Observation of light nuclei with PAMELA Roberta Sparvoli Laura Marcelli, Valeria Malvezzi, Cristian...

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


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


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


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.


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.


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


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).


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


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


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


Charge discrimination: Charge discrimination: TOF TOF scintillatorsscintillators

Paddle S2

Paddle S3

Paddle resolution in flight consistent with measurements at GSI


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 !


• 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


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


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).


PAMELA stand-alone data

Boron/Carbon ratio: 1-100 Boron/Carbon ratio: 1-100 GeV/n GeV/n

Very preliminary

Statistical errors only !!


PAMELA stand-alone data

Berillium/Boron ratio : 1-100 Berillium/Boron ratio : 1-100 GeV/n GeV/n

Very preliminary



Lithium/Carbon ratio : 1-100 Lithium/Carbon ratio : 1-100 GeV/n GeV/n

Very preliminary



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;


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 !

Observation of light nuclei with PAMELA Roberta Sparvoli Laura Marcelli, Valeria Malvezzi, Cristian...

Documents

Transcript of Observation of light nuclei with PAMELA Roberta Sparvoli Laura Marcelli, Valeria Malvezzi, Cristian...