AN ORIGINAL MODEL FOR THE SIMULATION OF LOW ENERGY ANTIPROTONS S. Chauvie On behalf of Geant4 Low Energy Electromagnetic Group INFN, Sezione di Torino and Santa Croce e Carle Hospital, Cuneo, Italy Antiprotons in the Space Environment The first evidence of stopping power dependence on the particle charge dates back to Barkas in the ’50s; he measured different ranges for positive and negative pions at low energies (  < 0.5 ) and interpreted them as caused by the polarisation of the surrounding medium. “The Barkas Effect” Exotic sources Primordial Black Holes Annhilating/decaying Dark Matter in Galactic Halo WIMPS... Simmetry Breaks, ... Precise knowledge of Antiproton/Proton ratio of Cosmic Rays Energy Loss and Range of Negatively Charged Particles p: High Energy Cosmic Rays A: Interstellar Medium X: anything consistent with Charge and Baryonic number conservation is important for various particle physics experiments Status Doesn’t exist simulation tools to account for charge dependence of Stopping Power. Simulation without correction could lead to misunderstanding (e.g. 50% errors in range for 0.5 MeV Antiproton in Aluminum) Geant4 Low Energy Electromagnetic Package take care of it Algorithms encapsulated in objects Physics models handled through abstract classes Hadrons and ions Interchangeable and transparent access to data sets Hadron and ion processes in Geant4 Low Energy Electromagnetic Package Variety of models, depending on energy range, particle type and charge Positive charged hadrons Density correction for high energy Shell correction term for intermediate energy Spin dependent term Barkas and Bloch terms Chemical effect for compound materials Nuclear stopping power Bethe-Bloch model of energy loss, E > 2 MeV 5 parameterised models, E < 2 MeV based on Ziegler and ICRU reviews 3 models of energy loss fluctuations Positive charged ions Low energy extensions: hadrons and ions Effective charge model Nuclear stopping power Scaling: 0.01 < b < 0.05 parameterisations, Bragg peak based on Ziegler and ICRU reviews b < 0.01: Free Electron Gas Model Various models, depending on the energy range and charge E > 2 MeV  Bethe-Bloch 1 keV < E < 2 MeV  parameterisationsZiegler 1977, 1985 ICRU 49 corrections due to chemical formulae of materials nuclear stopping power E < 1 keV free electron gas model Negative charged hadrons Parameterisation of available experimental data Quantum Harmonic Oscillator Model Model original to Geant4 Negative charged ions: required, foreseen With the Generalised Oscillator Strength: Stopping Power Bethe Theory: the Stopping Power is related to the Coulomb excitation and ionisation of the electron of the stopping medium the interaction is treated within the first Born approximation In the case of projectile velocity much greater than bounded electron v >> ve Stopping Number Particle Bethe formula with the dimensionless Stopping Number L Stopping Number with Harmonic Oscillator Model is proportional to the conditional probabilitiy that the atom makes the transition to an excited state |n > upon receiving a momentum transfer q Material Harmonic Oscillator Model for Atoms Born expansion in power of Zh L0, L1, L2 terms have been calculated by the Theory Group at Aahrus University (Denmark) Thanks! implementation T > 2 MeV  Bethe-Bloch formula (50 keV) < T < 2 MeV  Quantum Harmonic Oscillator Model T < (50 keV)  Electron Gas Model Hp: Oscillator Strength f = Occupation Number w The atom is considered as an ensemble of j oscillators corresponding to the atomic shells Model Validation Results The Quantum Harmonic Oscillator Model is applied to calculate the energy loss of antiprotons in a material Experimental data come from CERN Antiproton Decelerator (AD) Stopping Number for Antiprotons in Silicon Stopping Power for Antiprotons in Aluminum ... Stopping Number (a.u) Kinetic Energy (eV) … Silicon ... L0 L L1 L2 Conclusions From Protons to Antiprotons Stopping Power for Antiprotons (40-60% to 1-10%) che vuol dire? Useful for various undergoing experiments and for space-related activities Easy to implement Physics Processes in Geant4 (the iterative-incremental implementation of the class took 1 week) Another alternative model (even for Protons) ... ... Gold.