Observation of excited $\Lambda^0_b$ baryons

Information

LHCb-PAPER-2012-012
CERN-PH-EP-2012-128
arXiv:1205.3452 [PDF]

(Submitted on 15 May 2012)
Phys. Rev. Lett. 109 (2012) 172003
Inspire 1114753

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Abstract

Using pp collision data corresponding to 1.0 fb-1 integrated luminosity collected by the LHCb detector, two narrow states are observed in the Lambda_b0pi+pi- spectrum with masses 5911.97 +- 0.12(stat) +- 0.02(syst) +- 0.66(Lambda_b0 mass) MeV/c^2 and 5919.77 +- 0.08(stat) +- 0.02(syst) +- 0.66(Lambda_b0 mass) MeV/c^2. The significances of the observations are 5.2 and 10.2 standard deviations, respectively. These states are interpreted as the orbitally-excited Lambda_b0 baryons, Lambda_b*0(5912) and Lambda_b*0(5920).

Figures and captions

Invariant mass spectrum of $\Lambda ^+_ c \pi ^- $ combinations. The points with error bars are the data, and the fitted $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^- $ signal and three background components ( $\Lambda ^0_ b \rightarrow \Lambda ^+_ c K ^- $ , partially-reconstructed and random background) are shown with different fill styles.	lb.pdf [25 KiB] HiDef png [342 KiB] Thumbnail [274 KiB] *.C file
Invariant mass spectrum of (a) $\Lambda ^0_ b \pi ^+\pi ^- $ and (b) $\Lambda ^0_ b \pi ^\pm \pi ^\pm $ combinations. The points with error bars are the data, the solid line is the fit result, the dashed line is the background contribution.	lbstar.pdf [28 KiB] HiDef png [222 KiB] Thumbnail [198 KiB] *.C file
	lbstar_bck.pdf [28 KiB] HiDef png [200 KiB] Thumbnail [193 KiB] *.C file
Invariant mass of the two pions from $\Lambda _{ b }^{*0}(5920) \rightarrow \Lambda ^0_ b \pi ^+\pi ^- $ decay. The points with the error bars are background-subtracted data, the solid histogram is the result of phase-space decay simulation.	mhh_splot.pdf [11 KiB] HiDef png [153 KiB] Thumbnail [156 KiB] *.C file
Animated gif made out of all figures.	PAPER-2012-012.gif Thumbnail