CMS-PAS-BPH-13-008 | ||
Precision lifetime measurements of b hadrons reconstructed in final states with a J/ψ meson | ||
CMS Collaboration | ||
May 2017 | ||
Abstract:
We present measurements of the lifetimes of the B0, B0s, Λ0b, and B+c hadrons using the decay channels B0→J/ψK∗(892)0, B0→J/ψKS, B0s→J/ψπ+π−, B0s→J/ψϕ(1020), Λ0b→J/ψΛ0, and B+c→J/ψπ+. The data sample, corresponding to 19.7 fb−1, was collected from proton-proton collisions at √s= 8 TeV using dedicated triggers to select oppositely charged muons in the J/ψ mass region. The lifetimes times the speed of light are measured to be cτB0= 453.0 ± 1.6 (stat) ± 1.5 (syst) μm (in J/ψK∗(892)0), cτB0= 457.8 ± 2.7 (stat) ± 2.7 (syst) μm (in J/ψKS), cτB0s= 504.3 ± 10.5 (stat) ± 3.7 (syst) μm (in J/ψπ+π−), cτB0s= 443.9 ± 2.0 (stat) ± 1.2 (syst) μm (in J/ψϕ(1020)), cτΛ0b= 443.1 ± 8.2 (stat) ± 2.7 (syst) μm, cτB+c= 162.3 ± 8.2 (stat) ± 4.7 (syst) ± 0.1 (τB+) μm, where the first uncertainty is statistical and the other is systematic. All results are in agreement with the current world average values. | ||
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These preliminary results are superseded in this paper, EPJC 78 (2018) 457. The superseded preliminary plots can be found here. |
Figures | |
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Figure 1:
Efficiency versus ct with a superimposed fit to a inverse power function for B+ (top left), B0→J/ψK∗0 (top right), B0→J/ψK0s (center left), Λ0b (center right), B0s→J/ψπ+π− (bottom left), and B0s→J/ψϕ(1020) (bottom right). The efficiency scale is arbitrary. |
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Figure 1-a:
Efficiency versus ct with a superimposed fit to a inverse power function for B+. The efficiency scale is arbitrary. |
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Figure 1-b:
Efficiency versus ct with a superimposed fit to a inverse power function for B0→J/ψK∗0. The efficiency scale is arbitrary. |
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Figure 1-c:
Efficiency versus ct with a superimposed fit to a inverse power function for B0→J/ψK0s. The efficiency scale is arbitrary. |
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Figure 1-d:
Efficiency versus ct with a superimposed fit to a inverse power function for Λ0b. The efficiency scale is arbitrary. |
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Figure 1-e:
Efficiency versus ct with a superimposed fit to a inverse power function for B0s→J/ψπ+π−. The efficiency scale is arbitrary. |
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Figure 1-f:
Efficiency versus ct with a superimposed fit to a inverse power function for B0s→J/ψϕ(1020). The efficiency scale is arbitrary. |
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Figure 2:
Invariant mass (left) and ct (right) distributions for B+ candidates. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |
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Figure 2-a:
Invariant mass distribution for B+ candidates. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. |
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Figure 2-b:
ct distribution for B+ candidates. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel shows the difference between the observed data and the fit divided by the data uncertainty. |
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Figure 3:
Invariant mass (left) and ct (right) distributions for B0 candidates reconstructed from J/ψK∗0 decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |
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Figure 3-a:
Invariant mass distribution for B0 candidates reconstructed from J/ψK∗0 decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. |
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Figure 3-b:
ct distribution for B0 candidates reconstructed from J/ψK∗0 decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. |
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Figure 4:
Invariant mass (left) and ct (right) distributions for B0 candidates reconstructed from J/ψK0s decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |
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Figure 4-a:
Invariant mass distribution for B0 candidates reconstructed from J/ψK0s decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. |
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Figure 4-b:
ct distribution for B0 candidates reconstructed from J/ψK0s decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |
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Figure 5:
Invariant mass (left) and ct (right) distributions for B0s candidates reconstructed from J/ψπ+π− decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), combinatorial background (dotted), misidentified B+→J/ψK+ background (dashed-dotted), partially reconstructed and (other) misidentified B backgrounds (vertical dashed), and the sum of signal and backgrounds (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |
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Figure 5-a:
Invariant mass distribution for B0s candidates reconstructed from J/ψπ+π− decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), combinatorial background (dotted), misidentified B+→J/ψK+ background (dashed-dotted), partially reconstructed and (other) misidentified B backgrounds (vertical dashed), and the sum of signal and backgrounds (solid) shown. |
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Figure 5-b:
ct distribution for B0s candidates reconstructed from J/ψπ+π− decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), combinatorial background (dotted), misidentified B+→J/ψK+ background (dashed-dotted), partially reconstructed and (other) misidentified B backgrounds (vertical dashed), and the sum of signal and backgrounds (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |
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Figure 6:
Invariant mass (left) and ct (right) distributions for B0s candidates reconstructed from J/ψϕ1020 decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |
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Figure 6-a:
Invariant mass distribution for B0s candidates reconstructed from J/ψϕ1020 decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. |
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Figure 6-b:
ct distribution for B0s candidates reconstructed from J/ψϕ1020 decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |
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Figure 7:
Invariant mass (left) and ct (right) distributions for Λ0b candidates. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown.The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |
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Figure 7-a:
Invariant mass distribution for Λ0b candidates. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. |
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Figure 7-b:
ct distribution for Λ0b candidates. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown.The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |
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Figure 8:
The J/ψπ+ invariant mass distribution (left). The solid line represents the signal-plus-background fit. The dashed line represents the signal component, the dotted line the combinatorial background, and the dashed-dotted line the contribution from Bc→J/ψK+ decays. The J/ψK+ invariant mass distribution (right). The result of the fit is superimposed with a solid line. The signal is shown with a dashed line, the dotted-dashed curves represent the B+→J/ψπ+ and B0 contributions, and the dotted curve the combinatorial background. |
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Figure 8-a:
The J/ψπ+ invariant mass distribution. The solid line represents the signal-plus-background fit. The dashed line represents the signal component, the dotted line the combinatorial background, and the dashed-dotted line the contribution from Bc→J/ψK+ decays. |
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Figure 8-b:
The J/ψK+ invariant mass distribution. The result of the fit is superimposed with a solid line. The signal is shown with a dashed line, the dotted-dashed curves represent the B+→J/ψπ+ and B0 contributions, and the dotted curve the combinatorial background. |
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Figure 9:
The yield (left) of B+c→J/ψπ+ and B+→J/ψK+ events as a function of ct, normalized to the bin width, as determined from fits to the invariant mass distributions. Ratio (right) of the Bc and B+ efficiency distributions as a function of ct. |
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Figure 9-a:
The yield of B+c→J/ψπ+ and B+→J/ψK+ events as a function of ct, normalized to the bin width, as determined from fits to the invariant mass distributions. |
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Figure 9-b:
Ratio of the Bc and B+ efficiency distributions as a function of ct. |
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Figure 10:
Ratio of the efficiency-corrected ct distributions for Bc and B+ signals. The line shows the result of fitting with an exponential function. |
Tables | |
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Table 1:
Summary of the systematic uncertainties on the lifetime measurements (in μm). The total systematic uncertainty is the sum in quadrature of all systematic sources. |
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Table 2:
Summary of the systematic uncertainties on the ΔΓ and τBc measurements. |
Summary |
The lifetime measurements of the B0, B0s, Bc, and Λ0b hadrons, exploiting the decay channels B0→J/ψK∗0, B0→J/ψK0s, B0s→J/ψπ+π−, B0s→J/ψϕ, Λ0b→J/ψΛ0, and B+→J/ψπ+, have been presented, using proton proton collision events collected by the CMS detector at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 fb−1. All measurements are in agreement with the world average values and some are at the precision of the world average of these parameters. |
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Compact Muon Solenoid LHC, CERN |
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