# First observation of forward $Z \to b\overline{b}$ production in $pp$ collisions at $\sqrt{s}$ = 8 TeV

LHCb Collaboration; Bernet, R; Müller, K; Serra, N; Steinkamp, O; Straumann, U; Vollhardt, A; et al (2018). First observation of forward $Z \to b\overline{b}$ production in $pp$ collisions at $\sqrt{s}$ = 8 TeV. Physics Letters B, B776:430-439.

## Abstract

The decay $Z \to b\overline{b}$ is reconstructed in $pp$ collision data, corresponding to 2fb$^{−1}$ of integrated luminosity, collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}$ = 8 TeV. The product of the $Z$ production cross-section and the $Z \to b\overline{b}$ branching fraction is measured for candidates in the fiducial region defined by two particle-level $b$-quark jets with pseudorapidities in the range $2.2 < \eta < 4.2$, with transverse momenta $p_T > 20 GeV$ and dijet invariant mass in the range $45 < m_{jj} < 165 GeV$. From a signal yield of $5462 \pm 763 Z \to b\overline{b}$ events, where the uncertainty is statistical, a production cross-section times branching fraction of $332 \pm 46 \pm 59$ pb is obtained, where the first uncertainty is statistical and the second systematic. The measured significance of the signal yield is 6.0 standard deviations. This measurement represents the first observation of the $Z \to b\overline{b}$ production in the forward region of $pp$ collisions.

## Abstract

The decay $Z \to b\overline{b}$ is reconstructed in $pp$ collision data, corresponding to 2fb$^{−1}$ of integrated luminosity, collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}$ = 8 TeV. The product of the $Z$ production cross-section and the $Z \to b\overline{b}$ branching fraction is measured for candidates in the fiducial region defined by two particle-level $b$-quark jets with pseudorapidities in the range $2.2 < \eta < 4.2$, with transverse momenta $p_T > 20 GeV$ and dijet invariant mass in the range $45 < m_{jj} < 165 GeV$. From a signal yield of $5462 \pm 763 Z \to b\overline{b}$ events, where the uncertainty is statistical, a production cross-section times branching fraction of $332 \pm 46 \pm 59$ pb is obtained, where the first uncertainty is statistical and the second systematic. The measured significance of the signal yield is 6.0 standard deviations. This measurement represents the first observation of the $Z \to b\overline{b}$ production in the forward region of $pp$ collisions.

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