Performance of the CMS Drift Tube Local Trigger


The performance pf the DT Local Trigger (DTLT) was checked using Run 2 data and compared to Run 1. The events were selected to contain a "Global Muon" reconstructed in the barrel.

Trigger Efficiency

The DTLT efficiency was defined and measured as the ratio between the number of observed and expected triggers.

The expected triggers were defined requiring the presence in a chamber of a reconstructed track segment, belonging to the Gobal Muon and having at least 4 associated hits in the Phi view. The DTLT was then considered efficient if a trigger primitive was delivered at the correct bunch crossing in the same chamber.

In the following plots the computed efficiency is shown as a function of the Global Muon pseudorapidity and compared to the corresponding results obtained in Run 1.

DTLTefficiency_eta.png

DT Local trigger efficiency as a function of muon pseudorapidity in Run 1 and in Run 2

The efficiency observed in the present data is slightly better than previously, especially in the gaps between the barrel wheels.

In the following plot the computed efficiency is shown as a function of the Global Muon transverse momentum for the four DT stations: no dependencies on momentum are observed.

DTLTefficiency_pt.png

DT Local trigger efficiency as a function of muon transverse momentum for the four DT stations

Trigger Quality

The DTLT quality is defined from the number and position of hits that were found aligned by the logic implemented in the Trigger Board, and therefore associated in a trigger primitive.

The comparison between Run 2 and Run 1 results, in the following plots, shows that the DTLT quality has increased in all of the four DT stations.

DTLTquality.png

DT Local Trigger quality distributions in the four DT stations, in Run 2 and Run 1

Fraction of "ghost" triggers

Two more observables are relevant to assess the DTLT performance: the fraction of "ghost" triggers that may be either "in time" (i.e. a second primitive delivered in the same chamber at the same bunch crossing) or "out of time" (i.e. a second trigger primitive delivered in the same chamber but at a different bunch crossing).

See here for a detailed description of ghost triggers and a precise definition of ghost fractions.

The following plot shows the fraction of in-time ghost triggers, as a function of the Global Muon transverse momentum, in the MB1 stations, where the track multiplicity is maximum. Results are compatible or better w.r.t. Run 1. No dependency on track momentum is observed.

DTLTintime_pt.png

Fraction of in-time ghost triggers in the MB1 DT chambers, as a function of transverse momentum, in Run II and Run I

The fraction of out-of-time ghost triggers is shown in the following plot as a function of Global Muon transverse momentum, for the four DT stations. No dependency on track momentum is observed.

DTLTootime_pt.png

Fraction of out-of-time ghost triggers in the four DT stations, as a function of transverse momentum

Conclusion

The DT Local Trigger performance in 2015 is slightly better than in Run 1: the efficiency is somewhat higher in the gaps between the barrel wheels, the quality has improved, the fraction of in-time ghosts is the same or smaller.

This improvement is due to the hardware repairs performed during the Long Shutdown 1, and to a better trigger synchronization.

-- FrancescaCavallo - 2015-12-14

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Topic revision: r1 - 2015-12-14 - FrancescaCavallo
 
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