rpp2010-rev-eta1440 - 1 THE(1405(1475 f1(1420 AND f1(1510...

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– 1– THE η (1405), η (1475), f 1 (1420), AND f 1 (1510) Revised February 2010 by C. Amsler (Z¨urich) and A. Masoni (INFN Cagliari). The first observation of the η (1440) was made in p p anni- hilation at rest into η (1440) π + π , η (1440) K [1]. This state was reported to decay through a 0 (980) π and K (892) K with roughly equal contributions. The η (1440) was also ob- served in radiative J/ψ (1 S ) decay into K [2–4] and γρ [5]. There is now evidence for the existence of two pseudoscalars in this mass region, the η (1405) and η (1475). The former decays mainly through a 0 (980) π (or direct K ) and the latter mainly to K (892) K . The simultaneous observation of two pseudoscalars is re- ported in three production mechanisms: π p [6,7]; radiative J/ψ (1 S ) decay [8,9]; and pp annihilation at rest [11–14]. All of them give values for the masses, widths, and decay modes in reasonable agreement. However, Ref. [9] favors a state decay- ing into K (892) K at a lower mass than the state decaying into a 0 (980) π , although agreement with MARK-III is not excluded. In J/ψ (1 S ) radiative decay, the η (1405) decays into K through a 0 (980) π , and hence a signal is also expected in the ηππ mass spectrum. This was indeed observed by MARK III in ηπ + π [15], which reports a mass of 1400 MeV, in line with the existence of the η (1405) decaying into a 0 (980) π . BES [10] reports an enhancement in K + K π 0 around 1.44 GeV in J/ψ (1 S ) decay, recoiling against an ω (but not a φ ) without re- solving the presence of two states nor performing a spin-parity analysis, due to low statistics. This state could also be the f 1 (1420) (see below). The η (1405) is also observed in pp annihilation at rest into ηπ + π π 0 π 0 , where it decays into ηππ [16]. The intermedi- ate a 0 (980) π accounts for roughly half of the ηππ signal, in agreement with MARK III [15] and DM2 [4]. The η (1295) has been observed by four π p experiments [7,17–19], and evidence is reported in pp annihilation [23–25]. In J/ψ (1 S ) radiative decay, an η (1295) signal is evident in the 0 + ηππ wave of the DM2 data [9]. Also BaBar [20] reports evidence for a signal around 1295 MeV in B decays into ηππK . CITATION: K. Nakamura et al. (Particle Data Group), JPG 37 , 075021 (2010) (URL: http://pdg.lbl.gov) July 30, 2010 14:34
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– 2– However, the existence of the η (1295) is questioned in Refs. [21] and [22]. The authors claim a single pseudoscalar meson in the 1400 MeV region. This conclusion is based on properties of the wave functions in the 3 P 0 model (and on an unpublished analysis of the annihilation ¯ pp 4 πη ). The pseudoscalar signal
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