GEM Detector for CMS Upgrade Imran Awan ICTPNCP

GEM Detector for CMS Upgrade Imran Awan ICTP-NCP School on LHC Physics Islamabad, Pakistan November 24, 2014

Introduction § § § § Large Hadron Collider Compact Muon Solenoid The Muon System Upgrade and high eta region Trigger motivation GEM detector Redundancy Study Summary 11/24/2014 ICTP-NCP School on LHC Physics 2

LHC Injection Chain 7 Te. V Protons 11/24/2014 7 Te. V Protons ICTP-NCP School on LHC Physics 3

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LHC Upgrade q Currently protons are not accelerated to their full energy. q LHC accelerated protons at 4 Te. V uptil now. q In Upcoming years LHC will be upgraded to higher luminosities 11/24/2014 ICTP-NCP School on LHC Physics 5

The CMS Muon System Three different Technologies All are Gaseous q Drift Tubes (Barrel, |η|1. 2) q CSC (Endcap, 1<|η|<2. 4) q RPC (Barrel + Endcap, |η|1. 6) Post: LS 2 Proposed GE 1/1 Station |η|>1. 6 has least redundancy and highest rates During LHC run 1, the inclusive muon trigger covered the region upto |η|=2. 4 with typical threshold of PT ~ 20 -25 Ge. V. Several analysis excluded the region between 2. 1 and 2. 4 to avoid misreconstructed muons. 11/24/2014 ICTP-NCP School on LHC Physics 6

Forward Region High |η|>1. 6 q Background particles rates are highest. Could be MHz/cm 2 q Bending in the magnetic field is the lowest q This leads to reduced resolution and longevity issues At Present, high η region is entirely based on the CSC 11/24/2014 ICTP-NCP School on LHC Physics 7

Ø A sufficient gas gain for detecting minimum ionizing particles can be obtained by using one GEM foil or cascading several GEM foils Ø Each foil perforated with bi conical holes is kapton sheet with copper coated on both sides COMPASS PHENIX STAR TOTEM LHCb 11/24/2014 Experiments have used GEM ICTP-NCP School on LHC Physics 8

Triple GEMs for CMS q Restore redundancy at high |η| upto 2. 2 q Enhance and optimize the readout (η, φ) granularity q Rate Capability: 105 Hz / cm 2 q Spatial / Time Resolution: 100µm / 4 -5 ns q Efficiency ≈ 98% q Gas Mixture: Ar-CO 2 -CF 4 (non-flammable mixture) 11/24/2014 ICTP-NCP School on LHC Physics 9

Trigger Motivation Adding GE 1/1 chambers with ME 1/1 significantly increase the lever arm and allow for a good separation of soft and harder muons with CSC+GEM A large trigger reduction is achievable when measuring the bending angle in the forward region 11/24/2014 ICTP-NCP School on LHC Physics 10

Trigger Motivation q PT mismeasurement and multiple scattering in the iron yoke contribute fake triggers to the high PT tail of the single muon trigger rate (Red) thus requiring to increase threshold with the allocated band width. q Considerably lower fake contribution, reduce the trigger rate which allows to lower the trigger threshold. q For some physics channels, such as H 2 Tau, a trigger threshold of about 15 Ge. V nearly doubles the sensitivity since the muons from the subsequent Tau decays are of low-medium PT and are strongly affected by the trigger threshold. 11/24/2014 ICTP-NCP School on LHC Physics 11

Physics Performance q For many signatures, such as H 4 Mu and H 2 Tau, about 20% of the events have one or more final state muons in the GE 1/1 instrumented region. q Those events would be lost if the existing CSC chambers malfunction or perform at reduced efficiency. q Redundancy would guarantee those events. 11/24/2014 ICTP-NCP School on LHC Physics 12

Single Muon Efficiency q How much do we lose for X% of non-working CSC, randomly distributed? q How much can we gain by adding GEM disks? q What if CSC degrade losing in local efficiency? q To trigger an individual muon depends on what happened to the 3 crossed CSC chambers q For the study 3 discs of CSCs are considered with X% of randomly distributed non-working chambers q CSC track finder requires at least 3 segments including the first station to trigger L 1 muon 11/24/2014 ICTP-NCP School on LHC Physics 13

Single Muon Efficiency Probability of finding a muon: with 3 CSC q Q = X + ( 1 – X )( 1 – ε ) q X = % of broken chambers q ε = Local efficiency with 3 CSC+GEM 11/24/2014 ICTP-NCP School on LHC Physics 14

Single Muon Efficiency As an example, If the CSC local efficiency reduced to 95%, an additional GE 1/1 will recover this 5% and provide 100% detection efficiency. This becomes important for channels with small cross section GEM detector can be used as a backup in case of less percentage of operational CSCs 11/24/2014 ICTP-NCP School on LHC Physics 15

Production of Simulated data • Generation • Simulation Sets of outgoing particles are produced in the interactions between two incoming particles by event generator Produce Simhits • Each Simhits knows the ID of the detector where it was produced • Position and direction with respect to local detector coordinate system • Time of flight when it was produced after the beams interaction • Energy loss in this hit due to passing through heirarchy of volumes and materials • Digitization Response of detector readout electronics • Reconstruction Making of Full event with Tracking and vertexing 11/24/2014 ICTP-NCP School on LHC Physics 16

Channel • Events with Z boson decay into two muons are easy to separate from various background • The main production mechanism at the LHC is Drell Yan process 11/24/2014 ICTP-NCP School on LHC Physics 17

Eta Distribution of RECO Muons • 14 Te. V-PU 50 Sample without GEM • 14 Te. V-PU 0 Sample with GEM Muons in GEM region 11/24/2014 ICTP-NCP School on LHC Physics 18

PT Distribution of Muons Generatot level and Reconstructed level muons are in agreement for both the samples 14 Te. V-PU 0 Sample 14 Te. V-PU 50 Sample 11/24/2014 ICTP-NCP School on LHC Physics 19

Summary § MC sample 14 Te. V-PU 0 of with GEM geometry is produced privately and tested. § Kinematic distributions of Reconstructed Muons on different of 14 Te. V-PU 50 and 14 Te. V-PU 0 samples are normalized to 1 and compared. § The effect is seen on different PU scenario. § Redundancy study has been discussed and it has been seen that there is an improvement in finding the muon particle with the inclusion of GEM detector. The studies shows that the GEM detector can also be used as a backup in case of less percentage of operational CSCs. 11/24/2014 ICTP-NCP School on LHC Physics 20

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