-- RoumyanaHadjiiska - 2019-07-03

RPC Performance results for 2018

Intro - RPC Geometry

CMS quadrant plot: The Barrel RPC system consists of 5 wheels, and a wheel consists of 4 muon stations (RB1, RB2, RB3 and RB4) at increasing radius (R) and is divided in 12 sectors in φ. A station consists of 2 layers in the inner two stations: RB1in, RB1out, RB2in and RB2out and a single layer in RB3 and RB4. The RPC system has two endcaps: negative and positive, according to the z-coordinate of CMS. Each endcap consists of 4 stations (RE±1-4, the so-called disks) installed on the iron endcap yokes. Each stations in the Endcap consists of 3 rings. RPCs are installed on the second and third ring. Each of them consists of 36 chambers. Depend on its position, every RPC chamber is subdivided in two or three eta partitions, called rolls. More about RPC geometry might be found in [1]. pdf file.

RPC Run-2 Performance History Plots

RPC performance results and history for Run-2, obtained with Tag and Probe method with tracker extrapolation, exploring single muon triggered dataset. Probe muons are reconstructed using the tracker muon algorithm which is independent to RPC system, equiring at least one segment to be matched in local x position within 3 cm and pull ≤ 3. Probe muons are also required to have at least 10 GeV in transverse momentum. More about the method might be found in [2].

Gas history:

RPC – Isobutane history [2]. As it is shown on the plot, in 2016 the Isobutane concentration in the RPC gas working mixture was higher because of mass flow controller problem. The two red lines on the plot mark the limits for optimal performance of the CMS RPCs. With green color is given the Isobutane concentration from the mixer. The gas coming from the system before purifier 2 is shown with red color. The blue dots represent the gas going back to RPCs. In 2016, because of higher Isobutane concentration (5.3%), efficiency was lower as the HV working points (WP) were not changed to compensate the wrong gas mixture. After the deployment of the new WP in September 2016, the efficiency increased by ~1% and cluster size increased sharply. Gas concentration was back at 4.5 % in 2017 but the WP were not changed. The efficiency of the system remained unchanged (running in the plateau of the sigmoid curve), however a new increase of the cluster size have been observed. New WP have been deployed by end of 2017, which lead to a slight decrease of the efficiency but sensible reduction of the cluster size [2].

Figures

Overall performance

RPC overall efficiency distributions: Overall efficiency distribution of RPC rolls during the LHC Run-2 (2015-2018) for barrel (left) and endcap (right) region. The underflow entries are from rolls with efficiency lower than 70%, caused by known hardware problems - threshold control, chambers switched off because of the gas leak problems. The numbers given on the plots show the average efficiency for the well performing and the fraction of the problematic RPC rolls. The RPC efficiencies measured in 2015-2018 are comparable and in agreement with the expectations. Contact: cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch

Efficiency and Cluster size history during Run-2 vs Time

RPC efficiency and cluster size history vs time for the four barrel stations: Each point corresponds to an average efficiency or cluster size per station in a given LHC fill. Data points with low statistics or temporary problems are excluded from the distributions. The x-axis is a date and the y-axis - average efficiency or cluster size for the detector part under study. Grey lines and areas correspond to the planned technical stops (TS) and year end technical stops (YETS). The efficiency and cluster size history follow the changes of the applied high voltage working points and changes of the Isobutane concentration in the working gas mixture. The drop of the efficiency during 01. Aug. 2018 - 19. Aug.2018 is caused by a known configuration setting problem. Contact: cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch

RPC efficiency and cluster size history vs time for the four stations in the positive endcap: Each point corresponds to an average efficiency or cluster size per station in a given LHC fill. Data points with low statistics or temporary problems are excluded from the distributions. The x-axis is a date and the y-axis - average efficiency or cluster size for the detector part under study. Grey lines and areas correspond to the planned technical stops (TS) and year end technical stops (YETS). The efficiency and cluster size history follow the changes of the applied high voltage working points and changes of the Isobutane concentration in the working gas mixture. The spread in 2015 cluster size distribution is caused by a threshold control problems, solved in October 2015. Small drop of the RE+4 cluster size in 2016 is caused of a temporary LV problem, solved in the end of August 2016. The drop of the efficiency during 01. Aug. 2018 - 19. Aug.2018 is caused by a known configuration setting problem. Contact: cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch

RPC efficiency and cluster size history vs time for the four stations in the negative endcap: Each point corresponds to an average efficiency or cluster size per station in a given LHC fill. Data points with low statistics or temporary problems are excluded from the distributions. The x-axis is a date and the y-axis - average efficiency or cluster size for the detector part under study. Grey lines and areas correspond to the planned technical stops (TS) and year end technical stops (YETS). The efficiency and cluster size history follow the changes of the applied high voltage working points and changes of the Isobutane concentration in the working gas mixture. The spread in 2015 cluster size distribution is caused by a threshold control problems, solved in October 2015. Small drop of the RE-4 cluster size in 2016 is caused of a temporary LV problem, solved in the end of August 2016. The drop of the efficiency during 01. Aug. 2018 - 19. Aug.2018 is caused by a known configuration setting problem. Contact: cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch

Efficiency and Cluster size history vs Integrated luminosity

RPC efficiency and cluster size history vs integrated luminosity for the four barrel stations: The plots represent Run-2 history. (Run-1 integrated luminosity is 27 fb-1). Each point corresponds to an average efficiency or cluster size per station in a given LHC fill. Data points with low statistics or temporary problems are excluded from the distributions. The x-axis shows the integrated luminosity a date and the y-axis - average efficiency or cluster size for the detector part under study. Red lines are the planned technical stops (TS) and the grey ones - year end technical stops (YETS). The trend of the curves follows the changes of the applied high voltage working points and changes of the Isobutane concentration in the working gas mixture. The drop of the efficiency during 01. Aug. 2018 - 19. Aug.2018 is caused by a known configuration setting problem. Contact: cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch

RPC efficiency and cluster size history vs integrated luminosity for the four stations in the positive endcap: The plots represent Run-2 history. (Run-1 integrated luminosity is 27 fb-1). Each point corresponds to an average efficiency or cluster size per station in a given LHC fill. Data points with low statistics or temporary problems are excluded from the distributions. The x-axis shows the integrated luminosity a date and the y-axis - average efficiency or cluster size for the detector part under study. Red lines are the planned technical stops (TS) and the grey ones - year end technical stops (YETS). The trend of the curves follows the changes of the applied high voltage working points and changes of the Isobutane concentration in the working gas mixture and are well understood. The drop of the efficiency and cluster size during 01. Aug. 2018 - 19. Aug.2018 is caused by a known configuration setting problem. Contact: cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch

RPC efficiency and cluster size history vs integrated luminosity for the four stations in the negative endcap: The plots represent Run-2 history. (Run-1 integrated luminosity is 27 fb-1). Each point corresponds to an average efficiency or cluster size per station in a given LHC fill. Data points with low statistics or temporary problems are excluded from the distributions. The x-axis shows the integrated luminosity a date and the y-axis - average efficiency or cluster size for the detector part under study. Red lines are the planned technical stops (TS) and the grey ones - year end technical stops (YETS). The trend of the curves follows the changes of the applied high voltage working points and changes of the Isobutane concentration in the working gas mixture and are well understood. The drop of the efficiency and cluster size during 01. Aug. 2018 - 19. Aug.2018 is caused by a known configuration setting problem. Contact: cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch

RPC Background Plots

Hit Rate Definition

Figures

Background radiation in the CMS muon system is an important factor in the performance monitoring and longevity studies of the detectors. A clear understanding of the background plays a crucial role not only on the performance of the existing muon system, but also in the design and preparation for the upgraded detector for the HL-LHC. The RPC hit rate is measured at the strip level during LHC pp collision runs. The strip rate is calculated by using the incremental counts of the RPC trigger Link Boards. The incremental counts are taken during typical time intervals of order of 100 s. The resulting rates are then averaged over the total runtime and normalized to the strip area. The instantaneous luminosity is averaged over the same runtime. Normalized rates in Hz/cm2 are presented. No trigger selection is applied at this stage, resulting in an inclusive measurement of the radiation background rates [3, 4].

RPC hit rate vs instantaneous luminosity: The RPC hit rate vs instantaneous luminosity distributions for the RPC Barrel wheels (on the left) and layers (on the right), are shown on the plots. Results obtained with 2018 proton-proton collision data (after TS2). Selected runs with stable beams and number of colliding bunches > 600. Luminosity values provided by the oficial CMS luminosity tool, mean rate values are defined as the average rate on all the rolls in the corresponding wheel or layer. Contact: cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch

RPC hit rate vs instantaneous luminosity: The RPC hit rate vs instantaneous luminosity distributions for the RPC Endcap stations are shown on the plots. Results obtained with 2018 proton-proton collision data (after TS2). Selected runs with stable beams and number of colliding bunches > 600. Luminosity values provided by the oficial CMS luminosity tool, mean rate values are defined as the average rate on all the rolls in the corresponding station. Contact: cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch

RPC Hit Rates - φ distribution in Endcaps at L=1.5x1034cm-2s-1: The RPC hit rates at instantaneous luminosity of 1.5x1034cm-2s-1 have been evaluated from the linear dependence of the rate on the instantaneous luminosity. The plots represent the φ distributions of the rate measured in the endcap chambers. Contact: cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch

RPC Hit Rates - φ distribution in Endcaps at L=5x1034cm-2s-1: The plots represent the φ distributions of the rate in the endcap chambers. The RPC hit rates at instantaneous luminosity of 5x1034cm-2s-1 have been evaluated from the linear dependence of the rate on the instantaneous luminosity and extrapolation to the HL-LHC. Contact: cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch

RPC hit rate as a function of pseudorapidity (η)

Common information: CMS explores cylindrical geometry conception and it is worth to recoil that pseudorapidity is a function both on the radius (distance to the beam pipe) and Z (distance from the interaction point along the beam pipe). In the barrel the RPC hit rate is averaged in φ for all the chambers of a given layer (same R) in a given wheel (same Z), while in the endcap the rate is averaged over all the 36 RPC rolls (η partitions) from a given ring (same R) at a given station (same Z). The pseudorapidity values correspond to the middle of the considered η partition. The rates at instantaneous luminosity of 1.5x10³⁴cm^-2s^-1 are taken from the fit of the linear dependence of the rate on the instantaneous luminosity. The values at 5x10³⁴cm^-2s^-1 are obtained after the extrapolation of the linear fit.

Figures

RPC hit rate vs η: The plots show an overlay of the inner and outer layers of the first (on the left) and second (on the right) barrel stations and the rates measured in the first and second endcap stations, respectively. In the overlap region (0.8 < |η| < 1.1) the fist endcap chambers are installed at larger radius comparing to the barrel ones, which is a reason for the measured lower rate in the first endcap station. The rates measured in the barrel layers of the first (RB1in and RB1out) and second (RB2in and RB2out) stations are comparable. Because of these, an average values of them is taken for the rest of the studies. C file RB1 and RE1, gif file RB1 and RE1, pdf file RB1 and RE1, png file RB1 and RE1, root file RB1 and RE1; C file RB2 and RE2, gif file RB2 and RE2, pdf file RB2 and RE2, png file RB2 and RE2, root file RB2 and RE2. Contact: cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch

RPC hit rate vs η at inst. luminosity 1.5x1034cm-2s-1: The full markers show the rates in the barrel, while the empty ones - in the endcap. The upper plots show the average of the sub-layers within the first and second barrel (RB1 and RB2) and endcap (RE1 and RE2) stations. The plots at the bottom show the distributions of the third (RB3 and RE3) and fourth (RB4 and RE4) stations. C file for all system, gif file for all system, pdf file for all system, png file for all system, root file for all system. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

RPC hit rate vs η at inst. luminosity 5x1034cm-2s-1: The full markers show the rates in the barrel, while the empty ones - in the endcap. The upper plots show the average of the sub-layers within the first and second barrel (RB1 and RB2) and endcap (RE1 and RE2) stations. The plots at the bottom show the distributions of the third (RB3 and RE3) and fourth (RB4 and RE4) stations. C file for all system, gif file for all system, pdf file for all system, png file for all system, root file for all system. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

RPC Hit Rates vs Fluka Simulation: pseudorapidity (η) distribution

Particle fluxes obtained from MC studies with Fluka, have been convoluted with the RPC sensitivities (estimated with a standalone GEANT4 simulation) to a given particle types. Sensitivities used in this study are as follow: neutrons: 0.26 % ±0.03 %; gammas: 1.6 %±0.2 %; e+e-: 35 % ±16 %. The obtained distributions have been compared to the experimentally measured ones. The comparison shows good agreement between the MC and the experimentally measured values in the barrel and small difference in the endcap part up to the factor of 2. Nevertheless the distributions show coherent trends.

Figures

RPC Hit Rates vs Fluka Simulation: η distribution at inst. luminosity 1.5x1034cm-2s-1. The plots represent a comparison between the experimentally measured RPC hit rates (in blue) and the rates predicted by FLUKA (in red). The full markers correspond to the barrel part, while the empty ones - to the endcap. The plots show a good agreement between the experimentally obtained results and MC predicted ones. C file 4 RPC sections, gif file 4 RPC sections, pdf file 4 RPC sections, png file 4 RPC sections, root file 4 RPC sections. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

RPC Hit Rates vs Fluka Simulation: η distribution at inst. luminosity 1.5x1034cm-2s-1. The plots represent a comparison between the experimentally measured RPC hit rates (in blue) and the rates predicted by FLUKA (in red) for the first and second endcap stations, respectively. In the overlap region (0.8 < |η| < 1.1) the fist endcap chambers are installed at larger radius comparing to the barrel ones, which is a reason for the measured lower rate in the first endcap station. The plots show a good agreement between the experimentally obtained results and MC predicted ones. C file RPC Layer 1, gif file RPC Layer 1, pdf file RPC Layer 1, png file RPC Layer 1, root file RPC Layer 1; C file RPC Layer 2, gif file RPC Layer 2, pdf file RPC Layer 2, png file RPC Layer 2, root file RPC Layer 2. Contact: cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch

References

[1] CMS Collaboration, RPC Performance Results for 2016, CMS-DP-2017-053; CERN-CMS-DP-2017-053

[2] RPC Detector Performance Results for 2016 and 2017, CMS-DP-2018-001 ; CERN-CMS-DP-2018-001

[3] R.I. Rabadan-Trejo et al., Long-term performance and longevity studies ofthe CMS Resistive Plate Chambers,2018 JINST13 P08024

[4] S. Costantini et al., Radiation background with the CMS RPCs at theLHC, 2015 JINST10 C05031