0.4_{\rm QED+EW})\,10^{-10} & \quad [\tau {\rm -based}], \\ \end{array} \right. $$ where the errors account for the hadronic, light-by-light (LBL) scattering and electroweak contributions. The deviations from the measurement at BNL are found to be $(22.1 \pm 7.2 \pm 3.5 \pm 8.0) 10^{-10}$ (1.9 $\sigma$ ) and $(7.4 \pm 5.8 \pm 3.5 \pm 8.0) 10^{-10}$ (0.7 $\sigma$ ) for the e + e -- and $\tau$ -based estimates, respectively, where the second error is from the LBL contribution and the third one from the BNL measurement.

Interpreting the new Brookhavengμ−2result

The latest g_mu - 2 measurement by Brookhaven confirms the earlier measurement with twice the precision. However, interpretation of the result requires specific assumptions regarding the errors in the hadronic light by light (LbL) correction and in the hadronic vacuum polarization correction. Under the assumption that the analysis on LbL correction of Knecht and Nyffeler and the revised analysis of Hayakawa and Kinoshita are valid the new BNL result implies a deviation between experiment and the standard model of 1.6 sigma -2.6 sigma depending on the estimate of the hadronic vacuum polarization correction. We revisit the g_mu - 2 constraint for mSUGRA and its implications for the direct detection of sparticles at colliders and for the search for supersymmetric dark matter in view of the new evaluation.

Scalar and pseudoscalar meson pole terms in the hadronic light-by-light contributions to aμhad

Third QED order hadronic light-by-light (LBL) contributions a μ LBL( M) to the anomalous magnetic moment of the muon a μ had from the pole terms of scalar σ, a 0(980) and pseudoscalar π 0, η, η′ mesons ( M) in the framework of the linearized extended Nambu–Jona–Lasinio model are evaluated. The off-shell structure of the photon–photon–meson vertices is taken into account by means of constituent quark triangle loops. The mass of the quark is taken to be m u = m d = m q =(280±20) MeV. The unknown strong coupling constants of π 0, η, η′ and a 0 mesons with quarks are evaluated in a comparison of the corresponding theoretical two-photon widths calculated in the framework of our approach with experimental ones. The σ-meson coupling constant is taken to be equal to π 0-meson coupling constant as it follows from the linearized Nambu–Jona–Lasinio model Lagrangian. Then one obtains a μ LBL( π 0)=(81.83±16.50)×10 −11, a μ LBL( η)=(5.62±1.25)×10 −11, a μ LBL( η′)=(8.00±1.74)×10 −11, a μ LBL( σ)=(11.67±2.38)×10 −11 and a μ LBL( a 0)=(0.62±0.24)×10 −11. The total contribution of meson poles in LBL is a μ LBL( M)=(107.74±16.81)×10 −11.