Search for beautiful tetraquarks in the $\Upsilon(1S)\mu^+\mu^-$ invariant-mass spectrum

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Abstract

The $\Upsilon(1S)\mu^+\mu^-$ invariant-mass distribution is investigated for a possible exotic meson state composed of two $b$ quarks and two $\overline{b}$ quarks, $X_{b\overline{b}b\overline{b}}$. The analysis is based on a data sample of $pp$ collisions recorded with the LHCb detector at centre-of-mass energies $\sqrt{s} =$ 7, 8 and 13 TeV, corresponding to an integrated luminosity of 6.3 fb$^{-1}$. No significant excess is found, and upper limits are set on the product of the production cross-section and the branching fraction as functions of the mass of the $X_{b\overline{b}b\overline{b}}$ state. The limits are set in the fiducial volume where all muons have pseudorapidity in the range $[2.0,5.0]$, and the $X_{b\overline{b}b\overline{b}}$ state has rapidity in the range $[2.0,4.5]$ and transverse momentum less than 15 GeV/$c$.

Figures and captions

 Linear fit to the ratio of the $X$ and $\Y1S$ widths as a function of the $X$ mass as determined from fits to simulated data samples. The error bars represent the statistical uncertainty arising from the finite size of the simulated samples. fig1a.pdf [14 KiB] HiDef png [129 KiB] Thumbnail [50 KiB] *.C file Distributions of $m(\mu ^+\mu ^- )$ for the normalisation datasets at $p p$ centre-of-mass energies of (a) 7 $\mathrm{\,Te V}$ , (b) 8 $\mathrm{\,Te V}$ , (c) 13 $\mathrm{\,Te V}$ and (d) all combined. The total fit function (solid blue line), the combinatorial background (dashed red line) and the $\Y1S$, $\Y2S$ and $\Y3S$ components (hatched magenta area) are shown overlaid. fig2a.pdf [49 KiB] HiDef png [236 KiB] Thumbnail [66 KiB] *.C file fig2b.pdf [49 KiB] HiDef png [240 KiB] Thumbnail [67 KiB] *.C file fig2c.pdf [49 KiB] HiDef png [250 KiB] Thumbnail [72 KiB] *.C file fig2d.pdf [49 KiB] HiDef png [246 KiB] Thumbnail [70 KiB] *.C file Distributions of $m(2\mu^+2\mu^-)$ for the signal datasets at $p p$ centre-of-mass energies of (a) 7 $\mathrm{\,Te V}$ , (b) 8 $\mathrm{\,Te V}$ , (c) 13 $\mathrm{\,Te V}$ and (d) all combined, using a bin size comparable to the expected $X$ mass resolution. In each case the region around the corresponding $\Y1S$ peak has been selected. The background-only fit function (solid blue line) is shown overlaid. The dotted black lines indicate the range in which limits are set on the product of the $X$ production cross-section and branching fractions. The dash-dotted red and long-dashed green lines show the positions of the $\eta_b\eta_b$ and $\Y1S\Y1S$ thresholds, respectively. fig3a.pdf [26 KiB] HiDef png [216 KiB] Thumbnail [78 KiB] *.C file fig3b.pdf [27 KiB] HiDef png [234 KiB] Thumbnail [85 KiB] *.C file fig3c.pdf [31 KiB] HiDef png [271 KiB] Thumbnail [101 KiB] *.C file fig3d.pdf [31 KiB] HiDef png [276 KiB] Thumbnail [103 KiB] *.C file The 95 % CL upper limits on $S\equiv \sigma( p p \rightarrow X)\times\mathcal{B}(X\rightarrow \Y1S\mu ^+\mu ^- ) \times \mathcal{B}(\Y1S\rightarrow \mu^+\mu^-)$ as functions of the $X$ mass hypothesis at $p p$ centre-of-mass energies of (a) 7 $\mathrm{\,Te V}$ , (b) 8 $\mathrm{\,Te V}$ and (c) 13 $\mathrm{\,Te V}$ and (d) all combined. fig4a.pdf [17 KiB] HiDef png [194 KiB] Thumbnail [63 KiB] *.C file fig4b.pdf [17 KiB] HiDef png [225 KiB] Thumbnail [68 KiB] *.C file fig4c.pdf [17 KiB] HiDef png [251 KiB] Thumbnail [74 KiB] *.C file fig4d.pdf [17 KiB] HiDef png [252 KiB] Thumbnail [75 KiB] *.C file The kinematic distribution of (black) simulated $X$ particles in (a) $p_{\mathrm{ T}}$ and (b) rapidity, and (c) the 2D distribution. For comparison, the kinematic distribution of (red) simulated $\Y4S$ particles is also shown. fig5a.pdf [13 KiB] HiDef png [113 KiB] Thumbnail [45 KiB] *.C file fig5b.pdf [12 KiB] HiDef png [51 KiB] Thumbnail [24 KiB] *.C file fig5c.pdf [13 KiB] HiDef png [95 KiB] Thumbnail [40 KiB] *.C file fig5d.pdf [20 KiB] HiDef png [212 KiB] Thumbnail [98 KiB] *.C file Animated gif made out of all figures. PAPER-2018-027.gif Thumbnail

Tables and captions

 Upper limits on $\sigma( p p \rightarrow X) \times \mathcal{B}(X\rightarrow \Y1S\mu ^+\mu ^- ) \times \mathcal{B}(\Y1S\rightarrow \mu ^+\mu ^- )$ for different $X$ mass hypotheses in the range $[17.5,18.4] {\mathrm{\,Ge V\!/}c^2}$. Table_1.pdf [32 KiB] HiDef png [570 KiB] Thumbnail [95 KiB] tex code Upper limits on $\sigma( p p \rightarrow X) \times \mathcal{B}(X\rightarrow \Y1S\mu ^+\mu ^- ) \times \mathcal{B}(\Y1S\rightarrow \mu ^+\mu ^- )$ for different $X$ mass hypotheses in the range $[18.4,19.3] {\mathrm{\,Ge V\!/}c^2}$. Table_2.pdf [32 KiB] HiDef png [551 KiB] Thumbnail [93 KiB] tex code Upper limits on $\sigma( p p \rightarrow X) \times \mathcal{B}(X\rightarrow \Y1S\mu ^+\mu ^- ) \times \mathcal{B}(\Y1S\rightarrow \mu ^+\mu ^- )$ for different $X$ mass hypotheses in the range $[19.3,20.0] {\mathrm{\,Ge V\!/}c^2}$. Table_3.pdf [32 KiB] HiDef png [468 KiB] Thumbnail [77 KiB] tex code

Created on 19 April 2019.Citation count from INSPIRE on 24 April 2019.