Neutron Background and GIF++ Test Beam Studies in CMS CSCs

NEW Page created December 8, 2017

This twiki page contains the plots in CMS DP-2017/025, which summarizes neutron background studies in 2016H CMS data and 2016 GIF++ muon test beam studies in the context of HL-LHC. Clicking on a small image will open a full-size PNG. If a PDF version of a plot is available, click the pdf version link at the top of the image to display or download it (web-browser dependent).

Abstract

Among the many challenges to be brought by the high luminosities of the HL-LHC is the impact of increased hit rates in the cathode strip chambers of the CMS endcap muon system. These chambers are used for all levels of trigger as well as offline reconstruction. Neutrons (both fast and thermal) induce background hits via nuclear interactions and capture, followed by gamma emission and (mainly) Compton scatter off electrons that subsequently ionize the chamber gas. This note describes recent efforts to improve the understanding of such neutron-induced background through detailed comparison of CMS pp collision data, Geant4 simulation, and the response of CMS detectors placed in the CERN high-intensity gamma irradiation facility, GIF++. Projections for the effect of such neutron-induced background hits on trigger and reconstruction at the HL-LHC are described.

Contacts

CMS DPG conveners of the Muon subdetectors

subdetector email
Muon DPG Office cms-muon-DPGO@cernNOSPAMPLEASE.ch
RPC cms-dpg-conveners-rpc@cernNOSPAMPLEASE.ch
DT cms-dpg-conveners-dt@cernNOSPAMPLEASE.ch
CSC cms-dpg-conveners-csc@cernNOSPAMPLEASE.ch

References

This is the link to CMS DP-2017/025

This is the public link to the EPS HEP 2017 (Venice) poster contribution using these plots

This is the public link to the APS DPF 2017 (Fermilab) parallel talk using these plots

Plots

Figure Caption
pdf version
Eff 21 LCTScint L1A.png

LCT Efficiency vs. Anode Wire Current for ME2/1 at GIF++

The data shown were collected during a muon test beam at the CERN Gamma Irradiation Facility (GIF++) with a CMS endcap cathode strip chamber (CSC) from the inner ring of the second station of the CMS endcap muon system (ME2/1). The chamber anode current changes when the 13.9 TBq 137Cs gamma irradiation source intensity is varied. Plotted is trigger primitive efficiency relative to the efficiency at zero current (irradiation source turned off), because the overall setup did not lend itself to understanding an absolute trigger efficiency. Trigger primitive efficiency is defined as the number of triggers that resulted in the creation of a trigger primitive, divided by the number of triggers received. Trigger primitives are created within the area shadowed by a scintillator mounted near the chamber whose coincidence with two other scintillators upstream and downstream of the test beam provides the trigger. Here, a trigger primitive is a set of correlated digitizations of detector responses that are used in the CMS muon trigger. A decrease in the number of trigger primitives constructed is observed.

pdf version
ED GIF 3384 ME21 9.png

CSC Trigger Primitive Event Display for ME2/1 at GIF++

Display showing an event collected during a muon test beam at the CERN Gamma Irradiation Facility (GIF++) with a CMS endcap cathode strip chamber (CSC) from the inner ring of the second station of the CMS endcap muon system (ME2/1). Display shows digitized detector responses: anode wire (η-coordinate) responses (wire group hits), cathode half-strip (φ-coordinate) responses (comparator half-strip hits), and cathode strip analog-to-digital-converter (ADC) counts proportional to deposited charge. Each display is organized by the gas gap layer and the strip or wire number in which the response occurred. In the plot, A represents the attenuating factor applied to the 13.9 TBq 137Cs gamma irradiation source and I is the chamber anode wire current. This display illustrates a mechanism by which a photon-induced hit can displace a muon hit; the large amount of deposited charge seen at the left edge of the ADC counts resulted in a corresponding shifted comparator hit.

pdf version
RH GIF 3384 ME21 9.png

CSC RecHit Event Display for ME2/1 at GIF++

Display showing an event collected during a muon test beam at the CERN Gamma Irradiation Facility (GIF++) with a CMS endcap cathode strip chamber (CSC) from the inner ring of the second station of the CMS endcap muon system (ME2/1). Display shows offline reconstructed detector responses (RecHits), projected along the anode wire axis and the cathode strip axis (black dots). Blue lines indicate the offline reconstructed muon segment created by a straight-line fit to the red highlighted RecHits. In the plot, A represents the attenuating factor applied to the 13.9 TBq 137Cs gamma irradiation source and I is the chamber anode wire current. This display illustrates a mechanism by which a photon-induced hit can displace a muon hit; the reconstructed hit in layer 3 was displaced by a photon and subsequently excluded from the segment fit.

pdf version
SegNHitsFrac ME21 all.png

Segment Hit Multiplicity Fractions for ME2/1 at GIF++

Fraction of offline reconstructed muon segments, categorized by the number of reconstructed hits used to form them, vs. chamber anode current, which changes when the 13.9 TBq 137Cs gamma irradiation source intensity is varied. The data were collected during a muon test beam at the CERN Gamma Irradiation Facility (GIF++) with a CMS endcap cathode strip chamber (CSC) from the inner ring of the second station of the CMS endcap muon system (ME2/1). As the source intensity is increased, the fraction of good quality 6 hit segments decreases, while the fraction of lower quality 3 hit segments increases.

pdf version
LastEvsTOF.png

Final Simulated Neutron Energy vs. Time since pp Collision of SimHit

Final energy of simulated neutron vs. the time since pp collision of simulated detector hit for hits in CMS endcap muon cathode strip chambers (CSC). Hits are induced by electrons which are produced from photons which are produced from thermal or resonant neutron capture or from neutron inelastic scattering. Red dots indicate simulated hits induced by thermal and resonant neutron captures and blue dots indicate simulated hits induced by neutron inelastic scatters. Plot is made with Geant4 simulated minimum-bias proton-proton collisions at 13 TeV using the High Precision (HP) neutron interaction cross section library and the 2015 CMS simulated geometry.

pdf version
neut gamma proc energy.png

Production Processes for SimHit Electrons from Neutron-Induced Photons

Stacked histogram of the final energy of simulated photons at the time they produce simulated electrons that lead to simulated detector hits. The photons are categorized by the process by which the electrons were created or scattered. Plot is made with Geant4 simulated minimum-bias proton-proton collisions at 13 TeV using the High Precision (HP) neutron interaction cross section library and the 2015 CMS simulated geometry. The most common process by which electrons that eventually lead to simulated hits are formed is Compton scattering.

pdf version
BXstructure.png

LHC Bunch Crossing Occupancy

Histogram of bunch crossing number in a particular CMS data taking period during LHC proton-proton collisions in 2016, showing the gaps of various sizes in the LHC bunch structure.

pdf version
Rainbow wire 11.png

ME1/1 Anode Wire Group Occupancy as a function of Bunch Crossing and Time Bin

2D histogram of number of anode wire hits from CMS endcap cathode strip chambers (CSC) in the inner ring of the first station of the CMS endcap muon system, in CMS data collected during LHC proton-proton collisions taken during 2016. The histogram is plotted as a function of number of bunch crossings (BX) after an LHC bunch gap of at least 35 BX in bunch trains that are exactly 48 BX in length. vs. chamber readout time bin. Each time bin and BX correspond to a 25 ns time window. Hits in the lower left triangle occur at the end of an LHC bunch gap and predominantly come from thermal neutron captures. Hits in the middle boxed region are hits in BX where readout time bins are within bunch trains and from thermal neutron captures and fast neutrons, as well as prompt hits from pp collisions in other BX. Hits in the upper right triangle are hits that occur at the beginning of the next LHC bunch gap and are a mix of hits caused by fast neutrons and thermal neutron captures. The hits in readout time bin 0 contain hits from the previous bunch crossing due to the length of electronic pulses and are therefore not considered. Readout time bin 8 is in time with the triggering muon.

pdf version
occupancy 21 wire early AREA TIME PP XS ThermalON.png

ME2/1 Anode Wire Group Occupancy for CMS Data and XS MC Simulation

Histogram of candidate thermal-neutron induced anode wire hits for CMS data collected during LHC proton-proton collisions in 2016 by the inner ring of the second station (ME2/1) of the CMS endcap muon cathode strip chambers. CMS data are compared to the Geant4 High Precision (HP) and XS neutron interaction cross section libraries in a specially configured simulation intended to simulate neutrons in minimum-bias proton-proton collisions at 13 TeV using the 2015 CMS simulated geometry.

pdf version
occupancy 21 wire early AREA TIME PP HP ThermalON.png

ME2/1 Anode Wire Group Occupancy for CMS Data and HP MC Simulation

Histogram of candidate thermal-neutron induced anode wire hits for CMS data collected during LHC proton-proton collisions in 2016 by the inner ring of the second station (ME2/1) of the CMS endcap muon cathode strip chambers. CMS data are compared to the Geant4 High Precision (HP) and XS neutron interaction cross section libraries in a specially configured simulation intended to simulate neutrons in minimum-bias proton-proton collisions at 13 TeV using the 2015 CMS simulated geometry.

pdf version
BGPatterns P5.png

Neutron-Induced Background Hit Cluster Patterns in CMS Data

Candidate thermal neutron induced pattern spectrum in CMS data collected during LHC proton-proton collisions in 2016 by the CMS endcap muon cathode strip chambers (CSC). For each 3×3 pattern, cathode half-strips in the CSC are represented horizontally and layers in the CSC are represented vertically. The red boxes in a pattern indicate the presence of a candidate thermal neutron induced hit in a cathode half-strip and layer. For example, three boxes stacked on top of each other represents a hit pattern where neutrons induce hits on the same cathode half-strip on three consecutive layers and two adjacent boxes represents a hit pattern where there were hits on adjacent cathode half-strips on the same layer. The shaded patterns are suppressed by CSC firmware electronics.

pdf version
BGPatterns MC.png

Neutron-Induced Background Hit Cluster Patterns in MC Simulation

Candidate thermal neutron induced pattern spectrum in Geant4 simulated minimum-bias proton-proton collisions at 13 TeV using the High Precision (HP) neutron interaction cross section library and the 2015 CMS simulated geometry in simulated CMS endcap muon cathode strip chambers (CSC). For each 3×3 pattern, cathode half-strips in the CSC are represented horizontally and layers in the CSC are represented vertically. The red boxes in a pattern indicate the presence of a candidate thermal neutron induced hit in a cathode half-strip and layer. For example, three boxes stacked on top of each other represents a hit pattern where neutrons induce hits on the same cathode half-strip on three consecutive layers and two adjacent boxes represents a hit pattern where there were hits on adjacent cathode half-strips on the same layer. The shaded patterns are suppressed by CSC firmware electronics.

-- AbhigyanDasgupta - 2017-12-08

Topic attachments
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PDFpdf BGPatterns_MC.pdf r1 manage 15.0 K 2017-12-07 - 17:32 AbhigyanDasgupta  
PNGpng BGPatterns_MC.png r1 manage 331.7 K 2017-12-07 - 17:32 AbhigyanDasgupta  
PDFpdf BGPatterns_P5.pdf r1 manage 15.0 K 2017-12-07 - 17:32 AbhigyanDasgupta  
PNGpng BGPatterns_P5.png r1 manage 339.0 K 2017-12-07 - 17:32 AbhigyanDasgupta  
PDFpdf BXstructure.pdf r1 manage 151.0 K 2017-12-07 - 17:32 AbhigyanDasgupta  
PNGpng BXstructure.png r1 manage 559.6 K 2017-12-07 - 17:32 AbhigyanDasgupta  
PDFpdf ED_GIF_3384_ME21_9.pdf r1 manage 165.1 K 2017-12-07 - 17:32 AbhigyanDasgupta  
PNGpng ED_GIF_3384_ME21_9.png r1 manage 1496.6 K 2017-12-07 - 17:32 AbhigyanDasgupta  
PDFpdf Eff_21_LCTScint_L1A.pdf r1 manage 132.9 K 2017-12-07 - 17:32 AbhigyanDasgupta  
PNGpng Eff_21_LCTScint_L1A.png r1 manage 502.4 K 2017-12-07 - 17:32 AbhigyanDasgupta  
PDFpdf LastEvsTOF.pdf r1 manage 163.5 K 2017-12-07 - 17:33 AbhigyanDasgupta  
PNGpng LastEvsTOF.png r1 manage 764.9 K 2017-12-07 - 17:33 AbhigyanDasgupta  
PDFpdf RH_GIF_3384_ME21_9.pdf r1 manage 141.4 K 2017-12-07 - 17:33 AbhigyanDasgupta  
PNGpng RH_GIF_3384_ME21_9.png r1 manage 562.7 K 2017-12-07 - 17:33 AbhigyanDasgupta  
PDFpdf Rainbow_wire_11.pdf r1 manage 140.7 K 2017-12-07 - 17:33 AbhigyanDasgupta  
PNGpng Rainbow_wire_11.png r1 manage 958.8 K 2017-12-07 - 17:33 AbhigyanDasgupta  
PDFpdf SegNHitsFrac_ME21_all.pdf r1 manage 136.6 K 2017-12-07 - 17:33 AbhigyanDasgupta  
PNGpng SegNHitsFrac_ME21_all.png r1 manage 977.9 K 2017-12-07 - 17:33 AbhigyanDasgupta  
PDFpdf neut_gamma_proc_energy.pdf r2 r1 manage 14.6 K 2017-12-08 - 14:13 AbhigyanDasgupta  
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PDFpdf occupancy_21_wire_early_AREA_TIME_PP_HP_ThermalON.pdf r1 manage 53.0 K 2017-12-07 - 17:33 AbhigyanDasgupta  
PNGpng occupancy_21_wire_early_AREA_TIME_PP_HP_ThermalON.png r1 manage 868.3 K 2017-12-07 - 17:33 AbhigyanDasgupta  
PDFpdf occupancy_21_wire_early_AREA_TIME_PP_XS_ThermalON.pdf r1 manage 53.0 K 2017-12-07 - 17:33 AbhigyanDasgupta  
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