# Model-independent evidence for $J/\psi p$ contributions to $\Lambda_b^0\to J/\psi p K^-$ decays

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## Abstract

The data sample of $\Lambda_b^0\to J/\psi p K^-$ decays acquired with the LHCb detector from 7 and 8 TeV $pp$ collisions, corresponding to an integrated luminosity of 3 fb$^{-1}$, is inspected for the presence of $J/\psi p$ or $J/\psi K^-$ contributions with minimal assumptions about $K^- p$ contributions. It is demonstrated at more than 9 standard deviations that $\Lambda_b^0\to J/\psi p K^-$ decays cannot be described with $K^- p$ contributions alone, and that $J/\psi p$ contributions play a dominant role in this incompatibility. These model-independent results support the previously obtained model-dependent evidence for $P_c^+\to J/\psi p$ charmonium-pentaquark states in the same data sample.

## Figures and captions

 Excitations of the $\Lambda$ baryon. States predicted in Ref. [7] are shown as short horizontal bars (black) and experimentally well-established $\Lambda ^*$ states are shown as green boxes covering the mass ranges from $M_0-\Gamma_0$ to $M_0+\Gamma_0$. The $m_{Kp}$ mass range probed in $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p K ^-$ decays is shown by long horizontal lines (blue). The $l_{\rm max}(m_{Kp})$ filter is shown as a stepped line (red). All contributions from $\Lambda ^*$ states with $J^P$ values to the left of the red line are accepted by the filter. The filter works well also for the excitations of the $\Sigma$ baryon [11,7] (not shown). lmax_new.pdf [14 KiB] HiDef png [139 KiB] Thumbnail [56 KiB] *.C file Efficiency-corrected and background-subtracted $m_{Kp}$ distribution of the data (black points with error bars), with $\cal F(m_{Kp}|H_0)$ superimposed (solid blue line). $\cal F(m_{Kp}|H_0)$ fits the data by construction. Data_mkp.pdf [25 KiB] HiDef png [126 KiB] Thumbnail [41 KiB] *.C file Legendre moments of $\cos\theta_{\Lambda ^*}$ as a function of $m_{Kp}$ in the data. Regions excluded by the $l\lel_{\rm max}(m_{Kp})$ filter are shaded. UMom_A[..].pdf [40 KiB] HiDef png [459 KiB] Thumbnail [141 KiB] *.C file Efficiency-corrected and background-subtracted $m_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p}$ distribution of the data (black points with error bars), with $\cal F(m_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p}|H_0)$ (solid blue line) and $\cal F(m_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p}|H_1)$ (dashed black line) superimposed. Data_m[..].pdf [31 KiB] HiDef png [150 KiB] Thumbnail [42 KiB] *.C file Distributions of $\Delta(\!-2\ln L\!)$ in the model-independent pseudoexperiments corresponding to $H_0$ (red falling hatched) compared to the distributions for pseudoexperiments generated from various amplitude models and, in the inset, to the bifurcated Gaussian fit function (solid line) and the value obtained for the data (vertical bar). dll.pdf [24 KiB] HiDef png [592 KiB] Thumbnail [125 KiB] *.C file Efficiency-corrected and background-subtracted $m_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K}$ distribution of the data (black points with error bars), with $\cal F(m_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K}|H_0)$ (solid blue line) and $\cal F(m_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K}|H_1)$ (dashed black line) superimposed. Data_m[..].pdf [73 KiB] HiDef png [149 KiB] Thumbnail [41 KiB] *.C file Distribution of $m_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p K}$ in the data with the fit of signal and background components superimposed [3]. The fit is used to determine the background fraction $\beta$ in the $\pm2\sigma$ signal region around the $\Lambda ^0_ b$ peak (shown by the vertical red bars). The sidebands used in the background subtraction are also shown. mjpsipk.pdf [28 KiB] HiDef png [182 KiB] Thumbnail [56 KiB] *.C file Background-subtracted and efficiency-corrected distribution of the cosine of the $\Lambda ^*$ helicity angle versus $m_{Kp}$ for the data. Data_K[..].pdf [46 KiB] HiDef png [903 KiB] Thumbnail [213 KiB] *.C file Distribution in a pseudoexperiment of the cosine of the $\Lambda ^*$ helicity angle versus $m_{Kp}$ for the amplitude model with $\Lambda ^*$ resonances only. Lz_KpR[..].pdf [52 KiB] HiDef png [713 KiB] Thumbnail [165 KiB] *.C file Distribution in a pseudoexperiment of the cosine of the $\Lambda ^*$ helicity angle versus $m_{Kp}$ for the amplitude model with the $P_c(4380)^+$ and $P_c(4450)^+$ resonances only. TwoPc_[..].pdf [51 KiB] HiDef png [674 KiB] Thumbnail [161 KiB] *.C file Legendre moments of $\cos\theta_{\Lambda ^*}$ as a function of $m_{Kp}$ for the simulated data from the amplitude models with only $\Lambda ^*$ (solid blue lines) and with only $P_c(4380)^+$, $P_c(4450)^+$ contributions (dashed red lines), scaled by $0.5$. The regions excluded by the $l\lel_{\rm max}(m_{Kp})$ filter are shaded. UMom_C[..].pdf [96 KiB] HiDef png [583 KiB] Thumbnail [156 KiB] *.C file Legendre moments of $\cos\theta_{\Lambda ^*}$ as a function of $m_{Kp}$ for the simulated data from amplitude models with only $P_c(4380)^+$ (solid blue lines) and only $P_c(4450)^+$ contributions (dashed red line). UMom_IndPc.pdf [59 KiB] HiDef png [696 KiB] Thumbnail [178 KiB] *.C file Animated gif made out of all figures. PAPER-2016-009.gif Thumbnail

## Supplementary Material [file]

 Fig9.pdf [52 KiB] HiDef png [713 KiB] Thumbnail [165 KiB] *C file Fig10.pdf [51 KiB] HiDef png [674 KiB] Thumbnail [161 KiB] *C file Fig11.pdf [96 KiB] HiDef png [583 KiB] Thumbnail [156 KiB] *C file Fig12.pdf [59 KiB] HiDef png [696 KiB] Thumbnail [178 KiB] *C file LHCb-P[..].pdf [511 KiB] HiDef png [178 KiB] Thumbnail [31 KiB] *C file Fig7.pdf [28 KiB] HiDef png [182 KiB] Thumbnail [56 KiB] *C file Fig8.pdf [46 KiB] HiDef png [903 KiB] Thumbnail [213 KiB] *C file

Created on 19 April 2019.Citation count from INSPIRE on 25 April 2019.