PEBS - Positron Electron Balloon Spectrometer Prof. Dr. Stefan Schael I. Physikalisches Institut B RWTH Aachen 1
Dark Matter Searches AMS e +, p, D, Charged particles γ,ν Antares, Km3, Amanda, Icecube GLAST CANGAROO, HESS, MAGIC, Veritas, Colliders Direct detection Dama, CDMS, GENIUS, CRESST, Edelweiss, FNAL, LHC, ILC Ge ~20% energy Ionization WIMP Ge, Si Liquid Xe Heat Al 2 O 3, LiF ~100% energy NaI, Xe Light ~few % energy cryogenic detectors 2 CaWo 4, BGO
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From astrophysics and cosmology we get: Ω CDM h 2 = 0.120 ± 0.005 BR(B X s γ ) exp = (3.39 +0.30 0.27 ) 10 4 BR(B X s γ ) SM = (3.70 ± 0.30) 10 4 tan β = 50, µ > 0, A 0 = 0 m 1/2 = 350 GeV m = 144 GeV χ 5
DM Annihilation in Supersymmetry χ χ ~ f f f χ χ A f f χ χ Z f f χ χ χ W χ ± χ 0 W χ Z Z 37 gammas Dominant χ + χ A b bbar quark pair B-Fragmentation known! Hence Spectra of Positrons, Gammas and Antiprotons known! Galaxy = Super B-Fabrik with rate 10 40 x B-Factory 6
AMS-01: STS-91 1998 Flight Results Data taking 135 hours Shuttle altitude 370 km Trigger rate 100 700 Hz 100 million events recorded Energy Range: 100 MeV/n<E k < 300 GeV/n Electronics channels: 70000 Power: 1 kw Weight: 3 t 7
AMS-01 8
Tracker Mechanics & Alignment System MIR docking 9
Positron Identification with AMS-01 - tracks H. Gast, J. Olzem, RWTH Aachen astro-ph/0605254 + tracks - tracks + tracks 10
1015 83 11
J.J Beatty et al., PRL 93 (2004) 241102 A SUSY Model (LSP of 91 GeV) 12
Suspect m χ1 0 = 87GeV B.F. = 12 ± 3 χ 2 / ndf = 40 / 33 Isajet m χ1 0 = 84GeV B.F. = 36 ± 8 χ 2 / ndf = 40 / 33 13
Constraints for a dedicated Balloon Experiment to measure the positron fraction Geometrical Acceptance: >1000 cm 2 sr Proton Rejection: ~10 6 Weight: ~1500 kg Power: ~ 600 Watt 14
What could we measure with a 2500 cm 2 sr Experiment? PAMELA: 20 cm 2 sr 20 days PEBS = 7 years PAMELA AMS-02: 500 cm 2 sr = 100 days AMS-02 What ever PAMELA or AMS-02 might discover in the positron fraction, we need an independent verification. 15
Tracker: Scintillating fibres with Silicon Photo-Multiplier (SiPM) readout; power: 260W Magnet: Pair of superconducting Helmholtz coils, Helium cryostat, mean B = 1T, weight: 850kg
Time-of-Flight system 2 x 2 x 5 mm 3 scintillator, SiPM readout; trigger system! Transition Radiation Detector (TRD): 2 x 8 x ( 2cm fleece radiator + 6mm straw tube Xe/CO 2 80:20 ) ECAL: 3D imaging, 80 layers (1mm Pb + scintillating fibre) with SiPM readout 14.3 X0, weight: 550kg
test balloon launch OLIMPO experiment (2008) NASA ULDB altitude profile High-altitude (~40km), long-duration (~20 days) balloon flights from Svalbard balloonport Interesting alternative to space, allows recalibration of experiment and multiple journeys
TOF Positron acceptance: tracker+ecal width=0.76m, length=1m 2500 cm 2 sr magnet cryostat TRD TRD tracker ECAL length: 3.23 m
Magnet design 1.90 m ISOMAX magnet (1998) flown on high-altitude balloon Magnet design by Scientific Magnetics for superconducting pair of Helmholtz coils in He cryostat, mean field 1 Tesla, opening 80x80x80 cm 3, acceptance (width=0.8m, length=0.8m): 4000 cm 2 sr weight: 850kg
0.80 m tracker superlayer 3.2 cm 2x4x128 fibres 4 superlayers of 2 layers of double-layered modules of scintillating fibres, d=250 m stack of fibres accumulates light on SiPM readout of SiPMs by dedicated VA64 chip tracker module CF skin + Rohacell foam
Fiber Tracker Construction 0.250 mm Fiber diameter, Diameter tolerance 2% <=> 0.005 mm 0.250 mm fishing line 600 mm 40 mm 40 mm 22
2 x 4 SiPM, 8 x 1 mm, 32 channels Fiber Tracker Readout x 4x1 readout scheme (column-wise) with weighted cluster mean => better spatial resolution (~40 µm) than pitch/ 12 (=80 µm), depending on photo electron yield 6 x 1 mm, 16 channels 23
1 mm 24
light collection in scintillating fibre in Geant4 simulation 25
PEBS fibre tracker testbeam setup AMS02 panel cooling pipe trigger scintillators beam telescope: 4 Si strip modules scintillating fibre bunch + SiPMs + PMT trigger scintillators
PEBS testbeam copper block 2 fibre bunches: 3x10 square fibres, d=300 m 3 fibres each to SiPM in copper block
SiPM: example of a MIP spectrum dark spectrum: beam telescope hit away from fibre 0 1 2 3 4 5 6 SiPM type 0606EXP with reflective foil on PMT excess noise: fibre area = 0.27 x SiPM area mean: 6.0 photo electrons 7 8 9 10 11 12 photo electrons 1 mm
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Spatial resolution vs angle of incidence mean= 11.2 distribution of incident 35 angle projected to bending-plane for PEBS detector p.e. yield of testbeam fibre stack with reflective foil Hamamatsu SiPM with 60% photo detection efficiency, i.e. 50% better Use round fibers without white paint, 30% better
Tracker performance: Momentum resolution Muon momentum resolution from G4 simulation using testbeam parameters, d = 250µm, B=1T p p = a 2 bp 2 p.e. efficiency = 1 x testbeam efficiency p.e. efficiency = 1.5 x testbeam efficiency p.e. efficiency = 2 x testbeam efficiency a = 2% a = 2% b = 0.19%/GeV b = 0.14%/GeV a = 2% b = 0.12%/GeV
ECAL layout 3x3mm 2 SiPM 8 superlayers of ten layers of lead-scintillating fibre sandwich, with alternating orientation 1mm lead fibre: 1mm height, 8mm width, read out by SiPMs 14.3 X0 in total, ECAL weight: 550 kg 3x3 mm 2 array: 8100 pixel 3 x 3 mm 2 76 cm 16 cm
ECAL shower t max 50 GeV e+ 38 GeV e+ 26 GeV e+ 14GeV e+ 5 GeV positron 50 GeV protons de t=x/x 0 dt = E b (bt)a 1 e bt 0 Γ(a) longitudinal shower profiles ECAL shower in Geant4 simulation
Example event 44.5 GeV positron in event display
ECAL performance ECAL energy matching ECAL shower maximum positrons protons reconstructed momentum positrons protons angle between reconstructed track and shower positrons protons ratio of ECAL energy within one Moliere radius
ECAL proton rejection and energy resolution Simulated 40000 positrons and 1700000 protons proton rejection ~5000 at high energies ECAL energy resolution
Intrinsic limits on rejection example event: p p 0 X before last tracker layer generated: p gen =35.4 GeV 0 momentum: 18.9 GeV e.m. shower reconstructed: p reco =19.5 GeV intrinsic resolution limited by high-energy or in first layers of ECAL 0 production in front of
TRD design radiator 2 x 8 layers of fleece radiator, TR x-ray photons absorbed by Xe/CO2 mixture (80:20), in 6mm straw tubes with 30 m tungsten wire Design equivalent to AMS02 space experiment TRD superlayer in G4 simulation straw tubes Tasks: proton suppression and tracking in non-bending plane e p 2.2 m 10.1 cm AMS02 TRD octagon integrated at RWTH Aachen workshop
TRD Straw Modules 39
electrons Analysis of TRD prototype testbeam data, using first 16 layers protons TRD 20-layer prototype testbeam data e p proton rejection for positron measurement proton rejection ~1000
TRD performance: boron / carbon compilation of B/C measurements and GALPROP prediction 11 B 12 C boron/carbon separation at 5 GeV/n in Geant4 simulation needs to be studied in more detail
40 km altitude: 3.7 g/cm 2 remaining atmosphere Background contributions primary positrons atmospheric positrons misidentified protons misreconstructed electrons Event numbers for 20-day flight for efficiency = 50% composition of positron component according to PLANETOCOSMICS simulation of atmospheric background and contributions from p/e- misidentification
Summary A dedicated balloon experiment could provide a competitive measurement of the cosmic ray positron flux. The spectrometer is based on a scintillating fiber tracker with SiPM readout in a superconducting magnet with BL 2 =0.8Tm 2. The proton rejection of ~10 6 can be achieved by a combination of ToF, TRD, ECAL and Tracker. Key parameters: Acceptance: ~2500 cm 2 sr Weight: ~1600 kg Power: ~600 Watt R&D Phase: January 2006 - June 2008 Construction Phase: July 2008 - Mai 2010 Flight: Summer 2010 43
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Comparison with HEAT Acceptance 320 cm 2 sr Electron tracking efficiency ~30% 45
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ECAL: Longitudinal Shower Shape de dt = E b (bt)a 1 e bt 0 Γ(a) 10 GeV e + 10 GeV e + 10 GeV p 10 GeV p 47
GAPD Use APDs operating in limited Geiger mode Advantage: single photon counting very high intrinsic gain (~10 6 ) Disadvantage: no dynamic range at all Dark counts limits the area to < 200 µm Ø combine many small APD pixels onto the same substrate with a common anode gain dynamic range in addition to single photon resolution 48
TRD FE-Electronic: 2 Watt for 512 channels => multiplexed pulsheight only +1600 V 49