Observation of a $J/\psi\Lambda$ resonance consistent with a strange pentaquark candidate in $B^-\to J/\psi\Lambda\bar{p}$ decays

Information

LHCb-PAPER-2022-031
CERN-EP-2022-198
arXiv:2210.10346 [PDF]

(Submitted on 19 Oct 2022)
Phys. Rev. Lett. 131 (2023) 031901
Inspire 2678048

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Abstract

An amplitude analysis of $B^-\to J/\psi\Lambda\bar{p}$ decays is performed using about 4400 signal candidates selected on a data sample of $pp$ collisions recorded at center-of-mass energies of 7, 8 and 13 TeV with the LHCb detector, corresponding to an integrated luminosity of 9 fb$^{-1}$. A narrow resonance in the $J/\psi\Lambda$ system, consistent with a pentaquark candidate with strangeness, is observed with high significance. The mass and the width of this new state are measured to be $4338.2\pm 0.7\pm 0.4$MeV and ${7.0\pm1.2\pm1.3}$MeV, where the first uncertainty is statistical and the second systematic. The spin is determined to be $1/2$ and negative parity is preferred. Due to the small $Q$-value of the reaction, the most precise single measurement of the $B^-$ mass to date, $5279.44\pm0.05\pm0.07$MeV, is obtained.

Figures and captions

Invariant mass distribution of the $ { J \mskip -3mu/\mskip -2mu\psi }$ $\Lambda$ $\overline p $ candidates. The data are overlaid with the results of the fit.	Fig1.pdf [36 KiB] HiDef png [268 KiB] Thumbnail [229 KiB] *.C file
Dalitz distribution for $ B ^- $ candidates in the signal region.	Fig2.pdf [136 KiB] HiDef png [363 KiB] Thumbnail [180 KiB] *.C file
Distributions of invariant mass and $\cos\theta_{K^*}$ Fit results to data using the nominal model are superimposed. The null-hypothesis model fit results are also shown in grey. The $\varXi_c^+D^-$ baryon-meson threshold at 4.337 $\text{ Ge V}$ is indicated with a vertical dashed line in the $m( { J \mskip -3mu/\mskip -2mu\psi } \Lambda )$ invariant mass distribution.	Fig3a.pdf [24 KiB] HiDef png [322 KiB] Thumbnail [304 KiB] *.C file
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Definition of the helicity angles used in the decay amplitudes. The notation $\hat{p}^X_Y$ indicates the direction of the $X$ particle in the $Y$ rest frame. The $\theta_{K^}$ is the helicity angle of $\Lambda$ in the rest frame of $K^$, the $\theta_{P_{\psi}^{N}}$ is the helicity angle of $\overline p $ in the rest frame of $P_{\psi}^{N-}$, and the $\theta_{P_{\psi s}^{\Lambda }}$ is the helicity angle of $ { J \mskip -3mu/\mskip -2mu\psi }$ in the rest frame of the ${P_{\psi s}^{\Lambda }}^0$.		[Failure to get the plot]
${P}_{\psi s}^{\Lambda }(4338)^0$ helicity angular moments as a function of $m( { J \mskip -3mu/\mskip -2mu\psi } \Lambda )$ invariant mass. The black points represent the data while the blue line is the nominal model.	Fig4a.pdf [15 KiB] HiDef png [213 KiB] Thumbnail [216 KiB] *.C file
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Efficiency corrected and background subtracted distributions for $m(\overline p \Lambda)$, $m(J/\psi \overline p )$, $m(J/\psi\Lambda)$ and $\cos{\theta_{K^*}}$.	Fig5a.pdf [14 KiB] HiDef png [119 KiB] Thumbnail [68 KiB] *.C file
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Animated gif made out of all figures.	PAPER-2022-031.gif Thumbnail

Tables and captions

Systematic uncertainties on the mass ($M_{P_{\psi s}^{\Lambda }}$) and width ($\Gamma_{P_{\psi s}^{\Lambda }}$) of the ${P_{\psi s}^{\Lambda }}^0$ state (in $\text{ Me V}$ ), and on the fit fractions $f_{P_{\psi s}^{\Lambda }}$, $f_{\textrm{NR} ( { J \mskip -3mu/\mskip -2mu\psi } \overline p )}$ and $f_{\textrm{NR} (\Lambda \overline p )}$ of the pentaquark candidate and nonresonant contributions (in %).	Table_1.pdf [82 KiB] HiDef png [92 KiB] Thumbnail [43 KiB] tex code
Parameters determined from the fit to data using the nominal model where uncertainties are statistical only.		[Error creating the table]

Supplementary Material [file]

Supplementary material full pdf	supple[..].pdf [271 KiB]
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