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BG studies with LAT CU Beam Test

BG studies with LAT CU Beam Test. Tsunefumi Mizuno, Hiromitsu Takahashi, Hideaki Katagiri and Yasushi Fukazawa (Hiroshima Univ.) Hiro Tajima (SLAC). Objective Dominant Particle DC2 BG data analysis/BG property (1)~(4) What’s necessary to estimate BG? Toy MC of e+ run Summary. Objective.

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BG studies with LAT CU Beam Test

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  1. BG studies with LAT CU Beam Test Tsunefumi Mizuno, Hiromitsu Takahashi, Hideaki Katagiriand Yasushi Fukazawa (Hiroshima Univ.) Hiro Tajima (SLAC) • Objective • Dominant Particle • DC2 BG data analysis/BG property (1)~(4) • What’s necessary to estimate BG? • Toy MC of e+ run • Summary BeamTest_BG_2006-05-17.ppt

  2. Objective • Bill's talk at DC2 kickoff showed larger than expected BG level. • BG exceeds 1/10 of extragalactic -rays with E < a few 100 MeV. • BG level is close to extragalactic -ray flux for E < 100 MeV. • Reliable BG modeling is required • Monitor the flux/estimate the contamination to photon events. • Minimize impact on the diffuse/faint source study by GLAST. • Beam Test for BG study • Establish a way to estimate BG in orbit • Minimum impact on calibration runs. primary proton secondary e+/e- secondary proton primary alpha atmospheric gamma BeamTest_BG_2006-05-17.ppt

  3. What contributes to BG? • Proton primary, positron reentrant/splash and Earth10 (atmospheric gamma) are dominant. • Most of e+ reentrant background are due to annihilation. Correlated BG https://confluence.slac.stanford.edu/display/SCIGRPS/Residual+background+and+diffuse+emission From Bill’s talk at kickoff meeting BeamTest_BG_2006-05-17.ppt

  4. Analysis of DC2 data • Analyze DC2 BG data to study BG property (particle type, direction and energy of those which contribute to BG). • Use DC2 BG data (v7r3p5): backgndDC2-GR-v7r3p5-merit*.root (total 1.5day) • Select GoodEvent1. (further cuts with CTBBestZDir and FT1ZenithTheta were applied for DC2) BeamTest_BG_2006-05-17.ppt

  5. BG property (1): e+ reentrant • Most of e+ reentrant backgrounds are due to annihilation at blanket or meteorite shield or top ACD tiles. • Particle energy peak at ~100 MeV. Significant contribution from e+ of ~1GeV Intersect position of particle trajectory and LAT (imaginary box which encloses LAT). hitz hity McEnergy (MeV) hitx (mm) BeamTest_BG_2006-05-17.ppt

  6. BG property (2): proton primary hitz hity hitz(mm) hitx (mm) • Interaction in CAL contributes to BG. • Measured energy is much less than proton energy FT1Energy (MeV) McEnergy (MeV) BeamTest_BG_2006-05-17.ppt

  7. BG property (3): atmospheric gammas • Most of atmospheric gamma-ray BGs are coming downward relative to LAT and can be distinguish from celestial gammas. Significant fraction of gammas from back of CAL. • Measured energy is close to gamma-rayenergy. CTBBestZDir FT1Energy (MeV) McZDir upward McEnergy (MeV) sideway BeamTest_BG_2006-05-17.ppt

  8. BG property (4): positron splash hitz hity hitz(mm) hitx (mm) • Interaction in CAL contributes to BG. • Measured energy is close to positron energy. FT1Energy (MeV) McEnergy (MeV) BeamTest_BG_2006-05-17.ppt

  9. Positron Reentrant: • Large uncertainty in positron secondary flux – needs to be monitored. • They could be monitored by observing two photon events. • BG estimation heavily relies on MC. • positron annihilation process of G4 needs to be validated. • Proton Primary: • Primary proton flux is well known. (in ~10%) • Interaction inCAL needs to be understood. • Atmospheric gamma: • Flux is uncertain but can be monitored by LAT. • Interaction in CAL needs to be understood. • Positron Splash: • Upward e+ also contributes to BG. So does the upward e-. • Interaction in CAL needs to be understood. What is necessary to estimate BG? BG run with CU (in priority order) • Positron runs with blanket and meteorite shield or equivalent • Proton runs from back/side of CAL • Gamma runs from back/side of CAL • Electron runs from back/side of CAL BeamTest_BG_2006-05-17.ppt

  10. Do we have enough two gamma? To see how many gammas will be generate in e+ run, we ran a very simplified LAT. e+ (normal incidence) 500 MeV and 1 GeV (1M each) • Equivalent to Blanket + meteorite shield: • Carbon of 0.39 g cm-2 • ACD: • Plastic scintillator of 1cm • “Perfect” Tracker which is made of vacuum but has 100% detection efficiency BeamTest_BG_2006-05-17.ppt

  11. # of gammas expected All events (1M) 1GeV e+ no hits in ACD (162) 50 events with eGamMin>30 MeV Lower Energy of gamma # of gammas in LAT higher Energy of gamma (MeV) 500 MeV e+ 102 events with eGamMin>30 MeV 343 events. • Lower energy is preferred. • At least a few million triggers is required for sufficient statistics. (See also “CERN Beam Test Plan” by Benoit and Eduardo) BeamTest_BG_2006-05-17.ppt

  12. Summary • Positron annihilation and proton interaction in CAL is the dominant component of LAT BG. Upard gammas/positrons/electrons also contribute to BG. • Positron flux is fairly uncertain – needs to be monitored. Annihilation process needs to be validated. • Positron runs with blanket/meteorite shield or equivalent. • Lower energy is preferred. • At least a few million triggers are necessary • Significant fraction of 2 gamma events in annihilation events. • Proton flux is well known. Interaction in CAL needs to be validated. • Proton runs from back/side of CAL. • Upward gammas/positrons/electrons also contributes to BG • Gammas/electron runs from back/side of CAL. • Calibration Unit simulation is necessary to estimate the sufficient number of triggers. BeamTest_BG_2006-05-17.ppt

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