GasPixel Transition Radiation Tracker GasPixel Transition Radiation Tracker Victor Blanco Carballo, Max Chefdeville, Fred Hartjes, Martin Fransen, Serguei Morozov, Serguei Konovalov, Anatoli Romaniouk, Harry Van der Graaf Motivation Test beam prototype MC model Tracking Particle ID Timing First test beam results Plans

Motivation Pixelization of the information from the particle track offers new possibilities to combine in one detector many features: 1. Precise coordinate measurements (well below diffusion limit). 2. Vector track reconstruction. 3. Very good multi-track resolution (not covered in this talk). 4. Powerful pattern recognition features (not covered in this talk). 5. dE/dX measurements. 6. Enhanced Transition Radiation separation. 7. Good timing properties This technique definitely has a wide range of applications but Inner Trackers of the collider experiments may have a particular interest.

In addition to the particle identification Transition Radiation Detector normally situated at the outer radii of the Inner Tracker. Because of large leaver arm this area is very much important for momentum measurements -> a precision tracking demand. h Possible layout Sensitive layers are interleaved with the TR radiator. In addition to the particle identification the Gas Pixel TRT will provide: 1. Precision space points X,Y 2. Vector direction f, h Very important for the pattern recognition: f f, h - cone to search for the partners

Gas Pixel TRT Test Beam Prototype, What we should expect to get Everything starts from the first step : Gas Pixel TRT Test Beam Prototype, InGrid TimePix detector, 14 x 14 mm2 256 x 256 pixels L = 18 mm 0.05 mm V0 V1 h or 90o - h Minimum L for TR absorption is ~ 18 mm TR-Radiator Beam E 20o e- Some Chamber Parameters Vo~ 520 V V1= 4500 V, Edrift ~ 2000 V/cm Gas mixture 70%Xe+30%CO2 Total drift time ~ 400 ns Ion signal ~ 80 ns Transverse diffusion sT ~200 mm/cm1/2 Longitudinal diffusion sL ~120 mm/cm1/2 What we should expect to get from this prototype?

Toy MC simulation: model Particle tracking including all interactions + geometry - GEANT3 Ionisation losses - PAI model TR generation - ATLAS TRT code Change of the parameters through the configuration files. It allows to set: The test beam set-up configuration Chamber parameters Beam energy and particle sort Beam parameters (position, spread) Radiator parameters Gas mixture composition Drift velocity and diffusion Gas gain fluctuation type (Exponential, Polya) Ion collection time Ion signal shape Electronics response shape Registration thresholds Output files : Pixelman compatible format No FE electronics response -Time -Electrons With FE electronics response: -Time mode -Time over Thr. mode Colour map numbers correspond to a hit arrival time- the coreect time would be (400-T)*10 ns

Signal parameters used in simulation Electrons Ions 80 ns Electronics current d-function response (variable parameter) Pixel single electron current function Response to one electron 180 ns T1 T2 T1 OR DT=T2-T1 are measured Threshold (variable parameter)

The results of the analysis shown below are very preliminary! The programme is the same for the MC and the experimental data. Analysis parameters can be changed through the configuration files. Type of files to be analysed. Events to process. Parameters for tack reconstruction. Threshold for TR cluster definition. Some others. 2 events, pions 20 GeV Red dots indicate reconstructed track. Number of electrons per track slice (2 pixels) Ionisation clusters Threshold to detect clusters Y X The results of the analysis shown below are very preliminary! MC Pixels with the hits above the threshold.

Analysis: tracking (MC data source) pions 20 GeV Space point in f direction (X) Space point in Z direction (Y) s=17 mm s=18 mm Difference between real and reconstructed space point across the track. Difference between real and reconstructed space point along the track.

Analysis: tracking (MC data source) pions 20 GeV Angle f Angle h s =0.65o s =0.3o Difference between real and reconstructed angle of the track. Difference between real and reconstructed angle of the track.

Vector track reconstruction.

What we can measure with the beam? -> Pseudo track parameters pions 20 GeV MC MC s=33 mm s =0.8o Difference between reconstructed space points for two pseudo tracks. Difference between angle of the track for two pseudo tracks.

Particle ID: use TR and dE/dX information TB prototype: dE/dx total Number of primary Collisions vs gamma Pions Plato Fremi : Mean 4 Min. ionising: Mean 2.7 Number of primary collisions per cm of Xe Factor 1.36 ln g MC Relativistic rise vs d-electron energy dE/dx, arb. units Number of clusters above ~1 keV Plato Fremi : Mean 2.7 Min. ionising: Mean 1.2 For 2 kev d-electrons Factor of 2 Detailed knowledge of the ionisation structure of the track gives more information for the particle ID. B. Dolgoshein, NIM A326 (1993) 434

TR generation. Set up as shown above. Number of photos per event MC MC Average: 2.5 TR photons. No TR photons: 125 out of 1000 20 keV TR spectrum Number of photos per event

TR registration: The main issue is to separate dE/dX from TR Use the low: X-ray absorption probabilities. Something we don’t know yet (see Exp. Data). 1+2 == 3 13% 6% 3% 9% MC Pions Electrons + TR Total energy deposition in the chamber. B. Dolgoshein, NIM A326 (1993) 434

TR registration Event 2003 TR clusters Time information Amplitude information

TR registration TR clusters Event TR clusters MC Threshold to detect candidates to the TR clusters (30 in this units). Total number of electrons in the area with R=sT is calculated All the rest is treated as dE/dX

TR registration TR absorption in the chamber. MC MC This distribution is flat for the d-electron Number of photons Absorption position in the chamber, cm. X-ray energy, keV. Number of the TR photons absorbed in the chamber vs depth.

Electron/Pion separation Electrons Pions MC MC 0-bin =96 out of 1000 No TR 125 0-bin =>753 out of 1000 Some electrons without TR Produced clusters Total number of electrons in the clusters for electrons and pions (20 GeV) Now we have detailed information about the track structure How to use it?

Electron/Pion separation The best is likelihood method but other algorithms almost as powerful can be used. Demonstrative exercise (far to be a complete analysis) Two classes of events: Events with 0 or 1 cluster. Events with more then 1 clusters. 0 and 1 cluster events 1 cluster events 408 e 963 pions 224 pi 316 e MC MC Size of the cluster Normalised dE/dX Size of the cluster Pixel position Electrons are coloured

Electron/Pion separation 2 and more clusters 37 pi (3.7%) 592 e (59%) Pions are in pink MC MC Sum of the clusters Normalised dE/dX Size of the maximum cluster Pixel position for the cluster with lowest energy Very simplified approach gives pion rejection factor >10 at electron efficiency slightly less than 90% for already one radiator-chamber set Up to now NO Time information used yet (apart of ToT).

Timing. Very important to separate bunch crossings in the collider experiments Strongly affected by electronics shaping time MC 140 ns 25 ns Electronics Shaping function Arrival time for the first electron 20 ns 100 ns Timing jitter at the pixel threshold of 1 electron Timing jitter at the pixel threshold of 0.1 electron 140 ns peaking time 100 ns 50 ns

At low threshold total jitter can be reduced below 25 ns. Timing. 25 ns peaking time MC MC Timing jitter at the pixel threshold of 1 electron Timing jitter at the pixel threshold of 0.1 electron 25 ns 55 ns At low threshold total jitter can be reduced below 25 ns. But there is a question about dynamic range of the ToT measurement!

Amplitude measurement saturation. Threshold 0.1 el. Events 2051 and 2052 measured with electron counting and ToT methods (MC) Number of electrons MC Time over Threshold Peak suppressed Detailed simulations are required to reach a reasonable balance!

First tests with the beam (6 GeV). Should be considered as a preparatory step for a real tests beam. Very little time. Time measurements only (no ToT information). Some problem with the chamber (E-field distortion). Tracking (experiment). Pseudo track reconstruction Space point Angle

Particle Identification Pions (left) Electrons (right) TR clusters Most of the TRT clusters are out of track!? TR angle = 1/10000 - NO Multiple scattering angle = 5/10000 - NO Photo-electron path - UNLIKELY To be understood and used if it is not artefact! Results of the analysis based on the cluster presence information only : Electrons ID efficiency: ~90% Pions Rejection factor: ~10

Brief summary: First estimate of the Transition Radiation Tracker properties based on the Pixel technology show large potential of this detector which combines precision tracking, particle Identifications and powerful pattern recognition features. Simplified MC which contains all basic physics processes allows to make detector optimization and realistically estimate its performance (yet for the test beam set up). Analysis program is the same for MC and tests beam data what allows to get fast feed back and use it as an express online tool. For the further steps a good quality of the test beam data are required to tune MC and Data Analysis Model and optimize the detector parameters and FE read out. Test beams: 19-24 May, October-November 2008 These are the firsts steps on the long way to a real detector!

Back-up slides TR clusters

Electron Drift Velocity and Transverse Diffusion. Gas properties 20%, 30% and 40% CO2 Electron Drift Velocity and Transverse Diffusion.

Electron Longitudinal Diffusion. Gas properties Electron Longitudinal Diffusion. Lorentz angle is rather large. In a real detector its effect must be taken into account as a part of the calibration procedure.

TR registration Event 2004 TR clusters Time information Amplitude information

Particle Identification ToT is absolutely necessary for particle ID Calibration is a very important step X-ray run with ToT shown reasonable energy resolution. Sample of the events with 6 keV events (Fe55) and spectrum for all calibration data. sE/E~13%