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Observation of a charged scalar a0(1817)* in Charmed-strange meson Ds decay

2022-10-31 Author:
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 The BESIII Collaboration recently reported the observation of an a0-like state with mass of 1.817 GeV/c2 in DS decays with the data sets collected at the center-of-mass energy region between 4.178 GeV and 4.226 GeV. The paper has been published online in Physical Review Letter. [Phys. Rev. Lett. 129, 182001 (2022) ].

Scalar mesons are of wide interest yet their detailed nature remains unclear. Their production in charmed-strange meson weak decays provides an ideal environment for studies which can help to understand their internal structure. The a0(980) and a0(1450) are the isospin one partners of the isospin zero f0(500), f0(980), f0(1370), and f0(1500). However, the isospin one partner of the f0(1710), predicted by theorists, is not established yet.  

The f0(1710) has long been considered a possible candidates for a scalar glueball or a vector-vector molecule. One decisive way to determine whether the nature of the f0(1710) is to search for and investigate its isospin one partner. BESIII reports the observation of a charged a0-like state with mass of 1.817 GeV in the KSK+ mass spectrum in an amplitude analysis of the DS+→KSK+π0 decay as shown in Fig. 1. The branching fraction of DS+ → a0(1817)+π0 is determined to be (3.44 ± 0.52 ± 0.32)%. The mass and width of a0(1817)+ are measured to be  (1.817±0.008±0.020) GeV/c2 and (0.097±0.022±0.015) GeV/c2, respectively. In a previous relavent study [Phys. Rev. D Letter, 105, L051103 (2022)], BESIII presents the observation of an enhancement in the KS0KS0 mass spectrum in an amplitude analysis of DS+ -> KS0KS0π+. This enhancement may imply the inteference of the f0(1710) and a neutral charged a0-like state.

   The discovery of these a0-like state is crucial to pin down the nature of scalar mesons and inspires some exciting questions, such as whether the charged and neutral ones are in a set of isospin triplet or two irrelevant resonances. Our results are consistent with the prediction assuming these new a0-like is the candidate isospin one partner of the f0(1710) meson. However, the higher than expected mass may imply instead that this a0-like state is the partner with isospin one of the X(1812). A more sophisticated study of this a0-like state is expected in a simultaneous amplitude analysis of DS+ to KS0KS0π+, K+K-π+ and KS0K+π0 in the future.


Fig. 1. The projections of the Dalitz plot onto KS0K+ mass spectrum in the DS+KS0K+π0 decay.

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