A new baryon state is observed in the $\Lambda_b^0\pi^+\pi^-$ mass spectrum with high significance using a data sample of $pp$ collisions, collected with the LHCb detector at centre-of-mass energies $\sqrt{s}=7, 8$ and 13TeV, corresponding to an integrated luminosity of 9fb$^{-1}$. The mass and natural width of the new state are measured to be \begin{eqnarray*} m & = & 6072.3 \pm 2.9 \pm 0.6 \pm 0.2 MeV , \Gamma & = & 72 \pm 11 \pm 2 MeV , \end{eqnarray*} where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the $\Lambda_b^0$ baryon mass. The new state is consistent with the first radial excitation of the $\Lambda_b^0$ baryon, the $\Lambda_b(2S)^0$ resonance. Updated measurements of the masses and the upper limits on the natural widths of the previously observed $\Lambda_b(5912)^0$ and $\Lambda_b(5920)^0$ states are also reported.
Mass distributions for selected (left) $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^- $ and (right) $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p K ^- $ candidates after BDT selection. A fit, composed of a sum of a double-sided Crystal Ball function [46] and a smooth background component, is overlaid. |
Fig_1.pdf [125 KiB] HiDef png [212 KiB] Thumbnail [155 KiB] *.C file tex code |
|
Mass spectra of selected (top) $\Lambda ^0_ b \pi ^+ \pi ^- $, (middle) $\Lambda ^0_ b \pi ^+ \pi ^+ $ and (bottom) $\Lambda ^0_ b \pi ^- \pi ^- $ combinations for the $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^- $ sample. A simultaneous fit, described in the text, is superimposed. |
Fig_2.pdf [171 KiB] HiDef png [595 KiB] Thumbnail [443 KiB] *.C file tex code |
|
Mass spectra of selected (top) $\Lambda ^0_ b \pi ^+ \pi ^- $, (middle) $\Lambda ^0_ b \pi ^+ \pi ^+ $ and (bottom) $\Lambda ^0_ b \pi ^- \pi ^- $ combinations for the $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p K ^- $ sample. A simultaneous fit, described in the text, is superimposed. |
Fig_3.pdf [141 KiB] HiDef png [544 KiB] Thumbnail [412 KiB] *.C file tex code |
|
(Top) Spectra of $\Lambda ^0_ b \pi ^{\pm}$ mass with $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^- $ for $\Lambda ^0_ b \pi ^+ \pi ^- $ combinations (red points with error bars) and $\Lambda ^0_ b \pi ^{\pm}\pi ^{\pm}$ combinations (open blue histogram). (Bottom) Difference between $\Lambda ^0_ b \pi $ mass spectra from $\Lambda ^0_ b \pi ^+ \pi ^- $ and $\Lambda ^0_ b \pi ^{\pm}\pi ^{\pm}$ combinations. The structures near $5.81$ and $5.83\mathrm{ Ge V} $ correspond to the $\Sigma_{ b }^{\pm} \rightarrow \Lambda ^0_ b \pi ^{\pm} $ and $\Sigma_{ b }^{\ast\pm} \rightarrow \Lambda ^0_ b \pi ^{\pm} $ signals, respectively. |
Fig_4.pdf [154 KiB] HiDef png [279 KiB] Thumbnail [307 KiB] *.C file tex code |
|
Mass spectra of selected (top) $\Lambda ^0_ b \pi ^+ \pi ^- $, (middle) $\Lambda ^0_ b \pi ^+ \pi ^+ $ and (bottom) $\Lambda ^0_ b \pi ^- \pi ^- $ combinations for for the $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^- $ sample. A simultaneous fit, described in the text, is superimposed. |
Fig_5.pdf [118 KiB] HiDef png [432 KiB] Thumbnail [350 KiB] *.C file tex code |
|
Mass spectra of selected (top) $\Lambda ^0_ b \pi ^+ \pi ^- $, (middle) $\Lambda ^0_ b \pi ^+ \pi ^+ $ and (bottom) $\Lambda ^0_ b \pi ^- \pi ^- $ combinations for for the $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p K ^- $ sample. A simultaneous fit, described in the text, is superimposed. |
Fig_6.pdf [118 KiB] HiDef png [445 KiB] Thumbnail [371 KiB] *.C file tex code |
|
Animated gif made out of all figures. |
PAPER-2019-045.gif Thumbnail |
Quark-model predictions for the masses of the lightest $\Lambda_{ b }$ and $\Sigma_{ b }^{(\ast)}$ states (in $\mathrm{ Me V}$ ). |
Table_1.pdf [43 KiB] HiDef png [90 KiB] Thumbnail [39 KiB] tex code |
|
Yields of excited baryons from the simultaneous fit to $\Lambda ^0_ b \pi \pi $ spectra with $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^- $ and $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p K ^- $. |
Table_2.pdf [53 KiB] HiDef png [40 KiB] Thumbnail [19 KiB] tex code |
|
Results of the combined fit to the low-mass $\Lambda ^0_ b \pi \pi $ spectra. |
Table_3.pdf [70 KiB] HiDef png [52 KiB] Thumbnail [24 KiB] tex code |
|
Summary of systematic uncertainties for the mass difference with respect to the ground state $\Lambda ^0_ b $ and natural width of the $\Lambda _{ b }^{\ast\ast 0}$ state and the massdash-differences for the $\Lambda_{ b }\mathrm{(5912)}^0$ and $\Lambda_{ b }\mathrm{(5920)}^0$ states, $\Delta m_{\Lambda_{ b }\mathrm{(1P)}^0}$. |
Table_4.pdf [65 KiB] HiDef png [77 KiB] Thumbnail [35 KiB] tex code |
Supplementary material full pdf |
supple[..].pdf [323 KiB] |
|
This ZIP file contains supplemetary material for the publication LHCb-PAPER-2019-045. The files are: Supplementary.pdf : An overview of the extra figures Fig*_supp.pdf/png/eps : The figures in variuous formats, sutabel for tuning in LaTeX (no legends and axies labels) Figure*_supp.pdf/png/eps : "Ready-to-use" figures in varius formats |
Fig1_supp.pdf [37 KiB] HiDef png [205 KiB] Thumbnail [146 KiB] *C file |
|
Fig2_supp.pdf [37 KiB] HiDef png [194 KiB] Thumbnail [135 KiB] *C file |
||
Fig3_supp.pdf [37 KiB] HiDef png [407 KiB] Thumbnail [266 KiB] *C file |
||
Figure[..].pdf [101 KiB] HiDef png [248 KiB] Thumbnail [249 KiB] *C file |
||
Figure[..].pdf [94 KiB] HiDef png [227 KiB] Thumbnail [228 KiB] *C file |
||
Figure[..].pdf [128 KiB] HiDef png [415 KiB] Thumbnail [373 KiB] *C file |
||
lhcb-logo.pdf [4 KiB] HiDef png [269 KiB] Thumbnail [142 KiB] *C file |
Created on 26 April 2024.