Measurement of η meson production in γγ interactions and Γ(η → γγ) with the KLOE detector

Babusci, D.; Badoni, D.; Balwierz-Pytko, I.; Bencivenni, G.; Bini, C.; Bloise, C.; Bossi, F.; Branchini, P.; Budano, A.; Balkeståhl, L. Caldeira; Capon, G.; Ceradini, F.; Ciambrone, P.; Czerwiński, E.; Dané, E.; Lucia, E. De; Robertis, G. De; Santis, A. De; Domenico, A. Di; Donato, C. Di; Salvo, R. Di; Domenici, D.; Erriquez, O.; Fanizzi, G.; Fantini, A.; Felici, G.; Fiore, S.; Franzini, P.; Gauzzi, P.; Giardina, G.; Giovannella, S.; Gonnella, F.; Graziani, E.; Happacher, F.; Heijkenskjöld, L.; Höistad, B.; Iafolla, L.; Jacewicz, M.; Johansson, T.; Kupść, A.; Lee‐Franzini, J.; Leverington, B.; Loddo, F.; Loffredo, S.; Mandaglio, G.; Martemianov, M.; Martini, M.; Mascolo, M.; Messi, R.; Miscetti, S.; Morello, G.; Moricciani, D.; Moskal, P.; Nguyen, F.; Passeri, A.; Patera, V.; Longhi, I. Prado; Ranieri, A.; Redmer, C. F.; Santangelo, P.; Sarra, I.; Schioppa, M.; Sciascia, B.; Silarski, M.; Taccini, C.; Tortora, L.; Venanzoni, G.; Wiślicki, W.; Wolke, M.; Zdebik, J.

doi:10.1007/jhep01(2013)119

Cited by 26 publications

(17 citation statements)

References 33 publications

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“…and the experimental values [44,53] Γ exp (η → γγ) = 4.36 (14) KeV, Γ exp (η → γγ) = 0.516(18) KeV, (3.10) the ratio R J/ψ becomes a function which only depends on the mixing angle φ. In Fig.…”

Section: Numerical Resultsmentioning

confidence: 81%

Revisiting the radiative decays J/ψ → γη(′) in perturbative QCD

Yang

2019

Nuclear Physics B

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In the framework of perturbative QCD, the radiative decays J/ψ → γη ( ) are revisited in detail, where the involved one-loop integrals are evaluated analytically with the light quark masses kept. We have found that the sum of loop integrals is insensitive to the light quark masses and the branching ratios B(J/ψ → γη ( ) ) barely depend on the shapes of η ( ) distribution amplitudes. With the parameters of η − η mixing extracted from low energy processes and J/ψ → γη ( ) by means of nonperturbative matrix elements 0|G a µνG a,µν |η ( ) based on U A (1) anomaly dominance argument, we could not give the ratio R J/ψ in agreement with experimental result. However, using the parameters, especially the mixing angle φ = 33.5 • ± 0.9 • , extracted from γ * γ − η transition form factor measured at q 2 = 112 GeV 2 by BaBar collaboration, we obtain R J/ψ = 4.70 in good agreement with R exp J/ψ = 4.65 ± 0.21. As a crossing check, with Γ exp (η ( ) → γγ) and our results for J/ψ → γη ( ) , we get φ = 33.9 • ± 0.6 • . The difference between the determinations of φ is briefly discussed.

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Section: Numerical Resultsmentioning

confidence: 81%

Revisiting the radiative decays J/ψ → γη(′) in perturbative QCD

Yang

2019

Nuclear Physics B

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“…η and η 0 transition form factors For both the η and η 0 TFFs, we collect the experimental data from the CELLO, 3 CLEO, L3, and BABAR Collaborations [32][33][34][35]. As stated, we include in our final step the values Γ η→γγ ¼ 0.516ð18Þ keV (obtained after combining the PDG average [36] together with the recent KLOE-2 result [37]) and Γ η 0 →γγ ¼ 4.35ð14Þ keV from the PDG fit [36]. Since the asymptotic values of the spacelike and timelike TFFs are expected to be very similar, we also comment on the results when including in our analysis the timelike measurements 4 for the η and η 0 reported by the BABAR Collaboration [38].…”

Section: η and η 0 Transition Form Factors At Low And Intermediatmentioning

confidence: 99%

ηandη′transition form factors from rational approximants

2014

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The η and η 0 transition form factors in the spacelike region are analyzed at low and intermediate energies in a model-independent way through the use of rational approximants. The slope and curvature parameters of the form factors as well as their values at zero and infinity are extracted from experimental data. The impact of these results on the mixing parameters of the η-η 0 system and the pseudoscalar-exchange contributions to the hadronic light-by-light scattering part of the anomalous magnetic moment a μ are also discussed.

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“…Since the photon flux associated with each nucleus scales with the square of the number of protons, the cross section is strongly enhanced relative to proton-proton (pp) collisions.The γγ → γγ reaction has also been measured in photon scattering in the Coulomb field of a nucleus (Delbrück scattering) [19][20][21][22] and in the photon-splitting process [23]. A related process, in which initial photons fuse to form a pseudoscalar meson that subsequently decays into a pair of photons, has been studied at electron-positron colliders [24][25][26][27].The previous ATLAS and CMS measurements were based on the Pb+Pb dataset of 0.4 nb −1 recorded in 2015 at a center-of-mass energy of √ s NN = 5.02 TeV [12, 13]. The present Letter describes a new measurement exploiting 1.73 nb −1 of Pb+Pb collisions at √ s NN = 5.02 TeV, recorded in November 2018 with the ATLAS detector at the LHC.…”

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confidence: 99%

Observation of Light-by-Light Scattering in Ultraperipheral Pb+Pb Collisions with the ATLAS Detector

Aad¹,

Abbott²,

Abbott³

et al. 2019

Phys. Rev. Lett.

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121

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The ATLAS CollaborationThis letter describes the observation of the light-by-light scattering process, γγ → γγ, in Pb+Pb collisions at √ s NN = 5.02 TeV. The analysis is conducted using a data sample corresponding to an integrated luminosity of 1.73 nb −1 , collected in November 2018 by the ATLAS experiment at the LHC. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy E γ T > 3 GeV and pseudorapidity |η γ | < 2.4, diphoton invariant mass above 6 GeV, and small diphoton transverse momentum and acoplanarity. After applying all selection criteria, 59 candidate events are observed for a background expectation of 12 ± 3 events. The observed excess of events over the expected background has a significance of 8.2 standard deviations. The measured fiducial cross section is 78 ± 13 (stat.) ± 7 (syst.) ± 3 (lumi.) nb.Light-by-light scattering, γγ → γγ, is a quantum-mechanical process that is forbidden in the classical theory of electrodynamics [1, 2]. In the Standard Model (SM), the γγ → γγ reaction proceeds at one-loop level at order α 4 (where α is the fine-structure constant) via virtual box diagrams involving electrically charged fermions (leptons and quarks) or W ± bosons. However, in various extensions of the SM, extra contributions are possible, making the measurement of γγ → γγ scattering sensitive to new physics. Relevant examples are magnetic monopoles [3], vector-like fermions [4] and axion-like particles [5,6]. The light-by-light cross section is also sensitive to the effect of possible non-SM operators in an effective field theory [7][8][9]. Light-by-light scattering graphs with electron loops also contribute to the anomalous magnetic moment of the electron and muon [10,11].Strong evidence for this process in relativistic heavy-ion (Pb+Pb) collisions at the Large Hadron Collider (LHC) has been reported by the ATLAS [12] and CMS [13] collaborations with observed significances of 4.4 and 4.1 standard deviations, respectively. Exclusive light-by-light scattering can occur in these collisions at impact parameters larger than about twice the radius of the ions, as demonstrated for the first time in Ref. [14]. The strong interaction becomes less significant and the electromagnetic (EM) interaction becomes more important in these ultraperipheral collision (UPC) events. In general, this allows to study processes involving nuclear photoexcitation, photoproduction of hadrons, and two-photon interactions [15,16]. The EM fields produced by the colliding Pb nuclei can be described as a beam of quasi-real photons with a small virtuality of Q 2 < 1/R 2 , where R is the radius of the charge distribution and so Q 2 < 10 −3 GeV 2 [17, 18]. The cross section for the elastic reaction Pb+Pb (γγ) → Pb+Pb γγ can then be calculated by convolving the appropriate photon flux with the elementary cross section for the process γγ → γγ. Since the photon flux associated with each nucleus scales with the square of the number of protons, the cross section is strongl...

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Measurement of η meson production in γγ interactions and Γ(η → γγ) with the KLOE detector

Cited by 26 publications

References 33 publications

Revisiting the radiative decays J/ψ → γη(′) in perturbative QCD

Revisiting the radiative decays J/ψ → γη(′) in perturbative QCD

ηandη′transition form factors from rational approximants

Observation of Light-by-Light Scattering in Ultraperipheral Pb+Pb Collisions with the ATLAS Detector

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Measurement of η meson production in γγ interactions and Γ(η → γγ) with the KLOE detector

Cited by 26 publications

References 33 publications

Revisiting the radiative decays J/ψ → γη(′) in perturbative QCD

Revisiting the radiative decays J/ψ → γη(′) in perturbative QCD

ηandη′transition form factors from rational approximants

Observation of Light-by-Light Scattering in Ultraperipheral Pb+Pb Collisions with the ATLAS Detector

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Product

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Revisiting the radiative decays J/ψ → γη(′) in perturbative QCD

Revisiting the radiative decays J/ψ → γη(′) in perturbative QCD