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Samios, N.; Plano, R.J.; Prodell, A.; Schwartz, M.; Steinberger, J.

doi:10.1103/physrev.126.1844

Cited by 41 publications

(29 citation statements)

References 10 publications

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“…Our branching ratio result is in agreement with previous measurements [7]. The parameters of the π 0 γ * γ * coupling are found by maximizing an unbinned likelihood function composed of the differential decay rate in terms of ten phase-space variables.…”

Section: Arxiv:08022064v2 [Hep-ex] 11 May 2008supporting

confidence: 80%

Determination of the Parity of the Neutral Pion via Its Four-Electron Decay

et al. 2008

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We present a new determination of the parity of the neutral pion via the double Dalitz decay π 0 → e + e − e + e − . Our sample, which consists of 30 511 candidate decays, was collected from KL → π 0 π 0 π 0 decays in flight at the KTeV-E799 experiment at Fermi National Accelerator Laboratory. We confirm the negative π 0 parity, and place a limit on scalar contributions to the π 0 → e + e − e + e − decay amplitude of less than 3.3% assuming CPT conservation. The π 0 γ * γ * form factor is well described by a momentum-dependent model with a slope parameter fit to the final state phase space distribution. Additionally, we have measured the branching ratio of this mode to be B(π 0 → e + e − e + e − ) = (3.26 ± 0.18) × 10 −5 .PACS numbers: 14.40.Aq, 13.40.GpThe parity of the neutral pion has been determined indirectly by studying negative pions captured on deuterium [1,2]. The observed reactions imply that the π − is a pseudoscalar and that the parities of the π − and the π 0 are the same. It has long been known that the decay π 0 → γγ in principle offers a direct means of determining the π 0 parity through the polarizations of the photons [3,4]. Given that there are no available methods for measuring the polarization of a high-energy photon, this measurement has never been performed. However, it was soon noted that the double Dalitz decay π 0 → e + e − e + e − , which proceeds through an intermediate state with two virtual photons (see Fig. 1), is sensitive to the parity of the pion since the plane of a Dalitz pair is correlated with the polarization of the virtual photon [5,6]. This process was studied in a 1962 hydrogen bubble chamber experiment using stopping negative pion capture (π − p → nπ 0 ). That group observed 206 π 0 → e + e − e + e − events and reported that the observed distribution of the e + e − planes was consistent with a pseudoscalar pion and disfavored a scalar pion at the level of 3.6 standard deviations [7]; this experiment also produced a measurement of the branching ratio of this decay, which remains the most precise result to date. Using a sample of more than 30 000 π 0 → e + e − e + e − decays, we report new precise measurements of the properties of this decay. Our modeling of the decay includes for the first time a proper treatment of the exchange contribution to the matrix element, and consideration

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Section: Arxiv:08022064v2 [Hep-ex] 11 May 2008supporting

confidence: 80%

Determination of the Parity of the Neutral Pion via Its Four-Electron Decay

et al. 2008

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“…Interestingly enough, double-virtual effects have never been measured, and are relevant for predicting the hadronic light-by-light contribution to the anomalous magnetic moment of the muon [23,24]. On the other hand, the angular distribution associated to the lepton planes (ϕ ≡ ϕl l;l 0 l 0 ) is a CP-sensitive observable and was indeed the first experimental evidence for the parity of the π 0 [12,25]. Since no significant amount of CP violation is expected in these processes within the standard model, any signal of this would be very interesting.…”

Section: Introductionmentioning

confidence: 99%

“…Double-Dalitz decays of pseudoscalar mesons (P →lll 0 l 0 ) have attracted attention over the years, both theoretically [1][2][3][4][5][6][7][8][9][10][11] and experimentally [12][13][14][15][16][17][18][19][20][21][22], for different reasons. On the one hand, they contain important-Direct-information about the pseudoscalar meson structure, which is encoded in their double-virtual transition form factors (TFFs).…”

Section: Introductionmentioning

confidence: 99%

Radiative corrections to double-Dalitz decays revisited

2018

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In this study, we revisit and complete the full next-to-leading order corrections to pseudoscalar doubleDalitz decays within the soft-photon approximation. Comparing to the previous study, we find small differences, which are nevertheless relevant for extracting information about the pseudoscalar transition form factors. Concerning the latter, these processes could offer the opportunity to test them-for the first time-in their double-virtual regime.

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“…The first experimental observation of a double Dalitz decay was published in 1962 [6,7]. A total of 206 examples of the decay π 0 → e + e − e + e − were observed by Samios in a sample of some 800,000 bubble chamber photographs.…”

Section: Introductionmentioning

confidence: 99%

Radiative corrections to double Dalitz decays: Effects on invariant mass distributions and angular correlations

et al. 2003

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We review the theory of meson decays to two lepton pairs, including the cases of identical as well as non-identical leptons, as well as CP-conserving and CP-violating couplings. A complete lowestorder calculation of QED radiative corrections to these decays is discussed, and comparisons of predicted rates and kinematic distributions between tree-level and one-loop-corrected calculations are presented for both π 0 and K 0 decays. PACS numbers: 12.15.Lk, 13.20.Cz, 13.20.Eb, 13.40.Gp, 13.40.Hq I. BACKGROUNDMeson decays to two photons should exhibit interesting correlations between the photon polarizations [1]. Although existing particle detectors cannot measure photon polarizations directly, it has long been known that the polarization correlations can be measured indirectly by studying angular correlations in the related double Dalitz decays [2] in which both photons undergo internal conversion to a lepton pair. More recently, it has been pointed out [3] that a detailed study of these correlations can be used to determine the relative amount of two possible meson-γγ couplings (one CP-conserving and one CP-violating for mesons that are CP eigenstates) that can contribute to this process.Dalitz and double Dalitz decays are also of interest because they can be exploited to perform a measurement of the electromagnetic form factor of the decaying mesonthat is, how the meson couples to one real and one virtual photon (Dalitz decay) or two virtual photons (double Dalitz) depends on the q 2 values of the photon(s). An accurate knowledge of this form factor is essential, for example, to calculate the so-called long-distance contribution to the rare decay K L → µ + µ − . The short-distance contribution to this process, mediated by loops involving heavy quarks and massive vector bosons, is sensitive to the CKM matrix element V td , but this contribution cannot be extracted from the accurate experimental measurement of the partial width unless the long-distance amplitude is precisely known.The tree-level rates for several double Dalitz processes have been published in various forms [2,3,4,5]. The first experimental observation of a double Dalitz decay was published in 1962 [6,7]. A total of 206 examples of the decay π 0 → e + e − e + e − were observed by Samios in a sample of some 800,000 bubble chamber photographs. Based on the observed angular correlations, Samios was * E-mail: tonyb@cuhep.colorado.edu † Current address: Department of Physics, 104 Davey Lab, Pennsylvania State University, University Park, PA 16802-6300. able to exclude the possibility that the π 0 was a scalar particle (with a CP-conserving decay) at the 3.3σ confidence level. His measurement of the branching ratio for that process remains the only one published to date.Experimental observations of the much rarer kaon double Dalitz decays began to appear in the 1990's. Several measurements have been made of the decay K L → e + e − e + e − [8,9,10,11,12,13,14], the most recent of which are based on several hundred observed events. The still rarer doub...

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Parity of the Neutral Pion and the Decayπ0→2e++2e

Cited by 41 publications

References 10 publications

Determination of the Parity of the Neutral Pion via Its Four-Electron Decay

Determination of the Parity of the Neutral Pion via Its Four-Electron Decay

Radiative corrections to double-Dalitz decays revisited

Radiative corrections to double Dalitz decays: Effects on invariant mass distributions and angular correlations

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