Approval Plots for Redundancy study

Enhancement of performance in nominal muon coverage

Introduction
In CMS the high momentum resolution is provided by the very precise resolution of the tracker system. For the high momentum muons, the muon system can contribute substantially to the overall momentum measurement since the curvature resolution scales as the square of the lever arm and the muon system provides a much larger lever arm than the tracker alone. However in the forward region we observe a poor momentum resolution with respect to the one in the barrel region caused by magnetic field inhomogeneity, by showering effects at high momenta and by the lower number of measured points with respect to the rest of the CMS muon system. Additional detectors in the muon system, with good spatial resolution, can improve limited pT resolution in the current endcap region and will provide higher efficiency in a high background environment.
Figure (click on figure for pdf)
Caption
The RMS of the multiple scattering displacement as a function of muon pT > for the different forward muon stations. All of the electromagnetic processes such as bremsstrahlung and magnetic field effect are included in the simulation.
Description

| Additional detectors in the muon system, with good spatial resolution, can improve limited p_T resolution in the current endcap region and will provide higher efficiency in a high background environment. The spatial resolution lower limit, set by the multiple scattering experienced by muons in traversing the CMS material, has been estimated from simulation, assuming the current geometry scenario, and the results are depicted in Figure, which shows the displacements as a function of p_T in the different endcap stations, at a fixed eta and phi ((eta,phi)=(2,0)) in Figure). The RMS of the displacement for p_T > 100 GeV (values for which the muon system can start to contribute to the momentum resolution) is <700 µm at the surface of ME0, <900 µm at GE1/1, <2 mm at GE2/1, and reaches <4 mm at the fourth station (RE4/1) as can be seen on the figure.

Redundancy plot for STA reconstruction: 2019 scenario, PU = 0

Introduction
While the present muon system in the barrel region is redundant enough to maintain performance at HL-LHC, the lack of redundancy of the system in the forward region will be an important issue if parts of or entire CSC chambers will lose efficiency. We have studied how the performance of the q/pT resolution, of the charge mis-identification and of the reconstruction efficiency will be affected in the three configurations mentioned above, considering the case in which one segment in CSC is lost. The q/pT resolution is defined as the Gaussian width of the q/pT residual distribution:: δ( q/pT) / q/pT = (qrec/precT - qsim/psimT) / (qsim/psimT) plotted in the range [-6,+6], where q is the charge and psimT and precT are the simulated and reconstructed transverse momenta. Sigma of the q/pT residual distribution is obtained from its gaussian fit in the range of [(mean - RMS), (mean + RMS)].
Figure (click on figure for pdf)
Caption
Restoration of q/pT resolution by adding GE1/1 in case of ME1/1 failure in the “2019 scenario”.
Description
One can see the improvement in the gaussian width of the q/pT distribution provided by the addition of the GE1/1 chambers (squared markers), in case of failure of ME1/1 chambers (cross markers). For the sigma of the q/pT residual distribution, GE1/1 can nearly (90%) compensate such failure, since the contribution of ME1/1 and GE1/1 in the resolution is nearly equivalent. It has been noted that additional hits from new detectors (additional GE1/1 hits to the first station, circle markers in Figure) in track fitting do not change substantially the core of the distribution , represented by the gaussian width, of the current muon system (triangle markers in Figure), but are very effective to reduce the tails of the distribution, which will affect the RMS measurement.

Redundancy plot for STA reconstruction in 2023 scenario, PU = 140: RMS of q/p_T resolution

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Caption
Restoration of RMS of q/pT distribution as a function of the simulated eta for pT=100 GeV at 140 PU by adding the upgrade detectors in case of ME1/1 failure in the “2023 scenario” at PU = 140.
Description
The Figure shows the recover, obtained thanks to the additional station (squared markers), of the standalone muon system resolution in the case of failure of ME1/1 station with respect to the no upgrade case (cross markers). The gain obtained with the upgraded system (circle markers) with respect to no upgrade case (triangle markers) is also shown in the same Figure

Redundancy plot for STA reconstruction in 2023 scenario, PU = 140: Ratio of RMS of q/p_T resolution

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Caption
The gain obtained as a function of the simulated eta for pT=100 GeV at 140 PU by adding new detectors to each failure configuration, is shown, as ratio of RMS of q/pT resolution.
Description
The Figure shows that the standalone muon performance is restored in case of failure of either ME1/1 or ME2/1 or ME3/1 or ME4/1 station adding new detector (GE1/1, GE2/1, RE3/1, RE4/1 respectively). Again the RMS is taken from the histogram of gaussian width of q/pT resolution plotted in the range of [-6,+6]. The effect is reported for each station as improvement of the performance adding new detector with respect to the case of non-operational ME station. As expected the major recovery (up to 60\%) is obtained by adding GE1/1 (squared filled markers) and GE2/1 (triangles filled markers), due to the high spatial resolution, comparable with the CSC one.

Performance plots for PU = 140 sample in 2023 scenario: Sigma of q/p_T resolution

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Caption
Improvements with added redundancy of the upgrade forward muon detectors, for standalone muons, as a function of the simulated eta for pT=100 GeV at 140 PU: plot shows sigma of the q/pT resolution for the ``2023 scenario'' (filled markers) and ``no upgrade'' (empty markers).

Description

Improvements in the Sigma of q/pT resolution with added redundancy of the upgrade forward muon detectors, for standalone muons, as a function of the simulated eta; for pT = 100 GeV at 140 PU. The range between [mean-RMS, mean+RMS] is used for fitting of the q/pT resolution plotted in the range of [-6,+6]. The hits from new detectors provide also a maximum improvement of about 10% in the sigma of the q/pT.

Performance plots for PU = 140 sample in 2023 scenario: RMS of q/p_T resolution

Figure (click on figure for pdf)
Caption
Improvements with added redundancy of the upgrade forward muon detectors, for standalone muons, as a function of the simulated eta for pT=100 GeV at 140 PU: RMS of the fractional q/pT resolutions for the ``2023 scenario'' (filled markers) and ``no upgrade'' (empty markers).
Description
Improvements in the RMS of q/pT resolution with added redundancy of the upgrade forward muon detectors, for standalone muons, as a function of the simulated eta; for pT = 100 GeV at 140 PU. Again the RMS is taken from the histogram of gaussian width of q/pT plotted in the range of [-6,+6]. The hits from new detectors improves the RMS of the q/pT resolution up to ∼35% as seen in the figure with (circles markers) and without (triangle markers) upgrade.

Performance plots for PU = 140 in 2023 scenario: charge mis-identification

Figure (click on figure for pdf)
Caption
Improvements with added redundancy of the upgrade forward muon detectors, for standalone muons, as a function of the simulated eta for pT=100 GeV at 140 PU: the charge mis-identification probabilities for the ``2023 scenario'' (filled markers) and ``no upgrade'' (empty markers).
Description

| Improvements in the Charge mis-identification probability with added redundancy of the upgrade forward muon detectors, for standalone muons, as a function of the simulated eta; for p_T = 100 GeV at 140 PU. In the “2023 scenario” the additional hits from new detectors in track fitting will also improve the muon track resolution and reduce the charge mis-identification probability, which in case of “no upgrade” scenario degrade with 140 PU. We can see from the figure that adding the new detectors improved the charge mis-identification probability up to ∼50.

Muon Reconstruction efficiency in case of detector degradation

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Caption
Muon reconstruction efficiency versus h for various uniform degradations of segment (DT, CSC) and hit (GEM, iRPC) efficiencies. The top plot (2015 Geometry) illustrates the situation without the new forward muon detectors, while they are included in the bottom plot (2023 Geometry). In both cases, the black line represents the situation in Run 1.
Description
The basic idea was to understand how much of the reconstruction efficiency we would loose if the detection efficiency (segment reconstruction efficiency or hit reconstruction efficiency) goes down from the current situation (~99% for segments, ~95% for hits) to lower levels due to electronics malfunctioning/ageing/entire chambers being off/... This study is performed with a simple toy model where the amount of available hits and segments used for Stand-Alone Muon reconstruction are analyzed. In each eta bin we have a percentage of the muons reconstructed with X segments and Y hits. If we then apply an additional degeneration of the segment or hit reconstruction efficiency, one can observe cases in which crucial segments or hits are lost, such that a Stand Alone muon can n not be reconstructed anymore, leading to a reduced muon reconstruction efficiency. As a starting point the Post-LS1 Stand Alone Muon reconstruction efficiency is used, the colored lines give an indication of the deterioration of the muon reconstruction & id efficiency if the muon stations rec hit efficiency goes down. It is clearly visible that in the detector regions where we currently lack redundancy, the deterioration of the muon reconstruction & id efficiency is the worst. One can also see that in the 2023 geometry, where the redundancy of the muon system at high pseudorapidities (1.6 < eta < 2.4) is restored, the effect of failing hit reconstruction (due to chambers off/electronics problems, ...) is mitigated.