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BFEM Balloon Analysis

This report details the BFEM balloon flight analysis aimed at validating the LAT design and its performance in high-background environments. Key objectives included data collection on cosmic events, analysis of gamma-ray identification, and noise studies related to balloon flight conditions. Preliminary findings from flight data are discussed, alongside future plans for refining event selection algorithms, continuing gamma event filtering, and improving simulation techniques for enhanced tracking. The results aim to support the GLAST Instrument Operation Center’s requirements.

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BFEM Balloon Analysis

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  1. BFEM Balloon Analysis • Balloon flight • first look • detailed look • G4 validation • gamma ray identification • noise studies • neutral event studies • future plans

  2. BFEM Report (D. Thompson) • http://www-glast.stanford.edu/protected/mail/balloon/alt-0271/01-BFEM_Report.doc (email of D. Thompson to the balloon flight mailing list, September26, 2001) • Rationale/Goals: The original rationale for a balloon flight was stated in the NASA Announcement of Opportunity: "The LAT proposer must also demonstrate by a balloon flight of a representative model of the flight instrument or by some other effective means the ability of the proposed instrument to reject adequately the harsh background of a realistic space environment. ? A software simulation is not deemed adequate for this purpose." • Objectives: • a) Validate the basic LAT design at the single tower level. • b) Show ability to take data in the high isotropic background flux of energetic particles in the balloon environment. • c) Recording all or partial particle incidences in an unbiased way that can be used as a background event data base. • d) Find an efficient data analysis chain that meet the requirement for the future Instrument Operation Center of GLAST.

  3. Some pictures Aug 4, 2001, 12:00

  4. Balloon Flight Housekeeping seconds Mexico gulf

  5. Trigger/Event rate

  6. ROOT data files available data files in ROOT format (download from ftp-glast.slac.stanford.edu/glast.u05/bfem/data/flight/RWv5r7p1_DIGIv2r7): • run #53 (nsbf_r000053_20010804_072159_ivte-raw.root), taken before the launch. 30529 events. • run #54 (nsbf_r000054_20010804_104748_ivte-raw.root), taken during ascent. 109866 events. • run #55 (nsbf_r000055_20010804_143059_ivte-raw.root), taken on float altitude. 104819 events.

  7. Analysis objectives • G4 validation (cosmic ray generator) • gamma ray event identification • noise studies • neutrals • other activities

  8. G4 validation (Tune et al.) Objective: understand the balloon data by comparing with the G4 3.2 based balloonsim simulation. Uses ROOT macros. First step: identify proton/muon events by requiring • hit in top ACD tiles • no hit in side ACD tiles • only consider events with one (x and y) track reconstructed • 80% (13 out of 16) of the last layers should have a hit. The top 10 layers are ignored because they were not fully equipped with ladders. • use some criteria to select "straight" tracks. E.g., c². • modify bfemApp (GFcontrol).

  9. Angular distributions

  10. gamma ray event identification (GSFC) • Objective: find gamma events (this is what GLAST will be built for) • A set of filters is defined in perl scripts. These scripts read the raw, recon, and ntuple files, and write the filtered events into new raw, recon, and ntuple files. • Filters: • base are complex cuts from AOrecon. Most are based on CAL, and cannot be used yet. • complete ACD veto • cut for albedo particles (e.g., energy in CAL > 100MeV)

  11. selected events

  12. gamma ray goal run 55: 1298 events

  13. noise study (Leon) • Objective: noise study of tracker using flight data. Uses the UserAlg feature (tutorial Friday) of bfemApp. • "noisy" strip selection: • straight, clean, single tracks (essentially the same as for G4 validation) • no ACD cuts were imposed (nor CAL) • ignore hits on and near the track • assume remaining hits are due to noise • Finds a noise rate of 2E-5, about an order of magnitude lower than reported by UCSC for the BTEM tracker. • Event selection can be improved. Pisa inherited and will continue.

  14. gamma + splash

  15. understanding "neutrals" • Observations: • L1T rate 500Hz (expected "200-250Hz") • neutral (no ACD hit) fraction 8-10% (expected 3%) • "extra" hits primarily in or below the super-GLAST layers • electron spectrum down to 10MeV extrapolated. Reproduces the rate but not the distribution. • positron and gamma spectrum newly implemented. Looks better. • plan to implement muons.

  16. "first layer hit" distribution positron gamma electron proton

  17. "layers hit" multiplicity positron gamma electron proton

  18. "neutrals" simulation Electrons, originating from below the tracker

  19. future activities • continuing activities • proton event rate and distribution (Roterman) • gamma event filter (GSFC) • strip noise studies (Pisa), keeping the full LAT in mind • G4 balloonsim developement (Mizuno) • event display (Pisa) • G4 validation for the full LAT (GLAST Italy) • balloonsim simulation of gamma events at various energies (Pisa) • event pattern for improvement/rewrite of tracking algorithms • false "noise" hits for noise studies • simulation (balloonsim?) of soft electrons hitting the CAL (Pisa)

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