A search is presented for massive longlived particles, in the 2060 GeV mass range with lifetimes between 5 and 100 ps. The dataset used corresponds to 0.62 1\fb of protonproton collision data collected by the LHCb detector at sqrt(s)=7 TeV. The particles are assumed to be pairproduced by the decay of a Higgslike boson with mass between 80 and 140 GeV. No excess above the background expectation is observed and limits are set on the production crosssection as a function of the longlived particle mass and lifetime and of the Higgslike boson mass.
Data (black dots) and simulated distributions after preselection normalised to unit integral. There are two LLP candidates per event. The simulated $ b \overline b $ background is shown by the filled red histograms with error bars. The dashed (blue), dotted (purple) and solid (green) lines are distributions for fully simulated signal models. The subplots show (a) number of tracks used to reconstruct the LLP candidates, (b) LLP transverse momentum, (c) LLP invariant mass, (d) radial distance, $ R_{\rm xy}$ , (e) uncertainty of the radial position, $\sigma_{\rm R}$ , and (f) uncertainty of the longitudinal position, $\sigma_{\rm Z}$ , of the LLP vertex. 
fig1_a.pdf [10 KiB] HiDef png [415 KiB] Thumbnail [156 KiB] *.C file 

fig1_b.pdf [11 KiB] HiDef png [394 KiB] Thumbnail [152 KiB] *.C file 

fig1_c.pdf [12 KiB] HiDef png [287 KiB] Thumbnail [126 KiB] *.C file 

fig1_d.pdf [12 KiB] HiDef png [558 KiB] Thumbnail [196 KiB] *.C file 

fig1_e.pdf [13 KiB] HiDef png [423 KiB] Thumbnail [162 KiB] *.C file 

fig1_f.pdf [13 KiB] HiDef png [383 KiB] Thumbnail [151 KiB] *.C file 

Distributions for (a) the LLP distance of flight from the PV, and, (b), the radial distance of the LLP vertex, $ R_{\rm xy}$ . The fully simulated signal models are chosen with LLP lifetimes of 5, 10, and 50 $ {\rm ps}$ . Symbols are defined as in Fig. 1. 
fig2_a.pdf [12 KiB] HiDef png [346 KiB] Thumbnail [144 KiB] *.C file 

fig2_b.pdf [12 KiB] HiDef png [552 KiB] Thumbnail [195 KiB] *.C file 

Distributions for (a) the $p_{\rm T}$ of the Higgslike candidate, and (b), its invariant mass. Symbols are defined as in Fig. 1. 
fig3_a.pdf [11 KiB] HiDef png [409 KiB] Thumbnail [152 KiB] *.C file 

fig3_b.pdf [11 KiB] HiDef png [342 KiB] Thumbnail [140 KiB] *.C file 

Results of the fit based on the model BV48 10ps mH114. In (a) log distribution and (b) linear scale with pull distribution. Dots with error bars are the data, the dotted (red) and the dashed (green) histograms show the fitted background and signal contributions, respectively. The purple histogram is the total fitted distribution. 
fig4_a.pdf [36 KiB] HiDef png [237 KiB] Thumbnail [166 KiB] *.C file 

fig4_b.pdf [41 KiB] HiDef png [240 KiB] Thumbnail [173 KiB] *.C file 

Results of the fit based on the model BV48 10ps mH114, for different combinations of signal and background selections, (a) signal from $\rm Sel_1$ and background from $\rm Bkg_2$ , (b) signal from $\rm Sel_2$ and background from $\rm Bkg_1$ . Dots with error bars are data, the dashed (green) line is the fitted signal and the dotted (red) line the background. In both cases the fitted signal is negative. The histogram (blue) is the total fitted function. 
fig5_a.pdf [36 KiB] HiDef png [253 KiB] Thumbnail [172 KiB] *.C file 

fig5_b.pdf [36 KiB] HiDef png [230 KiB] Thumbnail [160 KiB] *.C file 

Results of the fit to the data to which 10 signal events have been added randomly chosen following the signal model. For the theoretical model BV48 10ps mH100, in (a), the fitted signal is $11.1\pm7.0$ events; for BV48 10ps mH125, in (b), the result is $9.3\pm5.6$ events. 
fig6_a.pdf [37 KiB] HiDef png [258 KiB] Thumbnail [184 KiB] *.C file 

fig6_b.pdf [37 KiB] HiDef png [265 KiB] Thumbnail [187 KiB] *.C file 

Expected (open dots with 1$\sigma$ and 2$\sigma$ bands) and observed (full dots) upper limits at 95% confidence level, (a)  (c) shown for different masses of the Higgslike particle, (d) and (f) for different LLP lifetimes, and (e) as a function of the LLP mass. The values of the other parameters are indicated on the plots. Results inferred from the fast simulation. 
fig7_a.pdf [281 KiB] HiDef png [227 KiB] Thumbnail [164 KiB] *.C file 

fig7_b.pdf [176 KiB] HiDef png [209 KiB] Thumbnail [151 KiB] *.C file 

fig7_c.pdf [176 KiB] HiDef png [200 KiB] Thumbnail [146 KiB] *.C file 

fig7_d.pdf [176 KiB] HiDef png [246 KiB] Thumbnail [182 KiB] *.C file 

fig7_e.pdf [281 KiB] HiDef png [245 KiB] Thumbnail [185 KiB] *.C file 

fig7_f.pdf [176 KiB] HiDef png [248 KiB] Thumbnail [187 KiB] *.C file 

Animated gif made out of all figures. 
PAPER2016014.gif Thumbnail 
Definition of the criteria used for the signal determination. Selections $\rm Sel_1$ and $\rm Bkg_1$ are the baseline selections used in the fit, $\rm Sel_2$ and $\rm Bkg_2$ are used for the determination of systematic effects. The material veto and the requirement $ R_{\rm xy} >0.4$ $\rm mm$ are applied to both LLP candidates. The last column gives the number of data events selected, for a diLLP reconstructed mass above 19 $ {\mathrm{ Ge V /}c^2}$ . 
Table_1.pdf [33 KiB] HiDef png [47 KiB] Thumbnail [24 KiB] tex code 

Values of the fitted signal and background events for the different fully simulated signal models. The signal/background combinations are defined in the first row. 
Table_2.pdf [45 KiB] HiDef png [135 KiB] Thumbnail [72 KiB] tex code 

Contributions to the systematic uncertainty for fully simulated models. For the analysis based on the fast simulation the same total systematic uncertainty is adopted augmented by 5% to account for the relative imprecision of the fast and full simulations. The contributions from the signal and the datadriven background models used in the diLLP mass fit are discussed in the text. 
Table_3.pdf [32 KiB] HiDef png [190 KiB] Thumbnail [80 KiB] tex code 

Detection efficiency with total uncertainty, and upper limits at 95% CL on the crosssection times branching ratio for the process $ pp \rightarrow \mathrm{h}^0 X$, $\mathrm{h}^0 \rightarrow\tilde{\chi}^{0}_{1} \tilde{\chi}^{0}_{1} \rightarrow 6q$ for the fully simulated models. 
Table_4.pdf [47 KiB] HiDef png [129 KiB] Thumbnail [65 KiB] tex code 

Parameters of the signal models generated by Pythia and fully simulated. 
Table_5.pdf [38 KiB] HiDef png [106 KiB] Thumbnail [54 KiB] tex code 

Detection efficiency values in percent estimated by the fast simulation as a function of $ m_{\rm h^0}$ and $ m_{\rm{LLP}}$ . The LLP lifetime is 10 ps. The statistical uncertainty is 10% for $\epsilon \sim 0.02\%$, 5 \% for $\epsilon \sim 0.1\%$, 3\% for $\epsilon \sim 0.5\%$, and 2\% for $\epsilon \sim 1\%$. 
Table_6.pdf [35 KiB] HiDef png [134 KiB] Thumbnail [56 KiB] tex code 

Detection efficiency in percent estimated by the fast simulation as a function of the $ m_{\rm{LLP}}$ and $\tau_{\rm{LLP}}$ , for $ m_{\rm h^0}$ =114 GeV/c$^2$. The statistical uncertainty is 10% for $\epsilon \sim 0.02\%$, 5 \% for $\epsilon \sim 0.1\%$, 3\% for $\epsilon \sim 0.5\%$, and 2\% for $\epsilon \sim 1\%$. 
Table_7.pdf [28 KiB] HiDef png [156 KiB] Thumbnail [77 KiB] tex code 

Expected and observed 95% CL crosssection times branching ratio upper limits as a function of $ m_{\rm h^0}$ , with $ m_{\rm{LLP}} =35 {\mathrm{ Ge V /}c^2} $, and $\tau_{\rm{LLP}} =10 {\rm ps} $, estimated by the fast simulation. 
Table_8.pdf [39 KiB] HiDef png [166 KiB] Thumbnail [84 KiB] tex code 

Expected and observed 95% CL crosssection times branching ratio upper limits as a function of $ m_{\rm h^0}$ , for LLP masses of 40, 48, 55, and 60 $ {\mathrm{ Ge V /}c^2}$ , $\tau_{\rm{LLP}} =10 {\rm ps} $, estimated by the fast simulation. 
Table_9.pdf [39 KiB] HiDef png [301 KiB] Thumbnail [154 KiB] tex code 

Expected and observed 95% CL crosssection times branching ratio upper limits as a function of the LLP lifetime, for $ m_{\rm h^0} = 100 {\mathrm{ Ge V /}c^2} $ and $ m_{\rm{LLP}} =40 {\mathrm{ Ge V /}c^2} $, and for $ m_{\rm h^0} = 125 {\mathrm{ Ge V /}c^2} $ and $ m_{\rm{LLP}} =48 {\mathrm{ Ge V /}c^2} $, estimated by the fast simulation. 
Table_10.pdf [39 KiB] HiDef png [256 KiB] Thumbnail [128 KiB] tex code 

Expected and observed 95% CL crosssection times branching ratio upper limits as a function of the LLP mass, with $ m_{\rm h^0} =125 {\mathrm{ Ge V /}c^2} $ and $\tau_{\rm{LLP}} =10 {\rm ps} $, estimated by the fast simulation. 
Table_11.pdf [39 KiB] HiDef png [124 KiB] Thumbnail [65 KiB] tex code 
Created on 11 January 2020.