1 Performance of a Magnetised Scintillating Detector for a Neutrino Factory Scoping Study Meeting Rutherford Appleton Lab Tuesday 25 th April 2006 M. Ellis & A. Bross

2 Outline  Detector description  Simulation  Digitisation  Data set  Example events  Reconstruction  Performance: u Points per track u Track Length u Position Resolution u Reconstruction efficiency u Charge mis-ID rate u Momentum resolution u P from track length u Electron identification u Electron reconstruction  Next steps

3 Detector Description  All scintillator box (15m x 15m x 100m) sitting inside a magnetic field (e.g. ATLAS style air toroid).  Basic unit is a triangular pyramid: u base 3 cm u height 1.5 cm u length 15 m  Uniform magnetic fields simulated: u 0.15 T u 0.30 T u 0.45 T  Digitisation takes into account dE/dx in scintillator slab and reasonable light yield, but does not take into account propagation effects (small effect).

4 Real Scintillator (from MINER A)

5 Small Detector

6 Full Detector 15 m 100 m Total mass: 22.5 kT

7 Simulation  GEANT4 (6.2.p02) simulation  Each slab is modeled in the G4 description (parameterised solids to build an “X” and “Y” plane. Many modules containing one of each are placed down the z axis).  All relevant physics processes are switched on.  Magnetic field is simulated as a uniform field.  Primary particles are generated as either positrons or positive muons.  Three momentum ranges studied: u “Low”: 100 MeV/c – 500 MeV/c initial momentum u “Medium”: 500 MeV/c – 2.5 GeV/c initial momentum u “High”: 2.5 GeV/c – 12.5 GeV/c initial momentum u Momentum distribution is flat in all three cases  Initial position just inside the “entrance” to the detector (i.e. upstream if there were a neutrino beam).  Flat initial position between +10 and -10 cm in X and Y  Initial direction gaussian with a width of 100 mrad in X’ and Y’

8 Digitisation  Detector is broken up into: u 3333 Modules (X and Y plane) u Each plane contains 1000 slabs u Total: 6.7M channels (single-ended readout)  All hits on the same slab are collected into a single Digit.  dE/dx in scintillator is scaled to be equivalent to 20 Photo Electrons for a muon passing through the full height of the pyramid (i.e. 1.5 cm).  Energy resolution of the readout electronics is simulated to be 2.0 Photo Electrons  0.5 Photo Electron cut is applied after merging hits into a single digit.  No timing information is simulated u potential improvement for future runs u may well be useful for pattern recognition! u requires more serious thought about plausible front end electronics choices

9 Data Set  Muons: u Approximately equal statistics for the three magnetic fields: s Low momentum: 100k events each s Medium momentum: 45k events each s High momentum: 10k events each  Positrons: u Only simulated in a 0.3T field: s Low momentum: 100k events s Medium momentum: 49k events s High momentum: 14k events  Total 635k events took approximately 3 CPU-days and occupies 8 GB (zipped).  Potential for higher statistics studies without too much difficulty.  Main limitation is file size of output file.

10 High Momentum Muon

11 High Momentum Positron

12 Reconstruction  Pattern recognition cheats using Monte Carlo information: u Muons – select hits from primary muon (discard delta rays). No attempt is made to find kink from delta production. u Positrons – select all hits in the event (i.e. complete shower).  Real pattern recognition will need to be written to study neutrino events (primary lepton vs hadronic jet, etc).  Space points reconstructed using “ADC” information (no timing is digitised)  Tracks are built from all space points under two hypotheses: u positive charge u negative charge  Momentum resolution, efficiency, etc are determined from the fit to a positive charge.  Charge mis-identification rate is found by counting the number of tracks for which the  2 of the fit as a negative particle is better than that for a positive particle.

13 Reconstructed High P Muon 10 GeV/c Muon Blue points: Hits from the primary muon Black points: All other hits

14 Reconstructed High P Positron 10 GeV/c Positron Blue points: Hits from the primary positron Black points: All other hits

15 Performance Red Red: 0.15 T Magnetic Field Green Green: 0.30 T Magnetic Field Blue Blue: 0.45 T Magnetic Field

16 Position Resolution Position resolution ~ 4.5 mm

17 Reconstruction Efficiency Red Red: 0.15 T Magnetic Field Green Green: 0.30 T Magnetic Field Blue Blue: 0.45 T Magnetic Field

18 Charge mis-Identification Red Red: 0.15 T Magnetic Field Green Green: 0.30 T Magnetic Field Blue Blue: 0.45 T Magnetic Field

19 Momentum Resolution Red Red: 0.15 T Magnetic Field Green Green: 0.30 T Magnetic Field Blue Blue: 0.45 T Magnetic Field

20 Momentum from Track Length Red Red: 0.15 T Magnetic Field * Track fit ° Track length Green Green: 0.30 T Magnetic Field * Track fit ° Track length Blue Blue: 0.45 T Magnetic Field * Track fit ° Track length 12% Resolution

21 Electron Identification Red Red: Positrons (0.3T) Blue Blue: Muons (0.3T)

22 Electron Reconstruction Red Red: 0.30 T e + Full Track Blue Blue: 0.30 T e + Short Track Green Green: 0.30 T  + Full Track

23 Summary  Muons are reconstructed with a high efficiency (i.e. if Pattern Recognition succeeds, the track fit is good) above about 200 MeV/c  A combination of momentum determination by track fit at low momentum and track length at high momentum gives an overall resolution that is reasonably flat at about 12%.  Positrons are reconstructed with a resolution which is slightly worse than that for muons, however this has not been optimised.  Charge mis-identification rate is of order 10% at very low and very high momentum and drops to as little as 0.1% at 500 MeV/c.  Electron and Muon identification through the measurement of dE/dx in the scintillator appears possible above about 700 MeV/c.  More work required in several areas: u Muon track fit can be improved at medium-high momentum, should improve momentum resolution u Track fit (dE/dx model, MCS, etc) has not been optimised for electrons u Realistic pattern recognition needs to be implemented (especially for positrons, fit the clear track before it showers).

24 Next Steps  Tune muon reconstruction to get better fit quality across full momentum range.  Study Detector optimisations: u Air gap between modules (i.e. same mass, greater length). u Double ended readout? u TDC as well as ADC information (very useful for PR and Reconstruction)  Implement real pattern recognition to identify tracks: u Search for multiple muon-like tracks in an event u Search for showers and jets  Implement calorimetry in reconstruction  Repeat study with single tracks  Simulate neutrino interactions  Study detector performance after reconstructing  and e events.