malvezzi icatpp 2005 ppt

Neutron Detector and Bottom Trigger Scintillator Performance : 

Neutron Detector and Bottom Trigger Scintillator Performance Valeria Malvezzi on behalf of the PAMELA Collaboration INFN and University of Rome “Tor Vergata”, Italy

Outline of the talk: 

Outline of the talk PAMELA scientific program PAMELA detectors: Bottom Scintillator (S4) Neutron Detector (ND) ND performance: Ground and test beam data S4 performance: Calibration Threshold Efficiency Conclusions

PAMELA mission: 

PAMELA mission PAMELA Sensitivity: energy range particles/3 years Proton 80 MeV - 700 GeV 3x108 Antiproton 80 MeV - 190 GeV >3x104 Electron 50 MeV – 2 TeV 6x106 Positron 50 MeV – 270 GeV >3x105 Light Nuclei (up to Z=6) 80 MeV - 700 GeV/n He/Be/C: 4x107/4/5 Main Scientific Objectives Unprecedented Statistics and new Energy Range in Cosmic Rays Present limits: antip&positrons  40 GeV To measure the Antiproton and Positron Spectra up to few hundred GeV To search for hints for Exotic Sources of Antiprotons/Positrons, e.g.from SUSY - WIMPs Direct Antimatter Search for e.g. AntiHelium (from sources outside our local cluster -> R>20 Mpc, AntiHe C.R. production rate ~10-14 )

Slide4: 

PAMELA detectors (I) Around the main structure detectors are arranged:

PAMELA detectors (II): 

PAMELA detectors (II) Used for: Lepton/hadron separation by n. of neutrons produced in showers Neutron Detector Size: 600 ×550×150 mm3 Flight Model

PAMELA detectors (III): 

PAMELA detectors (III) Flight Model Single square scintillator paddle 10 mm thick 482×482 mm2 6 PMTs Dynamic range of 1÷1000 mip Bottom Scintillator Used for: a) Trigger for ND to detect super high energy electrons in conjunction with Calo b) Shower tail catcher

On ground cosmic-ray acquisition in Rome and Samara : 

On ground cosmic-ray acquisition in Rome and Samara Number of “good” events collected by Neutron Detector: 286275 Number of “good” events collected by Neutron Detector: 132448 Total acquisition time about 600 hours From the data acquired by cosmic-ray acquisitions we analyzed PAMELA ND and S4 response PAMELA has been switched on the 10th of January 2005 First session of cosmic-ray acquisition started in Rome the 12 th of February until 24th of March 2005 Number of “good” events collected by S4: 344071 Second session of cosmic-ray acquisition started in Samara the 12th of May 2005 until 24th of same month (acceptance test) Total acquisition time about 140 hours Number of “good” events collected by S4: 133884

Slide8: 

Distributions of S4 values

S4 performance (I): 

S4 performance (I) Exponential calibration function

S4 performance (II): 

S4 performance (II) Threshold value can assume values in the range 0 ÷ 4000 (HEX value) corresponding to 0 ÷ 128 mip. S4 Threshold

S4 performance (III): 

S4 performance (III) We selected the good (at least one track in TRK) events, interacting or not, releasing a positive amount of energy in the last calorimeter plane (plane 22 , view X). S4 Efficiency Both in Rome and in Samara data sample, the statistics for high energy is rather low, therefore it is not possible to study S4 efficiencies for energy released in Calo22x > 6 MIPs.

ND performance : 

ND performance

ND and beam test data: 

SPS, September 2003 In September 2003 PAMELA Flight Model was exposed to beam tests to study physical performance. ND and beam test data Simulated data Number of neutron counted by the neutron detector

Slide14: 

Small number of neutrons generate in photonuclear interactions and giant resonance Hadronic showers produce more neutrons than electromagnetic ones Simulation CERN data Gaussian fit 150 GeV interacting protons 180 GeV electrons Simulation CERN data Gaussian fit Gaussian fit Gaussian fit

Interacting event: 

Interacting event

ND performance (II): 

ND performance (II) Behavior of ND with good interacting (applying CALO standard cuts) particles, both for Rome and Samara data. Very low response, due to the low particles energy.

Non-interacting event: 

Non-interacting event

Conclusions: 

Conclusions S4 We have exponential function for detector calibration When the detector is in trigger the threshold works in a good way Efficiency increase with energy; this is important for trigger ND at high energy to discriminate positrons, protons and electrons. ND Background performance shows right behavior of the detector From test beam a good agreement between experimental data and simulated one is obtained. Neutron distribution from ground data looks different from that obtained on beam test data due to low energy (very few events producing few neutrons). Neutron distribution for straight particles is consistent with expectations (no neutrons produced)