Observation of light nuclei with PAMELA Roberta Sparvoli Laura Marcelli, Valeria Malvezzi, Cristian De Santis and the PAMELA Collaboration

 Roberta Sparvoli  May 11 th, 2009  PAMELA Physics Workshop Bethe Bloch ionization energy-loss of heavy (M>>me) charged particles 1 st plane p d 3 He 4 He Li Be B,C track average e±e± (  saturation) Plane S31 Z measurement in PAMELA

 Roberta Sparvoli  May 11 th, 2009  PAMELA Physics Workshop 3He 4He Rigidity Beta H D Rigidity Beta Rigidity Beta H D 3He 4He Beta Rigidity Mass measurements: Beta versus rigidity Z = 1 Z = 2

 Roberta Sparvoli  May 11 th, 2009  PAMELA Physics Workshop dE/dx tracker (average) Rigidity 4He 3He H D Mass measurements: TRK dE/dx versus rigidity

 Roberta Sparvoli  May 11 th, 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 flight Plane S31 The 6 information can be composed in a weighted average to provide a global Z (tof) with its resolution.

 Roberta Sparvoli  May 11 th, 2009  PAMELA Physics Workshop Tracker charge resolution in flight Redundant 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 11 th, 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). 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 B C

 Roberta Sparvoli  May 11 th, 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 11 th, 2009  PAMELA Physics Workshop PAMELA TM beam tests at GSI 16/02/ /02/ cm TOF : 6 channels ADC and 6 channels TDC, same PAMELA flight electronics with different gain Tracker without magnet 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 m double view

 Roberta Sparvoli  May 11 th, 2009  PAMELA Physics Workshop Ionization losses discrimination: Tracker silicon layers Z2Z2 Sav (ADC channels) Saturation limit Good charge discrimination of H and He Single-channel saturation at ~10MIP affects B/C discrimination

 Roberta Sparvoli  May 11 th, 2009  PAMELA Physics Workshop He Li BeB C Ionization losses discrimination: TOF scintillators All secondary nuclei obtained by fragmentation of the initial Carbon beam

 Roberta Sparvoli  May 11 th, 2009  PAMELA Physics Workshop Charge discrimination: TOF scintillators Paddle S2 Paddle S3 Paddle resolution in flight consistent with measurements at GSI

 Roberta Sparvoli  May 11 th, 2009  PAMELA Physics Workshop Li/C, Be/C, B/C Determination of the secondary/primary ratios: Work in progress !

 Roberta Sparvoli  May 11 th, 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 selection

 Roberta Sparvoli  May 11 th, 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 Consistency of charge (within 1.5 sigma) in S11 && S12 && S2 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 11 th, 2009  PAMELA Physics Workshop Statistics collected Statistics collected from July 2006 until December 2008:  C nuclei  B nuclei  Be nuclei  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 11 th, 2009  PAMELA Physics Workshop PAMELA stand-alone data Boron/Carbon ratio: GeV/n Very preliminary Statistical errors only !!

 Roberta Sparvoli  May 11 th, 2009  PAMELA Physics Workshop PAMELA stand-alone data Berillium/Boron ratio : GeV/n Very preliminary Statistical errors only !!

 Roberta Sparvoli  May 11 th, 2009  PAMELA Physics Workshop Lithium/Carbon ratio : GeV/n Very preliminary Statistical errors only !!

 Roberta Sparvoli  May 11 th, 2009  PAMELA 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 11 th, 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 !