Giuseppe Ruggiero CERN Straw Chamber WG meeting 07/02/2011 Spectrometer Reconstruction: Pattern recognition and Efficiency 07/02/ G.Ruggiero - Spectrometer Efficiency

Introduction Spectrometer Layout (MC) Reconstruction L-R ambiguity resolution Pattern Recognition algorithm Straw tubes performances vs 1 track reconstruction Full set-up Minimal set-up (2012) Conclusions 07/02/ G.Ruggiero - Spectrometer Efficiency

Full Spectrometer Simulation Layout: 4 Chambers 4 Views / Chamber (UVXY) 4 Single tube planes / View Geometry from TD Chamber and tube positions from Beatch file 11/06/2010. Physical/instrumental effect:  rays, effective radius, uniform inefficiency, gaussian smearing of R measurement,  hadronic interactions,  decays. Reconstruction algorithm built using       events. Analysis performed using a sample of  events Generated between and m 07/02/ G.Ruggiero - Spectrometer Efficiency

Spectrometer Reconstruction Requiremets: High resolution (against backgrounds constrained by kinematics) also in case of multi-track events High efficiency (signal acceptance and rejection of multi-track background π + π + π -, K e4 ) also in case of multi-track events As much as possible independent from the sources of inefficiency of the straws (effective radius, smooth inefficiency…) 07/02/ G.Ruggiero - Spectrometer Efficiency Why multi-track environment ?  (t) straw ≈ 7 ns  t ≈ 3  (t) ≈ 20 ns Rate per chamber ≈ 10 MHz Prob(> 1 hit/view) ≈ 0.18 ≈ Prob(> 1 track)

L – R ambiguity resolution 4 hit fired: not allowed by geometry. 3 hits fired: 1 tube hit close to the wire, the other 2 tubes are hit close to the edges. LR solution always possible. 2 hits fired: both tubes are hit in the central part. LR solution always possible. 1 hit fired: only close to the beam hole and in case of straw tube inefficiency. LR solution never possible. Steps: Look for contiguous tubes fired. Sum or subtract the measured R in one tube to the position of the tube according to the pattern of contiguous tubes. 07/02/ G.Ruggiero - Spectrometer Efficiency

Hits and Clusters Definitions Hit: one straw tube fired. Measured infos: 1-D coordinate of the impact point of the track on the tube (or the position of the tube if the LR ambiguity is not solved). Time (Not used in the present work). Cluster: group of Hits in one view used to solve their LR ambiguity. Types: 1-Hit, 2-Hits, 3-Hits according to the impact point of the track on the view planes. Measured infos (extracted by linear interpolation of the hits forming the cluster): 1-D coordinate of the impact point of the track extrapolated at an average Z Slope of the track. 07/02/ G.Ruggiero - Spectrometer Efficiency Each cluster is defined by a coordinate AND by a slope (track slope)

Single hit reconstruction 07/02/2011 G.Ruggiero - Spectrometer Efficiency 7 Effective radius 5 mm No  rays pileup No smooth inefficiency No R smearing  hadronic interactions  decays Effective radius 4.7 mm  rays pileup allowed 3% smooth inefficiency R smearing (  m)  hadronic interactions  decays Ideal configurationReal configuration

Single hit reconstruction (cont’d) 07/02/2011 G.Ruggiero - Spectrometer Efficiency  m17  m Ideal configurationReal configuration

1 hit clusters regions 07/02/2011 G.Ruggiero - Spectrometer Efficiency 9 Ideal configurationReal configuration more

Pattern recognition algorithm Kalman filter approach starting to the last chamber and adding the clusters down to the first chamber: Initialization step profits from the a-priori knowledge of the track slope. Complications: at least 2 views needed for the initialization of the X-Y angle of the track. The number of the views fired in one chamber depends on the track impact point on the chambers. Momentum initialization possible at the level of the second chamber only. Step 0: all the possible cluster combinations in chambers 4 are considered. And each combination is propagated back in chamber 3 down to a view with at least 1 cluster. Step 1: A cluster in this view is chosen according to the difference between the measured position and the position expected on the basis of the estimated track parameters, divided by the corresponding errors. Step 2: a “good” cluster is added, the track parameters recomputed, some model of MS added to the correlation matrix of the track parameters and track propagated back again (step 1). Process ends when no more views with clusters are found 07/02/ G.Ruggiero - Spectrometer Efficiency INIT FILTER Identification of the clusters in the different views and chambers belonging to the same track

Pattern recognition algorithm Further complications (short examples): One track with a cluster in only 1 view in chamber 4. A not parallael view in chamber 3 needed for a suitable initialization. No clusters in chamber 4. Clusters in chamber 3 used for initialization. One track with clusters in chamber 4 and another track without chamber 4… No cluster in chamber 2, or 1 cluster in chamber 2 in Y direction. A cluster in chamber 1 is needed to initialize the track momentum. … Output: sets of combinations. Track candidates chosen among the combinations on the basis of a suitable  2. Added features: track candidates are indetified also in case of clusters in 3 chambers only (the case of any chamber missing is addressed). Algorithm tuned using       events. 07/02/ G.Ruggiero - Spectrometer Efficiency

1-track event results Results presented as a function of the effective radius Real Configuration 07/02/ G.Ruggiero - Spectrometer Efficiency Clusters per track vs effective radius hit per clusters per track vs effective radius

1-track event results 07/02/ G.Ruggiero - Spectrometer Efficiency 1 hit cluster 3 hits cluster 2 hits cluster Real configuration

Spectrometer efficiency (1-track) 07/02/ G.Ruggiero - Spectrometer Efficiency 3 Chambers 4 Chambers Total: 95% Effect from  hadronic interactions and  decay included

Efficiency vs P (1-track) 07/02/ G.Ruggiero - Spectrometer Efficiency Effective radius between 5.0 and 4.5 mm: no visible effect vs track momentum Geometrical acceptance (beam hole)

Minimal Spectrometer Layout (2012) Layout: 4 Chambers 2 Views / Chamber : Chamber 12 XY, Chamber 34 UV 4 Single tube planes / View Geometry from TD Chamber and tube positions from Beatch file 11/06/2010. Analysis performed using a sample of  events Generated between and m 07/02/ G.Ruggiero - Spectrometer Efficiency

Minimal Spectrometer Layout Results studied as a function of the effective radius Real Configuration 07/02/ G.Ruggiero - Spectrometer Efficiency Clusters per track vs effective radius (hit per clusters ) per track vs effective radius

Minimal Spectrometer Layout 07/02/ G.Ruggiero - Spectrometer Efficiency 3 Chambers 4 Chambers Total: 75% Efficiency vs Effective Radius

Minimal Spectrometer Layout 07/02/ G.Ruggiero - Spectrometer Efficiency Efficiency vs P

Conclusions 07/02/ G.Ruggiero - Spectrometer Efficiency Time to build a “realistic” reconstruction of the Spectrometer L-R resolution algorithm developed: Independent from the geometry of the planes Provide position and first track slope estimation Pattern recognition algorithm started: Use of a Kalman Filter technique Most part of possible cases addressed and solved. Works in multi-track environments (some refinement still needed)

Conclusions (cont’d) 07/02/ G.Ruggiero - Spectrometer Efficiency Straw performances vs 1 track events: Reconstruction efficiency almost not dependent on the effective radius Reconstruction quality does depend on the effective radius Spectrometer efficiency (including geometry,  interactions,  decays, 3% smooth efficiency of the straws, 4.7 mm effective radius): 95% (90% for tracks with 4 chambers) full set-up (16 views) 75% (70% for tracks with 4 chambers) minimal set-up (8 views). Reconstruction quality to be addressed. A further step in the reconstruction needed to reach the highest level of resolution (next talk.)