The LHCb Trigger and its Performance in 2011

[to restricted-access page]

Abstract

This paper presents the design of the LHCb trigger and its performance on data taken at the LHC in 2011. A principal goal of LHCb is to perform flavour physics measurements, and the trigger is designed to distinguish charm and beauty decays from the light quark background. Using a combination of lepton identification and measurements of the particles' transverse momenta the trigger selects particles originating from charm and beauty hadrons, which typically fly a finite distance before decaying. The trigger reduces the roughly 11 MHz of bunch-bunch crossings that contain at least one inelastic $pp$ interaction to 3 kHz. This reduction takes place in two stages; the first stage is implemented in hardware and the second stage is a software application that runs on a large computer farm. A data-driven method is used to evaluate the performance of the trigger on several charm and beauty decay modes.

Figures and captions

 Layout of the LHCb detector. y-LHCb[..].eps [1 MiB] HiDef png [826 KiB] Thumbnail [388 KiB] Comparison of the $p_T$ distributions of $D^+\rightarrow K^-\pi^+\pi^+$ selected in NoBias and TIS events. D2HHH_pt.eps [9 KiB] HiDef png [125 KiB] Thumbnail [140 KiB] Efficiency $\epsilon^{\rm TOS}$ of $B^+\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} (\mu^+\mu^-)K^+$ as a function of $p_T$ ( ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ ) for {\tt L0Muon} and {\tt L0DiMuon} lines. L0_Psi[..].eps [8 KiB] HiDef png [104 KiB] Thumbnail [114 KiB] L0_Had[..].eps [20 KiB] HiDef png [173 KiB] Thumbnail [191 KiB] The efficiency $\epsilon^{\rm TOS}$ of {\tt L0Electron} is shown for ${B}^0\rightarrow J/\psi{(\rm e^+e^-)}K^{*0}$ as a function of $p_T$ ( ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ ). L0_Psi[..].eps [8 KiB] HiDef png [91 KiB] Thumbnail [101 KiB] Efficiency $\epsilon^{\rm TOS}$ of {\tt Hlt1TrackMuon}, {\tt Hlt1DiMuonHighMass} and {\tt Hlt1DiMuonLowMass} for $B^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} (\mu^+\mu^-) K^+$ as a function of the $p_T$ and lifetime of the $B^+$. HLT1mu[..].eps [9 KiB] HiDef png [155 KiB] Thumbnail [162 KiB] HLT1mu[..].eps [8 KiB] HiDef png [140 KiB] Thumbnail [145 KiB] Efficiency $\epsilon^{\rm TOS}$ of {\tt Hlt1TrackAllL0} is shown for $B ^- \rightarrow D ^0 \pi ^-$ , $B ^0 \rightarrow D ^- \pi ^+$ , $D^0\rightarrow K^-\pi^+$ and $D^+\rightarrow K^-\pi^+\pi^+$ as a function of $p_T$ and $\tau$ of the $B$ -meson and prompt $D$ -meson respectively. Hlt1_H[..].eps [20 KiB] HiDef png [178 KiB] Thumbnail [198 KiB] Hlt1_H[..].eps [20 KiB] HiDef png [143 KiB] Thumbnail [156 KiB] Efficiencies $\epsilon^{\rm TOS}$ of {\tt Hlt2DiMuonJPsiHighPT} and {\tt Hlt2DiMuonDetachedJPsi} for $B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+$ as a function of $p_T$ and $\tau$ of the $B^+$. pt_1.eps [11 KiB] HiDef png [162 KiB] Thumbnail [172 KiB] t_1.eps [9 KiB] HiDef png [136 KiB] Thumbnail [141 KiB] Efficiency $\epsilon^{\rm TOS}$ if at least one of the lines {\tt Hlt2Topo$n$Body}, with $n=2,3$, selected the event for $B ^- \rightarrow D ^0 \pi ^-$ and one of the lines with $n=2,3,4$ for $B ^0 \rightarrow D ^- \pi ^+$ as a function of $p_T$ and $\tau$ of the $B$ -meson. The efficiency is measured relative to events that are TOS in {\tt Hlt1TrackAllL0}. Hlt2_T[..].eps [11 KiB] HiDef png [119 KiB] Thumbnail [127 KiB] Hlt2_T[..].eps [9 KiB] HiDef png [105 KiB] Thumbnail [111 KiB] Efficiency $\epsilon^{\rm TOS}$ if at least one of the lines {\tt Hlt2Topo$n$Body} or {\tt Hlt2TopoMu$n$Body}, with $n=2,3$, selected events for $B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+$ , as a function of $p_T$ and $\tau$ of the $B$ -meson. Also shown is $\epsilon^{\rm TOS}$ if the line {\tt Hlt2Topo$n$Body}, with $n=2,3$, selected the events. {\tt Hlt2Topo2Body} shows the inclusive performance of the topological lines. The efficiency is measured relative to events that are TOS in either {\tt Hlt1TrackAllL0} or {\tt Hlt1TrackMuon}. HLT2_J[..].eps [9 KiB] HiDef png [148 KiB] Thumbnail [159 KiB] HLT2_J[..].eps [9 KiB] HiDef png [138 KiB] Thumbnail [149 KiB] Efficiency $\epsilon^{\rm TOS}$ of the lines {\tt Hlt2CharmHadD2HHH} and {\tt Hlt2CharmHadD02HH$\_$D02KPi} for $D^+\rightarrow K^-\pi^+\pi^+$ and $D^0\rightarrow K^-\pi^+$ respectively as a function of $p_T$ and $\tau$ of the $D$ -meson. The efficiency is measured relative to events that are TOS in {\tt Hlt1TrackAllL0}. Hlt2_D[..].eps [11 KiB] HiDef png [121 KiB] Thumbnail [127 KiB] Hlt2_D[..].eps [9 KiB] HiDef png [111 KiB] Thumbnail [114 KiB] Animated gif made out of all figures. DP-2012-004.gif Thumbnail

Tables and captions

 MC signal samples used to train the BBDT, where $K$ means $K^\pm$ and $\pi$ means $\pi^\pm$. Table_1.pdf [52 KiB] HiDef png [50 KiB] Thumbnail [19 KiB] tex code Allowed mapping points in the BBDT. The variables are explained in the text. Table_2.pdf [55 KiB] HiDef png [61 KiB] Thumbnail [30 KiB] tex code Cuts of L0 lines and their rates prior to throttling. The definition of the trigger lines is given in Section 2. Table_3.pdf [65 KiB] HiDef png [55 KiB] Thumbnail [27 KiB] tex code HLT1 muon lines and their cuts. The rate is measured on events accepted by {\tt L0Muon} or {\tt L0DiMuon}. Table_4.pdf [52 KiB] HiDef png [86 KiB] Thumbnail [42 KiB] tex code The cuts applied in {\tt Hlt1TrackAllL0} and {\tt Hlt1TrackPhoton} lines. The rate is measured on events accepted by L0. Table_5.pdf [57 KiB] HiDef png [77 KiB] Thumbnail [40 KiB] tex code HLT2 lines based on one identified muon. Table_6.pdf [50 KiB] HiDef png [99 KiB] Thumbnail [48 KiB] tex code HLT2 lines based on two identified muon. Table_7.pdf [59 KiB] HiDef png [54 KiB] Thumbnail [27 KiB] tex code HLT2 lines based on two identified muons. Table_8.pdf [58 KiB] HiDef png [69 KiB] Thumbnail [35 KiB] tex code HLT2 selection cuts applied for the exclusive lines {\tt Hlt2CharmHadD02HH$\_$D02KPi} and {\tt Hlt2CharmHadD2HHH}. The 2-track cuts refer to a candidate constructed of two tracks, and $m_{\rm corr}$ is defined in equation 2. The angle $\alpha$ is the angle between the momentum of the $D$ and the vector connecting the PV with the $D$ vertex. Some selections require that at least one or two tracks pass a cut, indicated with "$\geqq$". [Error creating the table]

Created on 12 October 2019.