Measurement of fragmentation cross-section of 400 MeV/u 12 C beam on thin targets

Transcription

1 Measurement of fragmentation cross-section of 400 MeV/u 12 C beam on thin targets Candidate: Abdul Haneefa Kummali Supervisor : Dr. Vincenzo Monaco PhD School - Department of Physics XXVII cycle 14-February-2014

2 Outlook Introduction and Motivations Experimental Setup Reconstruction and Simulation Studies on Detector Performance Preliminary Cross-section Measurements Future Perspective Conferences and Publications 2

3 1. Introduction and Motivation Fragmentation measurements are important for hadrontherapy and space radiation protection. Hadrontherapy Better spatial selectivity in dose deposition: (p, 12 C) Reduced lateral and longitudinal diffusion ( 12 C) High biological effectiveness ( 12 C) Treatment of highly radiation resistent tumours, sparing surrounding OAR. 3

4 Introduction and Motivation (2) The dose distributions in hadrontherapy is affected by the fragments produced along the path. Dose due to fragmentation Fragmentation reduces the quality of beam Treatment planning systems must take into account this effect for accurate dose optimization. Fragmentation processes can provide the online evaluation of the dose using + decays (PET imaging) or prompt gamma imaging (researches are going on) 4

5 Introduction and Motivation (3) Double differential quantities (angular, energy) have larger discrepancies in different models used in Monte Carlo codes. 400 MeV/u 12 C on water: limited angle measurements. Bolhen et al, Phys. Med. Biol. 55 (2010) Lack of measurements to constrain the models: Only total cross sections, very few data at the energies of interest ( MeV/u). Almost no double differential cross sections in the energies of interest. Few measurements on thin targets. 5

6 Introduction and Motivation (4) Peripheral collision Head-on collision Monte Carlo (FLUKA) simulation of 400 MeV/u 12 C beam on 5 mm graphite target Widely spread low Z ions From the simulation: An experiment for cross section measurement of 12 C beam on thin target is designed to cover: 6 Forward peaked high Z fragments. To cover widely distributed low Z ions.

7 2.FIRST Experimental Setup of Ions Relevant for FIRSTFragmentation Space and Therapy EXPERIMENT Proposal: Measurement of fragmentation differential cross-sections (as function of angle and energy) for different beam energies between 100 and 1000 MeV/u. At SIS accelerator of GSI laboratory in Darmstadat Germany. During August 2011 using 12 C beam of 400 MeV/u. 8 mm graphite and 5 mm gold targets 28 x 10 6 events with graphite target and 3 x 10 6 with gold target 7 x 10 6 calibration events (no target) Beam direction New detectors (Interaction region) X Start counter Z Beam monitor Target Vertex P-Tagger Already existing detectors (Large area detectors) Aladin magnet Music chamber (TPC) Veto ToFWall LAND The FIRST experiment at GSI NIM vol.678, c m ~ 6 m Not in scale

8 FIRST Experimental Setup (2) Start Counter: 150 µm thick disc, 52 mm diameter of fast plastic scintillator with radial fibers read-out. Efficiency > 99%. Time resolution of 150 ps. Reference time for time of flight and trigger. Beam Monitor (Drift Ionization Chamber): Drift chamber with 6 planes of wires arranged in 2 orthogonal directions (alternated horizontal and vertical). Tracking efficiency ~ 99%. Single wire spatial resolution 150 μm. Tracking of the arriving carbon, with a precision on the impact point on the target of the order of ~ 100 µm. 8

9 Vertex: 4 planes of silicon pixel detectors with digital readout Fragment emission angles θ,ф & charge. Pitch 18.4 µm Cluster size is related with the energy loss. Large integration time (probability to acquire more than one carbon in each trigger) BM track is used to identify the right vertex in case of pile-up. FIRST Experimental Setup (3) ± 40 0 p-tagger Scintillator system used to detect fragments emitted at > 5 degrees. Optimized to detect large angle protons are helium with a time resolution of 250 ps. Detect large angle fragments, measures impact position, TOF and de/dx. 9

10 ALADIN Magnet: FIRST Experimental Setup (4) Charged particles emitted at low angles (< 6 o ) are deflected in the magnetic field in order to measure their momentum. MUSIC (Time Projection Chamber): To measure the particle trajectory and charge after the magnet. Not in operational condition. ToF Wall detector: 2 Planes separated by 1.25cm. 12 modules each with 8 scintillator bars 192 individual slats 110 x 1.0 x 2.5 cm 3 ( Length x Thickness x Width) Total active area : 100 x 240 cm 2. Energy loss, impact point (X,Y) and time of flight. Single module 8 slats 10

11 3. Reconstruction and Simulation The MUSIC detector was not working during the data acquisition. We must rely only on Vertex and ToFWall for the measurements at low angle. y z x Reconstruction: For each combination of tracks at the vertex and hit in the ToFWall, Z pc From Vertex. Energy loss in the ToFWall (and Vertex) Track bending (knowing magnetic field map, initial position and direction, Z and impact point on the ToFWall) track length c TOF Mass pc Track selection: Minimum difference in y (impact position) for vertex tracks (projected) and ToF Wall hits from all the combinations. 11

12 Reconstruction and Simulation (2) Simulation : FLUKA FIRST detectors in MC New detector region Aladin Magnet Music chamber ToFWall 1.Setup configuration: Detector geometry, materials and magnetic field. 2.Scoring : Particle trajectories and energy depositions from scoring planes 3.Signal Modeling and Digitization: Detectors resolutions, efficiency. Based on calibration studies from the data. 4. Storing: Stored in ROOT files analyzed with the same reconstruction code used for real events. 12

13 4. Detector Performance (ToFWall ) What I am doing/done: Analysis of events at low angles (using ToFWall and Vertex). Tuning of the simulation ToFWall studies Reconstruction studies Measurement of cross-sections My works on ToFWall : Cross-check of calibration Resolution studies to tune in MC Efficiency of proton to tune in MC Clustering of ToF Wall hits Charge (Z) identification 13

14 ToFWall Detector Performance (2) Implementation of detector geometry in simulation Position and angle of Vertex and target Survey points on Beam Monitor positions Aladin magnetic map Detector positions implemented in the Monte Carlo according to survey measurements of single detectors and alignment studies on data. Magnetic field map from previous measurements with hall probes 14

15 ToFWall Detector Performance (3) Single slat of ToFWall Cross-check of calibrations y 0 ΔE ADC top, TDC top L y 2 L 2 y E k ADC Vslat y 2 c y ln 2 TOF TDC TDC ADC ADC ADC TDC TDC s t top b t b b t bot t t b b ADC bot, TDC bot Were, k = Energy calibartion factors taking consider the attenuation factors (λ). V light = velocity of light through scintillator Δt and Δb are the calibration factors considering all the delays in electronic chain. Δs accounts delay from start counter to ToFWall Sweep run:- Special runs for calibration, without target with known beam energy (400 MeV/u) deflected in the X-axis by changing the magnetic field ( y = 0). The calibration factors are determined for each slat 15

16 ToFWall Detector Performance (4) After applying calibration constant Cross-check of calibrations 2 DT = TDC t -TDC b DT of 0.1 ns / 2 cm precision in y 16

17 ToFWall Detector Performance (5) Resolution studies on DATA to tune Monte Carlo Energy resolution σ(e ToF -E BB )/E BB σ(e FRONT -E REAR )/E MEAN Energy loss predicted by the Bethe-Bloch (E BB ) is compared with the energy loss measured in the TOFWall (E TOF ). σ(e ToF -E BB )/E BB E BB [MeV] E mean [MeV] Energy loss in the front and rear slats compared to find the energy resolution. σ(e FRONT -E REAR )/E MEAN 17

18 Y resolution ToFWall Detector Performance (6) Y and TOF resolution studies from DATA to tune MC Front /Rear comparison reconstructed y (particle impact position in Y- coordinate). y resolution of ~ 7 cm. Resolution can be improved by taking y from ADCs TOF resolution Compare Time of Flight measured from front and rear slats. σ TOF of ~ 800 ps. 18

19 ToFWall Detector Performance (7) DATA/ Monte carlo comparison after tuning of the resolutions E loss Y TOF E loss (log) Y (log) TOF(log) 19 Pile-up not simulated

20 TDC efficiency ADC counts ToFWall Detector Performance (8) Studies to simulate the efficiency for proton detection in the Monte Carlo Minimum ADC values needed for a valid TDC hit determined for each channel. Top ADC counts Slat No ADC thresholds are translated to minimum energy loss [MeV] as a function of slat number and y (taking into account pedestals, calibration factors, Birk corrections, attenuations, etc...) when measurements from at least one of TDCs is available. Minimum energy loss in ToFWall Mean energy loss in ToFWall The mean energy threshold for detection of a particle in the ToFWall is < 2 MeV All protons are detected, but lower efficiency in some regions of the ToFWall. 20

21 ToFWall Detector Performance (9) Clustering of ToFWall hits in different planes Vertex Magnet ToFWall Y Z Clustering: Hits in two different planes compatible with the same reconstructed track are merged in order to avoid to select 2 different tracks in the reconstruction. Clustering criteria studied using MC informations: The clustering criteria is based on distance in X and Y between the two hits. Clustering parameters optimized with a study with the Monte Carlo in order to minimize the probability to have wrong matches between TOFWall hits and Vertex tracks. Fraction of tracks with wrong TOFWall/Vertex match reduced from 19 % to 13 % after clustering. 21

22 ToFWall Detector Performance (10) Charge (Z) identification on ToFWall Once everything is calibrated, DATA E Z BB E Z BB 2 a 2 2 b ln x E tw = Energy loss at ToFWall corrected for the particle impact angle (Cos θ) Sqrt(ΔE TW /cosθ)/δe BB *Z 2 ) Projection in X-axis The ratio of energy loss at ToFWall and Bethe-Bloch prediction (β from reconstruction) gives Z 2. z ETOF Z E cos BB p He Li Be B C 22 Sqrt(ΔE TW /cosθ)/δe BB *Z 2 )

23 5. Cross-section Measurements Comparison of reconstructed and generated quantities Ch 1 Ch 2 Ch 1 Ch 2 23

24 Cross-section Measurements (2) Resolutions of reconstruction Difference between reconstructed and generated quantities Angular resolution resolution Momentum resolution (Boron) 0.05 o independent of charge Fragment charge 2 % independent of charge Momentum Resolution [MeV and %] 1 20 ( 2 %) ( 3 %) ( 3,5 %) ( 4%) ( 4 %) 24

25 Cross-section Measurements (3) Reconstruction/generator comparisons: Resolutions Mass Mass Mass Mass resolution Difficult to separate different isotopes for Z 3 (limited by the momentum resolution) 25

26 Cross-section Measurements (4) Comparison of DATA / Monte Carlo after tunning MC based on the studies on DATA Beta Beta Mass Mass distribution Momentum Angular distribution Angular Mass [u] 26 Momentum [GeV/c] Angle [θ]

27 [Z] Cross-section Measurements (5) Charge assignment quality after the reconstruction Reconstructed charge compared with Monte Carlo charge at vertex 27 [Z]

28 Cross-section Measurements (6) Efficiency and Purity Efficiency ( Z, B) reco & gene( Z, B) gene( Z, B) Purity ( Z, B) reco & gene( Z, B) reco( Z, B) gene (Z,B) = No. of generated particles with charge Z in bin B. reco (Z,B) = No. of reconstructed particles with charge Z in bin B. Efficiency and Purity of different fragmnets as a function of polar angle 28 Bin definitions must be optimized

29 (Z, ) ( Z, E) E N 12 C N' N N' N data 12 C Cross-section Measurements (7) data t ( Z, E) N E t Single differential cross-section (Z, ) (, ) N' data pur( Z, B) * N eff ( Z, B) N c 12 = Trigger counts N t = Density of target data ( Z, B) Preliminary cross-section of different fragments as a function of the polar angle and kinetic energy over atomic mass. 29

30 Cross-section Measurements (8) Bin definitions Strong biases when comparing reconstructed and generated quantities (beta, KE, momentum, mass, etc...) resulting in very low efficiencies and purities (difficult and unstable unfolding procedures). DATA From the MC study it results that these biases comes from reconstructed tracks with a wrong match between the vertex and the ToFWall hit. 30 The probability of wrong matches can be reduced by comparing the TOF charge with the cluster size of the Vertex track.

31 Cross-section Measurements (9) Bin definitions 2 Charge Ytdc total tracks (% wrong mathes) Yadc total tracks (% wrong matches) Vertex Charge New sim used (% of wrong matches) Vertex Charge + Yadc (% of wrong matches) Vertex Charge + Yadc+ BM-match (% of wrong matches) 1 (30,23 %) (21,02 %) (18,34 %) (16,53 %) (13,47 %) 2 (12,54 %) (13,02 %) (12,16 %) (11,05 %) (9,15 %) 3 (9,23 %) (7,91 %) (6,13 %) (5,15 %) (3,96 %) 4 (9,31 %) (8,03 %) (8,8 %) (7,86 %) (6,55 %) 5 (2,21 %) (0,68 %) (1,86 %) (1,49 %) (0,29 %) 6 (0,04 %) (0,02 %) (0,02 %) (0,02 %) (0,08 %) Work on-going to reduce the fraction of bad reconstructed tracks (worng matches), by using a better measurement of the Y in the ToFWall, the information on the charge measured with the Vertex in the selection of reconstructed tracks. Remaining wrong matches mainly from high multiplicity events. 31

32 6. Future Perspective Reduce the fraction of wrong reconstructed tracks as much as possible. Define a optimal bin definition to optimize efficiencies and purities. Robust unfolding procedure Fit the masses distributions for each Z and bin to evaluate the contribution of different isotopes Evaluation of systematic errors Full double-differential cross section measurement 32

33 7. Conference and Publication Conference proceedings of FIRST project (January December 2013) 1. 99th SIF conference, September 2013,Trieste -Italy. 2. Fourth International Conference on Nuclear Fragmentation (NUFRA2013), 29 September October 2013, Kemer (Antalya), Turkey. 3. IEEE Nuclear Science Symposium and Medical Imaging Conference, 26 October - 2 November, 2013, Seoul, Korea. 4. AIFM (Associazione Italiana di Fisica Medica ) conference, November 2013, Turin, Italy th SIF conference, 17-21September 2012, Naples-Italy. 33

34 Thanks for your attention FIRST : Fragmentation of Ions Relevant for Space and Therapy. 34