The LHCb Trigger and its Performance in 2011

Information

LHCb-DP-2012-004
arXiv:1211.3055 [PDF]

(Submitted on 13 Nov 2012)
JINST 8 P04022
Inspire 1202496

Tools

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 [867 KiB] Thumbnail [409 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 [99 KiB] Thumbnail [60 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 [82 KiB] Thumbnail [50 KiB]
	L0_Had[..].eps [20 KiB] HiDef png [138 KiB] Thumbnail [83 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 [72 KiB] Thumbnail [43 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 [123 KiB] Thumbnail [70 KiB]
	HLT1mu[..].eps [8 KiB] HiDef png [111 KiB] Thumbnail [63 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 [141 KiB] Thumbnail [86 KiB]
	Hlt1_H[..].eps [20 KiB] HiDef png [113 KiB] Thumbnail [67 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 [128 KiB] Thumbnail [74 KiB]
	t_1.eps [9 KiB] HiDef png [107 KiB] Thumbnail [61 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 [93 KiB] Thumbnail [55 KiB]
	Hlt2_T[..].eps [9 KiB] HiDef png [82 KiB] Thumbnail [49 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 [117 KiB] Thumbnail [69 KiB]
	HLT2_J[..].eps [9 KiB] HiDef png [108 KiB] Thumbnail [65 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 [96 KiB] Thumbnail [55 KiB]
	Hlt2_D[..].eps [9 KiB] HiDef png [87 KiB] Thumbnail [50 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 [42 KiB] Thumbnail [15 KiB] tex code
Allowed mapping points in the BBDT. The variables are explained in the text.	Table_2.pdf [55 KiB] HiDef png [51 KiB] Thumbnail [23 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 [47 KiB] Thumbnail [21 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 [69 KiB] Thumbnail [33 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 [63 KiB] Thumbnail [31 KiB] tex code
HLT2 lines based on one identified muon.	Table_6.pdf [50 KiB] HiDef png [81 KiB] Thumbnail [39 KiB] tex code
HLT2 lines based on two identified muon.	Table_7.pdf [59 KiB] HiDef png [45 KiB] Thumbnail [21 KiB] tex code
HLT2 lines based on two identified muons.	Table_8.pdf [58 KiB] HiDef png [56 KiB] Thumbnail [27 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]