Line Shapes of the Z4430 - High Energy Physics - PhenomenologyReport as inadecuate

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Abstract: The Belle Collaboration recently discovered the first manifestly exoticmeson: Z^+4430, which decays into psi- pi^+ and therefore has quark content cc-bar u d-bar. The proximity of its mass to the D 1 D-bar^* threshold hasmotivated the interpretation of the Z^+ as a charm meson molecule whoseconstituents are an S-wave superposition of D 1^+ D-bar^{*0}$ and D^{*+}D-bar 1^0$. If this interpretation is correct, the small ratio of the bindingenergy of the Z^+ to the width Gamma 1 of its constituent D 1 can be exploitedto predict properties of its line shapes. Its full width at half maximum in thechannel psi- pi^+ should be approximately sqrt{3} Gamma 1 = 35 MeV, which isconsistent with the measured width of the Z^+. The Z^+ should also decay intoD^* D-bar^* pi through decay of its constituent D 1. The peak in the line shapefor D^* D-bar^* pi should be at a higher energy than the peak in the line shapefor psi- pi^+ by about Gamma 1-sqrt{12} = 6 MeV. The line shape in D^* D-bar^*pi should also be broader and asymmetric, with a shoulder on the high energyside that can be attributed to a threshold enhancement in the production of D 1D-bar^*.

Author: Eric Braaten, Meng Lu


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