CERN Accelerating science

Schematic longitudinal view of one quarter of the CMS detector. The orange square highlights the region where the DT chambers (MB1, MB2, MB3 and MB4) are located.

Left: Structure of a DT Chamber with three superlayers composed of 4 layers each of drift cells. Right: Layout of a drift cell showing the electric field lines in the gas volume.

Left: Structure of a DT Chamber with three superlayers composed of 4 layers each of drift cells. Right: Layout of a drift cell showing the electric field lines in the gas volume.

Integrated dose over the irradiated layers (L1 and L4) in SL1. Only the periods when they were on are considered in the computation. The data taking is divided into two periods: the first, called era A, started in October 2017 and ended in April 2018, after submitting the chamber to an amount of radiation equivalent to that expected for the full HL-LHC run. After that period, the DT chamber was open and a few wires were extracted for inspection. The era B started at the end of October 2018 and continued until February 2019.

Normalized Current for aged (SL1L1 and SL1L4) and non-aged (SL1L3) layers as a function of the integrated luminosity. Values are scaled with respect to the initial value in SL1L3. Each point corresponds to the mean current in a day.

Hit efficiency for the aged layers (SL1L1 and SL1L4) using cosmic muons as a function of integrated luminosity (left) and as a function of the wire HV for different integrated luminosities (right). The integrated luminosity corresponds to that expected for the MB1 chambers in the external wheels of the CMS detector (YB$\pm2$) during the HL-LHC.

Hit efficiency for the aged layers (SL1L1 and SL1L4) using cosmic muons as a function of integrated luminosity (left) and as a function of the wire HV for different integrated luminosities (right). The integrated luminosity corresponds to that expected for the MB1 chambers in the external wheels of the CMS detector (YB$\pm2$) during the HL-LHC.

Left: Hit efficiency for test beam muons as a function of instantaneous dose for aged layers (SL1L1 and SL1L4) and a non-aged layer (SL1L3). Data taken after an accumulated dose equivalent to an HL-LHC integrated luminosity of 3600~\fbi. Right: Hit efficiency for cosmic muons as a function of integrated luminosity for the aged layer SL1L1 at a background rate corresponding to a instantaneous luminosity of $5.8 \cdot 10^{34} \uinstlumi$). The data is fitted using an exponential model ($\varepsilon_{hit} = 0.053 + 0.879 \cdot e^{-1.546 \cdot 10^{-4}\mathcal{L}_{int}}$).

Left: Hit efficiency for test beam muons as a function of instantaneous dose for aged layers (SL1L1 and SL1L4) and a non-aged layer (SL1L3). Data taken after an accumulated dose equivalent to an HL-LHC integrated luminosity of 3600~\fbi. Right: Hit efficiency for cosmic muons as a function of integrated luminosity for the aged layer SL1L1 at a background rate corresponding to a instantaneous luminosity of $5.8 \cdot 10^{34} \uinstlumi$). The data is fitted using an exponential model ($\varepsilon_{hit} = 0.053 + 0.879 \cdot e^{-1.546 \cdot 10^{-4}\mathcal{L}_{int}}$).

Estimated hit efficiencies at the end of the HL-LHC for all the DT chambers of the CMS muon system, MB4 chambers (upper) and for MB1, MB2 and MB3 (lower). These efficiencies have been estimated considering a safety factor of 2 for the expected HL-LHC background rate ($10^{35} \uinstlumi$) and a safety factor of 2 for the expected integrated luminosity (6000~\fbi) to obtain the expected hit efficiency for the MB1 chambers in wheels ±2 and extrapolating to the rest of the CMS muon system using the expected integrated charge at the end of HL-LHC.