Transcript Diapositiva 1 - Istituto Nazionale di Fisica Nucleare

Observation of light nuclei
with PAMELA
Roberta Sparvoli
Laura Marcelli, Valeria Malvezzi, Cristian De Santis
and the PAMELA Collaboration
Z measurement in PAMELA
Bethe Bloch
ionization energy-loss of
heavy (M>>me)
charged particles
track average
(saturation)
4He
B,C
Plane S31
3He
(saturation)
d
p
1st plane
e±
 Roberta Sparvoli  May 11th, 2009  PAMELA Physics Workshop
Be
Li
Mass measurements: Beta versus rigidity
Z=1
Beta
Beta
Beta
Beta
Z=2
3He 3He
HH
4He
4He
DD
Rigidity
Rigidity
 Roberta Sparvoli  May 11th, 2009  PAMELA Physics Workshop
Rigidity
Rigidity
dE/dx tracker (average)
Mass measurements:
TRK dE/dx versus rigidity
4He
3He
D
H
Rigidity
 Roberta Sparvoli  May 11th, 2009  PAMELA Physics Workshop
ToF charge resolution in flight
Redundant Z information
from 6 different scintillation
layers, each of them
composed by different
paddles.
0.11
0.14
0.18
0.21Plane S31
Every layer can be calibrated
(de/dx vx beta) so to provide
a charge measurement with
its relative sigma.
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 flight
Redundant Z information
from 6 different silicon layers.
0.16
0.23
0.28
0.34
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 flight
Redundant Z information
from 44 (22 X&Y) different
silicon layers.
The first calorimeter plane
gives a good charge
resolution (Z calo).
0.20
0.23
B
0.26
C
0.29
Be
Li
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.
 Roberta Sparvoli  May 11th, 2009  PAMELA Physics Workshop
Nuclei 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 GSI
16/02/2006 --- 20/02/2006
TOF system: single
paddles of PAMELA TOF
S1 : 0.7 cm thick
S2 : 0.5 cm thick
S3 : 0.7 cm thick
TRACKER system: same
silicon wafers of PAMELA
P1,P2,P3,P4,P5 :
300 mm double view
80 cm
TOF : 6 channels ADC and 6 channels TDC, same PAMELA flight
electronics with different gain
 Roberta
Sparvoli  May 11th, 2009  PAMELA Physics Workshop
Tracker without
magnet
Sav (ADC channels)
Ionization losses discrimination:
Tracker silicon layers
Z2
Sav (ADC channels)
Saturation limit
• Good charge discrimination of H and He
th, 2009 affects
• Single-channel
at 11
~10MIP
discrimination
 Robertasaturation
Sparvoli  May
PAMELA B/C
Physics
Workshop
Ionization losses discrimination:
TOF scintillators
C
B
Be
Li
He
All secondary nuclei
obtained by fragmentation of the initial Carbon beam
 Roberta Sparvoli  May 11th, 2009  PAMELA Physics Workshop
Charge discrimination: TOF scintillators
Paddle S2
Paddle S3
Paddle resolution in flight consistent with measurements at GSI
 Roberta Sparvoli  May 11th, 2009  PAMELA Physics Workshop
Determination of the
secondary/primary ratios:
Li/C, Be/C, B/C
Work in progress !
 Roberta Sparvoli  May 11th, 2009  PAMELA Physics Workshop
Data analysis (I): sample selection
• 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)
 Roberta Sparvoli  May 11th, 2009  PAMELA Physics Workshop
Data analysis (II): particle ID
Particle ID is performed by the TOF detector, asking for
charge consistency in 3 layers:
Consistency of charge (within 1.5 sigma) in
S11 && S12 && S2 (mean of S21 and S22)
The particle energy is determined by the spectrometer
Other detectors are used for independent selection of the
efficiency samples
 Roberta Sparvoli  May 11th, 2009  PAMELA Physics Workshop
Statistics 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
Boron/Carbon ratio: 1-100 GeV/n
PAMELA stand-alone data
 Roberta Sparvoli 
May 11th, 2009
PAMELA
Statistical
errorsonly
!! Physics Workshop
Berillium/Boron ratio : 1-100 GeV/n
PAMELA stand-alone data
 Roberta Sparvoli 
May 11th, 2009
PAMELA
Statistical
errorsonly
!! Physics Workshop
Lithium/Carbon ratio : 1-100 GeV/n
 Roberta Sparvoli 
May 11th, 2009
PAMELA
Statistical
errorsonly
!! Physics Workshop
Effects to be better evaluated
• 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
Conclusions
• 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 !
 Roberta Sparvoli  May 11th, 2009  PAMELA Physics Workshop