Direct Measurement of theφ(1020)Leptonic Branching Ratio

Abstract

The process e(+)e(-)-->mu(+)mu(-) has been studied by the SND detector at the VEPP-2M e(+)e(-) collider in the phi(1020)-resonance energy region. The measured effective phi meson leptonic branching ratio B(phi-->l(+)l(-)) identical with square root of B(phi-->e(+)e(-))B(phi-->mu(+)mu(-))] = (2.89 +/- 0.10 +/- 0.06) x 10(-4) agrees well with the Particle Data Group value B(phi-->e(+)e(-)) = (2.91 +/- 0.07) x 10(-4), confirming mu-e universality. Without additional assumption of mu-e universality the branching ratio B(phi-->mu(+)mu(-)) = (2.87 +/- 0.20 +/- 0.14) x 10(-4) was obtained.

Physics with the KLOE-2 experiment at the upgraded DAΦNE

“…Recently, a model for implementing systematic corrections to the standard VMD calculations has been proposed [267] which correctly describes the ω → π 0 µ + µ − experimental results, and predicts deviation from standard VMD for the φ → ηe + e − decay spectrum. The only existing data on the latter process come from the SND experiment at Novosibirsk which has measured the M ee invariant mass distribution on the basis of 74 events [268]. The accuracy on the shape does not allow any conclusion on the models.…”

“…The kink in the curve just above 0. is for constant form factor F φηγ * (q 2 ) = 1, whereas the lower curve is for the single-pole fit F φηγ * (q 2 ) = 1/(1 − 3.8GeV −2 q 2 ) from Ref. [268]. Bottom: The reach in e + e − with single-pole form factor as above is compared with the corresponding reach in µ + µ − (gray curve).…”

Measurement of the leptonic decay widths of the ϕ-meson with the KLOE detector

“…There is no direct measurement of the leptonic width. The only direct measurement is B(φ → e + e − )B(φ → µ + µ − )=(2.89±0.10±0.06)×10 −4 [3]. In Fig.…”

CMD-2 and SND results on the ρ, ω and ϕ

“…The accuracy of the parameters B(φ → e + e − )B(φ → ηγ) and B(φ → e + e − )B(φ → K S K L ) was improved also. Using the CMD-2 and SND results [44,104,58,60,42,50,10] the B(φ → e + e − ) = (2.90 ± 0.04) × 10 −4 was obtained. This value deviates from the KLOE result B(φ → e + e − ) = (3.10 ± 0.05) × 10 −4 [105] by three standard deviations.…”