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Performance of the Muon Identification at LHCb

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Abstract

The performance of the muon identification in LHCb is extracted from data using muons and hadrons produced in J/\psi->\mu\mu, \Lambda->p\pi and D^{\star}->\pi D0(K\pi) decays. The muon identification procedure is based on the pattern of hits in the muon chambers. A momentum dependent binary requirement is used to reduce the probability of hadrons to be misidentified as muons to the level of 1%, keeping the muon efficiency in the range of 95-98%. As further refinement, a likelihood is built for the muon and non-muon hypotheses. Adding a requirement on this likelihood that provides a total muon efficiency at the level of 93%, the hadron misidentification rates are below 0.6%.

Figures and captions

Schematic view of the LHCb experiment. The muon stations are seen as the five green vertical bars, the second one placed just after the calorimeters, shown as the blue rectangles.

lhcb-light.pdf [297 KiB]
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lhcb-light.pdf

Schematic view of one muon system station (reproduced from [7]).

muonre[..].png [19 KiB]
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muonregions.png

Average square distance significance distributions for muons, protons, pions and kaons (a) and the corresponding muDLL distributions (b).

hDist_allp.pdf [17 KiB]
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hDist_allp.pdf
muDLL_allp.pdf [16 KiB]
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muDLL_allp.pdf

Normalized NShared distributions for muons, protons, kaons and pions.

Nshare[..].pdf [13 KiB]
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Nshared_allp.pdf

IsMuon efficiency and misidentification probabilities, as a function of momentum, in ranges of transverse momentum: $\varepsilon_{IM} $ (a), $\wp_{IM}(p\rightarrow\mu) $ (b), $\wp_{IM}(\pi\rightarrow\mu) $ (c) and $\wp_{IM}(K\rightarrow\mu) $ (d).

dllFit[..].pdf [16 KiB]
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dllFit_mu_IMvsPvsPt.pdf
dllFit[..].pdf [16 KiB]
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dllFit_P_IMvsPvsPt.pdf
dllFit[..].pdf [15 KiB]
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dllFit_pi_IMvsPvsPt.pdf
dllFit[..].pdf [15 KiB]
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dllFit_ka_IMvsPvsPt.pdf

IsMuon efficiency $\varepsilon_{IM} $ (a) and $\wp_{IM} $ for protons (b), pions (c) and kaons (d) as a function of momentum for different ranges of the number of trajectories reconstructed in the event (ntracks).

dllFit[..].pdf [16 KiB]
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dllFit_mu_IMvsPvsntk.pdf
dllFit[..].pdf [16 KiB]
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dllFit_P_IMvsPvsntk.pdf
dllFit[..].pdf [15 KiB]
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dllFit_pi_IMvsPvstk.pdf
dllFit[..].pdf [15 KiB]
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dllFit_ka_IMvsPvstk.pdf

The efficiency $\varepsilon_{\rm muDLL} $ as a function of muon DLL cut for muons (a) and $ {\rm misidentification} {\rm probabilities}$ for protons (b), pions (c) and kaons (d). The black solid line shows the average values integrated over $p>3 $ $ {\mathrm{ Ge V /}c}$ . The blue dotted line correspond to particles in the range $3<p<10 $ $ {\mathrm{ Ge V /}c}$ . The red dashed lines show results for $10<p<20 $ $ {\mathrm{ Ge V /}c}$ and the green dashed-dotted for $p>20 $ $ {\mathrm{ Ge V /}c}$ .

muDLLE[..].pdf [16 KiB]
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muDLLEff_jpsi_mu.pdf
muDLLE[..].pdf [16 KiB]
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muDLLEff_lambda_p.pdf
muDLLE[..].pdf [16 KiB]
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muDLLEff_d0_pi.pdf
muDLLE[..].pdf [16 KiB]
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muDLLEff_d0_ka.pdf

Muon efficiency (a) and $ {\rm misidentification} {\rm probabilities}$ for protons (b), pions (c) and kaons (d) as a function of the particle momentum for the IsMuon requirement alone (black solid circles) and with the additional cuts muDLL$\geq$1.74 (red triangles) and muDLL$\geq$2.25 (blue open circles).

muon_m[..].pdf [15 KiB]
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muon_muDLL2_effvsp.pdf
proton[..].pdf [15 KiB]
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proton_muDLL2_effvsp.pdf
pion_m[..].pdf [14 KiB]
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pion_muDLL2_effvsp.pdf
kaon_m[..].pdf [15 KiB]
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kaon_muDLL2_effvsp.pdf

Average efficiency $\varepsilon_{\rm DLL} $ as a function of the pion (a) and kaon (b) $ {\rm misidentification} {\rm probabilities}$ for particles with momentum in the range $p>3$ $ $ $ {\mathrm{ Ge V /}c}$ . The dotted lines show the DLL performance, while the muon DLL performance is shown with a solid line.

roc_mu[..].pdf [16 KiB]
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roc_muDLLDLL_pion_allp.pdf
roc_mu[..].pdf [15 KiB]
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roc_muDLLDLL_kaon_allp.pdf

Muon efficiency $\varepsilon_{\rm NShared} $ as a function of the pion and proton $ {\rm misidentification} {\rm probabilities}$ . The average values, for all particles with $p>3 $ $ {\mathrm{ Ge V /}c}$ , are shown with a black line, compared to the three momentum ranges separately, as for Fig. 7.

roc_ns[..].pdf [14 KiB]
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roc_nsh_pion_zoom.pdf
roc_ns[..].pdf [14 KiB]
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roc_nsh_proton_zoom.pdf

Animated gif made out of all figures.

DP-2013-001.gif
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thumbnail_DP-2013-001.gif

Tables and captions

Muon stations required to trigger the IsMuon decision as a function of momentum range.

Table_1.pdf [22 KiB]
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Table_1.pdf

Average IsMuon efficiency and $ {\rm misidentification} {\rm probabilities}$ in different transverse momentum intervals (%). Uncertainties are statistical.

Table_2.pdf [37 KiB]
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Table_2.pdf

Created on 12 October 2019.