The new ATLAS Track Extrapolation In a case study of a future high precision W mass measurement Andreas Salzburger , CERN PH-ATC & University of Innsbruck, Austria
Outline • Track extrapolation - concept / applications • Design of the new ATLAS Track extrapolatino engine - realization in the new Event Data Model - material integration • Combined Testbeam 2004 - first test of new software frame • Validation procedure - from reconstruction to simulation • Prospect of a future W mass measurement - scenario for a praxis test Andreas Salzburger – OEPG, Vienna, 27/09/2005
Track extrapolation: Introduction The transport of track parameters and their associated covariances is an underlying process of most track fitting Global Frame algorithms. B-Field x LHC with its high event rates and track multiplicity requires a very stable and reliable framework for these operations. p 3 ATLAS with ist complex geometry B a 3 (material distribution) and magnetic field a 1 needs very precise algorithms to match z a 2 the requirements of the challenging p 1 p 2 physics goals. y Andreas Salzburger – OEPG, Vienna, 27/09/2005
Track extrapolation: Definition and Applications Can be divided into two basic realms: • geometrical transportation of parameters and covariances • update of parameters and covariance matrix taking multiple Coulomb scattering and energy loss effects into accout Applicaitons: • global and iterative Fitters • track – calorimeter matching • holes on track search • vertex fitter • new InDet MC Simulation Illustration of a typical step in a Kalman filter aplication. Andreas Salzburger – OEPG, Vienna, 27/09/2005
And this should look like ... Surfaces TrackParameters TrackParameters ATHENA IExtrapolator ALGTOOL StraightLinePropagator HelixPropagator IMaterial RungeKuttaPropagator Effects STEP_Propagator ATHENA ATHENA ATHENA IPropagator IPropagator INavigator Updator ALGTOOL ALGTOOL ALGTOOL IGeometry Builder ATHENA ALGTOOL Andreas Salzburger – OEPG, Vienna, 27/09/2005
Navigation The TrackingGeometry enables navigation through the TrackingVolumes which are taken as an interface for material and magnetic field access. n p If a boundary surface of a p TrackingVolume is hit, a simple n projection of the momentum vector onto the normal vector of the surface at this point is enough to now the next PixelNegEndcap PixelPosEndcap PixelBarrel TrackingVolume , as the BoundarySurface object owns: TrackingVolume* m_outsideVolume; TrackingVolumeArray* m_outsideVolumeArray; TrackingVolume* m_insideVolume; TrackingVolumeArray* m_insideVolumeArray; owns TrackingGeometry, ATHENA INavigator handles search and navigation ALGTOOL Andreas Salzburger – OEPG, Vienna, 27/09/2005
Material Integration • TrackingGeometry provides mechanism for “ Layer based” and “ Volume based” material description. Necessarily the TrackingVolume has to be able to hold a Layer or a LayerArray . Material properties should be retrieved from Common Detector “Layer based” “Volume based” Description !! material description material description (if possible) (point-like update) (continuous update) steers, IMaterial decides, Effects STEP_ ATHENA ATHENA ATHENA configures Updator Propagator Extrapolator ALGTOOL ALGTOOL ALGTOOL Andreas Salzburger – OEPG, Vienna, 27/09/2005
Magnetic Field Access Inside SCT Barrel: Magnetic Field map parameterized as a Solenoid Outside SCT Barrel: SCT Barrel Realistic Field Inner Detector • The TrackingVolumes have to be identical or synchronized with MagneticVolumes • The CTB 2004 showed: be as flexible as possible, scaling, shifting, etc. etc. For the moment, TrackingVolumes have a 2 nd part: pointer to the Propagation in realistic field MagneticFieldTool which IMagnetic holds synchronized 1 st part: ATHENA FieldTool MagneticFieldVolumes. ALGTOOL Propagation in solenoidal map Andreas Salzburger – OEPG, Vienna, 27/09/2005
Combined Testbeam 2004: A First Testbed • New Extrapolation has been 9 GeV, Pions, B=0 successfully used in the new Kalman Fitter, the new Gaussian Sum Filter and a new Global Chi 2 Fitter. ATLANTIS Event Display Residual gained for ϕ Full simulation geometry To gain full validation of new software chain, a controlled testbed was needed. Andreas Salzburger – OEPG, Vienna, 27/09/2005
Suddenly ... ... I remembered vaguely that I‘ve once written a diploma thesis ... ... and I remembered what I didn‘t like so much about the fast simulation ... ATLFAST is in principle not a fast simulation, it is a fast simulation and reconstruction! Which had as a consequence that the fast simulation so far could not be used for any studies that needed hit information, or interaction with the offline reconstruction software. Andreas Salzburger – OEPG, Vienna, 27/09/2005
Validation testbed: InDetMC_Simulation • We need a controlled validation testbed - full simulation turned out to be too complex for understanding single underlying processes • How to create our ‘perfect’ tracks for validation of the TrkTools Navigator of Extrapolation can ‘in principle’ predict the track through the InnerDetector (as connective TrackingGeometry exists). ATHENA trajectory INavigator ALGTOOL TrackParameters ATHENA IExtrapolator ALGTOOL IMaterial InDet::MC_ Effects ATHENA ATHENA TrackCreator Updator ALGTOOL ALGTOOL Special flavour: PRD, RIO, TSOS production MC_MaterialEffectsUpdator Trk::Track (enriched with RndGenerator) Andreas Salzburger – OEPG, Vienna, 27/09/2005
Interaction: InDetMC_Simulation • Allows interaction: - resolution of detectors InDet:: - efficiency (holes on track creation) MC_Track - misalignment etc. - clustering, RIO_OnTrackCreation ATHENA Creator ALGTOOL IGeometry • Allows interaction: - detector setup Builder - material distribution ATHENA ALGTOOL • Allows interaction: IMaterial - particle type Effects - different models for E-Loss/MS ATHENA Updator ALGTOOL • Allows: - simple switch between used fitting technique, - cross checks, etc. ATHENA IFitter ALGTOOL Cake - Prolonging the Magic – “You turn the screws” Andreas Salzburger – OEPG, Vienna, 27/09/2005
Application: W mass measured to 0.014% at the Z pole The W mass in the Standard model: πα 1 2 = m W θ − ∆ 2 sin ( 1 r ) 2 G W F radiative corrections, known to 0.0009 % from muon lifetime dominated by m t , m H measured precicely at LEP (0.004 %) W mass is sensitive for Higgs mass, but also for new physics such as SUSY particles due to loop corrections. Andreas Salzburger – OEPG, Vienna, 27/09/2005
Application: W mass measurement in ATLAS In p-p collisions, the W mass can be obtained from the leptonic decay channels: W → ν l where l = e, µ Longitudinal momentum of neutrino can not be measured, measurement is done by an extraction from the transverse mass distribution ν = − ∆ φ m 2 p l p ( 1 cos ) T T T E T p T e The transverse neutrino momentum is reconstructed p T W using teh transverse momenta of the lepton and the hadronic recoil of the underlying event. Neutrino Due to high event rate, the measurement error will be completely determined by systematical error. E T H a d r o n i c r e c o i l Andreas Salzburger – OEPG, Vienna, 27/09/2005
Systematic Errors: W mass measurement in ATLAS Thanks to Esben Klinkby et al. Andreas Salzburger – OEPG, Vienna, 27/09/2005
The analysis: W mass measurement in ATLAS The kinematic boundary is smeared by the detector response, this smearing has to be perfectly understood (maerial distribution, magnetic field properties) to guarantee the fit. Generating large event numbers with full simulation and different input W mass values and fit the edge in comparison to taken data would be a strategy, but this is almost inpossible due to the time- consuming Geant4 simulation. The idea is to retry that with the new InDetMC_Simulation , that is up to two to three magnitudes faster. + full control of the sim/reco material + full control of the sim/reco magnetic field Andreas Salzburger – OEPG, Vienna, 27/09/2005
Current Status: Simulation and refitting of single tracks InDetTrackingGeometry Material distribution Proof of principle with + Navigation + calibration framework InDetMC_Simulation and validation finished established new Kalman Fitter Todos : • redo with adapted material to different ATLAS layouts • interface InDetMC_Simulation with generator output • feed fast simulated and reconstructed files into existing W mass measurement framework • chagne sim/reco material and deduce the systematics Andreas Salzburger – OEPG, Vienna, 27/09/2005
Conclusion: so far • New Track extrapolation scheme has been established - used in CTB 2004 reconstruction - base of many new fitters and filters in the ATLAS offline software - also used in physics analysis applications already • Two basic novelties - STEP propagator (continous material effect update) - Full connective TrackingGeometry (Navigation) • Navigation enables new fast MC Simulation for ATLAS - more than smearing can be done - used for various validation studies already, but need improvement • Prospect of a future W mass measurement - can we answer the questions of lepton energy scale ? Andreas Salzburger – OEPG, Vienna, 27/09/2005
Backup slides … Andreas Salzburger – OEPG, Vienna, 27/09/2005
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