The performance of the jet trigger for the ATLAS detector during 2011 data taking

Abstract

The performance of the jet trigger for the ATLAS detector at the LHC during the 2011 data taking period is described. During 2011 the LHC provided proton-proton collisions with a centre-of-mass energy of 7 TeV and heavy ion collisions with a 2.76 TeV per nucleon-nucleon collision energy. The ATLAS trigger is a three level system designed to reduce the rate of events from the 40 MHz nominal maximum bunch crossing rate to the approximate 400 Hz which can be written to offline storage. The ATLAS jet trigger is the primary means for the online selection of events containing jets. Events are accepted by the trigger if they contain one or more jets above some transverse energy threshold. During 2011 data taking the jet trigger was fully efficient for jets with transverse energy above 25 GeV for triggers seeded randomly at Level 1. For triggers which require a jet to be identified at each of the three trigger levels, full efficiency is reached for offline jets with transverse energy above 60 GeV. Jets reconstructed in the final trigger level and corresponding to offline jets with transverse energy greater than 60 GeV, are reconstructed with a resolution in transverse energy with respect to offline jets, of better than 4 % in the central region and better than 2.5 % in the forward direction.

Fig. 1

The ATLAS trigger system

Fig. 2

The stages of algorithm processing in the Event Filter for several inclusive single jet triggers with different $E_{\mathrm{T}}$ thresholds. The case illustrated shows two sets of signatures, each set with a different jet radius parameter

Fig. 3

The luminosity measurement at the ATLAS interaction region for 2011 data taking [29]: a the maximum instantaneous luminosity versus day delivered to ATLAS during stable beam operation; b the cumulative luminosity versus day delivered to (green), and recorded by (yellow) ATLAS during stable beam operation for pp collisions at 7 TeV centre-of-mass energy

Fig. 4

The jet trigger rates versus instantaneous luminosity, before application of prescale factors, for triggers operating in 2011 a, c, e for several single inclusive jet triggers; b, d, f for multi-jet triggers. Shown are the rates for L1, L2 and EF signatures

Fig. 5

The processing time for the L2 jet trigger: a the full algorithm time; b the data preparation time; c the algorithm processing CPU time. The full algorithm time includes both the data preparation and algorithm processing times. The solid lines show the processing time per call, and the dashed lines show the processing times per event

Fig. 6

The processing times for the Event Filter jet trigger: a the time for the data preparation for the full calorimeter data; b the processing time for the topological clustering; c, d the times for the actual jet finding for the anti-$k_t$ algorithm, for instances with radius parameters c $R=0.4$, and d $R=1.0$

Fig. 7

The distribution of $\mathrm{\Delta }R$ between the offline jets and the closest matching trigger jet: a for L1; b for L2; c for the EF. In each case the differences are shown with respect to offline jets above the $p_{\text{T}}$ thresholds indicated such that the trigger for each threshold is fully efficient. Statistical uncertainties only are shown

Fig. 8

The mean relative offset for the EF trigger jets with respect to offline jets at the EM+JES energy scale as a function of the offline jet $\mathit{\eta }$ in four different ranges of jet $p_{\text{T}}$: a $p_{\mathrm{T}}^{\mathrm{Offline}}$ $>60$ GeV; b $p_{\mathrm{T}}^{\mathrm{Offline}}$ $>100$ GeV; c $p_{\mathrm{T}}^{\mathrm{Offline}}$ $>135$ GeV; and d $p_{\mathrm{T}}^{\mathrm{Offline}}$ $>170$ GeV. Statistical uncertainties only are shown: the data are shown as the solid points with error bars, and the Herwigsimulated sample as the hatched band.

Fig. 9

The mean relative offset for the EF trigger jets with respect to offline jets at the EM+JES energy scale as a function of the offline jet $p_{\text{T}}$, in four different regions of offline jet pseudorapidity: a $|{\mathit{\eta }}^{\mathrm{Offline}}|<0.75$; b $0.75\le |{\mathit{\eta }}^{\mathrm{Offline}}|<1.5$, c $1.5\le |{\mathit{\eta }}^{\mathrm{Offline}}|<2$; and d $2\le |{\mathit{\eta }}^{\mathrm{Offline}}|<2.8$. Statistical uncertainties only are shown: the data are shown as the solid points with error bars, and the Herwigsimulated sample as the hatched band.

Fig. 10

The resolution for the EF trigger jets with respect to offline jets at the EM+JES energy scale as a function of the offline jet $\mathit{\eta }$ in four different ranges of jet offline $p_{\text{T}}$: a $p_{\mathrm{T}}^{\mathrm{Offline}}$ $>60$ GeV; b $p_{\mathrm{T}}^{\mathrm{Offline}}$ $>100$ GeV; c $p_{\mathrm{T}}^{\mathrm{Offline}}$ $>135$ GeV; and d $p_{\mathrm{T}}^{\mathrm{Offline}}$ $>170$ GeV. Statistical uncertainties only are shown: the data are shown as the solid points with error bars, and the Herwigsimulated sample as the hatched band.

Fig. 11

The resolution for the EF trigger jets with respect to offline jets at the EM+JES energy scale, as a function of the offline jet $p_{\text{T}}$, in four different regions of offline jet pseudorapidity: a $|{\mathit{\eta }}^{\mathrm{Offline}}|<0.75$; b $0.75\le |{\mathit{\eta }}^{\mathrm{Offline}}|<1.5$; c $1.5\le |{\mathit{\eta }}^{\mathrm{Offline}}|<2$; and d $2\le |{\mathit{\eta }}^{\mathrm{Offline}}|<2.8$. Statistical uncertainties only are shown: the data are shown as the solid points with error bars, and the Herwigsimulated sample as the hatched band.

Fig. 12

The performance for the EF forward trigger jets with respect to offline jets at the EM+JES energy scale as a function of the offline jet $p_{\text{T}}$ for jets with $3.6<|{\mathit{\eta }}^{\mathrm{Offline}}|<4.4$: a The mean relative offset; and b the resolution. Statistical uncertainties only are shown: the data are shown as the solid points with error bars, and the Herwigsimulated sample as the hatched band.

Fig. 13

The mean relative offset for the EF trigger jets with respect to offline jets at the EM energy scale as a function: a of the offline jet $\mathit{\eta }$ for jets with $p_{\text{T}}$ $>60$ GeV; b as a function of the offline jet $p_{\text{T}}$ at the hadronic energy scale for jets in the range $|{\mathit{\eta }}^{\mathrm{Offline}}|<2.8$. Statistical uncertainties only are shown: the data are shown as the solid points with error bars, and the Herwigsimulated sample as the hatched band.

Fig. 14

The resolution for the EF trigger jets with respect to offline jets at the EM energy scale: (a) as a function of the offline jet $\mathit{\eta }$ for jets with offline $p_{\text{T}}$ $>60$ GeV; (b) as a function of the offline jet $p_{\text{T}}$ at the hadronic energy scale for jets in the range $|{\mathit{\eta }}^{\mathrm{Offline}}|<2.8$. Statistical uncertainties only are shown: the data are shown as the solid points with error bars, and the Herwigsimulated sample as the hatched band.

Fig. 15

The efficiency as a function of offline jet $E_{\mathrm{T}}$ for various single inclusive jet triggers. Shown are the efficiency for data, and for the Herwig simulated sample for: a L1; b L2; and c the EF triggers. For data, the efficiency is computed with respect to events taken by an independent trigger that is 100 % efficient in the relevant region. Statistical uncertainties only are shown: the data are shown as the solid points with error bars, and the Herwigsimulated sample as the hatched band.

Fig. 16

The efficiency for various EF triggers as a function of offline jet $E_{\mathrm{T}}$. Shown are the efficiencies for data and the Herwig simulated sample for the: a EF triggers seeded by L2_j95 and L1_J75; b EF triggers seeded by a random trigger at L1 and passed through L2. Statistical uncertainties only are shown: the data are shown as the solid points with error bars, and the Herwigsimulated sample as the hatched band.

Fig. 17

The efficiency for various forward jet triggers in data and the Herwig simulated sample as a function of offline jet $E_{\mathrm{T}}$ for: a L1_FJ10, L1_FJ30 and L1_FJ50; b L2_fj25, L2_fj50 and L2_fj70; c EF_fj30, EF_fj55 and EF_fj75. Statistical uncertainties only are shown: the data are shown as the solid points with error bars, and the Herwigsimulated sample as the hatched band.

Fig. 18

The single inclusive jet trigger efficiency integrated over the $E_{\mathrm{T}}$ of the rising edge of the trigger, as a function of $\mathit{\eta }$ for the triggers: a L1_J75; b L2_j95; c EF_j100. The data are shown as the solid points with error bars with the simulated sample shown as a shaded band. Statistical uncertainties only are shown.

Fig. 19

The efficiency for the three-jet and five-jet chains with a 30 GeV threshold at the EF, as a function of: a the third jet $E_{\mathrm{T}}$ for the three jet chains; and b as a function of the fifth jet $E_{\mathrm{T}}$ for the five jet trigger chains. Shown are the absolute trigger efficiencies: the L2 efficiency also includes that for L1 and the EF efficiency includes that from both L1 and L2. Statistical uncertainties only are shown: the data are shown as the solid points with error bars, and the Herwigsimulated sample as the hatched band.

Fig. 20

The sigmoid fit to the rising edge of the efficiency and the fit purely to the plateau region for the EF_3j30 trigger, without any jet isolation requirement. The parameter $c_0$ represents the plateau efficiency, $c_1$ represents the midpoint of the rising edge, $c_2$ is related to the sharpness of the rising edge, and $c_3$ is the efficiency prior to the rising edge. The horizontal solid blue line indicates the plateau efficiency. The vertical dashed lines indicate the rising edge midpoint ($c_1$), and the start of the plateau ($c_1+5c_2$)

Fig. 21

The efficiency as a function of the fifth jet $E_{\mathrm{T}}$ for the five-jet EF trigger, where no jet isolation is required (dashed line) and where jet isolation is required (solid line). Shown are the absolute trigger efficiency, including both the L1 and L2 efficiencies. Statistical uncertainties only are shown.

Fig. 22

The efficiency for the trigger requiring both $H_{\mathrm{T}}$ $>400$ GeV and a leading jet with $E_{\mathrm{T}}>100$ GeV at the trigger level shown as a function of offline $H_{\mathrm{T}}$ for: a various leading offline jet $p_{\text{T}}$ selections, where the offline $H_{\mathrm{T}}$ is calculated from offline jets with $p_{\text{T}}>50$ GeV; b various offline jet $p_{\text{T}}$ selections for the definition of offline $H_{\mathrm{T}}$, where the leading offline jet $p_{\text{T}}$ selection is 170 GeV

Fig. 23

The efficiency of the large-$R$ jet trigger, EF_j240_a10tc (open markers), compared to the standard EF_j240_a4tc trigger (filled markers), both with respect to offline $R=1.0$ jets, for both data and simulation

Fig. 24

The effect of jet width on efficiency, for data and Monte Carlo, with respect to offline $R=1.0$ jets: a when the standard jet trigger, EF_j240_a4tc, is used; and b where the large-$R$ jet trigger, EF_j240_a10tc, is used. Inclusive jet widths (open markers) and widths restricted to $w<0.15$ (filled markers) are shown

Fig. 25

The distribution of the transverse energy deposited in forward calorimeter, FCal $\mathrm{\Sigma }{E}_{\mathrm{T}}$, divided into 10 % centrality bins [53]

Fig. 26

The mean transverse energy subtracted from offline jets with $R=0.4$, as a function of jet $E_{\mathrm{T}}$ for five centrality bins for the heavy ion data

Fig. 27

The trigger efficiency versus jet $E_{\mathrm{T}}$ for heavy ion events: a for anti-$k_t$ $R=0.4$ offline jets in five centrality bins for a trigger threshold of 20 GeV; b in central and peripheral collisions for anti-$k_t$ $R=0.2,0.3,0.4$ and 0.5 offline jets, also with a trigger threshold of 20 GeV

Fig. 28

The trigger efficiency for heavy ion events with a requirement of an EF jet with $E_{\mathrm{T}}>20$ GeV: a for peripheral collisions; and b for central collisions. Shown are results for offline jets reconstructed with the anti-$k_t$ algorithm using $R=0.2$, 0.3, 0.4 and 0.5, both with (closed points), and without (open points) fake-jet rejection

Fig. 29

The angular resolution for $R=0.2$ jets with $E_{\mathrm{T}}>20$ GeV reconstructed in the EF, with respect to $R=0.2$, and $R=0.4$ offline jets, for different centralities in the heavy ion data; the residuals in a $\mathit{\eta }$ and b $\mathit{\varphi }$ between trigger jets and offline $R=0.2$ jets for different centrality bins; the residuals in c $\mathit{\eta }$ and d $\mathit{\varphi }$ between trigger jets and offline $R=0.4$ jets for different centrality bins