CMS DT Longevity Studies - new HGCal geometry

This report includes:
  • Hit Efficiency as a function of the track angle
  • Updates of hit efficiency expected at 3000 fb-1 and at 1000 fb-1 integrated luminosity including the angle corrections and the last 2019 Fluka results of 30% rate increase in the MB1 YB+/2 DT chambers
  • Results from new wires irradiated during era B

The hit efficiency expected at the end of HL-LHC, from the results of the irradiation tests at GIF++ of a CMS Drift Tubes (DT) chamber, presented at [1], are updated here for taking into account the increase of the flux at HL-LHC as suggested by the last simulations (including the new endcap calorimeter nose, the new CMS beam pipe and the calorimeter services as described in the internal Fluka CMS simulation with v3.7.19.1 and v3.7.18.0 geometry). The simulation shows indeed an impact in the flux expected in the DT chambers with an 30% increase in the MB1 most external wheels (MB1 YB+/-2), chambers used as reference for the CMS DT longevity results.

The hit efficiency tables presented here include also the extrapolation of the muon beam results at GIF taking into account the effect of the average track angle in each chamber at P5 (angle corrections not included in [1]) .

The results of the irradiation of seven new wires and of the other irradiated wires of layer 1 and layer 4 are also presented .

References: [1] CMS DT Longevity Studies (February, 2019) https://cds.cern.ch/record/2682229/files/DP2019_018.pdf

Dose definition and extrapolation

At GIF++, the dose rate is measured with a REMUS dosimeter situated inside the GIF++ bunker. Several dose rate measurements were done with a portable dosimeter in different positions of the MB2 chamber to extrapolate the REMUS measurement to the dose rate on the surface of the MB2 chamber, public results at here.

As reported in [1], the dose rate and integrated dose are converted to expected instantaneous and integrated luminosity for the MB1 chambers on the external wheels (YB±2) expected at the HL-LHC from extrapolation of Run2 measurements. Conversion factors were calculated comparing currents in the MB2 chamber at GIF++ for a given dose rate in not aged layers with currents of DT chambers at P5 for a given instantaneous luminosity. Since the gain at the high dose rate used to irradiate at GIF++ is lower than at HL-LHC, the dose rate to instantaneous luminosity conversion was calculated at the expected HL-LHC background rate (and here taking into account the expected increase of 30% according to the simulation): 1034 cm-2s-1 = 0.0142 mGy/h, while the integrated dose to integrated luminosity was calculated at GIF++ aging rate (~10xHL-LHC): 1 fb-1 = 0.549 mGy.

List of Plots

Figure Caption
[1] Integrated dose [mGy] as a function of time for the irradiation period of the CMS DT spare chamber ‘MB2’ at GIF++. The layers 1 and 4 from superlayer 1 were irradiated with HV on (3550 V). The rest of the chamber was irradiated with HV in standby (1900 V) and used as reference. The vertical grey lines correspond to the 2017 and 2018 winter breaks when the chamber is kept off and the vertical orange lines mark the two irradiation and data-taking periods (eras). During summer 2018, 8 wires were extracted for later inspection and replaced with new wires and irradiated along the subsequent irradiation period. The green line shows the dose absorbed by these superlayer 1 layer 1 new wires. The axis on the right shows the equivalent expected luminosity for MB1 chambers in the external wheels for the HL- LHC.
[2] Hit efficiency for cosmic muons as a function of integrated luminosity for the aged layers (SL1L1 and SL1L4) at 3550 V and the front-end threshold 30 mV. Each of the points in this plot corresponds to the data-taking during HV scans (with the source off) that were collected about every week. The DT auto trigger was used for cosmic muon tracks identifying a track in both projections on SL2 and SL3 of the DT chamber, avoiding any bias on the layers irradiated with HV on. The integrated luminosity used in these studies corresponds to the integrated luminosity expected for the MB1 chambers in the external wheels of the CMS detector (YB+/-2) during the HL-LHC. No atmospheric condition corrections have been applied.
[3] Hit efficiency for cosmic muons as a function of HV for the aged layers (SL1L1 and SL1L4) when the source is off and the front-end threshold 30 mV. The DT auto trigger was used for cosmic muon tracks, identifying a track in both projections on SL2 and SL3 of the DT chamber, avoiding any bias on the layers irradiated with HV on. There are three series of datasets each corresponding to a different integrated luminosity: beginning, middle and end of the irradiation period of MB2. The integrated luminosity used in these studies corresponds to the integrated luminosity expected for the MB1 chambers in the external wheels of the CMS detector (YB+/-2) during the HL-LHC.
[4] Hit efficiency for cosmic muons as a function of HV for the aged layers (SL1L1 and SL1L4) when the source is off. It shows the comparison of the hit efficiency for the front-end threshold values of 20 mV and 30 mV at the end of the irradiation period. The DT auto trigger was used for cosmic muon tracks, identifying a track in both projections on SL2 and SL3 of the DT chamber, avoiding any bias on the layers irradiated with HV on. The integrated luminosity, 4400 fb-1, corresponds to the integrated luminosity expected for the MB1 chambers in the external wheels of the CMS detector (YB+/-2) during the HL-LHC.
[5] Hit efficiency for cosmic muons as a function of instantaneous luminosity for the aged layers (SL1L1 and SL1L4) at 3550 V and for SL1L3 (reference) at 3600 V at a front-end threshold of 20 mV. The DT auto trigger was used for cosmic muon tracks, identifying a track in both projections on SL2 and SL3 of the DT chamber, avoiding any bias on the layers irradiated with HV on. There are three series of datasets each corresponding to a different integrated luminosity. The integrated luminosity used in these studies corresponds to the integrated luminosity expected for the MB1 chambers in the external wheels of the CMS detector (YB+/-2) during the HL-LHC.

[6] Hit efficiency for test beam muons as a function of instantaneous luminosity for the aged layers (SL1L1 and SL1L4) at 3550 V and for SL1L3 (non-aged) at 3600 V at a front-end threshold of 20 mV. The external trigger scintillators were used for muon tracks, identifying a track in both projections on SL2 and SL3 of the DT chamber in coincidence with the scintillators, avoiding any bias on the layers irradiated with HV on. The test beam was performed after an irradiation integrated dose equivalent to an HL-LHC integrated luminosity of 2800 fb-1.
[7] Hit efficiency for test beam muons as a function of instantaneous luminosity for the aged layers (SL1L1 and SL1L4) at 3550 V at a front-end threshold of 20 mV. The external trigger scintillators were used for muon tracks, identifying a track in both projections on SL2 and SL3 of the DT chamber in coincidence with the scintillators, avoiding any bias on the layers irradiated with HV on. The test beam was performed after an irradiation integrated dose equivalent to an HL-LHC integrated luminosity of 2800 fb-1. An exponential is used to fit the hit efficiency of SL1L1 and SL1L4 layers resulting in:
* for SL1L1
* for SL1L4.
[8] Normalized Current for aged (SL1L1 and SL1L4 ) and non-aged (SL1L3) layers at 3550 V. The normalized current is defined as the ratio between the instantaneous current and the instantaneous dose. Values are scaled with respect to the initial value measured in SL1L3. Currents are corrected for the measured pressure in the bunker. Each of the points in this plot corresponds to the mean current of reading along a day. Gaps are caused by the loss of monitoring. The integrated luminosity used in these studies corresponds to the integrated luminosity expected for the MB1 chambers in the external wheels of the CMS detector (YB+/-2) during the HL-LHC.

[9] Hit efficiencies of layer 4 of SL1 as a function of the track angle in the "theta" wires plane in cosmic events recorded with the chamber internal trigger. Tracks with a larger angle have a larger path along the wire, then have a larger primary ionization and a larger probability to drift to the anode wire and to produce a signal above the FrontEnd threshold. The effect is more relevant when the high voltage is below the plateau efficiency (as shown here, 3400 V) or when, for other reasons as aging effects, the anode amplification is low. In the plot the range of the polar angle of the MB1 station in the different wheels of CMS is reported. The dependence of the hit efficiency on the angle between the track and the wire direction has been studied using a special collision run taken at P5 with reduced HV. The results are shown in [2] . [2] Approved plot reference GMM04/11/2019 F.Cavallo].

[10] Hit efficiency for cosmic muons as a function of integrated luminosity for the aged layer SL1L1 taken with the source on at a background rate similar to the expected background rate at the HL-LHC (corresponding to an instantaneous luminosity of 4.45x1034 cm-2s-1) at 3550 V and at a front-end threshold of 20 mV. The data are fitted using an exponential model, . The DT auto trigger was used for cosmic muon tracks, identifying a track in both projections on SL2 and SL3 of the DT chamber, avoiding any bias on the layers irradiated with HV on. The integrated luminosity corresponds to the integrated luminosity expected for the MB1 chambers in the external wheels of the CMS detector (YB+/-2) during the HL-LHC.
[11] Expected 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 (10x1034 cm-2s-1) and a safety factor of 2 for the expected integrated luminosity (2*3000 fb-1) and taking into account the angular effect of prompt muon tracks and the expected integrated charge at the end of HL-LHC in each chamber. For the MB1 chambers in wheels ±2 the increase of 30% of the background rate, shown by the preliminary Fluka simulation comparing 2019 to 2018 geometry, has been included.
[12] Expected hit efficiencies at 1/3 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 (10x1034 cm-2s-1) and a safety factor of 2 for the expected integrated luminosity (2*1000 fb-1) and taking into account the angular effect of prompt muon tracks and the expected integrated charge at the end of HL-LHC in each chamber. For the MB1 chambers in wheels ±2 the increase of 30% of the background rate, as shown by the preliminary Fluka simulation comparing 2019 to 2018 geometry, has been included.
[13] Hit efficiency for test beam muons as a function of instantaneous dose for the aged layers (SL1L1 and SL1L4) at 3550 V at a front-end threshold of 20 mV. The external trigger scintillators were used for muon tracks, identifying a track in both projections on SL2 and SL3 of the DT chamber in coincidence with the scintillators, avoiding any bias on the layers irradiated with HV on. The test beam was performed after an irradiation integrated dose of 1500 mGy. An exponential is used to fit the hit efficiency of SL1L1 and SL1L4 layers resulting in:
* for SL1L1
* for SL1L4.
[14] Hit efficiency for cosmic muons as a function of integrated dose for the irradiated layer SL1L1 taken with the source on at a background rate slightly higher than the expected background rate at the HL-LHC (corresponding to a instantaneous dose of 0.063 mGy/h) at 3550 V and at a front-end threshold of 20 mV. The data are fitted using an exponential model, . The DT auto trigger was used for cosmic muon tracks, identifying a track in both projections on SL2 and SL3 of the DT chamber, avoiding any bias on the layers irradiated with HV on.
[15] Hit efficiency for cosmic muons as a function of instantaneous luminosity for the irradiated New wires in SL1L1 layer at 3550 V and SL1L3 non-aged wires at 3600 V at a front-end threshold of 20 mV. The DT auto trigger was used for cosmic muon tracks, identifying a track in both projections on SL2 and SL3 of the DT chamber, avoiding any bias on the layers irradiated with HV on. Colors refer to measurements performed at different integrated luminosity; their values correspond to the integrated luminosity expected for the MB1 chambers in the external wheels of the CMS detector (YB+/-2) during the HL-LHC. For the new wires there is no degradation of the hit efficiency: the similar values are measured at different integrated and instantaneous luminosities.
[16] Hit efficiency for cosmic muons as a function of instantaneous luminosity for the old wires in SL1L1 layer at 3550 V at a front-end threshold of 20 mV. The DT auto trigger was used for cosmic muon tracks, identifying a track in both projections on SL2 and SL3 of the DT chamber, avoiding any bias on the layers irradiated with HV on. The integrated luminosity used in these studies corresponds to the integrated luminosity expected for the MB1 chambers in the external wheels of the CMS detector (YB+/-2) during the HL-LHC. For the SL1L1 and SL1L4 aged wires on eras A and B there is a degradation of the hit efficiency at different instantaneous luminosities which increases with the integrated luminosity.
[17] Normalized current for the wires of layers irradiated all along the irradiation test (SL1L1 and SL1L4) and for the New Wires in SL1L1 layer, all at 3550 V. The normalized current is defined as the ratio between the instantaneous current and the current measured in SL1L3 layer, a non-aged layer. Currents are corrected for the measured pressure in the bunker. Each of the points in this plot corresponds to the mean current of reading along a day. Gaps are caused by the loss of monitoring. The normalized current of the new wires is shown as well. The integrated luminosity used in these studies corresponds to the integrated luminosity expected for the MB1 chambers in the external wheels of the CMS detector (YB+/-2) during the HL-LHC.

-- FrancescaCavallo - 2019-11-08

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