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Search for the rare decay $\Lambda_{c}^{+} \to p\mu^+\mu^-$

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Abstract

A search for the flavor-changing neutral-current decay $\Lambda_{c}^{+} \to p\mu^+\mu^-$ is reported using a data set corresponding to an integrated luminosity of $3.0\rm fb^{-1}$ collected by the LHCb collaboration. No significant signal is observed outside of the dimuon mass regions around the $\phi$ and $\omega$ resonances and an upper limit is placed on the branching fraction of $\mathcal{B} (\Lambda_{c}^{+} \to p\mu^+\mu^-) < 7.7 (9.6)\times 10^{-8} {\rm at} 90\% (95\%)$ confidence level. A significant signal is observed in the $\omega$ dimuon mass region for the first time.

Figures and captions

Mass distribution of $\Lambda ^+_ c \!\rightarrow p \mu ^+\mu ^- $ candidates in the $\phi$ region after the first BDT requirement. The solid line shows the result of the fit described in the text, while the dashed line indicates the background component.

Lc2pPh[..].pdf [19 KiB]
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Lc2pPhi_presel.pdf

The efficiency weights for $\Lambda ^+_ c \!\rightarrow p \mu ^+\mu ^- $ as a function of the dimuon invariant mass squared $m^{2}(\mu ^+\mu ^- )$ and by the invariant mass of the proton and the negatively charged muon squared $m^{2}( p \mu^-)$. The weights are normalized to the average efficiency.

dalitz[..].pdf [14 KiB]
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dalitz_weights.pdf

Mass distribution for selected $ p $ $\mu ^+\mu ^-$ candidates in the three regions of the dimuon invariant mass: a) nonresonant region, b) $\phi$ region, c) $\omega$ region. The solid lines show the results of the fit as described in the text. The dashed lines indicate the background component.

pmumu_[..].pdf [33 KiB]
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pmumu_masses.pdf

Invariant mass distribution $m({\mu ^+\mu ^- })$ for $\Lambda ^+_ c \!\rightarrow p \mu ^+\mu ^- $ candidates with mass $\pm 25 {\mathrm{\,MeV\!/}c^2} $ around the $\Lambda ^+_ c $ mass. The solid line shows the result of the fit, while the dashed line indicates the background component.

Lc_mum[..].pdf [18 KiB]
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Lc_mumu_mass_fit_sel.pdf

The CL$_{\rm s}$ value as a function of the $ {\cal B}(\Lambda ^+_ c ) { p \mu ^+\mu ^- }$ branching fraction. The median expected value of an ensemble (assuming no signal component) is shown by the dashed line, with the $\pm 1\sigma$ and $\pm 2\sigma$ regions shaded. The observed distribution is shown by the solid line.

Lc2pmu[..].pdf [17 KiB]
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Lc2pmumu_bf90.pdf

Animated gif made out of all figures.

PAPER-2017-039.gif
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thumbnail_PAPER-2017-039.gif

Tables and captions

Systematic uncertainties on the efficiency ratio used in the determination of the branching fraction in the nonresonant and $\omega$ regions.

Table_1.pdf [53 KiB]
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tex code
Table_1.pdf

Created on 11 December 2018.Citation count from INSPIRE on 11 December 2018.