Te V Muon Reconstruction Vladimir Palichik JINR Dubna

Te. V Muon Reconstruction Vladimir Palichik JINR, Dubna NEC’ 2007 Varna, September 10 -17, 2007

Outline • Motivation • Muon reconstruction in CMS: local, regional and global • Problems with high Pt muon reconstruction • Current status of Te. V muon reconstruction

Motivation üCMS physical program in particular includes the searching of new Te. V-mass resonances in dimuon channel and the testing of Standard Model prediction for the Drell-Yan continuum up to Te. V energy scale ü studies with hard*) muons at CMS can lead to new physical phenomena discoveries and also be a tool for testing of reconstruction algorithms on their efficiency and a precision of measurements ü precision of measurements in the muon system plays a leading role in achieving of the required resolution on transverse momentum and mass reconstruction for the processes with hard muons ü Dubna group is responsible for ME 1/1 production ME 1/1 is the most precise station in the muon endcap system: (ME 1/1) : (ME 2 4) ~ 1 : 2 a special interest to high-p. T muons (~ 1 Te. V), where a role of the muon system increases *) hard muons – the muons with high transverse momenta from several hundred Ge. V up to Te. V region

Bremsstrahlung and e-m showering closed to hard muons lead to the problems with reconstruction in the muon system

Muon Reconstruction Local (individ. detectors) Regional (Muon system) Global (Muon & Tracker system) Local pattern recognition: 1. DT: time-space conversion of Digis *) into Rec. Hits; CSC: clusters of Digis fitted into Rec. Hits, i. e. position of hits in the detector layers. 2. Track-segment building (track following & track road methods) with the compatible Rec. Hits in muon chambers. 3. The track-segments are selected by a goodness of fit criteria ( c 2 ). *) “Digis” – digitized electronic signals CSC s(rj) ~ 1 -2% of strip width, i. e. 150 -300 m

SK Algorithm of Local pattern recognition in CSC: CSC track-segment building (track road method) with Rec. Hits array in muon chamber: - start with the first and the last Rec. Hits and build a straight line from them; collect hits in a narrow road around the line (usually at least 4 hits ); the track-segments are selected by a goodness of fit criteria ( c 2 ); “used” hits are excluded for the next iteration; if number of track-segments < 2 in a narrow road, try to build them in a wide road. CSC segment building road 2. 5 algorithms for segment building in the CSCs in the current release of CMSSW – due to MTCC data handling Wide CSC clusters of Digis fitted into Rec. Hits Narrow road 1. Specifics for Te. V muons: - high multiplicity of Rec. Hits; - distortion of muon signals by d-rays

ME 1/1 (top) resolution with MTCC 2 data (results by CMSSW_1_2_2) 1) CSCRec. Hit. B package with 2) Calibration DB is used to find 3) the Rec. Hits; 4) 2) make Gatti distribution more 5) broader; Resolution of the ME 1/1 upper part is 118 microns s = 118 mm 3) SK algorithm for CSC 4) track-segments building; 5) 4) requires 5, 6 hits on a track 6) segment; 7) 5) cut on large angles of muons: 8) dx/dz < 0. 25 9) 10) 6) c 2 < 6 dy/dz <1. 5 MTCC – Magnetic Test & Cosmic Challenge held in the 2006 year at CERN

Regional Muon Reconstruction e. m. showers& punchthrough Multiple scattering, energy losses, bremsstrahlung, e+ epair production etc. from Hadron Calorimeter (HCAL) in Iron Yokes (I Y) IY and RPC): Station 4 IY Station 3 IY Station 2 H C A L Station 1 Standalone Muon system (DT, CSC Recursive track fitting (from hit to hit in endcap; with use segments in barrel) by the least squares method ( Kalman filter propagation & parameter estimation) Specifics for Te. V muons: - distorted Rec. Hits - concurrent track-segments in a closed region

Global Muon Reconstruction inclusion of tracker hits regional track reconstruction is performed using Tracker starts from standalone reconstructed muons, propagated through calorimeters to outer tracker surface hits within this (h, j)-region; to resolve the ambiguities, all the reconstructed tracks are then refitted including the tracks in the muon chambers significantly improves Pt resolution – by factor of 10 for low Pt muons (comparing with standalone muon reconstruction) creating seed(s) for each propagated muon in (h, j)-window Specifics for Te. V muons: hard muons look like straight lines in the Tracker --> muon momentum can be reconstructed correctly only in the total tracking (Muon+Tracker) system

1 Te. V Muon Reconstruction in current CMSSW release Transverse momentum resolution = 9. 6% Efficiency of reconstruction = 97. 6% Endcap region 1. 2 < h < 2. 1

Progress with Single Pt = 1 Te. V Muon Reconstruction in endcap (1. 2 <h < 2. 1) region efficiency 2002 2003 2004 2005 2007 100 % 95 % 90 % 85 % 80 % release 6. 3. 0 d. Pt/Pt 7. 3. 0 7. 6. 1 8. 0. 1 8. 2. 0 ORCA releases 8. 4. 0 8. 7. 3 8. 13. 2 1. 6. 0 CMSSW release 15 % 10 % release - HLT - GMR

Drell-Yan di-muon Mass Reconstruction in the previous CMS software (ORCA) (off-line simulation) e=94 % s(d. M/M) = 4. 0 % sample with di-muon invariant mass cut-off 1 Te. V

Summary ü A significant progress in efficiency and transverse momentum reconstruction for single hard muons in the CMSSW: for Pt=1 Te. V the efficiency of reconstruction in the Endcap region is 97. 6% & Pt-resolution stays less than 10% ü Consequently it is expected to obtain in this CMSSW version (1. 6. 0) mass resolution for dimuon processes in the Te. V mass region üFirst MTCC data with cosmic muons gave a possibility to verify and adapt CMSSW to real data handling (calibrations, algorithms etc. )

Thank you for your attention

Single hard muon Reconstruction in 4 eta-regions (off-line) barrel e=97 % overlap e=96. 5 % 0. 8 <|h| < 1. 2 |h | < 0. 8 s(d. Ptinv/Ptinv) = 5. 2 % e=94. 5 % endcap 1. 2<|h| < 2. 1 s(d. Ptinv/Ptinv) = 10. 8 % s(d. Ptinv/Ptinv) = 6. 2 % e=94 % endcap |h | >2. 1 s(d. Ptinv/Ptinv) = 32 %