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Updated search for long-lived particles decaying to jet pairs

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Abstract

A search is presented for long-lived particles with a mass between 25 and 50 GeV/$c^2$ and a lifetime between 2 and 500 ps, using proton-proton collision data corresponding to an integrated luminosity of 2.0 fb$^{-1}$, collected by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The particles are assumed to be pair-produced in the decay of a 125 GeV/$c^2$ Standard-Model-like Higgs boson. The experimental signature is a single long-lived particle, identified by a displaced vertex with two associated jets. No excess above background is observed and limits are set on the production cross-section as a function of the mass and lifetime of the long-lived particle.

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Dijet invariant mass distribution in the different $ R_{xy}$ {} bins, for the 2011 data sample. For illustration, the best fit with a signal $\pi_{\text{v}}$ {} model with mass \SI{35}{\GeVcc} and lifetime \SI{10}{\pico\second} is overlaid. The solid blue line indicates the total background model, the short-dashed green line indicates the signal model for signal strength $\mu=1$, and the long-dashed red line indicates the best-fit signal strength.

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Dijet invariant mass distribution in the different $ R_{xy}$ {} bins, for the 2012 data sample. For illustration, the best fit with a signal $\pi_{\text{v}}$ {} model with mass \SI{35}{\GeVcc} and lifetime \SI{10}{\pico\second} is overlaid. The solid blue line indicates the total background model, the short-dashed green line indicates the signal model for signal strength $\mu=1$, and the long-dashed red line indicates the best-fit signal strength.

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Expected (open circles and dotted line) and observed (filled circles and solid line) upper limit versus lifetime for different $\pi_{\text{v}}$ {} masses and decay modes. The green (dark) and yellow (light) bands indicate the quantiles of the expected upper limit corresponding to \(\pm 1\sigma\) and \(\pm 2\sigma\) for a Gaussian distribution. The decay $\pi_{\text{v}}{}\!\rightarrow b\overline b{}$ is assumed, unless specified otherwise.

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Observed upper limit versus lifetime for different $\pi_{\text{v}}$ {} masses and decay modes. The decay $\pi_{\text{v}}{}\!\rightarrow b\overline b{}$ is assumed, unless specified otherwise.

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Supplementary Material [file]

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Created on 16 February 2019.Citation count from INSPIRE on 16 February 2019.