Observation of the resonant character of the $Z(4430)^-$ state

Information

LHCb-PAPER-2014-014
CERN-PH-EP-2014-061
arXiv:1404.1903 [PDF]

(Submitted on 07 Apr 2014)
Phys. Rev. Lett. 112 (2014) 222002
Inspire 1288881

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Abstract

Resonant structures in $B^0\to\psi'\pi^-K^+$ decays are analyzed by performing a four-dimensional fit of the decay amplitude, using $pp$ collision data corresponding to $\rm 3 fb^{-1}$ collected with the LHCb detector. The data cannot be described with $K^+\pi^-$ resonances alone, which is confirmed with a model-independent approach. A highly significant $Z(4430)^-\to\psi'\pi^-$ component is required, thus confirming the existence of this state. The observed evolution of the $Z(4430)^-$ amplitude with the $\psi'\pi^-$ mass establishes the resonant nature of this particle. The mass and width measurements are substantially improved. The spin-parity is determined unambiguously to be $1^+$.

Figures and captions

Background-subtracted and efficiency-corrected $m_{\psi'\pi^-}$ distribution (black data points), superimposed with the reflections of $\cos\theta_{K^}$ moments up to order four allowing for $J(K^)\le 2$ (blue line) and their correlated statistical uncertainty (yellow band bounded by blue dashed lines). The distributions have been normalized to unity.	manal2.pdf [20 KiB] HiDef png [218 KiB] Thumbnail [162 KiB] *.C file
Distributions of the fit variables (black data points) together with the projections of the 4D fit. The red solid (brown dashed) histogram represents the total amplitude with (without) the $ Z_1^-$ . The other points illustrate various subcomponents of the fit that includes the $ Z_1^-$ : the upper (lower) blue points represent the $ Z_1^-$ component removed (taken alone). The orange, magenta, cyan, yellow, green, and red points represent the $K^(892)$, total $S$-wave, $K^(1410)$, $K^(1680)$, $K^_2(1430)$ and background terms, respectively.	mpsippi2.pdf [39 KiB] HiDef png [293 KiB] Thumbnail [194 KiB] *.C file
	mkpi2.pdf [64 KiB] HiDef png [436 KiB] Thumbnail [256 KiB] *.C file
	cospsip.pdf [40 KiB] HiDef png [329 KiB] Thumbnail [215 KiB] *.C file
	phi.pdf [25 KiB] HiDef png [209 KiB] Thumbnail [163 KiB] *.C file
Fitted values of the $ Z_1^-$ amplitude in six $m_{\psi'\pi^-}^2$ bins, shown in an Argand diagram (connected points with the error bars, $m_{\psi'\pi^-}^2$ increases counterclockwise). The red curve is the prediction from the Breit-Wigner formula with a resonance mass (width) of 4475 (172) $\mathrm{ Me V}$ and magnitude scaled to intersect the bin with the largest magnitude centered at (4477 MeV)$^2$. Units are arbitrary. The phase convention assumes the helicity-zero $K^*(892)$ amplitude to be real.	argand.pdf [14 KiB] HiDef png [146 KiB] Thumbnail [130 KiB] *.C file
Distribution of $m_{\psi'\pi^-}^2$ in the data (black points) for $1.0<m_{K^+\pi^-}^2<1.8$ GeV$^2$ ($K^(892)$, $K^_2(1430)$ veto region) compared with the fit with two, $0^-$ and $1^+$ (solid-line red histogram) and only one $1^+$ (dashed-line green histogram) $Z^-$ resonances. Individual $Z^-$ terms (blue points) are shown for the fit with two $Z^-$ resonances.	twoz.pdf [28 KiB] HiDef png [196 KiB] Thumbnail [156 KiB] *.C file
Animated gif made out of all figures.	PAPER-2014-014.gif Thumbnail

Supplementary Material [file]

Supplementary material full pdf	supple[..].pdf [620 KiB]
This ZIP file contains supplemetary material for the publication LHCb-PAPER-2014-014. The files are: supplementary.pdf : An overview of the extra figures *.pdf : The figures in the PDF format	Fig10S.pdf [20 KiB] HiDef png [176 KiB] Thumbnail [158 KiB] *C file
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