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Observation of light Observation of light nuclei nuclei with PAMELAwith PAMELA
Roberta SparvoliLaura Marcelli, Valeria Malvezzi, Cristian De
Santisand the PAMELA Collaboration
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
Bethe Bloch ionization energy-loss of heavy (M>>me) charged particles
1st plane
pd
3He
4He
Li
Be
B,C
track average
e±
(saturation)
(saturation)Plane S31
Z measurement in Z measurement in PAMELAPAMELA
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
3He
4He
Rigidity
Bet
a
H
D
Rigidity
Bet
a
Rigidity
Bet
a
H
D
3He
4He
Bet
a
Rigidity
Mass measurements:Mass measurements: Beta Beta versus rigidityversus rigidity
Z = 1 Z = 2
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
dE/d
x tr
acke
r (a
vera
ge)
Rigidity
4He
3He
H
D
Mass measurements: Mass measurements: TRK dE/dx versus rigidityTRK dE/dx versus rigidity
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
Redundant Z information from 6 different scintillation layers, each of them composed by different paddles.
Every layer can be calibrated (de/dx vx beta) so to provide a charge measurement with its relative sigma.
ToF charge resolution in ToF charge resolution in flightflight
0.11 0.14 0.18 0.21Plane S31
The 6 information can be composed in a weighted average to provide a global Z (tof) with its resolution.
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
Tracker charge resolution in Tracker charge resolution in flightflight
0.16 0.23 0.28 0.34Redundant Z information from 6 different silicon layers.
Every layer can be calibrated (de/dx vx beta or R) so to provide a charge measurement with its relative sigma.
A weighted average gives the global tracker charge (Z trk) with its resolution.Single-channel saturation at ~10 MIP affects the resolution for
particles heavier than Lithium.
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
Calo charge resolution in Calo charge resolution in flightflight
0.20 0.23 0.26 0.29Redundant Z information from 44 (22 X&Y) different silicon layers.
The first calorimeter plane gives a good charge resolution (Z calo).
It is possible to combine in many different ways the redundant calo information (weighted average, truncated mean, …), reaching an excellent charge resolution, however the W samplings favour interactions and affect the nuclear abundances.Loss of efficiency.
Li
Be
BC
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
Nuclei beam testsNuclei beam tests
• Before launch PAMELA was tested for p and e- several times;
• No time for a nuclei beam test of the whole detector;
• Calorimeter stand-alone tested in Uppsala under nuclei;
• PAMELA Technological Model tested at GSI after launch (no-calo and no-magnet configuration).
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
PAMELA TM beam tests at PAMELA TM beam tests at GSIGSI 16/02/2006 --- 20/02/200616/02/2006 --- 20/02/2006
80 cm
TOF : 6 channels ADC and 6 channels TDC, same PAMELA flight electronics with different gainTracker without magnet
TOF system: single paddles of PAMELA TOF
S1 : 0.7 cm thickS2 : 0.5 cm thickS3 : 0.7 cm thick
TRACKER system: same silicon wafers of PAMELA
P1,P2,P3,P4,P5 :300 m double view
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
Ionization losses discrimination: Ionization losses discrimination: Tracker silicon layersTracker silicon layers
Z2
Sav (
AD
C c
hannels
)Sav (ADC channels) Saturation limit
• Good charge discrimination of H and He• Single-channel saturation at ~10MIP affects B/C discrimination
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
He
Li
Be
B
C
Ionization losses Ionization losses discrimination: discrimination: TOF TOF scintillatorsscintillators
All secondary nuclei obtained by fragmentation of the initial Carbon beam
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
Charge discrimination: Charge discrimination: TOF TOF scintillatorsscintillators
Paddle S2
Paddle S3
Paddle resolution in flight consistent with measurements at GSI
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
Li/C, Be/C, B/CLi/C, Be/C, B/C
Determination of the Determination of the secondary/primary secondary/primary ratios:ratios:
Work in progress !
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
• Data quality check (good calibration)• Positive particles (positive curvature in TRK)• Single-track events (no double
tracks/interaction in TRK)• Track quality check (cut on chi-square of
the track fitting algorithm)• No albedo (positive beta from TOF)• No interactions (request of single/double
paddle hit in S1)• Cut on SAA (no events taken in Saa)
Data analysis (I): sample Data analysis (I): sample selectionselection
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
Data analysis (II): particle IDData analysis (II): particle ID
Particle ID is performed by the TOF detector, asking for charge consistency in 3 layers:
Consistency of chargeConsistency of charge (within 1.5 sigma) in S11 && S12 && S2S11 && S12 && S2 (mean of S21 and S22)
The particle energy is determined by the The particle energy is determined by the spectrometerspectrometer
Other detectors are used for independent selection of the
efficiency samplesefficiency samples
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
Statistics collectedStatistics collected Statistics collected from July 2006 until December 2008:
120.000 C nuclei 45.000 B nuclei 16.000 Be nuclei 30.000 Li nuclei
between 200 MeV/n and 100 GeV/n, with the current selection cuts (50% efficiency and <1% contamination among species).
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
PAMELA stand-alone data
Boron/Carbon ratio: 1-100 Boron/Carbon ratio: 1-100 GeV/n GeV/n
Very preliminary
Statistical errors only !!
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
PAMELA stand-alone data
Berillium/Boron ratio : 1-100 Berillium/Boron ratio : 1-100 GeV/n GeV/n
Very preliminary
Statistical errors only !!
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
Lithium/Carbon ratio : 1-100 Lithium/Carbon ratio : 1-100 GeV/n GeV/n
Very preliminary
Statistical errors only !!
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
Effects to be better Effects to be better evaluatedevaluated• Fragmentation in the dome and in
the detector:• Currently studied with MC; important effects
for light nuclei, though no significan variations among species found in MC.
• Tracking efficiency at high energy:• Ebergy measurements in flight based on TOF
and CALO limited to low energies;
Roberta Sparvoli May 11th, 2009 PAMELA Physics Workshop
ConclusionsConclusions• PAMELA is capable of measuring ratios
of secondaries/primaries in CR and their fluxes with very good statistics in a wide energy range;
• Preliminary results have been shown: they have to be taken with care since sistematic effects are not yet fully under control;
• Low energy region not shown since solar modulation plays an important role;
• The collected statistics allows to go beyond the current 100 GeV/n shown.
Results will be ready soon !