CERN Accelerating science

 
Search for dark photons produced in 13 TeV $pp$ collisions - Aaij, Roel et al - arXiv:1710.02867LHCB-PAPER-2017-038CERN-EP-2017-248
 
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Prompt-like mass spectrum, where the categorization of the data as prompt $\mu^+\mu^-$, $\mu_Q\mu_Q$, and $hh+h\mu_Q$ is determined using the fits described in the text.
Regions of the \maeps parameter space excluded at 90\% CL by the prompt-like \aprime search compared to the best existing limits~\cite{Lees:2014xha,KLOE:2016lwm}.
Ratio of the observed upper limit on \naobe at 90\% CL to its expected value, where regions less than unity are excluded. There are no constraints from previous experiments in this region.
Three-dimensional distribution of $\chi^2_{\rm DF}$ versus $t$ versus \mmm, which is fit to determine the long-lived signal yields. The data are consistent with being predominantly due to $b$-hadron decays at small $t$, and due to \KS decays for large $t$ and $\mmm \gtrsim 280\mev$. The largest signal-like excess occurs at $\ma = 239\mev$ and $\ta = 0.86\ps$.
Efficiency ratio \effr for long-lived dark photons, integrated over decay time. The sharp decrease at larger values of $\varepsilon^2$ is due to the stringent \mxip criterion applied in the 2016 trigger.
Long-lived \atomm candidates (black points) showing $t$ versus \mmm in bins of $\chi^2_{\rm DF}$, compared to the pulls from binned fits performed without a signal contribution (color axis). Positive pulls denote an excess of data candidates.
Long-lived \atomm candidates (black points) showing $t$ versus \mmm in bins of $\chi^2_{\rm DF}$, compared to the pulls from binned fits performed without a signal contribution (color axis). Positive pulls denote an excess of data candidates.
Long-lived \atomm candidates (black points) showing $t$ versus \mmm in bins of $\chi^2_{\rm DF}$, compared to the pulls from binned fits performed without a signal contribution (color axis). Positive pulls denote an excess of data candidates.
Long-lived \atomm candidates (black points) showing $t$ versus \mmm in bins of $\chi^2_{\rm DF}$, compared to the pulls from binned fits performed without a signal contribution (color axis). Positive pulls denote an excess of data candidates.
Mass spectrum selected by the prompt-like \atomm trigger.
Example $\mxip^{1/2}$ distributions with fit results overlaid for prompt-like candidates near (left) $\ma=0.5$, (middle) 5, and (right) 50\gev. The square root of \mxip is used in the fits to increase the bin occupancies at large \mxip values.
Example $\mxip^{1/2}$ distributions with fit results overlaid for prompt-like candidates near (left) $\ma=0.5$, (middle) 5, and (right) 50\gev. The square root of \mxip is used in the fits to increase the bin occupancies at large \mxip values.
Example $\mxip^{1/2}$ distributions with fit results overlaid for prompt-like candidates near (left) $\ma=0.5$, (middle) 5, and (right) 50\gev. The square root of \mxip is used in the fits to increase the bin occupancies at large \mxip values.
Comparison of the results presented in this Letter to existing constraints from previous experiments (see Ref.~\cite{Alexander:2016aln} for details about previous experiments).