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Measurement of the S-wave fraction in B0K+πμ+μ decays and the B0K(892)0μ+μ differential branching fraction

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Information

Abstract

A measurement of the differential branching fraction of the decay B0K(892)0μ+μ is presented together with a determination of the S-wave fraction of the K+π system in the decay B0K+πμ+μ. The analysis is based on pp-collision data corresponding to an integrated luminosity of 3 fb1 collected with the LHCb experiment. The measurements are made in bins of the invariant mass squared of the dimuon system, q2. Precise theoretical predictions for the differential branching fraction of B0K(892)0μ+μ decays are available for the q2 region 1.1<q2<6.0GeV2/c4. In this q2 region, for the K+π invariant mass range 796<mKπ<996MeV/c2, the S-wave fraction of the K+π system in B0K+πμ+μ decays is found to be FS=0.101±0.017(stat)±0.009(syst), and the differential branching fraction of B0K(892)0μ+μ decays is determined to be dB/dq2=(0.342+0.0170.017(stat)±0.009(syst)±0.023(norm))×107c4/GeV2. The differential branching fraction measurements presented are the most precise to date and are found to be in agreement with Standard Model predictions.

Figures and captions

Invariant mass mKπμμ of (left) the B0J/ψK0 decay and (right) the signal decay B0K0μ+μ integrated over the q2 regions described in the text. The individual signal (blue shaded area) and background (red hatched area) components are shown. The solid line denotes the total fitted distribution.

jpsi_n[..].pdf [31 KiB]
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jpsi_nice_mass_fit.pdf
rare_n[..].pdf [30 KiB]
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rare_nice_mass_fit.pdf

Two-dimensional projections of the efficiency (left) in the cosθK--q2 plane and (right) in the mKπ--q2 plane, determined from a principal moments analysis of simulated four-body B0K+πμ+μ phase-space decays. The colour scale denotes the efficiency in arbitrary units. The lack of entries in the top right corner of the mKπ--q2 distribution is due to the limited phase space available in the decay of the B0 meson.

ctkq2.pdf [80 KiB]
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ctkq2.pdf
mkpiq2.pdf [61 KiB]
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mkpiq2.pdf

Angular and mass distributions for the q2 bin 1.1<q2<6.0GeV2/c4. The distributions of cosθK and mKπ are shown for candidates in the signal mKπμμ window of ±50MeV/c2 around the known B0 mass. The solid line denotes the total fitted distribution. The individual components, signal (blue shaded area) and background (red hatched area), are also shown.

mass_n[..].pdf [21 KiB]
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mass_nice_8.pdf
mkpi_s[..].pdf [19 KiB]
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mkpi_signal_nice_8.pdf
ctk_si[..].pdf [18 KiB]
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ctk_signal_nice_8.pdf

Results for the S-wave fraction (FS) in bins of q2 in the range (left) 644<mKπ<1200MeV/c2 and (right) 796<mKπ<996MeV/c2. The uncertainties shown are the quadratic sum of the statistical and systematic uncertainties. The shape of FS is found to be compatible with the smoothly varying distribution of FL, as measured in Ref. [27].

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FSWide.pdf
FSNarr.pdf [14 KiB]
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FSNarr.pdf

Differential branching fraction of B0K(892)0μ+μ decays as a function of q2. The data are overlaid with the SM prediction from Refs. [50,51]. No SM prediction is included in the region close to the narrow cˉc resonances. The result in the wider q2 bin 15.0<q2<19.0GeV2/c4 is also presented. The uncertainties shown are the quadratic sum of the statistical and systematic uncertainties, and include the uncertainty on the B0J/ψK0 and J/ψμ+μ branching fractions.

dBNormal.pdf [14 KiB]
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dBNormal.pdf

Angular and mass distributions for the q2 bins 1.1<q2<6.0GeV2/c4 (left) and 15.0<q2<19.0GeV2/c4 (right). The distributions of cosθK and mKπ are shown for candidates in the signal mKπμμ window of ±50MeV/c2 around the known B0 mass.

mass_n[..].pdf [21 KiB]
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mass_nice_8.pdf
mass_n[..].pdf [21 KiB]
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mass_nice_9.pdf
mkpi_s[..].pdf [19 KiB]
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mkpi_signal_nice_8.pdf
mkpi_s[..].pdf [19 KiB]
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mkpi_signal_nice_9.pdf
ctk_si[..].pdf [18 KiB]
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ctk_signal_nice_8.pdf
ctk_si[..].pdf [18 KiB]
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ctk_signal_nice_9.pdf

The K+πμ+μ invariant mass distributions for the fine q2 bins.

mass_n[..].pdf [21 KiB]
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mass_nice_0.pdf
mass_n[..].pdf [21 KiB]
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mass_nice_1.pdf
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mass_nice_6.pdf
mass_n[..].pdf [21 KiB]
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mass_nice_7.pdf

The K+π invariant mass distributions for the fine q2 bins for candidates in the signal mKπμμ window of ±50MeV/c2 around the known B0 mass.

mkpi_s[..].pdf [18 KiB]
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mkpi_signal_nice_0.pdf
mkpi_s[..].pdf [19 KiB]
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mkpi_signal_nice_1.pdf
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mkpi_signal_nice_2.pdf
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mkpi_signal_nice_4.pdf
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mkpi_signal_nice_6.pdf
mkpi_s[..].pdf [18 KiB]
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mkpi_signal_nice_7.pdf

The cosθK angular distributions for the fine q2 bins for candidates in the signal mKπμμ window of ±50MeV/c2 around the known B0 mass.

ctk_si[..].pdf [18 KiB]
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ctk_signal_nice_0.pdf
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ctk_signal_nice_1.pdf
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ctk_signal_nice_2.pdf
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ctk_signal_nice_3.pdf
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ctk_signal_nice_5.pdf
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ctk_signal_nice_6.pdf
ctk_si[..].pdf [18 KiB]
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ctk_signal_nice_7.pdf

Animated gif made out of all figures.

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Tables and captions

S-wave fraction (FS) in bins of q2 for two mKπ regions. The first uncertainty is statistical and the second systematic.

Table_1.pdf [57 KiB]
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Table_1.pdf

Differential branching fraction of B0K(892)0μ+μ decays in bins of q2. The first uncertainty is statistical, the second systematic and the third due to the uncertainty on the B0J/ψK0 and J/ψμ+μ branching fractions.

Table_2.pdf [57 KiB]
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Table_2.pdf

Summary of the main sources of systematic uncertainty on FS|1200644 and dB/dq2. Typical ranges are quoted in order to summarise the effect the systematic uncertainties have across the various q2 bins.

Table_3.pdf [63 KiB]
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Table_3.pdf

Created on 21 December 2024.