cern.ch

Study of $\chi_{b}$ meson production in pp collisions at $\sqrt{s}=7$ and 8TeV and observation of the decay $\chi_{b}(3P) \rightarrow \Upsilon(3S) \gamma$

[to restricted-access page]

Abstract

A study of $\chi_{b}$ meson production at LHCb is performed on proton-proton collision data, corresponding to 3.0fb$^{-1}$ of integrated luminosity collected at centre-of-mass energies $\sqrt{s}=7$ and 8TeV. The fraction of $\Upsilon(nS)$ mesons originating from $\chi_{b}$ decays is measured as a function of the $\Upsilon$ transverse momentum in the rapidity range $2.0 < y^{\Upsilon} < 4.5$. The radiative transition of the $\chi_{b}(3P)$ meson to $\Upsilon(3S)$ is observed for the first time. The $\chi_{b1}(3P)$ mass is determined to be $$m(\chi_{b1}(3P)) = 10\,511.3 \pm 1.7 \pm 2.5 MeV/c^2,$$ where the first uncertainty is statistical and the second is systematic.

Figures and captions

Invariant mass distributions for selected dimuon candidates in the kinematic range $6<p_{\mathrm{T}}^{\mu ^+\mu ^- }<40 {\mathrm{\,GeV\!/}c} $ and $2.0<y^{\mu ^+\mu ^- }<4.5$ for (left) data collected at $\sqrt{s} =7\,\mathrm{TeV}$ and (right) $8\,\mathrm{TeV}$. The three peaks on each plot correspond to the $\Upsilon\mathrm{(1S)}$ , $\Upsilon\mathrm{(2S)}$ and $\Upsilon\mathrm{(3S)}$ signals\,(low-mass to high-mass). The result of the fit, described in the text, is illustrated with a red solid line, while the background component is shown with a blue dashed line.

Fig_1.pdf [161 KiB]
HiDef png [172 KiB]
Thumbnail [53 KiB]
*.C file
tex code
Fig_1.pdf

Distributions of the corrected mass $m_{\Upsilon\mathrm{(nS)} \gamma }$ for the selected $\chi _{ b }$ candidates (black points) decaying into (top row) $\Upsilon\mathrm{(1S)}$ , (middle row) $\Upsilon\mathrm{(2S)}$ and (bottom row) $\Upsilon\mathrm{(3S)}$ , in the transverse momentum ranges given in the text, for (left) $\sqrt{s} =7\,\mathrm{TeV}$ and (right) $8\,\mathrm{TeV}$ data. Each plot shows also the result of the fit (solid red curve), including the background (dotted blue curve) and the signal (dashed green and magenta curves) contributions. The green dashed curve corresponds to the $\chi _{ b 1}$ signal and the magenta dashed curve to the $\chi _{ b 2}$ signal.

Fig_2.pdf [164 KiB]
HiDef png [558 KiB]
Thumbnail [135 KiB]
*.C file
tex code
Fig_2.pdf

Fractions $\mathcal{R}^{\chi _{ b }\mathrm{(mP)} }_{\Upsilon\mathrm{(nS)} }$ as functions of $p_{\mathrm{T}}^{\Upsilon }$. Points with blue open (red solid) symbols correspond to data collected at $\sqrt{s} =7(8)\,\mathrm{TeV}$, respectively. For better visualization the data points are slightly displaced from the bin centres. The inner error bars represent statistical uncertainties, while the outer error bars indicate statistical and systematic uncertainties added in quadrature.

Fig_3.pdf [121 KiB]
HiDef png [230 KiB]
Thumbnail [70 KiB]
*.C file
tex code
Fig_3.pdf

Animated gif made out of all figures.

PAPER-2014-031.gif
Thumbnail
thumbnail_PAPER-2014-031.gif

Tables and captions

Yields of $\Upsilon\mathrm{(nS)}$ mesons, determined by fitting the dimuon invariant mass in the range $6<p_{\mathrm{T}}^{\mu ^+\mu ^- }<40 {\mathrm{\,GeV\!/}c} $ and $2.0<y^{\mu ^+\mu ^- }<4.5$, for data collected at $\sqrt{s} =7$ and $8\,\mathrm{TeV}$. Only statistical uncertainties are shown.

Table_1.pdf [37 KiB]
HiDef png [53 KiB]
Thumbnail [8 KiB]
tex code
Table_1.pdf

Signal yields resulting from fits to the corrected mass $m_{\Upsilon\mathrm{(nS)} \gamma }$ distributions in the transverse momentum ranges $14<p_{\mathrm{T}}^{\Upsilon\mathrm{(1S)} }<40 {\mathrm{\,GeV\!/}c} $, $18<p_{\mathrm{T}}^{\Upsilon\mathrm{(2S)} }<40 {\mathrm{\,GeV\!/}c} $ and $24<p_{\mathrm{T}}^{\Upsilon\mathrm{(3S)} }<40 {\mathrm{\,GeV\!/}c} $. Only statistical uncertainties are shown.

Table_2.pdf [58 KiB]
HiDef png [84 KiB]
Thumbnail [13 KiB]
tex code
Table_2.pdf

Summary of the relative systematic uncertainties for the fractions $\mathcal{R}^{\chi _{ b }\mathrm{(mP)} }_{\Upsilon\mathrm{(nS)} }$.

Table_3.pdf [61 KiB]
HiDef png [91 KiB]
Thumbnail [13 KiB]
tex code
Table_3.pdf

Summary of systematic uncertainties for $m_{\chi _{ b 1}\mathrm{(3P)} }$.

Table_4.pdf [68 KiB]
HiDef png [76 KiB]
Thumbnail [10 KiB]
tex code
Table_4.pdf

Fractions $\mathcal{R}^{\chi _{ b }\mathrm{(mP)} }_{\Upsilon\mathrm{(nS)} }$ in bins of $p_{\mathrm{T}}^{\Upsilon }$, measured for data collected at $\sqrt{s} =7\,\mathrm{TeV}$. The first block corresponds to $\mathcal{R}^{\chi _{ b }\mathrm{(mP)} }_{\Upsilon\mathrm{(1S)} }$, the second to $\mathcal{R}^{\chi _{ b }\mathrm{(mP)} }_{\Upsilon\mathrm{(2S)} }$ and the third to $\mathcal{R}^{\chi _{ b }\mathrm{(mP)} }_{\Upsilon\mathrm{(3S)} }$. The first uncertainty is statistical and the second systematic.

Table_5.pdf [59 KiB]
HiDef png [89 KiB]
Thumbnail [16 KiB]
tex code
Table_5.pdf

Fractions $\mathcal{R}^{\chi _{ b }\mathrm{(mP)} }_{\Upsilon\mathrm{(nS)} }$ in bins of $p_{\mathrm{T}}^{\Upsilon }$, measured for data collected at $\sqrt{s} =8\,\mathrm{TeV}$. The first block corresponds to $\mathcal{R}^{\chi _{ b }\mathrm{(mP)} }_{\Upsilon\mathrm{(1S)} }$, the second to $\mathcal{R}^{\chi _{ b }\mathrm{(mP)} }_{\Upsilon\mathrm{(2S)} }$ and the third to $\mathcal{R}^{\chi _{ b }\mathrm{(mP)} }_{\Upsilon\mathrm{(3S)} }$. The first uncertainty is statistical and the second systematic.

Table_6.pdf [59 KiB]
HiDef png [89 KiB]
Thumbnail [16 KiB]
tex code
Table_6.pdf

Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.