Amplitude analysis of the $\Lambda^+_c\to pK^-\pi^+$ decay and $\Lambda^+_c$ baryon polarization measurement in semileptonic beauty hadron decays

Information

LHCb-PAPER-2022-002
CERN-EP-2022-124
arXiv:2208.03262 [PDF]

(Submitted on 05 Aug 2022)
Phys. Rev. D 108 (2023) 012023
Inspire 2683025

Tools

Abstract

An amplitude analysis of $\Lambda^+_c \to pK^-\pi^+$ decays together with a measurement of the $\Lambda^+_c$ polarization vector in semileptonic beauty hadron decays is presented. A sample of $400 000$ candidates is selected from proton-proton collisions recorded by the LHCb detector at a center-of-mass energy of 13 TeV. An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. The mass and width of the $\Lambda(2000)$ state are also determined. A significant $\Lambda^+_c$ polarization is found. A large sensitivity of the $\Lambda^+_c \to pK^-\pi^+$ decay to the polarization is seen, making the amplitude model suitable for $\Lambda^+_c$ polarization measurements in other systems.

Figures and captions

Invariant mass distribution of selected $pK^-\pi^+$ candidates from the total dataset. The results from the fit described in the text are also shown.	Fig1.pdf [35 KiB] HiDef png [184 KiB] Thumbnail [155 KiB] *.C file
Dalitz plot for the total sample of $\Lambda ^+_ c \rightarrow pK^-\pi^+$ candidates.	Fig2.pdf [169 KiB] HiDef png [1 MiB] Thumbnail [476 KiB] *.C file
Distributions for selected candidates together with amplitude fit projections in the lab system for (top row) invariant mass squared projections; (bottom row) decay orientation angle projections.	Fig3.pdf [277 KiB] HiDef png [768 KiB] Thumbnail [391 KiB] *.C file
Distributions for selected candidates together with amplitude fit projections in the $\tilde{B}$ system for (top row) invariant mass squared projections; (bottom row) decay orientation angle projections.	Fig4.pdf [277 KiB] HiDef png [783 KiB] Thumbnail [396 KiB] *.C file
Definition of the $\Lambda ^+_ c $ polarization system. The $\bm{\hat{y}}_{\Lambda ^+_ c }$ axis is orthogonal to the page, towards the reader.	Fig_5.pdf [89 KiB] HiDef png [25 KiB] Thumbnail [13 KiB] *.C file tex code
Definition of the Euler angles describing the rotation from the $\Lambda ^+_ c $ polarization system to the decay plane reference system: (left) proton polar and azimuthal angles and (right) $\chi$ angle.	Fig_6.pdf [88 KiB] HiDef png [34 KiB] Thumbnail [17 KiB] *.C file tex code
Animated gif made out of all figures.	PAPER-2022-002.gif Thumbnail

Tables and captions

Resonant composition of the default $\Lambda ^+_ c \rightarrow pK^-\pi^+$ amplitude model, with spin-parity $J^P$, and the Breit--Wigner mass and width parameters, which, in the amplitude fit, are left free within the reported range or fixed to the given value if no interval is quoted.	Table_1.pdf [68 KiB] HiDef png [119 KiB] Thumbnail [58 KiB] tex code
Systematic uncertainty contributions on fit parameters describing the $\Lambda $ contributions. Total* includes all contributions except for the choice of the amplitude model.	Table_2.pdf [72 KiB] HiDef png [199 KiB] Thumbnail [90 KiB] tex code
Systematic uncertainty contributions on fit parameters describing the $K^$ and $\Delta ^{++}$ contributions. Total includes all contributions except for the choice of the amplitude model.	Table_3.pdf [94 KiB] HiDef png [200 KiB] Thumbnail [87 KiB] tex code
Systematic uncertainty contributions on polarization components in percentage. Total* includes all contributions except for the choice of the amplitude model.	Table_4.pdf [57 KiB] HiDef png [53 KiB] Thumbnail [23 KiB] tex code
Systematic uncertainty contributions on fit fractions. Total* includes all contributions except for the choice of the amplitude model.	Table_5.pdf [56 KiB] HiDef png [120 KiB] Thumbnail [48 KiB] tex code
Systematic uncertainties on $\sqrt{3}S$ and decay asymmetry parameters. Total* includes all contributions except for the choice of the amplitude model.	Table_6.pdf [63 KiB] HiDef png [109 KiB] Thumbnail [29 KiB] tex code
Measured polarization components. The first uncertainty is statistical, the second is the amplitude model choice systematic contribution and the third is the combination of the other systematic uncertainties.	Table_7.pdf [61 KiB] HiDef png [106 KiB] Thumbnail [51 KiB] tex code
Default amplitude model measured fit parameters describing the $\Lambda $ contributions.	Table_8.pdf [71 KiB] HiDef png [211 KiB] Thumbnail [101 KiB] tex code
Default amplitude model measured fit parameters describing the $K^*$ and $\Delta ^{++}$ contributions.	Table_9.pdf [93 KiB] HiDef png [207 KiB] Thumbnail [101 KiB] tex code
Fit fractions of the resonant contributions included in the default amplitude model. The first uncertainty is statistical, the second is amplitude model choice systematic contribution, the third is the combination of the other systematic uncertainties.	Table_10.pdf [54 KiB] HiDef png [91 KiB] Thumbnail [43 KiB] tex code
Sensitivity to polarization $\sqrt{3}S$ of the default amplitude model and decay asymmetry $\alpha$ parameters of single resonant contributions. The first uncertainty is statistical, the second is the amplitude model choice systematic contribution, the third is the combination of the other systematic uncertainties.	Table_11.pdf [61 KiB] HiDef png [123 KiB] Thumbnail [59 KiB] tex code